57 files changed, 24623 insertions, 80 deletions

diff --git a/.gitignore b/.gitignore
index 7a23ede7..2c40503c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,3 +15,4 @@ upload-docs
 *.ps
 *.prof
 res/rtorrent-sessiondir
+/.stack-work/
diff --git a/ConduitServer.hs b/ConduitServer.hs
new file mode 100644
index 00000000..0838ce26
--- /dev/null
+++ b/ConduitServer.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Main where
+
+import Data.Conduit.Binary
+import Data.Conduit.Network
+import Data.Conduit
+import qualified Data.Conduit.List as CL
+import qualified Data.ByteString.Char8 as S
+
+import Network.Socket (Family(..))
+import Data.HList
+import ServerC
+
+{-
+data AppData m = AppData
+    { appSource :: Source m ByteString
+    , appSink :: Sink ByteString m ()
+    , appSockAddr :: SockAddr
+    , appLocalAddr :: Maybe SockAddr
+    }
+-}
+
+-- handleConnection will simply output everything
+-- it sees from the connection to the terminal
+handleConnection :: AppData IO -> IO ()
+handleConnection appdata = do
+    sourceLbs "<stream>\n" $$ appSink appdata -- send bytestring
+    appSource appdata $$ CL.mapM_ S.putStrLn -- display inbound bytestring
+
+mainOld = do
+    -- Listen to port 5222 and invoke handleConnection on every
+    -- inbound connection.
+    runTCPServer (serverSettings 5222 HostAny) handleConnection
+    return ()
+
+
+
+
+handleC st src snk = do
+    sourceLbs "<stream>\n" $$ snk
+    src $$ CL.mapM_ S.putStrLn
+
+mainC = do
+    doServer (AF_INET .*. 5222 .*. HNil) handleC
+    _ <- getLine
+    return ()
+
+main = mainC
diff --git a/Connection.hs b/Connection.hs
new file mode 100644
index 00000000..3287bc1b
--- /dev/null
+++ b/Connection.hs
@@ -0,0 +1,58 @@
+{-# LANGUAGE DeriveFunctor #-}
+module Connection where
+
+import Control.Applicative
+import Control.Arrow
+import Control.Concurrent.STM
+import qualified Data.Map as Map
+         ;import Data.Map (Map)
+
+import PingMachine
+
+data Status status
+    = Dormant
+    | InProgress status
+    | Established
+ deriving Functor
+
+data Policy
+    = RefusingToConnect
+    | OpenToConnect
+    | TryingToConnect
+
+data Connection status = Connection
+    { connStatus    :: STM (Status status)
+    , connPolicy    :: STM Policy
+    , connPingLogic :: PingMachine
+    }
+ deriving Functor
+
+data Manager status k = Manager
+    { setPolicy    :: k -> Policy -> IO ()
+    , connections  :: STM (Map k (Connection status))
+    , stringToKey  :: String -> Maybe k
+    , showProgress :: status -> String
+    , showKey      :: k -> String
+    }
+
+showStatus :: Manager status k -> Status status -> String
+showStatus mgr Dormant        = "dormant"
+showStatus mgr Established    = "established"
+showStatus mgr (InProgress s) = "in progress ("++showProgress mgr s++")"
+
+
+addManagers :: (Ord kA, Ord kB) =>
+            Manager statusA kA
+            -> Manager statusB kB
+            -> Manager (Either statusA statusB) (Either kA kB)
+addManagers mgrA mgrB = Manager
+    { setPolicy = either (setPolicy mgrA) (setPolicy mgrB)
+    , connections = do
+        as <- Map.toList <$> connections mgrA
+        bs <- Map.toList <$> connections mgrB
+        return $ Map.fromList $ map (Left *** fmap Left) as ++ map (Right *** fmap Right) bs
+    , stringToKey = \str ->  Left <$> stringToKey mgrA str
+                        <|> Right <$> stringToKey mgrB str
+    , showProgress = either (showProgress mgrA) (showProgress mgrB)
+    , showKey = either (showKey mgrA) (showKey mgrB)
+    }
diff --git a/Control/Concurrent/STM/StatusCache.hs b/Control/Concurrent/STM/StatusCache.hs
new file mode 100644
index 00000000..d1c977ae
--- /dev/null
+++ b/Control/Concurrent/STM/StatusCache.hs
@@ -0,0 +1,160 @@
+---------------------------------------------------------------------------
+-- |
+-- Module      :  Control.Concurrent.STM.StatusCache
+--
+--
+-- Maintainer  :  joe@jerkface.net
+-- Stability   :  experimental
+--
+-- Motivation: Suppose you must communicate state changes over a stream.  If
+-- the stream is consumed slowly, then it may occur that backlogged state
+-- changes are obsoleted by newer changes in state.  In this case, it is
+-- desirable to discard the obsolete messages from the stream.
+--
+-- A streamed status message might be very large, and it would be wasteful in
+-- both time and space, to treat it as a monolithic blob that must be built
+-- completely before it can be sent.  Therefore, we require that each message
+-- consist of a stream of smaller chunks of type @x@ and we require predicates
+-- that indicate when a chunk starts a new message and when it ends a message.
+--
+-- In the folowing example, our chunk type is Char and complete messages are
+-- delimited by the characters '(' and ')'.  We process the input stream
+-- \"(aaa(a))(bb)(cc(c)cc)\" first with a delayed processor and then again with
+-- an efficient dedicated thread. The result follows:
+--
+-- > Backlogged consumer: (cc(c)cc)
+-- > Fast consumer: (aaa(a))(bb)(cc(c)cc)
+--
+-- The complete source code:
+--
+-- > import Control.Monad      (when, forever, (>=>))
+-- > import Control.Monad.STM  (atomically)
+-- > import Control.Concurrent (forkIO, threadDelay)
+-- > import System.IO          (hFlush, stdout)
+-- > import qualified Control.Concurrent.STM.StatusCache as Cache
+-- >
+-- > main = do q <- atomically $ Cache.new (== '(') (==')')
+-- >           backlog q "(aaa(a))(bb)(cc(c)cc)"
+-- >           fast    q "(aaa(a))(bb)(cc(c)cc)"
+-- >
+-- > while pred body = pred >>= flip when (body >> while pred body)
+-- >
+-- > backlog q xs = do putStr $ "Backlogged consumer: "
+-- >                   mapM_ (atomically . Cache.push q) xs
+-- >                   while (atomically $ fmap not $ Cache.isEmpty q) $ do
+-- >                       c <- atomically $ Cache.pull q
+-- >                       putChar c
+-- >                   putStrLn ""
+-- >                   hFlush stdout
+-- >
+-- > fast q xs = do putStr "Fast consumer: "
+-- >                forkIO $ forever $ do
+-- >                        c <- atomically $ Cache.pull q
+-- >                        putChar c
+-- >                        hFlush stdout
+-- >                mapM_ (atomically . Cache.push q >=> const (threadDelay 10000))
+-- >                      xs
+-- >                putStrLn ""
+--
+-- As shown above, it is intended that this module be imported qualified.
+--
+{-# LANGUAGE DoAndIfThenElse #-}
+module Control.Concurrent.STM.StatusCache
+    ( StatusCache
+    , new
+    , push
+    , pull
+    , pullDepth
+    , isStopper
+    , isStarter
+    , isEmpty
+    ) where
+import Control.Monad
+import Control.Monad.STM
+import Control.Concurrent.STM.TVar
+import Control.Concurrent.STM.TChan
+
+data StatusCache x =
+    StatusCache { feed :: TVar (TChan x)
+                , cache :: TVar (TChan x)
+                , feedFlag :: TVar Bool
+                , pushDepth :: TVar Int
+                , pullDepth :: TVar Int -- ^ current nesting depth of next-to-pull data
+                , isStarter :: x -> Bool -- ^ True if the given chunk begins a message.
+                , isStopper :: x -> Bool -- ^ True if the given chunk ends a message.
+                }
+
+-- | @new isStart isStop@
+--
+-- The @isStart@ and @isStop@ predicates indicate when an element
+-- begins or ends a message.
+new :: (x -> Bool) -> (x -> Bool) -> STM (StatusCache x)
+new isStart isStop = do
+    feed <- newTChan >>= newTVar
+    cache <- newTChan >>= newTVar
+    flag <- newTVar True
+    pushd <- newTVar 0
+    pulld <- newTVar 0
+    return StatusCache { feed = feed
+                       , cache = cache
+                       , feedFlag = flag
+                       , pushDepth = pushd
+                       , pullDepth = pulld
+                       , isStarter = isStart
+                       , isStopper = isStop
+                       }
+
+
+-- | Pull off a chunk from the 'StatusCache' for processing.
+--
+-- If chunks are not pulled off quickly, they may be obsoleted
+-- and discarded when new messages are 'push'ed.
+pull :: StatusCache x -> STM x
+pull q = do
+    hasCache <- readTVar (feedFlag q)
+    exhausted <- readTVar (feed q) >>= isEmptyTChan
+    when (hasCache && exhausted) $ do
+        next <- newTChan >>= swapTVar (cache q)
+        writeTVar (feedFlag q) False
+        writeTVar (feed q) next
+    chan <- readTVar $ feed q
+    exhausted <- isEmptyTChan chan
+    if exhausted then retry
+    else do
+        v <- readTChan chan
+        when (isStarter q v) $ do
+            depth <- readTVar (pullDepth q)
+            modifyTVar' (pullDepth q) (+1)
+            when (depth==0)
+                $ writeTVar (feedFlag q) False
+        when (isStopper q v)
+            $ modifyTVar' (pullDepth q) (subtract 1)
+        return v
+
+-- | Enqueue a chunk into the 'StatusCache'.
+push :: StatusCache a -> a -> STM ()
+push q v = do
+    shouldCache <- readTVar (feedFlag q)
+    depth <- readTVar (pushDepth q)
+    when (isStopper q v) $ do
+        modifyTVar' (pushDepth q) (subtract 1)
+        when (depth==0)
+            $ writeTVar (feedFlag q) True
+    when (isStarter q v)
+        $ modifyTVar' (pushDepth q) (+1)
+    chan <-
+        if shouldCache then do
+            when (depth==0 && isStarter q v)
+                $ newTChan
+                  >>= writeTVar (cache q)
+            readTVar $ cache q
+        else do
+            readTVar $ feed q
+    writeTChan chan v
+
+-- | True when the 'StatusCache' is completely exhuasted.
+isEmpty :: StatusCache x -> STM Bool
+isEmpty q = do
+    empty_feed  <- readTVar (feed q) >>= isEmptyTChan
+    empty_cache <- readTVar (cache q) >>= isEmptyTChan
+    return $ empty_feed && empty_cache
diff --git a/Control/Concurrent/STM/UpdateStream.hs b/Control/Concurrent/STM/UpdateStream.hs
new file mode 100644
index 00000000..b01fc0bc
--- /dev/null
+++ b/Control/Concurrent/STM/UpdateStream.hs
@@ -0,0 +1,169 @@
+---------------------------------------------------------------------------
+-- |
+-- Module      :  Control.Concurrent.STM.UpdateStream
+--
+--
+-- Maintainer  :  joe@jerkface.net
+-- Stability   :  experimental
+--
+-- An UpdateSream consists of pass-through messages that are queued up and 
+-- slotted messages which might be obsoleted and discarded if they are not
+-- consumed before newer slotted messages with the same slot value occur.
+-- 
+-- Slots are implemented with "Control.Concurrent.STM.StatusCache" and it is
+-- recommended that you read that documentation first.
+--
+-- For example, the output
+--
+-- > Backlogged consumer: (set x = 5)(set y = 100)(Hello)(Joe)(was)(here)
+-- > Fast consumer: (set x = 2)(Hello)(set y = 23)(Joe)(set y = 100)(was)(set x = 5)(here)
+--
+-- is produced by the following code:
+--
+-- > import Control.Monad      (when, forever, (>=>))
+-- > import Control.Monad.STM  (atomically)
+-- > import Control.Concurrent (forkIO, threadDelay)
+-- > import System.IO          (hFlush, stdout)
+-- > import qualified Control.Concurrent.STM.UpdateStream as Cache
+-- > 
+-- > messages :: [(Maybe String, Char)]
+-- > messages = concat
+-- >     [ slot "x" "(set x = 2)"
+-- >     , message  "(Hello)"
+-- >     , slot "y" "(set y = 23)"
+-- >     , message  "(Joe)"
+-- >     , slot "y" "(set y = 100)"
+-- >     , message  "(was)"
+-- >     , slot "x" "(set x = 5)"
+-- >     , message  "(here)"
+-- >     ]
+-- >  where
+-- >     slot v cs = map ((,) (Just v)) cs
+-- >     message cs = map ((,) Nothing) cs
+-- > 
+-- > main = do
+-- >     q <- atomically $ Cache.new (== '(') (==')')
+-- >     let go = mapM_ (atomically . (uncurry $ Cache.push q)
+-- >                      >=> const (threadDelay 10000))
+-- >                    messages
+-- >         slowly = do
+-- >             while (atomically $ fmap not $ Cache.isEmpty q) $ do
+-- >                 c <- atomically $ Cache.pull q
+-- >                 putChar c
+-- >             putStrLn ""
+-- >             hFlush stdout
+-- >                           where while pred body =
+-- >                                  pred >>= flip when (body >> while pred body)
+-- >         quickly = forkIO . forever $ do
+-- >                     c <- atomically $ Cache.pull q
+-- >                     putChar c
+-- >                     hFlush stdout
+-- >     putStr $ "Backlogged consumer: "
+-- >     go >> slowly
+-- >     putStr "Fast consumer: "
+-- >     quickly >> go
+-- >     putStrLn ""
+--
+module Control.Concurrent.STM.UpdateStream
+    ( UpdateStream
+    , new
+    , push
+    , pull
+    , isStopper
+    , isStarter
+    , isEmpty
+    ) where
+
+import Control.Monad
+import Control.Monad.STM
+import Control.Concurrent.STM.TVar
+import Control.Concurrent.STM.TChan
+import Control.Concurrent.STM.StatusCache (StatusCache)
+import qualified Control.Concurrent.STM.StatusCache as Status
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Maybe
+import Data.Foldable (foldlM)
+
+data UpdateStream slot x =
+    UpdateStream { cache :: TVar (Map slot (StatusCache x))
+                 , events :: TChan x
+                 , inMessage :: TVar (Maybe (StatusCache x))
+                 , isStarter :: x -> Bool -- ^ True if the given chunk begins a message.
+                 , isStopper :: x -> Bool -- ^ True if the given chunk ends a message.
+                 }
+
+-- | @new isStart isStop@
+--
+-- The @isStart@ and @isStop@ predicates indicate when an element
+-- begins or ends a message.
+new :: Ord slot => (x->Bool) -> (x->Bool) -> STM (UpdateStream slot x)
+new isStart isStop = do
+    cache <- newTVar Map.empty
+    events <- newTChan
+    inMessage <- newTVar Nothing
+    return UpdateStream { cache = cache
+                        , events = events
+                        , inMessage = inMessage
+                        , isStarter = isStart
+                        , isStopper = isStop
+                        }
+
+-- | Enqueue a chunk into the 'UpdateStream'
+--
+-- If a slot is provided, then the message may be obsoleted when a new message
+-- starts with the same slot value.  Otherwise, the chunk is preserved.  Note
+-- that the same slot value must be passed again for every chunk of the message
+-- as it is not remembered.
+--
+-- Note that although a slot value is provided on each push, it is assumed that
+-- messages will be pushed in contiguous streams.  To change this, we would
+-- need to add a mutable integer to track the nesting level of the primary
+-- (non-slotted) stream.
+push :: Ord slot => UpdateStream slot x -> Maybe slot -> x -> STM ()
+push u Nothing x = writeTChan (events u) x
+push u (Just n) x = do
+    smap <- readTVar (cache u)
+    scache <-
+        case Map.lookup n smap of
+            Just scache -> return scache
+            Nothing -> do
+                scache <- Status.new (isStarter u) (isStopper u)
+                modifyTVar (cache u) (Map.insert n scache)
+                return scache
+
+    Status.push scache x
+
+-- | Pull off a chunk from the 'UpdateStream' for processing.
+-- 
+-- If chunks are not pulled off quickly, they may be obsoleted
+-- and discarded when new messages are 'push'ed.
+pull :: Ord slot => UpdateStream slot x -> STM x
+pull u = do
+    mbscache <- readTVar $ inMessage u
+    let action =
+         case mbscache of
+            Just scache -> do
+                x <- Status.pull scache
+                nesting <- readTVar (Status.pullDepth scache)
+                when (nesting==0) $ writeTVar (inMessage u) Nothing
+                return x
+            Nothing -> do
+                cs <- fmap (Map.toList) $ readTVar (cache u)
+                cs <- filterM (return . not <=< Status.isEmpty . snd)
+                              cs
+                maybe (readTChan $ events u)
+                      (\(n,scache) -> do
+                            writeTVar (inMessage u) (Just scache) -- (Just n)
+                            Status.pull scache)
+                      (listToMaybe cs)
+    x <- action
+    return x
+
+-- | True when the 'UpdateStream' is completely exhuasted.
+isEmpty :: UpdateStream slot x -> STM Bool
+isEmpty q = do
+    e <- isEmptyTChan (events q)
+    qs <- readTVar (cache q)
+    d <- foldlM (\b s -> fmap (b &&) $ Status.isEmpty s) True qs
+    return $ e && d
diff --git a/Data/BitSyntax.hs b/Data/BitSyntax.hs
new file mode 100644
index 00000000..dbb43f45
--- /dev/null
+++ b/Data/BitSyntax.hs
@@ -0,0 +1,429 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+-- | This module contains fuctions and templates for building up and breaking
+--   down packed bit structures. It's something like Erlang's bit-syntax (or,
+--   actually, more like Python's struct module).
+--
+--   This code uses Data.ByteString which is included in GHC 6.5 and you can
+--   get it for 6.4 at <http://www.cse.unsw.edu.au/~dons/fps.html>
+module Data.BitSyntax (
+  -- * Building bit structures
+  -- | The core function here is makeBits, which is a perfectly normal function.
+  --   Here's an example which makes a SOCKS4a request header:
+  -- @
+  --   makeBits [U8 4, U8 1, U16 80, U32 10, NullTerminated \"username\",
+  --             NullTerminated \"www.haskell.org\"]
+  -- @
+  BitBlock(..),
+  makeBits,
+  -- * Breaking up bit structures
+  -- | The main function for this is bitSyn, which is a template function and
+  --   so you'll need to run with @-fth@ to enable template haskell
+  --   <http://www.haskell.org/th/>.
+  --
+  --   To expand the function you use the splice command:
+  -- @
+  --   $(bitSyn [...])
+  -- @
+  --
+  -- The expanded function has type @ByteString -> (...)@ where the elements of
+  -- the tuple depend of the argument to bitSyn (that's why it has to be a template
+  -- function).
+  --
+  -- Heres an example, translated from the Erlang manual, which parses an IP header:
+  --
+  -- @
+  -- decodeOptions bs ([_, hlen], _, _, _, _, _, _, _, _, _)
+  --   | hlen > 5  = return $ BS.splitAt (fromIntegral ((hlen - 5) * 4)) bs
+  --   | otherwise = return (BS.empty, bs)
+  -- @
+  --
+  -- @
+  -- ipDecode = $(bitSyn [PackedBits [4, 4], Unsigned 1, Unsigned 2, Unsigned 2,
+  --                      PackedBits [3, 13], Unsigned 1, Unsigned 1, Unsigned 2,
+  --                      Fixed 4, Fixed 4, Context \'decodeOptions, Rest])
+  -- @
+  --
+  -- @
+  -- ipPacket = BS.pack [0x45, 0, 0, 0x34, 0xd8, 0xd2, 0x40, 0, 0x40, 0x06,
+  --                     0xa0, 0xca, 0xac, 0x12, 0x68, 0x4d, 0xac, 0x18,
+  --                     0x00, 0xaf]
+  -- @
+  --
+  -- This function has several weaknesses compared to the Erlang version: The
+  -- elements of the bit structure are not named in place, instead you have to
+  -- do a pattern match on the resulting tuple and match up the indexes. The
+  -- type system helps in this, but it's still not quite as nice.
+
+  ReadType(..), bitSyn,
+
+  -- I get errors if these aren't exported (Can't find interface-file
+  -- declaration for Data.BitSyntax.decodeU16)
+  decodeU8, decodeU16, decodeU32, decodeU16LE, decodeU32LE) where
+
+import Language.Haskell.TH.Lib
+import Language.Haskell.TH.Syntax
+
+import qualified Data.ByteString as BS
+import Data.Char (ord)
+import Control.Monad
+-- import Test.QuickCheck (Arbitrary(), arbitrary, Gen())
+
+import Foreign
+
+foreign import ccall unsafe "htonl" htonl :: Word32 -> Word32
+foreign import ccall unsafe "htons" htons :: Word16 -> Word16
+
+-- There's no good way to convert to little-endian. The htons functions only
+-- convert to big endian and they don't have any little endian friends. So we
+-- need to detect which kind of system we are on and act accordingly. We can
+-- detect the type of system by seeing if htonl actaully doesn't anything (it's
+-- the identity function on big-endian systems, of course). If it doesn't we're
+-- on a big-endian system and so need to do the byte-swapping in Haskell because
+-- the C functions are no-ops
+
+-- | A native Haskell version of htonl for the case where we need to convert
+--   to little-endian on a big-endian system
+endianSwitch32 :: Word32 -> Word32
+endianSwitch32 a = ((a .&. 0xff) `shiftL` 24) .|.
+                   ((a .&. 0xff00) `shiftL` 8) .|.
+                   ((a .&. 0xff0000) `shiftR` 8) .|.
+                   (a `shiftR` 24)
+
+-- | A native Haskell version of htons for the case where we need to convert
+--   to little-endian on a big-endian system
+endianSwitch16 :: Word16 -> Word16
+endianSwitch16 a = ((a .&. 0xff) `shiftL` 8) .|.
+                   (a `shiftR` 8)
+
+littleEndian32 :: Word32 -> Word32
+littleEndian32 a = if htonl 1 == 1
+                     then endianSwitch32 a
+                     else a
+
+littleEndian16 :: Word16 -> Word16
+littleEndian16 a = if htonl 1 == 1
+                     then endianSwitch16 a
+                     else a
+
+data BitBlock = -- | Unsigned 8-bit int
+                U8 Int |
+                -- | Unsigned 16-bit int
+                U16 Int |
+                -- | Unsigned 32-bit int
+                U32 Int |
+                -- | Little-endian, unsigned 16-bit int
+                U16LE Int |
+                -- | Little-endian, unsigned 32-bit int
+                U32LE Int |
+                -- | Appends the string with a trailing NUL byte
+                NullTerminated String |
+                -- | Appends the string without any terminator
+                RawString String |
+                -- | Appends a ByteString
+                RawByteString BS.ByteString |
+                -- | Packs a series of bit fields together. The argument is
+                --   a list of pairs where the first element is the size
+                --   (in bits) and the second is the value. The sum of the
+                --   sizes for a given PackBits must be a multiple of 8
+                PackBits [(Int, Int)]
+                deriving (Show)
+
+-- Encodes a member of the Bits class as a series of bytes and returns the
+-- ByteString of those bytes.
+getBytes :: (Integral a, Bounded a, Bits a) => a -> BS.ByteString
+getBytes input =
+    let getByte _ 0 = []
+        getByte x remaining = (fromIntegral $ (x .&. 0xff)) :
+                              getByte (shiftR x 8) (remaining - 1)
+        in
+        if (bitSize input `mod` 8) /= 0
+           then error "Input data bit size must be a multiple of 8"
+           else BS.pack $ getByte input (bitSize input `div` 8)
+
+-- Performs the work behind PackBits
+packBits :: (Word8, Int, [Word8])  -- ^ The current byte, the number of bits
+                                   --   used in that byte and the (reverse)
+                                   --   list of produced bytes
+         -> (Int, Int)  -- ^ The size (in bits) of the value, and the value
+         -> (Word8, Int, [Word8])  -- See first argument
+packBits (current, used, bytes) (size, value) =
+  if bitsWritten < size
+    then packBits (0, 0, current' : bytes) (size - bitsWritten, value)
+    else if used' == 8
+           then (0, 0, current' : bytes)
+           else (current', used', bytes)
+  where
+    top = size - 1
+    topOfByte = 7 - used
+    aligned = value `shift` (topOfByte - top)
+    newBits = (fromIntegral aligned) :: Word8
+    current' = current .|. newBits
+    bitsWritten = min (8 - used) size
+    used' = used + bitsWritten
+
+bits :: BitBlock -> BS.ByteString
+bits (U8 v) = BS.pack [((fromIntegral v) :: Word8)]
+bits (U16 v) = getBytes ((htons $ fromIntegral v) :: Word16)
+bits (U32 v) = getBytes ((htonl $ fromIntegral v) :: Word32)
+bits (U16LE v) = getBytes (littleEndian16 $ fromIntegral v)
+bits (U32LE v) = getBytes (littleEndian32 $ fromIntegral v)
+bits (NullTerminated str) = BS.pack $ (map (fromIntegral . ord) str) ++ [0]
+bits (RawString str) = BS.pack $ map (fromIntegral . ord) str
+bits (RawByteString bs) = bs
+bits (PackBits bitspec) =
+  if (sum $ map fst bitspec) `mod` 8 /= 0
+    then error "Sum of sizes of a bit spec must == 0 mod 8"
+    else (\(_, _, a) -> BS.pack $ reverse a) $ foldl packBits (0, 0, []) bitspec
+
+-- | Make a binary string from the list of elements given
+makeBits :: [BitBlock] -> BS.ByteString
+makeBits = BS.concat . (map bits)
+
+data ReadType = -- | An unsigned number of some number of bytes. Valid
+                --   arguments are 1, 2 and 4
+                Unsigned Integer |
+                -- | An unsigned, little-endian integer of some number of
+                --   bytes. Valid arguments are 2 and 4
+                UnsignedLE Integer |
+                -- | A variable length element to be decoded by a custom
+                --   function. The function's name is given as the single
+                --   argument and should have type
+                --   @Monad m => ByteString -> m (v, ByteString)@
+                Variable Name |
+                -- | Skip some number of bytes
+                Skip Integer |
+                -- | A fixed size field, the result of which is a ByteString
+                --   of that length.
+                Fixed Integer |
+                -- | Decode a value and ignore it (the result will not be part
+                --   of the returned tuple)
+                Ignore ReadType |
+                -- | Like variable, but the decoding function is passed the
+                --   entire result tuple so far. Thus the function whose name
+                --   passed has type
+                --   @Monad m => ByteString -> (...) -> m (v, ByteString)@
+                Context Name |
+                -- | Takes the most recent element of the result tuple and
+                --   interprets it as the length of this field. Results in
+                --   a ByteString
+                LengthPrefixed |
+                -- | Decode a series of bit fields, results in a list of
+                --   Integers. Each element of the argument is the length of
+                --   the bit field. The sums of the lengths must be a multiple
+                --   of 8
+                PackedBits [Integer] |
+                -- | Results in a ByteString containing the undecoded bytes so
+                --   far. Generally used at the end to return the trailing body
+                --   of a structure, it can actually be used at any point in the
+                --   decoding to return the trailing part at that point.
+                Rest
+
+fromBytes :: (Num a, Bits a) => [a] -> a
+fromBytes input =
+    let dofb accum [] = accum
+        dofb accum (x:xs) = dofb ((shiftL accum 8) .|. x) xs
+        in
+        dofb 0 $ reverse input
+
+decodeU8 :: BS.ByteString -> Word8
+decodeU8 = fromIntegral . head . BS.unpack
+decodeU16 :: BS.ByteString -> Word16
+decodeU16 = htons . fromBytes . map fromIntegral . BS.unpack
+decodeU32 :: BS.ByteString -> Word32
+decodeU32 = htonl . fromBytes . map fromIntegral . BS.unpack
+decodeU16LE :: BS.ByteString -> Word16
+decodeU16LE = littleEndian16 . fromBytes . map fromIntegral . BS.unpack
+decodeU32LE :: BS.ByteString -> Word32
+decodeU32LE = littleEndian32 . fromBytes . map fromIntegral . BS.unpack
+
+decodeBits :: [Integer] -> BS.ByteString -> [Integer]
+decodeBits sizes bs =
+  reverse values
+  where
+    (values, _, _) = foldl unpackBits ([], 0, BS.unpack bitdata) sizes
+    bytesize = (sum sizes) `shiftR` 3
+    (bitdata, _) = BS.splitAt (fromIntegral bytesize) bs
+
+unpackBits :: ([Integer], Integer, [Word8]) -> Integer -> ([Integer], Integer, [Word8])
+unpackBits state size = unpackBitsInner 0 state size
+
+unpackBitsInner :: Integer ->
+                   ([Integer], Integer, [Word8]) ->
+                   Integer ->
+                   ([Integer], Integer, [Word8])
+unpackBitsInner _ (output, used, []) _ = (output, used, [])
+unpackBitsInner val (output, used, current : input) bitsToGet =
+  if bitsToGet' > 0
+    then unpackBitsInner val'' (output, 0, input) bitsToGet'
+    else if used' < 8
+           then (val'' : output, used', current'' : input)
+           else (val'' : output, 0, input)
+  where
+    bitsAv = 8 - used
+    bitsTaken = min bitsAv bitsToGet
+    val' = val `shift` (fromIntegral bitsTaken)
+    current' = current `shiftR` (fromIntegral (8 - bitsTaken))
+    current'' = current `shiftL` (fromIntegral bitsTaken)
+    val'' = val' .|. (fromIntegral current')
+    bitsToGet' = bitsToGet - bitsTaken
+    used' = used + bitsTaken
+
+readElement :: ([Stmt], Name, [Name]) -> ReadType -> Q ([Stmt], Name, [Name])
+
+readElement (stmts, inputname, tuplenames) (Context funcname) = do
+  valname <- newName "val"
+  restname <- newName "rest"
+
+  let stmt = BindS (TupP [VarP valname, VarP restname])
+                   (AppE (AppE (VarE funcname)
+                               (VarE inputname))
+                         (TupE $ map VarE $ reverse tuplenames))
+
+  return (stmt : stmts, restname, valname : tuplenames)
+
+readElement (stmts, inputname, tuplenames) (Fixed n) = do
+  valname <- newName "val"
+  restname <- newName "rest"
+  let dec1 = ValD (TupP [VarP valname, VarP restname])
+                  (NormalB $ AppE (AppE (VarE 'BS.splitAt)
+                                        (LitE (IntegerL n)))
+                                  (VarE inputname))
+                  []
+
+  return (LetS [dec1] : stmts, restname, valname : tuplenames)
+
+readElement state@(_, _, tuplenames) (Ignore n) = do
+  (a, b, _) <- readElement state n
+  return (a, b, tuplenames)
+
+readElement (stmts, inputname, tuplenames) LengthPrefixed = do
+  valname <- newName "val"
+  restname <- newName "rest"
+
+  let sourcename = head tuplenames
+      dec = ValD (TupP [VarP valname, VarP restname])
+                 (NormalB $ AppE (AppE (VarE 'BS.splitAt)
+                                       (AppE (VarE 'fromIntegral)
+                                             (VarE sourcename)))
+                                 (VarE inputname))
+                 []
+
+  return (LetS [dec] : stmts, restname, valname : tuplenames)
+
+readElement (stmts, inputname, tuplenames) (Variable funcname) = do
+  valname <- newName "val"
+  restname <- newName "rest"
+
+  let stmt = BindS (TupP [VarP valname, VarP restname])
+                   (AppE (VarE funcname) (VarE inputname))
+
+  return (stmt : stmts, restname, valname : tuplenames)
+
+readElement (stmts, inputname, tuplenames) Rest = do
+  restname <- newName "rest"
+  let dec = ValD (VarP restname)
+                 (NormalB $ VarE inputname)
+                 []
+  return (LetS [dec] : stmts, inputname, restname : tuplenames)
+
+readElement (stmts, inputname, tuplenames) (Skip n) = do
+  -- Expands to something like:
+  --   rest = Data.ByteString.drop n input
+  restname <- newName "rest"
+  let dec = ValD (VarP restname)
+                 (NormalB $ AppE (AppE (VarE 'BS.drop)
+                                       (LitE (IntegerL n)))
+                                 (VarE inputname))
+                 []
+  return (LetS [dec] : stmts, restname, tuplenames)
+
+readElement state (Unsigned size) = do
+  -- Expands to something like:
+  --    (aval, arest) = Data.ByteString.splitAt 1 input
+  --    a = BitSyntax.decodeU8 aval
+  let decodefunc = case size of
+                     1 -> 'decodeU8
+                     2 -> 'decodeU16
+                     _ -> 'decodeU32 -- Default to 32
+  decodeHelper state (VarE decodefunc) size
+
+readElement state (UnsignedLE size) = do
+  -- Expands to something like:
+  --    (aval, arest) = Data.ByteString.splitAt 1 input
+  --    a = BitSyntax.decodeU8LE aval
+  let decodefunc = case size of
+                     2 -> 'decodeU16LE
+                     _ -> 'decodeU32LE -- Default to 4
+  decodeHelper state (VarE decodefunc) size
+
+readElement state (PackedBits sizes) =
+  if sum sizes `mod` 8 /= 0
+    then error "Sizes of packed bits must == 0 mod 8"
+    else decodeHelper state
+                      (AppE (VarE 'decodeBits)
+                            (ListE $ map (LitE . IntegerL) sizes))
+                      ((sum sizes) `shiftR` 3)
+
+decodeHelper :: ([Stmt], Name, [Name])      -> Exp
+                                            -> Integer
+                                            -> Q ([Stmt], Name, [Name])
+decodeHelper (stmts, inputname, tuplenames) decodefunc size = do
+  valname <- newName "val"
+  restname <- newName "rest"
+  tuplename <- newName "tup"
+  let dec1 = ValD (TupP [VarP valname, VarP restname])
+                  (NormalB $ AppE (AppE (VarE 'BS.splitAt)
+                                        (LitE (IntegerL size)))
+                                  (VarE inputname))
+                  []
+  let dec2 = ValD (VarP tuplename)
+                  (NormalB $ AppE decodefunc (VarE valname))
+                  []
+
+  return (LetS [dec1, dec2] : stmts, restname, tuplename : tuplenames)
+
+decGetName :: Dec -> Name
+decGetName (ValD (VarP name) _ _) = name
+decGetName _                      = undefined -- Error!
+
+bitSyn :: [ReadType] -> Q Exp
+bitSyn elements = do
+    inputname <- newName "input"
+    (stmts, restname, tuplenames) <- foldM readElement ([], inputname, []) elements
+    returnS <- NoBindS `liftM` [| return $(tupE . map varE $ reverse tuplenames) |]
+    return $ LamE [VarP inputname] (DoE . reverse $ returnS : stmts)
+
+
+-- Tests
+prop_bitPacking :: [(Int, Int)] -> Bool
+prop_bitPacking fields =
+  prevalues == (map fromIntegral postvalues) ||
+  any (< 1) (map fst fields) ||
+  any (< 0) (map snd fields)
+  where
+    undershoot = sum (map fst fields) `mod` 8
+    fields' = if undershoot > 0
+                then (8 - undershoot, 1) : fields
+                else fields
+    prevalues = map snd fields'
+    packed = bits $ PackBits fields'
+    postvalues = decodeBits (map (fromIntegral . fst) fields') packed
+
+{-
+instance Arbitrary Word16 where
+  arbitrary = (arbitrary :: Gen Int) >>= return . fromIntegral
+instance Arbitrary Word32 where
+  arbitrary = (arbitrary :: Gen Int) >>= return . fromIntegral
+-}
+
+-- | This only works on little-endian machines as it checks that the foreign
+--   functions (htonl and htons) match the native ones
+prop_nativeByteShuffle32 :: Word32 -> Bool
+prop_nativeByteShuffle32 x = endianSwitch32 x == htonl x
+prop_nativeByteShuffle16 :: Word16 -> Bool
+prop_nativeByteShuffle16 x = endianSwitch16 x == htons x
+prop_littleEndian16 :: Word16 -> Bool
+prop_littleEndian16 x = littleEndian16 x == x
+prop_littleEndian32 :: Word32 -> Bool
+prop_littleEndian32 x = littleEndian32 x == x
diff --git a/PingMachine.hs b/PingMachine.hs
new file mode 100644
index 00000000..b714d71e
--- /dev/null
+++ b/PingMachine.hs
@@ -0,0 +1,113 @@
+{-# LANGUAGE CPP #-}
+module PingMachine where
+
+import Control.Monad
+import Data.Function
+#ifdef THREAD_DEBUG
+import Control.Concurrent.Lifted.Instrument
+#else
+import Control.Concurrent.Lifted
+import GHC.Conc                  (labelThread)
+#endif
+import Control.Concurrent.STM
+
+import InterruptibleDelay
+
+type Miliseconds = Int
+type TimeOut = Miliseconds
+type PingInterval = Miliseconds
+
+-- | Events that occur as a result of the 'PingMachine' watchdog.
+--
+-- Use 'pingWait' to wait for one of these to occur.
+data PingEvent
+    = PingIdle    -- ^ You should send a ping if you observe this event.
+    | PingTimeOut -- ^ You should give up on the connection in case of this event.
+
+data PingMachine = PingMachine
+    { pingFlag          :: TVar Bool
+    , pingInterruptible :: InterruptibleDelay
+    , pingEvent         :: TMVar PingEvent
+    , pingStarted       :: TMVar Bool
+    }
+
+-- | Fork a thread to monitor a connection for a ping timeout.
+--
+-- If 'pingBump' is not invoked after a idle is signaled, a timeout event will
+-- occur.  When that happens, even if the caller chooses to ignore this event,
+-- the watchdog thread will be terminated and no more ping events will be
+-- signaled.
+--
+-- An idle connection will be signaled by:
+--
+--   (1) 'pingFlag' is set 'True'
+--
+--   (2) 'pingWait' returns 'PingIdle'
+--
+-- Either may be tested to determine whether a ping should be sent but
+-- 'pingFlag' is difficult to use properly because it is up to the caller to
+-- remember that the ping is already in progress.
+forkPingMachine
+    :: PingInterval -- ^ Milliseconds of idle before a ping is considered necessary.
+    -> TimeOut      -- ^ Milliseconds after 'PingIdle' before we signal 'PingTimeOut'.
+    -> IO PingMachine
+forkPingMachine idle timeout = do
+    d <- interruptibleDelay
+    flag <- atomically $ newTVar False
+    canceled <- atomically $ newTVar False
+    event <- atomically newEmptyTMVar
+    started <- atomically $ newEmptyTMVar
+    when (idle/=0) $ void . forkIO $ do
+        myThreadId >>= flip labelThread ("ping.watchdog")
+        (>>=) (atomically (readTMVar started)) $ flip when $ do
+        fix $ \loop -> do
+            atomically $ writeTVar flag False
+            fin <- startDelay d (1000*idle)
+            (>>=) (atomically (readTMVar started)) $ flip when $ do
+            if (not fin) then loop
+            else do
+            -- Idle event
+            atomically $ do
+                tryTakeTMVar event
+                putTMVar event PingIdle
+                writeTVar flag True
+            fin <- startDelay d (1000*timeout)
+            (>>=) (atomically (readTMVar started)) $ flip when $ do
+            me <- myThreadId
+            if (not fin) then loop
+            else do
+            -- Timeout event
+            atomically $ do
+                tryTakeTMVar event
+                writeTVar flag False
+                putTMVar event PingTimeOut
+    return PingMachine
+        { pingFlag          = flag
+        , pingInterruptible = d
+        , pingEvent         = event
+        , pingStarted       = started
+        }
+
+-- | Terminate the watchdog thread.  Call this upon connection close.
+--
+-- You should ensure no threads are waiting on 'pingWait' because there is no
+-- 'PingEvent' signaling termination.
+pingCancel :: PingMachine -> IO ()
+pingCancel me = do
+    atomically $ do tryTakeTMVar (pingStarted me)
+                    putTMVar (pingStarted me) False
+    interruptDelay (pingInterruptible me)
+
+-- | Reset the ping timer.  Call this regularly to prevent 'PingTimeOut'.
+pingBump :: PingMachine -> IO ()
+pingBump me = do
+    atomically $ do
+            b <- tryReadTMVar (pingStarted me)
+            when (b/=Just False) $ do
+                tryTakeTMVar (pingStarted me)
+                putTMVar (pingStarted me) True
+    interruptDelay (pingInterruptible me)
+
+-- | Retries until a 'PingEvent' occurs.
+pingWait :: PingMachine -> STM PingEvent
+pingWait me = takeTMVar (pingEvent me)
diff --git a/Presence/ByteStringOperators.hs b/Presence/ByteStringOperators.hs
new file mode 100644
index 00000000..4453aca0
--- /dev/null
+++ b/Presence/ByteStringOperators.hs
@@ -0,0 +1,50 @@
+{-# LANGUAGE CPP #-}
+module ByteStringOperators where
+
+import qualified Data.ByteString as S (ByteString)
+import Data.ByteString.Lazy.Char8 as L 
+import Control.Applicative
+
+-- These two were imported to provide an NFData instance.
+import qualified Data.ByteString.Lazy.Internal as L (ByteString(..))
+import Control.DeepSeq
+
+
+(<++>) :: ByteString -> ByteString -> ByteString
+(<++.>) :: ByteString -> S.ByteString -> ByteString
+(<.++>) :: S.ByteString -> ByteString -> ByteString
+(<.++.>) :: S.ByteString -> S.ByteString -> ByteString
+a <++> b =  L.append a b
+a <++.> b = L.append a (fromChunks [b])
+a <.++> b = L.append (fromChunks [a]) b
+a <.++.> b = fromChunks [a,b]
+infixr 5 <.++.>
+infixr 5 <.++>
+infixr 5 <++>
+infixr 5 <++.>
+
+a <++$> b = fmap (a<++>) b
+a <$++> b = fmap (<++>b) a
+a <$++$> b = liftA2 (<++>) a b
+infixr 6 <++$>
+infixr 6 <$++>
+infixr 6 <$++$>
+
+Nothing <?++> b = b
+Just a  <?++> b = a <++> b
+infixr 5 <?++>
+
+a <++?> Nothing = a
+a <++?> Just b  = a <++> b
+infixr 5 <++?>
+
+bshow :: Show a => a -> ByteString
+bshow = L.pack . show
+
+
+#if MIN_VERSION_bytestring(0,10,0)
+#else
+instance NFData L.ByteString where
+    rnf L.Empty       = ()
+    rnf (L.Chunk _ b) = rnf b
+#endif
diff --git a/Presence/ClientState.hs b/Presence/ClientState.hs
new file mode 100644
index 00000000..30a53131
--- /dev/null
+++ b/Presence/ClientState.hs
@@ -0,0 +1,34 @@
+module ClientState where
+
+import Control.Concurrent.STM
+import Data.Text ( Text )
+import Data.Int  ( Int8 )
+import Data.Bits ( (.&.) )
+
+import UTmp       ( ProcessID )
+import XMPPServer ( Stanza )
+
+data ClientState = ClientState
+    { clientResource :: Text
+    , clientUser :: Text
+    , clientPid :: Maybe ProcessID
+    , clientStatus :: TVar (Maybe Stanza)
+    , clientFlags :: TVar Int8
+    }
+
+cf_available :: Int8
+cf_available = 0x1
+cf_interested :: Int8
+cf_interested = 0x2
+
+-- | True if the client has sent an initial presence
+clientIsAvailable :: ClientState -> STM Bool
+clientIsAvailable c  = do
+    flgs <- readTVar (clientFlags c)
+    return $ flgs .&. cf_available /= 0
+
+-- | True if the client has requested a roster
+clientIsInterested :: ClientState -> STM Bool
+clientIsInterested c = do
+    flgs <- readTVar (clientFlags c)
+    return $ flgs .&. cf_interested /= 0
diff --git a/Presence/ConfigFiles.hs b/Presence/ConfigFiles.hs
new file mode 100644
index 00000000..808e6dd8
--- /dev/null
+++ b/Presence/ConfigFiles.hs
@@ -0,0 +1,130 @@
+{-# LANGUAGE OverloadedStrings #-}
+module ConfigFiles where
+
+import Data.ByteString.Lazy.Char8 as L
+import System.Posix.User
+import System.Posix.Files (fileExist)
+import System.FilePath
+import System.Directory
+import System.IO
+-- import System.IO.Strict
+import System.IO.Error
+import Control.Exception
+import Control.Monad
+import Control.DeepSeq
+import ByteStringOperators () -- For NFData instance
+import ControlMaybe
+import Data.List (partition)
+import Data.Maybe (catMaybes,isJust)
+
+type User = ByteString
+
+configDir = ".presence"
+buddyFile = "buddies"
+subscriberFile = "subscribers"
+otherFile = "others"
+pendingFile = "pending"
+solicitedFile = "solicited"
+
+
+configPath :: User -> String -> IO String
+configPath user filename = do
+    ue <- getUserEntryForName (unpack user)
+    return $ (++("/"++configDir++"/"++filename)) $ homeDirectory ue
+
+
+createConfigFile tag path = do
+    let dir = dropFileName path
+    doesDirectoryExist dir >>= flip unless (do
+            createDirectory dir 
+        )
+    withFile path WriteMode $ \h -> do
+        L.hPutStrLn h tag
+
+addItem item tag path =
+    let doit = do
+         handle (\e -> when (isDoesNotExistError e) 
+                       (createConfigFile tag path >> doit))
+           $ do exists <- fileExist path
+                if exists
+                  then withFile path AppendMode $ \h ->
+                         L.hPutStrLn h item
+                  else withFile path WriteMode $ \h -> do
+                         L.hPutStrLn h tag
+                         L.hPutStrLn h item
+    in doit
+
+
+modifyFile ::
+  (ByteString,FilePath)
+  -> ByteString
+  -> (ByteString -> IO (Maybe ByteString))
+  -> Maybe ByteString
+  -> IO Bool -- Returns True if test function ever returned Nothing
+modifyFile (tag,file) user test appending = configPath user file >>= doit
+    where
+        doit path = do
+         handle (\e -> if (isDoesNotExistError e) 
+                        then (createConfigFile tag path >> doit path)
+                        else return False)
+           $ do exists <- fileExist path
+                if exists
+                  then do
+                    xs <- withFile path ReadMode $ \h -> do
+                             contents <- L.hGetContents h
+                             case L.lines contents of
+                              x:xs -> mapM test xs
+                              _    -> return []
+                    let (keepers,deleted) = partition isJust xs
+                    withFile path WriteMode $ \h -> do
+                        L.hPutStrLn h tag
+                        forM_ (catMaybes keepers) (L.hPutStrLn h)
+                        withJust appending (L.hPutStrLn h)
+                    return . not . Prelude.null $ deleted
+                  else do
+                    withFile path WriteMode $ \h -> do
+                        L.hPutStrLn h tag
+                        withJust appending (L.hPutStrLn h)
+                    return False 
+
+
+modifySolicited  = modifyFile ("<? solicited ?>" , solicitedFile)
+modifyBuddies    = modifyFile ("<? buddies ?>"   , buddyFile)
+modifyOthers     = modifyFile ("<? others ?>"    , otherFile)
+modifyPending    = modifyFile ("<? pending ?>"   , pendingFile)
+modifySubscribers = modifyFile ("<? subscribers ?>", subscriberFile)
+
+addBuddy :: User -> ByteString -> IO ()
+addBuddy user buddy =
+    configPath user buddyFile >>= addItem buddy "<? buddies ?>"
+
+addSubscriber :: User -> ByteString -> IO ()
+addSubscriber user subscriber =
+    configPath user subscriberFile >>= addItem subscriber "<? subscribers ?>"
+
+addSolicited :: User -> ByteString -> IO ()
+addSolicited user solicited =
+    configPath user solicitedFile >>= addItem solicited "<? solicited ?>"
+
+
+getConfigList path = 
+  handle (\e -> if isDoesNotExistError e then (return []) else throw e)
+    $ withFile path ReadMode $
+        L.hGetContents 
+        >=> return . Prelude.tail . L.lines 
+        >=> (\a -> seq (rnf a) (return a))
+
+getBuddies :: User -> IO [ByteString]
+getBuddies user = configPath user buddyFile >>= getConfigList
+
+getSubscribers :: User -> IO [ByteString]
+getSubscribers user = configPath user subscriberFile >>= getConfigList
+
+getOthers :: User -> IO [ByteString]
+getOthers user = configPath user otherFile >>= getConfigList
+
+getPending :: User -> IO [ByteString]
+getPending user = configPath user pendingFile >>= getConfigList
+
+getSolicited :: User -> IO [ByteString]
+getSolicited user = configPath user solicitedFile >>= getConfigList
diff --git a/Presence/ConnectionKey.hs b/Presence/ConnectionKey.hs
new file mode 100644
index 00000000..944f4f6f
--- /dev/null
+++ b/Presence/ConnectionKey.hs
@@ -0,0 +1,10 @@
+module ConnectionKey where
+
+import Network.Socket ( SockAddr(..) )
+import SockAddr ()
+
+data ConnectionKey
+       = PeerKey { callBackAddress :: SockAddr }
+       | ClientKey { localAddress :: SockAddr }
+ deriving (Show, Ord, Eq)
+
diff --git a/Presence/ConsoleWriter.hs b/Presence/ConsoleWriter.hs
new file mode 100644
index 00000000..986294f4
--- /dev/null
+++ b/Presence/ConsoleWriter.hs
@@ -0,0 +1,411 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
+module ConsoleWriter
+    ( ConsoleWriter(cwPresenceChan)
+    , newConsoleWriter
+    , writeActiveTTY
+    , writeAllPty
+    , cwClients
+    ) where
+
+import Control.Monad
+-- import Control.Applicative
+import Control.Concurrent
+import Control.Concurrent.STM
+import Data.Monoid
+import Data.Char
+import Data.Maybe
+import System.Environment hiding (setEnv)
+import System.Exit ( ExitCode(ExitSuccess) )
+import System.Posix.Env     ( setEnv )
+import System.Posix.Process ( forkProcess, exitImmediately, executeFile )
+import System.Posix.User  ( setUserID, getUserEntryForName, userID )
+import System.Posix.Files ( getFileStatus, fileMode )
+import System.INotify ( initINotify, EventVariety(Modify), addWatch )
+import Data.Word      ( Word8 )
+import Data.Text      ( Text )
+import Data.Map       ( Map )
+import Data.List      ( foldl', groupBy )
+import Data.Bits      ( (.&.) )
+import qualified Data.Map as Map
+import qualified Data.Traversable as Traversable
+import qualified Data.Text as Text
+-- import qualified Data.Text.IO as Text
+import qualified Network.BSD as BSD
+
+import UTmp           ( users2, utmp_file, UtmpRecord(..), UT_Type(..) )
+import FGConsole      ( forkTTYMonitor )
+import XMPPServer     ( Stanza, makePresenceStanza, JabberShow(..), stanzaType
+                      , LangSpecificMessage(..), msgLangMap, cloneStanza, stanzaFrom )
+import ControlMaybe   ( handleIO_ )
+import ClientState
+
+data ConsoleWriter = ConsoleWriter
+    { cwPresenceChan :: TMVar (ClientState,Stanza)
+    -- ^ tty switches and logins are announced on this mvar
+    , csActiveTTY :: TVar Word8
+    , csUtmp :: TVar (Map Text (TVar (Maybe UtmpRecord)))
+    , cwClients :: TVar (Map Text ClientState)
+    -- ^ This 'TVar' holds a map from resource id (tty name)
+    --   to ClientState for all active TTYs and PTYs.
+    }
+
+tshow :: forall a. Show a => a -> Text
+tshow x = Text.pack . show $ x
+
+retryWhen :: forall b. STM b -> (b -> Bool) -> STM b
+retryWhen var pred = do
+    value <- var
+    if pred value then retry
+                  else return value
+
+
+onLogin ::
+    forall t.
+    ConsoleWriter
+    -> (STM (Word8, Maybe UtmpRecord)
+        -> TVar (Maybe UtmpRecord) -> IO ())
+    -> t
+    -> IO ()
+onLogin cs start = \e -> do
+    us <- UTmp.users2
+    let (m,cruft) =
+            foldl' (\(m,cruft) x ->
+                        case utmpType x of
+                         USER_PROCESS
+                           -> (Map.insert (utmpTty x) x m,cruft)
+                         DEAD_PROCESS | utmpPid x /= 0
+                           -> (m,Map.insert (utmpTty x) x cruft)
+                         _ -> (m,cruft))
+                   (Map.empty,Map.empty)
+                   us
+    forM_ (Map.elems cruft) $ \c -> do
+        putStrLn $ "cruft " ++ show (utmpTty c, utmpPid c,utmpHost c, utmpRemoteAddr c)
+    newborn <- atomically $ do
+        old <- readTVar (csUtmp cs) -- swapTVar (csUtmp cs) m
+        newborn <- flip Traversable.mapM (m Map.\\ old)
+                    $ newTVar . Just
+        updated <- let upd v u = writeTVar v $ Just u
+                   in Traversable.sequence $ Map.intersectionWith upd old m
+        let dead = old Map.\\ m
+        Traversable.mapM (flip writeTVar Nothing) dead
+        writeTVar (csUtmp cs) $ (old `Map.union` newborn) Map.\\ dead
+        return newborn
+    let getActive = do
+            tty <- readTVar $ csActiveTTY cs
+            utmp <- readTVar $ csUtmp cs
+            flip (maybe $ return (tty,Nothing))
+                 (Map.lookup ("tty"<>tshow tty) utmp)
+                $ \tuvar -> do
+            tu <- readTVar tuvar
+            return (tty,tu)
+            
+    forM_ (Map.elems newborn) $ 
+        forkIO . start getActive
+    -- forM_ (Map.elems dead   ) $ putStrLn . ("gone: "++) . show
+
+-- | Sets up threads to monitor tty switches and logins that are
+-- written to the system utmp file and returns a 'ConsoleWriter'
+-- object for interacting with that information.
+newConsoleWriter :: IO (Maybe ConsoleWriter)
+newConsoleWriter = do
+    chan <- atomically $ newEmptyTMVar
+    cs <- atomically $ do
+        ttyvar <- newTVar 0
+        utmpvar <- newTVar Map.empty
+        clients <- newTVar Map.empty
+        return $ ConsoleWriter { cwPresenceChan = chan
+                               , csActiveTTY = ttyvar
+                               , csUtmp = utmpvar
+                               , cwClients = clients
+                               }
+    outvar <- atomically $ newTMVar ()
+    let logit outvar s = do
+            {-
+            atomically $ takeTMVar outvar
+            Text.putStrLn s
+            atomically $ putTMVar outvar ()
+            -}
+            return ()
+        onTTY outvar cs vtnum = do
+            logit outvar $ "switch: " <> tshow vtnum
+            atomically $ writeTVar (csActiveTTY cs) vtnum
+
+    inotify <- initINotify
+
+    -- get active tty
+    mtty <- forkTTYMonitor (onTTY outvar cs)
+    forM mtty $ \_ -> do
+    atomically $ retryWhen (readTVar $ csActiveTTY cs) (==0)
+
+    -- read utmp
+    onLogin cs (newCon (logit outvar) cs) Modify
+
+    -- monitor utmp
+    wd <- addWatch
+            inotify
+            [Modify] -- [CloseWrite,Open,Close,Access,Modify,Move]
+            utmp_file
+            (onLogin cs (newCon (logit outvar) cs))
+    return cs
+
+-- Transforms a string of form language[_territory][.codeset][@modifier]
+-- typically used in LC_ locale variables into the BCP 47
+-- language codes used in xml:lang attributes.
+toBCP47 :: [Char] -> [Char]
+toBCP47 lang = map hyphen $ takeWhile (/='.') lang
+ where hyphen '_' = '-'
+       hyphen  c  =  c
+
+#if MIN_VERSION_base(4,6,0)
+#else
+lookupEnv k = fmap (lookup k) getEnvironment
+#endif
+
+getPreferedLang :: IO Text
+getPreferedLang = do
+    lang <- do
+        lc_all <- lookupEnv "LC_ALL"
+        lc_messages <- lookupEnv "LC_MESSAGES"
+        lang <- lookupEnv "LANG"
+        return $ lc_all `mplus` lc_messages `mplus` lang
+    return $ maybe "en" (Text.pack . toBCP47) lang
+
+cimatch :: Text -> Text -> Bool
+cimatch w t = Text.toLower w == Text.toLower t
+
+cimatches :: Text -> [Text] -> [Text]
+cimatches w ts = dropWhile (not . cimatch w) ts
+
+-- rfc4647 lookup of best match language tag
+lookupLang :: [Text] -> [Text] -> Maybe Text
+lookupLang (w:ws) tags
+    | Text.null w = lookupLang ws tags
+    | otherwise   = case cimatches w tags of
+                        (t:_) -> Just t
+                        []    -> lookupLang (reduce w:ws) tags
+ where
+    reduce w = Text.concat $ reverse nopriv
+        where
+            rparts = reverse . init $ Text.groupBy (\_ c -> c/='-') w
+            nopriv = dropWhile ispriv rparts
+            ispriv t = Text.length t == 2 && Text.head t == '-'
+
+lookupLang [] tags | "" `elem` tags = Just ""
+                   | otherwise      = listToMaybe $ tags
+
+
+messageText :: Stanza -> IO Text
+messageText msg = do
+    pref <- getPreferedLang
+    let m = msgLangMap (stanzaType msg)
+        key = lookupLang [pref] (map fst m)
+        choice = do
+            k <- key
+            lookup k m
+    flip (maybe $ return "") choice $ \choice -> do
+    let subj = fmap ("Subject: " <>) $ msgSubject choice
+        ts = catMaybes [subj, msgBody choice]
+    return $ Text.intercalate "\n\n" ts
+
+readEnvFile :: String -> FilePath -> IO (Maybe String)
+readEnvFile var file = fmap parse $ readFile file
+ where
+    parse xs = listToMaybe $ map (drop 1 . concat . drop 1) $ filter ofinterest bs
+     where
+        bs = map (groupBy (\_ x -> x/='=')) $ split (/='\0') xs
+        ofinterest (k:vs) | k==var = True
+        ofinterest _               = False
+
+    split pred xs = take 1 gs ++ map (drop 1) (drop 1 gs)
+     where
+        gs = groupBy (\_ x -> pred x) xs
+
+-- | Delivers an XMPP message stanza to the currently active
+-- tty.  If that is a linux console, it will write to it similar
+-- to the manner of the BSD write command.  If that is an X11
+-- display, it will attempt to notify the user via a libnotify
+-- interface.
+writeActiveTTY :: ConsoleWriter -> Stanza -> IO Bool
+writeActiveTTY cw msg = do
+    putStrLn $ "writeActiveTTY"
+    -- TODO: Do not deliver if the detination user does not own the active tty!
+    (tty, mbu) <- atomically $ do
+                num <- readTVar $ csActiveTTY cw
+                utmp <- readTVar $ csUtmp cw
+                mbu <- maybe (return Nothing) readTVar
+                        $ Map.lookup ("tty"<>tshow num) utmp
+                return ( "/dev/tty" <> tshow num
+                       , mbu )
+    flip (maybe $ return False) mbu $ \utmp -> do
+    display <- fmap (fmap Text.pack)
+        $ readEnvFile "DISPLAY" ("/proc/" ++ show (utmpPid utmp) ++ "/environ")
+    case fmap (==utmpHost utmp) display of
+        Just True -> deliverGUIMessage cw tty utmp msg
+        _ -> deliverTerminalMessage cw tty utmp msg
+
+deliverGUIMessage ::
+    forall t t1. t -> t1 -> UtmpRecord -> Stanza -> IO Bool
+deliverGUIMessage cw tty utmp msg = do
+    text <- do
+        t <- messageText msg
+        return $ Text.unpack
+            $ case stanzaFrom msg of
+                Just from -> from <> ": " <> t
+                Nothing -> t
+    putStrLn $ "deliverGUI: " ++ text
+    handleIO_ (return False) $ do
+    uentry <- getUserEntryForName (Text.unpack $ utmpUser utmp)
+    let display = Text.unpack $ utmpHost utmp
+    pid <- forkProcess $ do
+        setUserID (userID uentry)
+        setEnv "DISPLAY" display True
+        -- rawSystem "/usr/bin/notify-send" [text]
+        executeFile "/usr/bin/notify-send" False [text] (Just [("DISPLAY",display)])
+        exitImmediately ExitSuccess
+    return True
+
+crlf :: Text -> Text
+crlf t = Text.unlines $ map cr (Text.lines t)
+ where
+    cr t | Text.last t == '\r'  = t
+         | otherwise            = t <> "\r"
+
+deliverTerminalMessage ::
+    forall t t1. t -> Text -> t1 -> Stanza -> IO Bool
+deliverTerminalMessage cw tty utmp msg = do
+    mode <- fmap fileMode (getFileStatus $ Text.unpack tty)
+    let mesgy = mode .&. 0o020 /= 0 -- verify mode g+w
+    if not mesgy then return False else do
+    text <- do
+        t <- messageText msg
+        return $ Text.unpack
+            $ case stanzaFrom msg of
+                Just from -> "\r\n" <> from <> " says...\r\n" <> crlf t <> "\r\n"
+                Nothing -> crlf t <> "\r\n"
+    writeFile (Text.unpack tty) text
+    return True -- return True if a message was delivered
+
+-- | Deliver the given message to all a user's PTYs.
+writeAllPty :: ConsoleWriter -> Stanza -> IO Bool
+writeAllPty cw msg = do
+    -- TODO: filter only ptys owned by the destination user.
+    us <- atomically $ readTVar (csUtmp cw)
+    let ptys = Map.filterWithKey ispty us
+        ispty k _ = "pts/" `Text.isPrefixOf` k
+                    && Text.all isDigit (Text.drop 4 k)
+    bs <- forM (Map.toList ptys) $ \(tty,utmp) -> do
+        deliverTerminalMessage cw ("/dev/" <> tty) utmp msg
+    return $ or bs 
+
+resource :: UtmpRecord -> Text
+resource u =
+    case utmpTty u of
+        s | Text.take 3 s == "tty" -> s
+        s | Text.take 4 s == "pts/" -> "pty" <> Text.drop 4 s <> ":" <> utmpHost u
+        s -> escapeR s <> ":" <> utmpHost u
+ where
+    escapeR s = s
+
+textHostName :: IO Text
+textHostName = fmap Text.pack BSD.getHostName
+
+ujid :: UtmpRecord -> IO Text
+ujid u = do
+    h <- textHostName
+    return $ utmpUser u <> "@" <> h <> "/" <> resource u
+
+newCon :: (Text -> IO ())
+             -> ConsoleWriter
+             -> STM (Word8,Maybe UtmpRecord)
+             -> TVar (Maybe UtmpRecord)
+             -> IO ()
+newCon log cw activeTTY utmp = do
+    ((tty,tu),u) <- atomically $
+        liftM2 (,) activeTTY
+                   (readTVar utmp)
+    flip (maybe $ return ()) u $ \u -> do
+    jid <- ujid u
+    log $ status (resource u) tty tu <> " " <> jid <> "  pid=" <> tshow (utmpPid u)
+            <> (if istty (resource u)
+                 then " host=" <> tshow (utmpHost u)
+                 else "")
+            <> " session=" <> tshow (utmpSession u)
+            <> " addr=" <> tshow (utmpRemoteAddr u)
+    let r = resource u
+    stanza <- makePresenceStanza
+                            "jabber:client"
+                            (Just jid)
+                            (jstatus r tty tu)
+    statusv <- atomically $ newTVar (Just stanza)
+    flgs <- atomically $ newTVar 0
+    let client = ClientState { clientResource = r
+                             , clientUser = utmpUser u
+                             , clientPid = Nothing
+                             , clientStatus = statusv
+                             , clientFlags = flgs }
+    atomically $ do
+        modifyTVar (cwClients cw) $ Map.insert r client
+        putTMVar (cwPresenceChan cw) (client,stanza)
+    loop client tty tu (Just u)
+ where
+    bstatus r ttynum mtu
+        =  r == ttystr
+        || match mtu
+        where ttystr = "tty" <> tshow ttynum
+              searchstr mtu = maybe ttystr utmpHost $ do
+                tu <- mtu
+                guard (not $ Text.null $ utmpHost tu)
+                return tu
+              match mtu = searchstr mtu `Text.isInfixOf` Text.dropWhile (/=':') r
+    jstatus r ttynum tu = 
+        if bstatus r ttynum tu
+            then Available
+            else Away
+    status r ttynum tu = tshow $ jstatus r ttynum tu
+
+    istty r = fst3 == "tty" && Text.all isDigit rst
+     where
+        (fst3,rst) = Text.splitAt 3 r
+
+    loop client tty tu u = do
+        what <- atomically $ foldr1 orElse
+            [ do (tty',tu') <- retryWhen activeTTY
+                            (\ttyu -> bstatus r tty tu == uncurry (bstatus r) ttyu)
+                 return $ ttyChanged tty' tu'
+            , do u' <- retryWhen (readTVar utmp) (==u)
+                 return $ utmpChanged u'
+            ]
+        what
+      where
+        r = maybe "" resource u
+
+        ttyChanged tty' tu' = do
+            jid <- maybe (return "") ujid u
+            stanza <- makePresenceStanza
+                            "jabber:client"
+                            (Just jid)
+                            (jstatus r tty' tu')
+            dup <- cloneStanza stanza
+            atomically $ do
+                writeTVar (clientStatus client) $ Just dup
+                putTMVar (cwPresenceChan cw) (client,stanza)
+            log $ status r tty' tu' <> " " <> jid
+            loop client tty' tu' u
+
+        utmpChanged u' = maybe dead changed u'
+         where
+            changed u' = do
+                jid0 <- maybe (return "") ujid u
+                jid <- ujid u'
+                log $ "changed: " <> jid0 <> " --> " <> jid
+                loop client tty tu (Just u')
+            dead = do
+                jid <- maybe (return "") ujid u
+                stanza <- makePresenceStanza "jabber:client" (Just jid) Offline
+                atomically $ do
+                    modifyTVar (cwClients cw) $ Map.delete (clientResource client)
+                    putTMVar (cwPresenceChan cw) (client,stanza)
+                log $ "Offline   " <> jid
+
diff --git a/Presence/ControlMaybe.hs b/Presence/ControlMaybe.hs
new file mode 100644
index 00000000..659dab74
--- /dev/null
+++ b/Presence/ControlMaybe.hs
@@ -0,0 +1,29 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+module ControlMaybe where
+
+-- import GHC.IO.Exception (IOException(..))
+import Control.Exception as Exception (IOException(..),catch)
+
+
+withJust :: Monad m => Maybe x -> (x -> m ()) -> m ()
+withJust (Just x) f = f x
+withJust Nothing  f = return ()
+
+whenJust :: Monad m => m (Maybe x) -> (x -> m ()) -> m ()
+whenJust acn f = do
+    x <- acn
+    withJust x f
+
+
+catchIO_ :: IO a -> IO a -> IO a
+catchIO_ a h = Exception.catch a (\(_ :: IOException) -> h)
+
+catchIO :: IO a -> (IOException -> IO a)  -> IO a
+catchIO body handler = Exception.catch body handler
+
+handleIO_ :: IO a -> IO a -> IO a
+handleIO_ = flip catchIO_
+
+
+handleIO :: (IOException -> IO a) -> IO a -> IO a
+handleIO = flip catchIO
diff --git a/Presence/DNSCache.hs b/Presence/DNSCache.hs
new file mode 100644
index 00000000..aaf1a7be
--- /dev/null
+++ b/Presence/DNSCache.hs
@@ -0,0 +1,270 @@
+-- | Both 'getAddrInfo' and 'getHostByAddr' have hard-coded timeouts for
+-- waiting upon network queries that can be a little too long for some use
+-- cases. This module wraps both of them so that they block for at most one
+-- second.  It caches late-arriving results so that they can be returned by
+-- repeated timed-out queries.
+--
+-- In order to achieve the shorter timeout, it is likely that the you will need
+-- to build with GHC's -threaded option.  Otherwise, if the wrapped FFI calls
+-- to resolve the address will block Haskell threads.  Note: I didn't verify
+-- this.
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE RankNTypes    #-}
+{-# LANGUAGE CPP           #-}
+module DNSCache
+    ( DNSCache
+    , reverseResolve
+    , forwardResolve
+    , newDNSCache
+    , parseAddress
+    , strip_brackets
+    , withPort
+    ) where
+
+#ifdef THREAD_DEBUG
+import Control.Concurrent.Lifted.Instrument
+#else
+import Control.Concurrent.Lifted
+import GHC.Conc                  (labelThread)
+#endif
+import Control.Concurrent.STM
+import Data.Text       ( Text )
+import Network.Socket  ( SockAddr(..), AddrInfoFlag(..), defaultHints, getAddrInfo, AddrInfo(..) )
+import Data.Time.Clock ( UTCTime, getCurrentTime, diffUTCTime )
+import System.IO.Error ( isDoesNotExistError )
+import System.Endian   ( fromBE32, toBE32 )
+import Control.Exception ( handle )
+import Data.Map        ( Map )
+import qualified Data.Map    as Map
+import qualified Network.BSD as BSD
+import qualified Data.Text   as Text
+import Control.Monad
+import Data.Function
+import Data.List
+import Data.Ord
+import Data.Maybe
+import System.IO
+import System.IO.Error
+
+import SockAddr      ()
+import ControlMaybe  ( handleIO_ )
+import GetHostByAddr ( getHostByAddr )
+import InterruptibleDelay
+
+type TimeStamp = UTCTime
+
+data DNSCache =
+    DNSCache
+    { fcache :: TVar (Map Text [(TimeStamp, SockAddr)])
+    , rcache :: TVar (Map SockAddr [(TimeStamp, Text)])
+    }
+
+
+newDNSCache :: IO DNSCache
+newDNSCache = do
+        fcache <- newTVarIO Map.empty
+        rcache <- newTVarIO Map.empty
+        return DNSCache { fcache=fcache, rcache=rcache }
+
+updateCache :: Eq x =>
+    Bool -> TimeStamp -> [x] -> Maybe [(TimeStamp,x)] -> Maybe [(TimeStamp,x)]
+updateCache withScrub utc xs mys = do
+    let ys = maybe [] id mys
+        ys' = filter scrub ys
+        ys'' = map (utc,) xs ++ ys'
+        minute = 60
+        scrub (t,x) | withScrub && diffUTCTime utc t < minute = False
+        scrub (t,x) | x `elem` xs = False
+        scrub _ = True
+    guard $ not (null ys'')
+    return ys''
+
+dnsObserve :: DNSCache -> Bool -> TimeStamp -> [(Text,SockAddr)] -> STM ()
+dnsObserve dns withScrub utc obs = do
+    f <- readTVar $ fcache dns
+    r <- readTVar $ rcache dns
+    let obs' = map (\(n,a)->(n,a `withPort` 0)) obs
+        gs = do
+            g <- groupBy ((==) `on` fst) $ sortBy (comparing fst) obs'
+            (n,_) <- take 1 g
+            return (n,map snd g)
+        f' = foldl' updatef f gs
+        hs = do
+            h <- groupBy ((==) `on` snd) $ sortBy (comparing snd) obs'
+            (_,a) <- take 1 h
+            return (a,map fst h)
+        r' = foldl' updater r hs
+    writeTVar (fcache dns) f'
+    writeTVar (rcache dns) r'
+ where
+    updatef f (n,addrs) = Map.alter (updateCache withScrub utc addrs) n f
+    updater r (a,ns) = Map.alter (updateCache withScrub utc ns) a r
+
+make6mapped4 :: SockAddr -> SockAddr
+make6mapped4 addr@(SockAddrInet6 {}) = addr
+make6mapped4 addr@(SockAddrInet port a) = SockAddrInet6 port 0 (0,0,0xFFFF,fromBE32 a) 0
+
+tryForkOS :: IO () -> IO ThreadId
+tryForkOS action = catchIOError (forkOS action) $ \e -> do
+    hPutStrLn stderr $ "DNSCache: Link with -threaded to avoid excessively long time-out."
+    forkIO action
+
+
+-- Attempt to resolve the given domain name.  Returns an empty list if the
+-- resolve operation takes longer than the timeout, but the 'DNSCache' will be
+-- updated when the resolve completes.
+--
+-- When the resolve operation does complete, any entries less than a minute old
+-- will be overwritten with the new results.  Older entries are allowed to
+-- persist for reasons I don't understand as of this writing. (See 'updateCache')
+rawForwardResolve ::
+    DNSCache -> (Text -> IO ()) -> Int -> Text -> IO [SockAddr]
+rawForwardResolve dns onFail timeout addrtext = do
+    r <- atomically newEmptyTMVar
+    mvar <- interruptibleDelay
+    rt <- tryForkOS $ do
+        myThreadId >>= flip labelThread ("resolve."++show addrtext)
+        resolver r mvar
+    startDelay mvar timeout
+    did <- atomically $ tryPutTMVar r []
+    when did (onFail addrtext)
+    atomically $ readTMVar r
+ where
+    resolver r mvar = do
+      xs <- handle (\e -> let _ = isDoesNotExistError e in return [])
+            $ do fmap (nub . map (make6mapped4 . addrAddress)) $ 
+                  getAddrInfo (Just $ defaultHints { addrFlags = [ AI_CANONNAME, AI_V4MAPPED ]})
+                    (Just $ Text.unpack $ strip_brackets addrtext)
+                    (Just "5269")
+      did <- atomically $ tryPutTMVar r xs
+      when did $ do
+      interruptDelay mvar
+      utc <- getCurrentTime
+      atomically $ dnsObserve dns True utc $ map (addrtext,) xs
+      return ()
+
+strip_brackets :: Text -> Text
+strip_brackets s = 
+      case Text.uncons s of
+          Just ('[',t) -> Text.takeWhile (/=']') t
+          _            -> s
+
+
+reportTimeout :: forall a. Show a => a -> IO ()
+reportTimeout addrtext = do
+      hPutStrLn stderr $ "timeout resolving: "++show addrtext
+      -- killThread rt
+
+unmap6mapped4 :: SockAddr -> SockAddr
+unmap6mapped4 addr@(SockAddrInet6 port _ (0,0,0xFFFF,a) _) =
+    SockAddrInet port (toBE32 a)
+unmap6mapped4 addr = addr
+
+rawReverseResolve ::
+    DNSCache -> (SockAddr -> IO ()) -> Int -> SockAddr -> IO [Text]
+rawReverseResolve dns onFail timeout addr = do
+    r <- atomically newEmptyTMVar
+    mvar <- interruptibleDelay
+    rt <- forkOS $ resolver r mvar
+    startDelay mvar timeout
+    did <- atomically $ tryPutTMVar r []
+    when did (onFail addr)
+    atomically $ readTMVar r
+ where
+    resolver r mvar = 
+      handleIO_ (return ()) $ do
+        ent <- getHostByAddr (unmap6mapped4 addr) --  AF_UNSPEC addr
+        let names = BSD.hostName ent : BSD.hostAliases ent
+            xs = map Text.pack $ nub names
+        forkIO $ do
+            utc <- getCurrentTime
+            atomically $ dnsObserve dns False utc $ map (,addr) xs
+        atomically $ putTMVar r  xs
+
+-- Returns expired (older than a minute) cached reverse-dns results
+-- and removes them from the cache.
+expiredReverse :: DNSCache -> SockAddr -> IO [Text]
+expiredReverse dns addr = do
+    utc <- getCurrentTime
+    addr <- return $ addr `withPort` 0
+    es <- atomically $ do
+        r <- readTVar $ rcache dns
+        let ns = maybe [] id $ Map.lookup addr r
+            minute = 60 -- seconds
+            -- XXX: Is this right?  flip diffUTCTime utc returns the age of the 
+            -- cache entry?
+            (es0,ns') = partition ( (>=minute) . flip diffUTCTime utc . fst ) ns
+            es = map snd es0
+        modifyTVar' (rcache dns) $ Map.insert addr ns'
+        f <- readTVar $ fcache dns
+        let f' = foldl' (flip $ Map.alter (expire utc)) f es
+            expire utc Nothing   = Nothing
+            expire utc (Just as) = if null as' then Nothing else Just as'
+                where as' = filter ( (<minute) . flip diffUTCTime utc . fst) as
+        writeTVar (fcache dns) f'
+        return es
+    return es
+
+cachedReverse :: DNSCache -> SockAddr -> IO [Text]
+cachedReverse dns addr = do
+    utc <- getCurrentTime
+    addr <- return $ addr `withPort` 0
+    atomically $ do
+        r <- readTVar (rcache dns)
+        let ns = maybe [] id $ Map.lookup addr r
+        {-
+            ns' = filter ( (<minute) . flip diffUTCTime utc . fst) ns
+            minute = 60 -- seconds
+        modifyTVar' (rcache dns) $ Map.insert addr ns'
+        return $ map snd ns'
+        -}
+        return $ map snd ns
+
+-- Returns any dns query results for the given name that were observed less
+-- than a minute ago and updates the forward-cache to remove any results older
+-- than that.
+cachedForward :: DNSCache -> Text -> IO [SockAddr]
+cachedForward dns n = do
+    utc <- getCurrentTime
+    atomically $ do
+        f <- readTVar (fcache dns)
+        let as = maybe [] id $ Map.lookup n f
+            as' = filter ( (<minute) . flip diffUTCTime utc . fst) as
+            minute = 60 -- seconds
+        modifyTVar' (fcache dns) $ Map.insert n as'
+        return $ map snd as'
+
+-- Reverse-resolves an address to a domain name.  Returns both the result of a
+-- new query and any freshly cached results.  Cache entries older than a minute
+-- will not be returned, but will be refreshed in spawned threads so that they
+-- may be available for the next call.
+reverseResolve :: DNSCache -> SockAddr -> IO [Text]
+reverseResolve dns addr = do
+    expired <- expiredReverse dns addr
+    forM_ expired $ \n -> forkIO $ do
+        rawForwardResolve dns (const $ return ()) 1000000 n
+        return ()
+    xs <- rawReverseResolve dns (const $ return ()) 1000000 addr
+    cs <- cachedReverse dns addr
+    return $ xs ++ filter (not . flip elem xs) cs
+
+-- Resolves a name, if there's no result within one second, then any cached
+-- results that are less than a minute old are returned.
+forwardResolve :: DNSCache -> Text -> IO [SockAddr]
+forwardResolve dns n = do
+    as <- rawForwardResolve dns (const $ return ()) 1000000 n
+    if null as
+      then cachedForward dns n
+      else return as
+
+parseAddress :: Text -> IO (Maybe SockAddr)
+parseAddress addr_str = do
+    info <- getAddrInfo (Just $ defaultHints { addrFlags = [ AI_NUMERICHOST ] }) 
+                        (Just . Text.unpack $ addr_str) 
+                        (Just "0")
+    return . listToMaybe $ map addrAddress info
+
+
+withPort :: SockAddr -> Int -> SockAddr
+withPort (SockAddrInet _ a)      port = SockAddrInet (toEnum port) a
+withPort (SockAddrInet6 _ a b c) port = SockAddrInet6 (toEnum port) a b c
diff --git a/Presence/EventUtil.hs b/Presence/EventUtil.hs
new file mode 100644
index 00000000..908e09e0
--- /dev/null
+++ b/Presence/EventUtil.hs
@@ -0,0 +1,83 @@
+{-# LANGUAGE OverloadedStrings #-}
+module EventUtil where
+
+import Control.Monad
+import Data.XML.Types as XML
+import qualified Data.List as List
+import Data.Text (Text)
+
+-- getStreamName (EventBeginElement name _) = name
+
+isEventBeginElement :: Event -> Bool
+isEventBeginElement (EventBeginElement {}) = True
+isEventBeginElement _ = False
+
+isEventEndElement :: Event -> Bool
+isEventEndElement (EventEndElement {}) = True
+isEventEndElement _ = False
+
+-- Note: This function ignores name space qualification
+elementAttrs ::
+  MonadPlus m =>
+  Text -> Event -> m [(Name, [Content])]
+elementAttrs expected (EventBeginElement name attrs)
+    | nameLocalName name==expected 
+    = return attrs
+elementAttrs _ _ = mzero
+
+streamP :: Text -> Name
+streamP name = Name name (Just "http://etherx.jabber.org/streams") (Just "stream")
+
+attr :: Name -> Text -> (Name,[Content])
+attr   name value = (name,[ContentText value])
+
+isServerIQOf :: Event -> Text -> Bool
+isServerIQOf (EventBeginElement name attrs) testType 
+    | name=="{jabber:server}iq" 
+    && matchAttrib "type" testType attrs
+    = True
+isServerIQOf _ _ = False
+
+isClientIQOf :: Event -> Text -> Bool
+isClientIQOf (EventBeginElement name attrs) testType 
+    | name=="{jabber:client}iq" 
+    && matchAttrib "type" testType attrs
+    = True
+isClientIQOf _ _ = False
+
+matchAttrib :: Name -> Text -> [(Name, [Content])] -> Bool
+matchAttrib name value attrs = 
+    case List.find ( (==name) . fst) attrs of
+        Just (_,[ContentText x])   | x==value -> True
+        Just (_,[ContentEntity x]) | x==value -> True
+        _                                     -> False
+
+lookupAttrib :: Name -> [(Name, [Content])] -> Maybe Text
+lookupAttrib name attrs =
+    case List.find ( (==name) . fst) attrs of
+        Just (_,[ContentText x])   -> Just x
+        Just (_,[ContentEntity x]) -> Just x
+        _                          -> Nothing
+
+tagAttrs :: Event -> [(Name, [Content])]
+tagAttrs (EventBeginElement _ xs) = xs
+tagAttrs _                        = []
+
+    
+{-
+iqTypeSet    = "set"
+iqTypeGet    = "get"
+iqTypeResult = "result"
+iqTypeError  = "error"
+-}
+
+
+tagName :: Event -> Name
+tagName (EventBeginElement n _) = n
+tagName _                       = ""
+
+closerFor :: Event -> Event
+closerFor (EventBeginElement n _) = EventEndElement n
+closerFor _ = error "closerFor: unsupported event"
+
+
diff --git a/Presence/FGConsole.hs b/Presence/FGConsole.hs
new file mode 100644
index 00000000..03aaebf2
--- /dev/null
+++ b/Presence/FGConsole.hs
@@ -0,0 +1,67 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+module FGConsole where
+
+import Data.Word
+import System.Posix.IO
+import System.Posix.Types
+import Control.Concurrent
+-- import GHC.IO.Handle
+import Unsafe.Coerce
+import Control.Exception as E
+-- import Prelude as E
+import Control.Monad
+import Foreign.C
+
+import Logging
+import System.Posix.Signals
+
+-- c_monitorTTY fd = trace "c_monitorTTY" (return ()) -- (trace "WTF" todo)
+
+foreign import ccall "monitorTTY" c_monitorTTY :: Fd -> IO CInt
+foreign import ccall "closeTTY" c_closeTTY :: IO ()
+
+forkTTYMonitor :: (Word8 -> IO ()) -> IO (Maybe (Fd,ThreadId))
+forkTTYMonitor handler =  do
+    (rfd,wfd) <- createPipe
+    retvar <- newEmptyMVar
+    thread <- forkIO $ do
+        let cleanup = do
+                trace "quitting monitorTTY thread." (return ())
+                closeFd wfd `E.catch` \(e::IOException) -> return ()
+                closeFd rfd `E.catch` \(e::IOException) -> return ()
+                c_closeTTY
+        -- rh <- fdToHandle rfd
+        didfork <- c_monitorTTY wfd
+        putMVar retvar didfork
+        when (didfork == 0) $ do
+        let monitor =
+                (do
+                    threadWaitRead rfd
+                    (cs,cnt) <- fdRead rfd 1
+                    forM_ cs (handler . unsafeCoerce {- . trace "read byte" -})
+                    monitor)
+                `E.catch`
+                      \(e :: IOException) -> do
+                        err <- getErrno
+                        case () of
+                         _ | err==eAGAIN -> monitor
+                         _ | otherwise   -> cleanup
+                `E.catch`
+                      \(e ::  AsyncException) -> cleanup
+        monitor
+    didfork <- takeMVar retvar
+    if didfork == 0
+        then return $! Just (rfd,thread)
+        else return $! Nothing
+
+killTTYMonitor :: (Fd, ThreadId) -> IO ()
+killTTYMonitor (rfd,thread) = do
+    closeFd rfd
+    yield
+    killThread thread
+    raiseSignal sigUSR1
+    -- threadDelay 1000000
+
+
+-- vim:ft=haskell:
diff --git a/Presence/GetHostByAddr.hs b/Presence/GetHostByAddr.hs
new file mode 100644
index 00000000..45bca5e9
--- /dev/null
+++ b/Presence/GetHostByAddr.hs
@@ -0,0 +1,77 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+module GetHostByAddr where
+
+import Network.BSD
+import Foreign.Ptr
+import Foreign.C.Types
+import Foreign.Storable (Storable(..))
+import Foreign.Marshal.Utils (with)
+import Foreign.Marshal.Alloc
+import Control.Concurrent
+import System.IO.Unsafe
+import System.IO.Error (ioeSetErrorString, mkIOError)
+import Network.Socket
+import GHC.IO.Exception
+
+
+throwNoSuchThingIfNull :: String -> String -> IO (Ptr a) -> IO (Ptr a)
+throwNoSuchThingIfNull loc desc act = do
+  ptr <- act
+  if (ptr == nullPtr)
+       then ioError (ioeSetErrorString (mkIOError NoSuchThing loc Nothing Nothing) desc)
+       else return ptr
+
+{-# NOINLINE lock #-}
+lock :: MVar ()
+lock = unsafePerformIO $ newMVar ()
+
+withLock :: IO a -> IO a
+withLock act = withMVar lock (\_ -> act)
+
+trySysCall :: IO a -> IO a
+trySysCall act = act
+
+{-
+-- The locking of gethostbyaddr is similar to gethostbyname.
+-- | Get a 'HostEntry' corresponding to the given address and family.
+-- Note that only IPv4 is currently supported.
+getHostByAddr :: Family -> SockAddr -> IO HostEntry
+getHostByAddr family addr = do
+ withSockAddr addr $ \ ptr_addr len -> withLock $ do
+ throwNoSuchThingIfNull         "getHostByAddr" "no such host entry"
+   $ trySysCall $ c_gethostbyaddr ptr_addr (fromIntegral len) (packFamily family)
+ >>= peek
+-}
+
+
+-- The locking of gethostbyaddr is similar to gethostbyname.
+-- | Get a 'HostEntry' corresponding to the given address and family.
+-- Note that only IPv4 is currently supported.
+-- getHostByAddr :: Family -> HostAddress -> IO HostEntry
+-- getHostByAddr family addr = do
+getHostByAddr :: SockAddr -> IO HostEntry
+getHostByAddr (SockAddrInet port addr ) = do
+ let family = AF_INET
+ with addr $ \ ptr_addr -> withLock $ do
+ throwNoSuchThingIfNull         "getHostByAddr" "no such host entry"
+   $ trySysCall $ c_gethostbyaddr ptr_addr (fromIntegral (sizeOf addr)) (packFamily family)
+ >>= peek
+getHostByAddr (SockAddrInet6 port flow (a,b,c,d) scope) = do
+ let family = AF_INET6
+ allocaBytes 16 $ \ ptr_addr -> do
+ pokeElemOff ptr_addr 0 a
+ pokeElemOff ptr_addr 1 b
+ pokeElemOff ptr_addr 2 c
+ pokeElemOff ptr_addr 3 d
+ withLock $ do
+ throwNoSuchThingIfNull         "getHostByAddr" "no such host entry"
+   $ trySysCall $ c_gethostbyaddr ptr_addr 16 (packFamily family)
+ >>= peek
+
+
+foreign import ccall safe "gethostbyaddr"
+   c_gethostbyaddr :: Ptr a -> CInt -> CInt -> IO (Ptr HostEntry)
+
+
+
+-- vim:ft=haskell:
diff --git a/Presence/IDMangler.hs b/Presence/IDMangler.hs
new file mode 100644
index 00000000..664d4f54
--- /dev/null
+++ b/Presence/IDMangler.hs
@@ -0,0 +1,68 @@
+---------------------------------------------------------------------------
+-- |
+-- Module : IDMangler
+--
+-- This library is useful for generating id attributes for use in an XMPP
+-- application.  It conveniently encodes a key value for looking up context and
+-- an original id attribute in case of forwarded messages.
+--
+-- For example, an id attribute with an embedded 'XMPPServer.ConnectionKey'
+-- for a forwarded message with an original id attribute of \"purplecfa6168a\"
+-- might look something like this:
+--
+-- > AAAAAAAAAAIBksnqOQiYmtmupcLxbXakI9zcmUl4:purplecfa6168a
+--
+{-# LANGUAGE OverloadedStrings #-}
+module IDMangler
+    ( IDMangler
+    , newIDMangler
+    , generateUniqueID
+    , unmangleId
+    ) where
+
+import Control.Monad.STM
+import Control.Concurrent.STM
+import Data.Text (Text)
+import qualified Data.Text as Text
+import qualified Data.ByteString.Lazy as LazyByteString
+import Data.Binary
+import qualified Codec.Binary.Base64 as Base64
+import Control.Monad
+import Data.Monoid ( (<>) )
+
+
+data IDMangler k
+ = IDMangler { idmCounter :: TVar Int }
+
+newIDMangler :: IO (IDMangler k)
+newIDMangler = do
+    nv <- atomically $ newTVar 0
+    return $ IDMangler nv
+
+-- | Use the given state and optional data to generate a unique id attribute
+-- suitable for xml.  To recover the optional encoded data, see 'unmangleId'.
+generateUniqueID :: Binary k =>
+    IDMangler k   -- ^ the state (a counter) for ensuring uniqueness
+    -> Maybe k    -- ^ optional recoverable key for context
+    -> Maybe Text -- ^ optional recoverable auxilary id attribute
+    -> IO Text    -- ^ unique id attribute with encoded data
+generateUniqueID mangler mkey mid = do
+    n <- atomically $ do
+        modifyTVar' (idmCounter mangler) (+1)
+        readTVar (idmCounter mangler)
+    let bs = encode (n,mkey)
+        base64 = Base64.encode (LazyByteString.unpack bs)
+        suf = maybe "" (":" <>) mid
+    return $ Text.pack base64 <> suf
+
+-- | Recover data from an encoded id attribute.
+unmangleId :: Binary k => Text -> (Maybe k, Maybe Text)
+unmangleId encoded = (k,mid)
+ where
+    (e,postcolon) = Text.span (/=':') encoded
+    bytes = Base64.decode (Text.unpack e)
+    decoded = fmap (decode . LazyByteString.pack) bytes
+    k = decoded >>= (\(n,k) -> let _ = n :: Int in k)
+    mid = do guard (not . Text.null $ postcolon)
+             return $ Text.drop 1 postcolon
+
diff --git a/Presence/LocalPeerCred.hs b/Presence/LocalPeerCred.hs
new file mode 100644
index 00000000..9054f180
--- /dev/null
+++ b/Presence/LocalPeerCred.hs
@@ -0,0 +1,234 @@
+{-# LANGUAGE ViewPatterns  #-}
+{-# LANGUAGE TupleSections #-}
+module LocalPeerCred where
+
+import System.Endian
+import qualified Data.ByteString.Lazy.Char8 as L
+ -- hiding (map,putStrLn,tail,splitAt,tails,filter)
+ --  import qualified Data.ByteString.Lazy.Char8 as L (splitAt)
+import qualified Data.ByteString.Lazy as W8
+import Data.List as List (tails,groupBy)
+import System.IO ( withFile, IOMode(..))
+import System.Directory
+import Control.Arrow (first)
+import Data.Char
+import Data.Maybe
+import Data.Bits
+import Data.Serialize
+import Data.Word
+import System.Posix.Types
+import System.Posix.Files
+import Logging
+import Network.SocketLike
+import ControlMaybe
+import Data.String
+import System.IO
+
+(??) :: (Num t, Ord t) => [a] -> t -> Maybe a
+xs     ?? n | n < 0 =  Nothing
+[]     ?? _         =  Nothing
+(x:_)  ?? 0         =  Just x
+(_:xs) ?? n         =  xs ?? (n-1)
+
+parseHex :: W8.ByteString -> W8.ByteString
+parseHex bs = L.concat . parseHex' $ bs
+ where
+  parseHex' bs =
+      let (dnib,ts) = L.splitAt 2 bs
+          parseNibble x = W8.pack $ group2 toW8 (W8.unpack $ W8.map hexDigit x)
+          hexDigit d = d - (if d>0x39 then 0x37 else 0x30)
+          group2 f (x:y:ys) = f x y : group2 f ys
+          group2 _ _        = []
+          toW8 a b = shift a 4 .|. b
+      in parseNibble dnib :
+          if L.null ts 
+              then []
+              else parseHex' ts
+
+getLocalPeerCred' :: SockAddr -> IO (Maybe (UserID, W8.ByteString))
+getLocalPeerCred' (unmap6mapped4 -> SockAddrInet portn host) = do
+    let port = fromEnum portn
+    {- trace ("tcp4 "++show(port,host)) $ -} 
+    withFile "/proc/net/tcp"  ReadMode (parseProcNet port host)
+
+getLocalPeerCred' (unmap6mapped4 -> SockAddrInet6 portn flow host scope) = do
+    let port = fromEnum portn
+        (a,b,c,d) = host
+        host' = (toBE32 a, toBE32 b, toBE32 c, toBE32 d)
+    withFile "/proc/net/tcp6" ReadMode (parseProcNet port host')
+
+getLocalPeerCred' (unmap6mapped4 -> addr@(SockAddrUnix _)) =
+    -- TODO:  parse /proc/net/unix
+    -- see also: Network.Socket.getPeerCred
+    return Nothing
+
+getLocalPeerCred :: SocketLike sock => sock -> IO (Maybe UserID)
+getLocalPeerCred sock = do
+    addr <- getPeerName sock
+    muid <- getLocalPeerCred' addr
+    case muid of
+        Just (uid,inode) -> return (Just uid)
+        Nothing  -> trace "proc failed." $ fmap (validate . CUid . fromIntegral . sndOf3) (getPeerCred sock)
+                     where sndOf3 (pid,uid,gid) = uid
+ where
+    validate uid = Just uid -- TODO
+
+from16 :: Word16 -> Int
+from16 = fromEnum
+
+as16 :: Word16 -> Word16
+as16 = id
+
+parseProcNet :: (Serialize t, Num t1, Eq t, Eq t1) =>
+          t1
+          -> t
+          -> Handle
+          -> IO (Maybe (UserID, W8.ByteString))
+parseProcNet port host h = do
+        tcp <- L.hGetContents h -- Failed: tcp <- hFileSize h >>= hGet h . fromIntegral
+        let u = do
+                    ls <- listToMaybe . tail . tails . L.lines $ tcp
+                    let ws = map L.words ls
+                    let rs = ( catMaybes . flip map ws $ \xs -> do
+                          let ys = snd (Prelude.splitAt 1 xs)
+                          localaddr <- listToMaybe ys
+                          let zs = L.splitWith (==':') localaddr
+                          addr <- fmap parseHex $ listToMaybe zs
+                          port <- either (const Nothing) (Just . fromIntegral . as16) . decode . L.toStrict . parseHex
+                                  =<< listToMaybe (snd (Prelude.splitAt 1 zs))
+                          let ys' = snd (Prelude.splitAt 5 (tail ys))
+                              ys'' = snd (Prelude.splitAt 2 ys')
+                          uid <- listToMaybe ys'
+                          inode <- listToMaybe ys''
+                          peer <- either (const Nothing) Just $ do
+                            a <- decode $ L.toStrict addr
+                            return (port,a)
+                          let user = toEnum (read (L.unpack uid) ::Int) ::UserID  -- CUid . fromIntegral $ (read (unpack uid)::Int)
+                          return $ {-trace ("peer:"++show(peer,user,inode))-} (peer,(user,inode))
+                          )
+                    fmap snd . listToMaybe $ filter ((==(port,host)).fst) rs 
+        {- trace ("found: "++show u) -} 
+        u `seq` return u
+ {-
+ where
+    a === b = let r= a==b in  trace ("Comparing "++show (a,b)++"-->"++show r) r
+    -}
+
+
+-- PEER NAME: [::ffff:127.0.0.1]:34307
+unmap6mapped4 :: SockAddr -> SockAddr
+unmap6mapped4 addr@(SockAddrInet6 port _ (0,0,0xFFFF,a) _) = SockAddrInet port (toBE32 a)
+unmap6mapped4 addr = addr
+
+identifyTTY ::
+  [(W8.ByteString, ProcessID)]
+  -> UserID -> W8.ByteString -> IO (Maybe W8.ByteString, Maybe CPid)
+identifyTTY tty_pids uid inode = do
+    pid <- scanProc (show uid) (L.unpack inode)
+    -- putStrLn $ "scanProc --> "++show pid
+    flip (maybe (return (Nothing,Nothing))) pid $ \(pid,ttydev) -> do
+    tty <- ttyOrDisplay pid ttydev
+    -- putStrLn $ "users = " ++ show tty_pids
+    dts <- ttyToXorgs tty_pids
+    -- putStrLn $ "displays = " ++ show dts 
+    -- putStrLn $ "tty = " ++ show tty
+    -- -- displays = [(":5",Chunk "tty7" Empty)]
+    let tty' = if take 3 tty=="tty" 
+                then Just (L.pack tty) 
+                else lookup (parseTty tty) (map (first parseTty) dts)
+    return (tty',Just pid)
+    where
+        parseTty :: String -> Float
+        parseTty = read .  tail . dropWhile (/=':') 
+
+ttyToXorgs :: Show a => [(t, a)] -> IO [([Char], t)]
+ttyToXorgs tty_pids = do
+    dts' <- flip mapM tty_pids $ \(tty,pid) -> do
+        cmd' <- readFile $ "/proc/"++show pid++"/cmdline"
+        case listToMaybe . words . takeWhile (/='\0') $ cmd' of
+          Nothing  -> return Nothing
+          Just cmd -> do
+            if notElem cmd ["gdm-session-worker"]
+                then return Nothing
+                else do
+                  display <- readDisplayVariable pid
+                  return (fmap ( (,tty) . snd ) display)
+    let dts = catMaybes dts'
+    return dts
+
+
+scanProc :: t -> [Char] -> IO (Maybe (CPid, FilePath))
+scanProc uid inode = do
+    contents <- getDirectoryContents "/proc" `catchIO_` return []
+    let pids = reverse $ filter (\n -> not (null n) && isDigit (head n)) contents
+    let searchPids []         = return Nothing
+        searchPids (pid:pids) =  do
+            loginuid <- fmap makeUidStr $ readFile $ "/proc/"++pid++"/loginuid"
+            if False -- (uid/=loginuid) -- this check proved bad when mcabber ran on tty3
+             then searchPids pids
+             else do
+                -- putStrLn $ "pid "++show pid ++ " --> uid "++show loginuid
+                let loop [] = return Nothing
+                    loop ("0":fds) = loop fds
+                    loop (fd:fds) = do
+                      handleIO_ (loop fds) $ do
+                          what <- readSymbolicLink $ "/proc/"++pid++"/fd/"++fd
+                          -- putStrLn $ " what= "++show what
+                          if (what=="socket:["++inode++"]")
+                            then do
+                              tty <- readSymbolicLink $ "/proc/"++pid++"/fd/0"
+                              return (Just (pid,tty))
+                            else loop fds
+                -- requires root (or same user as for pid)...
+                fds <- getDirectoryContents ("/proc/"++pid++"/fd") `catchIO_` return []
+                mb <- loop fds
+                maybe (searchPids pids) (return . Just) mb
+
+    fmap (fmap (first (read :: String -> CPid))) $ searchPids pids
+
+ttyOrDisplay :: Show a => a -> FilePath -> IO [Char]
+ttyOrDisplay pid ttydev = do
+    ptty <- searchParentsForTTY (show pid) ttydev
+    case ptty of
+        Just tty -> return tty
+        Nothing  -> do
+            display <- readDisplayVariable pid
+            -- putStrLn $ "display = " ++ show display
+            case display of
+                Just (_,disp) -> return disp
+                _             -> return ttydev
+
+
+readDisplayVariable :: Show a => a -> IO (Maybe ([Char], [Char]))
+readDisplayVariable pid = do
+            env <- handleIO_ (return "") 
+                    . readFile $ "/proc/"++show pid++"/environ"
+            let vs = unzero $ List.groupBy (\_ c->c/='\0') env
+                unzero []     = []
+                unzero (v:vs) = v:map tail vs
+                keyvalue xs = (key,value) 
+                  where
+                    (key,ys) = break (=='=') xs
+                    value = case ys of { [] -> [];  (_:ys') -> ys' }
+                display = listToMaybe 
+                            . filter ((=="DISPLAY").fst) 
+                            . map keyvalue 
+                            $ vs
+            return display 
+
+
+makeUidStr :: (Data.String.IsString t, Eq t) => t -> t
+makeUidStr "4294967295" = "invalid"
+makeUidStr uid          = uid
+
+
+searchParentsForTTY :: String -> FilePath -> IO (Maybe [Char])
+searchParentsForTTY pid  ttydev | take 8 ttydev == "/dev/tty" = return . Just $ drop 5 ttydev
+searchParentsForTTY "1"  ttydev | otherwise                   = return Nothing
+searchParentsForTTY pid ttydev = do
+    stat <- handleIO_ (return "") . readFile $ "/proc/"++pid++"/stat"
+    case words stat ?? 3 of
+        Nothing   -> return Nothing
+        Just ppid -> do
+          tty <- handleIO_ (return "") $ readSymbolicLink $ "/proc/"++ppid++"/fd/0"
+          searchParentsForTTY ppid tty
diff --git a/Presence/LockedChan.hs b/Presence/LockedChan.hs
new file mode 100644
index 00000000..eac2b5ad
--- /dev/null
+++ b/Presence/LockedChan.hs
@@ -0,0 +1,78 @@
+{-# LANGUAGE CPP #-}
+module LockedChan
+  ( LockedChan
+  , cloneLChan
+  , newLockedChan
+  , peekLChan
+  , unlockChan 
+  , writeLChan )
+ where
+
+
+import Control.Monad.STM
+import Control.Concurrent.STM
+
+data LockedChan a = LockedChan
+    { lock :: TVar Bool
+    , chan :: TChan a
+    }
+
+unlockChan :: LockedChan a -> IO (TChan a)
+unlockChan c = do
+    waslocked <- atomically $ swapTVar (lock c) False
+    if waslocked
+        then return (chan c) 
+        else error "Attempt to read unlocked channel"
+
+writeLChan :: LockedChan a -> a -> STM ()
+writeLChan c a = writeTChan (chan c) a
+
+-- This one blocks rather than throwing an exception...
+-- todo: probably this should be changed to conform to the rest
+-- of the api.
+peekLChan :: LockedChan a -> STM a
+peekLChan c = do
+    readTVar (lock c) >>= check
+    peekTChan (chan c)
+
+newLockedChan :: STM (LockedChan a)
+newLockedChan = do
+    lock <- newTVar True
+    chan <- newTChan
+    return $ LockedChan lock chan
+
+cloneLChan :: LockedChan a -> IO (LockedChan a)
+cloneLChan c = do
+    mchan <- atomically $ do
+        locked <- readTVar (lock c)
+        if locked
+            then fmap Just $ do
+                    c2 <- cloneTChan (chan c)
+                    l2 <- newTVar True
+                    return $ LockedChan l2 c2
+            else return Nothing
+    maybe (do putStrLn "LockedChan: Attempt to clone unlocked channel"
+              error "Attempt to clone unlocked channel")
+          return
+          mchan
+
+#if MIN_VERSION_stm(2,4,0)
+#else
+-- |Clone a 'TChan': similar to dupTChan, but the cloned channel starts with the
+-- same content available as the original channel.
+--
+-- Terrible inefficient implementation provided to build against older libraries.
+cloneTChan :: TChan a -> STM (TChan a)
+cloneTChan chan = do
+    contents <- chanContents' chan
+    chan2 <- dupTChan chan
+    mapM_ (writeTChan chan) contents
+    return chan2
+ where
+    chanContents' chan = do
+        b <- isEmptyTChan chan
+        if b then return [] else do
+        x <- readTChan chan
+        xs <- chanContents' chan
+        return (x:xs)
+#endif
diff --git a/Presence/Logging.hs b/Presence/Logging.hs
new file mode 100644
index 00000000..b997d341
--- /dev/null
+++ b/Presence/Logging.hs
@@ -0,0 +1,25 @@
+{-# LANGUAGE RankNTypes #-}
+module Logging where
+
+import qualified Data.ByteString.Lazy.Char8 as L
+import qualified Data.ByteString.Char8 as S
+import qualified Data.Text.IO as Text
+import qualified Data.Text as Text
+import qualified Debug.Trace as Debug
+
+debugL :: L.ByteString -> IO ()
+debugS :: S.ByteString -> IO ()
+debugStr :: String -> IO ()
+debugText :: Text.Text -> IO ()
+trace :: forall a. String -> a -> a
+
+
+debugStr str = putStrLn str
+
+debugL bs = L.putStrLn bs
+
+debugS bs = S.putStrLn bs
+
+debugText text = Text.putStrLn text
+
+trace str a = Debug.trace str a
diff --git a/Presence/Nesting.hs b/Presence/Nesting.hs
new file mode 100644
index 00000000..720237fd
--- /dev/null
+++ b/Presence/Nesting.hs
@@ -0,0 +1,88 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE FlexibleContexts #-}
+module Nesting where
+
+import Data.Conduit
+import Data.Conduit.Lift
+import Data.XML.Types
+import qualified Data.Text as S
+import Control.Monad.State.Strict
+import qualified Data.List as List
+
+type Lang = S.Text
+
+data StrictList a = a :! !(StrictList a) | StrictNil
+
+data XMLState = XMLState { 
+        nestingLevel :: Int,
+        langStack :: StrictList (Int,Lang)
+}
+
+type NestingXML o m a = ConduitM Event o (StateT XMLState m) a
+
+doNestingXML :: Monad m => NestingXML o m r -> ConduitM Event o m r
+doNestingXML m = 
+    evalStateC (XMLState 0 StrictNil) (trackNesting =$= m)
+
+nesting :: Monad m => NestingXML o m Int
+nesting = lift $ (return . nestingLevel) =<< get
+
+xmlLang :: Monad m => NestingXML o m (Maybe Lang)
+xmlLang = fmap (fmap snd . top . langStack) (lift get)
+  where
+    top ( a :! _as ) = Just a
+    top _           = Nothing
+
+trackNesting :: Monad m => Conduit Event (StateT XMLState m) Event
+trackNesting = awaitForever doit
+ where
+  doit xml = do
+    XMLState lvl langs <- lift get
+    lift . put $ case xml of
+              EventBeginElement _ attrs -> 
+                case lookupLang attrs of
+                  Nothing   -> XMLState (lvl+1) langs
+                  Just lang -> XMLState (lvl+1) ( (lvl+1,lang) :! langs)
+              EventEndElement _     -> 
+                case langs of 
+                  (llvl,_) :! ls | llvl==lvl -> XMLState (lvl-1) ls
+                  _              | otherwise -> XMLState (lvl-1) langs
+              _  -> XMLState lvl langs
+    yield xml
+
+
+lookupLang :: [(Name, [Content])] -> Maybe S.Text
+lookupLang attrs =
+    case List.find ( (=="xml:lang") . fst) attrs of
+        Just (_,[ContentText x])   -> Just x
+        Just (_,[ContentEntity x]) -> Just x
+        _                          -> Nothing
+
+
+awaitCloser :: Monad m => Int -> NestingXML o m ()
+awaitCloser lvl =
+    fix $ \loop -> do
+        lvl' <- nesting
+        when (lvl' >= lvl) $ do
+        xml <- await
+        maybe (return ()) (const loop) xml
+
+withXML ::
+    Monad m =>
+    (i -> ConduitM i o m ()) -> ConduitM i o m ()
+withXML f = await >>= maybe (return ()) f
+
+nextElement :: Monad m => NestingXML o m (Maybe Event)
+nextElement = do
+    lvl <- nesting
+    fix $ \loop  -> do
+        xml <- await
+        case xml of
+            Nothing                      -> return Nothing
+            Just (EventBeginElement _ _) -> return xml
+            Just _ -> do
+                lvl' <- nesting
+                if (lvl'>=lvl) then loop 
+                               else return Nothing
+
+
diff --git a/Presence/Paths.hs b/Presence/Paths.hs
new file mode 100644
index 00000000..9d51b66e
--- /dev/null
+++ b/Presence/Paths.hs
@@ -0,0 +1,62 @@
+{-# LANGUAGE CPP #-}
+module Paths where
+
+#include <paths.h>
+
+bshell :: String
+console :: String
+cshell :: String
+devdb :: String
+devnull :: String
+drum :: String
+gshadow :: String
+klog :: String
+kmem :: String
+lastlog :: String
+maildir :: String
+man :: String
+mem :: String
+mnttab :: String
+mounted :: String
+nologin :: String
+preserve :: String
+rwhodir :: String
+sendmail :: String
+shadow :: String
+shells :: String
+tty :: String
+unix :: String
+utmp :: String
+vi :: String
+wtmp :: String
+
+
+
+bshell = _PATH_BSHELL
+console = _PATH_CONSOLE
+cshell = _PATH_CSHELL
+devdb = _PATH_DEVDB
+devnull = _PATH_DEVNULL
+drum = _PATH_DRUM
+gshadow = _PATH_GSHADOW
+klog = _PATH_KLOG
+kmem = _PATH_KMEM
+lastlog = _PATH_LASTLOG
+maildir = _PATH_MAILDIR
+man = _PATH_MAN
+mem = _PATH_MEM
+mnttab = _PATH_MNTTAB
+mounted = _PATH_MOUNTED
+nologin = _PATH_NOLOGIN
+preserve = _PATH_PRESERVE
+rwhodir = _PATH_RWHODIR
+sendmail = _PATH_SENDMAIL
+shadow = _PATH_SHADOW
+shells = _PATH_SHELLS
+tty = _PATH_TTY
+unix = _PATH_UNIX
+utmp = _PATH_UTMP
+vi = _PATH_VI
+wtmp = _PATH_WTMP
+
+
diff --git a/Presence/PeerResolve.hs b/Presence/PeerResolve.hs
new file mode 100644
index 00000000..0854b365
--- /dev/null
+++ b/Presence/PeerResolve.hs
@@ -0,0 +1,39 @@
+module PeerResolve
+    ( peerKeyToResolvedNames
+    , resolvePeer
+    , parseAddress
+    , strip_brackets
+    , withPort
+    ) where
+
+import Data.List       ( nub )
+import Data.Text       ( Text )
+import Network.Socket  ( SockAddr(..) )
+import System.Endian   ( fromBE32, toBE32 )
+import System.IO.Error ( isDoesNotExistError )
+import Control.Exception ( handle, ErrorCall(..) )
+import qualified Network.BSD as BSD
+import qualified Data.Text   as Text
+import Control.Concurrent
+import Control.Concurrent.STM
+import Control.Monad
+import Data.Maybe
+import System.IO.Unsafe
+
+import GetHostByAddr
+import DNSCache
+import ConnectionKey
+import ControlMaybe
+
+{-# NOINLINE global_dns_cache #-}
+global_dns_cache :: DNSCache
+global_dns_cache = unsafePerformIO $ newDNSCache
+
+resolvePeer :: Text -> IO [SockAddr]
+resolvePeer addrtext = forwardResolve global_dns_cache addrtext
+
+peerKeyToResolvedNames :: ConnectionKey -> IO [Text]
+peerKeyToResolvedNames k@(ClientKey { localAddress=addr }) = return []
+peerKeyToResolvedNames k@(PeerKey { callBackAddress=addr }) = do
+    reverseResolve global_dns_cache addr
+
diff --git a/Presence/Presence.hs b/Presence/Presence.hs
new file mode 100644
index 00000000..15775857
--- /dev/null
+++ b/Presence/Presence.hs
@@ -0,0 +1,1041 @@
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE LambdaCase                #-}
+{-# LANGUAGE OverloadedStrings         #-}
+{-# LANGUAGE TupleSections             #-}
+module Presence where
+
+import System.Environment
+import System.Posix.Signals
+import Control.Concurrent (threadDelay,forkIO,forkOS,killThread,throwTo)
+import Control.Concurrent.STM
+import Control.Concurrent.STM.TMVar
+import Control.Monad.Trans.Resource (runResourceT)
+import Control.Monad.Trans
+import Control.Monad.IO.Class (MonadIO, liftIO)
+import Network.Socket ( SockAddr(..) )
+import System.Endian (fromBE32)
+import Data.List (nub, (\\), intersect, groupBy, sort, sortBy )
+import Data.Ord (comparing )
+import Data.Monoid ( (<>), Sum(..), getSum )
+import qualified Data.Text as Text
+import qualified Data.Text.IO as Text
+import qualified Data.Text.Encoding as Text
+import Control.Monad
+import Control.Monad.Fix
+import qualified Network.BSD as BSD
+import qualified Data.Text as Text
+import Data.Text (Text)
+import qualified Data.Map as Map
+import Data.Map (Map)
+import Control.Exception ({-evaluate,-}handle,SomeException(..),bracketOnError,ErrorCall(..))
+import System.IO.Error (isDoesNotExistError)
+import System.Posix.User (getUserEntryForID,userName)
+import qualified Data.ByteString.Lazy.Char8 as L
+import qualified ConfigFiles
+import Data.Maybe (maybeToList,listToMaybe,mapMaybe)
+import Data.Bits
+import Data.Int (Int8)
+import Data.XML.Types (Event)
+import System.Posix.Types (UserID,CPid)
+import Control.Applicative
+
+import LockedChan (LockedChan)
+import TraversableT
+import UTmp (ProcessID,users)
+import LocalPeerCred
+import XMPPServer
+import PeerResolve
+import ConsoleWriter
+import ClientState
+import Util
+import qualified Connection
+
+isPeerKey :: ConnectionKey -> Bool
+isPeerKey k = case k of { PeerKey {} -> True ; _ -> False }
+
+isClientKey :: ConnectionKey -> Bool
+isClientKey k = case k of { ClientKey {} -> True ; _ -> False }
+
+localJID :: Text -> Text -> IO Text
+localJID user resource = do
+    hostname <- textHostName
+    return $ user <> "@" <> hostname <> "/" <> resource
+
+data PresenceState = forall status. PresenceState
+    { clients         :: TVar (Map ConnectionKey ClientState)
+    , clientsByUser   :: TVar (Map Text LocalPresence)
+    , remotesByPeer   :: TVar (Map ConnectionKey
+                                   (Map UserName RemotePresence))
+    , server          :: TMVar (XMPPServer, Connection.Manager status Text)
+    , keyToChan       :: TVar (Map ConnectionKey Conn)
+    , consoleWriter   :: Maybe ConsoleWriter
+    }
+
+
+newPresenceState cw xmpp = atomically $ do
+        clients <- newTVar Map.empty
+        clientsByUser <- newTVar Map.empty
+        remotesByPeer <- newTVar Map.empty
+        keyToChan <- newTVar Map.empty
+        return PresenceState
+            { clients = clients
+            , clientsByUser = clientsByUser
+            , remotesByPeer = remotesByPeer
+            , keyToChan = keyToChan
+            , server = xmpp
+            , consoleWriter = cw
+            }
+
+
+presenceHooks state verbosity = XMPPServerParameters
+    { xmppChooseResourceName        = chooseResourceName state
+    , xmppTellClientHisName         = tellClientHisName state
+    , xmppTellMyNameToClient        = textHostName
+    , xmppTellMyNameToPeer          = \addr -> return $ addrToText addr
+    , xmppTellPeerHisName           = return . peerKeyToText
+    , xmppTellClientNameOfPeer      = flip peerKeyToResolvedName
+    , xmppNewConnection             = newConn state
+    , xmppEOF                       = eofConn state
+    , xmppRosterBuddies             = rosterGetBuddies state
+    , xmppRosterSubscribers         = rosterGetSubscribers state
+    , xmppRosterSolicited           = rosterGetSolicited state
+    , xmppRosterOthers              = rosterGetOthers state
+    , xmppSubscribeToRoster         = informSentRoster state
+    , xmppDeliverMessage            = deliverMessage state
+    , xmppInformClientPresence      = informClientPresence state
+    , xmppInformPeerPresence        = informPeerPresence state
+    , xmppAnswerProbe               = \k stanza chan -> answerProbe state (stanzaTo stanza) k chan
+    , xmppClientSubscriptionRequest = clientSubscriptionRequest state
+    , xmppPeerSubscriptionRequest   = peerSubscriptionRequest state
+    , xmppClientInformSubscription  = clientInformSubscription state
+    , xmppPeerInformSubscription    = peerInformSubscription state
+    , xmppVerbosity                 = return verbosity
+    }
+
+
+data LocalPresence = LocalPresence
+    { networkClients :: Map ConnectionKey ClientState
+    -- TODO: loginClients
+    }
+
+data RemotePresence = RemotePresence
+    { resources :: Map Text Stanza
+    -- , localSubscribers :: Map Text ()
+    -- ^ subset of clientsByUser who should be
+    -- notified about this presence.
+    }
+
+
+
+pcSingletonNetworkClient :: ConnectionKey
+                          -> ClientState -> LocalPresence
+pcSingletonNetworkClient key client =
+    LocalPresence
+    { networkClients = Map.singleton key client
+    }
+
+pcInsertNetworkClient :: ConnectionKey -> ClientState -> LocalPresence -> LocalPresence
+pcInsertNetworkClient key client pc =
+    pc { networkClients = Map.insert key client (networkClients pc) }
+
+pcRemoveNewtworkClient :: ConnectionKey
+                        -> LocalPresence -> Maybe LocalPresence
+pcRemoveNewtworkClient key pc = if pcIsEmpty pc' then Nothing
+                                                 else Just pc'
+ where
+    pc' = pc { networkClients = Map.delete key (networkClients pc) }
+
+pcIsEmpty :: LocalPresence -> Bool
+pcIsEmpty pc = Map.null (networkClients pc)
+
+
+
+getConsolePids :: PresenceState -> IO [(Text,ProcessID)]
+getConsolePids state = do
+    us <- UTmp.users
+    return $ map (\(_,tty,pid)->(lazyByteStringToText tty,pid)) us
+
+identifyTTY' :: [(Text, ProcessID)]
+              -> System.Posix.Types.UserID
+              -> L.ByteString
+              -> IO (Maybe Text, Maybe System.Posix.Types.CPid)
+identifyTTY' ttypids uid inode = ttypid
+ where ttypids' = map (\(tty,pid)->(L.fromChunks [Text.encodeUtf8 tty], pid)) ttypids
+       ttypid = fmap textify $ identifyTTY ttypids' uid inode
+       textify (tty,pid) = (fmap lazyByteStringToText tty, pid)
+
+chooseResourceName :: PresenceState
+                    -> ConnectionKey -> SockAddr -> t -> IO Text
+chooseResourceName state k addr desired = do
+    muid <- getLocalPeerCred' addr
+    (mtty,pid) <- getTTYandPID muid
+    user <- getJabberUserForId muid
+    status <- atomically $ newTVar Nothing
+    flgs <- atomically $ newTVar 0
+    let client = ClientState { clientResource = maybe "fallback" id mtty
+                             , clientUser = user
+                             , clientPid = pid
+                             , clientStatus = status
+                             , clientFlags = flgs }
+
+    do -- forward-lookup of the buddies so that it is cached for reversing.
+       buds <- configText ConfigFiles.getBuddies (clientUser client)
+       forM_ buds $ \bud -> do
+            let (_,h,_) = splitJID bud
+            forkIO $ void $ resolvePeer h
+
+    atomically $ do
+        modifyTVar' (clients state) $ Map.insert k client
+        modifyTVar' (clientsByUser state) $ flip Map.alter (clientUser client)
+            $ \mb -> Just $ maybe (pcSingletonNetworkClient k client)
+                                  (pcInsertNetworkClient k client)
+                                  mb
+
+    localJID (clientUser client) (clientResource client)
+
+  where
+    getTTYandPID muid = do
+        -- us <- fmap (map (second fst) . Map.toList) . readTVarIO $ activeUsers state
+        ttypids <- getConsolePids state
+        -- let tailOf3 ((_,a),b) = (a,b)
+        (t,pid) <- case muid of
+                      Just (uid,inode) -> identifyTTY' ttypids uid inode
+                      Nothing          -> return (Nothing,Nothing)
+        let rsc = t `mplus` fmap ( ("pid."<>) . Text.pack . show ) pid
+        return (rsc,pid)
+
+    getJabberUserForId muid =
+             maybe (return "nobody")
+                   (\(uid,_) ->
+                        handle (\(SomeException _) ->
+                                return . (<> "uid.") . Text.pack . show $ uid)
+                          $ do
+                             user <- fmap userName $ getUserEntryForID uid
+                             return (Text.pack user)
+                        )
+                   muid
+
+forClient :: PresenceState
+           -> ConnectionKey -> IO b -> (ClientState -> IO b) -> IO b
+forClient state k fallback f = do
+    mclient <- atomically $ do
+        cs <- readTVar (clients state)
+        return $ Map.lookup k cs
+    maybe fallback f mclient
+
+tellClientHisName :: PresenceState -> ConnectionKey -> IO Text
+tellClientHisName state k = forClient state k fallback go
+ where
+    fallback  = localJID "nobody" "fallback"
+    go client = localJID (clientUser client) (clientResource client)
+
+toMapUnit :: Ord k => [k] -> Map k ()
+toMapUnit xs = Map.fromList $ map (,()) xs
+
+resolveAllPeers :: [Text] -> IO (Map SockAddr ())
+resolveAllPeers hosts = fmap (toMapUnit . concat) $ Prelude.mapM (fmap (take 1) . resolvePeer) hosts
+
+
+rosterGetStuff
+  :: (L.ByteString -> IO [L.ByteString])
+     -> PresenceState -> ConnectionKey -> IO [Text]
+rosterGetStuff what state k = forClient state k (return [])
+    $ \client -> do
+    jids <- configText what (clientUser client)
+    let hosts = map ((\(_,h,_)->h) . splitJID) jids
+    case state of
+      PresenceState { server = svVar } -> do
+        (sv,conns) <- atomically $ takeTMVar svVar
+        -- Grok peers to associate with from the roster:
+        forM_ hosts $ \host -> Connection.setPolicy conns host Connection.TryingToConnect
+        atomically $ putTMVar svVar (sv,conns)
+        return jids
+
+rosterGetBuddies :: PresenceState -> ConnectionKey -> IO [Text]
+rosterGetBuddies state k = rosterGetStuff ConfigFiles.getBuddies state k
+
+rosterGetSolicited :: PresenceState -> ConnectionKey -> IO [Text]
+rosterGetSolicited = rosterGetStuff ConfigFiles.getSolicited
+
+rosterGetOthers :: PresenceState -> ConnectionKey -> IO [Text]
+rosterGetOthers = rosterGetStuff ConfigFiles.getOthers
+
+rosterGetSubscribers :: PresenceState -> ConnectionKey -> IO [Text]
+rosterGetSubscribers = rosterGetStuff ConfigFiles.getSubscribers
+
+data Conn = Conn { connChan :: TChan Stanza
+                 , auxAddr :: SockAddr }
+
+configText :: Functor f =>
+            (L.ByteString -> f [L.ByteString]) -> Text -> f [Text]
+configText what u = fmap (map lazyByteStringToText)
+                        $ what (textToLazyByteString u)
+
+getBuddies' :: Text -> IO [Text]
+getBuddies' = configText ConfigFiles.getBuddies
+getSolicited' :: Text -> IO [Text]
+getSolicited' = configText ConfigFiles.getSolicited
+
+sendProbesAndSolicitations :: PresenceState
+                            -> ConnectionKey -> SockAddr -> TChan Stanza -> IO ()
+sendProbesAndSolicitations state k laddr chan = do
+    -- get all buddies & solicited matching k for all users
+    xs <- runTraversableT $ do
+        cbu <- lift $ atomically $ readTVar $ clientsByUser state
+        user <- liftT $ Map.keys cbu
+        (isbud,getter) <- liftT [(True ,getBuddies'  )
+                                ,(False,getSolicited')]
+        bud  <- liftMT $ getter user
+        let (u,h,r) = splitJID bud
+        addr <- liftMT $ nub `fmap` resolvePeer h
+        liftT $ guard (PeerKey addr == k)
+        -- Note: Earlier I was tempted to do all the IO
+        -- within the TraversableT monad.  That apparently
+        -- is a bad idea.  Perhaps due to laziness and an
+        -- unforced list?  Instead, we will return a list
+        -- of (Bool,Text) for processing outside.
+        return (isbud,u,if isbud then "" else user)
+    -- XXX: The following O(n²) nub may be a little
+    --      too onerous.
+    forM_ (nub xs) $ \(isbud,u,user) -> do
+        let make = if isbud then presenceProbe
+                            else presenceSolicitation
+            toh = peerKeyToText k
+            jid = unsplitJID (u,toh,Nothing)
+            me = addrToText laddr
+            from = if isbud then me -- probe from server
+                            else -- solicitation from particular user
+                                 unsplitJID (Just user,me,Nothing)
+        stanza <- make from jid
+        -- send probes for buddies, solicitations for solicited.
+        putStrLn $ "probing "++show k++" for: " ++ show (isbud,jid)
+        atomically $ writeTChan chan stanza
+    -- reverse xs `seq` return ()
+
+newConn :: PresenceState -> ConnectionKey -> SockAddr -> TChan Stanza -> IO ()
+newConn state k addr outchan = do
+    atomically $ modifyTVar' (keyToChan state)
+        $ Map.insert k Conn { connChan = outchan
+                            , auxAddr  = addr }
+    when (isPeerKey k)
+        $ sendProbesAndSolicitations state k addr outchan
+
+delclient :: (Alternative m, Monad m) =>
+           ConnectionKey -> m LocalPresence -> m LocalPresence
+delclient k mlp = do
+    lp <- mlp
+    let nc = Map.delete k $ networkClients lp
+    guard $ not (Map.null nc)
+    return $ lp { networkClients = nc }
+
+eofConn :: PresenceState -> ConnectionKey -> IO ()
+eofConn state k = do
+    atomically $ modifyTVar' (keyToChan state) $ Map.delete k
+    case k of
+        ClientKey {} -> do
+            forClient state k (return ()) $ \client -> do
+            stanza <- makePresenceStanza "jabber:server" Nothing Offline
+            informClientPresence state k stanza
+            atomically $ do
+                modifyTVar' (clientsByUser state)
+                    $ Map.alter (delclient k) (clientUser client)
+        PeerKey {} -> do
+            let h = peerKeyToText k
+            jids <- atomically $ do
+                rbp <- readTVar (remotesByPeer state)
+                return $ do
+                    umap <- maybeToList $ Map.lookup k rbp
+                    (u,rp) <- Map.toList umap
+                    r <- Map.keys (resources rp)
+                    return $ unsplitJID (Just u, h, Just r)
+            forM_ jids $ \jid -> do
+            stanza <- makePresenceStanza "jabber:client" (Just jid) Offline
+            informPeerPresence state k stanza
+
+{-
+rewriteJIDForClient1:: Text -> IO (Maybe ((Maybe Text,Text,Maybe Text),SockAddr))
+rewriteJIDForClient1 jid = do
+    let (n,h,r) = splitJID jid
+    maddr <- fmap listToMaybe $ resolvePeer h
+    flip (maybe $ return Nothing) maddr $ \addr -> do
+        h' <- peerKeyToResolvedName (PeerKey addr)
+        return $ Just ((n,h',r), addr)
+-}
+
+-- | The given address is taken to be the local address for the socket this JID
+-- came in on.  The returned JID parts are suitable for unsplitJID to create a
+-- valid JID for communicating to a client.  The returned Bool is True when the
+-- host part refers to this local host (i.e. it equals the given SockAddr).
+-- If there are multiple results, it will prefer one which is a member of the
+-- given list in the last argument.
+rewriteJIDForClient :: SockAddr -> Text -> [Text] -> IO (Bool,(Maybe Text,Text,Maybe Text))
+rewriteJIDForClient laddr jid buds = do
+    let (n,h,r) = splitJID jid
+    maddr <- parseAddress (strip_brackets h)
+    flip (maybe $ return (False,(n,ip6literal h,r))) maddr $ \addr -> do
+    let mine =  laddr `withPort` 0  == addr `withPort` 0
+    h' <- if mine then textHostName
+                  else peerKeyToResolvedName buds (PeerKey addr)
+    return (mine,(n,h',r))
+
+peerKeyToResolvedName :: [Text] -> ConnectionKey -> IO Text
+peerKeyToResolvedName buds k@(ClientKey { localAddress=addr }) = return "ErrorClIeNt1"
+peerKeyToResolvedName buds pk = do
+    ns <- peerKeyToResolvedNames pk
+    let hs = map (\jid -> let (_,h,_)=splitJID jid in h) buds
+        ns' = sortBy (comparing $ not . flip elem hs) ns
+    return $ maybe (peerKeyToText pk) id (listToMaybe ns')
+
+
+multiplyJIDForClient :: SockAddr -> Text -> IO (Bool,[(Maybe Text,Text,Maybe Text)])
+multiplyJIDForClient laddr jid = do
+    let (n,h,r) = splitJID jid
+    maddr <- parseAddress (strip_brackets h)
+    flip (maybe $ return (False,[(n,ip6literal h,r)])) maddr $ \addr -> do
+    let mine =  sameAddress laddr addr
+    names <- if mine then fmap (:[]) textHostName
+                     else peerKeyToResolvedNames (PeerKey addr)
+    return (mine,map (\h' -> (n,h',r)) names)
+
+
+addrTextToKey :: Text -> IO (Maybe ConnectionKey)
+addrTextToKey h = do
+    maddr <- parseAddress (strip_brackets h)
+    return (fmap PeerKey maddr)
+
+guardPortStrippedAddress :: Text -> SockAddr -> IO (Maybe ())
+guardPortStrippedAddress h laddr = do
+    maddr <- fmap (fmap (`withPort` 0)) $ parseAddress (strip_brackets h)
+    let laddr' = laddr `withPort` 0
+    return $ maddr >>= guard . (==laddr')
+
+
+-- | Accepts a textual representation of a domainname
+-- JID suitable for client connections, and returns the
+-- coresponding ipv6 address JID suitable for peers paired
+-- with a SockAddr with the address part of that JID in
+-- binary form.  If no suitable address could be resolved
+-- for the given name, Nothing is returned.
+rewriteJIDForPeer :: Text -> IO (Maybe (Text,SockAddr))
+rewriteJIDForPeer jid = do
+    let (n,h,r) = splitJID jid
+    maddr <- fmap listToMaybe $ resolvePeer h
+    return $ flip fmap maddr $ \addr ->
+        let h' = addrToText addr
+            to' = unsplitJID (n,h',r)
+        in (to',addr)
+
+deliverToConsole :: PresenceState -> IO () -> Stanza -> IO ()
+deliverToConsole PresenceState{ consoleWriter = Just cw } fail msg = do
+    did1 <- writeActiveTTY cw msg
+    did2 <- writeAllPty cw msg
+    if not (did1 || did2) then fail else return ()
+deliverToConsole _ fail _ = fail
+
+-- | deliver <message/> or error stanza
+deliverMessage :: PresenceState
+                -> IO ()
+                -> StanzaWrap (LockedChan Event)
+                -> IO ()
+deliverMessage state fail msg =
+    case stanzaOrigin msg of
+      NetworkOrigin senderk@(ClientKey {}) _ -> do
+        -- Case 1.  Client -> Peer
+        mto <- do
+            flip (maybe $ return Nothing) (stanzaTo msg) $ \to -> do
+            rewriteJIDForPeer to
+        flip (maybe fail {- reverse lookup failure -})
+             mto
+            $ \(to',addr) -> do
+        let k = PeerKey addr
+        chans <- atomically $ readTVar (keyToChan state)
+        flip (maybe fail) (Map.lookup k chans) $ \(Conn { connChan=chan
+                                                        , auxAddr=laddr }) -> do
+        (n,r) <- forClient state senderk (return (Nothing,Nothing))
+                        $ \c -> return (Just (clientUser c), Just (clientResource c))
+        -- original 'from' address is discarded.
+        let from' = unsplitJID (n,addrToText laddr,r)
+        -- dup <- atomically $ cloneStanza (msg { stanzaTo=Just to', stanzaFrom=Just from' })
+        let dup = (msg { stanzaTo=Just to', stanzaFrom=Just from' })
+        sendModifiedStanzaToPeer dup chan
+      NetworkOrigin senderk@(PeerKey {}) _ -> do
+        key_to_chan <- atomically $ readTVar (keyToChan state)
+        flip (maybe fail) (Map.lookup senderk key_to_chan)
+            $ \(Conn { connChan=sender_chan
+                     , auxAddr=laddr }) -> do
+        flip (maybe fail) (stanzaTo msg) $ \to -> do
+        (mine,(n,h,r)) <- rewriteJIDForClient laddr to []
+        if not mine then fail else do
+        let to' = unsplitJID (n,h,r)
+        cmap <- atomically . readTVar $ clientsByUser state
+        (from',chans,ks) <- do
+            flip (maybe $ return (Nothing,[],[])) n $ \n -> do
+            buds <- configText ConfigFiles.getBuddies n
+            from' <- do
+                flip (maybe $ return Nothing) (stanzaFrom msg) $ \from -> do
+                (_,trip) <- rewriteJIDForClient laddr from buds
+                return . Just $ unsplitJID trip
+            let nope = return (from',[],[])
+            flip (maybe nope) (Map.lookup n cmap) $ \presence_container -> do
+            let ks = Map.keys (networkClients presence_container)
+                chans = mapMaybe (flip Map.lookup key_to_chan) ks
+            return (from',chans,ks)
+        putStrLn $ "chan count: " ++ show (length chans)
+        let msg' = msg { stanzaTo=Just to'
+                       , stanzaFrom=from' }
+        if null chans then deliverToConsole state fail msg' else do
+        forM_ chans $ \Conn { connChan=chan} -> do
+        putStrLn $ "sending "++show (stanzaId msg)++" to clients "++show ks
+        -- TODO: Cloning isn't really neccessary unless there are multiple
+        -- destinations and we should probably transition to minimal cloning,
+        -- or else we should distinguish between announcable stanzas and
+        -- consumable stanzas and announcables use write-only broadcast
+        -- channels that must be cloned in order to be consumed.
+        -- For now, we are doing redundant cloning.
+        dup <- cloneStanza msg'
+        sendModifiedStanzaToClient dup
+                                  chan
+
+
+setClientFlag :: PresenceState -> ConnectionKey -> Int8 -> IO ()
+setClientFlag state k flag =
+    atomically $ do
+        cmap <- readTVar (clients state)
+        flip (maybe $ return ()) (Map.lookup k cmap) $ \client -> do
+        setClientFlag0 client flag
+
+setClientFlag0 :: ClientState -> Int8 -> STM ()
+setClientFlag0 client flag =
+    modifyTVar' (clientFlags client) (\flgs -> flgs .|. flag)
+
+informSentRoster :: PresenceState -> ConnectionKey -> IO ()
+informSentRoster state k = do
+    setClientFlag state k cf_interested
+
+
+subscribedPeers :: Text -> IO [SockAddr]
+subscribedPeers user = do
+    jids <- configText ConfigFiles.getSubscribers user
+    let hosts = map ((\(_,h,_)->h) . splitJID) jids
+    fmap Map.keys $ resolveAllPeers hosts
+
+-- | this JID is suitable for peers, not clients.
+clientJID :: Conn -> ClientState -> Text
+clientJID con client = unsplitJID ( Just $ clientUser client
+                                  , addrToText $ auxAddr con
+                                  , Just $ clientResource client)
+
+-- | Send presence notification to subscribed peers.
+-- Note that a full JID from address will be added to the
+-- stanza if it is not present.
+informClientPresence :: PresenceState
+                        -> ConnectionKey -> StanzaWrap (LockedChan Event) -> IO ()
+informClientPresence state k stanza = do
+    forClient state k (return ()) $ \client -> do
+    informClientPresence0 state (Just k) client stanza
+
+informClientPresence0 :: PresenceState
+                       -> Maybe ConnectionKey
+                       -> ClientState
+                       -> StanzaWrap (LockedChan Event)
+                       -> IO ()
+informClientPresence0 state mbk client stanza = do
+    dup <- cloneStanza stanza
+    atomically $ writeTVar (clientStatus client) $ Just dup
+    is_avail <- atomically $ clientIsAvailable client
+    when (not is_avail) $ do
+        atomically $ setClientFlag0 client cf_available
+        maybe (return ()) (sendCachedPresence state) mbk
+    addrs <- subscribedPeers (clientUser client)
+    ktc <- atomically $ readTVar (keyToChan state)
+    let connected = mapMaybe (flip Map.lookup ktc . PeerKey) addrs
+    forM_ connected $ \con -> do
+    let from' = clientJID con client
+    mto <- runTraversableT $ do
+            to <- liftT $ stanzaTo stanza
+            (to',_) <- liftMT $ rewriteJIDForPeer to
+            return to'
+    dup <- cloneStanza stanza
+    sendModifiedStanzaToPeer dup { stanzaFrom = Just from'
+                                 , stanzaTo = mto }
+                             (connChan con)
+
+informPeerPresence :: PresenceState
+                    -> ConnectionKey
+                    -> StanzaWrap (LockedChan Event)
+                    -> IO ()
+informPeerPresence state k stanza = do
+    -- Presence must indicate full JID with resource...
+    putStrLn $ "xmppInformPeerPresence checking from address..."
+    flip (maybe $ return ()) (stanzaFrom stanza) $ \from -> do
+    let (muser,h,mresource) = splitJID from
+    putStrLn $ "xmppInformPeerPresence from  = " ++ show from
+    -- flip (maybe $ return ()) mresource       $ \resource -> do
+    flip (maybe $ return ()) muser           $ \user -> do
+
+    clients <- atomically $ do
+
+        -- Update remotesByPeer...
+        rbp <- readTVar (remotesByPeer state)
+        let umap = maybe Map.empty id $ Map.lookup k rbp
+            rp = case (presenceShow $ stanzaType stanza) of
+                    Offline ->
+                        maybe Map.empty
+                              (\resource ->
+                                  maybe (Map.empty)
+                                     (Map.delete resource . resources)
+                                   $ Map.lookup user umap)
+                              mresource
+
+                    _ ->maybe Map.empty
+                              (\resource ->
+                                  maybe (Map.singleton resource stanza)
+                                     (Map.insert resource stanza . resources )
+                                    $ Map.lookup user umap)
+                              mresource
+            umap' = Map.insert user (RemotePresence rp) umap
+
+        flip (maybe $ return []) (case presenceShow $ stanzaType stanza of
+                                     Offline -> Just ()
+                                     _ -> mresource >> Just ())
+            $ \_ -> do
+        writeTVar (remotesByPeer state) $ Map.insert k umap' rbp
+        -- TODO: Store or delete the stanza (remotesByPeer)
+
+        -- all clients, we'll filter available/authorized later
+
+        ktc <- readTVar (keyToChan state)
+        runTraversableT $ do
+        (ck,client) <- liftMT $ fmap Map.toList $ readTVar (clients state)
+        con <- liftMaybe $ Map.lookup ck ktc
+        return (ck,con,client)
+    putStrLn $ "xmppInformPeerPresence (length clients="++show (length clients)++")"
+    forM_ clients $ \(ck,con,client) -> do
+        -- (TODO: appropriately authorized clients only.)
+        -- For now, all "available" clients (available = sent initial presence)
+        is_avail <- atomically $ clientIsAvailable client
+        when is_avail $ do
+        putStrLn $ "reversing for client: " ++ show from
+        froms <- do -- flip (maybe $ return [from]) k . const $ do
+            let ClientKey laddr = ck
+            (_,trip) <- multiplyJIDForClient laddr from
+            return (map unsplitJID trip)
+
+        putStrLn $ "sending to client: " ++ show (stanzaType stanza,froms)
+        forM_ froms $ \from' -> do
+        dup <- cloneStanza stanza
+        sendModifiedStanzaToClient (dup { stanzaFrom=Just from' })
+                                   (connChan con)
+
+consoleClients :: PresenceState -> STM (Map Text ClientState)
+consoleClients PresenceState{ consoleWriter = Just cw } = readTVar (cwClients cw)
+consoleClients _                                        = return Map.empty
+
+
+answerProbe :: PresenceState
+             -> Maybe Text -> ConnectionKey -> TChan Stanza -> IO ()
+answerProbe state mto k chan = do
+    -- putStrLn $ "answerProbe! " ++ show (stanzaType stanza)
+    ktc <- atomically $ readTVar (keyToChan state)
+    muser <- runTraversableT $ do
+        to <- liftT $ mto
+        conn <- liftT $ Map.lookup k ktc
+        let (mu,h,_) = splitJID to -- TODO: currently resource-id is ignored on presence
+                                   --  probes.  Is this correct? Check the spec.
+        liftMT $ guardPortStrippedAddress h (auxAddr conn)
+        u <- liftT mu
+        let ch = addrToText (auxAddr conn)
+        return (u,conn,ch)
+
+    flip (maybe $ return ()) muser $ \(u,conn,ch) -> do
+
+    resolved_subs <- resolvedFromRoster ConfigFiles.getSubscribers u
+    let gaddrs = groupBy (\a b -> snd a == snd b) (sort resolved_subs)
+        whitelist = do
+            xs <- gaddrs
+            x <- take 1 xs
+            guard $ snd x==k
+            mapMaybe fst xs
+
+    -- -- only subscribed peers should get probe replies
+    -- addrs <- subscribedPeers u
+
+    -- TODO: notify remote peer that they are unsubscribed?
+    --   reply <- makeInformSubscription "jabber:server" to from False
+    when (not $ null whitelist) $ do
+
+    replies <- runTraversableT $ do
+        cbu <- lift . atomically $ readTVar (clientsByUser state)
+        let lpres = maybeToList $ Map.lookup u cbu
+        cw <- lift . atomically $ consoleClients state
+        clientState <- liftT $ (lpres >>= Map.elems . networkClients)
+                                ++ Map.elems cw
+        stanza <- liftIOMaybe $ atomically (readTVar (clientStatus clientState))
+        stanza <- lift $ cloneStanza stanza
+        let jid = unsplitJID (Just $ clientUser clientState
+                             , ch
+                             ,Just $ clientResource clientState)
+        return stanza { stanzaFrom = Just jid
+                      , stanzaType = (stanzaType stanza)
+                        { presenceWhiteList = whitelist }
+                      }
+
+    forM_ replies $ \reply -> do
+        sendModifiedStanzaToPeer reply chan
+
+    -- if no presence, send offline message
+    when (null replies) $ do
+        let jid = unsplitJID (Just u,ch,Nothing)
+        pstanza <- makePresenceStanza "jabber:server" (Just jid) Offline
+        atomically $ writeTChan (connChan conn) pstanza
+
+sendCachedPresence :: PresenceState -> ConnectionKey -> IO ()
+sendCachedPresence state k = do
+    forClient state k (return ()) $ \client -> do
+    rbp <- atomically $ readTVar (remotesByPeer state)
+    jids <- configText ConfigFiles.getBuddies (clientUser client)
+    let hosts = map ((\(_,h,_)->h) . splitJID) jids
+    addrs <- resolveAllPeers hosts
+    let onlines = rbp `Map.intersection` Map.mapKeys PeerKey addrs
+        ClientKey laddr = k
+    mcon <- atomically $ do ktc <- readTVar (keyToChan state)
+                            return $ Map.lookup k ktc
+    flip (maybe $ return ()) mcon $ \con -> do
+    -- me <- textHostName
+    forM_ (Map.toList onlines) $ \(pk, umap) -> do
+        forM_ (Map.toList umap) $ \(user,rp) -> do
+        let h = peerKeyToText pk
+        forM_ (Map.toList $ resources rp) $ \(resource,stanza) -> do
+        let jid = unsplitJID (Just user,h,Just resource)
+        (mine,js) <- multiplyJIDForClient laddr jid
+        forM_ js $ \jid -> do
+        let from' = unsplitJID jid
+        dup <- cloneStanza stanza
+        sendModifiedStanzaToClient (dup { stanzaFrom=Just from' })
+                                   (connChan con)
+
+    pending <- configText ConfigFiles.getPending (clientUser client)
+    hostname <- textHostName
+    forM_ pending $ \pending_jid -> do
+        let cjid = unsplitJID ( Just $ clientUser client
+                              , hostname
+                              , Nothing )
+        ask <- presenceSolicitation pending_jid cjid
+        sendModifiedStanzaToClient ask (connChan con)
+
+    -- Note: relying on self peer connection to send
+    -- send local buddies.
+    return ()
+
+addToRosterFile :: (MonadPlus t, Traversable t) =>
+                 (L.ByteString -> (L.ByteString -> IO (t L.ByteString))
+                  -> Maybe L.ByteString
+                  -> t1)
+                 -> Text -> Text -> [SockAddr] -> t1
+addToRosterFile doit whose to addrs =
+    modifyRosterFile doit whose to addrs True
+
+removeFromRosterFile :: (MonadPlus t, Traversable t) =>
+                      (L.ByteString -> (L.ByteString -> IO (t L.ByteString))
+                       -> Maybe L.ByteString
+                       -> t1)
+                      -> Text -> Text -> [SockAddr] -> t1
+removeFromRosterFile doit whose to addrs =
+    modifyRosterFile doit whose to addrs False
+
+modifyRosterFile :: (Traversable t, MonadPlus t) =>
+                  (L.ByteString -> (L.ByteString -> IO (t L.ByteString))
+                   -> Maybe L.ByteString
+                   -> t1)
+                  -> Text -> Text -> [SockAddr] -> Bool -> t1
+modifyRosterFile doit whose to addrs bAdd = do
+    let (mu,_,_) = splitJID to
+        cmp jid = runTraversableT $ do
+            let (msu,stored_h,mr) = splitJID (lazyByteStringToText jid)
+            -- Delete from file if a resource is present in file
+            (\f -> maybe f (const mzero) mr) $ do
+            -- Delete from file if no user is present in file
+            flip (maybe mzero) msu $ \stored_u -> do
+            -- do not delete anything if no user was specified
+            flip (maybe $ return jid) mu $ \u -> do
+            -- do not delete if stored user is same as specified
+            if stored_u /= u then return jid else do
+            stored_addrs <- lift $ resolvePeer stored_h
+            -- do not delete if failed to resolve
+            if null stored_addrs then return jid else do
+            -- delete if specified address matches stored
+            if null (stored_addrs \\ addrs) then mzero else do
+            -- keep
+            return jid
+    doit (textToLazyByteString whose)
+         cmp
+         (guard bAdd >> Just (textToLazyByteString to))
+
+clientSubscriptionRequest :: PresenceState -> IO () -> ConnectionKey -> Stanza -> TChan Stanza -> IO ()
+clientSubscriptionRequest state fail k stanza chan = do
+    forClient state k fail $ \client -> do
+    flip (maybe fail) (stanzaTo stanza) $ \to -> do
+    putStrLn $ "Forwarding solictation to peer"
+    let (mu,h,_) = splitJID to
+    to <- return $ unsplitJID (mu,h,Nothing) -- delete resource
+    flip (maybe fail) mu $ \u -> do
+    -- add to-address to from's solicited
+    addrs <- resolvePeer h
+    addToRosterFile ConfigFiles.modifySolicited (clientUser client) to addrs
+    removeFromRosterFile ConfigFiles.modifyBuddies (clientUser client) to addrs
+    resolved_subs <- resolvedFromRoster ConfigFiles.getSubscribers (clientUser client)
+    let is_subscribed = not . null $ intersect (map ((mu,).PeerKey) addrs) resolved_subs
+    -- subscribers: "from"
+    -- buddies: "to"
+
+    case state of
+      PresenceState { server = svVar } -> do
+
+        (ktc,(sv,conns)) <- atomically $
+            liftM2 (,) (readTVar $ keyToChan state)
+                       (takeTMVar svVar)
+
+        case stanzaType stanza of
+         PresenceRequestSubscription True -> do
+            hostname <- textHostName
+            let cjid = unsplitJID (Just $ clientUser client, hostname,Nothing)
+            chans <- clientCons state ktc (clientUser client)
+            forM_ chans $ \( Conn { connChan=chan }, client ) -> do
+                -- roster update ask="subscribe"
+                update <- makeRosterUpdate cjid to
+                    [ ("ask","subscribe")
+                    , if is_subscribed then ("subscription","from")
+                                       else ("subscription","none")
+                    ]
+                sendModifiedStanzaToClient update chan
+         _ -> return ()
+
+        let dsts = Map.fromList $ map ((,()) . PeerKey) addrs
+            cdsts = ktc `Map.intersection` dsts
+        forM_ (Map.toList cdsts) $ \(pk,con) -> do
+            -- if already connected, send solicitation ...
+            -- let from = clientJID con client
+            let from = unsplitJID ( Just $ clientUser client
+                                  , addrToText $ auxAddr con
+                                  , Nothing )
+            mb <- rewriteJIDForPeer to
+            flip (maybe $ return ()) mb $ \(to',addr) -> do
+            dup <- cloneStanza stanza
+            sendModifiedStanzaToPeer (dup { stanzaTo = Just to'
+                                          , stanzaFrom = Just from })
+                                     (connChan con)
+        let addrm = Map.fromList (map (,()) addrs)
+        -- Add peer if we are not already associated ...
+        Connection.setPolicy conns h Connection.TryingToConnect
+        atomically $ putTMVar svVar (sv,conns)
+
+
+resolvedFromRoster
+  :: (L.ByteString -> IO [L.ByteString])
+     -> UserName -> IO [(Maybe UserName, ConnectionKey)]
+resolvedFromRoster doit u = do
+    subs <- configText doit u
+    runTraversableT $ do
+            (mu,h,_) <- liftT $ splitJID `fmap` subs
+            addr <- liftMT $ fmap nub $ resolvePeer h
+            return (mu,PeerKey addr)
+
+clientCons :: PresenceState
+            -> Map ConnectionKey t -> Text -> IO [(t, ClientState)]
+clientCons state ktc u = do
+    mlp <- atomically $ do
+            cmap <- readTVar $ clientsByUser state
+            return $ Map.lookup u cmap
+    let ks = do lp <- maybeToList mlp
+                Map.toList (networkClients lp)
+        doit (k,client) = do
+            con <- Map.lookup k ktc
+            return (con,client)
+    return $ mapMaybe doit ks
+
+peerSubscriptionRequest :: PresenceState -> IO () -> ConnectionKey -> Stanza -> TChan Stanza -> IO ()
+peerSubscriptionRequest state fail k stanza chan = do
+    putStrLn $ "Handling pending subscription from remote"
+    flip (maybe fail) (stanzaFrom stanza) $ \from -> do
+    flip (maybe fail) (stanzaTo stanza) $ \to -> do
+    let (mto_u,h,_) = splitJID to
+        (mfrom_u,from_h,_) = splitJID from
+    to <- return $ unsplitJID (mto_u,h,Nothing) -- delete resource
+    from <- return $ unsplitJID (mfrom_u,from_h,Nothing) -- delete resource
+    ktc <- atomically . readTVar $ keyToChan state
+    flip (maybe fail) (Map.lookup k ktc)
+         $ \Conn { auxAddr=laddr } -> do
+    (mine,totup) <- rewriteJIDForClient laddr to []
+    if not mine then fail else do
+    (_,fromtup) <- rewriteJIDForClient laddr from []
+    flip (maybe fail) mto_u $ \u -> do
+    flip (maybe fail) mfrom_u $ \from_u -> do
+    resolved_subs <- resolvedFromRoster ConfigFiles.getSubscribers u
+    let already_subscribed = elem (mfrom_u,k) resolved_subs
+        is_wanted = case stanzaType stanza of
+                      PresenceRequestSubscription b -> b
+                      _ -> False -- Shouldn't happen.
+    --    Section 8 says (for presence of type "subscribe", the server MUST
+    --    adhere to the rules defined under Section 3 and summarized under
+    --    see Appendix A. (pariticularly Appendex A.3.1)
+    if already_subscribed == is_wanted
+     then do
+        -- contact ∈ subscribers --> SHOULD NOT, already handled
+        -- already subscribed, reply and quit
+        -- (note: swapping to and from for reply)
+        reply <- makeInformSubscription "jabber:server" to from is_wanted
+        sendModifiedStanzaToPeer reply chan
+        answerProbe state (Just to) k chan
+     else do
+
+    -- TODO: if peer-connection is to self, then auto-approve local user.
+
+    -- add from-address to to's pending
+    addrs <- resolvePeer from_h
+
+    -- Catch exception in case the user does not exist
+    if null addrs then fail else do
+
+    let from' = unsplitJID fromtup
+
+    already_pending <-
+      if is_wanted then
+        addToRosterFile ConfigFiles.modifyPending u from' addrs
+      else do
+        removeFromRosterFile ConfigFiles.modifySubscribers u from' addrs
+        reply <- makeInformSubscription "jabber:server" to from is_wanted
+        sendModifiedStanzaToPeer reply chan
+        return False
+
+    -- contact ∉ subscribers & contact ∈ pending --> SHOULD NOT
+    when (not already_pending) $ do
+    -- contact ∉ subscribers & contact ∉ pending --> MUST
+
+    chans <- clientCons state ktc u
+    forM_ chans $ \( Conn { connChan=chan }, client ) -> do
+    -- send to clients
+    -- TODO: interested/available clients only?
+    dup <- cloneStanza stanza
+    sendModifiedStanzaToClient dup { stanzaFrom = Just $ from'
+                                   , stanzaTo = Just $ unsplitJID totup }
+                               chan
+
+
+clientInformSubscription :: PresenceState
+                          -> IO ()
+                          -> ConnectionKey
+                          -> StanzaWrap (LockedChan Event)
+                          -> IO ()
+clientInformSubscription state fail k stanza = do
+    forClient state k fail $ \client -> do
+    flip (maybe fail) (stanzaTo stanza) $ \to -> do
+    putStrLn $ "clientInformSubscription"
+    let (mu,h,mr) = splitJID to
+    addrs <- resolvePeer h
+    -- remove from pending
+    buds <- resolvedFromRoster ConfigFiles.getBuddies (clientUser client)
+    let is_buddy = not . null $ map ((mu,) . PeerKey) addrs `intersect` buds
+    removeFromRosterFile ConfigFiles.modifyPending (clientUser client) to addrs
+    let (relationship,addf,remf) =
+         case stanzaType stanza of
+           PresenceInformSubscription True ->
+                ( ("subscription", if is_buddy then "both"
+                                               else "from" )
+                , ConfigFiles.modifySubscribers
+                , ConfigFiles.modifyOthers )
+           _ -> ( ("subscription", if is_buddy then "to"
+                                               else "none" )
+                , ConfigFiles.modifyOthers
+                , ConfigFiles.modifySubscribers )
+    addToRosterFile      addf (clientUser client) to addrs
+    removeFromRosterFile remf (clientUser client) to addrs
+
+    do
+        cbu <- atomically $ readTVar (clientsByUser state)
+        putStrLn $ "cbu = " ++ show (fmap (fmap clientPid . networkClients) cbu)
+
+    -- send roster update to clients
+    (clients,ktc) <- atomically $ do
+        cbu <- readTVar (clientsByUser state)
+        let mlp = Map.lookup (clientUser client) cbu
+        let cs = maybe [] (Map.toList . networkClients) mlp
+        ktc <- readTVar (keyToChan state)
+        return (cs,ktc)
+    forM_ clients $ \(ck, client) -> do
+        is_intereseted <- atomically $ clientIsInterested client
+        putStrLn $ "clientIsInterested: "++show is_intereseted
+        is_intereseted <- atomically $ clientIsInterested client
+        when is_intereseted $ do
+        flip (maybe $ return ()) (Map.lookup ck ktc) $ \con -> do
+        hostname <- textHostName
+        -- TODO: Should cjid include the resource?
+        let cjid = unsplitJID (mu, hostname, Nothing)
+        update <- makeRosterUpdate cjid to [relationship]
+        sendModifiedStanzaToClient update (connChan con)
+
+    -- notify peer
+    let dsts = Map.fromList $ map ((,()) . PeerKey) addrs
+        cdsts = ktc `Map.intersection` dsts
+    forM_ (Map.toList cdsts) $ \(pk,con) -> do
+        let from = clientJID con client
+            to' = unsplitJID (mu, peerKeyToText pk, Nothing)
+        dup <- cloneStanza stanza
+        sendModifiedStanzaToPeer (dup { stanzaTo = Just $ to'
+                                      , stanzaFrom = Just from })
+                                 (connChan con)
+        answerProbe state (Just from) pk (connChan con)
+
+peerInformSubscription :: PresenceState
+                        -> IO ()
+                        -> ConnectionKey
+                        -> StanzaWrap (LockedChan Event)
+                        -> IO ()
+peerInformSubscription state fail k stanza = do
+    putStrLn $ "TODO: peerInformSubscription"
+    -- remove from solicited
+    flip (maybe fail) (stanzaFrom stanza) $ \from -> do
+    ktc <- atomically $ readTVar (keyToChan state)
+    flip (maybe fail) (Map.lookup k ktc)
+        $ \(Conn { connChan=sender_chan
+                 , auxAddr=laddr }) -> do
+    (_,(from_u,from_h,_)) <- rewriteJIDForClient laddr from []
+    let from'' = unsplitJID (from_u,from_h,Nothing)
+        muser = do
+            to <- stanzaTo stanza
+            let (mu,to_h,to_r) = splitJID to
+            mu
+    -- TODO muser = Nothing when wanted=False
+    -- should probably mean unsubscribed for all users.
+    -- This would allow us to answer anonymous probes with 'unsubscribed'.
+    flip (maybe fail) muser $ \user -> do
+    addrs <- resolvePeer from_h
+    was_solicited <- removeFromRosterFile ConfigFiles.modifySolicited user from'' addrs
+    subs <- resolvedFromRoster ConfigFiles.getSubscribers user
+    let is_sub = not . null $ map ((from_u,) . PeerKey) addrs `intersect` subs
+    let (relationship,addf,remf) =
+         case stanzaType stanza of
+           PresenceInformSubscription True ->
+                ( ("subscription", if is_sub then "both"
+                                             else "to" )
+                , ConfigFiles.modifyBuddies
+                , ConfigFiles.modifyOthers )
+           _ -> ( ("subscription", if is_sub then "from"
+                                             else "none")
+                , ConfigFiles.modifyOthers
+                , ConfigFiles.modifyBuddies )
+    addToRosterFile      addf user from'' addrs
+    removeFromRosterFile remf user from'' addrs
+
+    hostname <- textHostName
+    let to' = unsplitJID (Just user, hostname, Nothing)
+    chans <- clientCons state ktc user
+    forM_ chans $ \(Conn { connChan=chan }, client) -> do
+    update <- makeRosterUpdate to' from'' [relationship]
+    is_intereseted <- atomically $ clientIsInterested client
+    when is_intereseted $ do
+        sendModifiedStanzaToClient update chan
+    -- TODO: interested/availabe clients only?
+    dup <- cloneStanza stanza
+    sendModifiedStanzaToClient dup { stanzaFrom = Just $ from''
+                                   , stanzaTo = Just to' }
+                               chan
diff --git a/Presence/Server.hs b/Presence/Server.hs
new file mode 100644
index 00000000..c38aec2a
--- /dev/null
+++ b/Presence/Server.hs
@@ -0,0 +1,826 @@
+{-# OPTIONS_HADDOCK prune #-}
+{-# LANGUAGE CPP                #-}
+{-# LANGUAGE DoAndIfThenElse    #-}
+{-# LANGUAGE FlexibleInstances  #-}
+{-# LANGUAGE OverloadedStrings  #-}
+{-# LANGUAGE RankNTypes         #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TupleSections      #-}
+{-# LANGUAGE LambdaCase         #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Server
+--
+-- Maintainer  :  joe@jerkface.net
+-- Stability   :  experimental
+--
+-- A TCP client/server library.
+--
+-- TODO:
+--
+--  * interface tweaks
+--
+module Server
+    ( module Server
+    , module PingMachine ) where
+
+import Data.ByteString (ByteString,hGetNonBlocking)
+import qualified Data.ByteString.Char8 as S -- ( hPutStrLn, hPutStr, pack)
+import Data.Conduit ( Source, Sink, Flush )
+#if MIN_VERSION_containers(0,5,0)
+import qualified Data.Map.Strict as Map
+import           Data.Map.Strict (Map)
+#else
+import qualified Data.Map as Map
+import           Data.Map (Map)
+#endif
+import Data.Monoid ( (<>) )
+#ifdef THREAD_DEBUG
+import Control.Concurrent.Lifted.Instrument
+#else
+import Control.Concurrent.Lifted
+import GHC.Conc                  (labelThread)
+#endif
+
+import Control.Concurrent.STM
+-- import Control.Concurrent.STM.TMVar
+-- import Control.Concurrent.STM.TChan
+-- import Control.Concurrent.STM.Delay
+import Control.Exception ({-evaluate,-}handle,SomeException(..),ErrorCall(..),onException)
+import Control.Monad
+import Control.Monad.Fix
+-- import Control.Monad.STM
+-- import Control.Monad.Trans.Resource
+import Control.Monad.IO.Class (MonadIO (liftIO))
+import System.IO.Error (isDoesNotExistError)
+import System.IO
+    ( IOMode(..)
+    , hSetBuffering
+    , BufferMode(..)
+    , hWaitForInput
+    , hClose
+    , hIsEOF
+    , stderr
+    , Handle
+    , hFlush
+    , hPutStrLn
+    )
+import Network.Socket as Socket
+import Network.BSD
+    ( getProtocolNumber
+    )
+import Debug.Trace
+import Data.Time.Clock (getCurrentTime,diffUTCTime)
+-- import SockAddr ()
+-- import System.Locale (defaultTimeLocale)
+
+import InterruptibleDelay
+import PingMachine
+import Network.StreamServer
+import Network.SocketLike hiding (sClose)
+import qualified Connection as G
+         ;import Connection (Manager (..), Policy(..))
+
+
+type Microseconds = Int
+
+-- | This object is passed with the 'Listen' and 'Connect'
+-- instructions in order to control the behavior of the
+-- connections that are established.  It is parameterized
+-- by a user-suplied type @conkey@ that is used as a lookup
+-- key for connections.
+data ConnectionParameters conkey u =
+  ConnectionParameters
+    { pingInterval :: PingInterval
+    -- ^ The miliseconds of idle to allow before a 'RequiresPing'
+    -- event is signaled.
+    , timeout :: TimeOut
+    -- ^ The miliseconds of idle after 'RequiresPing' is signaled
+    -- that are necessary for the connection to be considered
+    -- lost and signalling 'EOF'.
+    , makeConnKey :: RestrictedSocket -> IO (conkey,u)
+    -- ^ This action creates a lookup key for a new connection.  If 'duplex'
+    -- is 'True' and the result is already assocatied with an established
+    -- connection, then an 'EOF' will be forced before the the new
+    -- connection becomes active.
+    --
+    , duplex :: Bool
+    -- ^ If True, then the connection will be treated as a normal
+    -- two-way socket.  Otherwise, a readable socket is established
+    -- with 'Listen' and a writable socket is established with
+    -- 'Connect' and they are associated when 'makeConnKey' yields
+    -- same value for each.
+    }
+
+-- | Use this function to select appropriate default values for
+-- 'ConnectionParameters' other than 'makeConnKey'.
+--
+-- Current defaults:
+--
+--  * 'pingInterval' = 28000
+--
+--  * 'timeout' = 2000
+--
+--  * 'duplex' = True
+--
+connectionDefaults
+  :: (RestrictedSocket -> IO (conkey,u)) -> ConnectionParameters conkey u
+connectionDefaults f = ConnectionParameters
+    { pingInterval = 28000
+    , timeout = 2000
+    , makeConnKey = f
+    , duplex = True
+    }
+
+-- | Instructions for a 'Server' object
+--
+-- To issue a command, put it into the 'serverCommand' TMVar.
+data ServerInstruction conkey u
+    = Quit
+    -- ^ kill the server.  This command is automatically issued when
+    -- the server is released.
+    | Listen PortNumber (ConnectionParameters conkey u)
+    -- ^ listen for incoming connections
+    | Connect SockAddr  (ConnectionParameters conkey u)
+    -- ^ connect to addresses
+    | ConnectWithEndlessRetry SockAddr
+                              (ConnectionParameters conkey u)
+                              Miliseconds
+    -- ^ keep retrying the connection
+    | Ignore PortNumber
+    -- ^ stop listening on specified port
+    | Send conkey ByteString
+    -- ^ send bytes to an established connection
+
+#ifdef TEST
+deriving instance Show conkey => Show (ServerInstruction conkey u)
+instance Show (a -> b) where show _ = "<function>"
+deriving instance Show conkey => Show (ConnectionParameters conkey u)
+#endif
+
+-- | This type specifies which which half of a half-duplex
+-- connection is of interest.
+data InOrOut = In | Out
+ deriving (Enum,Eq,Ord,Show,Read)
+
+-- | These events may be read from 'serverEvent' TChannel.
+--
+data ConnectionEvent b
+    = Connection (STM Bool) (Source IO b) (Sink (Flush b) IO ())
+    -- ^ A new connection was established
+    | ConnectFailure SockAddr
+    -- ^ A 'Connect' command failed.
+    | HalfConnection InOrOut
+    -- ^ Half of a half-duplex connection is avaliable.
+    | EOF
+    -- ^ A connection was terminated
+    | RequiresPing
+    -- ^ 'pingInterval' miliseconds of idle was experienced
+
+#ifdef TEST
+instance Show (IO a) where show _ = "<IO action>"
+instance Show (STM a) where show _ = "<STM action>"
+instance Eq (ByteString -> IO Bool) where (==) _ _ = True
+instance Eq (IO (Maybe ByteString)) where (==) _ _ = True
+instance Eq (STM Bool) where (==) _ _ = True
+deriving instance Show b => Show (ConnectionEvent b)
+deriving instance Eq   b => Eq   (ConnectionEvent b)
+#endif
+
+-- | This is the per-connection state.
+data ConnectionRecord u
+ = ConnectionRecord { ckont  :: TMVar (STM (IO ())) -- ^ used to pass a continuation to update the eof-handler
+                    , cstate :: ConnectionState     -- ^ used to send/receive data to the connection
+                    , cdata  :: u                   -- ^ user data, stored in the connection map for convenience
+                    }
+
+-- | This object accepts commands and signals events and maintains
+-- the list of currently listening ports and established connections.
+data Server a u releaseKey b
+ = Server { serverCommand    :: TMVar (ServerInstruction a u)
+          , serverEvent      :: TChan ((a,u), ConnectionEvent b)
+          , serverReleaseKey :: releaseKey
+          , conmap           :: TVar (Map a (ConnectionRecord u))
+          , listenmap        :: TVar (Map PortNumber ServerHandle)
+          , retrymap         :: TVar (Map SockAddr (TVar Bool,InterruptibleDelay))
+          }
+
+control :: Server a u releaseKey b -> ServerInstruction a u -> IO ()
+control sv = atomically . putTMVar (serverCommand sv)
+
+type Allocate releaseKey m = forall b. IO b -> (b -> IO ()) -> m (releaseKey, b)
+
+noCleanUp :: MonadIO m => Allocate () m
+noCleanUp io _ = ( (,) () ) `liftM` liftIO io
+
+-- | Construct a 'Server' object.  Use 'Control.Monad.Trans.Resource.ResourceT'
+-- to ensure proper cleanup.  For example,
+--
+-- > import Server
+-- > import Control.Monad.Trans.Resource (runResourceT)
+-- > import Control.Monad.IO.Class       (liftIO)
+-- > import Control.Monad.STM            (atomically)
+-- > import Control.Concurrent.STM.TMVar (putTMVar)
+-- > import Control.Concurrent.STM.TChan (readTChan)
+-- >
+-- > main = runResourceT $ do
+-- >   sv <- server allocate
+-- >   let params = connectionDefaults (return . snd)
+-- >   liftIO . atomically $ putTMVar (serverCommand sv) (Listen 2942 params)
+-- >   let loop = do
+-- >          (_,event) <- atomically $ readTChan (serverEvent sv)
+-- >          case event of
+-- >            Connection getPingFlag readData writeData -> do
+-- >              forkIO $ do
+-- >                fix $ \readLoop -> do
+-- >                    readData >>= mapM $ \bytes ->
+-- >                        putStrLn $ "got: " ++ show bytes
+-- >                        readLoop
+-- >          case event of EOF -> return ()
+-- >                        _   -> loop
+-- >   liftIO loop
+--
+-- Using 'Control.Monad.Trans.Resource.ResourceT' is optional.  Pass 'noCleanUp'
+-- to do without automatic cleanup and be sure to remember to write 'Quit' to
+-- the 'serverCommand' variable.
+server ::
+    -- forall (m :: * -> *) a u conkey releaseKey.
+    (Show conkey, MonadIO m, Ord conkey) =>
+    Allocate releaseKey m
+    -> ( IO (Maybe ByteString) -> (ByteString -> IO Bool) -> ( Source IO x, Sink (Flush x) IO () ) )
+    -> m (Server conkey u releaseKey x)
+server allocate sessionConduits = do
+    (key,cmds) <- allocate (atomically newEmptyTMVar)
+                           (atomically . flip putTMVar Quit)
+    server <- liftIO . atomically $ do
+        tchan    <- newTChan
+        conmap   <- newTVar Map.empty
+        listenmap<- newTVar Map.empty
+        retrymap <- newTVar Map.empty
+        return Server { serverCommand = cmds
+                      , serverEvent = tchan
+                      , serverReleaseKey = key
+                      , conmap = conmap
+                      , listenmap = listenmap
+                      , retrymap = retrymap
+                      }
+    liftIO $ do
+        tid <- forkIO $ fix $ \loop -> do
+            instr <- atomically $ takeTMVar cmds
+            -- warn $ "instr = " <> bshow instr
+            let again = do doit server instr
+                           -- warn $ "finished " <> bshow instr
+                           loop
+            case instr of Quit -> closeAll server
+                          _    -> again
+        labelThread tid "server"
+        return server
+ where
+  closeAll server = do
+    listening <- atomically . readTVar $ listenmap server
+    mapM_ quitListening   (Map.elems listening)
+    let stopRetry (v,d) = do atomically $ writeTVar v False
+                             interruptDelay d
+    retriers <- atomically $ do
+        rmap <- readTVar $ retrymap server
+        writeTVar (retrymap server) Map.empty
+        return rmap
+    mapM_ stopRetry (Map.elems retriers)
+    cons <- atomically . readTVar $ conmap server
+    atomically $ mapM_ (connClose . cstate) (Map.elems cons)
+    atomically $ mapM_ (connWait . cstate) (Map.elems cons)
+    atomically $ writeTVar (conmap server) Map.empty
+
+
+  doit server (Listen port params) = do
+
+    listening <- Map.member port
+                 `fmap` atomically (readTVar $ listenmap server)
+    when (not listening) $ do
+
+    hPutStrLn stderr $ "Started listening on "++show port
+
+    let family  = AF_INET6
+        address = case family of
+            AF_INET  -> SockAddrInet port iNADDR_ANY
+            AF_INET6 -> SockAddrInet6 port 0 iN6ADDR_ANY 0
+
+    sserv <- flip streamServer address ServerConfig
+        { serverWarn    = hPutStrLn stderr
+        , serverSession = \sock _ h -> do
+            (conkey,u) <- makeConnKey params sock
+            _ <- newConnection server sessionConduits params conkey u h In
+            return ()
+        }
+
+    atomically $ listenmap server `modifyTVar'` Map.insert port sserv
+
+  doit server (Ignore port) = do
+    hPutStrLn stderr $ "Stopping listen on "++show port
+    mb <- atomically $ do
+        map <- readTVar $ listenmap server
+        modifyTVar' (listenmap server) $ Map.delete port
+        return $ Map.lookup port map
+    maybe (return ()) quitListening $ mb
+
+  doit server (Send con bs) = do -- . void . forkIO $ do
+    map <- atomically $ readTVar (conmap server)
+    let post False = (trace ("cant send: "++show bs) $ return ())
+        post True  = return ()
+    maybe (post False)
+          (post <=< flip connWrite bs . cstate)
+      $ Map.lookup con map
+
+  doit server (Connect addr params) = join $ atomically $ do
+    Map.lookup addr <$> readTVar (retrymap server)
+      >>= return . \case
+        Nothing    -> forkit
+        Just (v,d) -> do b <- atomically $ readTVar v
+                         interruptDelay d
+                         when (not b) forkit
+    where
+    forkit = void . forkIO $ do
+        myThreadId >>= flip labelThread ( "Connect." ++ show addr )
+        proto <- getProtocolNumber "tcp"
+        sock <- socket (socketFamily addr) Stream proto
+        handle (\e -> do -- let t = ioeGetErrorType e
+                         when (isDoesNotExistError e) $ return () -- warn "GOTCHA"
+                         -- warn $ "connect-error: " <> bshow e
+                         (conkey,u) <- makeConnKey params (restrictSocket sock) -- XXX: ?
+                         Socket.close sock
+                         atomically
+                            $ writeTChan (serverEvent server)
+                                $ ((conkey,u),ConnectFailure addr))
+               $ do
+        connect sock addr
+        (conkey,u) <- makeConnKey params (restrictSocket sock)
+        h <- socketToHandle sock ReadWriteMode
+        newConnection server sessionConduits params conkey u h Out
+        return ()
+
+  doit server (ConnectWithEndlessRetry addr params interval) = do
+    proto <- getProtocolNumber "tcp"
+    void . forkIO $ do
+        myThreadId >>= flip labelThread ("ConnectWithEndlessRetry." ++ show addr)
+        timer <- interruptibleDelay
+        (retryVar,action) <- atomically $ do
+            map <- readTVar (retrymap server)
+            action <- case Map.lookup addr map of
+                Nothing    -> return $ return ()
+                Just (v,d) -> do writeTVar v False
+                                 return $ interruptDelay d
+            v <- newTVar True
+            writeTVar (retrymap server) $! Map.insert addr (v,timer) map
+            return (v,action :: IO ())
+        action
+        fix $ \retryLoop -> do
+        utc <- getCurrentTime
+        shouldRetry <- do
+            handle (\(SomeException e) -> do
+                -- Exceptions thrown by 'socket' need to be handled specially
+                -- since we don't have enough information to broadcast a ConnectFailure
+                -- on serverEvent.
+                warn $ "Failed to create socket: " <> bshow e
+                atomically $ readTVar retryVar) $ do
+            sock <- socket (socketFamily addr) Stream proto
+            handle (\(SomeException e) -> do
+                -- Any thing else goes wrong and we broadcast ConnectFailure.
+                do (conkey,u) <- makeConnKey params (restrictSocket sock)
+                   Socket.close sock
+                   atomically $ writeTChan (serverEvent server) ((conkey,u),ConnectFailure addr)
+                 `onException` return ()
+                atomically $ readTVar retryVar) $ do
+            connect sock addr
+            (conkey,u) <- makeConnKey params (restrictSocket sock)
+            h <- socketToHandle sock ReadWriteMode
+            threads <- newConnection server sessionConduits params conkey u h Out
+            atomically $ do threadsWait threads
+                            readTVar retryVar
+        fin_utc <- getCurrentTime
+        when shouldRetry $ do
+        let elapsed = 1000.0 * (fin_utc `diffUTCTime` utc)
+            expected = fromIntegral interval
+        when (shouldRetry && elapsed < expected) $ do
+            debugNoise $ "Waiting to retry " <> bshow addr
+            void $ startDelay timer (round $ 1000 * (expected-elapsed))
+        debugNoise $ "retry " <> bshow (shouldRetry,addr)
+        when shouldRetry $ retryLoop
+
+
+-- INTERNAL ----------------------------------------------------------
+
+{-
+hWriteUntilNothing h outs =
+    fix $ \loop -> do
+        mb <- atomically $ takeTMVar outs
+        case mb of Just bs -> do S.hPutStrLn h bs
+                                 warn $ "wrote " <> bs
+                                 loop
+                   Nothing -> do warn $ "wrote Nothing"
+                                 hClose h
+
+-}
+connRead :: ConnectionState -> IO (Maybe ByteString)
+connRead (WriteOnlyConnection w) = do
+    -- atomically $ discardContents (threadsChannel w)
+    return Nothing
+connRead conn = do
+    c <- atomically $ getThreads
+    threadsRead c
+ where
+    getThreads =
+        case conn of SaneConnection c     -> return c
+                     ReadOnlyConnection c -> return c
+                     ConnectionPair c w   -> do
+                        -- discardContents (threadsChannel w)
+                        return c
+
+socketFamily :: SockAddr -> Family
+socketFamily (SockAddrInet _ _)      = AF_INET
+socketFamily (SockAddrInet6 _ _ _ _) = AF_INET6
+socketFamily (SockAddrUnix _)        = AF_UNIX
+
+
+conevent :: ( IO (Maybe ByteString) -> (ByteString -> IO Bool) -> ( Source IO x, Sink (Flush x) IO () ) )
+            -> ConnectionState
+            -> ConnectionEvent x
+conevent sessionConduits con = Connection pingflag read write
+ where
+    pingflag     = swapTVar (pingFlag (connPingTimer con)) False
+    (read,write) = sessionConduits (connRead con) (connWrite con)
+
+newConnection :: Ord a
+                 => Server a u1 releaseKey x
+                 -> ( IO (Maybe ByteString) -> (ByteString -> IO Bool) -> ( Source IO x, Sink (Flush x) IO () ) )
+                 -> ConnectionParameters conkey u
+                 -> a
+                 -> u1
+                 -> Handle
+                 -> InOrOut
+                 -> IO ConnectionThreads
+newConnection server sessionConduits params conkey u h inout = do
+    hSetBuffering h NoBuffering
+    let (idle_ms,timeout_ms) =
+            case (inout,duplex params) of
+                (Out,False) -> ( 0, 0 )
+                _ -> ( pingInterval params
+                     , timeout params )
+
+    new <- do pinglogic <- forkPingMachine idle_ms timeout_ms
+              connectionThreads h pinglogic
+    started <- atomically $ newEmptyTMVar
+    kontvar <- atomically newEmptyTMVar
+    -- XXX: Why does kontvar store STM (IO ()) instead of just IO () ?
+    let _ = kontvar :: TMVar (STM (IO ()))
+    forkIO $ do
+        myThreadId >>= flip labelThread ("connecting...")
+        getkont <- atomically $ takeTMVar kontvar
+        kont <- atomically getkont
+        kont
+
+    atomically $ do
+        current <- fmap (Map.lookup conkey) $ readTVar (conmap server)
+        case current of
+          Nothing -> do
+            (newCon,e) <- return $
+              if duplex params
+                then let newcon = SaneConnection new
+                     in ( newcon, ((conkey,u), conevent sessionConduits newcon) )
+                else ( case inout of
+                        In  -> ReadOnlyConnection new
+                        Out -> WriteOnlyConnection new
+                     , ((conkey,u), HalfConnection inout) )
+            modifyTVar' (conmap server) $ Map.insert conkey
+                ConnectionRecord { ckont = kontvar
+                                 , cstate = newCon
+                                 , cdata = u }
+            announce e
+            putTMVar kontvar $ return $ do
+                myThreadId >>= flip labelThread ("connection."++show inout) -- XXX: more info would be nice.
+                atomically $ putTMVar started ()
+                -- Wait for something interesting.
+                handleEOF conkey u kontvar newCon
+          Just what@ConnectionRecord { ckont =mvar }-> do
+            putTMVar kontvar $ return $ return () -- Kill redundant "connecting..." thread.
+            putTMVar mvar $ do
+                -- The action returned by updateConMap, eventually invokes handleEOF,
+                -- so the sequencer thread will not be terminated.
+                kont <- updateConMap conkey u new what
+                putTMVar started ()
+                return kont
+    return new
+ where
+
+  announce e = writeTChan (serverEvent server) e
+
+  -- This function loops and will not quit unless an action is posted to the
+  -- mvar that does not in turn invoke this function, or if an EOF occurs.
+  handleEOF conkey u mvar newCon = do
+    action <- atomically . foldr1 orElse $
+        [ takeTMVar mvar >>= id -- passed continuation
+        , connWait newCon     >> return eof
+        , connWaitPing newCon >>= return . sendPing
+        -- , pingWait pingTimer >>= return . sendPing
+        ]
+    action :: IO ()
+   where
+    eof = do
+            -- warn $ "EOF " <>bshow conkey
+            connCancelPing newCon
+            atomically $ do connFlush newCon
+                            announce ((conkey,u),EOF)
+                            modifyTVar' (conmap server)
+                                        $ Map.delete conkey
+            -- warn $ "fin-EOF "<>bshow conkey
+
+    sendPing PingTimeOut = do
+        {-
+        utc <- getCurrentTime
+        let utc' = formatTime defaultTimeLocale "%s" utc
+        warn $ "ping:TIMEOUT " <> bshow utc'
+        -}
+        atomically (connClose newCon)
+        eof
+
+    sendPing PingIdle = do
+        {-
+        utc <- getCurrentTime
+        let utc' = formatTime defaultTimeLocale "%s" utc
+        -- warn $ "ping:IDLE " <> bshow utc'
+        -}
+        atomically $ announce ((conkey,u),RequiresPing)
+        handleEOF conkey u mvar newCon
+
+
+  updateConMap conkey u new (ConnectionRecord { ckont=mvar, cstate=replaced, cdata=u0 }) = do
+    new' <-
+        if duplex params then do
+            announce ((conkey,u),EOF)
+            connClose replaced
+            let newcon = SaneConnection new
+            announce $ ((conkey,u),conevent sessionConduits newcon)
+            return $ newcon
+        else
+         case replaced of
+            WriteOnlyConnection w | inout==In ->
+                 do let newcon = ConnectionPair new w
+                    announce ((conkey,u),conevent sessionConduits newcon)
+                    return newcon
+            ReadOnlyConnection r  | inout==Out ->
+                 do let newcon = ConnectionPair r new
+                    announce ((conkey,u),conevent sessionConduits newcon)
+                    return newcon
+            _ -> do -- connFlush todo
+                    announce ((conkey,u0), EOF)
+                    connClose replaced
+                    announce ((conkey,u), HalfConnection inout)
+                    return $ case inout of
+                                In  -> ReadOnlyConnection new
+                                Out -> WriteOnlyConnection new
+    modifyTVar' (conmap server) $ Map.insert conkey
+        ConnectionRecord { ckont = mvar
+                         , cstate = new'
+                         , cdata = u }
+    return $ handleEOF conkey u mvar new'
+
+
+getPacket :: Handle -> IO ByteString
+getPacket h = do hWaitForInput h (-1)
+                 hGetNonBlocking h 1024
+
+
+
+-- | 'ConnectionThreads' is an interface to a pair of threads
+-- that are reading and writing a 'Handle'.
+data ConnectionThreads = ConnectionThreads
+    { threadsWriter  :: TMVar (Maybe ByteString)
+    , threadsChannel :: TChan ByteString
+    , threadsWait    :: STM () -- ^ waits for a 'ConnectionThreads' object to close
+    , threadsPing    :: PingMachine
+    }
+
+-- | This spawns the reader and writer threads and returns a newly
+-- constructed 'ConnectionThreads' object.
+connectionThreads :: Handle -> PingMachine -> IO ConnectionThreads
+connectionThreads h pinglogic = do
+
+    (donew,outs) <- atomically $ liftM2 (,) newEmptyTMVar newEmptyTMVar
+
+    (doner,incomming) <- atomically $ liftM2 (,) newEmptyTMVar newTChan
+    readerThread <- forkIO $ do
+        myThreadId >>= flip labelThread ("readerThread")
+        let finished e  = do
+                          hClose h
+                          -- warn $ "finished read: " <> bshow (fmap ioeGetErrorType e)
+                          -- let _ = fmap ioeGetErrorType e -- type hint
+                          let _ = fmap what e where what (SomeException _) = undefined
+                          atomically $ do tryTakeTMVar outs
+                                          putTMVar outs Nothing -- quit writer
+                                          putTMVar doner ()
+        handle (finished . Just) $ do
+            pingBump pinglogic -- start the ping timer
+            fix $ \loop -> do
+            packet <- getPacket h
+            -- warn $ "read: " <> S.take 60 packet
+            atomically $ writeTChan incomming packet
+            pingBump pinglogic
+            -- warn $ "bumped: " <> S.take 60 packet
+            isEof <- hIsEOF h
+            if isEof then finished Nothing else loop
+
+    writerThread <- forkIO . fix $ \loop -> do
+        myThreadId >>= flip labelThread ("writerThread")
+        let finished = do -- warn $ "finished write"
+                          -- hClose h -- quit reader
+                          throwTo readerThread (ErrorCall "EOF")
+                          atomically $ putTMVar donew ()
+        mb <- atomically $ readTMVar outs
+        case mb of Just bs -> handle (\(SomeException e)->finished)
+                                     (do -- warn $ "writing: " <> S.take 60 bs
+                                         S.hPutStr h bs
+                                         -- warn $ "wrote: " <> S.take 60 bs
+                                         atomically $ takeTMVar outs
+                                         loop)
+                   Nothing -> finished
+
+    let wait = do readTMVar donew
+                  readTMVar doner
+                  return ()
+    return ConnectionThreads { threadsWriter  = outs
+                             , threadsChannel = incomming
+                             , threadsWait    = wait
+                             , threadsPing    = pinglogic }
+
+
+-- | 'threadsWrite' writes the given 'ByteString' to the
+-- 'ConnectionThreads' object.  It blocks until the ByteString
+-- is written and 'True' is returned, or the connection is
+-- interrupted and 'False' is returned.
+threadsWrite :: ConnectionThreads -> ByteString -> IO Bool
+threadsWrite c bs = atomically $
+    orElse (const False `fmap` threadsWait c)
+           (const True  `fmap` putTMVar (threadsWriter c) (Just bs))
+
+-- | 'threadsClose' signals for the 'ConnectionThreads' object
+-- to quit and close the associated 'Handle'.  This operation
+-- is non-blocking, follow it with 'threadsWait' if you want
+-- to wait for the operation to complete.
+threadsClose :: ConnectionThreads -> STM ()
+threadsClose c = do
+    let mvar = threadsWriter c
+    v <- tryReadTMVar mvar
+    case v of
+        Just Nothing -> return () -- already closed
+        _            -> putTMVar mvar Nothing
+
+-- | 'threadsRead' blocks until a 'ByteString' is available which
+-- is returned to the caller, or the connection is interrupted and
+-- 'Nothing' is returned.
+threadsRead :: ConnectionThreads -> IO (Maybe ByteString)
+threadsRead c = atomically $
+    orElse (const Nothing `fmap` threadsWait c)
+           (Just          `fmap` readTChan (threadsChannel c))
+
+-- | A 'ConnectionState' is an interface to a single 'ConnectionThreads'
+-- or to a pair of 'ConnectionThreads' objects that are considered as one
+-- connection.
+data ConnectionState =
+        SaneConnection ConnectionThreads
+        -- ^ ordinary read/write connection
+        | WriteOnlyConnection ConnectionThreads
+        | ReadOnlyConnection ConnectionThreads
+        | ConnectionPair ConnectionThreads ConnectionThreads
+        -- ^ Two 'ConnectionThreads' objects, read operations use the
+        -- first, write operations use the second.
+
+
+
+connWrite :: ConnectionState -> ByteString -> IO Bool
+connWrite (ReadOnlyConnection _) bs = return False
+connWrite conn bs = threadsWrite c bs
+ where
+    c = case conn of SaneConnection c      -> c
+                     WriteOnlyConnection c -> c
+                     ConnectionPair _ c    -> c
+
+
+mapConn :: Bool ->
+            (ConnectionThreads -> STM ()) -> ConnectionState -> STM ()
+mapConn both action c =
+    case c of
+        SaneConnection rw     -> action rw
+        ReadOnlyConnection r  -> action r
+        WriteOnlyConnection w -> action w
+        ConnectionPair r w -> do
+            rem <- orElse (const w `fmap` action r)
+                          (const r `fmap` action w)
+            when both $ action rem
+
+connClose :: ConnectionState -> STM ()
+connClose c = mapConn True threadsClose c
+
+connWait :: ConnectionState -> STM ()
+connWait c = doit -- mapConn False threadsWait c
+ where
+    action = threadsWait
+    doit =
+      case c of
+        SaneConnection rw     -> action rw
+        ReadOnlyConnection r  -> action r
+        WriteOnlyConnection w -> action w
+        ConnectionPair r w -> do
+            rem <- orElse (const w `fmap` action r)
+                          (const r `fmap` action w)
+            threadsClose rem
+
+connPingTimer :: ConnectionState -> PingMachine
+connPingTimer c =
+    case c of
+        SaneConnection rw     -> threadsPing rw
+        ReadOnlyConnection r  -> threadsPing r
+        WriteOnlyConnection w -> threadsPing w -- should be disabled.
+        ConnectionPair r w    -> threadsPing r
+
+connCancelPing :: ConnectionState -> IO ()
+connCancelPing c = pingCancel (connPingTimer c)
+
+connWaitPing :: ConnectionState -> STM PingEvent
+connWaitPing c = pingWait (connPingTimer c)
+
+connFlush :: ConnectionState -> STM ()
+connFlush c =
+    case c of
+        SaneConnection rw     -> waitChan rw
+        ReadOnlyConnection r  -> waitChan r
+        WriteOnlyConnection w -> return ()
+        ConnectionPair r w    -> waitChan r
+  where
+    waitChan t = do
+        b <- isEmptyTChan (threadsChannel t)
+        when (not b) retry
+
+bshow :: Show a => a -> ByteString
+bshow e = S.pack . show $ e
+
+warn :: ByteString -> IO ()
+warn str = S.hPutStrLn stderr str >> hFlush stderr
+
+debugNoise :: Monad m => t -> m ()
+debugNoise str = return ()
+
+data TCPStatus = Resolving | AwaitingRead | AwaitingWrite
+
+tcpManager :: ( Show k, Ord k, Ord conkey ) =>
+              (conkey -> (SockAddr, ConnectionParameters conkey u, Miliseconds))
+              -> (String -> Maybe k)
+              -> (k -> IO (Maybe conkey))
+              -> Server conkey u releaseKey x
+              -> IO (Manager TCPStatus k)
+tcpManager grokKey s2k resolvKey sv = do
+    rmap <- atomically $ newTVar Map.empty -- Map k (Maybe conkey)
+    nullping <- forkPingMachine 0 0
+    return Manager {
+      setPolicy = \k -> \case
+        TryingToConnect -> join $ atomically $ do
+            r <- readTVar rmap
+            case Map.lookup k r of
+                Just {} -> return $ return () -- Connection already in progress.
+                Nothing -> do
+                    modifyTVar' rmap $ Map.insert k Nothing
+                    return $ void $ forkIO $ do
+                    myThreadId >>= flip labelThread ("resolve."++show k)
+                    mconkey <- resolvKey k
+                    case mconkey of
+                        Nothing     -> atomically $ modifyTVar' rmap $ Map.delete k
+                        Just conkey -> do
+                            control sv $ case grokKey conkey of
+                                    (saddr,params,ms) -> ConnectWithEndlessRetry saddr params ms
+        OpenToConnect     -> hPutStrLn stderr "TODO: TCP OpenToConnect"
+        RefusingToConnect -> hPutStrLn stderr "TODO: TCP RefusingToConnect"
+    , connections = do
+        c <- readTVar $ conmap sv
+        fmap (exportConnection nullping c) <$> readTVar rmap
+    , stringToKey = s2k
+    , showProgress = \case
+        Resolving     -> "resolving"
+        AwaitingRead  -> "awaiting inbound"
+        AwaitingWrite -> "awaiting outbound"
+    , showKey = show
+    }
+
+exportConnection :: Ord conkey => PingMachine -> Map conkey (ConnectionRecord u) -> Maybe conkey -> G.Connection TCPStatus
+exportConnection nullping conmap mkey = G.Connection
+    { G.connStatus    = case mkey of
+        Nothing     -> return $ G.Dormant
+        Just conkey -> case Map.lookup conkey conmap of
+            Nothing                                    -> return $ G.InProgress Resolving
+            Just (ConnectionRecord ckont cstate cdata) -> return $ case cstate of
+                SaneConnection      {} -> G.Established
+                ConnectionPair      {} -> G.Established
+                ReadOnlyConnection  {} -> G.InProgress AwaitingWrite
+                WriteOnlyConnection {} -> G.InProgress AwaitingRead
+    , G.connPolicy    = return TryingToConnect
+    , G.connPingLogic = case mkey >>= flip Map.lookup conmap of
+            Nothing                            -> nullping
+            Just (ConnectionRecord _ cstate _) -> connPingTimer cstate
+    }
diff --git a/Presence/SockAddr.hs b/Presence/SockAddr.hs
new file mode 100644
index 00000000..91a03870
--- /dev/null
+++ b/Presence/SockAddr.hs
@@ -0,0 +1,13 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE StandaloneDeriving #-}
+module SockAddr () where
+
+import Network.Socket ( SockAddr(..) )
+
+#if MIN_VERSION_network(2,4,0)
+#else
+deriving instance Ord SockAddr
+#endif
+
+
+
diff --git a/Presence/UTmp.hs b/Presence/UTmp.hs
new file mode 100644
index 00000000..b43278da
--- /dev/null
+++ b/Presence/UTmp.hs
@@ -0,0 +1,249 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE RankNTypes #-}
+module UTmp
+    ( users
+    , users2
+    , utmp_file
+    , UserName
+    , Tty
+    , ProcessID
+    , UtmpRecord(..)
+    , UT_Type(..)
+    ) where
+
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Char8 as C
+import qualified Data.ByteString.Lazy.Char8 as L
+import Data.BitSyntax
+import Data.Functor.Identity
+import Data.Maybe
+import System.Posix.Signals
+import System.Posix.Types
+import Control.Monad
+import Data.Word
+import Data.Int
+import Control.Monad.Error.Class
+import System.IO.Error
+import qualified Paths
+import Data.Text      ( Text )
+import Unsafe.Coerce  ( unsafeCoerce )
+import Network.Socket ( SockAddr(..) )
+import qualified Data.Text.Encoding as Text
+import SockAddr ()
+
+
+utmp_file :: String
+utmp_file = Paths.utmp -- "/var/run/utmp"
+
+utmp_bs :: IO C.ByteString
+utmp_bs = S.readFile utmp_file
+
+decode_utmp_bytestring ::
+    C.ByteString
+    -> (Word32,
+        Word32,
+        C.ByteString,
+        C.ByteString,
+        C.ByteString,
+        C.ByteString,
+        Word16,
+        Word16,
+        Word32,
+        C.ByteString,
+        Word32,
+        Word32,
+        Word32,
+        Word32)
+decode_utmp_bytestring = 
+    runIdentity 
+    . $(bitSyn [ UnsignedLE 4 -- type
+               , UnsignedLE 4 -- pid
+               , Fixed 32 -- tty
+               , Fixed 4 -- inittab id
+               , Fixed 32 -- username
+               , Fixed 256 -- remote host
+               , UnsignedLE 2 -- termination status
+               , UnsignedLE 2 -- exit status (int)
+               , UnsignedLE 4 -- session id  (int)
+               , Fixed 8 -- time entry was made
+               , Unsigned 4 -- remote addr v6 addr[0]
+               , Unsigned 4 -- remote addr v6 addr[1]
+               , Unsigned 4 -- remote addr v6 addr[2]
+               , Unsigned 4 -- remote addr v6 addr[3]
+               , Skip 20 -- reserved
+               ])
+
+utmp_size :: Int
+utmp_size = 384 -- 768
+
+
+utmp_records :: C.ByteString -> [C.ByteString]
+utmp_records bs | S.length bs >= utmp_size 
+    =  u:utmp_records us
+ where
+    (u,us) = S.splitAt utmp_size bs
+
+utmp_records bs = [bs]
+
+utmp ::
+    IO
+      [(Word32,
+        Word32,
+        C.ByteString,
+        C.ByteString,
+        C.ByteString,
+        C.ByteString,
+        Word16,
+        Word16,
+        Word32,
+        C.ByteString,
+        Word32,
+        Word32,
+        Word32,
+        Word32)]
+utmp = fmap (map decode_utmp_bytestring . utmp_records) utmp_bs
+
+toStr :: C.ByteString -> [Char]
+toStr = takeWhile (/='\0') . C.unpack
+
+interp_utmp_record ::
+    forall t t1 t2 t3 t4 t5 t6 t7 t8 a.
+    Integral a =>
+    (a,
+     Word32,
+     C.ByteString,
+     t,
+     C.ByteString,
+     C.ByteString,
+     t1,
+     t2,
+     t3,
+     t4,
+     t5,
+     t6,
+     t7,
+     t8)
+    -> (UT_Type, [Char], [Char], CPid, [Char])
+interp_utmp_record (typ,pid,tty,inittab,user,hostv4,term,exit,session,time
+                   ,addr0,addr1,addr2,addr3) =
+    ( (toEnum . fromIntegral) typ :: UT_Type
+    , toStr user, toStr tty, processId pid, toStr hostv4 )
+ where
+    processId = CPid . coerceToSigned
+
+coerceToSigned :: Word32 -> Int32
+coerceToSigned = unsafeCoerce
+
+
+data UT_Type
+ = EMPTY           -- No valid user accounting information.  */
+
+ | RUN_LVL         -- The system's runlevel.  */
+ | BOOT_TIME       -- Time of system boot.  */
+ | NEW_TIME        -- Time after system clock changed.  */
+ | OLD_TIME        -- Time when system clock changed.  */
+
+ | INIT_PROCESS    -- Process spawned by the init process.  */
+ | LOGIN_PROCESS   -- Session leader of a logged in user.  */
+ | USER_PROCESS    -- Normal process.  */
+ | DEAD_PROCESS    -- Terminated process.  */
+
+ | ACCOUNTING      
+
+ deriving (Enum,Show,Eq,Ord,Read)
+
+processAlive :: ProcessID -> IO Bool
+processAlive pid = do
+    catchError (do { signalProcess nullSignal pid ; return True })
+      $ \e -> do { return (not ( isDoesNotExistError e)); }
+
+type UserName = L.ByteString
+type Tty      = L.ByteString
+
+users :: IO [(UserName, Tty, ProcessID)]
+users = fmap (map only3) $ do
+    us <- utmp
+    let us' = map interp_utmp_record us
+        us'' = mapMaybe user_proc us'
+        user_proc (USER_PROCESS, u,tty,pid, hostv4)
+                    = Just (L.pack u,L.pack tty,pid,hostv4)
+        user_proc _ = Nothing
+        onThrd f (_,_,pid,_) = f pid
+    us3 <- filterM (onThrd processAlive) us''
+    return us3
+
+only3 :: forall t t1 t2 t3. (t1, t2, t3, t) -> (t1, t2, t3)
+only3 (a,b,c,_) = (a,b,c)
+
+data UtmpRecord = UtmpRecord
+  { utmpType :: UT_Type
+  , utmpUser :: Text
+  , utmpTty :: Text
+  , utmpPid :: CPid
+  , utmpHost :: Text
+  , utmpSession :: Int32
+  , utmpRemoteAddr :: Maybe SockAddr
+  }
+ deriving ( Show, Eq, Ord )
+
+toText :: C.ByteString -> Text
+toText bs = Text.decodeUtf8 $ C.takeWhile (/='\0') bs
+
+interp_utmp_record2 ::
+    forall t t1 t2 t3 a.
+    Integral a =>
+    (a,
+     Word32,
+     C.ByteString,
+     t,
+     C.ByteString,
+     C.ByteString,
+     t1,
+     t2,
+     Word32,
+     t3,
+     Word32,
+     Word32,
+     Word32,
+     Word32)
+    -> UtmpRecord
+interp_utmp_record2 (typ,pid,tty,inittab,user,hostv4
+                    ,term,exit,session,time,addr0,addr1,addr2,addr3) =
+    UtmpRecord
+        { utmpType = toEnum (fromIntegral typ) :: UT_Type
+        , utmpUser = toText user
+        , utmpTty  = toText tty
+        , utmpPid  = processId pid
+        , utmpHost = toText hostv4
+        , utmpSession = coerceToSigned session
+        , utmpRemoteAddr =
+            if all (==0) [addr1,addr2,addr3]
+             then do guard (addr0/=0)
+                     Just $ SockAddrInet6 0 0 (0,0,0xFFFF,addr0) 0
+             else Just $ SockAddrInet6 0 0 (addr0,addr1,addr2,addr3) 0
+        }
+ where
+    processId = CPid . coerceToSigned
+
+users2 :: IO [UtmpRecord]
+users2 = do
+    us <- utmp
+    let us' = map interp_utmp_record2 us
+    us3 <- filterM (processAlive . utmpPid) us'
+    return us3
+
+{- 
+ - This is how the w command reports idle time:
+/* stat the device file to get an idle time */
+static time_t idletime(const char *restrict const tty)
+{
+        struct stat sbuf;
+        if (stat(tty, &sbuf) != 0)
+                return 0;
+        return time(NULL) - sbuf.st_atime;
+}
+ - THis might be useful fo rimplementing
+ - xep-0012 Last Activity
+ - iq get {jabber:iq:last}query
+ - 
+ -}
diff --git a/Presence/Util.hs b/Presence/Util.hs
new file mode 100644
index 00000000..8d9a9494
--- /dev/null
+++ b/Presence/Util.hs
@@ -0,0 +1,59 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Util where
+
+import qualified Data.ByteString.Lazy as L
+import Data.Monoid
+import qualified Data.Text            as Text
+         ;import Data.Text            (Text)
+import qualified Data.Text.Encoding   as Text
+import qualified Network.BSD          as BSD
+import Network.Socket
+
+import Network.Address (setPort)
+
+type UserName = Text
+type ResourceName = Text
+
+
+unsplitJID :: (Maybe UserName,Text,Maybe ResourceName) -> Text
+unsplitJID (n,h,r) = username <> h <> resource
+ where
+    username = maybe "" (<>"@") n
+    resource = maybe "" ("/"<>) r
+
+splitJID :: Text -> (Maybe UserName,Text,Maybe ResourceName)
+splitJID bjid =
+    let xs = splitAll '@' bjid
+        ys = splitAll '/' (last xs)
+        splitAll c bjid = take 1 xs0 ++ map (Text.drop 1) (drop 1 xs0)
+            where xs0 = Text.groupBy (\x y-> y/=c) bjid
+        server = head ys
+        name = case xs of
+                (n:s:_) -> Just n
+                (s:_)   -> Nothing
+        rsrc = case ys of
+                (s:_:_) -> Just $ last ys
+                _       -> Nothing
+    in (name,server,rsrc)
+
+
+textHostName :: IO Text
+textHostName = fmap Text.pack BSD.getHostName
+
+textToLazyByteString :: Text -> L.ByteString
+textToLazyByteString s = L.fromChunks [Text.encodeUtf8 s]
+
+lazyByteStringToText :: L.ByteString -> Text
+lazyByteStringToText = (foldr1 (<>) . map Text.decodeUtf8 . L.toChunks)
+
+-- | for example:  2001-db8-85a3-8d3-1319-8a2e-370-7348.ipv6-literal.net
+ip6literal :: Text -> Text
+ip6literal addr = Text.map dash addr <> ".ipv6-literal.net"
+ where
+    dash ':' = '-'
+    dash x   = x
+
+sameAddress :: SockAddr -> SockAddr -> Bool
+sameAddress laddr addr = setPort 0 laddr == setPort 0 addr
+
+
diff --git a/Presence/XMPP.hs b/Presence/XMPP.hs
new file mode 100644
index 00000000..eab57da5
--- /dev/null
+++ b/Presence/XMPP.hs
@@ -0,0 +1,1461 @@
+{-# LANGUAGE OverloadedStrings   #-}
+{-# LANGUAGE FlexibleContexts    #-}
+{-# LANGUAGE ViewPatterns        #-}
+{-# LANGUAGE TypeFamilies        #-}
+{-# LANGUAGE CPP                 #-}
+module XMPP 
+    ( module XMPPTypes
+    , listenForXmppClients
+    , listenForRemotePeers
+    , newServerConnections
+    , seekRemotePeers
+    , quitListening
+    , OutBoundMessage(..)
+    , OutgoingConnections
+    , CachedMessages
+    , toPeer
+    , newOutgoingConnections
+    , sendMessage
+    )  where
+
+import ServerC
+import XMPPTypes
+import ByteStringOperators
+import ControlMaybe
+import XMLToByteStrings
+import SendMessage
+import Logging
+import Todo
+
+import Data.Maybe (catMaybes)
+import Data.HList hiding (hHead)
+import Network.Socket ( Family )
+import Control.Concurrent.STM
+import Control.Concurrent.STM.Delay
+import Data.Conduit
+import Data.Maybe
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Lazy.Char8 as L
+    ( fromChunks
+    )
+import Control.Concurrent.Async
+import Control.Exception as E ( finally )
+import System.IO.Error (isDoesNotExistError)
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Maybe
+import Text.XML.Stream.Parse (def,parseBytes,content)
+import Data.XML.Types as XML
+import qualified Data.Text as S (Text,takeWhile)
+import Data.Text.Encoding      as S (decodeUtf8,encodeUtf8)
+import Data.Text.Lazy.Encoding as L (decodeUtf8)
+import Data.Text.Lazy (toStrict)
+import qualified Data.Sequence as Seq
+import Data.Foldable (toList)
+import Data.List (find)
+import qualified Text.Show.ByteString as L
+import NestingXML
+import           Data.Set as Set (Set,(\\))
+import qualified Data.Set as Set
+import qualified Data.Map as Map
+import           Data.Map as Map (Map)
+
+#if MIN_VERSION_HList(0,3,0)
+#define HCONS HCons'
+#else
+#define HCONS HCons
+#endif
+
+hHead (HCONS x _) = x
+
+textToByteString x = L.fromChunks [S.encodeUtf8 x]
+
+
+
+xmlifyPresenceForClient :: Presence -> IO [XML.Event]
+xmlifyPresenceForClient (Presence jid stat) = do
+    let n   = name jid
+        rsc = resource jid
+    names <- getNamesForPeer (peer jid)
+    let tostr p = L.decodeUtf8 $ n <$++> "@" <?++> L.fromChunks [p] <++?>  "/" <++$> rsc
+        jidstrs = fmap (toStrict . tostr) names
+    return (concatMap presenceEvents jidstrs)
+ where
+    presenceEvents jidstr =
+      [ EventBeginElement "{jabber:client}presence" (("from",[ContentText jidstr]):typ stat) ] 
+      ++ ( shw stat >>= jabberShow ) ++
+      [ EventEndElement "{jabber:client}presence" ]
+    typ Offline = [("type",[ContentText "unavailable"])]
+    typ _       = []
+    shw ExtendedAway = ["xa"]
+    shw Chatty       = ["chat"]
+    shw Away         = ["away"]
+    shw DoNotDisturb = ["dnd"]
+    shw _            = []
+    jabberShow stat = 
+      [ EventBeginElement "{jabber:client}show" []
+      , EventContent (ContentText stat)
+      , EventEndElement "{jabber:client}show" ]
+
+prefix ## name = Name name Nothing (Just prefix)
+
+streamP name = Name name (Just "http://etherx.jabber.org/streams") (Just "stream")
+    
+greet host =
+    [ EventBeginDocument
+    , EventBeginElement (streamP "stream")
+        [("from",[ContentText host])
+        ,("id",[ContentText "someid"])
+        ,("xmlns",[ContentText "jabber:client"])
+        ,("xmlns:stream",[ContentText "http://etherx.jabber.org/streams"])
+        ,("version",[ContentText "1.0"])
+        ]
+    , EventBeginElement (streamP "features") []
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}bind" []
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+
+    {-
+    -- , "  <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>"
+    , " <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>"
+    -- , " <mechanism>DIGEST-MD5</mechanism>"
+    , " <mechanism>PLAIN</mechanism>"
+    , " </mechanisms> "
+    -}
+
+    , EventEndElement (streamP "features")
+    ]
+
+
+-- type Consumer i m r = forall o. ConduitM i o m r
+mawait :: Monad m => MaybeT (ConduitM i o m) i
+mawait = MaybeT await
+
+-- Note: This function ignores name space qualification
+elementAttrs expected (EventBeginElement name attrs)
+    | nameLocalName name==expected 
+    = return attrs
+elementAttrs _ _ = mzero
+     
+eventIsBeginElement (EventBeginElement _ _) = True
+eventIsBeginElement _                       = False
+
+eventIsEndElement (EventEndElement _) = True
+eventIsEndElement _                   = False
+
+filterMapElement::
+  (Monad m, MonadPlus mp) =>
+  (Event -> mp a) -> Event -> mp a -> MaybeT (ConduitM Event o m) (mp a)
+filterMapElement ret opentag empty = loop (empty `mplus` ret opentag) 1 
+ where
+    loop ts 0 = return ts
+    loop ts cnt = do
+        tag <- mawait
+        let ts' = mplus ts (ret tag)
+        case () of
+         _ | eventIsEndElement tag   -> loop ts' (cnt-1)
+         _ | eventIsBeginElement tag -> loop ts' (cnt+1)
+         _                           -> loop ts' cnt
+
+gatherElement ::
+  (Monad m, MonadPlus mp) =>
+  Event -> mp Event -> NestingXML o m (mp Event)
+gatherElement opentag empty = loop (empty `mplus` return opentag) 1 
+ where
+    loop ts 0 = return ts
+    loop ts cnt = do
+        maybeXML (return ts) $ \tag -> do
+        let ts' = mplus ts (return tag)
+        case () of
+         _ | eventIsEndElement tag   -> loop ts' (cnt-1)
+         _ | eventIsBeginElement tag -> loop ts' (cnt+1)
+         _                           -> loop ts' cnt
+
+
+voidMaybeT body = (>> return ()) . runMaybeT $ body
+fixMaybeT f = (>> return ()) . runMaybeT . fix $ f
+
+iq_bind_reply id jid =
+    [ EventBeginElement "{jabber:client}iq" [("type",[ContentText "result"]),("id",[ContentText id])]
+
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+        [("xmlns",[ContentText "urn:ietf:params:xml:ns:xmpp-bind"])]
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}jid" []
+    , EventContent (ContentText jid)
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-bind}jid"
+    , EventEndElement  "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+    , EventEndElement "{jabber:client}iq"
+    ]
+
+uncontent cs = head $ map getText cs
+ where
+    getText (ContentText x) = x
+    getText (ContentEntity x ) = x
+
+tagAttrs (EventBeginElement _ xs) = xs
+tagAttrs _                        = []
+
+tagName (EventBeginElement n _) = n
+tagName _                       = ""
+
+handleIQSetBind session cmdChan stanza_id = do
+    mchild <- nextElement
+    rsc <- case mchild of
+             Just child -> do
+                let unhandledBind = do
+                        liftIO $ debugStr $ "unhandled-bind: "++show child
+                        return ""
+                case tagName child of
+                    "{urn:ietf:params:xml:ns:xmpp-bind}resource"
+                      -> do
+                        rsc <- lift content
+                        return . textToByteString $ rsc
+                    _ -> unhandledBind
+             Nothing -> do
+                liftIO $ debugStr $ "empty bind request!"
+                return ""
+    liftIO $ do
+        debugL $ "iq-set-bind-resource " <++> rsc
+        setResource session rsc
+        jid <- getJID session
+        atomically $ do
+            writeTChan cmdChan (Send $ iq_bind_reply stanza_id (toStrict $ L.decodeUtf8 $ L.show jid) )
+            writeTChan cmdChan BoundToResource
+        forCachedPresence session $ \presence -> do
+            xs <- xmlifyPresenceForClient presence
+            atomically . writeTChan cmdChan . Send $ xs
+
+
+iq_session_reply host stanza_id =
+    [ EventBeginElement "{jabber:client}iq" 
+        [("id",[ContentText stanza_id])
+        ,("from",[ContentText host])
+        ,("type",[ContentText "result"])
+        ]
+    , EventEndElement "{jabber:client}iq"
+    ]
+
+handleIQSetSession session cmdChan stanza_id = do
+    host <- liftIO $ do
+        jid <- getJID session
+        names <- getNamesForPeer (peer jid)
+        return (S.decodeUtf8 . head $ names)
+    liftIO . atomically . writeTChan cmdChan . Send $ iq_session_reply host stanza_id
+
+handleIQSet session cmdChan tag = do
+    withJust (lookupAttrib "id" (tagAttrs tag)) $ \stanza_id -> do
+    whenJust nextElement $ \child -> do
+    let unhandledSet = liftIO $ debugStr ("iq-set: "++show (stanza_id,child))
+    case tagName child of
+      "{urn:ietf:params:xml:ns:xmpp-bind}bind" 
+        -> handleIQSetBind session cmdChan stanza_id
+      "{urn:ietf:params:xml:ns:xmpp-session}session"
+        -> handleIQSetSession session cmdChan stanza_id
+      _ -> unhandledSet
+
+matchAttrib name value attrs = 
+    case find ( (==name) . fst) attrs of
+        Just (_,[ContentText x])   | x==value -> True
+        Just (_,[ContentEntity x]) | x==value -> True
+        _                                     -> False
+
+lookupAttrib name attrs =
+    case find ( (==name) . fst) attrs of
+        Just (_,[ContentText x])   -> Just x
+        Just (_,[ContentEntity x]) -> Just x
+        _                          -> Nothing
+    
+iqTypeSet    = "set"
+iqTypeGet    = "get"
+iqTypeResult = "result"
+iqTypeError  = "error"
+
+isIQOf (EventBeginElement name attrs) testType 
+    | name=="{jabber:client}iq" 
+    && matchAttrib "type" testType attrs
+    = True
+isIQOf _ _ = False
+
+isServerIQOf (EventBeginElement name attrs) testType 
+    | name=="{jabber:server}iq" 
+    && matchAttrib "type" testType attrs
+    = True
+isServerIQOf _ _ = False
+
+iq_service_unavailable host iq_id mjid req =
+    [ EventBeginElement "{jabber:client}iq" 
+        [("type",[ContentText "error"])
+        ,("id",[ContentText iq_id])
+        -- , TODO: set "from" if isJust mjid
+        ]
+    , EventBeginElement req []
+    , EventEndElement req
+    , EventBeginElement "{jabber:client}error" [("type",[ContentText "cancel"])]
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable" []
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable"
+    , EventEndElement "{jabber:client}error"
+    , EventEndElement "{jabber:client}iq"
+    ]
+
+attr   name value = (name,[ContentText value])
+attrbs name value = (name,[ContentText (toStrict . L.decodeUtf8 $ value)])
+
+
+getRoster session iqid = do
+    let getlist f = do
+            bs <- f session
+            -- js <- mapM parseHostNameJID bs
+            return (Set.fromList bs) -- js)
+    buddies     <- getlist getMyBuddies
+    subscribers <- getlist getMySubscribers
+    solicited   <- getlist getMySolicited
+    subnone0     <- getlist getMyOthers
+    let subnone = subnone0 \\ (Set.union buddies subscribers)
+    let subto = buddies \\ subscribers
+    let subfrom = subscribers \\ buddies
+    let subboth = Set.intersection buddies subscribers
+        -- solicited -> ask='subscribe'
+    jid <- getJID session
+    let dest = toStrict . L.decodeUtf8 . bshow $ jid
+    let items= (xmlify solicited "to" subto) 
+               ++(xmlify solicited "from" subfrom)
+               ++(xmlify solicited "both" subboth)
+               ++(xmlify solicited "none" subnone)
+        openiq =  [EventBeginElement "{jabber:client}iq"
+                    [ attr "id" iqid
+                    , attr "to" dest
+                    , attr "type" "result" ]
+                  ,EventBeginElement "{jabber:iq:roster}query"
+                    [] -- todo: ver? 
+                  ]
+        closeiq = [EventEndElement "{jabber:iq:roster}query"
+                  ,EventEndElement "{jabber:client}iq"]
+    return $ openiq ++ items ++ closeiq
+ where
+    xmlify solicited stype set = flip concatMap (Set.toList set) 
+      $ \jid -> 
+        [ EventBeginElement "item" 
+            ([ attr "jid" (toStrict . L.decodeUtf8 $ jid)
+             , attr "subscription" stype
+             ]++if Set.member jid solicited 
+                 then [attr "ask" "subscribe"]
+                 else [] )
+        , EventEndElement "item"
+        ] 
+
+handleIQGet session cmdChan tag = do
+    withJust (lookupAttrib "id" (tagAttrs tag)) $ \stanza_id -> do
+    whenJust nextElement $ \child -> do
+    host <- liftIO $ do
+        jid <- getJID session
+        names <- getNamesForPeer (peer jid)
+        return (S.decodeUtf8 . head $ names)
+    let unhandledGet req = do
+            liftIO $ debugStr ("iq-get: "++show (stanza_id,child))
+            liftIO . atomically . writeTChan cmdChan . Send $ iq_service_unavailable host stanza_id Nothing req
+    case tagName child of
+        -- "{http://jabber.org/protocol/disco#items}query" -> liftIO $ debugStr "iq-get-query-items"
+        "{urn:xmpp:ping}ping" -> liftIO $ do
+            let mjid = lookupAttrib "from" (tagAttrs tag)
+            let pong = [ EventBeginElement "{jabber:client}iq" 
+                         $ (case mjid of
+                             Just jid -> (attr "to" jid :)
+                             _        -> id               )
+                             [ attr "type" "result"
+                             , attr "id"   stanza_id
+                             , attr "from" host
+                             ]
+                      , EventEndElement "{jabber:client}iq"
+                      ]
+            atomically . writeTChan cmdChan . Send $ pong
+        "{jabber:iq:roster}query" -> liftIO $ do
+            debugStr $ "REQUESTED ROSTER " ++ show tag
+            roster <- getRoster session stanza_id
+            atomically $ do
+                writeTChan cmdChan InterestedInRoster
+                writeTChan cmdChan . Send $ roster
+            sendPending session
+        req -> unhandledGet req
+    
+
+handleClientPresence session stanza = do
+    -- online (Available or Away)
+    let log  = liftIO . debugL . ("(C) " <++>)
+    log $ "handleClientPresence "<++>bshow stanza
+    jid <- liftIO $ getJID session
+    -- cjid <- liftIO $ parseAddressJID (textToByteString jid)
+    let parseChildren stat = do
+            child <- nextElement
+            log $ " child: "<++> bshow child
+            case child of
+                Just tag | tagName tag=="{jabber:client}show"
+                                      -> fmap toStat (lift content)
+                Just tag | otherwise  -> parseChildren stat
+                Nothing -> return stat
+        toStat "away" = Away
+        toStat "xa"   = ExtendedAway
+        toStat "dnd"  = DoNotDisturb
+        toStat "chat" = Chatty
+
+    stat' <- parseChildren Available
+    liftIO $ setPresence session stat'
+    log $ "requesting presence: "<++>bshow stat'
+    return ()
+
+
+fromClient :: (MonadThrow m,MonadIO m, JabberClientSession session) => 
+    session -> TChan ClientCommands -> Sink XML.Event m ()
+fromClient session cmdChan = doNestingXML $ do
+    let log  = liftIO . debugL . ("(C) " <++>)
+        send = liftIO . atomically . writeTChan cmdChan . Send
+    withXML $ \begindoc -> do
+    when (begindoc==EventBeginDocument) $ do
+    log "begin-doc"
+    withXML $ \xml -> do
+    withJust (elementAttrs "stream" xml) $ \stream_attrs -> do
+    log $ "stream atributes: " <++> bshow stream_attrs
+    host <- liftIO $ do
+        jid <- getJID session
+        names <- getNamesForPeer (peer jid)
+        return (S.decodeUtf8 . head $ names)
+    send $ greet host
+    
+    fix $ \loop -> do
+        log "waiting for stanza."
+        whenJust nextElement $ \stanza -> do
+            stanza_lvl <- nesting
+
+            liftIO . debugStr $ "stanza: "++show stanza
+
+            let unhandledStanza = do
+                    xs <- gatherElement stanza Seq.empty
+                    prettyPrint "unhandled-C: " (toList xs)
+            case () of
+             _ | stanza `isIQOf` iqTypeSet -> handleIQSet session cmdChan stanza
+             _ | stanza `isIQOf` iqTypeGet -> handleIQGet session cmdChan stanza
+             _ | stanza `isClientPresenceOf` presenceTypeSubscribe 
+                                           -> clientRequestsSubscription session cmdChan stanza
+             _ | stanza `isClientPresenceOf` presenceTypeSubscribed
+                                           -> clientApprovesSubscription session stanza
+             _ | stanza `isClientPresenceOf` presenceTypeUnsubscribed
+                                           -> clientRejectsSubscription session stanza
+             _ | stanza `isClientPresenceOf` presenceTypeOnline
+                                           -> handleClientPresence session stanza
+             _ | isMessageStanza stanza    -> handleClientMessage session stanza
+             _ | otherwise                 -> unhandledStanza
+
+            awaitCloser stanza_lvl
+            loop
+
+    log $ "end of stream"
+    withXML $ \xml -> do
+    log $ "end-of-document: " <++> bshow xml
+
+
+rosterPush to contact attrs = do
+    let n   = name to
+        rsc = resource to
+    names <- getNamesForPeer (peer to)
+    let tostr p = L.decodeUtf8 $ n <$++> "@" <?++> L.fromChunks [p] <++?>  "/" <++$> rsc
+        jidstrs = fmap (toStrict . tostr) names
+        tojid = head jidstrs
+    return
+      [ EventBeginElement "{jabber:client}iq" 
+            [ attr "to"   tojid
+            , attr "id"   "someid"
+            , attr "type" "set"
+            ]
+      , EventBeginElement "{jabber:iq:roster}query" []
+      , EventBeginElement "{jabber:iq:roster}item" (attr "jid" contact : attrs)
+      , EventEndElement   "{jabber:iq:roster}item"
+      , EventEndElement   "{jabber:iq:roster}query"
+      , EventEndElement "{jabber:client}iq"
+      ]
+
+data EventsForClient = CmdChan ClientCommands 
+                     | PChan   Presence
+                     | RChan   RosterEvent
+
+toClient :: (MonadIO m, JabberClientSession session ) => 
+    session -> TChan Presence -> TChan ClientCommands -> TChan RosterEvent -> Source m [XML.Event]
+toClient session pchan cmdChan rchan = toClient' False False 
+ where
+  toClient' isBound isInterested = do
+    let loop = toClient' isBound isInterested
+        send xs = yield xs >> prettyPrint ">C: " xs
+    event <- liftIO . atomically $ 
+              foldr1 orElse [fmap CmdChan $ readTChan cmdChan
+                            ,fmap RChan   $ readTChan rchan
+                            ,fmap PChan   $ readTChan pchan
+                            ]
+    case event of
+      CmdChan QuitThread -> return ()
+      CmdChan (Send xs)  -> send xs >> loop
+      CmdChan BoundToResource    -> toClient' True    isInterested
+      CmdChan InterestedInRoster -> do
+        liftIO . debugStr $ "Roster: interested"
+        toClient' isBound True
+      CmdChan (Chat msg) -> do
+        xs <- liftIO $ xmlifyMessageForClient msg
+        send xs
+        loop
+      -- CmdChan cmd        -> liftIO (debugStr $ "unhandled event: "++show cmd) >> loop
+      RChan   (RequestedSubscription who contact) ->  do
+        jid <- liftIO $ getJID session
+        when (isInterested && Just who==name jid) $ do
+            r <- liftIO $ rosterPush jid (toStrict . L.decodeUtf8 $ contact) [attr "ask" "subscribe"]
+            send r
+        loop
+      RChan   (NewBuddy who contact) ->  do
+        liftIO . debugStr $ "Roster push: NewBuddy "++show (isInterested,who,contact)
+        (jid,me) <- liftIO $ do
+                        jid <- getJID session
+                        me <- asHostNameJID jid
+                        return (jid,me)
+        withJust me $ \me -> do
+        when (isInterested && Just who==name jid) $ do
+            send [ EventBeginElement "{jabber:client}presence" 
+                    [ attrbs "from" contact
+                    , attrbs "to"   me
+                    , attr   "type" "subscribed"
+                    ]
+                 , EventEndElement "{jabber:client}presence" ]
+            let f True  = "both"
+                f False = "to"
+            subscription <- fmap f (liftIO $ isSubscribed session contact)
+            r <- liftIO . handleIO (\e -> debugStr ("Roster NewBuddy error: "++show e) >> return []) $ do
+                            rosterPush jid 
+                                     (toStrict . L.decodeUtf8 $ contact) 
+                                     [attr "subscription" subscription]
+            send r
+        loop
+      RChan   (RemovedBuddy who contact) ->  do
+        liftIO . debugStr $ "Roster push: RemovedBuddy "++show (isInterested,who,contact)
+        (jid,me) <- liftIO $ do
+                        jid <- getJID session
+                        me <- asHostNameJID jid
+                        return (jid,me)
+        withJust me $ \me -> do
+        when (isInterested && Just who==name jid) $ do
+            send [ EventBeginElement "{jabber:client}presence" 
+                    [ attrbs "from" contact
+                    , attrbs "to"   me
+                    , attr   "type" "unsubscribed"
+                    ]
+                 , EventEndElement "{jabber:client}presence" ]
+            let f True  = "from"
+                f False = "none"
+            subscription <- fmap f (liftIO $ isSubscribed session contact)
+            r <- liftIO . handleIO (\e -> debugStr ("Roster RemovedBuddy error: "++show e) >> return []) $ do
+                            rosterPush jid 
+                                     (toStrict . L.decodeUtf8 $ contact) 
+                                     [attr "subscription" subscription]
+            send r
+        loop
+      RChan   (NewSubscriber who contact) ->  do
+        liftIO . debugStr $ "Roster push: NewSubscriber "++show (isInterested,who,contact)
+        (jid,me) <- liftIO $ do
+                        jid <- getJID session
+                        me <- asHostNameJID jid
+                        return (jid,me)
+        withJust me $ \me -> do
+        when (isInterested && Just who==name jid) $ do
+            let f True  = "both"
+                f False = "from"
+            subscription <- fmap f (liftIO $ isBuddy session contact)
+            r <- liftIO . handleIO (\e -> debugStr ("Roster NewSubscriber error: "++show e) >> return []) $ do
+                            rosterPush jid 
+                                     (toStrict . L.decodeUtf8 $ contact) 
+                                     [attr "subscription" subscription]
+            send r
+        loop
+      RChan   (RejectSubscriber who contact) ->  do
+        liftIO . debugStr $ "Roster push: RejectSubscriber "++show (isInterested,who,contact)
+        (jid,me) <- liftIO $ do
+                        jid <- getJID session
+                        me <- asHostNameJID jid
+                        return (jid,me)
+        withJust me $ \me -> do
+        when (isInterested && Just who==name jid) $ do
+            let f True  = "to"
+                f False = "none"
+            subscription <- fmap f (liftIO $ isBuddy session contact)
+            r <- liftIO . handleIO (\e -> debugStr ("Roster RejectSubscriber error: "++show e) >> return []) $ do
+                            rosterPush jid 
+                                     (toStrict . L.decodeUtf8 $ contact) 
+                                     [attr "subscription" subscription]
+            send r
+        loop
+      RChan   (PendingSubscriber who contact) ->  do
+        liftIO . debugStr $ "Roster: Pending buddy "++show (isInterested,who,contact)
+        (jid,me) <- liftIO $ do
+                        jid <- getJID session
+                        me <- asHostNameJID jid
+                        return (jid,me)
+        withJust me $ \me -> do
+        when (isInterested && Just who==name jid) $ do
+            send [ EventBeginElement "{jabber:client}presence" 
+                    [ attrbs "from" contact
+                    , attrbs "to"   me
+                    , attr   "type" "subscribe"
+                    ]
+                 , EventEndElement "{jabber:client}presence" ]
+        loop
+      PChan presence   -> do 
+        when isBound $ do
+            xs <- liftIO $ xmlifyPresenceForClient presence
+            send xs
+        loop
+
+
+{-
+handleClient
+  :: (SocketLike sock, HHead l (XMPPClass session),
+      JabberClientSession session) =>
+     HCONS sock (HCONS t l) -> Source IO ByteString -> Sink ByteString IO () -> IO ()
+-}
+handleClient st src snk = do
+#if MIN_VERSION_HList(0,3,0)
+    let HCons' sock (HCons' _ st') = st
+#else
+    let HCons sock (HCons _ st') = st
+#endif
+        session_factory = hHead st'
+    pname <- getPeerName sock
+    session <- newSession session_factory sock
+    debugStr $ "PEER NAME: "++Prelude.show pname
+    pchan <- subscribe session Nothing
+    rchan <- subscribeToRoster session
+    let cmdChan = clientChannel session
+
+    writer <- async ( toClient session pchan cmdChan rchan `xmlToByteStrings` snk ) 
+    finally         ( src $= parseBytes def $$ fromClient session cmdChan )
+        $ do
+            atomically $ writeTChan cmdChan QuitThread
+            wait writer
+            closeSession session
+
+{-
+listenForXmppClients ::
+  (HList l, HHead l (XMPPClass session), HExtend e1 l2 l1,
+   HExtend e l1 (HCONS PortNumber l), JabberClientSession session) =>
+  Family -> e1 -> e -> l2 -> IO ServerHandle
+-}
+listenForXmppClients addr_family session_factory port st = do
+#if MIN_VERSION_HList(0,3,0)
+    doServer (HCons' addr_family $ HCons' port $ HCons' session_factory st) handleClient
+#else
+    doServer (HCons addr_family $ HCons port $ HCons session_factory st) handleClient
+#endif
+
+
+{-
+listenForRemotePeers
+  :: (HList l, HHead l (XMPPPeerClass session),
+      HExtend e l1 (HCONS PortNumber l), HExtend e1 l2 l1,
+      JabberPeerSession session) =>
+     Family -> e1 -> e -> l2 -> IO ServerHandle
+-}
+listenForRemotePeers addrfamily session_factory port st = do
+#if MIN_VERSION_HList(0,3,0)
+    doServer (HCons' addrfamily $ HCons' port $ HCons' session_factory st) handlePeer
+#else
+    doServer (HCons addrfamily $ HCons port $ HCons session_factory st) handlePeer
+#endif
+
+{-
+handlePeer
+  :: (HHead l (XMPPPeerClass session),
+      JabberPeerSession session) =>
+     HCONS RestrictedSocket (HCONS t1 l) -> Source IO ByteString -> t -> IO ()
+-}
+handlePeer st src snk = do
+#if MIN_VERSION_HList(0,3,0)
+    let HCons' sock (HCons' _ st') = st
+#else
+    let HCons sock (HCons _ st') = st
+#endif
+        session_factory = hHead st'
+    name <- fmap bshow $ getPeerName sock
+    debugL $ "(P) connected " <++> name
+    session <- newPeerSession session_factory sock
+
+    didClose <- newTVarIO False
+    finally ( src $= parseBytes def $$ fromPeer sock session didClose )
+        $ do 
+            debugL $ "(P) disconnected " <++> name
+            didc <- readTVarIO didClose
+            when (not didc) $ closePeerSession session
+
+
+handlePeerPresence session stanza False = do
+    -- Offline
+    liftIO . debugStr $ "PEER-OFFLINE: "++show stanza
+    withJust (lookupAttrib "from" (tagAttrs stanza)) $ \jid -> do
+    peer_jid <- liftIO $ parseAddressJID (textToByteString jid)
+    liftIO . debugStr $ "PEER-OFFLINE-JID: "++show peer_jid
+    liftIO $ announcePresence session (Presence peer_jid Offline)
+handlePeerPresence session stanza True = do
+    -- online (Available or Away)
+    let log  = liftIO . debugL . ("(P) " <++>)
+    withJust (lookupAttrib "from" (tagAttrs stanza)) $ \jid -> do
+    pjid <- liftIO $ parseAddressJID (textToByteString jid)
+    -- stat <- show element content
+    let parseChildren stat = do
+            child <- nextElement
+            case child of
+                Just tag | tagName tag=="{jabber:server}show"
+                                      -> fmap toStat (lift content)
+                Just tag | otherwise  -> parseChildren stat
+                Nothing -> return stat
+        toStat "away" = Away
+        toStat "xa"   = ExtendedAway
+        toStat "dnd"  = DoNotDisturb
+        toStat "chat" = Chatty
+
+    stat' <- parseChildren Available
+    liftIO . debugStr $ "announcing peer online: "++show (pjid,stat')
+    liftIO $ announcePresence session (Presence pjid stat')
+    log $ bshow (Presence pjid stat')
+
+handlePeerMessage session stanza = do
+    withJust (lookupAttrib "from" (tagAttrs stanza)) $ \fromstr-> do
+    withJust (lookupAttrib "to" (tagAttrs stanza)) $ \tostr -> do
+    fromjid <- liftIO $ parseAddressJID (textToByteString fromstr)
+    tojid <- liftIO $ parseAddressJID (textToByteString tostr)
+    let log  = liftIO . debugL . ("(P) " <++>)
+    log $ "handlePeerMessage "<++>bshow stanza
+    msg <- parseMessage ("{jabber:server}body"
+                        ,"{jabber:server}subject"
+                        ,"{jabber:server}thread"
+                        )
+                        log
+                        fromjid
+                        tojid
+                        stanza
+    liftIO $ sendChatToClient session msg
+
+matchAttribMaybe name (Just value) attrs = 
+    case find ( (==name) . fst) attrs of
+        Just (_,[ContentText x])   | x==value -> True
+        Just (_,[ContentEntity x]) | x==value -> True
+        _                                     -> False
+matchAttribMaybe name Nothing attrs  
+    | find ( (==name) . fst) attrs==Nothing
+    = True
+matchAttribMaybe name Nothing attrs  
+    | otherwise
+    = False
+
+presenceTypeOffline      = Just "unavailable"
+presenceTypeOnline       = Nothing
+presenceTypeProbe        = Just "probe"
+presenceTypeSubscribe    = Just "subscribe"
+presenceTypeSubscribed   = Just "subscribed"
+presenceTypeUnsubscribed = Just "unsubscribed"
+
+isPresenceOf (EventBeginElement name attrs) testType
+    | name=="{jabber:server}presence"
+    && matchAttribMaybe "type" testType attrs
+    = True
+isPresenceOf _ _ = False
+
+isMessageStanza (EventBeginElement name attrs) 
+    | name=="{jabber:client}message"
+    = True
+isMessageStanza (EventBeginElement name attrs) 
+    | name=="{jabber:server}message"
+    = True
+isMessageStanza _ = False
+
+isClientPresenceOf (EventBeginElement name attrs) testType
+    | name=="{jabber:client}presence"
+    && matchAttribMaybe "type" testType attrs
+    = True
+isClientPresenceOf _ _ = False
+
+
+handlePresenceProbe session stanza = do
+    withJust (lookupAttrib "to" (tagAttrs stanza)) $ \to -> do
+    -- withJust (lookupAttrib "from" (tagAttrs stanza)) $ \from -> do
+    jid <- liftIO $ parseAddressJID $ textToByteString to
+    withJust (name jid) $ \user -> do
+    liftIO $ debugL $ "RECEIVED PROBE "<++>bshow (peerAddress session,to)
+    liftIO $ do
+        subs <- getSubscribers (peerSessionFactory session) user
+        liftIO $ debugL $ "subscribers for "<++>bshow user<++>": " <++>bshow subs
+        forM_ subs $ \jidstr -> do
+            handleIO_ (return ()) $ do
+                debugL $ "parsing " <++>jidstr
+                sub <- parseHostNameJID jidstr
+                debugStr $ "comparing " ++show (peer sub , peerAddress session)
+                when (peer sub == discardPort (peerAddress session)) $ do
+                ps <- userStatus session user
+                -- todo: Consider making this a directed presence
+                forM_ ps $ \p ->  do
+                    debugStr ("PROBE-REPLY: "++show p)
+                mapM_ (sendPeerMessage session . OutBoundPresence) ps
+    return ()
+
+subscribeToPresence subscribers peer_jid user = do
+    pjid <- parseAddressJID peer_jid
+    if Set.member pjid subscribers
+        then return ()
+        else return ()
+
+bare (JID n host _) = JID n host Nothing
+
+presenceErrorRemoteNotFound iqid from to = return
+    [ EventBeginElement "{stream:client}presence" 
+        ( case iqid of { Nothing -> id; Just iqid -> ( attr "id" iqid :) }
+           $ [ attr "from" to
+             , attr "type" "error"
+             ] )
+    , EventBeginElement "{stream:client}error"
+        [ attr "type" "modify"]
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-stanzas}remote-server-not-found"
+        []
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-stanzas}remote-server-not-found"
+    , EventEndElement "{stream:client}error"
+    , EventEndElement "{stream:client}presence"
+    ]
+
+presenceSubscribed from = return
+    [ EventBeginElement "{stream:client}presence" 
+        [ attr "from" from
+        , attr "type" "subscribed"
+        ]
+    , EventEndElement   "{stream:client}presence"
+    ]
+
+clientRequestsSubscription session cmdChan stanza = do
+    liftIO $ do
+        debugStr $ "CLIENT PRESENCE SUBSCRIBE " ++ show stanza
+        withJust (lookupAttrib "to" (tagAttrs stanza)) $ \to_str0 -> do
+        let to_str = S.takeWhile (/='/') to_str0
+            from = lookupAttrib "from" (tagAttrs stanza)
+            iqid = lookupAttrib "id" (tagAttrs stanza)
+        let handleError e | isDoesNotExistError e = do
+                debugStr $ "remote-server-not-found"
+                r <- presenceErrorRemoteNotFound iqid from to_str
+                atomically $ writeTChan cmdChan (Send r)
+            handleError e = do
+                debugStr $ "ERROR: "++ show e
+        handleIO handleError $ do
+            let to_str' = textToByteString to_str
+            to_jid <- fmap bare $ parseHostNameJID to_str'
+            if (is_remote . peer) to_jid 
+             then do
+                addSolicited session to_str' to_jid
+                debugStr $ "added to solicited: " ++ show to_jid
+             else do
+                -- addLocalSubscriber session to_str
+                -- self <- getJID session
+                r <- presenceSubscribed to_str -- self
+                atomically $ writeTChan cmdChan (Send r)
+    return ()
+
+
+stanzaFromTo ::
+  JabberPeerSession session =>
+  session -> Event -> IO (Maybe (JID, JID))
+stanzaFromTo session stanza = 
+    let lookup key = fmap textToByteString (lookupAttrib key (tagAttrs stanza))
+        parse jidstr =  handleIO_ (return Nothing) (fmap Just $ parseAddressJID jidstr)
+    in case liftM2 (,) (lookup "from") (lookup "to") of
+        Nothing -> return Nothing
+        Just (from,to) ->  do
+            mfrom <- parse from
+            mto   <- parse to
+            case liftM2 (,) mfrom mto of
+                Nothing -> return Nothing
+                Just (from,to) -> do
+                    let fromjid = JID (name from) (peerAddress session) Nothing
+                    return $ Just (fromjid,to)
+
+peerRequestsSubsription session stanza = do
+    liftIO $ debugStr $ "PEER PRESENCE SUBSCRIBE " ++ show stanza
+
+    whenJust (liftIO . handleIO (\e -> debugStr ("peerRequestsSubsription: "++show e) >> return Nothing) 
+                $ stanzaFromTo session stanza) $ \(fromjid,tojid) -> do
+    withJust (name tojid) $ \user -> do
+
+    subs <- liftIO $ do
+             subs <- getSubscribers (peerSessionFactory session) user
+             msubs <- flip mapM subs $ \str -> do
+                        handleIO_ (return Nothing) 
+                                  (fmap Just $ parseHostNameJID str)
+             return (catMaybes msubs)
+    if elem fromjid subs
+      then do
+        liftIO . debugL $ bshow fromjid <++> " already subscribed to " <++> user
+        -- if already subscribed, reply
+        liftIO $ do
+             sendPeerMessage session (Approval tojid fromjid)
+             ps <- userStatus session user
+             -- todo: consider making this a directed presence
+             mapM_ (sendPeerMessage session . OutBoundPresence) ps
+      else
+        liftIO $ processRequest session user fromjid
+
+clientApprovesSubscription session stanza = do
+    liftIO $ debugStr $ "CLIENT APPROVES SUBSCRIPTION"
+    withJust (lookupAttrib "to" (tagAttrs stanza)) $ \to_str -> do
+    liftIO $ approveSubscriber session (textToByteString to_str)
+
+clientRejectsSubscription session stanza = do
+    liftIO $ debugStr $ "CLIENT REJECTS SUBSCRIPTION"
+    withJust (lookupAttrib "to" (tagAttrs stanza)) $ \to_str -> do
+    liftIO $ rejectSubscriber session (textToByteString to_str)
+
+peerApprovesSubscription session stanza = do
+    liftIO $ debugStr $ "PEER APPROVES SUBSCRIPTION"
+    whenJust (liftIO . handleIO (\e -> debugStr ("peerApprovesSubscription: "++show e) >> return Nothing) 
+             $ stanzaFromTo session stanza) $ \(fromjid,tojid) -> do
+    withJust (name tojid) $ \user -> do
+    liftIO $ processApproval session user fromjid
+
+peerRejectsSubscription session stanza = do
+    liftIO $ debugStr $ "PEER REJECTS SUBSCRIPTION"
+    whenJust (liftIO . handleIO (\e -> debugStr ("peerRejectsSubscription: "++show e) >> return Nothing) 
+             $ stanzaFromTo session stanza) $ \(fromjid,tojid) -> do
+    withJust (name tojid) $ \user -> do
+    liftIO $ processRejection session user fromjid
+
+handlePeerIQGet :: (JabberPeerSession session, MonadIO m) =>
+                        session -> XML.Event -> NestingXML o m ()
+handlePeerIQGet session tag = do
+    -- TODO: Pings should not require an id field.
+    withJust (lookupAttrib "id" (tagAttrs tag)) $ \stanza_id -> do
+    whenJust nextElement $ \child -> do
+    let unhandledGet req = do
+            liftIO $ debugStr ("iq-peer-get: "++show (stanza_id,child))
+            liftIO $
+              sendPeerMessage session (Unsupported (JID Nothing LocalHost Nothing)
+                                                   (JID Nothing (peerAddress session) Nothing)
+                                                   (Just (ContentText stanza_id))
+                                                   req)
+            -- Client equiv: liftIO . atomically . writeTChan cmdChan . Send $ iq_service_unavailable host stanza_id Nothing req
+    case tagName child of
+        -- "{http://jabber.org/protocol/disco#items}query" -> liftIO $ debugStr "iq-get-query-items"
+        "{urn:xmpp:ping}ping" -> liftIO $ do
+            sendPeerMessage session (Pong (JID Nothing LocalHost Nothing)
+                                          (JID Nothing (peerAddress session) Nothing)
+                                          (Just (ContentText stanza_id)))
+            -- Client equiv: atomically . writeTChan cmdChan . Send $ pong
+            return ()
+
+        req -> unhandledGet req
+
+fromPeer :: (MonadThrow m,MonadIO m, JabberPeerSession session) => 
+    RestrictedSocket -> session -> TVar Bool -> Sink XML.Event m ()
+fromPeer sock session didClose = doNestingXML $ do
+    let log  = liftIO . debugL . ("(P) " <++>)
+    withXML $ \begindoc -> do
+    when (begindoc==EventBeginDocument) $ do
+    log "begin-doc"
+    withXML $ \xml -> do
+    withJust (elementAttrs "stream" xml) $ \stream_attrs -> do
+    log $ "stream atributes: " <++> bshow stream_attrs
+
+    let doTimeout = Thunk $ do 
+                        atomically $ writeTVar didClose True
+                        closePeerSession session
+
+    fix $ \loop -> do
+        log "waiting for stanza."
+        whenJust nextElement $ \stanza -> do
+            stanza_lvl <- nesting
+
+            liftIO $ sendPeerMessage session (ActivityBump doTimeout) -- reset ping timer
+
+            let unhandledStanza = do
+                    xs <- gatherElement stanza Seq.empty
+                    prettyPrint "P: " (toList xs)
+            case () of
+              _ | stanza `isServerIQOf` iqTypeGet -> handlePeerIQGet session stanza
+              _ | stanza `isPresenceOf` presenceTypeOnline
+                    -> handlePeerPresence session stanza True
+              _ | stanza `isPresenceOf` presenceTypeOffline
+                    -> handlePeerPresence session stanza False
+              _ | stanza `isPresenceOf` presenceTypeProbe
+                    -> handlePresenceProbe session stanza
+              _ | stanza `isPresenceOf` presenceTypeSubscribe
+                    -> peerRequestsSubsription session stanza
+              _ | stanza `isPresenceOf` presenceTypeSubscribed
+                    -> peerApprovesSubscription session stanza
+              _ | stanza `isPresenceOf` presenceTypeUnsubscribed
+                    -> peerRejectsSubscription session stanza
+              _ | isMessageStanza stanza 
+                    -> handlePeerMessage session stanza
+              _ -> unhandledStanza
+
+            awaitCloser stanza_lvl
+            loop
+
+    log $ "end of stream"
+    withXML $ \xml -> do
+    log $ "end-of-document: " <++> bshow xml
+
+
+
+
+newServerConnections = newTVar Map.empty
+
+data CachedMessages = CachedMessages 
+    { presences :: Map JID JabberShow
+    , probes :: Map JID (Set (Bool,JID)) -- False means solicitation rather than probe
+    , approvals :: Map JID (Set (Bool,JID) ) -- False means rejection rather than approval
+    }
+
+instance CommandCache CachedMessages where
+    type CacheableCommand CachedMessages = OutBoundMessage
+    emptyCache = CachedMessages Map.empty Map.empty Map.empty
+
+    updateCache (OutBoundPresence (Presence jid Offline)) cache = 
+                cache { presences=Map.delete jid . presences $ cache }
+    updateCache (OutBoundPresence p@(Presence jid st)) cache =
+                cache { presences=Map.insert jid st . presences $ cache }
+    updateCache (PresenceProbe from to) cache =
+                cache { probes = mmInsert  (True,from) to $ probes cache }
+    updateCache (Solicitation from to) cache =
+                cache { probes= mmInsert (False,from) to $ probes cache }
+    updateCache (Approval from to) cache =
+                cache { approvals= mmInsert (True,from) to $ approvals cache }
+    updateCache (Rejection from to) cache =
+                cache { approvals= mmInsert (False,from) to $ approvals cache }
+    updateCache (OutBoundMessage msg) cache = cache -- TODO: cache chat?
+    updateCache (Pong _ _ _) cache = trace "(DISCARDING Pong)" cache          -- pings are not cached
+    updateCache (Unsupported _ _ _ _) cache = cache -- error messages are not cached
+    updateCache (ActivityBump sock) cache = cache
+
+instance ThreadChannelCommand OutBoundMessage where
+    isQuitCommand Disconnect = True
+    isQuitCommand _          = False
+
+mmInsert val key mm = Map.alter f key mm
+ where 
+    f Nothing    = Just $ Set.singleton val
+    f (Just set) = Just $ Set.insert val set
+
+
+greetPeer =
+    [ EventBeginDocument
+    , EventBeginElement (streamP "stream")
+        [ attr "xmlns"   "jabber:server"
+        , attr "version" "1.0"
+        ]
+    ]
+
+goodbyePeer = 
+    [ EventEndElement (streamP "stream")
+    , EventEndDocument
+    ]
+
+peerJidTextLocal sock jid = do
+    addr <- getSocketName sock
+    return .  toStrict . L.decodeUtf8 
+                       $ name jid <$++> "@" 
+                        <?++> showPeer (RemotePeer addr) 
+                        <++?>  "/" <++$> resource jid
+
+peerJidTextRemote sock jid = do
+    addr <- getPeerName sock
+    return .  toStrict . L.decodeUtf8 
+                       $ name jid <$++> "@" 
+                        <?++> showPeer (RemotePeer addr) 
+                        <++?>  "/" <++$> resource jid
+
+presenceStanza sock fromjid tojid typ = do
+    from <- peerJidTextLocal sock fromjid
+    let to = toStrict . L.decodeUtf8
+              $ name tojid <$++> "@"
+                <?++> showPeer (peer tojid)
+    return 
+      [ EventBeginElement "{jabber:server}presence"
+            [ attr "from" from
+            , attr "to"   to
+            , attr "type" typ
+            ]
+      , EventEndElement "{jabber:server}presence"
+      ]
+
+
+toPeer
+  :: SocketLike sock =>
+     sock
+     -> CachedMessages
+     -> TChan OutBoundMessage
+     -> (Maybe OutBoundMessage -> IO ())
+     -> ConduitM i [Event] IO ()
+toPeer sock cache chan fail = do
+    let -- log     = liftIO . debugL . ("(>P) " <++>)
+        send xs = yield xs >> prettyPrint ">P: " xs -- >> return (3::Int)
+        checkConnection cmd = do
+            liftIO $ catchIO (getPeerName sock >> return ())
+                           (\_ -> fail . Just $ cmd)
+        sendOrFail getXML cmd = do
+            checkConnection cmd
+            r <- liftIO $ getXML
+                    -- handleIO (\e -> debugStr ("ERROR: "++show e) >> return []) getXML
+            yieldOr r (fail . Just $ cmd)
+            prettyPrint ">P: " r
+        sendPresence presence =
+            sendOrFail (xmlifyPresenceForPeer sock presence)
+                       (OutBoundPresence presence)
+        sendProbe from to =
+            sendOrFail (presenceStanza sock from to "probe")
+                       (PresenceProbe from to)
+        sendSolicitation from to = 
+            sendOrFail (presenceStanza sock from to "subscribe")
+                       (Solicitation from to)
+        sendApproval approve from to = 
+            sendOrFail (presenceStanza sock from to 
+                          (if approve then "subscribed" else "unsubscribed"))
+                       (if approve then Approval from to
+                                   else Rejection from to)
+        sendMessage msg =
+            sendOrFail (xmlifyMessageForPeer sock msg)
+                       (OutBoundMessage msg)
+
+        sendPong from to mid = do
+            liftIO . debugL $ "SEND PONG" 
+            sendOrFail (xmlifyPong sock from to mid)
+                       (Pong from to mid)
+         where
+            xmlifyPong sock from to mid = do
+                fromjid <- peerJidTextLocal  sock to
+                tojid   <- peerJidTextRemote sock to
+                return $ [ EventBeginElement "{jabber:server}iq" 
+                          $ (case mid of
+                             Just c -> (("id",[c]):)
+                             _      -> id               )
+                             [ attr "type" "result"
+                             , attr "to"   tojid
+                             , attr "from" fromjid
+                             ]
+                      , EventEndElement "{jabber:server}iq"
+                      ]
+        sendUnsupported from to mid tag =
+            sendOrFail (xmlifyUnsupported sock from to mid tag)
+                       (Unsupported from to mid tag)
+         where
+            xmlifyUnsupported sock from to mid req = do
+                fromjid <- peerJidTextLocal  sock to
+                tojid   <- peerJidTextRemote sock to
+                return $ 
+                    [ EventBeginElement "{jabber:server}iq" 
+                     $ (case mid of
+                        Just c -> (("id",[c]):)
+                        _      -> id               )
+                        [("type",[ContentText "error"])
+                        , attr "to"   tojid
+                        , attr "from" fromjid
+                        ]
+                    , EventBeginElement req []
+                    , EventEndElement req
+                    , EventBeginElement "{jabber:server}error" [("type",[ContentText "cancel"])]
+                    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable" []
+                    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable"
+                    , EventEndElement "{jabber:server}error"
+                    , EventEndElement "{jabber:server}iq"
+                    ]
+
+
+    send greetPeer
+    forM_ (Map.assocs . approvals $ cache) $ \(to,froms) -> do
+        forM_ (Set.toList froms) $ \(approve,from) -> do
+            liftIO $ debugL "sending cached approval/rejection..."
+            sendApproval approve from to
+    forM_ (Map.assocs . presences $ cache) $ \(jid,st) -> do
+        sendPresence (Presence jid st)
+    forM_ (Map.assocs . probes $ cache) $ \(to,froms) -> do
+        forM_ (Set.toList froms) $ \(got,from) -> do
+            if got 
+              then do
+                    liftIO $ debugL "sending cached probe..."
+                    sendProbe from to
+              else do
+                    liftIO $ debugL "sending cached solicitation..."
+                    sendSolicitation from to
+
+
+    let five_sec = 5 * 1000000 :: Int
+    pingref <- liftIO $ do
+                    ping_timer <- liftIO $ newDelay five_sec
+                    newTVarIO (ping_timer,0::Int)
+
+    sockref <- liftIO $ atomically newEmptyTMVar
+    let bump fromsock = do
+            remote <- liftIO $ catchIO (fmap Just $ getPeerName sock)
+                                       (\_ -> return Nothing)
+            debugL $ "PING BUMP" <++?> fmap (showPeer . RemotePeer) remote
+            timer <- atomically $ do
+                        tryTakeTMVar sockref
+                        putTMVar sockref fromsock
+                        (timer,v) <-  readTVar pingref
+                        writeTVar pingref (timer,0)
+                        return timer
+            updateDelay timer five_sec
+        waitPing = do
+            (timer,v) <- readTVar pingref
+            waitDelay timer
+            return v
+
+    fix $ \loop -> do
+        liftIO . debugStr $ "LOOP waiting..."
+        event <- lift . atomically $ orElse (Left `fmap` readTChan chan) 
+                                            (Right `fmap` waitPing)
+        liftIO . debugStr $ "LOOP event = " ++ show event
+        let sendPing n = do
+                case n of
+                    0 -> do
+                            ping <- liftIO makePing
+                            yield ping 
+                            liftIO . debugL $ "SEND PING"
+                            prettyPrint ">P: " ping
+                            ping_timer <- liftIO $ newDelay five_sec
+                            liftIO . atomically $ writeTVar pingref (ping_timer,1)
+                            loop
+                    1 -> do
+                            remote <- liftIO $ getPeerName sock
+                            liftIO . debugL $ "PING TIMEOUT: " <++> showPeer (RemotePeer remote)
+                            fromsock <- liftIO $ atomically $ readTMVar sockref
+                            -- liftIO $ sClose fromsock
+                            liftIO $ runThunk fromsock
+
+                            return () -- PING TIMEOUT (loop quits)
+                    x -> error ("What? "++show x)
+              where makePing = do
+                        addr <- getSocketName sock
+                        remote <- getPeerName sock
+                        let from = toStrict . L.decodeUtf8 . showPeer $ RemotePeer addr
+                            to   = toStrict . L.decodeUtf8 . showPeer $ RemotePeer remote
+                            mid  = Just (ContentText "iduno")
+                        return $
+                           [ EventBeginElement "{jabber:server}iq"
+                             $ (case mid of
+                                Just c -> (("id",[c]):)
+                                _      -> id               )
+                                [ ("type",[ContentText "get"])
+                                , attr "to"   to
+                                , attr "from" from
+                                ]
+                           , EventBeginElement "{urn:xmpp:ping}ping" []
+                           , EventEndElement "{urn:xmpp:ping}ping"
+                           , EventEndElement "{jabber:server}iq" ]
+            chanEvent event = do
+             case event of
+                  OutBoundPresence p    -> sendPresence p
+                  PresenceProbe from to -> do
+                    liftIO $ debugL "sending live probe..."
+                    sendProbe from to
+                  Solicitation from to -> do
+                    liftIO $ debugL "sending live solicitation..."
+                    sendSolicitation from to
+                  Approval from to -> do
+                    liftIO . debugL $ "sending approval "<++>bshow (from,to)
+                    sendApproval True from to
+                  Rejection from to -> do
+                    liftIO . debugL $ "sending rejection "<++>bshow (from,to)
+                    sendApproval False from to
+                  OutBoundMessage msg -> sendMessage msg
+                  Pong from to mid -> do
+                    liftIO . debugL $ "sending pong "<++>bshow (from,to)
+                    sendPong from to mid
+                  Unsupported from to mid tag -> sendUnsupported from to mid tag
+                  Disconnect -> return ()
+                  ActivityBump fromsock -> liftIO (bump fromsock)
+             when (not . isQuitCommand $ event) loop
+        either chanEvent sendPing event
+    return ()
+    -- send goodbyePeer -- TODO: why does this cause an exception?
+                        --   Text/XML/Stream/Render.hs:169:5-15: 
+                        --      Irrefutable pattern failed for pattern (sl : s')
+
+
+
+
+seekRemotePeers :: JabberPeerSession config =>
+     XMPPPeerClass config -> TChan Presence -> OutgoingConnections CachedMessages -> IO b0
+seekRemotePeers config chan server_connections = do
+    fix $ \loop -> do
+        event <- atomically $ readTChan chan
+        case event of
+            p@(Presence jid stat) | not (is_remote (peer jid)) -> do
+              -- debugL $ "seekRemotePeers: " <++> L.show jid <++> " " <++> bshow stat
+              runMaybeT $ do
+                  u <- MaybeT . return $ name jid
+                  subscribers <- liftIO $ do
+                    subs <- getSubscribers config u
+                    mapM parseHostNameJID subs
+                  -- liftIO . debugL $ "subscribers: " <++> bshow subscribers
+                  let peers = Set.map peer (Set.fromList subscribers)
+                  forM_ (Set.toList peers) $ \peer -> do
+                    when (is_remote peer) $
+                        liftIO $ sendMessage server_connections (OutBoundPresence p) peer
+            _ -> return (Just ())
+        loop 
+
+xmlifyPresenceForPeer sock (Presence jid stat) = do
+    addr <- getSocketName sock
+    let n = name jid
+        rsc = resource jid
+        jidstr = toStrict . L.decodeUtf8 
+                  $ n <$++> "@" <?++> showPeer (RemotePeer addr) <++?>  "/" <++$> rsc 
+    return $
+      [ EventBeginElement "{jabber:server}presence" 
+            (attr "from" jidstr:typ stat) ]
+      ++ ( shw stat >>= jabberShow ) ++
+      [ EventEndElement "{jabber:server}presence" ]
+ where
+    typ Offline = [attr "type" "unavailable"]
+    typ _       = []
+
+    shw ExtendedAway = ["xa"]
+    shw Chatty       = ["chat"]
+    shw Away         = ["away"]
+    shw DoNotDisturb = ["dnd"]
+    shw _            = []
+    jabberShow stat = 
+      [ EventBeginElement "{jabber:server}show" []
+      , EventContent (ContentText stat)
+      , EventEndElement "{jabber:server}show" ]
+
+xmlifyMessageForClient msg = do
+    let tojid = msgTo msg
+        fromjid = msgFrom msg
+    tonames <- getNamesForPeer (peer tojid)
+    fromnames <- getNamesForPeer (peer fromjid)
+    let mk_str ns jid = toStrict . L.decodeUtf8 $ name jid <$++> "@" <?++> L.fromChunks [head ns] <++?> "/" <++$> resource jid
+        to_str   = mk_str tonames   tojid
+        from_str = mk_str fromnames fromjid
+        tags = ( "{jabber:client}subject"
+               , "{jabber:client}body" 
+               )
+    return $
+        [ EventBeginElement "{jabber:client}message" 
+            [ attr "from" from_str
+            , attr "to"   to_str
+            ]
+        ]
+        ++ xmlifyMsgElements tags (msgLangMap msg) ++
+        [ EventEndElement "{jabber:client}message" ]
+    
+
+xmlifyMessageForPeer sock msg = do
+    addr <- getSocketName sock
+    remote <- getPeerName sock
+    let n = name (msgFrom msg)
+        rsc = resource (msgFrom msg)
+        jidstr = toStrict . L.decodeUtf8 
+                  $ n <$++> "@" <?++> showPeer (RemotePeer addr) <++?>  "/" <++$> rsc 
+        tostr = toStrict . L.decodeUtf8 
+                  $ name (msgTo msg) <$++> "@" 
+                    <?++> showPeer (RemotePeer remote) <++?> "/" 
+                    <++$> resource (msgTo msg)
+        tags = ( "{jabber:server}subject"
+               , "{jabber:server}body" 
+               )
+    return $
+        [ EventBeginElement "{jabber:server}message" 
+            [ attr "from" jidstr
+            , attr "to"   tostr
+            ]
+        ]
+        ++ xmlifyMsgElements tags (msgLangMap msg) ++
+        [ EventEndElement "{jabber:server}message" ]
+
+xmlifyMsgElements tags langmap = concatMap (uncurry (langElements tags)) . Map.toList $ langmap
+
+langElements (subjecttag,bodytag) lang msg = 
+    ( maybeToList (msgSubject msg)
+         >>= wrap subjecttag )
+    ++ ( maybeToList (msgBody msg)
+         >>= wrap bodytag )
+    ++ ( Set.toList (msgElements msg)
+         >>= wrapTriple )
+ where
+    wrap name content = 
+        [ EventBeginElement name 
+            ( if lang/="" then [attr "xml:lang" lang] 
+                          else [] )
+        , EventContent (ContentText content)
+        , EventEndElement name
+        ]
+    wrapTriple (name,attrs,content) =
+        [ EventBeginElement name attrs -- Note: we assume lang specified in attrs
+        , EventContent (ContentText content)
+        , EventEndElement name
+        ]
+
+
+handleClientMessage session stanza = do
+    let log  = liftIO . debugL . ("(C) " <++>)
+    log $ "handleClientMessage "<++>bshow stanza
+    from <- liftIO $ getJID session
+    withJust (lookupAttrib "to" (tagAttrs stanza)) $ \to_str -> do
+    log $ "  to = "<++>bshow to_str
+    tojid <- liftIO $ parseHostNameJID (textToByteString to_str)
+    msg <- parseMessage ("{jabber:client}body"
+                        ,"{jabber:client}subject"
+                        ,"{jabber:client}thread"
+                        )
+                        log
+                        from
+                        tojid
+                        stanza
+    liftIO $ sendChat session msg
+
+{-
+unhandled-C: <message
+unhandled-C:   type="chat"
+unhandled-C:   id="purplea0a7fd24"
+unhandled-C:   to="user@vm2"
+unhandled-C:   xmlns="jabber:client">
+unhandled-C:     <active xmlns="http://jabber.org/protocol/chatstates"/>
+unhandled-C:     <body>
+unhandled-C:         hello dude
+unhandled-C:     </body>
+unhandled-C: </message>
+-}
+parseMessage (bodytag,subjecttag,threadtag) log from tojid stanza = do
+    let emptyMsg = LangSpecificMessage { msgBody=Nothing, msgSubject=Nothing, msgElements=Set.empty }
+        parseChildren (th,cmap) = do
+            child <- nextElement
+            lvl <- nesting
+            xmllang <- xmlLang 
+            let lang = maybe "" id xmllang
+            let c = maybe emptyMsg id (Map.lookup lang cmap)
+            log $ " child: "<++> bshow child
+            case child of
+                Just tag | tagName tag==bodytag
+                                    -> do
+                                        txt <- lift content
+                                        awaitCloser lvl
+                                        parseChildren (th,Map.insert lang (c { msgBody=Just txt }) cmap)
+                Just tag | tagName tag==subjecttag
+                                    -> do
+                                        txt <- lift content
+                                        awaitCloser lvl
+                                        parseChildren (th,Map.insert lang (c { msgSubject=Just txt }) cmap)
+                Just tag | tagName tag==threadtag
+                                    -> do
+                                        txt <- lift content
+                                        awaitCloser lvl
+                                        parseChildren (th {msgThreadContent=txt},cmap)
+                Just tag -> do
+                            let nm    = tagName tag
+                                attrs = tagAttrs tag
+                                elems = msgElements c
+                            txt <- lift content
+                            awaitCloser lvl
+                            parseChildren (th,Map.insert lang (c {msgElements=Set.insert (nm,attrs,txt) elems}) cmap)
+                Nothing -> return (th,cmap)
+    (th,langmap) <- parseChildren ( MessageThread {msgThreadParent=Nothing, msgThreadContent=""}
+                                  , Map.empty )
+    return Message { 
+        msgTo = tojid,
+        msgFrom = from,
+        msgLangMap = langmap,
+        msgThread = if msgThreadContent th/="" then Just th else Nothing
+    }
diff --git a/Presence/XMPPServer.hs b/Presence/XMPPServer.hs
new file mode 100644
index 00000000..c81cb9ce
--- /dev/null
+++ b/Presence/XMPPServer.hs
@@ -0,0 +1,1856 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE FlexibleInstances #-} -- instance for TChan Event
+{-# LANGUAGE DoAndIfThenElse #-}
+module XMPPServer
+    ( xmppServer
+    , ConnectionKey(..)
+    , XMPPServerParameters(..)
+    , XMPPServer
+    , xmppConnections
+    , StanzaWrap(..)
+    , Stanza(..)
+    , StanzaType(..)
+    , StanzaOrigin(..)
+    , cloneStanza
+    , LangSpecificMessage(..)
+    , peerKeyToText
+    , addrToText
+    , sendModifiedStanzaToPeer
+    , sendModifiedStanzaToClient
+    , presenceProbe
+    , presenceSolicitation
+    , makePresenceStanza
+    , makeInformSubscription
+    , makeRosterUpdate
+    , makeMessage
+    , JabberShow(..)
+    , Server
+    ) where
+
+import ConnectionKey
+import qualified Control.Concurrent.STM.UpdateStream as Slotted
+import Nesting
+import Server
+import EventUtil
+import ControlMaybe
+import LockedChan
+import PeerResolve
+import Blaze.ByteString.Builder (Builder)
+
+import Debug.Trace
+import System.IO (hFlush,stdout)
+import Control.Monad.Trans.Resource
+import Control.Monad.Trans (lift)
+import Control.Monad.IO.Class (MonadIO, liftIO)
+import Control.Monad.Fix (fix)
+import Control.Monad
+#ifdef THREAD_DEBUG
+import Control.Concurrent.Lifted.Instrument (forkIO,myThreadId,labelThread)
+#else
+import Control.Concurrent.Lifted (forkIO,myThreadId)
+import GHC.Conc                  (labelThread)
+#endif
+import Control.Concurrent.STM
+-- import Control.Concurrent.STM.TChan
+import Network.SocketLike
+import Text.Printf
+import System.Posix.Signals
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Char8 as Strict8
+-- import qualified Data.ByteString.Lazy.Char8 as Lazy8
+import Data.Int (Int8)
+
+import Data.Conduit
+import qualified Data.Conduit.List as CL
+import qualified Data.Conduit.Binary as CB
+import Data.Conduit.Blaze (builderToByteStringFlush)
+
+import qualified Text.XML.Stream.Render as XML hiding (content)
+import qualified Text.XML.Stream.Parse as XML
+import Data.XML.Types as XML
+import Data.Maybe
+import Data.List (nub)
+import Data.Monoid ( (<>) )
+import Data.Text (Text)
+import qualified Data.Text as Text (pack,unpack,words,intercalate)
+import Data.Char (toUpper,chr,ord)
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Set (Set, (\\) )
+import qualified Data.Set as Set
+import Data.String ( IsString(..) )
+import qualified System.Random
+import Data.Void (Void)
+import System.Endian (toBE32)
+import Control.Applicative
+import System.IO
+import qualified Connection
+
+peerport :: PortNumber
+peerport = 5269
+clientport :: PortNumber
+clientport = 5222
+
+my_uuid :: Text
+my_uuid = "154ae29f-98f2-4af4-826d-a40c8a188574"
+
+data JabberShow = Offline
+                | ExtendedAway
+                | Away
+                | DoNotDisturb
+                | Available
+                | Chatty
+ deriving (Show,Enum,Ord,Eq,Read)
+
+data MessageThread = MessageThread {
+        msgThreadParent  :: Maybe Text,
+        msgThreadContent :: Text
+    }
+  deriving (Show,Eq)
+
+data LangSpecificMessage =
+    LangSpecificMessage { msgBody :: Maybe Text
+                        , msgSubject :: Maybe Text
+                        }
+  deriving (Show,Eq)
+
+data RosterEventType
+    = RequestedSubscription
+    | NewBuddy -- preceded by PresenceInformSubscription True
+    | RemovedBuddy -- preceded by PresenceInformSubscription False
+    | PendingSubscriber -- same as PresenceRequestSubscription
+    | NewSubscriber
+    | RejectSubscriber
+ deriving (Show,Read,Ord,Eq,Enum)
+
+data ClientHack = SimulatedChatErrors
+ deriving (Show,Read,Ord,Eq,Enum)
+
+data StanzaType
+    = Unrecognized
+    | Ping
+    | Pong
+    | RequestResource (Maybe Text)
+    | SetResource
+    | SessionRequest
+    | UnrecognizedQuery Name
+    | RequestRoster
+    | Roster
+    | RosterEvent { rosterEventType :: RosterEventType
+                  , rosterUser :: Text
+                  , rosterContact :: Text }
+    | Error StanzaError XML.Event
+    | PresenceStatus { presenceShow :: JabberShow
+                     , presencePriority :: Maybe Int8
+                     , presenceStatus :: [(Lang,Text)]
+                     , presenceWhiteList :: [Text]
+                     }
+    | PresenceInformError
+    | PresenceInformSubscription Bool
+    | PresenceRequestStatus
+    | PresenceRequestSubscription Bool
+    | Message { msgThread :: Maybe MessageThread
+              , msgLangMap :: [(Lang,LangSpecificMessage)]
+              }
+    | NotifyClientVersion { versionName :: Text
+                          , versionVersion :: Text }
+    | InternalEnableHack ClientHack
+    | InternalCacheId Text
+ deriving (Show,Eq)
+
+data StanzaOrigin = LocalPeer | NetworkOrigin ConnectionKey (TChan Stanza)
+
+data StanzaWrap a = Stanza
+    { stanzaType :: StanzaType
+    , stanzaId :: Maybe Text
+    , stanzaTo :: Maybe Text
+    , stanzaFrom :: Maybe Text
+    , stanzaChan :: a
+    , stanzaClosers ::  TVar (Maybe [XML.Event])
+    , stanzaInterrupt :: TMVar ()
+    , stanzaOrigin :: StanzaOrigin
+    }
+
+type Stanza = StanzaWrap (LockedChan XML.Event)
+
+data XMPPServerParameters =
+    XMPPServerParameters
+    { -- | Called when a client requests a resource id.  The Maybe value is the
+      -- client's preference.
+      xmppChooseResourceName :: ConnectionKey -> SockAddr -> Maybe Text -> IO Text
+    , -- | This should indicate the server's hostname that all client's see.
+      xmppTellMyNameToClient :: IO Text
+    , xmppTellMyNameToPeer :: SockAddr -> IO Text
+    , xmppTellClientHisName :: ConnectionKey -> IO Text
+    , xmppTellPeerHisName :: ConnectionKey -> IO Text
+    , xmppNewConnection :: ConnectionKey -> SockAddr -> TChan Stanza -> IO ()
+    , xmppEOF :: ConnectionKey -> IO ()
+    , xmppRosterBuddies      :: ConnectionKey -> IO [Text]
+    , xmppRosterSubscribers  :: ConnectionKey -> IO [Text]
+    , xmppRosterSolicited    :: ConnectionKey -> IO [Text]
+    , xmppRosterOthers       :: ConnectionKey -> IO [Text]
+    , -- | Called when after sending a roster to a client.  Usually this  means
+      -- the client status should change from "available" to "interested".
+      xmppSubscribeToRoster :: ConnectionKey -> IO ()
+    -- , xmppLookupClientJID :: ConnectionKey -> IO Text
+    , xmppTellClientNameOfPeer :: ConnectionKey -> [Text] -> IO Text
+    , xmppDeliverMessage :: (IO ()) -> Stanza -> IO ()
+      -- | Called whenever a local client's presence changes.
+    , xmppInformClientPresence :: ConnectionKey -> Stanza -> IO ()
+      -- | Called whenever a remote peer's presence changes.
+    , xmppInformPeerPresence :: ConnectionKey -> Stanza -> IO ()
+    , -- | Called when a remote peer requests our status.
+      xmppAnswerProbe :: ConnectionKey -> Stanza -> TChan Stanza -> IO ()
+    , xmppClientSubscriptionRequest :: IO () -> ConnectionKey -> Stanza -> TChan Stanza -> IO ()
+    , -- | Called when a remote peer sends subscription request.
+      xmppPeerSubscriptionRequest :: IO () -> ConnectionKey -> Stanza -> TChan Stanza -> IO ()
+    , xmppClientInformSubscription :: IO () -> ConnectionKey -> Stanza -> IO ()
+    , -- | Called when a remote peer informs us of our subscription status.
+      xmppPeerInformSubscription :: IO () -> ConnectionKey -> Stanza -> IO ()
+    , xmppVerbosity :: IO Int
+    }
+
+
+enableClientHacks ::
+    forall t a.
+    (Eq a, IsString a) =>
+    a -> t -> TChan Stanza -> IO ()
+enableClientHacks "Pidgin" version replyto = do
+    wlog "Enabling hack SimulatedChatErrors for client Pidgin"
+    donevar <- atomically newEmptyTMVar
+    sendReply donevar
+              (InternalEnableHack SimulatedChatErrors)
+              []
+              replyto
+enableClientHacks "irssi-xmpp" version replyto = do
+    wlog "Enabling hack SimulatedChatErrors for client irssi-xmpp"
+    donevar <- atomically newEmptyTMVar
+    sendReply donevar
+              (InternalEnableHack SimulatedChatErrors)
+              []
+              replyto
+enableClientHacks _ _ _ = return ()
+
+cacheMessageId :: Text -> TChan Stanza -> IO ()
+cacheMessageId id' replyto = do
+    wlog $ "Caching id " ++ Text.unpack id'
+    donevar <- atomically newEmptyTMVar
+    sendReply donevar
+              (InternalCacheId id')
+              []
+              replyto
+
+
+-- TODO: http://xmpp.org/rfcs/rfc6120.html#rules-remote-error
+-- client connection
+-- socat script to send stanza fragment
+-- copyToChannel can keep a stack of closers to append to finish-off a stanza
+-- the TMVar () from forkConnection can be passed and with a stanza to detect interruption
+
+addrToText :: SockAddr -> Text
+addrToText (addr@(SockAddrInet _ _)) = Text.pack $ stripColon (show addr)
+ where stripColon s = pre where (pre,port) = break (==':') s
+addrToText (addr@(SockAddrInet6 _ _ _ _)) = Text.pack $ stripColon (show addr)
+ where stripColon s = if null bracket then pre else pre ++ "]"
+          where
+            (pre,bracket) = break (==']') s
+
+peerKeyToText :: ConnectionKey -> Text
+peerKeyToText (PeerKey { callBackAddress=addr }) = addrToText addr
+peerKeyToText (ClientKey { localAddress=addr }) = "ErrorClIeNt0"
+
+
+wlog :: String -> IO ()
+wlog s = putStrLn s >> hFlush stdout
+
+wlogb :: ByteString -> IO ()
+wlogb s = Strict8.putStrLn s >> hFlush stdout
+
+flushPassThrough :: Monad m => Conduit a m b -> Conduit (Flush a) m (Flush b)
+flushPassThrough c = getZipConduit $ ZipConduit (onlyChunks =$= mapOutput Chunk c) <* ZipConduit onlyFlushes
+  where
+    onlyChunks  :: Monad m => Conduit (Flush a) m a
+    onlyFlushes :: Monad m => Conduit (Flush a) m (Flush b)
+    onlyChunks           = awaitForever yieldChunk
+    onlyFlushes          = awaitForever yieldFlush
+    yieldFlush Flush     = yield Flush
+    yieldFlush _         = return ()
+    yieldChunk (Chunk x) = yield x
+    yieldChunk _         = return ()
+
+xmlStream :: ReadCommand -> WriteCommand -> ( Source IO XML.Event
+                                            , Sink (Flush XML.Event) IO () )
+xmlStream conread conwrite = (xsrc,xsnk)
+ where
+    xsrc = src $= XML.parseBytes XML.def
+    xsnk :: Sink (Flush Event) IO ()
+    xsnk = -- XML.renderBytes XML.def =$ snk
+        flushPassThrough (XML.renderBuilder XML.def)
+        =$= builderToByteStringFlush
+        =$= discardFlush
+        =$ snk
+      where
+        discardFlush :: Monad m => ConduitM (Flush a) a m ()
+        discardFlush = awaitForever yieldChunk
+        yieldChunk (Chunk x) = yield x
+        yieldChunk _ = return ()
+
+    src = do
+        v <- lift conread
+        maybe (return ()) -- lift . wlog $ "conread: Nothing")
+              (yield >=> const src)
+              v
+    snk = awaitForever $ liftIO . conwrite
+
+
+type FlagCommand = STM Bool
+type ReadCommand = IO (Maybe ByteString)
+type WriteCommand = ByteString -> IO Bool
+
+cloneStanza :: StanzaWrap (LockedChan a) -> IO (StanzaWrap (LockedChan a))
+cloneStanza stanza = do
+    dupped <- cloneLChan (stanzaChan stanza)
+    return stanza { stanzaChan = dupped }
+
+copyToChannel
+  :: MonadIO m =>
+     (Event -> a) -> LockedChan a -> TVar (Maybe [Event]) -> ConduitM Event Event m ()
+copyToChannel f chan closer_stack = awaitForever copy
+ where
+    copy x = do
+        liftIO . atomically $ writeLChan chan (f x)
+        case x of
+            EventBeginDocument {} -> do
+                let clsr = closerFor x
+                liftIO . atomically $
+                    modifyTVar' closer_stack (fmap (clsr:))
+            EventEndDocument {} -> do
+                liftIO . atomically $
+                    modifyTVar' closer_stack (fmap (drop 1))
+            _ -> return ()
+        yield x
+
+
+prettyPrint :: ByteString -> ConduitM Event Void IO ()
+prettyPrint prefix =
+        XML.renderBytes (XML.def { XML.rsPretty=True })
+        =$= CB.lines
+        =$ CL.mapM_ (wlogb . (prefix <>))
+
+swapNamespace :: Monad m => Text -> Text -> ConduitM Event Event m ()
+swapNamespace old new = awaitForever (yield . swapit old new)
+
+swapit :: Text -> Text -> Event -> Event
+swapit old new (EventBeginElement n as) | nameNamespace n==Just old =
+    EventBeginElement (n { nameNamespace = Just new }) as
+swapit old new (EventEndElement n) | nameNamespace n==Just old =
+    EventEndElement (n { nameNamespace = Just new })
+swapit old new x = x
+
+fixHeaders :: Monad m => Stanza -> ConduitM Event Event m ()
+fixHeaders Stanza { stanzaType=typ, stanzaTo=mto, stanzaFrom=mfrom } = do
+    x <- await
+    maybe (return ()) f x
+ where
+    f (EventBeginElement n as) = do yield $ EventBeginElement n (update n as)
+                                    awaitForever yield
+    f x = yield x >> awaitForever yield
+    update n as = as3
+     where
+        as' = maybe as (setAttrib "to" as) mto
+        as'' = maybe as' (setAttrib "from" as') mfrom
+        as3 = case typ of
+                PresenceStatus {} | nameNamespace n == Just "jabber:client"
+                  -> delAttrib "whitelist" as''
+                PresenceStatus {} | otherwise
+                  -> case presenceWhiteList typ of
+                        [] -> delAttrib "whitelist" as''
+                        ws -> setAttrib "whitelist" as'' (Text.intercalate " " ws)
+                _ -> as''
+
+        setAttrib akey as aval = attr akey aval:filter ((/=akey) . fst) as
+        delAttrib akey as = filter ((/=akey) . fst) as
+
+conduitToChan
+  :: Conduit () IO Event
+     -> IO (LockedChan Event, TVar (Maybe [Event]), TMVar a)
+conduitToChan c = do
+    chan <- atomically newLockedChan
+    clsrs <- atomically $ newTVar (Just [])
+    quitvar <- atomically $ newEmptyTMVar
+    forkIO $ do
+        c =$= copyToChannel id chan clsrs $$ awaitForever (const $ return ())
+        atomically $ writeTVar clsrs Nothing
+    return (chan,clsrs,quitvar)
+
+conduitToStanza
+  :: StanzaType
+     -> Maybe Text -- ^ id
+     -> Maybe Text -- ^ from
+     -> Maybe Text -- ^ to
+     -> Conduit () IO Event
+     -> IO Stanza
+conduitToStanza stype mid from to c = do
+    (chan,clsrs,quitvar) <- conduitToChan c
+    return
+        Stanza  { stanzaType = stype
+                , stanzaId = mid
+                , stanzaTo = to
+                , stanzaFrom = from
+                , stanzaChan = chan
+                , stanzaClosers = clsrs
+                , stanzaInterrupt = quitvar
+                , stanzaOrigin = LocalPeer
+                }
+
+
+ioWriteChan :: MonadIO m => TChan a -> a -> m ()
+ioWriteChan c v = liftIO . atomically $ writeTChan c v
+
+stanzaToConduit :: MonadIO m => Stanza -> ConduitM i Event m ()
+stanzaToConduit stanza = do
+    let xchan = stanzaChan stanza
+        xfin = stanzaClosers stanza
+        rdone = stanzaInterrupt stanza
+        loop = return ()
+    xchan <- liftIO $ unlockChan xchan
+    fix $ \inner -> do
+        what <- liftIO . atomically $ foldr1 orElse
+            [readTChan xchan >>= \xml -> return $ do
+                yield xml -- atomically $ Slotted.push slots Nothing xml
+                inner
+            ,do mb <- readTVar xfin
+                cempty <- isEmptyTChan xchan
+                if isNothing mb
+                    then if cempty then return loop else retry
+                    else do done <- tryReadTMVar rdone
+                            check (isJust done)
+                            trace "todo: send closers" retry
+            ,do isEmptyTChan xchan >>= check
+                readTMVar rdone
+                return (return ())]
+        what
+
+
+sendModifiedStanzaToPeer :: Stanza -> TChan Stanza -> IO ()
+sendModifiedStanzaToPeer stanza chan = do
+    (echan,clsrs,quitvar) <- conduitToChan c
+    ioWriteChan chan
+        stanza  { stanzaChan = echan
+                , stanzaClosers = clsrs
+                , stanzaInterrupt = quitvar
+                , stanzaType = processedType (stanzaType stanza)
+                -- TODO id? origin?
+                }
+ where
+    old = "jabber:client"
+    new = "jabber:server"
+    c = stanzaToConduit stanza =$= swapNamespace old new =$= fixHeaders stanza
+    processedType (Error cond tag) = Error cond (swapit old new tag)
+    processedType x = x
+
+
+sendModifiedStanzaToClient :: Stanza -> TChan Stanza -> IO ()
+sendModifiedStanzaToClient stanza chan = do
+    (echan,clsrs,quitvar) <- conduitToChan c
+    -- wlog $ "send-to-client " ++ show (stanzaId stanza)
+    ioWriteChan chan
+        stanza  { stanzaChan = echan
+                , stanzaClosers = clsrs
+                , stanzaInterrupt = quitvar
+                , stanzaType = processedType (stanzaType stanza)
+                -- TODO id? origin?
+                }
+ where
+    old = "jabber:server"
+    new = "jabber:client"
+    c = stanzaToConduit stanza =$= swapNamespace old new =$= fixHeaders stanza
+    processedType (Error cond tag) = Error cond (swapit old new tag)
+    processedType x = x
+
+
+-- id,to, and from are taken as-is from reply list
+-- todo: this should probably be restricted to IO monad
+sendReply :: (Functor m, MonadIO m) => TMVar () -> StanzaType -> [Event] -> TChan Stanza -> m ()
+sendReply donevar stype reply replychan = do
+    let stanzaTag = listToMaybe reply
+        mid   = stanzaTag >>= lookupAttrib "id" . tagAttrs
+        mfrom = stanzaTag >>= lookupAttrib "from" . tagAttrs
+        mto = stanzaTag >>= lookupAttrib "to" . tagAttrs
+        isInternal (InternalEnableHack {}) = True
+        isInternal (InternalCacheId {}) = True
+        isInternal _ = False
+    flip (maybe $ return ())
+         (fmap (const ()) stanzaTag `mplus` guard (isInternal stype))
+         . const $ do
+    replyStanza <- liftIO . atomically $ do
+        replyChan <- newLockedChan
+        replyClsrs <- newTVar (Just [])
+        return Stanza { stanzaType = stype
+                      , stanzaId = mid
+                      , stanzaTo = mto      -- as-is from reply list
+                      , stanzaFrom = mfrom  -- as-is from reply list
+                      , stanzaChan = replyChan
+                      , stanzaClosers = replyClsrs
+                      , stanzaInterrupt = donevar
+                      , stanzaOrigin = LocalPeer
+                      }
+    ioWriteChan replychan replyStanza
+    void . liftIO . forkIO $ do
+        mapM_ (liftIO . atomically . writeLChan (stanzaChan replyStanza)) reply
+        liftIO . atomically $ writeTVar (stanzaClosers replyStanza) Nothing
+        -- liftIO $ wlog "finished reply stanza"
+
+stanzaFromList :: StanzaType -> [Event] -> IO Stanza
+stanzaFromList stype reply = do
+    let stanzaTag = listToMaybe reply
+        mid   = stanzaTag >>= lookupAttrib "id" . tagAttrs
+        mfrom = stanzaTag >>= lookupAttrib "from" . tagAttrs
+        mto = stanzaTag >>= lookupAttrib "to" . tagAttrs
+        {-
+        isInternal (InternalEnableHack {}) = True
+        isInternal (InternalCacheId {}) = True
+        isInternal _ = False
+        -}
+    (donevar,replyChan,replyClsrs) <- atomically $ do
+        donevar <- newEmptyTMVar -- TMVar ()
+        replyChan <- newLockedChan
+        replyClsrs <- newTVar (Just [])
+        return (donevar,replyChan, replyClsrs)
+    forkIO $ do
+        forM_ reply $ atomically . writeLChan replyChan
+        atomically $ do putTMVar donevar ()
+                        writeTVar replyClsrs Nothing
+    return Stanza { stanzaType = stype
+                  , stanzaId = mid
+                  , stanzaTo = mto      -- as-is from reply list
+                  , stanzaFrom = mfrom  -- as-is from reply list
+                  , stanzaChan = replyChan
+                  , stanzaClosers = replyClsrs
+                  , stanzaInterrupt = donevar
+                  , stanzaOrigin = LocalPeer
+                  }
+
+grokStanzaIQGet :: Monad m => XML.Event -> NestingXML o m (Maybe StanzaType)
+grokStanzaIQGet stanza = do
+    mtag <- nextElement
+    flip (maybe $ return Nothing)  mtag $ \tag -> do
+    case tagName tag of
+        "{urn:xmpp:ping}ping" -> return $ Just Ping
+        "{jabber:iq:roster}query" -> return $ Just RequestRoster
+        name -> return . Just $ UnrecognizedQuery name
+
+parseClientVersion :: NestingXML o IO (Maybe StanzaType)
+parseClientVersion = parseit Nothing Nothing
+ where
+    reportit mname mver = return $ do
+        name <- mname
+        ver <- mver
+        return NotifyClientVersion { versionName=name, versionVersion=ver }
+    parseit :: Maybe Text -> Maybe Text -> NestingXML o IO (Maybe StanzaType)
+    parseit mname mver = do
+        mtag <- nextElement
+        flip (maybe $ reportit mname mver) mtag $ \tag -> do
+        case tagName tag of
+            "{jabber:iq:version}name" -> do
+                x <- XML.content
+                parseit (Just x) mver
+            "{jabber:iq:version}version" -> do
+                x <- XML.content
+                parseit mname (Just x)
+            _ -> parseit mname mver
+
+
+grokStanzaIQResult :: XML.Event -> NestingXML o IO (Maybe StanzaType)
+grokStanzaIQResult stanza = do
+    mtag <- nextElement
+    flip (maybe $ return (Just Pong))  mtag $ \tag -> do
+    case tagName tag of
+        "{jabber:iq:version}query" | nameNamespace (tagName stanza)==Just "jabber:client"
+            -> parseClientVersion
+        _ -> return Nothing
+
+grokStanzaIQSet :: XML.Event -> NestingXML o IO (Maybe StanzaType)
+grokStanzaIQSet stanza = do
+    mtag <- nextElement
+    flip (maybe $ return Nothing)  mtag $ \tag -> do
+    case tagName tag of
+        "{urn:ietf:params:xml:ns:xmpp-bind}bind" -> do
+            mchild <- nextElement
+            case fmap tagName mchild of
+                Just "{urn:ietf:params:xml:ns:xmpp-bind}resource" -> do
+                    rsc <- XML.content -- TODO: MonadThrow???
+                    return . Just $ RequestResource (Just rsc)
+                Just _ -> return Nothing
+                Nothing -> return . Just $ RequestResource Nothing
+        "{urn:ietf:params:xml:ns:xmpp-session}session" -> do
+            return $ Just SessionRequest
+        _ -> return Nothing
+
+
+{-
+C->Unrecognized <iq
+C->Unrecognized   type="set"
+C->Unrecognized   id="purpleae62d88f"
+C->Unrecognized   xmlns="jabber:client">
+C->Unrecognized     <bind xmlns="urn:ietf:params:xml:ns:xmpp-bind"/>
+C->Unrecognized </iq>
+-}
+chanContents :: TChan x -> IO [x]
+chanContents ch = do
+        x  <- atomically $ do
+            bempty <- isEmptyTChan ch
+            if bempty
+                then return Nothing
+                else fmap Just $ readTChan ch
+        maybe (return [])
+              (\x -> do
+                xs <- chanContents ch
+                return (x:xs))
+              x
+
+
+parsePresenceStatus
+  :: ( MonadThrow m
+     , MonadIO m
+     ) => Text -> XML.Event -> NestingXML o m (Maybe StanzaType)
+parsePresenceStatus ns stanzaTag = do
+
+    let toStat "away" = Away
+        toStat "xa"   = ExtendedAway
+        toStat "dnd"  = DoNotDisturb
+        toStat "chat" = Chatty
+
+    showv <- liftIO . atomically $ newTVar Available
+    priov <- liftIO . atomically $ newTVar Nothing
+    statusv <- liftIO . atomically $ newTChan
+    fix $ \loop -> do
+        mtag <- nextElement
+        flip (maybe $ return ()) mtag $ \tag -> do
+        when (nameNamespace (tagName tag) == Just ns) $ do
+            case nameLocalName (tagName tag) of
+                "show" -> do t <- XML.content
+                             liftIO . atomically $ writeTVar showv (toStat t)
+                "priority" -> do t <- XML.content
+                                 liftIO . handleIO_ (return ()) $ do
+                                 prio <- readIO (Text.unpack t)
+                                 atomically $ writeTVar priov (Just prio)
+                "status" -> do t <- XML.content
+                               lang <- xmlLang
+                               ioWriteChan statusv (maybe "" id lang,t)
+                _ -> return ()
+        loop
+    show <- liftIO . atomically $ readTVar showv
+    prio <- liftIO . atomically $ readTVar priov
+    status <- liftIO $ chanContents statusv -- Could use unsafeInterleaveIO to
+                                            -- avoid multiple passes, but whatever.
+    let wlist = do
+            w <- maybeToList $ lookupAttrib "whitelist" (tagAttrs stanzaTag)
+            Text.words w
+    return . Just $ PresenceStatus { presenceShow = show
+                                   , presencePriority = prio
+                                   , presenceStatus = status
+                                   , presenceWhiteList = wlist
+                                   }
+grokPresence
+  :: ( MonadThrow m
+     , MonadIO m
+     ) => Text -> XML.Event -> NestingXML o m (Maybe StanzaType)
+grokPresence ns stanzaTag = do
+    let typ = lookupAttrib "type" (tagAttrs stanzaTag)
+    case typ of
+        Nothing -> parsePresenceStatus ns stanzaTag
+        Just "unavailable"  -> fmap (fmap (\p -> p {presenceShow=Offline}))
+                                   $ parsePresenceStatus ns stanzaTag
+        Just "error"        -> return . Just $ PresenceInformError
+        Just "unsubscribed" -> return . Just $ PresenceInformSubscription False
+        Just "subscribed"   -> return . Just $ PresenceInformSubscription True
+        Just "probe"        -> return . Just $ PresenceRequestStatus
+        Just "unsubscribe"  -> return . Just $ PresenceRequestSubscription False
+        Just "subscribe"    -> return . Just $ PresenceRequestSubscription True
+        _                   -> return Nothing
+
+parseMessage
+  :: ( MonadThrow m
+     , MonadIO m
+     ) => Text -> XML.Event -> NestingXML o m StanzaType
+parseMessage ns stanza = do
+    let bodytag = Name { nameNamespace = Just ns
+                       , nameLocalName = "body"
+                       , namePrefix = Nothing }
+        subjecttag = Name { nameNamespace = Just ns
+                          , nameLocalName = "subject"
+                          , namePrefix = Nothing }
+        threadtag = Name { nameNamespace = Just ns
+                         , nameLocalName = "thread"
+                         , namePrefix = Nothing }
+    let emptyMsg = LangSpecificMessage { msgBody=Nothing, msgSubject=Nothing }
+        parseChildren (th,cmap) = do
+            child <- nextElement
+            lvl <- nesting
+            xmllang <- xmlLang
+            let lang = maybe "" id xmllang
+            let c = maybe emptyMsg id (Map.lookup lang cmap)
+            -- log $ " child: "<> bshow child
+            case child of
+                Just tag | tagName tag==bodytag
+                                    -> do
+                                        txt <- XML.content
+                                        awaitCloser lvl
+                                        parseChildren (th,Map.insert lang (c { msgBody=Just txt }) cmap)
+                Just tag | tagName tag==subjecttag
+                                    -> do
+                                        txt <- XML.content
+                                        awaitCloser lvl
+                                        parseChildren (th,Map.insert lang (c { msgSubject=Just txt }) cmap)
+                Just tag | tagName tag==threadtag
+                                    -> do
+                                        txt <- XML.content
+                                        awaitCloser lvl
+                                        parseChildren (th {msgThreadContent=txt},cmap)
+                Just tag -> do
+                            -- let nm    = tagName tag
+                            --    attrs = tagAttrs tag
+                            --    -- elems = msgElements c
+                            -- txt <- XML.content
+                            awaitCloser lvl
+                            parseChildren (th,Map.insert lang c cmap)
+                Nothing -> return (th,cmap)
+    (th,langmap) <- parseChildren ( MessageThread {msgThreadParent=Nothing, msgThreadContent=""}
+                                  , Map.empty )
+    return Message {
+        msgLangMap = Map.toList langmap,
+        msgThread = if msgThreadContent th/="" then Just th else Nothing
+    }
+
+findConditionTag :: Monad m => NestingXML o m (Maybe XML.Event)
+findConditionTag = do
+    x <- nextElement
+    flip (maybe $ return Nothing) x $ \x -> do
+    case nameNamespace (tagName x) of
+        Just "urn:ietf:params:xml:ns:xmpp-stanzas" -> return (Just x)
+        _ -> findConditionTag
+
+conditionFromText :: Text -> Maybe StanzaError
+conditionFromText t = fmap fst $ listToMaybe ss
+ where
+    es = [BadRequest .. UnexpectedRequest]
+    ts = map (\e->(e,errorTagLocalName e)) es
+    ss = dropWhile ((/=t) . snd) ts
+
+findErrorTag :: Monad m => Text -> NestingXML o m (Maybe StanzaError)
+findErrorTag ns = do
+    x <- nextElement
+    flip (maybe $ return Nothing) x $ \x -> do
+    case tagName x of
+        n | nameNamespace n==Just ns && nameLocalName n=="error"
+            -> do
+                 mtag <- findConditionTag
+                 return $ do
+                    tag <- {- trace ("mtag = "++show mtag) -} mtag
+                    let t = nameLocalName (tagName tag)
+                    conditionFromText t
+        _ -> findErrorTag ns
+
+grokMessage
+  :: ( MonadThrow m
+     , MonadIO m
+     ) => Text -> XML.Event -> NestingXML o m (Maybe StanzaType)
+grokMessage ns stanzaTag = do
+    let typ = lookupAttrib "type" (tagAttrs stanzaTag)
+    case typ of
+        Just "error" -> do
+            mb <- findErrorTag ns
+            return $ do
+                e <- mb
+                return $ Error e stanzaTag
+        _ -> do t <- parseMessage ns stanzaTag
+                return $ Just t
+
+
+
+grokStanza
+  ::  Text -> XML.Event -> NestingXML o IO (Maybe StanzaType)
+grokStanza "jabber:server" stanzaTag =
+            case () of
+                _ | stanzaTag `isServerIQOf` "get" -> grokStanzaIQGet stanzaTag
+                _ | stanzaTag `isServerIQOf` "result" -> grokStanzaIQResult stanzaTag
+                _ | tagName stanzaTag == "{jabber:server}presence" -> grokPresence "jabber:server" stanzaTag
+                _ | tagName stanzaTag == "{jabber:server}message" -> grokMessage "jabber:server" stanzaTag
+                _ -> return $ Just Unrecognized
+
+grokStanza "jabber:client" stanzaTag =
+            case () of
+                _ | stanzaTag `isClientIQOf` "get" -> grokStanzaIQGet stanzaTag
+                _ | stanzaTag `isClientIQOf` "set" -> grokStanzaIQSet stanzaTag
+                _ | stanzaTag `isClientIQOf` "result" -> grokStanzaIQResult stanzaTag
+                _ | tagName stanzaTag == "{jabber:client}presence" -> grokPresence "jabber:client" stanzaTag
+                _ | tagName stanzaTag == "{jabber:client}message" -> grokMessage "jabber:client" stanzaTag
+                _ -> return $ Just Unrecognized
+
+mkname :: Text -> Text -> XML.Name
+mkname namespace name = (Name name (Just namespace) Nothing)
+
+makeMessage :: Text -> Text -> Text -> Text -> IO Stanza
+makeMessage namespace from to bod =
+    stanzaFromList typ
+     $ [ EventBeginElement (mkname namespace "message")
+            [ attr "from" from
+            , attr "to" to
+            ]
+       , EventBeginElement (mkname namespace "body") []
+       , EventContent (ContentText bod)
+       , EventEndElement (mkname namespace "body")
+       , EventEndElement (mkname namespace "message") ]
+ where
+    typ = Message { msgThread = Nothing
+                  , msgLangMap = [("", lsm)]
+                  }
+    lsm = LangSpecificMessage
+            { msgBody = Just bod
+            , msgSubject = Nothing }
+
+makeInformSubscription :: Text -> Text -> Text -> Bool -> IO Stanza
+makeInformSubscription namespace from to approved =
+    stanzaFromList (PresenceInformSubscription approved)
+      $ [ EventBeginElement (mkname namespace "presence")
+            [ attr "from" from
+            , attr "to" to
+            , attr "type" $ if approved then "subscribed"
+                                        else "unsubscribed" ]
+        , EventEndElement (mkname namespace "presence")]
+
+makePresenceStanza :: Text -> Maybe Text -> JabberShow -> IO Stanza
+makePresenceStanza namespace mjid pstat = do
+    stanzaFromList PresenceStatus { presenceShow = pstat
+                                  , presencePriority = Nothing
+                                  , presenceStatus = []
+                                  , presenceWhiteList = []
+                                  }
+      $ [ EventBeginElement (mkname namespace "presence")
+            (setFrom $ typ pstat) ]
+        ++ (shw pstat >>= jabberShow) ++
+        [ EventEndElement (mkname namespace "presence")]
+ where
+    setFrom = maybe id
+                    (\jid -> (attr "from" jid :) )
+                    mjid
+    typ Offline = [attr "type" "unavailable"]
+    typ _       = []
+    shw ExtendedAway = ["xa"]
+    shw Chatty       = ["chat"]
+    shw Away         = ["away"]
+    shw DoNotDisturb = ["dnd"]
+    shw _            = []
+    jabberShow stat =
+      [ EventBeginElement "{jabber:client}show" []
+      , EventContent (ContentText stat)
+      , EventEndElement "{jabber:client}show" ]
+
+makeRosterUpdate :: Text -> Text -> [(Name, Text)] -> IO Stanza
+makeRosterUpdate tojid contact as = do
+    let attrs = map (uncurry attr) as
+    stanzaFromList Unrecognized
+      [ EventBeginElement "{jabber:client}iq"
+            [ attr "to"   tojid
+            , attr "id"   "someid"
+            , attr "type" "set"
+            ]
+      , EventBeginElement "{jabber:iq:roster}query" []
+      , EventBeginElement "{jabber:iq:roster}item" (attr "jid" contact : attrs)
+      , EventEndElement   "{jabber:iq:roster}item"
+      , EventEndElement   "{jabber:iq:roster}query"
+      , EventEndElement "{jabber:client}iq"
+      ]
+
+makePong :: Text -> Maybe Text -> Text -> Text -> [XML.Event]
+makePong namespace mid to from =
+       -- Note: similar to session reply
+       [ EventBeginElement (mkname namespace "iq")
+         $(case mid of
+               Just c -> (("id",[ContentText c]):)
+               _      -> id)
+               [ attr "type" "result"
+               , attr "to"   to
+               , attr "from" from
+               ]
+       , EventEndElement (mkname namespace "iq")
+       ]
+
+
+xmppInbound :: Server ConnectionKey SockAddr ReleaseKey XML.Event
+                -> XMPPServerParameters
+                -> ConnectionKey
+                -> SockAddr
+                -> FlagCommand -- ^ action to check whether the connection needs a ping
+                -> TChan Stanza -- ^ channel to announce incomming stanzas on
+                -> TChan Stanza -- ^ channel used to send stanzas
+                -> TMVar () -- ^ mvar that is filled when the connection quits
+                -> Sink XML.Event IO ()
+xmppInbound sv xmpp k laddr pingflag stanzas output donevar = doNestingXML $ do
+    let (namespace,tellmyname,tellyourname) = case k of
+            ClientKey {} -> ( "jabber:client"
+                            , xmppTellMyNameToClient xmpp
+                            , xmppTellClientHisName xmpp k
+                            )
+            PeerKey {} -> ( "jabber:server"
+                          , xmppTellMyNameToPeer xmpp laddr
+                          , xmppTellPeerHisName xmpp k
+                          )
+    me <- liftIO tellmyname
+    withXML $ \begindoc -> do
+    when (begindoc==EventBeginDocument) $ do
+    whenJust nextElement $ \xml -> do
+    withJust (elementAttrs "stream" xml) $ \stream_attrs -> do
+    fix $ \loop -> do
+    -- liftIO . wlog $ "waiting for stanza."
+    (chan,clsrs) <- liftIO . atomically $
+        liftM2 (,) newLockedChan (newTVar (Just []))
+    whenJust nextElement $ \stanzaTag -> do
+        stanza_lvl <- nesting
+        liftIO . atomically $ do
+            writeLChan chan stanzaTag
+            modifyTVar' clsrs (fmap (closerFor stanzaTag:))
+        copyToChannel id chan clsrs =$= do
+          let mid   = lookupAttrib "id" (tagAttrs stanzaTag)
+              mfrom = lookupAttrib "from" (tagAttrs stanzaTag)
+              mto = lookupAttrib "to" (tagAttrs stanzaTag)
+          dispatch <- grokStanza namespace stanzaTag
+          let unrecog = do
+                let stype = Unrecognized
+                s <- liftIO . atomically $ do
+                      return Stanza
+                              { stanzaType = stype
+                              , stanzaId = mid
+                              , stanzaTo = mto
+                              , stanzaFrom = mfrom
+                              , stanzaChan = chan
+                              , stanzaClosers = clsrs
+                              , stanzaInterrupt = donevar
+                              , stanzaOrigin = NetworkOrigin k output
+                              }
+                ioWriteChan stanzas s
+          you <- liftIO tellyourname
+          flip (maybe $ unrecog) dispatch $ \dispatch ->
+            case dispatch of
+              -- Checking that the to-address matches this server.
+              -- Otherwise it could be a client-to-client ping or a
+              -- client-to-server for some other server.
+              -- For now, assuming its for the immediate connection.
+              Ping | mto==Just me || mto==Nothing -> do
+                let pongto = maybe you id mfrom
+                    pongfrom = maybe me id mto
+                    pong = makePong namespace mid pongto pongfrom
+                sendReply donevar Pong pong output
+#ifdef PINGNOISE
+                -- TODO: Remove this, it is only to generate a debug print
+                ioWriteChan stanzas Stanza
+                            { stanzaType = Ping
+                            , stanzaId = mid
+                            , stanzaTo = mto
+                            , stanzaFrom = mfrom
+                            , stanzaChan = chan
+                            , stanzaClosers = clsrs
+                            , stanzaInterrupt = donevar
+                            , stanzaOrigin = NetworkOrigin k output
+                            }
+#endif
+              stype -> ioWriteChan stanzas Stanza
+                            { stanzaType = stype
+                            , stanzaId = mid
+                            , stanzaTo = mto
+                            , stanzaFrom = mfrom
+                            , stanzaChan = chan
+                            , stanzaClosers = clsrs
+                            , stanzaInterrupt = donevar
+                            , stanzaOrigin = NetworkOrigin k output
+                            }
+          awaitCloser stanza_lvl
+        liftIO . atomically $ writeTVar clsrs Nothing
+        loop
+
+
+while :: IO Bool -> IO a -> IO [a]
+while cond body = do
+    b <- cond
+    if b then do x <- body
+                 xs <- while cond body
+                 return (x:xs)
+         else return []
+
+readUntilNothing :: TChan (Maybe x) -> IO [x]
+readUntilNothing ch = do
+        x  <- atomically $ readTChan ch
+        maybe (return [])
+              (\x -> do
+                xs <- readUntilNothing ch
+                return (x:xs))
+              x
+
+
+streamFeatures :: Text -> [XML.Event]
+streamFeatures "jabber:client" =
+    [ EventBeginElement (streamP "features") []
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}bind" []
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+
+    {-
+    -- , "  <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>"
+    , " <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>"
+    -- , " <mechanism>DIGEST-MD5</mechanism>"
+    , " <mechanism>PLAIN</mechanism>"
+    , " </mechanisms> "
+    -}
+
+    , EventEndElement (streamP "features")
+    ]
+streamFeatures "jabber:server" =
+    []
+
+
+greet' :: Text -> Text -> [XML.Event]
+greet' namespace host = EventBeginDocument : greet'' namespace host
+
+greet'' :: Text -> Text -> [Event]
+greet'' namespace host =
+    [ EventBeginElement (streamP "stream")
+        [("from",[ContentText host])
+        ,("id",[ContentText "someid"])
+        ,("xmlns",[ContentText namespace])
+        ,("xmlns:stream",[ContentText "http://etherx.jabber.org/streams"])
+        ,("version",[ContentText "1.0"])
+        ]
+    ] ++ streamFeatures namespace
+
+consid :: Maybe Text -> [(Name, [Content])] -> [(Name, [Content])]
+consid Nothing = id
+consid (Just sid) = (("id",[ContentText sid]):)
+
+
+data XMPPState
+    = PingSlot
+ deriving (Eq,Ord)
+
+makePing :: Text -> Maybe Text -> Text -> Text -> [XML.Event]
+makePing namespace mid to from =
+       [ EventBeginElement (mkname namespace "iq")
+         $ (case mid of
+            Just c -> (("id",[ContentText c]):)
+            _      -> id               )
+            [ ("type",[ContentText "get"])
+            , attr "to"   to
+            , attr "from" from
+            ]
+       , EventBeginElement "{urn:xmpp:ping}ping" []
+       , EventEndElement "{urn:xmpp:ping}ping"
+       , EventEndElement $ mkname namespace "iq"]
+
+iq_bind_reply :: Maybe Text -> Text -> [XML.Event]
+iq_bind_reply mid jid =
+    [ EventBeginElement "{jabber:client}iq" (consid mid [("type",[ContentText "result"])])
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+        [("xmlns",[ContentText "urn:ietf:params:xml:ns:xmpp-bind"])]
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-bind}jid" []
+    , EventContent (ContentText jid)
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-bind}jid"
+    , EventEndElement  "{urn:ietf:params:xml:ns:xmpp-bind}bind"
+    , EventEndElement "{jabber:client}iq"
+
+    {-
+    -- query for client version
+    , EventBeginElement "{jabber:client}iq"
+                            [ attr "to" jid
+                            , attr "from" hostname
+                            , attr "type" "get"
+                            , attr "id" "version"]
+    , EventBeginElement "{jabber:iq:version}query" []
+    , EventEndElement "{jabber:iq:version}query"
+    , EventEndElement "{jabber:client}iq"
+    -}
+    ]
+
+iq_session_reply :: Maybe Text -> Text -> [XML.Event]
+iq_session_reply mid host =
+    -- Note: similar to Pong
+    [ EventBeginElement "{jabber:client}iq"
+        (consid mid [("from",[ContentText host])
+                    ,("type",[ContentText "result"])
+                    ])
+    , EventEndElement "{jabber:client}iq"
+    ]
+
+iq_service_unavailable :: Maybe Text -> Text -> XML.Name -> [XML.Event]
+iq_service_unavailable mid host {- mjid -} req =
+    [ EventBeginElement "{jabber:client}iq"
+        (consid mid [attr "type" "error"
+                    ,attr "from" host])
+    , EventBeginElement req []
+    , EventEndElement req
+    , EventBeginElement "{jabber:client}error"
+        [ attr "type" "cancel"
+        , attr "code" "503" ]
+    , EventBeginElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable" []
+    , EventEndElement "{urn:ietf:params:xml:ns:xmpp-stanzas}service-unavailable"
+    , EventEndElement "{jabber:client}error"
+    , EventEndElement "{jabber:client}iq"
+    ]
+
+
+wrapStanzaList :: [XML.Event] -> STM [Either (StanzaWrap XML.Event) XML.Event]
+wrapStanzaList xs = do
+    wrap <- do
+        clsrs <- newTVar Nothing
+        donev <- newTMVar ()
+        return $ \ x ->
+            Stanza { stanzaType = Unrecognized
+                   , stanzaId = mid
+                   , stanzaTo = mto
+                   , stanzaFrom = mfrom
+                   , stanzaClosers = clsrs
+                   , stanzaInterrupt = donev
+                   , stanzaOrigin = LocalPeer
+                   , stanzaChan = x
+                   }
+    return $ map (Left . wrap) (take 1 xs) ++ map Right (drop 1 xs)
+  where
+    m = listToMaybe xs
+    mto = m >>= lookupAttrib "to" . tagAttrs
+    mfrom = m >>= lookupAttrib "from" . tagAttrs
+    mid = m >>= lookupAttrib "id" . tagAttrs
+
+wrapStanzaConduit :: Monad m => StanzaWrap a -> ConduitM Event (Either (StanzaWrap Event) Event) m ()
+wrapStanzaConduit stanza = do
+    mfirst <- await
+    flip (maybe $ return ()) mfirst $ \first -> do
+    yield . Left $ stanza { stanzaChan = first }
+    awaitForever $ yield . Right
+
+
+
+{-
+greet namespace =
+    [ EventBeginDocument
+    , EventBeginElement (streamP "stream")
+        [ attr "xmlns"   namespace
+        , attr "version" "1.0"
+        ]
+    ]
+-}
+
+goodbye :: [XML.Event]
+goodbye =
+    [ EventEndElement (streamP "stream")
+    , EventEndDocument
+    ]
+
+simulateChatError :: StanzaError -> Maybe Text -> [Event]
+simulateChatError err mfrom =
+    [ EventBeginElement "{jabber:client}message"
+         ((maybe id (\t->(attr "from" t:)) mfrom)
+           [attr "type" "normal" ])
+    , EventBeginElement "{jabber:client}body" []
+    , EventContent $ ContentText ("/me " <> errorText err)
+    , EventEndElement "{jabber:client}body"
+    , EventBeginElement "{http://jabber.org/protocol/xhtml-im}html" []
+      , EventBeginElement "{http://www.w3.org/1999/xhtml}body" []
+        , EventBeginElement "{http://www.w3.org/1999/xhtml}p"
+             [ attr "style" "font-weight:bold; color:red"
+             ]
+        , EventContent $ ContentText ("/me " <> errorText err)
+        , EventEndElement "{http://www.w3.org/1999/xhtml}p"
+      , EventEndElement "{http://www.w3.org/1999/xhtml}body"
+    , EventEndElement "{http://jabber.org/protocol/xhtml-im}html"
+    , EventEndElement "{jabber:client}message"
+    ]
+
+
+presenceSolicitation :: Text -> Text -> IO Stanza
+presenceSolicitation = presenceStanza (PresenceRequestSubscription True) "subscribe"
+
+presenceProbe :: Text -> Text -> IO Stanza
+presenceProbe = presenceStanza PresenceRequestStatus "probe"
+
+presenceStanza :: StanzaType -> Text -> Text -> Text -> IO Stanza
+presenceStanza stanza_type type_attr me jid =
+    stanzaFromList stanza_type
+        [ EventBeginElement "{jabber:server}presence"
+                [ attr "to" jid
+                , attr "from" me
+                , attr "type" type_attr
+                ]
+        , EventEndElement "{jabber:server}presence" ]
+
+slotsToSource ::
+    Slotted.UpdateStream XMPPState (Either (StanzaWrap XML.Event) XML.Event)
+    -> TVar Int
+    -> TVar (Maybe (StanzaWrap XML.Event))
+    -> TVar Bool
+    -> TMVar ()
+    -> Source IO (Flush XML.Event)
+slotsToSource slots nesting lastStanza needsFlush rdone =
+    fix $ \slot_src -> join . lift . atomically $ foldr1 orElse
+                [Slotted.pull slots >>= \x -> do
+                    x <- case x of
+                            Left wrapped -> do
+                                writeTVar nesting 1
+                                writeTVar lastStanza (Just wrapped)
+                                return $ stanzaChan wrapped
+                            Right x      -> do
+                                when (isEventBeginElement x)
+                                    $ modifyTVar' nesting (+1)
+                                when (isEventEndElement x) $ do
+                                    n <- readTVar nesting
+                                    when (n==1) $ writeTVar lastStanza Nothing
+                                    modifyTVar' nesting (subtract 1)
+                                return x
+                    writeTVar needsFlush True
+                    return $ do
+                    -- liftIO $ wlog $ "yielding Chunk: " ++ show x
+                    yield (Chunk x)
+                    slot_src
+                ,do Slotted.isEmpty slots >>= check
+                    readTVar needsFlush >>= check
+                    writeTVar needsFlush False
+                    return $ do
+                    -- liftIO $ wlog "yielding Flush"
+                    yield Flush
+                    slot_src
+                ,readTMVar rdone >> return (return ())
+                ]
+
+forkConnection :: Server ConnectionKey SockAddr ReleaseKey XML.Event
+                -> XMPPServerParameters
+                -> ConnectionKey
+                -> SockAddr
+                -> FlagCommand
+                -> Source IO XML.Event
+                -> Sink (Flush XML.Event) IO ()
+                -> TChan Stanza
+                ->  IO (TChan Stanza)
+forkConnection sv xmpp k laddr pingflag src snk stanzas = do
+    let (namespace,tellmyname) = case k of
+                        ClientKey {} -> ("jabber:client", xmppTellMyNameToClient xmpp)
+                        PeerKey {} -> ("jabber:server",xmppTellMyNameToPeer xmpp laddr)
+    me <- tellmyname
+    rdone <- atomically newEmptyTMVar
+    let isStarter (Left _) = True
+        isStarter (Right e) | isEventBeginElement e = True
+        isStarter _ = False
+        isStopper (Left _) = False
+        isStopper (Right e) | isEventEndElement e = True
+        isStopper _ = False
+    slots <- atomically $ Slotted.new isStarter isStopper
+    needsFlush <- atomically $ newTVar False
+    lastStanza <- atomically $ newTVar Nothing
+    nesting <- atomically $ newTVar 0
+    let _ = slots :: Slotted.UpdateStream XMPPState (Either (StanzaWrap XML.Event) XML.Event)
+    let greet_src = do
+            CL.sourceList (greet' namespace me) =$= CL.map Chunk
+            yield Flush
+        slot_src = slotsToSource slots nesting lastStanza needsFlush rdone
+    forkIO $ do myThreadId >>= flip labelThread ("post-queue."++show k)
+                (greet_src >> slot_src) $$ snk
+                last <- atomically $ readTVar lastStanza
+                es <- while (atomically . fmap not $ Slotted.isEmpty slots)
+                            (atomically . Slotted.pull $ slots)
+                let es' = mapMaybe metadata es
+                    metadata (Left s) = Just s
+                    metadata _        = Nothing
+                -- TODO: Issuing RecipientUnavailable for all errors is a presence leak
+                --          and protocol violation
+                -- TODO: IDMangler can be used for better targetted error delivery.
+                let fail stanza = do
+                            wlog $ "failed delivery: " ++ show (stanzaId stanza)
+                            quitVar <- atomically newEmptyTMVar
+                            reply <- makeErrorStanza stanza
+                            tag <- stanzaFirstTag stanza
+                            -- sendReply quitVar (Error RecipientUnavailable tag) reply replyto
+                            replystanza <- stanzaFromList (Error RecipientUnavailable tag) reply
+                            xmppDeliverMessage xmpp (wlog $ "discarded error delivery fail") replystanza
+                    notError s = case stanzaType s of
+                                    Error {} -> False
+                                    _ -> True
+                -- TODO: Probably some stanzas should be queued or saved for re-connect.
+                mapM_ fail $ filter notError (maybeToList last ++ es')
+                wlog $ "end post-queue fork: " ++ show k
+
+    output <- atomically newTChan
+    hacks <- atomically $ newTVar Map.empty
+    msgids <- atomically $ newTVar []
+    forkIO $ do
+        -- mapM_ (atomically . Slotted.push slots Nothing) greetPeer
+        myThreadId >>= flip labelThread ("pre-queue."++show k)
+        verbosity <- xmppVerbosity xmpp
+        fix $ \loop -> do
+            what <- atomically $ foldr1 orElse
+                [readTChan output >>= \stanza -> return $ do
+                    let notping f
+                            | (verbosity==1) = case stanzaType stanza of Pong -> return ()
+                                                                         _ -> f
+                            | (verbosity>=2) = f
+                            | otherwise      = return ()
+                    -- isempty <- atomically $ isEmptyTChan (stanzaChan stanza)
+                    -- kwlog $ "queuing: "++show (isempty, stanzaId stanza)
+                    notping $ do
+                        dup <- cloneStanza stanza
+                        let typ = Strict8.pack $ c ++ "<-"++(concat . take 1 . words $ show (stanzaType dup))++" "
+                            c = case k of
+                                    ClientKey {} -> "C"
+                                    PeerKey {}   -> "P"
+                        wlog ""
+                        stanzaToConduit dup $$ prettyPrint typ
+                    -- wlog $ "hacks: "++show (stanzaId stanza)
+                    case stanzaType stanza of
+                        InternalEnableHack hack -> do
+                            -- wlog $ "enable hack: " ++ show hack
+                            atomically $ modifyTVar' hacks (Map.insert hack ())
+                        InternalCacheId x -> do
+                            -- wlog $ "cache id thread: " ++ show x
+                            atomically $ modifyTVar' msgids (take 3 . (x:))
+                        _ -> return ()
+                    stanzaToConduit stanza =$= wrapStanzaConduit stanza
+                        $$ awaitForever
+                            -- TODO: PresenceStatus stanzas should be pushed to appropriate slots
+                            $ liftIO . atomically . Slotted.push slots Nothing
+                    case stanzaType stanza of
+                        Error err tag | tagName tag=="{jabber:client}message" -> do
+                            wlog $ "handling Error hacks"
+                            b <- atomically $ do m <- readTVar hacks
+                                                 cached <- readTVar msgids
+                                                 flip (maybe $ return False) (stanzaId stanza) $ \id' -> do
+                                                 return $ Map.member SimulatedChatErrors m
+                                                            && elem id' cached
+                            ids <- atomically $ readTVar msgids
+                            wlog $ "ids = " ++ show (b,stanzaId stanza, ids)
+                            when b $ do
+                            let sim = simulateChatError err (stanzaFrom stanza)
+                            wlog $ "sending simulated chat for error message."
+                            CL.sourceList sim =$= wrapStanzaConduit stanza -- not quite right, but whatever
+                                $$ awaitForever
+                                    $ liftIO . atomically . Slotted.push slots Nothing
+                        Error e _ -> do
+                            wlog $ "no hacks for error: " ++ show e
+                        _ -> return ()
+                    loop
+                ,do pingflag >>= check
+                    return $ do
+                    to <- xmppTellPeerHisName xmpp k -- addrToText (callBackAddress k)
+                    let from = me -- Look it up from Server object
+                                  -- or pass it with Connection event.
+                        mid = Just "ping"
+                        ping0 = makePing namespace mid to from
+                    ping <- atomically $ wrapStanzaList ping0
+                    mapM_ (atomically . Slotted.push slots (Just $ PingSlot))
+                          ping
+#ifdef PINGNOISE
+                    wlog ""
+                    CL.sourceList ping0 $$ prettyPrint $ case k of
+                        ClientKey {} -> "C<-Ping"
+                        PeerKey {} -> "P<-Ping "
+#endif
+                    loop
+                ,readTMVar rdone >> return (return ())
+                ]
+            what
+        wlog $ "end pre-queue fork: " ++ show k
+    forkIO $ do
+        myThreadId >>= flip labelThread ("reader."++show k)
+        -- src $$ awaitForever (lift . putStrLn . takeWhile (/=' ') . show)
+        src $$ xmppInbound sv xmpp k laddr pingflag stanzas output rdone
+        atomically $ putTMVar rdone ()
+        wlog $ "end reader fork: " ++ show k
+    return output
+
+{-
+data Peer = Peer
+    { peerWanted :: TVar Bool -- ^ False when this peer is on a you-call-me basis
+    , peerState :: TVar PeerState
+    }
+data PeerState
+    = PeerPendingConnect UTCTime
+    | PeerPendingAccept UTCTime
+    | PeerConnected (TChan Stanza)
+-}
+
+peerKey :: SocketLike sock => sock -> IO (ConnectionKey,SockAddr)
+peerKey sock = do
+    addr <- getSocketName sock
+    peer <-
+      sIsConnected sock >>= \c ->
+        if c then getPeerName sock -- addr is normally socketName
+             else return addr      -- Weird hack: addr is would-be peer name
+    laddr <- getSocketName sock
+    return $ (PeerKey (peer `withPort` fromIntegral peerport),laddr)
+
+clientKey :: SocketLike sock => sock -> IO (ConnectionKey,SockAddr)
+clientKey sock = do
+    addr <- getSocketName sock
+    paddr <- getPeerName sock
+    return $ (ClientKey addr,paddr)
+
+xmlifyRosterItems :: Monad m => Set Text -> Text -> Set Text -> ConduitM i Event m ()
+xmlifyRosterItems solicited stype set = mapM_ item (Set.toList set)
+ where
+  item jid = do yield $ EventBeginElement "{jabber:iq:roster}item"
+                        ([ attr "jid" jid
+                         , attr "subscription" stype
+                         ]++if Set.member jid solicited
+                             then [attr "ask" "subscribe"]
+                             else [] )
+                yield $ EventEndElement "{jabber:iq:roster}item"
+
+sendRoster ::
+    StanzaWrap a
+    -> XMPPServerParameters
+    -> TChan Stanza
+    -> IO ()
+sendRoster query xmpp replyto = do
+    let k = case stanzaOrigin query of
+             NetworkOrigin k _ -> Just k
+             LocalPeer -> Nothing -- local peer requested roster?
+    flip (maybe $ return ()) k $ \k -> do
+    hostname <- xmppTellMyNameToClient xmpp
+    let getlist f = do
+            bs <- f xmpp k
+            return (Set.fromList bs) -- js)
+    buddies     <- getlist xmppRosterBuddies
+    subscribers <- getlist xmppRosterSubscribers
+    solicited   <- getlist xmppRosterSolicited
+    subnone0    <- getlist xmppRosterOthers
+    jid <- case k of
+                ClientKey {} -> xmppTellClientHisName xmpp k -- LookupClientJID xmpp k
+                PeerKey {}   -> xmppTellClientNameOfPeer xmpp k (Set.toList buddies)
+    let subnone = Set.union solicited subnone0 \\ Set.union buddies subscribers
+    let subto = buddies \\ subscribers
+    let subfrom = subscribers \\ buddies
+    let subboth = Set.intersection buddies subscribers
+    let roster = do
+            yield $ EventBeginElement "{jabber:client}iq"
+                        (consid (stanzaId query)
+                            [ attr "to" jid
+                            , attr "type" "result" ])
+            yield $ EventBeginElement "{jabber:iq:roster}query" [] -- todo: ver?
+            xmlifyRosterItems solicited "to" subto
+            xmlifyRosterItems solicited "from" subfrom
+            xmlifyRosterItems solicited "both" subboth
+            xmlifyRosterItems solicited "none" subnone
+            yield $ EventEndElement "{jabber:iq:roster}query"
+            yield $ EventEndElement "{jabber:client}iq"
+
+    conduitToStanza Roster
+                    (stanzaId query)
+                    Nothing
+                    (Just jid)
+                    roster >>= ioWriteChan replyto
+    {-
+    let debugpresence =
+                [ EventBeginElement "{jabber:client}presence"
+                    [ attr "from" "guest@oxio4inifatsetlx.onion"
+                    , attr "to" jid]
+                , EventEndElement "{jabber:client}presence"
+                ]
+    quitvar <- atomically newEmptyTMVar
+    sendReply quitvar Unrecognized debugpresence replyto
+    -}
+
+
+socketFromKey :: Server ConnectionKey SockAddr ReleaseKey XML.Event -> ConnectionKey -> IO SockAddr
+socketFromKey sv k = do
+    map <- atomically $ readTVar (conmap sv)
+    let mcd = Map.lookup k map
+    case mcd of
+        Nothing -> case k of
+                    ClientKey addr -> return addr
+                    PeerKey addr -> return addr
+                        -- XXX: ? wrong address
+                        -- Shouldnt happen anyway.
+        Just cd -> return $ cdata cd
+
+class StanzaFirstTag a where
+    stanzaFirstTag :: StanzaWrap a -> IO XML.Event
+instance StanzaFirstTag (TChan XML.Event) where
+    stanzaFirstTag stanza = do
+        e <-atomically $ peekTChan (stanzaChan stanza)
+        return e
+instance StanzaFirstTag (LockedChan XML.Event) where
+    stanzaFirstTag stanza = do
+        e <-atomically $ peekLChan (stanzaChan stanza)
+        return e
+instance StanzaFirstTag XML.Event where
+    stanzaFirstTag stanza = return (stanzaChan stanza)
+
+data StanzaError
+    = BadRequest
+    | Conflict
+    | FeatureNotImplemented
+    | Forbidden
+    | Gone
+    | InternalServerError
+    | ItemNotFound
+    | JidMalformed
+    | NotAcceptable
+    | NotAllowed
+    | NotAuthorized
+    | PaymentRequired
+    | RecipientUnavailable
+    | Redirect
+    | RegistrationRequired
+    | RemoteServerNotFound
+    | RemoteServerTimeout
+    | ResourceConstraint
+    | ServiceUnavailable
+    | SubscriptionRequired
+    | UndefinedCondition
+    | UnexpectedRequest
+ deriving (Show,Enum,Ord,Eq)
+
+xep0086 ::
+    forall t t1. (Num t1, IsString t) => StanzaError -> (t, t1)
+xep0086 e =
+  case e of
+    BadRequest            -> ("modify", 400)
+    Conflict              -> ("cancel", 409)
+    FeatureNotImplemented -> ("cancel", 501)
+    Forbidden             -> ("auth", 403)
+    Gone                  -> ("modify", 302)
+    InternalServerError   -> ("wait", 500)
+    ItemNotFound          -> ("cancel", 404)
+    JidMalformed          -> ("modify", 400)
+    NotAcceptable         -> ("modify", 406)
+    NotAllowed            -> ("cancel", 405)
+    NotAuthorized         -> ("auth", 401)
+    PaymentRequired       -> ("auth", 402)
+    RecipientUnavailable  -> ("wait", 404)
+    Redirect              -> ("modify", 302)
+    RegistrationRequired  -> ("auth", 407)
+    RemoteServerNotFound  -> ("cancel", 404)
+    RemoteServerTimeout   -> ("wait", 504)
+    ResourceConstraint    -> ("wait", 500)
+    ServiceUnavailable    -> ("cancel", 503)
+    SubscriptionRequired  -> ("auth", 407)
+    UndefinedCondition    -> ("", 500)
+    UnexpectedRequest     -> ("wait", 400)
+
+errorText :: StanzaError -> Text
+errorText e =
+ case e of
+    BadRequest            -> "Bad request"
+    Conflict              -> "Conflict"
+    FeatureNotImplemented -> "This feature is not implemented"
+    Forbidden             -> "Forbidden"
+    Gone                  -> "Recipient can no longer be contacted"
+    InternalServerError   -> "Internal server error"
+    ItemNotFound          -> "Item not found"
+    JidMalformed          -> "JID Malformed"
+    NotAcceptable         -> "Message was rejected"
+    NotAllowed            -> "Not allowed"
+    NotAuthorized         -> "Not authorized"
+    PaymentRequired       -> "Payment is required"
+    RecipientUnavailable  -> "Recipient is unavailable"
+    Redirect              -> "Redirect"
+    RegistrationRequired  -> "Registration required"
+    RemoteServerNotFound  -> "Recipient's server not found"
+    RemoteServerTimeout   -> "Remote server timeout"
+    ResourceConstraint    -> "The server is low on resources"
+    ServiceUnavailable    -> "The service is unavailable"
+    SubscriptionRequired  -> "A subscription is required"
+    UndefinedCondition    -> "Undefined condition"
+    UnexpectedRequest     -> "Unexpected request"
+
+eventContent :: Maybe [Content] -> Text
+eventContent cs = maybe "" (foldr1 (<>) . map content1) cs
+            where content1 (ContentText t)   = t
+                  content1 (ContentEntity t) = t
+
+errorTagLocalName :: forall a. Show a => a -> Text
+errorTagLocalName e = Text.pack . drop 1 $ do
+    c <- show e
+    if 'A' <= c && c <= 'Z'
+    then [ '-', chr( ord c - ord 'A' + ord 'a') ]
+    else return c
+
+makeErrorStanza :: StanzaFirstTag a => StanzaWrap a -> IO [XML.Event]
+makeErrorStanza stanza = do
+    startTag <- stanzaFirstTag stanza
+    let n = tagName startTag
+        endTag = EventEndElement n
+        amap0 = Map.fromList (tagAttrs startTag)
+        mto   = Map.lookup "to" amap0
+        mfrom = Map.lookup "from" amap0
+        mtype = Map.lookup "type" amap0
+        mid = Map.lookup "id" amap0
+        amap1 = Map.alter (const mto) "from" amap0
+        -- amap2 = Map.alter (const $ Just $ [ContentText "blackbird"]) {-mfrom)-} "to" amap1
+        amap2 = Map.alter (const mfrom) "to" amap1
+        amap3 = Map.insert "type" [XML.ContentText "error"] amap2
+        startTag' = EventBeginElement
+                        (tagName startTag)
+                        (Map.toList amap3)
+        -- err = Gone -- FeatureNotImplemented -- UndefinedCondition -- RecipientUnavailable
+        err = RecipientUnavailable
+        errname = n { nameLocalName = "error" }
+        -- errattrs = [attr "type" "wait"] --  "modify"]
+        errorAttribs e xs = ys ++ xs -- todo replace instead of append
+            where (typ,code) = xep0086 e
+                  ys = [attr "type" typ, attr "code" (Text.pack . show $ code)]
+        errorTagName = Name { nameNamespace = Just "urn:ietf:params:xml:ns:xmpp-stanzas"
+                            , nameLocalName = errorTagLocalName err
+                            , namePrefix = Nothing }
+        errattrs = errorAttribs err []
+    let wlogd v s = do
+            wlog $ "error "++show (lookupAttrib "id" $ tagAttrs startTag)++" " ++ v ++ " = " ++ show s
+    {-
+    wlogd "amap0" amap0
+    wlogd "mto" mto
+    wlogd "mfrom" mfrom
+    wlogd "amap3" amap3
+    -}
+    if eventContent mtype=="error" then return [] else do
+    return [ startTag'
+           , EventBeginElement errname errattrs
+           , EventBeginElement errorTagName []
+           , EventEndElement errorTagName
+           , EventEndElement errname
+            {-
+           , EventBeginElement "{jabber:client}body" []
+           , EventContent (ContentText "what?")
+           , EventEndElement "{jabber:client}body"
+            -}
+           {-
+           , EventBeginElement "{154ae29f-98f2-4af4-826d-a40c8a188574}dummy" []
+           , EventEndElement "{154ae29f-98f2-4af4-826d-a40c8a188574}dummy"
+           -}
+           , endTag
+           ]
+
+monitor ::
+    Server ConnectionKey SockAddr ReleaseKey XML.Event
+    -> ConnectionParameters ConnectionKey SockAddr
+    -> XMPPServerParameters
+    -> IO b
+monitor sv params xmpp = do
+    chan <- return $ serverEvent sv
+    stanzas <- atomically newTChan
+    quitVar <- atomically newEmptyTMVar
+    fix $ \loop -> do
+    action <- atomically $ foldr1 orElse
+      [ readTChan chan >>= \((k,u),e) -> return $ do
+        case e of
+            Connection pingflag xsrc xsnk -> do
+                wlog $ tomsg k "Connection"
+                outs <- forkConnection sv xmpp k u pingflag xsrc xsnk stanzas
+                xmppNewConnection xmpp k u outs
+            ConnectFailure addr -> return () -- wlog $ tomsg k "ConnectFailure"
+            EOF        -> do wlog $ tomsg k "EOF"
+                             xmppEOF xmpp k
+            HalfConnection In -> do
+                wlog $ tomsg k "ReadOnly"
+                control sv (Connect (callBackAddress k) params)
+            HalfConnection Out -> wlog $ tomsg k "WriteOnly"
+            RequiresPing -> return () -- wlog $ tomsg k "RequiresPing"
+      , readTChan stanzas >>= \stanza -> return $ do
+        {-
+        dup <- case stanzaType stanza of
+                -- Must dup anything that is going to be delivered...
+                Message {} -> do
+                    dup <- cloneStanza stanza -- dupped so we can make debug print
+                    return dup
+                Error {} -> do
+                    dup <- cloneStanza stanza -- dupped so we can make debug print
+                    return dup
+                _ -> return stanza
+        -}
+        dup <- cloneStanza stanza
+
+        forkIO $ do
+            case stanzaOrigin stanza of
+                NetworkOrigin k@(ClientKey {}) replyto ->
+                    case stanzaType stanza of
+                        RequestResource wanted -> do
+                            sockaddr <- socketFromKey sv k
+                            rsc <- xmppChooseResourceName xmpp k sockaddr wanted
+                            let reply = iq_bind_reply (stanzaId stanza) rsc
+                            -- sendReply quitVar SetResource reply replyto
+                            hostname <- xmppTellMyNameToClient xmpp
+                            let requestVersion :: Producer IO XML.Event
+                                requestVersion = do
+                                  yield $ EventBeginElement "{jabber:client}iq"
+                                              [ attr "to" rsc
+                                              , attr "from" hostname
+                                              , attr "type" "get"
+                                              , attr "id" "version"]
+                                  yield $ EventBeginElement "{jabber:iq:version}query" []
+                                  yield $ EventEndElement "{jabber:iq:version}query"
+                                  yield $ EventEndElement "{jabber:client}iq"
+                                  {-
+                                  -- XXX Debug chat:
+                                  yield $ EventBeginElement "{jabber:client}message"
+                                          [ attr "from" $ eventContent (Just [ContentText rsc])
+                                          , attr "type" "normal" ] -- "blackbird" ]
+                                  yield $ EventBeginElement "{jabber:client}body" []
+                                  yield $ EventContent $ ContentText ("hello?")
+                                  yield $ EventEndElement "{jabber:client}body"
+                                  yield $ EventEndElement "{jabber:client}message"
+                                  -}
+                            sendReply quitVar SetResource reply replyto
+                            conduitToStanza (UnrecognizedQuery "{jabber:iq:version}query")
+                                  Nothing -- id
+                                  (Just hostname) -- from
+                                  (Just rsc) -- to
+                                  requestVersion
+                              >>= ioWriteChan replyto
+                        SessionRequest -> do
+                            me <- xmppTellMyNameToClient xmpp
+                            let reply = iq_session_reply (stanzaId stanza) me
+                            sendReply quitVar Pong reply replyto
+                        RequestRoster -> do
+                            sendRoster stanza xmpp replyto
+                            xmppSubscribeToRoster xmpp k
+                        PresenceStatus {} -> do
+                            xmppInformClientPresence xmpp k stanza
+                        PresenceRequestSubscription {} -> do
+                            let fail = return () -- todo
+                            xmppClientSubscriptionRequest xmpp fail k stanza replyto
+                        PresenceInformSubscription {} -> do
+                            let fail = return () -- todo
+                            xmppClientInformSubscription xmpp fail k stanza
+                        NotifyClientVersion name version -> do
+                            enableClientHacks name version replyto
+                        UnrecognizedQuery query -> do
+                            me <- xmppTellMyNameToClient xmpp
+                            let reply = iq_service_unavailable (stanzaId stanza) me query
+                            sendReply quitVar (Error ServiceUnavailable (head reply)) reply replyto
+                        Message {} -> do
+                            -- wlog $ "LANGMAP "++show (stanzaId stanza, msgLangMap (stanzaType stanza))
+                            maybe (return ()) (flip cacheMessageId replyto) $ do
+                                guard . not . null . mapMaybe (msgBody . snd) $ msgLangMap (stanzaType stanza)
+                                stanzaId stanza
+                        _ -> return ()
+                NetworkOrigin k@(PeerKey {}) replyto ->
+                    case stanzaType stanza of
+                        PresenceRequestStatus {} -> do
+                            xmppAnswerProbe xmpp k stanza replyto
+                        PresenceStatus {} -> do
+                            xmppInformPeerPresence xmpp k stanza
+                        PresenceRequestSubscription {} -> do
+                            let fail = return () -- todo
+                            xmppPeerSubscriptionRequest xmpp fail k stanza replyto
+                        PresenceInformSubscription {} -> do
+                            let fail = return () -- todo
+                            xmppPeerInformSubscription xmpp fail k stanza
+                        _ -> return ()
+                _ -> return ()
+            let deliver replyto = do
+                    -- TODO: Issuing RecipientUnavailable for all errors is a presence leak
+                    --          and protocol violation
+                    let fail = do
+                            wlog $ "Failed delivery id="++show (stanzaId stanza) -- TODO
+                            reply <- makeErrorStanza stanza
+                            tag <- stanzaFirstTag stanza
+                            sendReply quitVar (Error RecipientUnavailable tag) reply replyto
+                    xmppDeliverMessage xmpp fail stanza
+                    -- -- bad idea:
+                    -- let newStream = greet'' "jabber:client" "blackbird"
+                    -- sendReply quitVar Error newStream replyto
+            case stanzaType stanza of
+                Message {} -> do
+                  case stanzaOrigin stanza of
+                    LocalPeer {} -> return ()
+                    NetworkOrigin _ replyto -> deliver replyto
+                Error {} -> do
+                  case stanzaOrigin stanza of
+                    LocalPeer {} -> return ()
+                    NetworkOrigin k replyto -> do
+                         -- wlog $ "delivering error: " ++show (stanzaId stanza)
+                         -- wlog $ " from: " ++ show k
+                         deliver replyto
+                _ -> return ()
+        -- We need to clone in the case the stanza is passed on as for Message.
+        verbosity <- xmppVerbosity xmpp
+        let notping f | (verbosity==1) = case stanzaType stanza of Pong -> return ()
+                                                                   _    -> f
+                      | (verbosity>=2) = f
+                      | otherwise      = return ()
+        notping $ do
+        let typ = Strict8.pack $ c ++ "->"++(concat . take 1 . words $ show (stanzaType stanza))++" "
+            c = case stanzaOrigin stanza of
+                    LocalPeer -> "*"
+                    NetworkOrigin (ClientKey {}) _ -> "C"
+                    NetworkOrigin (PeerKey {})   _ -> "P"
+        wlog ""
+        stanzaToConduit dup $$ prettyPrint typ
+
+      ]
+    action
+    loop
+ where
+    tomsg k str =  printf "%12s %s" str (show k)
+        where
+            _ = str :: String
+
+data XMPPServer
+    = XMPPServer { _xmpp_sv :: Server ConnectionKey SockAddr ReleaseKey XML.Event
+                 , _xmpp_peer_params :: ConnectionParameters ConnectionKey SockAddr
+                 }
+
+grokPeer :: XMPPServer -> ConnectionKey -> (SockAddr, ConnectionParameters ConnectionKey SockAddr, Miliseconds)
+grokPeer sv (PeerKey addr) = (addr, _xmpp_peer_params sv, 10000)
+
+xmppConnections :: XMPPServer -> IO (Connection.Manager TCPStatus Text)
+xmppConnections sv = tcpManager (grokPeer sv) (Just . Text.pack) resolvPeer (_xmpp_sv sv)
+ where
+    resolvPeer :: Text -> IO (Maybe ConnectionKey)
+    resolvPeer str = fmap PeerKey <$> listToMaybe <$> resolvePeer str
+
+xmppServer :: ( MonadResource m
+              , MonadIO m
+              ) => XMPPServerParameters -> m XMPPServer
+xmppServer xmpp = do
+    sv <- server allocate xmlStream
+    -- some fuzz helps avoid simultaneity
+    pingfuzz <- liftIO $ do
+        gen <- System.Random.getStdGen
+        let (r,gen') = System.Random.next gen
+        return $ r `mod` 2000 -- maximum 2 seconds of fuzz
+    liftIO . wlog $ "pingfuzz = " ++ show pingfuzz
+    let peer_params = (connectionDefaults peerKey)
+                          { pingInterval = 15000 + pingfuzz
+                          , timeout = 2000
+                          , duplex = False }
+        client_params = (connectionDefaults clientKey)
+                          { pingInterval = 0
+                          , timeout = 0
+                          }
+    liftIO $ do
+        forkIO $ do
+            myThreadId >>= flip labelThread ("XMPP.monitor")
+            monitor sv peer_params xmpp
+        hPutStrLn stderr $ "Starting peer listen"
+        control sv (Listen peerport peer_params)
+        hPutStrLn stderr $ "Starting client listen"
+        control sv (Listen clientport client_params)
+    return XMPPServer { _xmpp_sv = sv, _xmpp_peer_params = peer_params }
+
+#if MIN_VERSION_stm(2,4,0)
+#else
+-- |Clone a 'TChan': similar to dupTChan, but the cloned channel starts with the
+-- same content available as the original channel.
+--
+-- Terrible inefficient implementation provided to build against older libraries.
+cloneTChan :: TChan a -> STM (TChan a)
+cloneTChan chan = do
+    contents <- chanContents' chan
+    chan2 <- dupTChan chan
+    mapM_ (writeTChan chan) contents
+    return chan2
+ where
+    chanContents' chan = do
+        b <- isEmptyTChan chan
+        if b then return [] else do
+        x <- readTChan chan
+        xs <- chanContents' chan
+        return (x:xs)
+#endif
+
diff --git a/Presence/monitortty.c b/Presence/monitortty.c
new file mode 100644
index 00000000..7582aa56
--- /dev/null
+++ b/Presence/monitortty.c
@@ -0,0 +1,182 @@
+// monitortty.c
+
+#include <unistd.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+#include <linux/vt.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <linux/kd.h>
+#include <stdlib.h>
+
+static char *conspath[] = {
+        "/proc/self/fd/0",
+        "/dev/tty",
+        "/dev/tty0",
+        "/dev/vc/0",
+        "/dev/systty",
+        "/dev/console",
+        NULL
+};
+
+static int
+is_a_console(int fd) {
+        char arg;
+
+        arg = 0;
+        return (isatty (fd)
+                && ioctl(fd, KDGKBTYPE, &arg) == 0
+                && ((arg == KB_101) || (arg == KB_84)));
+}
+
+static int
+open_a_console(const char *fnam) {
+        int fd;
+
+        /*
+         * For ioctl purposes we only need some fd and permissions
+         * do not matter. But setfont:activatemap() does a write.
+         */
+        fd = open(fnam, O_RDWR);
+        if (fd < 0)
+                fd = open(fnam, O_WRONLY);
+        if (fd < 0)
+                fd = open(fnam, O_RDONLY);
+        if (fd < 0)
+                return -1;
+        return fd;
+}
+
+int ttyfd() {
+        // We try several things because opening /dev/console will fail
+        // if someone else used X (which does a chown on /dev/console).
+        int i;
+        int fd;
+        for (i = 0; conspath[i]; i++) {
+                if ((fd = open_a_console(conspath[i])) >= 0) {
+                        if (is_a_console(fd)) {
+                                printf("using %s\n",conspath[i]);
+                                return fd;
+                        }
+                        close(fd);
+                }
+        }
+        for (fd = 0; fd < 3; fd++)
+                if (is_a_console(fd))
+                        return fd;
+        printf("failed to find console fd\n");
+        return -1;
+}
+
+void vt_wait(int tty_fd) {
+        struct vt_event vt;
+        memset(&vt,'\0',sizeof(vt));
+        vt.event = VT_EVENT_SWITCH;
+        int res;
+        // printf("started wait\n");
+        res = ioctl (tty_fd, VT_WAITEVENT, &vt);
+        if (res==-1) {
+                printf("vt_wait error fd=%i\n",tty_fd);
+                perror("vt_wait");
+                // printf("vt_wait: %u - %s\n", errno, errmsg(errno));
+                sleep(1);
+        }
+        // printf("finished wait\n");
+}
+
+int8_t get_active(int tty_fd) {
+        struct vt_stat vtstat;
+        memset(&vtstat,'\0',sizeof(vtstat));
+        if (ioctl(tty_fd, VT_GETSTATE, &vtstat)) {
+                perror ("get_active: VT_GETSTATE");
+                return 7;
+        }
+        return vtstat.v_active;
+}
+
+void chvt(int tty_fd, int n) {
+        if (ioctl(tty_fd, VT_ACTIVATE, n)) {
+                perror ("chvt: VT_ACTIVATE");
+        }
+
+}
+
+pthread_mutex_t mu;
+pthread_t mt;
+int tty = -1;
+
+void *write_vtch(void *pfd) {
+        int fd = (int)(intptr_t)pfd;
+        printf("started VT_WAITEVENT loop fd=%i\n",fd);
+        pthread_mutex_lock(&mu);
+        tty = ttyfd();
+        pthread_mutex_unlock(&mu);
+        int8_t active_tty = get_active(tty);
+        int8_t reported_tty;
+        ssize_t e;
+
+        pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
+        for (;;) {
+                // ssize_t write(int fd, const void *buf, size_t count);
+                e = write(fd, &active_tty, 1);
+                if (e<0 ) {
+                        if( errno==EAGAIN) continue;
+                        break;
+                }
+                else if(e==1) {
+                        reported_tty = active_tty;
+                }
+                do {
+                        vt_wait(tty);
+                        // printf("vt_wait() finished. tty=%d fd=%d\n",tty,fd);
+                        active_tty = get_active(tty);
+                } while (active_tty==reported_tty);
+        }
+        
+        // TODO:
+        //  use VT_GETSTATE
+        //  use VT_WAITEVENT
+        printf("stopped VT_WAITEVENT loop\n");
+        tty = -1;
+        pthread_mutex_destroy(&mu);
+        return NULL;
+}
+
+
+// Returns 0 on success.
+int monitorTTY(int fd) {
+    int er = -1, dev = -1;
+        pthread_mutex_init(&mu,NULL);
+    // Ensure we can open a device before we bother forking a thread.
+        dev = ttyfd();
+    if( dev != -1 ) {
+        er = pthread_create (&mt, NULL, write_vtch, (void*)(intptr_t)fd);
+        return er;
+    }
+    else {
+        return -1;
+    }
+}
+
+void closeTTY() {
+        int fd = -1;
+        int active = 7;
+        pthread_mutex_lock(&mu);
+        active = get_active(tty);
+        fd = tty;
+        pthread_mutex_unlock(&mu);
+#ifndef VTHACK
+        pthread_cancel(mt);
+#endif
+        char cmd[40]; cmd[39] = '\0';
+        // Hack to wake up from VT_WAITEVENT ioctl
+#ifdef VTHACK
+        snprintf(cmd,39,"chvt %i;chvt %i",active+1,active);
+        system(cmd);
+        pthread_join(mt,NULL);
+#endif
+        close(fd);
+}
diff --git a/Setup.hs b/Setup.hs
index 9a994af6..d07decd4 100644
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,2 +1,96 @@
+import Control.Monad
+import Data.List
 import Distribution.Simple
-main = defaultMain
+import Distribution.Simple.LocalBuildInfo
+import Distribution.Simple.Setup
+import Distribution.Simple.Utils
+import System.Directory
+
+main = defaultMainWithHooks hooks
+
+hooks :: UserHooks
+hooks = simpleUserHooks
+    { buildHook = \pkgDesc localBuildInfo hooks flags -> do
+        let paths = (absoluteInstallDirs pkgDesc localBuildInfo dest)
+                {- libsubdir = "<undef>"
+                , datasubdir = "<undef>"
+                -}
+            dest = maybe NoCopyDest CopyTo $
+                   flagToMaybe $ buildDistPref flags
+        buildSystemDConfig localBuildInfo paths
+        buildHook simpleUserHooks pkgDesc localBuildInfo hooks flags
+    , copyHook = \pkgDesc localBuildInfo hooks flags -> do
+        let paths = (absoluteInstallDirs pkgDesc localBuildInfo (fromFlag $ copyDest flags))
+                {- libsubdir = "<undef>"
+                , datasubdir = "<undef>"
+                -}
+            dest = maybe NoCopyDest CopyTo $
+                   flagToMaybe $ copyDistPref flags
+        copySystemDConfig localBuildInfo paths flags
+        copyHook simpleUserHooks pkgDesc localBuildInfo hooks flags
+    }
+
+-- Drop a /-terminated prefix from a Filepath.  The / is not dropped.
+dropPrefix :: String -> FilePath -> FilePath
+dropPrefix prefix s | prefix `isPrefixOf` s = drop (length prefix - 1) s
+                    | otherwise             = s
+
+exestart :: FilePath -> InstallDirs FilePath -> String -> String
+exestart buildprefix paths cmd
+    | "ExecStart=" `isPrefixOf` cmd  = "ExecStart="++(dropPrefix buildprefix $ bindir paths) ++ "/presence"
+    | otherwise                      = cmd
+
+buildSystemDConfig :: LocalBuildInfo -> InstallDirs FilePath -> IO ()
+buildSystemDConfig buildInfo paths = do
+    template <- lines <$> readFile "presence.service"
+    let buildprefix = takeWhile (/='/') (buildDir buildInfo) ++ "/"
+        service = map (exestart buildprefix paths) template
+    createDirectoryIfMissing True (buildDir buildInfo)
+    writeFile (buildDir buildInfo ++ "/presence.service") $ unlines service
+
+preferredSystemDPath prefix =
+    case removeSlashes prefix of
+        ""    -> "/lib/systemd/system"
+        "usr" -> "/lib/systemd/system"
+        _     -> "/etc/systemd/system"
+
+removeSlashes prefix = reverse $ dropWhile (=='/') $ reverse $ dropWhile (=='/') prefix
+
+-- InstallDirs {prefix = "dest/usr/local"
+-- , bindir = "dest/usr/local/bin"
+-- , libdir = "dest/usr/local/lib/x86_64-linux-ghc-8.0.2/presence-0.0.1-1fqjx0Frxyf1ESoA9cNUiZ"
+-- , libsubdir = "<undef>"
+-- , dynlibdir = "dest/usr/local/lib/x86_64-linux-ghc-8.0.2"
+-- , libexecdir = "dest/usr/local/libexec"
+-- , includedir = "dest/usr/local/lib/x86_64-linux-ghc-8.0.2/presence-0.0.1-1fqjx0Frxyf1ESoA9cNUiZ/include"
+-- , datadir = "dest/usr/local/share/x86_64-linux-ghc-8.0.2/presence-0.0.1"
+-- , datasubdir = "<undef>"
+-- , docdir = "dest/usr/local/share/doc/x86_64-linux-ghc-8.0.2/presence-0.0.1"
+-- , mandir = "dest/usr/local/share/man"
+-- , htmldir = "dest/usr/local/share/doc/x86_64-linux-ghc-8.0.2/presence-0.0.1/html"
+-- , haddockdir = "dest/usr/local/share/doc/x86_64-linux-ghc-8.0.2/presence-0.0.1/html"
+-- , sysconfdir = "dest/usr/local/etc"}
+-- CopyFlags
+-- { copyDest = Flag (CopyTo "dest/")
+-- , copyDistPref = Flag "dist"
+-- , copyVerbosity = Flag Verbose}
+-- realprefix = dest/usr/local
+
+copySystemDConfig :: LocalBuildInfo -> InstallDirs FilePath -> CopyFlags -> IO ()
+copySystemDConfig buildInfo paths flags = do
+    -- print paths
+    -- print flags
+    let verbosity  = fromFlag (copyVerbosity flags)
+        built      = buildDir buildInfo ++ "/presence.service"
+        realprefix = dropPrefix dest (prefix paths)
+        dest       = case fromFlag (copyDest flags) of
+                        NoCopyDest -> ""
+                        CopyTo p   -> p
+        sysddir    = dest ++ drop 1 (preferredSystemDPath realprefix)
+        sysdpath   = sysddir ++ "/presence.service"
+    -- putStrLn $ "realprefix = " ++ realprefix
+    -- putStrLn $ "no slashes = " ++ removeSlashes realprefix
+    -- putStrLn $ "sysdpath   = " ++ sysdpath
+    createDirectoryIfMissing True sysddir
+    installOrdinaryFile verbosity built sysdpath
+
diff --git a/TraversableT.hs b/TraversableT.hs
new file mode 100644
index 00000000..c0e40853
--- /dev/null
+++ b/TraversableT.hs
@@ -0,0 +1,94 @@
+module TraversableT where
+
+import Data.Traversable
+import Control.Monad (join,MonadPlus(..))
+import Control.Monad.Trans.Class (MonadTrans(..))
+import Control.Applicative
+import Data.Foldable (Foldable(foldMap), toList)
+import Data.Maybe (maybeToList)
+
+-- | 
+--
+-- /Note:/ this does not yield a monad unless the argument monad is commutative.
+newtype TraversableT t m a = TraversableT { runTraversableT :: m (t a) }
+
+-- | Map between 'TraversableT' computations.
+--
+-- * @'runTraversableT' ('mapTraversableT' f m) = f ('runTraversableT' m)@
+mapTraversableT :: (m (t a) -> n (t b)) -> TraversableT t m a -> TraversableT t n b
+mapTraversableT f m = TraversableT $ f (runTraversableT m)
+
+
+instance (Functor m, Functor t) => Functor (TraversableT t m) where
+    fmap f = mapTraversableT $ fmap $ fmap f
+
+instance (Foldable f, Foldable t) => Foldable (TraversableT t f) where
+    foldMap f (TraversableT a) = foldMap (foldMap f) a
+
+instance (Traversable f, Traversable t) => Traversable (TraversableT t f) where
+    traverse f (TraversableT a) = TraversableT <$> traverse (traverse f) a
+
+instance (Applicative m,Applicative t) => Applicative (TraversableT t m) where
+    pure a  = TraversableT $ pure (pure a)
+    f <*> v = TraversableT $ (<*>) <$> runTraversableT f <*> runTraversableT v
+
+instance (Applicative m, Alternative t) => Alternative (TraversableT t m) where
+    empty   = TraversableT $ pure empty
+    m <|> n = TraversableT $ (<|>) <$> runTraversableT m <*> runTraversableT n
+
+instance (Monad m, Traversable t, Monad t) => Monad (TraversableT t m) where
+    return = TraversableT . return . return
+    m >>= k  = TraversableT $ do
+        a <- runTraversableT m
+        b <- forM a $ runTraversableT . k
+        return (join b)
+    fail s = TraversableT $ return (fail s)
+
+instance (Monad m, Traversable t, MonadPlus t) => MonadPlus (TraversableT t m) where
+    mzero       = TraversableT $ return mzero
+    m `mplus` n = TraversableT $ do
+        a <- runTraversableT m
+        b <- runTraversableT n
+        return (a `mplus` b)
+
+instance Applicative t => MonadTrans (TraversableT t) where
+    lift m = TraversableT $ do
+        a <- m
+        return (pure a)
+
+liftT :: Monad m => t a -> TraversableT t m a
+liftT = TraversableT . return
+
+liftMT :: m (t a) -> TraversableT t m a
+liftMT = TraversableT
+
+-- | Lift a @callCC@ operation to the new monad.
+liftCallCC :: Applicative t =>
+    ((( (t a) -> m (t b)) -> m (t a)) -> m (t a)) ->
+    ((a -> TraversableT t m b) -> TraversableT t m a) -> TraversableT t m a
+liftCallCC callCC f = TraversableT $
+    callCC $ \c ->
+    runTraversableT (f (\a -> TraversableT $ c (pure a)))
+
+-- | Lift a @catchError@ operation to the new monad.
+liftCatch :: (m (t a) -> (e -> m (t a)) -> m (t a)) ->
+    TraversableT t m a -> (e -> TraversableT t m a) -> TraversableT t m a
+liftCatch catchError m h = TraversableT $ runTraversableT m
+    `catchError` \e -> runTraversableT (h e)
+
+liftMaybe :: Monad m => Maybe a -> TraversableT [] m a
+liftMaybe = liftT . maybeToList
+
+liftIOMaybe :: IO (Maybe a) -> TraversableT [] IO a
+liftIOMaybe = liftMT . fmap maybeToList
+
+handleT :: ( Monad m
+           , Traversable t ) =>
+        (t a -> TraversableT t m a)
+        -> TraversableT t m a
+        -> TraversableT t m a
+handleT catcher body = TraversableT $ do
+    tx <- runTraversableT body
+    if null (toList tx)
+        then runTraversableT $ catcher tx
+        else return tx
diff --git a/b b/b
new file mode 100755
index 00000000..a116163e
--- /dev/null
+++ b/b
@@ -0,0 +1,16 @@
+#!/bin/bash
+args="-fwarn-unused-imports -rtsopts -DRENDERFLUSH"
+
+root=${0%/*}
+cd "$root"
+
+me=${0##*/}
+me=${me%.*}
+ghc                                  \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    $args                            \
+    -o presence                      \
+    Presence/monitortty.c            \
+    Presence/main                    \
+    "$@"
diff --git a/bp b/bp
new file mode 100755
index 00000000..8d3335d4
--- /dev/null
+++ b/bp
@@ -0,0 +1,20 @@
+#!/bin/bash
+args="-rtsopts -hisuf p_hi -osuf p_o -prof -fprof-auto -fprof-auto-exported"
+
+root=${0%/*}
+cd "$root"
+
+me=${0##*/}
+me=${me%.*}
+ghc                                  \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    Data/BitSyntax.hs
+ghc                                  \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    $args                            \
+    -o presence                      \
+    build/b/Presence/monitortty.o    \
+    Presence/main                    \
+    "$@"
diff --git a/consolation.hs b/consolation.hs
new file mode 100644
index 00000000..0c576dfc
--- /dev/null
+++ b/consolation.hs
@@ -0,0 +1,186 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Main where
+
+import Control.Monad
+import Control.Applicative
+import Control.Concurrent
+import Control.Concurrent.STM
+import Data.Monoid
+import Data.Char
+import System.INotify ( initINotify, EventVariety(Modify), addWatch )
+import Data.Word      ( Word8 )
+import Data.Text      ( Text )
+import Data.Map       ( Map )
+import Data.List      ( foldl' )
+import qualified Data.Map as Map
+import qualified Data.Traversable as Traversable
+import qualified Data.Text as Text
+import qualified Data.Text.IO as Text
+import qualified Network.BSD as BSD
+
+import WaitForSignal  ( waitForTermSignal )
+import UTmp           ( users2, utmp_file, UtmpRecord(..), UT_Type(..) )
+import FGConsole      ( monitorTTY )
+
+data ConsoleState = ConsoleState
+    { csActiveTTY :: TVar Word8
+    , csUtmp :: TVar (Map Text (TVar (Maybe UtmpRecord)))
+    }
+
+newConsoleState = atomically $
+    ConsoleState <$> newTVar 0 <*> newTVar Map.empty
+
+
+onLogin cs start = \e -> do
+    us <- UTmp.users2
+    let (m,cruft) =
+            foldl' (\(m,cruft) x ->
+                        case utmpType x of
+                         USER_PROCESS
+                           -> (Map.insert (utmpTty x) x m,cruft)
+                         DEAD_PROCESS | utmpPid x /= 0
+                           -> (m,Map.insert (utmpTty x) x cruft)
+                         _ -> (m,cruft))
+                   (Map.empty,Map.empty)
+                   us
+    forM_ (Map.elems cruft) $ \c -> do
+        putStrLn $ "cruft " ++ show (utmpTty c, utmpPid c,utmpHost c, utmpRemoteAddr c)
+    newborn <- atomically $ do
+        old <- readTVar (csUtmp cs) -- swapTVar (csUtmp cs) m
+        newborn <- flip Traversable.mapM (m Map.\\ old)
+                    $ newTVar . Just
+        updated <- let upd v u = writeTVar v $ Just u
+                   in Traversable.sequence $ Map.intersectionWith upd old m
+        let dead = old Map.\\ m
+        Traversable.mapM (flip writeTVar Nothing) dead
+        writeTVar (csUtmp cs) $ (old `Map.union` newborn) Map.\\ dead
+        return newborn
+    let getActive = do
+            tty <- readTVar $ csActiveTTY cs
+            utmp <- readTVar $ csUtmp cs
+            flip (maybe $ return (tty,Nothing))
+                 (Map.lookup ("tty"<>tshow tty) utmp)
+                $ \tuvar -> do
+            tu <- readTVar tuvar
+            return (tty,tu)
+            
+    forM_ (Map.elems newborn) $ 
+        forkIO . start getActive
+    -- forM_ (Map.elems dead   ) $ putStrLn . ("gone: "++) . show
+
+onTTY outvar cs vtnum = do
+    logit outvar $ "switch: " <> tshow vtnum
+    atomically $ writeTVar (csActiveTTY cs) vtnum
+
+retryWhen var pred = do
+    value <- var
+    if pred value then retry
+                  else return value
+
+tshow x = Text.pack . show $ x
+
+resource :: UtmpRecord -> Text
+resource u =
+    case utmpTty u of
+        s | Text.take 3 s == "tty" -> s
+        s | Text.take 4 s == "pts/" -> "pty" <> Text.drop 4 s <> ":" <> utmpHost u
+        s -> escapeR s <> ":" <> utmpHost u
+ where
+    escapeR s = s
+
+textHostName = fmap Text.pack BSD.getHostName
+
+ujid u = do
+    h <- textHostName
+    return $ utmpUser u <> "@" <> h <> "/" <> resource u
+
+newCon :: (Text -> IO ()) -> STM (Word8,Maybe UtmpRecord) -> TVar (Maybe UtmpRecord) -> IO ()
+newCon log activeTTY utmp = do
+    ((tty,tu),u) <- atomically $
+        liftM2 (,) activeTTY
+                   (readTVar utmp)
+    flip (maybe $ return ()) u $ \u -> do
+    jid <- ujid u
+    log $ status (resource u) tty tu <> " " <> jid <> "  pid=" <> tshow (utmpPid u)
+            <> (if istty (resource u)
+                 then " host=" <> tshow (utmpHost u)
+                 else "")
+            <> " session=" <> tshow (utmpSession u)
+            <> " addr=" <> tshow (utmpRemoteAddr u)
+    loop tty tu (Just u)
+ where
+    bstatus r ttynum mtu
+        =  r == ttystr
+        || match mtu
+        where ttystr = "tty" <> tshow ttynum
+              searchstr mtu = maybe ttystr utmpHost $ do
+                tu <- mtu
+                guard (not $ Text.null $ utmpHost tu)
+                return tu
+              match mtu = searchstr mtu `Text.isInfixOf` Text.dropWhile (/=':') r
+    status r ttynum tu =
+        if bstatus r ttynum tu
+            then "Available"
+            else "Away     "
+
+    istty r = fst3 == "tty" && Text.all isDigit rst
+     where
+        (fst3,rst) = Text.splitAt 3 r
+
+    loop tty tu u = do
+        what <- atomically $ foldr1 orElse
+            [ do (tty',tu') <- retryWhen activeTTY
+                            (\ttyu -> bstatus r tty tu == uncurry (bstatus r) ttyu)
+                 return $ ttyChanged tty' tu'
+            , do u' <- retryWhen (readTVar utmp) (==u)
+                 return $ utmpChanged u'
+            ]
+        what
+      where
+        r = maybe "" resource u
+
+        ttyChanged tty' tu' = do
+            jid <- maybe (return "") ujid u
+            log $ status r tty' tu' <> " " <> jid
+            loop tty' tu' u
+
+        utmpChanged u' = maybe dead changed u'
+         where
+            changed u' = do
+                jid0 <- maybe (return "") ujid u
+                jid <- ujid u'
+                log $ "changed: " <> jid0 <> " --> " <> jid
+                loop tty tu (Just u')
+            dead = do
+                jid <- maybe (return "") ujid u
+                log $ "Offline   " <> jid
+
+logit outvar s = do
+    atomically $ takeTMVar outvar
+    Text.putStrLn s
+    atomically $ putTMVar outvar ()
+
+
+main = do
+    outvar <- atomically $ newTMVar ()
+
+    cs <- newConsoleState
+    inotify <- initINotify
+
+    -- get active tty
+    mtty <- monitorTTY (onTTY outvar cs)
+    atomically $ retryWhen (readTVar $ csActiveTTY cs) (==0)
+
+    -- read utmp
+    onLogin cs (newCon $ logit outvar) Modify
+
+    -- monitor utmp
+    wd <- addWatch
+            inotify
+            [Modify] -- [CloseWrite,Open,Close,Access,Modify,Move]
+            utmp_file
+            (onLogin cs (newCon $ logit outvar))
+
+    waitForTermSignal
+
+    putStrLn "goodbye."
diff --git a/dht-client.cabal b/dht-client.cabal
index aa4de64c..b17ceb14 100644
--- a/dht-client.cabal
+++ b/dht-client.cabal
@@ -58,7 +58,7 @@ library
                      , OverloadedStrings
                      , RecordWildCards
                      , NondecreasingIndentation
-  hs-source-dirs:      src, cryptonite-backport, .
+  hs-source-dirs:      src, cryptonite-backport, ., Presence
   exposed-modules:  Network.SocketLike
                     Data.Digest.CRC32C
                     Data.Bits.ByteString
@@ -99,6 +99,34 @@ library
                     Roster
                     Announcer
                     InterruptibleDelay
+                    ByteStringOperators
+                    ClientState
+                    ConfigFiles
+                    ConnectionKey
+                    ConsoleWriter
+                    Control.Concurrent.STM.StatusCache
+                    Control.Concurrent.STM.UpdateStream
+                    ControlMaybe
+                    Data.BitSyntax
+                    DNSCache
+                    EventUtil
+                    FGConsole
+                    GetHostByAddr
+                    LocalPeerCred
+                    LockedChan
+                    Logging
+                    Nesting
+                    Paths
+                    PeerResolve
+                    Server
+                    SockAddr
+                    TraversableT
+                    UTmp
+                    XMPPServer
+                    Util
+                    Presence
+                    PingMachine
+                    Connection
 
   build-depends:      base
                     , containers
@@ -117,6 +145,7 @@ library
                     , directory
                     , bencoding
                     , contravariant
+                    , xml-types
 
                     , cryptonite
                     , memory
@@ -144,6 +173,15 @@ library
                     , ghc-prim
                     , sensible-directory
                     , temporary
+                    , transformers
+                    , conduit
+                    , conduit-extra
+                    , xml-conduit
+                    , unix
+                    , template-haskell
+                    , resourcet
+                    , blaze-builder
+                    , hinotify
 
   if impl(ghc < 8)
       Build-depends:  transformers
@@ -168,11 +206,12 @@ library
                        Crypto.Internal.Imports
                        Crypto.PubKey.Curve25519
 
-  C-sources:           cbits/cryptonite_xsalsa.c, cbits/cryptonite_salsa.c
+  C-sources:           cbits/cryptonite_xsalsa.c, cbits/cryptonite_salsa.c,
+                       Presence/monitortty.c
 
   -- if flag(aeson)
   build-depends: aeson, aeson-pretty, unordered-containers, vector
-  cpp-options:   -DBENCODE_AESON
+  cpp-options:   -DBENCODE_AESON -DRENDERFLUSH
   if flag(thread-debug)
     exposed-modules: Control.Concurrent.Lifted.Instrument
                      Control.Concurrent.Async.Lifted.Instrument
@@ -208,9 +247,10 @@ executable dhtd
                      , unordered-containers
                      , vector
                      , text
+                     , resourcet
 
   if flag(thread-debug)
     build-depends: time
-    cpp-options:   -DTHREAD_DEBUG
-  ghc-options:         -rtsopts  -fdefer-typed-holes
+    cpp-options:   -DTHREAD_DEBUG -DRENDERFLUSH
+  ghc-options:         -rtsopts  -fdefer-typed-holes -threaded
 
diff --git a/doc/rfc6120.html b/doc/rfc6120.html
new file mode 100644
index 00000000..fa7ef081
--- /dev/null
+++ b/doc/rfc6120.html
@@ -0,0 +1,9372 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html lang="en"><head><title>Extensible Messaging and Presence Protocol (XMPP): Core</title>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+<meta name="description" content="Extensible Messaging and Presence Protocol (XMPP): Core">
+<meta name="keywords" content="XMPP, Extensible Messaging and Presence Protocol, Jabber, Messaging, Instant Messaging, Presence, Extensible Markup Language, XML">
+<meta name="generator" content="xml2rfc v1.36 (http://xml.resource.org/)">
+<style type='text/css'><!--
+        body {
+                font-family: verdana, charcoal, helvetica, arial, sans-serif;
+                font-size: small; color: #000; background-color: #FFF;
+                margin: 2em;
+        }
+        h1, h2, h3, h4, h5, h6 {
+                font-family: helvetica, monaco, "MS Sans Serif", arial, sans-serif;
+                font-weight: bold; font-style: normal;
+        }
+        h1 { color: #900; background-color: transparent; text-align: right; }
+        h3 { color: #333; background-color: transparent; }
+
+        td.RFCbug {
+                font-size: x-small; text-decoration: none;
+                width: 30px; height: 30px; padding-top: 2px;
+                text-align: justify; vertical-align: middle;
+                background-color: #000;
+        }
+        td.RFCbug span.RFC {
+                font-family: monaco, charcoal, geneva, "MS Sans Serif", helvetica, verdana, sans-serif;
+                font-weight: bold; color: #666;
+        }
+        td.RFCbug span.hotText {
+                font-family: charcoal, monaco, geneva, "MS Sans Serif", helvetica, verdana, sans-serif;
+                font-weight: normal; text-align: center; color: #FFF;
+        }
+
+        table.TOCbug { width: 30px; height: 15px; }
+        td.TOCbug {
+                text-align: center; width: 30px; height: 15px;
+                color: #FFF; background-color: #900;
+        }
+        td.TOCbug a {
+                font-family: monaco, charcoal, geneva, "MS Sans Serif", helvetica, sans-serif;
+                font-weight: bold; font-size: x-small; text-decoration: none;
+                color: #FFF; background-color: transparent;
+        }
+
+        td.header {
+                font-family: arial, helvetica, sans-serif; font-size: x-small;
+                vertical-align: top; width: 33%;
+                color: #FFF; background-color: #666;
+        }
+        td.author { font-weight: bold; font-size: x-small; margin-left: 4em; }
+        td.author-text { font-size: x-small; }
+
+        /* info code from SantaKlauss at http://www.madaboutstyle.com/tooltip2.html */
+        a.info {
+                /* This is the key. */
+                position: relative;
+                z-index: 24;
+                text-decoration: none;
+        }
+        a.info:hover {
+                z-index: 25;
+                color: #FFF; background-color: #900;
+        }
+        a.info span { display: none; }
+        a.info:hover span.info {
+                /* The span will display just on :hover state. */
+                display: block;
+                position: absolute;
+                font-size: smaller;
+                top: 2em; left: -5em; width: 15em;
+                padding: 2px; border: 1px solid #333;
+                color: #900; background-color: #EEE;
+                text-align: left;
+        }
+
+        a { font-weight: bold; }
+        a:link    { color: #900; background-color: transparent; }
+        a:visited { color: #633; background-color: transparent; }
+        a:active  { color: #633; background-color: transparent; }
+
+        p { margin-left: 2em; margin-right: 2em; }
+        p.copyright { font-size: x-small; }
+        p.toc { font-size: small; font-weight: bold; margin-left: 3em; }
+        table.toc { margin: 0 0 0 3em; padding: 0; border: 0; vertical-align: text-top; }
+        td.toc { font-size: small; font-weight: bold; vertical-align: text-top; }
+
+        ol.text { margin-left: 2em; margin-right: 2em; }
+        ul.text { margin-left: 2em; margin-right: 2em; }
+        li      { margin-left: 3em; }
+
+        /* RFC-2629 <spanx>s and <artwork>s. */
+        em     { font-style: italic; }
+        strong { font-weight: bold; }
+        dfn    { font-weight: bold; font-style: normal; }
+        cite   { font-weight: normal; font-style: normal; }
+        tt     { color: #036; }
+        tt, pre, pre dfn, pre em, pre cite, pre span {
+                font-family: "Courier New", Courier, monospace; font-size: small;
+        }
+        pre {
+                text-align: left; padding: 4px;
+                color: #000; background-color: #CCC;
+        }
+        pre dfn  { color: #900; }
+        pre em   { color: #66F; background-color: #FFC; font-weight: normal; }
+        pre .key { color: #33C; font-weight: bold; }
+        pre .id  { color: #900; }
+        pre .str { color: #000; background-color: #CFF; }
+        pre .val { color: #066; }
+        pre .rep { color: #909; }
+        pre .oth { color: #000; background-color: #FCF; }
+        pre .err { background-color: #FCC; }
+
+        /* RFC-2629 <texttable>s. */
+        table.all, table.full, table.headers, table.none {
+                font-size: small; text-align: center; border-width: 2px;
+                vertical-align: top; border-collapse: collapse;
+        }
+        table.all, table.full { border-style: solid; border-color: black; }
+        table.headers, table.none { border-style: none; }
+        th {
+                font-weight: bold; border-color: black;
+                border-width: 2px 2px 3px 2px;
+        }
+        table.all th, table.full th { border-style: solid; }
+        table.headers th { border-style: none none solid none; }
+        table.none th { border-style: none; }
+        table.all td {
+                border-style: solid; border-color: #333;
+                border-width: 1px 2px;
+        }
+        table.full td, table.headers td, table.none td { border-style: none; }
+
+        hr { height: 1px; }
+        hr.insert {
+                width: 80%; border-style: none; border-width: 0;
+                color: #CCC; background-color: #CCC;
+        }
+--></style>
+</head>
+<body>
+
+<table border="0" cellpadding="0" cellspacing="2" width="30" align="right">
+    <tr>
+        <td class="RFCbug">
+                <span class="RFC">&nbsp;RFC&nbsp;</span><br /><span class="hotText">&nbsp;6120&nbsp;</span>
+        </td>
+    </tr>
+    <tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a><br /></td></tr>
+</table>
+<table summary="layout" width="66%" border="0" cellpadding="0" cellspacing="0"><tr><td><table summary="layout" width="100%" border="0" cellpadding="2" cellspacing="1">
+<tr><td class="header">Internet Engineering Task Force (IETF)</td><td class="header">P. Saint-Andre</td></tr>
+<tr><td class="header">Request for Comments: 6120</td><td class="header">Cisco</td></tr>
+<tr><td class="header">Obsoletes: <a href='http://tools.ietf.org/html/rfc3920'>3920</a></td><td class="header">March 2011</td></tr>
+<tr><td class="header">Category: Standards Track</td><td class="header">&nbsp;</td></tr>
+<tr><td class="header">ISSN: 2070-1721</td><td class="header">&nbsp;</td></tr>
+</table></td></tr></table>
+<h1><br />Extensible Messaging and Presence Protocol (XMPP): Core</h1>
+
+<h3>Abstract</h3>
+
+<p>The Extensible Messaging and Presence Protocol (XMPP) is an application profile of the Extensible Markup Language (XML) that enables the near-real-time exchange of structured yet extensible data between any two or more network entities.  This document defines XMPP's core protocol methods: setup and teardown of XML streams, channel encryption, authentication, error handling, and communication primitives for messaging, network availability ("presence"), and request-response interactions.  This document obsoletes RFC 3920.
+</p>
+<h3>Status of This Memo</h3>
+<p>
+This is an Internet Standards Track document.</p>
+<p>
+This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p>
+<p>
+Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6120.</p>
+
+<h3>Copyright Notice</h3>
+<p>
+Copyright (c) 2011 IETF Trust and the persons identified as the
+document authors.  All rights reserved.</p>
+<p>
+This document is subject to BCP 78 and the IETF Trust's Legal
+Provisions Relating to IETF Documents
+(http://trustee.ietf.org/license-info) in effect on the date of
+publication of this document.  Please review these documents
+carefully, as they describe your rights and restrictions with respect
+to this document. Code Components extracted from this document must
+include Simplified BSD License text as described in Section 4.e of
+the Trust Legal Provisions and are provided without warranty as
+described in the Simplified BSD License.</p>
+<a name="toc"></a><hr />
+
+<table border="0" cellpadding="0" cellspacing="2" width="30" align="right">
+    <tr>
+        <td class="RFCbug">
+                <span class="RFC">&nbsp;RFC&nbsp;</span><br /><span class="hotText">&nbsp;6120&nbsp;</span>
+        </td>
+    </tr>
+    <tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a><br /></td></tr>
+</table>
+<h3>Table of Contents</h3>
+<p class="toc">
+<a href="#intro">1.</a>&nbsp;
+Introduction<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-overview">1.1.</a>&nbsp;
+Overview<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-history">1.2.</a>&nbsp;
+History<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-summary">1.3.</a>&nbsp;
+Functional Summary<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-terms">1.4.</a>&nbsp;
+Terminology<br />
+<a href="#arch">2.</a>&nbsp;
+Architecture<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#arch-addresses">2.1.</a>&nbsp;
+Global Addresses<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#arch-presence">2.2.</a>&nbsp;
+Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#arch-streams">2.3.</a>&nbsp;
+Persistent Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#arch-data">2.4.</a>&nbsp;
+Structured Data<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#arch-network">2.5.</a>&nbsp;
+Distributed Network of Clients and Servers<br />
+<a href="#tcp">3.</a>&nbsp;
+TCP Binding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-scope">3.1.</a>&nbsp;
+Scope<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-resolution">3.2.</a>&nbsp;
+Resolution of Fully Qualified Domain Names<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-resolution-prefer">3.2.1.</a>&nbsp;
+Preferred Process: SRV Lookup<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-resolution-fallback">3.2.2.</a>&nbsp;
+Fallback Processes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-resolution-srvnot">3.2.3.</a>&nbsp;
+When Not to Use SRV<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-resolution-srvadd">3.2.4.</a>&nbsp;
+Use of SRV Records with Add-On Services<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tcp-reconnect">3.3.</a>&nbsp;
+Reconnection<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-reliability">3.4.</a>&nbsp;
+Reliability<br />
+<a href="#streams">4.</a>&nbsp;
+XML Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-fundamentals">4.1.</a>&nbsp;
+Stream Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-open">4.2.</a>&nbsp;
+Opening a Stream<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation">4.3.</a>&nbsp;
+Stream Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-basics">4.3.1.</a>&nbsp;
+Basic Concepts<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-features">4.3.2.</a>&nbsp;
+Stream Features Format<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-restart">4.3.3.</a>&nbsp;
+Restarts<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-resend">4.3.4.</a>&nbsp;
+Resending Features<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-complete">4.3.5.</a>&nbsp;
+Completion of Stream Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-address">4.3.6.</a>&nbsp;
+Determination of Addresses<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-negotiation-flowchart">4.3.7.</a>&nbsp;
+Flow Chart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-close">4.4.</a>&nbsp;
+Closing a Stream<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-direction">4.5.</a>&nbsp;
+Directionality<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-silence">4.6.</a>&nbsp;
+Handling of Silent Peers<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-silence-dead">4.6.1.</a>&nbsp;
+Dead Connection<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-silence-broken">4.6.2.</a>&nbsp;
+Broken Stream<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-silence-idle">4.6.3.</a>&nbsp;
+Idle Peer<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-silence-check">4.6.4.</a>&nbsp;
+Use of Checking Methods<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr">4.7.</a>&nbsp;
+Stream Attributes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-from">4.7.1.</a>&nbsp;
+from<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-to">4.7.2.</a>&nbsp;
+to<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-id">4.7.3.</a>&nbsp;
+id<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-xmllang">4.7.4.</a>&nbsp;
+xml:lang<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-version">4.7.5.</a>&nbsp;
+version<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-attr-summary">4.7.6.</a>&nbsp;
+Summary of Stream Attributes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns">4.8.</a>&nbsp;
+XML Namespaces<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns-stream">4.8.1.</a>&nbsp;
+Stream Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns-content">4.8.2.</a>&nbsp;
+Content Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns-xmpp">4.8.3.</a>&nbsp;
+XMPP Content Namespaces<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns-other">4.8.4.</a>&nbsp;
+Other Namespaces<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-ns-declarations">4.8.5.</a>&nbsp;
+Namespace Declarations and Prefixes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error">4.9.</a>&nbsp;
+Stream Errors<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-rules">4.9.1.</a>&nbsp;
+Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-rules-unrecoverable">4.9.1.1.</a>&nbsp;
+Stream Errors Are Unrecoverable<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-rules-setup">4.9.1.2.</a>&nbsp;
+Stream Errors Can Occur During Setup<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-rules-host">4.9.1.3.</a>&nbsp;
+Stream Errors When the Host Is Unspecified or Unknown<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-rules-where">4.9.1.4.</a>&nbsp;
+Where Stream Errors Are Sent<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-syntax">4.9.2.</a>&nbsp;
+Syntax<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions">4.9.3.</a>&nbsp;
+Defined Stream Error Conditions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-bad-format">4.9.3.1.</a>&nbsp;
+bad-format<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-bad-namespace-prefix">4.9.3.2.</a>&nbsp;
+bad-namespace-prefix<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-conflict">4.9.3.3.</a>&nbsp;
+conflict<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-connection-timeout">4.9.3.4.</a>&nbsp;
+connection-timeout<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-host-gone">4.9.3.5.</a>&nbsp;
+host-gone<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-host-unknown">4.9.3.6.</a>&nbsp;
+host-unknown<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-improper-addressing">4.9.3.7.</a>&nbsp;
+improper-addressing<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-internal-server-error">4.9.3.8.</a>&nbsp;
+internal-server-error<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-invalid-from">4.9.3.9.</a>&nbsp;
+invalid-from<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-invalid-namespace">4.9.3.10.</a>&nbsp;
+invalid-namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-invalid-xml">4.9.3.11.</a>&nbsp;
+invalid-xml<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-not-authorized">4.9.3.12.</a>&nbsp;
+not-authorized<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-not-well-formed">4.9.3.13.</a>&nbsp;
+not-well-formed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-policy-violation">4.9.3.14.</a>&nbsp;
+policy-violation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-remote-connection-failed">4.9.3.15.</a>&nbsp;
+remote-connection-failed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-reset">4.9.3.16.</a>&nbsp;
+reset<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-resource-constraint">4.9.3.17.</a>&nbsp;
+resource-constraint<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-restricted-xml">4.9.3.18.</a>&nbsp;
+restricted-xml<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-see-other-host">4.9.3.19.</a>&nbsp;
+see-other-host<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-system-shutdown">4.9.3.20.</a>&nbsp;
+system-shutdown<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-undefined-condition">4.9.3.21.</a>&nbsp;
+undefined-condition<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-unsupported-encoding">4.9.3.22.</a>&nbsp;
+unsupported-encoding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-unsupported-feature">4.9.3.23.</a>&nbsp;
+unsupported-feature<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-unsupported-stanza-type">4.9.3.24.</a>&nbsp;
+unsupported-stanza-type<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-conditions-unsupported-version">4.9.3.25.</a>&nbsp;
+unsupported-version<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-error-app">4.9.4.</a>&nbsp;
+Application-Specific Conditions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#streams-example">4.10.</a>&nbsp;
+Simplified Stream Examples<br />
+<a href="#tls">5.</a>&nbsp;
+STARTTLS Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-fundamentals">5.1.</a>&nbsp;
+Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-support">5.2.</a>&nbsp;
+Support<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules">5.3.</a>&nbsp;
+Stream Negotiation Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-mtn">5.3.1.</a>&nbsp;
+Mandatory-to-Negotiate<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-restart">5.3.2.</a>&nbsp;
+Restart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-data">5.3.3.</a>&nbsp;
+Data Formatting<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-order">5.3.4.</a>&nbsp;
+Order of TLS and SASL Negotiations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-renegotiation">5.3.5.</a>&nbsp;
+TLS Renegotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-rules-extensions">5.3.6.</a>&nbsp;
+TLS Extensions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process">5.4.</a>&nbsp;
+Process<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-stream">5.4.1.</a>&nbsp;
+Exchange of Stream Headers and Stream Features<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-initiate">5.4.2.</a>&nbsp;
+Initiation of STARTTLS Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-initiate-command">5.4.2.1.</a>&nbsp;
+STARTTLS Command<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-initiate-failure">5.4.2.2.</a>&nbsp;
+Failure Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-initiate-proceed">5.4.2.3.</a>&nbsp;
+Proceed Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-neg">5.4.3.</a>&nbsp;
+TLS Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-neg-rules">5.4.3.1.</a>&nbsp;
+Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-neg-failure">5.4.3.2.</a>&nbsp;
+TLS Failure<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#tls-process-neg-success">5.4.3.3.</a>&nbsp;
+TLS Success<br />
+<a href="#sasl">6.</a>&nbsp;
+SASL Negotiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-fundamentals">6.1.</a>&nbsp;
+Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-support">6.2.</a>&nbsp;
+Support<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules">6.3.</a>&nbsp;
+Stream Negotiation Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-mtn">6.3.1.</a>&nbsp;
+Mandatory-to-Negotiate<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-restart">6.3.2.</a>&nbsp;
+Restart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-preferences">6.3.3.</a>&nbsp;
+Mechanism Preferences<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-offers">6.3.4.</a>&nbsp;
+Mechanism Offers<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-data">6.3.5.</a>&nbsp;
+Data Formatting<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-layers">6.3.6.</a>&nbsp;
+Security Layers<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-username">6.3.7.</a>&nbsp;
+Simple User Name<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-authzid">6.3.8.</a>&nbsp;
+Authorization Identity<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-realms">6.3.9.</a>&nbsp;
+Realms<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-rules-roundtrips">6.3.10.</a>&nbsp;
+Round Trips<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process">6.4.</a>&nbsp;
+Process<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-stream">6.4.1.</a>&nbsp;
+Exchange of Stream Headers and Stream Features<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-neg-initiate">6.4.2.</a>&nbsp;
+Initiation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-neg-challengeresponse">6.4.3.</a>&nbsp;
+Challenge-Response Sequence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-neg-abort">6.4.4.</a>&nbsp;
+Abort<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-neg-failure">6.4.5.</a>&nbsp;
+SASL Failure<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-process-neg-success">6.4.6.</a>&nbsp;
+SASL Success<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors">6.5.</a>&nbsp;
+SASL Errors<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-aborted">6.5.1.</a>&nbsp;
+aborted<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-account-disabled">6.5.2.</a>&nbsp;
+account-disabled<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-credentials-expired">6.5.3.</a>&nbsp;
+credentials-expired<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-encryption-required">6.5.4.</a>&nbsp;
+encryption-required<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-incorrect-encoding">6.5.5.</a>&nbsp;
+incorrect-encoding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-invalid-authzid">6.5.6.</a>&nbsp;
+invalid-authzid<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-invalid-mechanism">6.5.7.</a>&nbsp;
+invalid-mechanism<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-malformed-request">6.5.8.</a>&nbsp;
+malformed-request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-mechanism-too-weak">6.5.9.</a>&nbsp;
+mechanism-too-weak<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-not-authorized">6.5.10.</a>&nbsp;
+not-authorized<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-errors-temporary-auth-failure">6.5.11.</a>&nbsp;
+temporary-auth-failure<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sasl-def">6.6.</a>&nbsp;
+SASL Definition<br />
+<a href="#bind">7.</a>&nbsp;
+Resource Binding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-fundamentals">7.1.</a>&nbsp;
+Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-support">7.2.</a>&nbsp;
+Support<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-rules">7.3.</a>&nbsp;
+Stream Negotiation Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-rules-mtn">7.3.1.</a>&nbsp;
+Mandatory-to-Negotiate<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-rules-restart">7.3.2.</a>&nbsp;
+Restart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-feature">7.4.</a>&nbsp;
+Advertising Support<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-generation">7.5.</a>&nbsp;
+Generation of Resource Identifiers<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-servergen">7.6.</a>&nbsp;
+Server-Generated Resource Identifier<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-servergen-success">7.6.1.</a>&nbsp;
+Success Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-servergen-error">7.6.2.</a>&nbsp;
+Error Cases<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-servergen-error-resourceconstraint">7.6.2.1.</a>&nbsp;
+Resource Constraint<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-servergen-error-notallowed">7.6.2.2.</a>&nbsp;
+Not Allowed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit">7.7.</a>&nbsp;
+Client-Submitted Resource Identifier<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit-success">7.7.1.</a>&nbsp;
+Success Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit-error">7.7.2.</a>&nbsp;
+Error Cases<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit-error-badrequest">7.7.2.1.</a>&nbsp;
+Bad Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit-error-conflict">7.7.2.2.</a>&nbsp;
+Conflict<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#bind-clientsubmit-retries">7.7.3.</a>&nbsp;
+Retries<br />
+<a href="#stanzas">8.</a>&nbsp;
+XML Stanzas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes">8.1.</a>&nbsp;
+Common Attributes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-to">8.1.1.</a>&nbsp;
+to<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-to-c2s">8.1.1.1.</a>&nbsp;
+Client-to-Server Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-to-s2s">8.1.1.2.</a>&nbsp;
+Server-to-Server Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-from">8.1.2.</a>&nbsp;
+from<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-from-c2s">8.1.2.1.</a>&nbsp;
+Client-to-Server Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-from-s2s">8.1.2.2.</a>&nbsp;
+Server-to-Server Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-id">8.1.3.</a>&nbsp;
+id<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-type">8.1.4.</a>&nbsp;
+type<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-attributes-lang">8.1.5.</a>&nbsp;
+xml:lang<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-semantics">8.2.</a>&nbsp;
+Basic Semantics<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-semantics-message">8.2.1.</a>&nbsp;
+Message Semantics<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-semantics-presence">8.2.2.</a>&nbsp;
+Presence Semantics<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-semantics-iq">8.2.3.</a>&nbsp;
+IQ Semantics<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error">8.3.</a>&nbsp;
+Stanza Errors<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-rules">8.3.1.</a>&nbsp;
+Rules<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-syntax">8.3.2.</a>&nbsp;
+Syntax<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions">8.3.3.</a>&nbsp;
+Defined Conditions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-bad-request">8.3.3.1.</a>&nbsp;
+bad-request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-conflict">8.3.3.2.</a>&nbsp;
+conflict<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-feature-not-implemented">8.3.3.3.</a>&nbsp;
+feature-not-implemented<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-forbidden">8.3.3.4.</a>&nbsp;
+forbidden<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-gone">8.3.3.5.</a>&nbsp;
+gone<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-internal-server-error">8.3.3.6.</a>&nbsp;
+internal-server-error<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-item-not-found">8.3.3.7.</a>&nbsp;
+item-not-found<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-jid-malformed">8.3.3.8.</a>&nbsp;
+jid-malformed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-not-acceptable">8.3.3.9.</a>&nbsp;
+not-acceptable<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-not-allowed">8.3.3.10.</a>&nbsp;
+not-allowed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-not-authorized">8.3.3.11.</a>&nbsp;
+not-authorized<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-policy-violation">8.3.3.12.</a>&nbsp;
+policy-violation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-recipient-unavailable">8.3.3.13.</a>&nbsp;
+recipient-unavailable<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-redirect">8.3.3.14.</a>&nbsp;
+redirect<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-registration-required">8.3.3.15.</a>&nbsp;
+registration-required<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-remote-server-not-found">8.3.3.16.</a>&nbsp;
+remote-server-not-found<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-remote-server-timeout">8.3.3.17.</a>&nbsp;
+remote-server-timeout<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-resource-constraint">8.3.3.18.</a>&nbsp;
+resource-constraint<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-service-unavailable">8.3.3.19.</a>&nbsp;
+service-unavailable<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-subscription-required">8.3.3.20.</a>&nbsp;
+subscription-required<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-undefined-condition">8.3.3.21.</a>&nbsp;
+undefined-condition<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-conditions-unexpected-request">8.3.3.22.</a>&nbsp;
+unexpected-request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-error-app">8.3.4.</a>&nbsp;
+Application-Specific Conditions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#stanzas-extended">8.4.</a>&nbsp;
+Extended Content<br />
+<a href="#examples">9.</a>&nbsp;
+Detailed Examples<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s">9.1.</a>&nbsp;
+Client-to-Server Examples<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s-tls">9.1.1.</a>&nbsp;
+TLS<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s-sasl">9.1.2.</a>&nbsp;
+SASL<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s-bind">9.1.3.</a>&nbsp;
+Resource Binding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s-stanzas">9.1.4.</a>&nbsp;
+Stanza Exchange<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-c2s-close">9.1.5.</a>&nbsp;
+Close<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-s2s">9.2.</a>&nbsp;
+Server-to-Server Examples<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-s2s-tls">9.2.1.</a>&nbsp;
+TLS<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-s2s-sasl">9.2.2.</a>&nbsp;
+SASL<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-s2s-stanzas">9.2.3.</a>&nbsp;
+Stanza Exchange<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#examples-s2s-close">9.2.4.</a>&nbsp;
+Close<br />
+<a href="#rules">10.</a>&nbsp;
+Server Rules for Processing XML Stanzas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-order">10.1.</a>&nbsp;
+In-Order Processing<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-gen">10.2.</a>&nbsp;
+General Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-noto">10.3.</a>&nbsp;
+No 'to' Address<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-noto-message">10.3.1.</a>&nbsp;
+Message<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-noto-presence">10.3.2.</a>&nbsp;
+Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-noto-IQ">10.3.3.</a>&nbsp;
+IQ<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-remote">10.4.</a>&nbsp;
+Remote Domain<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-remote-existing">10.4.1.</a>&nbsp;
+Existing Stream<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-remote-nostream">10.4.2.</a>&nbsp;
+No Existing Stream<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-remote-error">10.4.3.</a>&nbsp;
+Error Handling<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local">10.5.</a>&nbsp;
+Local Domain<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-domain">10.5.1.</a>&nbsp;
+domainpart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-domainresource">10.5.2.</a>&nbsp;
+domainpart/resourcepart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-barejid">10.5.3.</a>&nbsp;
+localpart@domainpart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-barejid-nosuchuser">10.5.3.1.</a>&nbsp;
+No Such User<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-barejid-userexists">10.5.3.2.</a>&nbsp;
+User Exists<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-fulljid">10.5.4.</a>&nbsp;
+localpart@domainpart/resourcepart<br />
+<a href="#xml">11.</a>&nbsp;
+XML Usage<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-restrictions">11.1.</a>&nbsp;
+XML Restrictions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-ns">11.2.</a>&nbsp;
+XML Namespace Names and Prefixes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-wellformed">11.3.</a>&nbsp;
+Well-Formedness<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-validation">11.4.</a>&nbsp;
+Validation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-declaration">11.5.</a>&nbsp;
+Inclusion of XML Declaration<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-encoding">11.6.</a>&nbsp;
+Character Encoding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-whitespace">11.7.</a>&nbsp;
+Whitespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#xml-versions">11.8.</a>&nbsp;
+XML Versions<br />
+<a href="#i18n">12.</a>&nbsp;
+Internationalization Considerations<br />
+<a href="#security">13.</a>&nbsp;
+Security Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-fundamentals">13.1.</a>&nbsp;
+Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-threats">13.2.</a>&nbsp;
+Threat Model<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-layers">13.3.</a>&nbsp;
+Order of Layers<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-confidentiality">13.4.</a>&nbsp;
+Confidentiality and Integrity<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-authentication">13.5.</a>&nbsp;
+Peer Entity Authentication<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-strong">13.6.</a>&nbsp;
+Strong Security<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates">13.7.</a>&nbsp;
+Certificates<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-generation">13.7.1.</a>&nbsp;
+Certificate Generation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-generation-general">13.7.1.1.</a>&nbsp;
+General Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-generation-server">13.7.1.2.</a>&nbsp;
+Server Certificates<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-generation-client">13.7.1.3.</a>&nbsp;
+Client Certificates<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-generation-xmppaddr">13.7.1.4.</a>&nbsp;
+XmppAddr Identifier Type<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-validation">13.7.2.</a>&nbsp;
+Certificate Validation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-validation-server">13.7.2.1.</a>&nbsp;
+Server Certificates<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-validation-client">13.7.2.2.</a>&nbsp;
+Client Certificates<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-validation-streams">13.7.2.3.</a>&nbsp;
+Checking of Certificates in Long-Lived Streams<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-certificates-validation-extensions">13.7.2.4.</a>&nbsp;
+Use of Certificates in XMPP Extensions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-mti">13.8.</a>&nbsp;
+Mandatory-to-Implement TLS and SASL Technologies<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-mti-auth">13.8.1.</a>&nbsp;
+For Authentication Only<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-mti-conf">13.8.2.</a>&nbsp;
+For Confidentiality Only<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-mti-bothpass">13.8.3.</a>&nbsp;
+For Confidentiality and Authentication with Passwords<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-mti-bothnopass">13.8.4.</a>&nbsp;
+For Confidentiality and Authentication without Passwords<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse">13.9.</a>&nbsp;
+Technology Reuse<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-base64">13.9.1.</a>&nbsp;
+Use of Base 64 in SASL<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-dns">13.9.2.</a>&nbsp;
+Use of DNS<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-hash">13.9.3.</a>&nbsp;
+Use of Hash Functions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-sasl">13.9.4.</a>&nbsp;
+Use of SASL<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-tls">13.9.5.</a>&nbsp;
+Use of TLS<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-utf8">13.9.6.</a>&nbsp;
+Use of UTF-8<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-reuse-xml">13.9.7.</a>&nbsp;
+Use of XML<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-leaks">13.10.</a>&nbsp;
+Information Leaks<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-leaks-ipaddress">13.10.1.</a>&nbsp;
+IP Addresses<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-leaks-presence">13.10.2.</a>&nbsp;
+Presence Information<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-harvesting">13.11.</a>&nbsp;
+Directory Harvesting<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-dos">13.12.</a>&nbsp;
+Denial of Service<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-firewalls">13.13.</a>&nbsp;
+Firewalls<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-federation">13.14.</a>&nbsp;
+Interdomain Federation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#security-nonrepudiation">13.15.</a>&nbsp;
+Non-Repudiation<br />
+<a href="#iana">14.</a>&nbsp;
+IANA Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ns-tls">14.1.</a>&nbsp;
+XML Namespace Name for TLS Data<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ns-sasl">14.2.</a>&nbsp;
+XML Namespace Name for SASL Data<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ns-streams">14.3.</a>&nbsp;
+XML Namespace Name for Stream Errors<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ns-bind">14.4.</a>&nbsp;
+XML Namespace Name for Resource Binding<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ns-stanzas">14.5.</a>&nbsp;
+XML Namespace Name for Stanza Errors<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-gssapi">14.6.</a>&nbsp;
+GSSAPI Service Name<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#iana-ports">14.7.</a>&nbsp;
+Port Numbers and Service Names<br />
+<a href="#conformance">15.</a>&nbsp;
+Conformance Requirements<br />
+<a href="#rfc.references1">16.</a>&nbsp;
+References<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references1">16.1.</a>&nbsp;
+Normative References<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references2">16.2.</a>&nbsp;
+Informative References<br />
+<a href="#schema">Appendix&nbsp;A.</a>&nbsp;
+XML Schemas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-stream">A.1.</a>&nbsp;
+Stream Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-streamerror">A.2.</a>&nbsp;
+Stream Error Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-starttls">A.3.</a>&nbsp;
+STARTTLS Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-sasl">A.4.</a>&nbsp;
+SASL Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-client">A.5.</a>&nbsp;
+Client Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-server">A.6.</a>&nbsp;
+Server Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-bind">A.7.</a>&nbsp;
+Resource Binding Namespace<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#schemas-stanzaerror">A.8.</a>&nbsp;
+Stanza Error Namespace<br />
+<a href="#contact">Appendix&nbsp;B.</a>&nbsp;
+Contact Addresses<br />
+<a href="#provisioning">Appendix&nbsp;C.</a>&nbsp;
+Account Provisioning<br />
+<a href="#diffs">Appendix&nbsp;D.</a>&nbsp;
+Differences from RFC 3920<br />
+<a href="#intro-ack">Appendix&nbsp;E.</a>&nbsp;
+Acknowledgements<br />
+</p>
+<br clear="all" />
+
+<a name="intro"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1"></a><h3>1.&nbsp;
+Introduction</h3>
+
+<a name="intro-overview"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.1"></a><h3>1.1.&nbsp;
+Overview</h3>
+
+<p>The Extensible Messaging and Presence Protocol (XMPP) is an application profile of the Extensible Markup Language <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a> that enables the near-real-time exchange of structured yet extensible data between any two or more network entities.  This document defines XMPP's core protocol methods: setup and teardown of XML streams, channel encryption, authentication, error handling, and communication primitives for messaging, network availability ("presence"), and request-response interactions.
+</p>
+<a name="intro-history"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.2"></a><h3>1.2.&nbsp;
+History</h3>
+
+<p>The basic syntax and semantics of XMPP were developed originally within the Jabber open-source community, mainly in 1999.  In late 2002, the XMPP Working Group was chartered with developing an adaptation of the base Jabber protocol that would be suitable as an IETF instant messaging (IM) and presence technology in accordance with <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a>.  In October 2004, <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> and <a class='info' href='#RFC3921'>[RFC3921]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; October&nbsp;2004.</span><span>)</span></a> were published, representing the most complete definition of XMPP at that time.
+</p>
+<p>Since 2004 the Internet community has gained extensive implementation and deployment experience with XMPP, including formal interoperability testing carried out under the auspices of the XMPP Standards Foundation (XSF).  This document incorporates comprehensive feedback from software developers and XMPP service providers, including a number of backward-compatible modifications summarized under <a class='info' href='#diffs'>Appendix&nbsp;D<span> (</span><span class='info'>Differences from RFC 3920</span><span>)</span></a>.  As a result, this document reflects the rough consensus of the Internet community regarding the core features of XMPP 1.0, thus obsoleting RFC 3920.
+</p>
+<a name="intro-summary"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.3"></a><h3>1.3.&nbsp;
+Functional Summary</h3>
+
+<p>This non-normative section provides a developer-friendly, functional summary of XMPP; refer to the sections that follow for a normative definition of XMPP.
+</p>
+<p>The purpose of XMPP is to enable the exchange of relatively small pieces of structured data (called "XML stanzas") over a network between any two (or more) entities.  XMPP is typically implemented using a distributed client-server architecture, wherein a client needs to connect to a server in order to gain access to the network and thus be allowed to exchange XML stanzas with other entities (which can be associated with other servers).  The process whereby a client connects to a server, exchanges XML stanzas, and ends the connection is:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Determine the IP address and port at which to connect,
+          typically based on resolution of a fully qualified domain name (<a class='info' href='#tcp-resolution'>Section&nbsp;3.2<span> (</span><span class='info'>Resolution of Fully Qualified Domain Names</span><span>)</span></a>)
+</li>
+<li>Open a Transmission Control Protocol <a class='info' href='#TCP'>[TCP]<span> (</span><span class='info'>Postel, J., &ldquo;Transmission Control Protocol,&rdquo; September&nbsp;1981.</span><span>)</span></a> connection
+</li>
+<li>Open an XML stream over TCP (<a class='info' href='#streams-open'>Section&nbsp;4.2<span> (</span><span class='info'>Opening a Stream</span><span>)</span></a>)
+</li>
+<li>Preferably negotiate Transport Layer Security <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a> for channel encryption (<a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>)
+</li>
+<li>Authenticate using a Simple Authentication and Security Layer <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a> mechanism (<a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>)
+</li>
+<li>Bind a resource to the stream (<a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>)
+</li>
+<li>Exchange an unbounded number of XML stanzas with other entities on the network (<a class='info' href='#stanzas'>Section&nbsp;8<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a>)
+</li>
+<li>Close the XML stream (<a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>)
+</li>
+<li>Close the TCP connection
+</li>
+</ol><p>
+      
+</p>
+<p>Within XMPP, one server can optionally connect to another server to enable inter-domain or inter-server communication.  For this to happen, the two servers need to negotiate a connection between themselves and then exchange XML stanzas; the process for doing so is:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Determine the IP address and port at which to connect,
+          typically based on resolution of a fully qualified domain name (<a class='info' href='#tcp-resolution'>Section&nbsp;3.2<span> (</span><span class='info'>Resolution of Fully Qualified Domain Names</span><span>)</span></a>)
+</li>
+<li>Open a TCP connection
+</li>
+<li>Open an XML stream (<a class='info' href='#streams-open'>Section&nbsp;4.2<span> (</span><span class='info'>Opening a Stream</span><span>)</span></a>)
+</li>
+<li>Preferably negotiate TLS for channel encryption (<a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>)
+</li>
+<li>Authenticate using a Simple Authentication and Security Layer <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a> mechanism (<a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>) *
+</li>
+<li>Exchange an unbounded number of XML stanzas both directly for the servers and indirectly on behalf of entities associated with each server, such as connected clients (<a class='info' href='#stanzas'>Section&nbsp;8<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a>)
+</li>
+<li>Close the XML stream (<a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>)
+</li>
+<li>Close the TCP connection
+</li>
+</ol><p>
+      
+</p>
+<p></p>
+<blockquote class="text">
+<p>* Interoperability Note: At the time of writing, most deployed servers still use the Server Dialback protocol <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a> to provide weak identity verification instead of using SASL with PKIX certificates to provide strong authentication, especially in cases where SASL negotiation would not result in strong authentication anyway (e.g., because TLS negotiation was not mandated by the peer server, or because the PKIX certificate presented by the peer server during TLS negotiation is self-signed and has not been previously accepted); for details, see <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>.  The solutions specified in this document offer a significantly stronger level of security (see also <a class='info' href='#security-strong'>Section&nbsp;13.6<span> (</span><span class='info'>Strong Security</span><span>)</span></a>).
+</p>
+</blockquote>
+
+<p>This document specifies how clients connect to servers and specifies the basic semantics of XML stanzas.  However, this document does not define the "payloads" of the XML stanzas that might be exchanged once a connection is successfully established; instead, those payloads are defined by various XMPP extensions.  For example, <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a> defines extensions for basic instant messaging and presence functionality.  In addition, various specifications produced in the XSF's XEP series <a class='info' href='#XEP-0001'>[XEP&#8209;0001]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XMPP Extension Protocols,&rdquo; March&nbsp;2010.</span><span>)</span></a> define extensions for a wide range of applications.
+</p>
+<a name="intro-terms"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.4"></a><h3>1.4.&nbsp;
+Terminology</h3>
+
+<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 <a class='info' href='#KEYWORDS'>[KEYWORDS]<span> (</span><span class='info'>Bradner, S., &ldquo;Key words for use in RFCs to Indicate Requirement Levels,&rdquo; March&nbsp;1997.</span><span>)</span></a>.
+</p>
+<p>Certain security-related terms are to be understood in the sense defined in <a class='info' href='#SEC-TERMS'>[SEC&#8209;TERMS]<span> (</span><span class='info'>Shirey, R., &ldquo;Internet Security Glossary, Version 2,&rdquo; August&nbsp;2007.</span><span>)</span></a>; such terms include, but are not limited to, "assurance", "attack", "authentication", "authorization", "certificate", "certification authority", "certification path", "confidentiality", "credential", "downgrade", "encryption", "hash value", "identity", "integrity", "signature", "self-signed certificate", "sign", "spoof", "tamper", "trust", "trust anchor", "validate", and "verify".
+</p>
+<p>Certain terms related to certificates, domains, and application service identity are to be understood in the sense defined in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a>; these include, but are not limited to, "PKIX certificate", "source domain", "derived domain", and the identifier types "CN-ID", "DNS-ID", and "SRV-ID".
+</p>
+<p>Other security-related terms are to be understood in the sense defined in the referenced specifications (for example, "denial of service" as described in <a class='info' href='#DOS'>[DOS]<span> (</span><span class='info'>Handley, M., Rescorla, E., and IAB, &ldquo;Internet Denial-of-Service Considerations,&rdquo; December&nbsp;2006.</span><span>)</span></a> or "end entity certificate" as described in <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a>).
+</p>
+<p>The term "whitespace" is used to refer to any character or characters matching the "S" production from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>, i.e., one or more instances of the SP, HTAB, CR, or LF rules defined in <a class='info' href='#ABNF'>[ABNF]<span> (</span><span class='info'>Crocker, D. and P. Overell, &ldquo;Augmented BNF for Syntax Specifications: ABNF,&rdquo; January&nbsp;2008.</span><span>)</span></a>.
+</p>
+<p>The terms "localpart", "domainpart", and "resourcepart" are defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>The term "bare JID" refers to an XMPP address of the form &lt;localpart@domainpart&gt; (for an account at a server) or of the form &lt;domainpart&gt; (for a server).
+</p>
+<p>The term "full JID" refers to an XMPP address of the form &lt;localpart@domainpart/resourcepart&gt; (for a particular authorized client or device associated with an account) or of the form &lt;domainpart/resourcepart&gt; (for a particular resource or script associated with a server).
+</p>
+<p>The term "XML stream" (also "stream") is defined under <a class='info' href='#streams-fundamentals'>Section&nbsp;4.1<span> (</span><span class='info'>Stream Fundamentals</span><span>)</span></a>.
+</p>
+<p>The term "XML stanza" (also "stanza") is defined under <a class='info' href='#streams-fundamentals'>Section&nbsp;4.1<span> (</span><span class='info'>Stream Fundamentals</span><span>)</span></a>.  There are three kinds of stanzas: message,
+presence, and IQ (short for "Info/Query").  These communication primitives are
+defined under Sections <a class='info' href='#stanzas-semantics-message'>8.2.1<span> (</span><span class='info'>Message Semantics</span><span>)</span></a>, <a class='info' href='#stanzas-semantics-presence'>8.2.2<span> (</span><span class='info'>Presence Semantics</span><span>)</span></a>, and <a class='info' href='#stanzas-semantics-iq'>8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>, respectively.
+</p>
+<p>The term "originating entity" refers to the entity that first generates a stanza that is sent over an XMPP network (e.g., a connected client, an add-on service, or a server).  The term "generated stanza" refers to the stanza so generated.
+</p>
+<p>The term "input stream" designates an XML stream over which a server receives data from a connected client or remote server, and the term "output stream" designates an XML stream over which a server sends data to a connected client or remote server.  The following terms designate some of the actions that a server can perform when processing data received over an input stream:
+</p>
+<p>
+        </p>
+<blockquote class="text">
+<p>
+            </p>
+<blockquote class="text"><dl>
+<dt>route:</dt>
+<dd>pass the data to a remote server for direct processing by the remote server or eventual delivery to a client associated with the remote server
+</dd>
+<dt>deliver:</dt>
+<dd>pass the data to a connected client
+</dd>
+<dt>ignore:</dt>
+<dd>discard the data without acting upon it or returning an error to the sender
+</dd>
+</dl></blockquote>
+          
+
+</blockquote><p>
+      
+</p>
+<p>When the term "ignore" is used with regard to client processing of data it receives, the phrase "without acting upon it" explicitly includes not presenting the data to a human user.
+</p>
+<p>Following the "XML Notation" used in <a class='info' href='#IRI'>[IRI]<span> (</span><span class='info'>Duerst, M. and M. Suignard, &ldquo;Internationalized Resource Identifiers (IRIs),&rdquo; January&nbsp;2005.</span><span>)</span></a> to represent characters that cannot be rendered in ASCII-only documents, some examples in this document use the form "&amp;#x...." as a notational device to represent <a class='info' href='#UNICODE'>[UNICODE]<span> (</span><span class='info'>The Unicode Consortium, &ldquo;The Unicode Standard, Version 6.0,&rdquo; 2010.</span><span>)</span></a> characters (e.g., the string "&amp;#x0159;" stands for the Unicode character LATIN SMALL LETTER R WITH CARON); this form is definitely not to be sent over the wire in XMPP systems.
+</p>
+<p>Consistent with the convention used in <a class='info' href='#URI'>[URI]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, &ldquo;Uniform Resource Identifier (URI): Generic Syntax,&rdquo; January&nbsp;2005.</span><span>)</span></a>
+      to represent Uniform Resource Identifiers, XMPP addresses in running text are enclosed between '&lt;' and '&gt;' (although natively they are not URIs).
+</p>
+<p>In examples, lines have been wrapped for improved readability, "[...]" means elision, and the following prepended strings are used (these prepended strings are not to be sent over the wire):
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>C: = a client
+</li>
+<li>E: = any XMPP entity
+</li>
+<li>I: = an initiating entity
+</li>
+<li>P: = a peer server
+</li>
+<li>R: = a receiving entity
+</li>
+<li>S: = a server
+</li>
+<li>S1: = server1
+</li>
+<li>S2: = server2
+</li>
+</ul><p>
+      
+</p>
+<p>Readers need to be aware that the examples are not exhaustive and that, in examples for some protocol flows, the alternate steps shown would not necessarily be triggered by the exact data sent in the previous step; in all cases the protocol definitions specified in this document or in normatively referenced documents rule over any examples provided here.  All examples are fictional and the information exchanged (e.g., usernames and passwords) does not represent any existing users or servers.
+</p>
+<a name="arch"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2"></a><h3>2.&nbsp;
+Architecture</h3>
+
+<p>XMPP provides a technology for the asynchronous, end-to-end
+    exchange of structured data by means of direct, persistent XML
+    streams among a distributed network of globally addressable, presence-aware clients and servers.  Because this architectural style involves ubiquitous knowledge of network availability and a conceptually unlimited number of concurrent information transactions in the context of a given client-to-server or server-to-server session, we label it "Availability for Concurrent Transactions" (ACT) to distinguish it from the "Representational State Transfer" <a class='info' href='#REST'>[REST]<span> (</span><span class='info'>Fielding, R., &ldquo;Architectural Styles and the Design of Network-based Software Architectures,&rdquo; .</span><span>)</span></a> architectural style familiar from the World Wide Web. &nbsp;Although the architecture of XMPP is similar in important ways to that of email (see <a class='info' href='#EMAIL-ARCH'>[EMAIL&#8209;ARCH]<span> (</span><span class='info'>Crocker, D., &ldquo;Internet Mail Architecture,&rdquo; July&nbsp;2009.</span><span>)</span></a>), it introduces several modifications to facilitate communication in close to real time.  The salient features of this ACTive architectural style are as follows.
+</p>
+<a name="arch-addresses"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1"></a><h3>2.1.&nbsp;
+Global Addresses</h3>
+
+<p>As with email, XMPP uses globally unique addresses (based on the Domain Name System) in order to route and deliver messages over the network.  All XMPP entities are addressable on the network, most particularly clients and servers but also various additional services that can be accessed by clients and servers.  In general, server addresses are of the form &lt;domainpart&gt; (e.g., &lt;im.example.com&gt;), accounts hosted at a server are of the form &lt;localpart@domainpart&gt; (e.g., &lt;juliet@im.example.com&gt;, called a "bare JID"), and a particular connected device or resource that is currently authorized for interaction on behalf of an account is of the form &lt;localpart@domainpart/resourcepart&gt; (e.g., &lt;juliet@im.example.com/balcony&gt;, called a "full JID").  For historical reasons, XMPP addresses are often called Jabber IDs or JIDs.  Because the formal specification of the XMPP address format depends on internationalization technologies that are in flux at the time of writing, the format is defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a> instead of this document.  The terms "localpart", "domainpart", and "resourcepart" are defined more formally in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="arch-presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.2"></a><h3>2.2.&nbsp;
+Presence</h3>
+
+<p>XMPP includes the ability for an entity to advertise its network availability or "presence" to other entities.  In XMPP, this availability for communication is signaled end-to-end by means of a dedicated communication primitive: the &lt;presence/&gt; stanza.  Although knowledge of network availability is not strictly necessary for the exchange of XMPP messages, it facilitates real-time interaction because the originator of a message can know before initiating communication that the intended recipient is online and available.  End-to-end presence is defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="arch-streams"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.3"></a><h3>2.3.&nbsp;
+Persistent Streams</h3>
+
+<p>Availability for communication is also built into each point-to-point "hop" through the use of persistent XML streams over long-lived TCP connections.  These "always-on" client-to-server and server-to-server streams enable each party to push data to the other party at any time for immediate routing or delivery.  XML streams are defined under <a class='info' href='#streams'>Section&nbsp;4<span> (</span><span class='info'>XML Streams</span><span>)</span></a>.
+</p>
+<a name="arch-data"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.4"></a><h3>2.4.&nbsp;
+Structured Data</h3>
+
+<p>The basic protocol data unit in XMPP is not an XML stream (which simply provides the transport for point-to-point communication) but an XML "stanza", which is essentially a fragment of XML that is sent over a stream.  The root element of a stanza includes routing attributes (such as "from" and "to" addresses), and the child elements of the stanza contain a payload for delivery to the intended recipient.  XML stanzas are defined under <a class='info' href='#stanzas'>Section&nbsp;8<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a>.
+</p>
+<a name="arch-network"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.5"></a><h3>2.5.&nbsp;
+Distributed Network of Clients and Servers</h3>
+
+<p>In practice, XMPP consists of a network of clients and servers that inter-communicate (however, communication between any two given deployed servers is strictly discretionary and a matter of local service policy).  Thus, for example, the user &lt;juliet@im.example.com&gt; associated with the server &lt;im.example.com&gt; might be able to exchange messages, presence, and other structured data with the user &lt;romeo@example.net&gt; associated with the server &lt;example.net&gt;.  This pattern is familiar from messaging protocols that make use of global addresses, such as the email network (see <a class='info' href='#SMTP'>[SMTP]<span> (</span><span class='info'>Klensin, J., &ldquo;Simple Mail Transfer Protocol,&rdquo; October&nbsp;2008.</span><span>)</span></a> and <a class='info' href='#EMAIL-ARCH'>[EMAIL&#8209;ARCH]<span> (</span><span class='info'>Crocker, D., &ldquo;Internet Mail Architecture,&rdquo; July&nbsp;2009.</span><span>)</span></a>).  As a result, end-to-end communication in XMPP is logically peer-to-peer but physically client-to-server-to-server-to-client, as illustrated in the following diagram.
+</p><br /><hr class="insert" />
+<a name="figure-1"></a>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+  example.net &lt;--------------&gt; im.example.com
+     ^                                ^
+     |                                |
+     v                                v
+romeo@example.net           juliet@im.example.com
+
+</pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;1: Distributed Client-Server Architecture&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
+
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Architectures that employ <a class='info' href='#streams'>XML streams<span> (</span><span class='info'>XML Streams</span><span>)</span></a> and <a class='info' href='#stanzas'>XML stanzas<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a> but that establish peer-to-peer connections directly between clients using technologies based on <a class='info' href='#LINKLOCAL'>[LINKLOCAL]<span> (</span><span class='info'>Cheshire, S., Aboba, B., and E. Guttman, &ldquo;Dynamic Configuration of IPv4 Link-Local Addresses,&rdquo; May&nbsp;2005.</span><span>)</span></a> have been deployed, but such architectures are not defined in this specification and are best described as "XMPP-like"; for details, see <a class='info' href='#XEP-0174'>[XEP&#8209;0174]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Link-Local Messaging,&rdquo; November&nbsp;2008.</span><span>)</span></a>.  In addition, XML streams can be established end-to-end over any reliable transport, including extensions to XMPP itself; however, such methods are out of scope for this specification.
+</p>
+</blockquote>
+
+<p>The following paragraphs describe the responsibilities of clients and servers on the network.
+</p>
+<p>A client is an entity that establishes an XML stream with a server by authenticating using the credentials of a registered account (via <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>) and that then completes <a class='info' href='#bind'>resource binding<span> (</span><span class='info'>Resource Binding</span><span>)</span></a> in order to enable delivery of XML stanzas between the server and the client over the negotiated stream.  The client then uses XMPP to communicate with its server, other clients, and any other entities on the network, where the server is responsible for delivering stanzas to other connected clients at the same server or routing them to remote servers.  Multiple clients can connect simultaneously to a server on behalf of the same registered account, where each client is differentiated by the resourcepart of an XMPP address (e.g., &lt;juliet@im.example.com/balcony&gt; vs. &lt;juliet@im.example.com/chamber&gt;), as defined under <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a> and <a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>.
+</p>
+<p>A server is an entity whose primary responsibilities are to:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Manage <a class='info' href='#streams'>XML streams<span> (</span><span class='info'>XML Streams</span><span>)</span></a> with connected clients and deliver <a class='info' href='#stanzas'>XML stanzas<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a> to those clients over the negotiated streams; this includes responsibility for ensuring that a client authenticates with the server before being granted access to the XMPP network.
+</li>
+<li>Subject to local service policies on server-to-server communication, manage <a class='info' href='#streams'>XML streams<span> (</span><span class='info'>XML Streams</span><span>)</span></a> with remote servers and route <a class='info' href='#stanzas'>XML stanzas<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a> to those servers over the negotiated streams.
+</li>
+</ul><p>
+      
+</p>
+<p>Depending on the application, the secondary responsibilities of an XMPP server can include:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Storing data that is used by clients (e.g., contact lists for users of XMPP-based instant messaging and presence applications as defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>); in this case, the relevant XML stanza is handled directly by the server itself on behalf of the client and is not routed to a remote server or delivered to a connected client.
+</li>
+<li>Hosting add-on services that also use XMPP as the basis for communication but that provide additional functionality beyond that defined in this document or in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>; examples include multi-user conferencing services as specified in <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2007.</span><span>)</span></a> and publish-subscribe services as specified in <a class='info' href='#XEP-0060'>[XEP&#8209;0060]<span> (</span><span class='info'>Millard, P., Saint-Andre, P., and R. Meijer, &ldquo;Publish-Subscribe,&rdquo; July&nbsp;2010.</span><span>)</span></a>.
+</li>
+</ul><p>
+      
+</p>
+<a name="tcp"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3"></a><h3>3.&nbsp;
+TCP Binding</h3>
+
+<a name="tcp-scope"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1"></a><h3>3.1.&nbsp;
+Scope</h3>
+
+<p>As XMPP is defined in this specification, an initiating entity (client or server) MUST open a Transmission Control Protocol <a class='info' href='#TCP'>[TCP]<span> (</span><span class='info'>Postel, J., &ldquo;Transmission Control Protocol,&rdquo; September&nbsp;1981.</span><span>)</span></a> connection to the receiving entity (server) before it negotiates XML streams with the receiving entity.  The parties then maintain that TCP connection for as long as the XML streams are in use.  The rules specified in the following sections apply to the TCP binding.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: There is no necessary coupling of XML streams to TCP, and other transports are possible.  For example, two entities could connect to each other by means of <a class='info' href='#HTTP'>[HTTP]<span> (</span><span class='info'>Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &ldquo;Hypertext Transfer Protocol -- HTTP/1.1,&rdquo; June&nbsp;1999.</span><span>)</span></a> as specified in <a class='info' href='#XEP-0124'>[XEP&#8209;0124]<span> (</span><span class='info'>Paterson, I., Smith, D., and P. Saint-Andre, &ldquo;Bidirectional-streams Over Synchronous HTTP (BOSH),&rdquo; July&nbsp;2010.</span><span>)</span></a> and <a class='info' href='#XEP-0206'>[XEP&#8209;0206]<span> (</span><span class='info'>Paterson, I. and P. Saint-Andre, &ldquo;XMPP Over BOSH,&rdquo; July&nbsp;2010.</span><span>)</span></a>.  However, this specification defines only a binding of XMPP to TCP.
+</p>
+</blockquote>
+
+<a name="tcp-resolution"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2"></a><h3>3.2.&nbsp;
+Resolution of Fully Qualified Domain Names</h3>
+
+<p>Because XML streams are sent over TCP, the initiating entity
+      needs to determine the IPv4 or IPv6 address (and port) of the
+      receiving entity before it can attempt to open an XML stream.
+      Typically this is done by resolving the receiving entity's fully
+      qualified domain name or FQDN (see <a class='info' href='#DNS-CONCEPTS'>[DNS&#8209;CONCEPTS]<span> (</span><span class='info'>Mockapetris, P., &ldquo;Domain names - concepts and facilities,&rdquo; November&nbsp;1987.</span><span>)</span></a>).
+</p>
+<a name="tcp-resolution-prefer"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.1"></a><h3>3.2.1.&nbsp;
+Preferred Process: SRV Lookup</h3>
+
+<p>The preferred process for FQDN resolution is to use <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a> records as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The initiating entity constructs a DNS SRV query whose inputs are:
+              
+<ul class="text">
+<li>a Service of "xmpp-client" (for client-to-server connections) or "xmpp-server" (for server-to-server connections)
+</li>
+<li>a Proto of "tcp"
+</li>
+<li>a Name corresponding to the "origin domain" <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> of the XMPP service to which the initiating entity wishes to connect (e.g., "example.net" or "im.example.com")
+</li>
+</ul>
+            
+</li>
+<li>The result is a query such as "_xmpp-client._tcp.example.net." or "_xmpp-server._tcp.im.example.com.".
+</li>
+<li>
+              If a response is received, it will contain one or more combinations of a port and FDQN, each of which is weighted and prioritized as described in <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a>.
+              
+              (However, if the result of the SRV lookup is a single resource record with a Target of ".", i.e., the root domain, then the initiating entity MUST abort SRV processing at this point because according to <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a> such a Target "means that the service is decidedly not available at this domain".)
+            
+</li>
+<li>The initiating entity chooses at least one of the returned FQDNs to resolve (following the rules in <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a>), which it does by performing DNS "A" or "AAAA" lookups on the FDQN; this will result in an IPv4 or IPv6 address.
+</li>
+<li>The initiating entity uses the IP address(es) from the successfully resolved FDQN (with the corresponding port number returned by the SRV lookup) as the connection address for the receiving entity.
+</li>
+<li>If the initiating entity fails to connect using that IP address but the "A" or "AAAA" lookups returned more than one IP address, then the initiating entity uses the next resolved IP address for that FDQN as the connection address.
+</li>
+<li>If the initiating entity fails to connect using all resolved IP addresses for a given FDQN, then it repeats the process of resolution and connection for the next FQDN returned by the SRV lookup based on the priority and weight as defined in <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a>.
+</li>
+<li>If the initiating entity receives a response to its SRV query but it is not able to establish an XMPP connection using the data received in the response, it SHOULD NOT attempt the fallback process described in the next section (this helps to prevent a state mismatch between inbound and outbound connections).
+</li>
+<li>If the initiating entity does not receive a response to its SRV query, it SHOULD attempt the fallback process described in the next section.
+</li>
+</ol><p>
+        
+</p>
+<a name="tcp-resolution-fallback"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.2"></a><h3>3.2.2.&nbsp;
+Fallback Processes</h3>
+
+<p>The fallback process SHOULD be a normal "A" or "AAAA" address record resolution to determine the IPv4 or IPv6 address of the origin domain, where the port used is the "xmpp-client" port of 5222 for client-to-server connections or the "xmpp-server" port of 5269 for server-to-server connections (these are the default ports as registered with the IANA as described under <a class='info' href='#iana-ports'>Section&nbsp;14.7<span> (</span><span class='info'>Port Numbers and Service Names</span><span>)</span></a>).
+</p>
+<p>If connections via TCP are unsuccessful, the initiating entity might attempt to find and use alternative connection methods such as the HTTP binding (see <a class='info' href='#XEP-0124'>[XEP&#8209;0124]<span> (</span><span class='info'>Paterson, I., Smith, D., and P. Saint-Andre, &ldquo;Bidirectional-streams Over Synchronous HTTP (BOSH),&rdquo; July&nbsp;2010.</span><span>)</span></a> and <a class='info' href='#XEP-0206'>[XEP&#8209;0206]<span> (</span><span class='info'>Paterson, I. and P. Saint-Andre, &ldquo;XMPP Over BOSH,&rdquo; July&nbsp;2010.</span><span>)</span></a>), which might be discovered using <a class='info' href='#DNS-TXT'>[DNS&#8209;TXT]<span> (</span><span class='info'>Rosenbaum, R., &ldquo;Using the Domain Name System To Store Arbitrary String Attributes,&rdquo; May&nbsp;1993.</span><span>)</span></a> records as described in <a class='info' href='#XEP-0156'>[XEP&#8209;0156]<span> (</span><span class='info'>Hildebrand, J. and P. Saint-Andre, &ldquo;Discovering Alternative XMPP Connection Methods,&rdquo; June&nbsp;2007.</span><span>)</span></a>.
+</p>
+<a name="tcp-resolution-srvnot"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.3"></a><h3>3.2.3.&nbsp;
+When Not to Use SRV</h3>
+
+<p>If the initiating entity has been explicitly configured to associate a particular FQDN (and potentially port) with the origin domain of the receiving entity (say, to "hardcode" an association from an origin domain of example.net to a configured FQDN of apps.example.com), the initiating entity is encouraged to use the configured name instead of performing the preferred SRV resolution process on the origin domain.
+</p>
+<a name="tcp-resolution-srvadd"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.4"></a><h3>3.2.4.&nbsp;
+Use of SRV Records with Add-On Services</h3>
+
+<p>Many XMPP servers are implemented in such a way that they can host add-on services (beyond those defined in this specification and <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>) at DNS domain names that typically are "subdomains" of the main XMPP service (e.g., conference.example.net for a <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2007.</span><span>)</span></a> service associated with the example.net XMPP service) or "subdomains" of the first-level domain of the underlying service (e.g., muc.example.com for a <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2007.</span><span>)</span></a> service associated with the im.example.com XMPP service).  If an entity associated with a remote XMPP server wishes to communicate with such an add-on service, it would generate an appropriate XML stanza and the remote server would attempt to resolve the add-on service's DNS domain name via an SRV lookup on resource records such as "_xmpp-server._tcp.conference.example.net." or "_xmpp-server._tcp.muc.example.com.".  Therefore, if the administrators of an XMPP service wish to enable entities associated with remote servers to access such add-on services, they need to advertise the appropriate "_xmpp-server" SRV records in addition to the "_xmpp-server" record for their main XMPP service.  In case SRV records are not available, the fallback methods described under <a class='info' href='#tcp-resolution-fallback'>Section&nbsp;3.2.2<span> (</span><span class='info'>Fallback Processes</span><span>)</span></a> can be used to resolve the DNS domain names of add-on services.
+</p>
+<a name="tcp-reconnect"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.3"></a><h3>3.3.&nbsp;
+Reconnection</h3>
+
+<p>It can happen that an XMPP server goes offline unexpectedly while servicing TCP connections from connected clients and remote servers.  Because the number of such connections can be quite large, the reconnection algorithm employed by entities that seek to reconnect can have a significant impact on software performance and network congestion.  If an entity chooses to reconnect, it:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>SHOULD set the number of seconds that expire before reconnecting to an unpredictable number between 0 and 60 (this helps to ensure that not all entities attempt to reconnect at exactly the same number of seconds after being disconnected).
+</li>
+<li>SHOULD back off increasingly on the time between subsequent reconnection attempts (e.g., in accordance with "truncated binary exponential backoff" as described in <a class='info' href='#ETHERNET'>[ETHERNET]<span> (</span><span class='info'>, &ldquo;Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications,&rdquo; September&nbsp;1998.</span><span>)</span></a>) if the first reconnection attempt does not succeed.
+</li>
+</ul><p>
+      
+</p>
+<p>It is RECOMMENDED to make use of TLS session resumption <a class='info' href='#TLS-RESUME'>[TLS&#8209;RESUME]<span> (</span><span class='info'>Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, &ldquo;Transport Layer Security (TLS) Session Resumption without Server-Side State,&rdquo; January&nbsp;2008.</span><span>)</span></a> when reconnecting.  A future version of this document, or a separate specification, might provide more detailed guidelines regarding methods for speeding the reconnection process.
+</p>
+<a name="streams-reliability"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.4"></a><h3>3.4.&nbsp;
+Reliability</h3>
+
+<p>The use of long-lived TCP connections in XMPP implies that the sending of XML stanzas over XML streams can be unreliable, since the parties to a long-lived TCP connection might not discover a connectivity disruption in a timely manner.  At the XMPP application layer, long connectivity disruptions can result in undelivered stanzas.  Although the core XMPP technology defined in this specification does not contain features to overcome this lack of reliability, there exist XMPP extensions for doing so (e.g., <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a>).
+</p>
+<a name="streams"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4"></a><h3>4.&nbsp;
+XML Streams</h3>
+
+<a name="streams-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.1"></a><h3>4.1.&nbsp;
+Stream Fundamentals</h3>
+
+<p>Two fundamental concepts make possible the rapid, asynchronous exchange of relatively small payloads of structured information between XMPP entities: XML streams and XML stanzas.  These terms are defined as follows.
+</p>
+<p>
+        </p>
+<blockquote class="text"><dl>
+<dt>Definition of XML Stream:</dt>
+<dd>An XML stream is a container for the exchange of XML elements between any two entities over a network.  The start of an XML stream is denoted unambiguously by an opening "stream header" (i.e., an XML &lt;stream&gt; tag with appropriate attributes and namespace declarations), while the end of the XML stream is denoted unambiguously by a closing XML &lt;/stream&gt; tag.  During the life of the stream, the entity that initiated it can send an unbounded number of XML elements over the stream, either elements used to negotiate the stream (e.g., to complete <a class='info' href='#tls'>TLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> or <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>) or XML stanzas.  The "initial stream" is negotiated from the initiating entity (typically a client or server) to the receiving entity (typically a server), and can be seen as corresponding to the initiating entity's "connection to" or "session with" the receiving entity.  The initial stream enables unidirectional communication from the initiating entity to the receiving entity; in order to enable exchange of stanzas from the receiving entity to the initiating entity, the receiving entity MUST negotiate a stream in the opposite direction (the "response stream").
+</dd>
+<dt>Definition of XML Stanza:</dt>
+<dd>An XML stanza is the basic unit of meaning in XMPP.  A stanza is a first-level element (at depth=1 of the stream) whose element name is "message", "presence", or "iq" and whose qualifying namespace is 'jabber:client' or 'jabber:server'.  By contrast, a first-level element qualified by any other namespace is not an XML stanza (stream errors, stream features, TLS-related elements, SASL-related elements, etc.), nor is a &lt;message/&gt;, &lt;presence/&gt;, or &lt;iq/&gt; element that is qualified by the 'jabber:client' or 'jabber:server' namespace but that occurs at a depth other than one (e.g., a &lt;message/&gt; element contained within an extension element (<a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a>) for reporting purposes), nor is a &lt;message/&gt;, &lt;presence/&gt;, or &lt;iq/&gt; element that is qualified by a namespace other than 'jabber:client' or 'jabber:server'.  An XML stanza typically contains one or more child elements (with accompanying attributes, elements, and XML character data) as necessary in order to convey the desired information, which MAY be qualified by any XML namespace (see <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a> as well as <a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a> in this specification).
+</dd>
+</dl></blockquote><p>
+      
+</p>
+<p>There are three kinds of stanzas: message, presence, and IQ (short for
+"Info/Query").  These stanza types provide three different communication
+primitives: a "push" mechanism for generalized messaging, a specialized
+"publish-subscribe" mechanism for broadcasting information about network
+availability, and a "request-response" mechanism for more structured exchanges
+of data (similar to <a class='info' href='#HTTP'>[HTTP]<span> (</span><span class='info'>Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &ldquo;Hypertext Transfer Protocol -- HTTP/1.1,&rdquo; June&nbsp;1999.</span><span>)</span></a>).  Further explanations are provided
+under Sections <a class='info' href='#stanzas-semantics-message'>8.2.1<span> (</span><span class='info'>Message Semantics</span><span>)</span></a>,
+<a class='info' href='#stanzas-semantics-presence'>8.2.2<span> (</span><span class='info'>Presence Semantics</span><span>)</span></a>, and <a class='info' href='#stanzas-semantics-iq'>8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>, respectively.
+</p>
+<p>Consider the example of a client's connection to a server.  The client initiates an XML stream by sending a stream header to the server, preferably preceded by an XML declaration specifying the XML version and the character encoding supported (see <a class='info' href='#xml-declaration'>Section&nbsp;11.5<span> (</span><span class='info'>Inclusion of XML Declaration</span><span>)</span></a> and <a class='info' href='#xml-encoding'>Section&nbsp;11.6<span> (</span><span class='info'>Character Encoding</span><span>)</span></a>).  Subject to local policies and service provisioning, the server then replies with a second XML stream back to the client, again preferably preceded by an XML declaration.  Once the client has completed <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> and <a class='info' href='#bind'>resource binding<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>, the client can send an unbounded number of XML stanzas over the stream.  When the client desires to close the stream, it simply sends a closing &lt;/stream&gt; tag to the server  as further described under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>.
+</p>
+<p>In essence, then, one XML stream functions as an envelope for the XML stanzas sent during a session and another XML stream functions as an envelope for the XML stanzas received during a session.  We can represent this in a simplistic fashion as follows.
+</p><br /><hr class="insert" />
+<a name="figure-2"></a>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++--------------------+--------------------+
+| INITIAL STREAM     |  RESPONSE STREAM   |
++--------------------+--------------------+
+| &lt;stream&gt;           |                    |
+|--------------------|--------------------|
+|                    | &lt;stream&gt;           |
+|--------------------|--------------------|
+| &lt;presence&gt;         |                    |
+|   &lt;show/&gt;          |                    |
+| &lt;/presence&gt;        |                    |
+|--------------------|--------------------|
+| &lt;message to='foo'&gt; |                    |
+|   &lt;body/&gt;          |                    |
+| &lt;/message&gt;         |                    |
+|--------------------|--------------------|
+| &lt;iq to='bar'       |                    |
+|     type='get'&gt;    |                    |
+|   &lt;query/&gt;         |                    |
+| &lt;/iq&gt;              |                    |
+|--------------------|--------------------|
+|                    | &lt;iq from='bar'     |
+|                    |     type='result'&gt; |
+|                    |   &lt;query/&gt;         |
+|                    | &lt;/iq&gt;              |
+|--------------------|--------------------|
+| [ ... ]            |                    |
+|--------------------|--------------------|
+|                    | [ ... ]            |
+|--------------------|--------------------|
+| &lt;/stream&gt;          |                    |
+|--------------------|--------------------|
+|                    | &lt;/stream&gt;          |
++--------------------+--------------------+
+</pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;2: A Simplistic View of Two Streams&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
+
+<p>Those who are accustomed to thinking of XML in a document-centric manner might find the following analogies useful:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>The two XML streams are like two "documents" (matching the "document" production from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>) that are built up through the accumulation of XML stanzas.
+</li>
+<li>The root &lt;stream/&gt; element is like the "document entity" for each "document" (as described in Section 4.8 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).
+</li>
+<li>The XML stanzas sent over the streams are like "fragments" of the "documents" (as described in <a class='info' href='#XML-FRAG'>[XML&#8209;FRAG]<span> (</span><span class='info'>Grosso, P. and D. Veillard, &ldquo;XML Fragment Interchange,&rdquo; February&nbsp;2001.</span><span>)</span></a>).
+</li>
+</ul><p>
+      
+</p>
+<p>However, these descriptions are merely analogies, because XMPP does not deal in documents and fragments but in streams and stanzas.
+</p>
+<p>The remainder of this section defines the following aspects of XML streams (along with related topics):
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>How to open a stream (<a class='info' href='#streams-open'>Section&nbsp;4.2<span> (</span><span class='info'>Opening a Stream</span><span>)</span></a>)
+</li>
+<li>The stream negotiation process (<a class='info' href='#streams-negotiation'>Section&nbsp;4.3<span> (</span><span class='info'>Stream Negotiation</span><span>)</span></a>)
+</li>
+<li>How to close a stream (<a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>)
+</li>
+<li>The directionality of XML streams (<a class='info' href='#streams-direction'>Section&nbsp;4.5<span> (</span><span class='info'>Directionality</span><span>)</span></a>)
+</li>
+<li>How to handle peers that are silent (<a class='info' href='#streams-silence'>Section&nbsp;4.6<span> (</span><span class='info'>Handling of Silent Peers</span><span>)</span></a>)
+</li>
+<li>The XML attributes of a stream (<a class='info' href='#streams-attr'>Section&nbsp;4.7<span> (</span><span class='info'>Stream Attributes</span><span>)</span></a>)
+</li>
+<li>The XML namespaces of a stream (<a class='info' href='#streams-ns'>Section&nbsp;4.8<span> (</span><span class='info'>XML Namespaces</span><span>)</span></a>)
+</li>
+<li>Error handling related to XML streams (<a class='info' href='#streams-error'>Section&nbsp;4.9<span> (</span><span class='info'>Stream Errors</span><span>)</span></a>)
+</li>
+</ul><p>
+      
+</p>
+<a name="streams-open"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2"></a><h3>4.2.&nbsp;
+Opening a Stream</h3>
+
+<p>After connecting to the appropriate IP address and port of the receiving entity, the initiating entity opens a stream by sending a stream header (the "initial stream header") to the receiving entity.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The receiving entity then replies by sending a stream header of its own (the "response stream header") to the initiating entity.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The entities can then proceed with the remainder of the stream negotiation process.
+</p>
+<a name="streams-negotiation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3"></a><h3>4.3.&nbsp;
+Stream Negotiation</h3>
+
+<a name="streams-negotiation-basics"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.1"></a><h3>4.3.1.&nbsp;
+Basic Concepts</h3>
+
+<p>Because the receiving entity for a stream acts as a gatekeeper to the domains it services, it imposes certain conditions for connecting as a client or as a peer server.  At a minimum, the initiating entity needs to authenticate with the receiving entity before it is allowed to send stanzas to the receiving entity (for client-to-server streams this means using SASL as described under <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>).  However, the receiving entity can consider conditions other than authentication to be mandatory-to-negotiate, such as encryption using TLS as described under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>.  The receiving entity informs the initiating entity about such conditions by communicating "stream features": the set of particular protocol interactions that the initiating entity needs to complete before the receiving entity will accept XML stanzas from the initiating entity, as well as any protocol interactions that are voluntary-to-negotiate but that might improve the handling of an XML stream (e.g., establishment of application-layer compression as described in <a class='info' href='#XEP-0138'>[XEP&#8209;0138]<span> (</span><span class='info'>Hildebrand, J. and P. Saint-Andre, &ldquo;Stream Compression,&rdquo; May&nbsp;2009.</span><span>)</span></a>).
+</p>
+<p>The existence of conditions for connecting implies that
+        streams need to be negotiated.  The order of layers (TCP, then
+        TLS, then SASL, then XMPP as described under
+        <a class='info' href='#security-layers'>Section&nbsp;13.3<span> (</span><span class='info'>Order of Layers</span><span>)</span></a>) implies that stream
+        negotiation is a multi-stage process.  Further structure is
+        imposed by two factors: (1) a given stream feature might be
+        offered only to certain entities or only after certain other
+        features have been negotiated (e.g., resource binding is
+        offered only after SASL authentication), and (2) stream
+        features can be either mandatory-to-negotiate or
+        voluntary-to-negotiate.  Finally, for security reasons the
+        parties to a stream need to discard knowledge that they gained
+        during the negotiation process after successfully completing
+        the protocol interactions defined for certain features (e.g.,
+        TLS in all cases and SASL in the case when a security layer
+        might be established, as defined in the specification for the
+        relevant SASL mechanism). This is done by flushing the old stream context and exchanging new stream headers over the existing TCP connection.
+</p>
+<a name="streams-negotiation-features"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.2"></a><h3>4.3.2.&nbsp;
+Stream Features Format</h3>
+
+<p>If the initiating entity includes in the initial stream header the 'version' attribute set to a value of at least "1.0" (see <a class='info' href='#streams-attr-version'>Section&nbsp;4.7.5<span> (</span><span class='info'>version</span><span>)</span></a>), after sending the response stream header the receiving entity MUST send a &lt;features/&gt; child element (typically prefixed by the stream namespace prefix as described under <a class='info' href='#streams-ns-declarations'>Section&nbsp;4.8.5<span> (</span><span class='info'>Namespace Declarations and Prefixes</span><span>)</span></a>) to the initiating entity in order to announce any conditions for continuation of the stream negotiation process.  Each condition takes the form of a child element of the &lt;features/&gt; element, qualified by a namespace that is different from the stream namespace and the content namespace.  The &lt;features/&gt; element can contain one child, contain multiple children, or be empty.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: The order of child elements contained in any given &lt;features/&gt; element is not significant.
+</p>
+</blockquote>
+
+<p>If a particular stream feature is or can be mandatory-to-negotiate, the definition of that feature needs to do one of the following:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Declare that the feature is always mandatory-to-negotiate (e.g., this is true of resource binding for XMPP clients); or
+</li>
+<li>Specify a way for the receiving entity to flag the feature as mandatory-to-negotiate for this interaction (e.g., for STARTTLS, this is done by including an empty &lt;required/&gt; element in the advertisement for that stream feature, but that is not a generic format for all stream features); it is RECOMMENDED that stream feature definitions for new mandatory-to-negotiate features do so by including an empty &lt;required/&gt; element as is done for STARTTLS.
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Because there is no generic format for indicating that a feature is mandatory-to-negotiate, it is possible that a feature that is not understood by the initiating entity might be considered mandatory-to-negotiate by the receiving entity, resulting in failure of the stream negotiation process.  Although such an outcome would be undesirable, the working group deemed it rare enough that a generic format was not needed.
+</p>
+</blockquote>
+
+<p>For security reasons, certain stream features necessitate the initiating entity to send a new initial stream header upon successful negotiation of the feature (e.g., TLS in all cases and SASL in the case when a security layer might be established).  If this is true of a given stream feature, the definition of that feature needs to specify that a stream restart is expected after negotiation of the feature.
+</p>
+<p>A &lt;features/&gt; element that contains at least one mandatory-to-negotiate feature indicates that the stream negotiation is not complete and that the initiating entity MUST negotiate further features.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'&gt;
+       &lt;required/&gt;
+     &lt;/starttls&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>A &lt;features/&gt; element MAY contain more than one mandatory-to-negotiate feature.  This means that the initiating entity can choose among the mandatory-to-negotiate features at this stage of the stream negotiation process.  As an example, perhaps a future technology will perform roughly the same function as TLS, so the receiving entity might advertise support for both TLS and the future technology at the same stage of the stream negotiation process.  However, this applies only at a given stage of the stream negotiation process and does not apply to features that are mandatory-to-negotiate at different stages (e.g., the receiving entity would not advertise both STARTTLS and SASL as mandatory-to-negotiate, or both SASL and resource binding as mandatory-to-negotiate, because TLS would need to be negotiated before SASL and because SASL would need to be negotiated before resource binding).
+</p>
+<p>A &lt;features/&gt; element that contains both mandatory-to-negotiate and voluntary-to-negotiate features indicates that the negotiation is not complete but that the initiating entity MAY complete the voluntary-to-negotiate feature(s) before it attempts to negotiate the mandatory-to-negotiate feature(s).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/&gt;
+     &lt;compression xmlns='http://jabber.org/features/compress'&gt;
+       &lt;method&gt;zlib&lt;/method&gt;
+       &lt;method&gt;lzw&lt;/method&gt;
+     &lt;/compression&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>A &lt;features/&gt; element that contains only voluntary-to-negotiate features indicates that the stream negotiation is complete and that the initiating entity is cleared to send XML stanzas, but that the initiating entity MAY negotiate further features if desired.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;compression xmlns='http://jabber.org/features/compress'&gt;
+       &lt;method&gt;zlib&lt;/method&gt;
+       &lt;method&gt;lzw&lt;/method&gt;
+     &lt;/compression&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>An empty &lt;features/&gt; element indicates that the stream negotiation is complete and that the initiating entity is cleared to send XML stanzas.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features/&gt;
+</pre></div>
+<a name="streams-negotiation-restart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.3"></a><h3>4.3.3.&nbsp;
+Restarts</h3>
+
+<p>On successful negotiation of a feature that necessitates a stream restart, both parties MUST consider the previous stream to be replaced but MUST NOT send a closing &lt;/stream&gt; tag and MUST NOT terminate the underlying TCP connection; instead, the parties MUST reuse the existing connection, which might be in a new state (e.g., encrypted as a result of TLS negotiation).  The initiating entity then MUST send a new initial stream header, which SHOULD be preceded by an XML declaration as described under <a class='info' href='#xml-declaration'>Section&nbsp;11.5<span> (</span><span class='info'>Inclusion of XML Declaration</span><span>)</span></a>.  When the receiving entity receives the new initial stream header, it MUST generate a new stream ID (instead of reusing the old stream ID) before sending a new response stream header (which SHOULD be preceded by an XML declaration as described under <a class='info' href='#xml-declaration'>Section&nbsp;11.5<span> (</span><span class='info'>Inclusion of XML Declaration</span><span>)</span></a>).
+</p>
+<a name="streams-negotiation-resend"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.4"></a><h3>4.3.4.&nbsp;
+Resending Features</h3>
+
+<p>The receiving entity MUST send an updated list of stream features to the initiating entity after a stream restart.  The list of updated features MAY be empty if there are no further features to be advertised or MAY include any combination of features.
+</p>
+<a name="streams-negotiation-complete"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.5"></a><h3>4.3.5.&nbsp;
+Completion of Stream Negotiation</h3>
+
+<p>The receiving entity indicates completion of the stream negotiation process by sending to the initiating entity either an empty &lt;features/&gt; element or a &lt;features/&gt; element that contains only voluntary-to-negotiate features.  After doing so, the receiving entity MAY send an empty &lt;features/&gt; element (e.g., after negotiation of such voluntary-to-negotiate features) but MUST NOT send additional stream features to the initiating entity (if the receiving entity has new features to offer, preferably limited to mandatory-to-negotiate or security-critical features, it can simply close the stream with a &lt;reset/&gt; stream error (<a class='info' href='#streams-error-conditions-reset'>Section&nbsp;4.9.3.16<span> (</span><span class='info'>reset</span><span>)</span></a>) and then advertise the new features when the initiating entity reconnects, preferably closing existing streams in a staggered way so that not all of the initiating entities reconnect at once).  Once stream negotiation is complete, the initiating entity is cleared to send XML stanzas over the stream for as long as the stream is maintained by both parties.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Resource binding as specified under <a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a> is an historical exception to the foregoing rule, since it is mandatory-to-negotiate for clients but uses XML stanzas for negotiation purposes.
+</p>
+</blockquote>
+
+<p>The initiating entity MUST NOT attempt to send <a class='info' href='#stanzas'>XML stanzas<span> (</span><span class='info'>XML Stanzas</span><span>)</span></a> to entities other than itself (i.e., the client's connected resource or any other authenticated resource of the client's account) or the server to which it is connected until stream negotiation has been completed.  Even if the initiating entity does attempt to do so, the receiving entity MUST NOT accept such stanzas and MUST close the stream with a &lt;not-authorized/&gt; stream error (<a class='info' href='#streams-error-conditions-not-authorized'>Section&nbsp;4.9.3.12<span> (</span><span class='info'>not-authorized</span><span>)</span></a>).  This rule applies to XML stanzas only (i.e., &lt;message/&gt;, &lt;presence/&gt;, and &lt;iq/&gt; elements qualified by the content namespace) and not to XML elements used for stream negotiation (e.g., elements used to complete <a class='info' href='#tls'>TLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> or <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>).
+</p>
+<a name="streams-negotiation-address"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.6"></a><h3>4.3.6.&nbsp;
+Determination of Addresses</h3>
+
+<p>After the parties to an XML stream have completed the appropriate aspects of stream negotiation, the receiving entity for a stream MUST determine the initiating entity's JID.
+</p>
+<p>For client-to-server communication, both <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> and <a class='info' href='#bind'>resource binding<span> (</span><span class='info'>Resource Binding</span><span>)</span></a> MUST be completed before the server can determine the client's address.  The client's bare JID (&lt;localpart@domainpart&gt;) MUST be the authorization identity (as defined by <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>), either (1) as directly communicated by the client during <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> or (2) as derived by the server from the authentication identity if no authorization identity was specified during SASL negotiation.  The resourcepart of the full JID (&lt;localpart@domainpart/resourcepart&gt;) MUST be the resource negotiated by the client and server during <a class='info' href='#bind'>resource binding<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>.  A client MUST NOT attempt to guess at its JID but instead MUST consider its JID to be whatever the server returns to it during resource binding.  The server MUST ensure that the resulting JID (including localpart, domainpart, resourcepart, and separator characters) conforms to the canonical format for XMPP addresses defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>; to meet this restriction, the server MAY replace the JID sent by the client with the canonicalized JID as determined by the server and communicate that JID to the client during resource binding.
+</p>
+<p>For server-to-server communication, the initiating server's bare JID (&lt;domainpart&gt;) MUST be the authorization identity (as defined by <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>), either (1) as directly communicated by the initiating server during <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> or (2) as derived by the receiving server from the authentication identity if no authorization identity was specified during SASL negotiation. In the absence of SASL negotiation, the receiving server MAY consider the authorization identity to be an identity negotiated within the relevant verification protocol (e.g., the 'from' attribute of the &lt;result/&gt; element in Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Because it is possible for a third party to tamper with information that is sent over the stream before a security layer such as TLS is successfully negotiated, it is advisable for the receiving server to treat any such unprotected information with caution; this applies especially to the 'from' and 'to' addresses on the first initial stream header sent by the initiating entity.
+</p>
+</blockquote>
+
+<a name="streams-negotiation-flowchart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.7"></a><h3>4.3.7.&nbsp;
+Flow Chart</h3>
+
+<p>We summarize the foregoing rules in the following non-normative flow chart for the stream negotiation process, presented from the perspective of the initiating entity.
+</p><br /><hr class="insert" />
+<a name="figure-3"></a>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+                +---------------------+
+                | open TCP connection |
+                +---------------------+
+                           |
+                           v
+                    +---------------+
+                    | send initial  |&lt;-------------------------+
+                    | stream header |                          ^
+                    +---------------+                          |
+                           |                                   |
+                           v                                   |
+                   +------------------+                        |
+                   | receive response |                        |
+                   | stream header    |                        |
+                   +------------------+                        |
+                           |                                   |
+                           v                                   |
+                    +----------------+                         |
+                    | receive stream |                         |
++------------------&gt;| features       |                         |
+^   {OPTIONAL}      +----------------+                         |
+|                          |                                   |
+|                          v                                   |
+|       +&lt;-----------------+                                   |
+|       |                                                      |
+|    {empty?} ----&gt; {all voluntary?} ----&gt; {some mandatory?}   |
+|       |      no          |          no         |             |
+|       | yes              | yes                 | yes         |
+|       |                  v                     v             |
+|       |           +---------------+    +----------------+    |
+|       |           | MAY negotiate |    | MUST negotiate |    |
+|       |           | any or none   |    | one feature    |    |
+|       |           +---------------+    +----------------+    |
+|       v                  |                     |             |
+|   +---------+            v                     |             |
+|   |  DONE   |&lt;----- {negotiate?}               |             |
+|   +---------+   no       |                     |             |
+|                     yes  |                     |             |
+|                          v                     v             |
+|                          +---------&gt;+&lt;---------+             |
+|                                     |                        |
+|                                     v                        |
++&lt;-------------------------- {restart mandatory?} ------------&gt;+
+               no                                     yes
+
+</pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;3: Stream Negotiation Flow Chart&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
+
+<a name="streams-close"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4"></a><h3>4.4.&nbsp;
+Closing a Stream</h3>
+
+<p>An XML stream from one entity to another can be closed at any time, either because a specific stream error (<a class='info' href='#streams-error'>Section&nbsp;4.9<span> (</span><span class='info'>Stream Errors</span><span>)</span></a>) has occurred or in the absence of an error (e.g., when a client simply ends its session).
+</p>
+<p>A stream is closed by sending a closing &lt;/stream&gt; tag.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+E: &lt;/stream:stream&gt;
+</pre></div>
+<p>If the parties are using either two streams over a single TCP connection or two streams over two TCP connections, the entity that sends the closing stream tag MUST behave as follows:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Wait for the other party to also close its outbound
+          stream before terminating the underlying TCP connection(s);
+          this gives the other party an opportunity to finish
+          transmitting any outbound data to the closing entity before
+          the termination of the TCP connection(s).
+</li>
+<li>Refrain from sending any further data over its outbound stream to the other entity, but continue to process data received from the other entity (and, if necessary, process such data).
+</li>
+<li>Consider both streams to be void if the other party does not send its closing stream tag within a reasonable amount of time (where the definition of "reasonable" is a matter of implementation or deployment).
+</li>
+<li>After receiving a reciprocal closing stream tag from the other party or waiting a reasonable amount of time with no response, terminate the underlying TCP connection(s).
+</li>
+</ol><p>
+      
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: In accordance with Section 7.2.1 of <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>, to help prevent a truncation attack the party that is closing the stream MUST send a TLS close_notify alert and MUST receive a responding close_notify alert from the other party before terminating the underlying TCP connection(s).
+</p>
+</blockquote>
+
+<p>If the parties are using multiple streams over multiple TCP connections, there is no defined pairing of streams and therefore the behavior is a matter for implementation.
+</p>
+<a name="streams-direction"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5"></a><h3>4.5.&nbsp;
+Directionality</h3>
+
+<p>An XML stream is always unidirectional, by which is meant that XML stanzas can be sent in only one direction over the stream (either from the initiating entity to the receiving entity or from the receiving entity to the initiating entity).
+</p>
+<p>Depending on the type of session that has been negotiated and the nature of the entities involved, the entities might use:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Two streams over a single TCP connection, where the security context negotiated for the first stream is applied to the second stream.  This is typical for client-to-server sessions, and a server MUST allow a client to use the same TCP connection for both streams.
+</li>
+<li>Two streams over two TCP connections, where each stream is separately secured.  In this approach, one TCP connection is used for the stream in which stanzas are sent from the initiating entity to the receiving entity, and the other TCP connection is used for the stream in which stanzas are sent from the receiving entity to the initiating entity.  This is typical for server-to-server sessions.
+</li>
+<li>Multiple streams over two or more TCP connections, where each stream is separately secured.  This approach is sometimes used for server-to-server communication between two large XMPP service providers; however, this can make it difficult to maintain coherence of data received over multiple streams in situations described under <a class='info' href='#rules-order'>Section&nbsp;10.1<span> (</span><span class='info'>In-Order Processing</span><span>)</span></a>, which is why a server MAY close the stream with a &lt;conflict/&gt; stream error (<a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>) if a remote server attempts to negotiate more than one stream (as described under <a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>).
+</li>
+</ul><p>
+      
+</p>
+<p>This concept of directionality applies only to stanzas and explicitly does not apply to first-level children of the stream root that are used to bootstrap or manage the stream (e.g., first-level elements used for TLS negotiation, SASL negotiation, Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>, and Stream Management <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a>).
+</p>
+<p>The foregoing considerations imply that while completing <a class='info' href='#tls'>STARTTLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> and <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> two servers would use one TCP connection, but after the stream negotiation process is done that original TCP connection would be used only for the initiating server to send XML stanzas to the receiving server.  In order for the receiving server to send XML stanzas to the initiating server, the receiving server would need to reverse the roles and negotiate an XML stream from the receiving server to the initiating server over a separate TCP connection.  This separate TCP connection is then secured using a new round of TLS and/or SASL negotiation.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: For historical reasons, a server-to-server session always uses two TCP connections.  While that approach remains the standard behavior described in this document, extensions such as <a class='info' href='#XEP-0288'>[XEP&#8209;0288]<span> (</span><span class='info'>Hancke, P. and D. Cridland, &ldquo;Bidirectional Server-to-Server Connections,&rdquo; October&nbsp;2010.</span><span>)</span></a> enable servers to negotiate the use of a single TCP connection for bidirectional stanza exchange.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Although XMPP developers sometimes apply the terms "unidirectional" and "bidirectional" to the underlying TCP connection (e.g., calling the TCP connection for a client-to-server session "bidirectional" and the TCP connection for a server-to-server session "unidirectional"), strictly speaking a stream is always unidirectional (because the initiating entity and receiving entity always have a minimum of two streams, one in each direction) and a TCP connection is always bidirectional (because TCP traffic can be sent in both directions).  Directionality applies to the application-layer traffic sent over the TCP connection, not to the transport-layer traffic sent over the TCP connection itself.
+</p>
+</blockquote>
+
+<a name="streams-silence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6"></a><h3>4.6.&nbsp;
+Handling of Silent Peers</h3>
+
+<p>When an entity that is a party to a stream has not received any XMPP traffic from its stream peer for some period of time, the peer might appear to be silent.  There are several reasons why this might happen:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>The underlying TCP connection is dead.
+</li>
+<li>The XML stream is broken despite the fact that the underlying TCP connection is alive.
+</li>
+<li>The peer is idle and simply has not sent any XMPP traffic over its XML stream to the entity.
+</li>
+</ol><p>
+      
+</p>
+<p>These three conditions are best handled separately, as described in the following sections.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note:  For the purpose of handling silent peers, we treat a two unidirectional TCP connections as conceptually equivalent to a single bidirectional TCP connection (see <a class='info' href='#streams-direction'>Section&nbsp;4.5<span> (</span><span class='info'>Directionality</span><span>)</span></a>); however, implementers need to be aware that, in the case of two unidirectional TCP connections, responses to traffic at the XMPP application layer will come back from the peer on the second TCP connection.  In addition, the use of multiple streams in each direction (which is a somewhat frequent deployment choice for server-to-server connectivity among large XMPP service providers) further complicates application-level checking of XMPP streams and their underlying TCP connections, because there is no necessary correlation between any given initial stream and any given response stream.
+</p>
+</blockquote>
+
+<a name="streams-silence-dead"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.1"></a><h3>4.6.1.&nbsp;
+Dead Connection</h3>
+
+<p>If the underlying TCP connection is dead, stream-level checks (e.g., <a class='info' href='#XEP-0199'>[XEP&#8209;0199]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XMPP Ping,&rdquo; June&nbsp;2009.</span><span>)</span></a> and <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a>) are ineffective.  Therefore, it is unnecessary to close the stream with or without an error, and it is appropriate instead to simply terminate the TCP connection.
+</p>
+<p>One common method for checking the TCP connection is to send a space character (U+0020) between XML stanzas, which is allowed for XML streams as described under <a class='info' href='#xml-whitespace'>Section&nbsp;11.7<span> (</span><span class='info'>Whitespace</span><span>)</span></a>; the sending of such a space character is properly called a "whitespace keepalive" (the term "whitespace ping" is often used, despite the fact that it is not a ping since no "pong" is possible).  However, this is not allowed during TLS negotiation or SASL negotiation, as described under <a class='info' href='#tls-rules-data'>Section&nbsp;5.3.3<span> (</span><span class='info'>Data Formatting</span><span>)</span></a> and <a class='info' href='#sasl-rules-data'>Section&nbsp;6.3.5<span> (</span><span class='info'>Data Formatting</span><span>)</span></a>.
+</p>
+<a name="streams-silence-broken"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.2"></a><h3>4.6.2.&nbsp;
+Broken Stream</h3>
+
+<p>Even if the underlying TCP connection is alive, the peer might never respond to XMPP traffic that the entity sends, whether normal stanzas or specialized stream-checking traffic such as the application-level pings defined in <a class='info' href='#XEP-0199'>[XEP&#8209;0199]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XMPP Ping,&rdquo; June&nbsp;2009.</span><span>)</span></a> or the more comprehensive Stream Management protocol defined in <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a>.  In this case, it is appropriate for the entity to close a broken stream with a &lt;connection-timeout/&gt; stream error (<a class='info' href='#streams-error-conditions-connection-timeout'>Section&nbsp;4.9.3.4<span> (</span><span class='info'>connection-timeout</span><span>)</span></a>).
+</p>
+<a name="streams-silence-idle"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.3"></a><h3>4.6.3.&nbsp;
+Idle Peer</h3>
+
+<p>Even if the underlying TCP connection is alive and the
+        stream is not broken, the peer might have sent no stanzas for
+        a certain period of time.  In this case, the peer itself MAY
+        close the stream (as described under
+        <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>) rather than leaving an unused
+        stream open.  If the idle peer does not close the stream, the
+        other party MAY either close the stream using the handshake
+        described under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a> or close the
+        stream with a stream error (e.g., &lt;resource-constraint/&gt;
+        (<a class='info' href='#streams-error-conditions-resource-constraint'>Section&nbsp;4.9.3.17<span> (</span><span class='info'>resource-constraint</span><span>)</span></a>) if
+        the entity has reached a limit on the number of open TCP
+        connections or &lt;policy-violation/&gt;
+        (<a class='info' href='#streams-error-conditions-policy-violation'>Section&nbsp;4.9.3.14<span> (</span><span class='info'>policy-violation</span><span>)</span></a>)
+        if the connection has exceeded a local timeout policy).
+        However, consistent with the order of layers (specified under
+        <a class='info' href='#security-layers'>Section&nbsp;13.3<span> (</span><span class='info'>Order of Layers</span><span>)</span></a>), the other party is advised
+        to verify that the underlying TCP connection is alive and the
+        stream is unbroken (as described above) before concluding that
+        the peer is idle.  Furthermore, it is preferable to be liberal
+        in accepting idle peers, since experience has shown that doing
+        so improves the reliability of communication over XMPP
+        networks and that it is typically more efficient to maintain a
+        stream between two servers than to aggressively time out such a stream.
+</p>
+<a name="streams-silence-check"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.4"></a><h3>4.6.4.&nbsp;
+Use of Checking Methods</h3>
+
+<p>Implementers are advised to support whichever
+        stream-checking and connection-checking methods they deem
+        appropriate, but to carefully weigh the network impact of such
+        methods against the benefits of discovering broken streams and
+        dead TCP connections in a timely manner.  The length of time
+        between the use of any particular check is very much a matter
+        of local service policy and depends strongly on the network
+        environment and usage scenarios of a given deployment and
+        connection type. At the time of writing, it is RECOMMENDED that any such check be performed not more than once every 5 minutes and that, ideally, such checks will be initiated by clients rather than servers.  Those who implement XMPP software and deploy XMPP services are encouraged to seek additional advice regarding appropriate timing of stream-checking and connection-checking methods, particularly when power-constrained devices are being used (e.g., in mobile environments).
+</p>
+<a name="streams-attr"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7"></a><h3>4.7.&nbsp;
+Stream Attributes</h3>
+
+<p>The attributes of the root &lt;stream/&gt; element are defined in the following sections.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Until and unless the confidentiality and integrity of the stream are protected via TLS as described under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> or an equivalent security layer (such as the SASL GSSAPI mechanism), the attributes provided in a stream header could be tampered with by an attacker.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: The attributes of the root &lt;stream/&gt; element are not prepended by a namespace prefix because, as explained in <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>, "[d]efault namespace declarations do not apply directly to attribute names; the interpretation of unprefixed attributes is determined by the element on which they appear."
+</p>
+</blockquote>
+
+<a name="streams-attr-from"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.1"></a><h3>4.7.1.&nbsp;
+from</h3>
+
+<p>The 'from' attribute specifies an XMPP identity of the entity sending the stream element.
+</p>
+<p>For initial stream headers in client-to-server communication, the 'from' attribute is the XMPP identity of the principal controlling the client, i.e., a JID of the form &lt;localpart@domainpart&gt;.  The client might not know the XMPP identity, e.g., because the XMPP identity is assigned at a level other than the XMPP application layer (as in the Generic Security Service Application Program Interface <a class='info' href='#GSS-API'>[GSS&#8209;API]<span> (</span><span class='info'>Linn, J., &ldquo;Generic Security Service Application Program Interface Version 2, Update 1,&rdquo; January&nbsp;2000.</span><span>)</span></a>) or is derived by the server from information provided by the client (as in some deployments of end-user certificates with the SASL EXTERNAL mechanism).  Furthermore, if the client considers the XMPP identity to be private information then it is advised not to include a 'from' attribute before the confidentiality and integrity of the stream are protected via TLS or an equivalent security layer.  However, if the client knows the XMPP identity then it SHOULD include the 'from' attribute after the confidentiality and integrity of the stream are protected via TLS or an equivalent security layer.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>For initial stream headers in server-to-server communication, the 'from' attribute is one of the configured FQDNs of the server, i.e., a JID of the form &lt;domainpart&gt;.  The initiating server might have more than one XMPP identity, e.g., in the case of a server that provides virtual hosting, so it will need to choose an identity that is associated with this output stream (e.g., based on the 'to' attribute of the stanza that triggered the stream negotiation attempt).  Because a server is a "public entity" on the XMPP network, it MUST include the 'from' attribute after the confidentiality and integrity of the stream are protected via TLS or an equivalent security layer.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='example.net'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>For response stream headers in both client-to-server and server-to-server communication, the receiving entity MUST include the 'from' attribute and MUST set its value to one of the receiving entity's FQDNs (which MAY be an FQDN other than that specified in the 'to' attribute of the initial stream header, as described under <a class='info' href='#streams-error-rules-host'>Section&nbsp;4.9.1.3<span> (</span><span class='info'>Stream Errors When the Host Is Unspecified or Unknown</span><span>)</span></a> and <a class='info' href='#streams-error-conditions-host-unknown'>Section&nbsp;4.9.3.6<span> (</span><span class='info'>host-unknown</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Whether or not the 'from' attribute is included, each entity MUST verify the identity of the other entity before exchanging XML stanzas with it, as described under <a class='info' href='#security-authentication'>Section&nbsp;13.5<span> (</span><span class='info'>Peer Entity Authentication</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: It is possible that implementations based on <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> will not include the 'from' address on any stream headers (even ones whose confidentiality and integrity are protected); an entity SHOULD be liberal in accepting such stream headers.
+</p>
+</blockquote>
+
+<a name="streams-attr-to"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.2"></a><h3>4.7.2.&nbsp;
+to</h3>
+
+<p>For initial stream headers in both client-to-server and server-to-server communication, the initiating entity MUST include the 'to' attribute and MUST set its value to a domainpart that the initiating entity knows or expects the receiving entity to service.  (The same information can be provided in other ways, such as a Server Name Indication during TLS negotiation as described in <a class='info' href='#TLS-EXT'>[TLS&#8209;EXT]<span> (</span><span class='info'>Eastlake 3rd, D., &ldquo;Transport Layer Security (TLS) Extensions: Extension Definitions,&rdquo; January&nbsp;2011.</span><span>)</span></a>.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>For response stream headers in client-to-server communication, if the client included a 'from' attribute in the initial stream header then the server MUST include a 'to' attribute in the response stream header and MUST set its value to the bare JID specified in the 'from' attribute of the initial stream header.  If the client did not include a 'from' attribute in the initial stream header then the server MUST NOT include a 'to' attribute in the response stream header.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>For response stream headers in server-to-server communication, the receiving entity MUST include a 'to' attribute in the response stream header and MUST set its value to the domainpart specified in the 'from' attribute of the initial stream header.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
+       to='example.net'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Whether or not the 'to' attribute is included, each entity MUST verify the identity of the other entity before exchanging XML stanzas with it, as described under <a class='info' href='#security-authentication'>Section&nbsp;13.5<span> (</span><span class='info'>Peer Entity Authentication</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: It is possible that implementations based on <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> will not include the 'to' address on stream headers; an entity SHOULD be liberal in accepting such stream headers.
+</p>
+</blockquote>
+
+<a name="streams-attr-id"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.3"></a><h3>4.7.3.&nbsp;
+id</h3>
+
+<p>The 'id' attribute specifies a unique identifier for the stream, called a "stream ID".  The stream ID MUST be generated by the receiving entity when it sends a response stream header and MUST BE unique within the receiving application (normally a server).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: The stream ID MUST be both unpredictable and non-repeating because it can be security-critical when reused by an authentication mechanisms, as is the case for Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a> and the "XMPP 0.9" authentication mechanism used before RFC 3920 defined the use of SASL in XMPP; for recommendations regarding randomness for security purposes, see <a class='info' href='#RANDOM'>[RANDOM]<span> (</span><span class='info'>Eastlake, D., Schiller, J., and S. Crocker, &ldquo;Randomness Requirements for Security,&rdquo; June&nbsp;2005.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>For initial stream headers, the initiating entity MUST NOT include the 'id' attribute; however, if the 'id' attribute is included, the receiving entity MUST ignore it.
+</p>
+<p>For response stream headers, the receiving entity MUST include the 'id' attribute.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: In RFC 3920, the text regarding inclusion of the 'id' attribute was ambiguous, leading some implementations to leave the attribute off the response stream header.
+</p>
+</blockquote>
+
+<a name="streams-attr-xmllang"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.4"></a><h3>4.7.4.&nbsp;
+xml:lang</h3>
+
+<p>The 'xml:lang' attribute specifies an entity's preferred or default language for any human-readable XML character data to be sent over the stream (an XML stanza can also possess an 'xml:lang' attribute, as discussed under <a class='info' href='#stanzas-attributes-lang'>Section&nbsp;8.1.5<span> (</span><span class='info'>xml:lang</span><span>)</span></a>).  The syntax of this attribute is defined in Section 2.12 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>; in particular, the value of the 'xml:lang' attribute MUST conform to the NMTOKEN datatype (as defined in Section 2.3 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>) and MUST conform to the language identifier format defined in <a class='info' href='#LANGTAGS'>[LANGTAGS]<span> (</span><span class='info'>Phillips, A. and M. Davis, &ldquo;Tags for Identifying Languages,&rdquo; September&nbsp;2009.</span><span>)</span></a>.
+</p>
+<p>For initial stream headers, the initiating entity SHOULD include the 'xml:lang' attribute.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>For response stream headers, the receiving entity MUST include the 'xml:lang' attribute.  The following rules apply:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>If the initiating entity included an 'xml:lang' attribute in its initial stream header and the receiving entity supports that language in the human-readable XML character data that it generates and sends to the initiating entity (e.g., in the &lt;text/&gt; element for stream and stanza errors), the value of the 'xml:lang' attribute MUST be the identifier for the initiating entity's preferred language (e.g., "de-CH").
+</li>
+<li>If the receiving entity supports a language that matches the initiating entity's preferred language according to the "lookup scheme" specified in Section 3.4 of <a class='info' href='#LANGMATCH'>[LANGMATCH]<span> (</span><span class='info'>Phillips, A. and M. Davis, &ldquo;Matching of Language Tags,&rdquo; September&nbsp;2006.</span><span>)</span></a> (e.g., "de" instead of "de-CH"), then the value of the 'xml:lang' attribute SHOULD be the identifier for the matching language.
+</li>
+<li>If the receiving entity does not support the initiating entity's preferred language or a matching language according to the lookup scheme (or if the initiating entity did not include the 'xml:lang' attribute in its initial stream header), then the value of the 'xml:lang' attribute MUST be the identifier for the default language of the receiving entity (e.g., "en").
+</li>
+</ul><p>
+        
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>If the initiating entity included the 'xml:lang' attribute in its initial stream header, the receiving entity SHOULD remember that value as the default xml:lang for all stanzas sent by the initiating entity over the current stream.  As described under <a class='info' href='#stanzas-attributes-lang'>Section&nbsp;8.1.5<span> (</span><span class='info'>xml:lang</span><span>)</span></a>, the initiating entity MAY include the 'xml:lang' attribute in any XML stanzas it sends over the stream.  If the initiating entity does not include the 'xml:lang' attribute in any such stanza, the receiving entity SHOULD add the 'xml:lang' attribute to the stanza when routing it to a remote server or delivering it to a connected client, where the value of the attribute MUST be the identifier for the language preferred by the initiating entity (even if the receiving entity does not support that language for human-readable XML character data it generates and sends to the initiating entity, such as in stream or stanza errors).  If the initiating entity includes the 'xml:lang' attribute in any such stanza, the receiving entity MUST NOT modify or delete it when routing it to a remote server or delivering it to a connected client.
+</p>
+<a name="streams-attr-version"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.5"></a><h3>4.7.5.&nbsp;
+version</h3>
+
+<p>The inclusion of the version attribute set to a value of at least "1.0" signals support for the stream-related protocols defined in this specification, including <a class='info' href='#tls'>TLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>, <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>, <a class='info' href='#streams-negotiation-features'>stream features<span> (</span><span class='info'>Stream Features Format</span><span>)</span></a>, and <a class='info' href='#streams-error'>stream errors<span> (</span><span class='info'>Stream Errors</span><span>)</span></a>.
+</p>
+<p>The version of XMPP specified in this specification is "1.0"; in
+particular, XMPP 1.0 encapsulates the stream-related protocols as well as the
+basic semantics of the three defined XML stanza types (&lt;message/&gt;,
+&lt;presence/&gt;, and &lt;iq/&gt; as described under Sections <a class='info' href='#stanzas-semantics-message'>8.2.1<span> (</span><span class='info'>Message Semantics</span><span>)</span></a>, <a class='info' href='#stanzas-semantics-presence'>8.2.2<span> (</span><span class='info'>Presence Semantics</span><span>)</span></a>, and <a class='info' href='#stanzas-semantics-iq'>8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>, respectively).
+</p>
+<p>The numbering scheme for XMPP versions is "&lt;major&gt;.&lt;minor&gt;".  The major and minor numbers MUST be treated as separate integers and each number MAY be incremented higher than a single digit.  Thus, "XMPP 2.4" would be a lower version than "XMPP 2.13", which in turn would be lower than "XMPP 12.3".  Leading zeros (e.g., "XMPP 6.01") MUST be ignored by recipients and MUST NOT be sent.
+</p>
+<p>The major version number will be incremented only if the stream and stanza formats or obligatory actions have changed so dramatically that an older version entity would not be able to interoperate with a newer version entity if it simply ignored the elements and attributes it did not understand and took the actions defined in the older specification.
+</p>
+<p>The minor version number will be incremented only if significant new capabilities have been added to the core protocol (e.g., a newly defined value of the 'type' attribute for message, presence, or IQ stanzas).  The minor version number MUST be ignored by an entity with a smaller minor version number, but MAY be used for informational purposes by the entity with the larger minor version number (e.g., the entity with the larger minor version number would simply note that its correspondent would not be able to understand that value of the 'type' attribute and therefore would not send it).
+</p>
+<p>The following rules apply to the generation and handling of the 'version' attribute within stream headers:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The initiating entity MUST set the value of the 'version' attribute in the initial stream header to the highest version number it supports (e.g., if the highest version number it supports is that defined in this specification, it MUST set the value to "1.0").
+</li>
+<li>The receiving entity MUST set the value of the 'version' attribute in the response stream header to either the value supplied by the initiating entity or the highest version number supported by the receiving entity, whichever is lower.  The receiving entity MUST perform a numeric comparison on the major and minor version numbers, not a string match on "&lt;major&gt;.&lt;minor&gt;".
+</li>
+<li>If the version number included in the response stream header is at least one major version lower than the version number included in the initial stream header and newer version entities cannot interoperate with older version entities as described, the initiating entity SHOULD close the stream with an &lt;unsupported-version/&gt; stream error (<a class='info' href='#streams-error-conditions-unsupported-version'>Section&nbsp;4.9.3.25<span> (</span><span class='info'>unsupported-version</span><span>)</span></a>).
+</li>
+<li>If either entity receives a stream header with no 'version' attribute, the entity MUST consider the version supported by the other entity to be "0.9" and SHOULD NOT include a 'version' attribute in the response stream header.
+</li>
+</ol><p>
+        
+</p>
+<a name="streams-attr-summary"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.6"></a><h3>4.7.6.&nbsp;
+Summary of Stream Attributes</h3>
+
+<p>The following table summarizes the attributes of the root &lt;stream/&gt; element.
+</p><br /><hr class="insert" />
+<a name="figure-4"></a>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++----------+--------------------------+-------------------------+
+|          | initiating to receiving  | receiving to initiating |
++----------+--------------------------+-------------------------+
+| to       | JID of receiver          | JID of initiator        |
+| from     | JID of initiator         | JID of receiver         |
+| id       | ignored                  | stream identifier       |
+| xml:lang | default language         | default language        |
+| version  | XMPP 1.0+ supported      | XMPP 1.0+ supported     |
++----------+--------------------------+-------------------------+
+</pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;4: Stream Attributes&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
+
+<a name="streams-ns"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8"></a><h3>4.8.&nbsp;
+XML Namespaces</h3>
+
+<p>Readers are referred to the specification of XML namespaces <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a> for a full understanding of the concepts used in this section, especially the concept of a "default namespace" as provided in Section 3 and Section 6.2 of that specification.
+</p>
+<a name="streams-ns-stream"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8.1"></a><h3>4.8.1.&nbsp;
+Stream Namespace</h3>
+
+<p>The root &lt;stream/&gt; element ("stream header") MUST be qualified by the namespace 'http://etherx.jabber.org/streams' (the "stream namespace").  If this rule is violated, the entity that receives the offending stream header MUST close the stream with a stream error, which SHOULD be &lt;invalid-namespace/&gt; (<a class='info' href='#streams-error-conditions-invalid-namespace'>Section&nbsp;4.9.3.10<span> (</span><span class='info'>invalid-namespace</span><span>)</span></a>), although some existing implementations send &lt;bad-format/&gt; (<a class='info' href='#streams-error-conditions-bad-format'>Section&nbsp;4.9.3.1<span> (</span><span class='info'>bad-format</span><span>)</span></a>) instead.
+</p>
+<a name="streams-ns-content"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8.2"></a><h3>4.8.2.&nbsp;
+Content Namespace</h3>
+
+<p>An entity MAY declare a "content namespace" as the default namespace for data sent over the stream (i.e., data other than elements qualified by the stream namespace).  If so, (1) the content namespace MUST be other than the stream namespace, and (2) the content namespace MUST be the same for the initial stream and the response stream so that both streams are qualified consistently.  The content namespace applies to all first-level child elements sent over the stream unless explicitly qualified by another namespace (i.e., the content namespace is the default namespace).
+</p>
+<p>Alternatively (i.e., instead of declaring the content namespace as the default namespace), an entity MAY explicitly qualify the namespace for each first-level child element of the stream, using so-called "prefix-free canonicalization".  These two styles are shown in the following examples.
+</p>
+<p>When a content namespace is declared as the default namespace, in rough outline a stream will look something like the following.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;stream:stream
+    from='juliet@im.example.com'
+    to='im.example.com'
+    version='1.0'
+    xml:lang='en'
+    xmlns='jabber:client'
+    xmlns:stream='http://etherx.jabber.org/streams'&gt;
+  &lt;message&gt;
+    &lt;body&gt;foo&lt;/body&gt;
+  &lt;/message&gt;
+&lt;/stream:stream&gt;
+</pre></div>
+<p>When a content namespace is not declared as the default namespace and so-called "prefix-free canonicalization" is used instead, in rough outline a stream will look something like the following.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;stream
+    from='juliet@im.example.com'
+    to='im.example.com'
+    version='1.0'
+    xml:lang='en'
+    xmlns='http://etherx.jabber.org/streams'&gt;
+  &lt;message xmlns='jabber:client'&gt;
+    &lt;body&gt;foo&lt;/body&gt;
+  &lt;/message&gt;
+&lt;/stream&gt;
+</pre></div>
+<p>Traditionally, most XMPP implementations have used the content-namespace-as-default-namespace style rather than the prefix-free canonicalization style for stream headers; however, both styles are acceptable since they are semantically equivalent.
+</p>
+<a name="streams-ns-xmpp"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8.3"></a><h3>4.8.3.&nbsp;
+XMPP Content Namespaces</h3>
+
+<p>XMPP as defined in this specification uses two content namespaces: 'jabber:client' and 'jabber:server'.  These namespaces are nearly identical but are used in different contexts (client-to-server communication for 'jabber:client' and server-to-server communication for 'jabber:server').  The only difference between the two is that the 'to' and 'from' attributes are OPTIONAL on stanzas sent over XML streams qualified by the 'jabber:client' namespace, whereas they are REQUIRED on stanzas sent over XML streams qualified by the 'jabber:server' namespace.  Support for these content namespaces implies support for the <a class='info' href='#stanzas-attributes'>common attributes<span> (</span><span class='info'>Common Attributes</span><span>)</span></a> and <a class='info' href='#stanzas-semantics'>basic semantics<span> (</span><span class='info'>Basic Semantics</span><span>)</span></a> of all three core stanza types (message, presence, and IQ).
+</p>
+<p>An implementation MAY support content namespaces other than 'jabber:client' or 'jabber:server'.  However, because such namespaces would define applications other than XMPP, they are to be defined in separate specifications.
+</p>
+<p>An implementation MAY refuse to support any other content namespaces as default namespaces.  If an entity receives a first-level child element qualified by a content namespace it does not support, it MUST close the stream with an &lt;invalid-namespace/&gt; stream error (<a class='info' href='#streams-error-conditions-invalid-namespace'>Section&nbsp;4.9.3.10<span> (</span><span class='info'>invalid-namespace</span><span>)</span></a>).
+</p>
+<p>Client implementations MUST support the 'jabber:client' content namespace as a default namespace.  The 'jabber:server' content namespace is out of scope for an XMPP client, and a client MUST NOT send stanzas qualified by the 'jabber:server' namespace.
+</p>
+<p>Server implementations MUST support as default content namespaces both the 'jabber:client' namespace (when the stream is used for communication between a client and a server) and the 'jabber:server' namespace (when the stream is used for communication between two servers).  When communicating with a connected client, a server MUST NOT send stanzas qualified by the 'jabber:server' namespace; when communicating with a peer server, a server MUST NOT send stanzas qualified by the 'jabber:client' namespace.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Because a client sends stanzas over a stream whose content namespace is 'jabber:client', if a server routes to a peer server a stanza it has received from a connected client then it needs to "re-scope" the stanza so that its content namespace is 'jabber:server'.  Similarly, if a server delivers to a connected client a stanza it has received from a peer server then it needs to "re-scope" the stanza so that its content namespace is 'jabber:client'.  This rule applies to XML stanzas as defined under <a class='info' href='#streams-fundamentals'>Section&nbsp;4.1<span> (</span><span class='info'>Stream Fundamentals</span><span>)</span></a> (i.e., a first-level &lt;message/&gt;, &lt;presence/&gt;, or &lt;iq/&gt; element qualified by the 'jabber:client' or 'jabber:server' namespace), and by namespace inheritance to all child elements of a stanza. However, the rule does not apply to elements qualified by namespaces other than 'jabber:client' and 'jabber:server' nor to any children of such elements (e.g., a &lt;message/&gt; element contained within an extension element (<a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a>) for reporting purposes).  Although it is not forbidden for an entity to generate stanzas in which an extension element contains a child element qualified by the 'jabber:client' or 'jabber:server' namespace, existing implementations handle such stanzas inconsistently; therefore, implementers are advised to weigh the likely lack of interoperability against the possible utility of such stanzas.  Finally, servers are advised to apply stanza re-scoping to other stream connection methods and alternative XMPP connection methods, such as those specified in <a class='info' href='#XEP-0124'>[XEP&#8209;0124]<span> (</span><span class='info'>Paterson, I., Smith, D., and P. Saint-Andre, &ldquo;Bidirectional-streams Over Synchronous HTTP (BOSH),&rdquo; July&nbsp;2010.</span><span>)</span></a>, <a class='info' href='#XEP-0206'>[XEP&#8209;0206]<span> (</span><span class='info'>Paterson, I. and P. Saint-Andre, &ldquo;XMPP Over BOSH,&rdquo; July&nbsp;2010.</span><span>)</span></a>, <a class='info' href='#XEP-0114'>[XEP&#8209;0114]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Jabber Component Protocol,&rdquo; March&nbsp;2005.</span><span>)</span></a>, and <a class='info' href='#XEP-0225'>[XEP&#8209;0225]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Component Connections,&rdquo; October&nbsp;2008.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="streams-ns-other"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8.4"></a><h3>4.8.4.&nbsp;
+Other Namespaces</h3>
+
+<p>Either party to a stream MAY send data qualified by namespaces other than the content namespace and the stream namespace.  For example, this is how data related to TLS negotiation and SASL negotiation are exchanged, as well as XMPP extensions such as Stream Management <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a> and Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: For historical reasons, some server implementations expect a declaration of the 'jabber:server:dialback' namespace on server-to-server streams, as explained in <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>However, an XMPP server MUST NOT route or deliver data received over an input stream if that data is (a) qualified by another namespace and (b) addressed to an entity other than the server, unless the other party to the output stream over which the server would send the data has explicitly negotiated or advertised support for receiving arbitrary data from the server.  This rule is included because XMPP is designed for the exchange of XML stanzas (not arbitrary XML data), and because allowing an entity to send arbitrary data to other entities could significantly increase the potential for exchanging malicious information.  As an example of this rule, the server hosting the example.net domain would not route the following first-level XML element from &lt;romeo@example.net&gt; to &lt;juliet@example.com&gt;:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+  &lt;ns1:foo xmlns:ns1='http://example.org/ns1'
+           from='romeo@example.net/resource1'
+           to='juliet@example.com'&gt;
+    &lt;ns1:bar/&gt;
+  &lt;/ns1:foo&gt;
+</pre></div>
+<p>This rule also applies to first-level elements that look like stanzas but that are improperly namespaced and therefore really are not stanzas at all (see also <a class='info' href='#streams-ns-declarations'>Section&nbsp;4.8.5<span> (</span><span class='info'>Namespace Declarations and Prefixes</span><span>)</span></a>), for example:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+  &lt;ns2:message xmlns:ns2='http://example.org/ns2'
+               from='romeo@example.net/resource1'
+               to='juliet@example.com'&gt;
+    &lt;body&gt;hi&lt;/body&gt;
+  &lt;/ns2:message&gt;
+</pre></div>
+<p>Upon receiving arbitrary first-level XML elements over an input stream, a server MUST either ignore the data or close the stream with a stream error, which SHOULD be &lt;unsupported-stanza-type/&gt; (<a class='info' href='#streams-error-conditions-unsupported-stanza-type'>Section&nbsp;4.9.3.24<span> (</span><span class='info'>unsupported-stanza-type</span><span>)</span></a>).
+</p>
+<a name="streams-ns-declarations"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.8.5"></a><h3>4.8.5.&nbsp;
+Namespace Declarations and Prefixes</h3>
+
+<p>Because the content namespace is other than the stream namespace, if a content namespace is declared as the default namespace then the following statements are true:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The stream header needs to contain a namespace declaration for both the content namespace and the stream namespace.
+</li>
+<li>The stream namespace declaration needs to include a namespace prefix for the stream namespace.
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: For historical reasons, an implementation MAY accept only the prefix 'stream' for the stream namespace (resulting in prefixed names such as &lt;stream:stream&gt; and &lt;stream:features&gt;); this specification retains that allowance from <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> for the purpose of backward compatibility.  Implementations are advised that using a prefix other than 'stream' for the stream namespace might result in interoperability problems.  If an entity receives a stream header with a stream namespace prefix it does not accept, it MUST close the stream with a stream error, which SHOULD be &lt;bad-namespace-prefix/&gt; (<a class='info' href='#streams-error-conditions-bad-namespace-prefix'>Section&nbsp;4.9.3.2<span> (</span><span class='info'>bad-namespace-prefix</span><span>)</span></a>), although some existing implementations send &lt;bad-format/&gt; (<a class='info' href='#streams-error-conditions-bad-format'>Section&nbsp;4.9.3.1<span> (</span><span class='info'>bad-format</span><span>)</span></a>) instead.
+</p>
+</blockquote>
+
+<p>An implementation MUST NOT generate namespace prefixes for elements qualified by the content namespace (i.e., the default namespace for data sent over the stream) if the content namespace is 'jabber:client' or 'jabber:server'.  For example, the following is illegal:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;stream:stream
+    from='juliet@im.example.com'
+    to='im.example.com'
+    version='1.0'
+    xml:lang='en'
+    xmlns='jabber:client'
+    xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+  &lt;foo:message xmlns:foo='jabber:client'&gt;
+    &lt;foo:body&gt;foo&lt;/foo:body&gt;
+  &lt;/foo:message&gt;
+</pre></div>
+<p>An XMPP entity SHOULD NOT accept data that violates this rule (in
+particular, an XMPP server MUST NOT route or deliver such data to another
+entity without first correcting the error); instead it SHOULD either ignore the data or close the stream with a stream error, which SHOULD be &lt;bad-namespace-prefix/&gt; (<a class='info' href='#streams-error-conditions-bad-namespace-prefix'>Section&nbsp;4.9.3.2<span> (</span><span class='info'>bad-namespace-prefix</span><span>)</span></a>).
+</p>
+<p>Namespaces declared in a stream header MUST apply only to that stream (e.g., the 'jabber:server:dialback' namespace used in Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>).  In particular, because XML stanzas intended for routing or delivery over streams with other entities will lose the namespace context declared in the header of the stream in which those stanzas originated, namespaces for extended content within such stanzas MUST NOT be declared in that stream header (see also <a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a>).  If either party to a stream declares such namespaces, the other party to the stream SHOULD close the stream with an &lt;invalid-namespace/&gt; stream error (<a class='info' href='#streams-error-conditions-invalid-namespace'>Section&nbsp;4.9.3.10<span> (</span><span class='info'>invalid-namespace</span><span>)</span></a>).  In any case, an entity MUST ensure that such namespaces are properly declared (according to this section) when routing or delivering stanzas from an input stream to an output stream.
+</p>
+<a name="streams-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9"></a><h3>4.9.&nbsp;
+Stream Errors</h3>
+
+<p>The root stream element MAY contain an &lt;error/&gt; child element that is qualified by the stream namespace.  The error child SHALL be sent by a compliant entity if it perceives that a stream-level error has occurred.
+</p>
+<a name="streams-error-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.1"></a><h3>4.9.1.&nbsp;
+Rules</h3>
+
+<p>The following rules apply to stream-level errors.
+</p>
+<a name="streams-error-rules-unrecoverable"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.1.1"></a><h3>4.9.1.1.&nbsp;
+Stream Errors Are Unrecoverable</h3>
+
+<p>Stream-level errors are unrecoverable.  Therefore, if an error occurs at the level of the stream, the entity that detects the error MUST send an &lt;error/&gt; element with an appropriate child element specifying the error condition and then immediately close the stream as described under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message&gt;&lt;body&gt;No closing tag!&lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;not-well-formed
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p>The entity that receives the stream error then SHALL close the stream as explained under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-rules-setup"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.1.2"></a><h3>4.9.1.2.&nbsp;
+Stream Errors Can Occur During Setup</h3>
+
+<p>If the error is triggered by the initial stream header, the receiving entity MUST still send the opening &lt;stream&gt; tag, include the &lt;error/&gt; element as a child of the stream element, and send the closing &lt;/stream&gt; tag (preferably in the same TCP packet).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://wrong.namespace.example.org/'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;invalid-namespace
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-rules-host"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.1.3"></a><h3>4.9.1.3.&nbsp;
+Stream Errors When the Host Is Unspecified or Unknown</h3>
+
+<p>If the initiating entity provides no 'to' attribute or provides an unknown host in the 'to' attribute and the error occurs during stream setup, the value of the 'from' attribute returned by the receiving entity in the stream header sent before closing the stream MUST be either an authoritative FQDN for the receiving entity or the empty string.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='unknown.host.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;host-unknown
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-rules-where"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.1.4"></a><h3>4.9.1.4.&nbsp;
+Where Stream Errors Are Sent</h3>
+
+<p>When two TCP connections are used between the initiating entity and the receiving entity (one in each direction) rather than using a single bidirectional connection, the following rules apply:
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>Stream-level errors related to the initial stream are returned by the receiving entity on the response stream via the same TCP connection.
+</li>
+<li>Stanza errors triggered by outbound stanzas sent from the initiating entity over the initial stream via the same TCP connection are returned by the receiving entity on the response stream via the other ("return") TCP connection, since they are inbound stanzas from the perspective of the initiating entity.
+</li>
+</ul><p>
+          
+</p>
+<a name="streams-error-syntax"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.2"></a><h3>4.9.2.&nbsp;
+Syntax</h3>
+
+<p>The syntax for stream errors is as follows, where XML data shown within the square brackets '[' and ']' is OPTIONAL.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;stream:error&gt;
+  &lt;defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+  [&lt;text xmlns='urn:ietf:params:xml:ns:xmpp-streams'
+         xml:lang='langcode'&gt;
+     OPTIONAL descriptive text
+  &lt;/text&gt;]
+  [OPTIONAL application-specific condition element]
+&lt;/stream:error&gt;
+</pre></div>
+<p>The "defined-condition" MUST correspond to one of the stream error conditions defined under <a class='info' href='#streams-error-conditions'>Section&nbsp;4.9.3<span> (</span><span class='info'>Defined Stream Error Conditions</span><span>)</span></a>.  However, because additional error conditions might be defined in the future, if an entity receives a stream error condition that it does not understand then it MUST treat the unknown condition as equivalent to &lt;undefined-condition/&gt; (<a class='info' href='#streams-error-conditions-undefined-condition'>Section&nbsp;4.9.3.21<span> (</span><span class='info'>undefined-condition</span><span>)</span></a>).  If the designers of an XMPP protocol extension or the developers of an XMPP implementation need to communicate a stream error condition that is not defined in this specification, they can do so by defining an application-specific error condition element qualified by an application-specific namespace.
+</p>
+<p>The &lt;error/&gt; element:
+</p>
+<p></p>
+<ul class="text">
+<li>MUST contain a child element corresponding to one of the <a class='info' href='#streams-error-conditions'>defined stream error conditions<span> (</span><span class='info'>Defined Stream Error Conditions</span><span>)</span></a>; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace.
+</li>
+<li>MAY contain a &lt;text/&gt; child element containing XML character data that describes the error in more detail; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace and SHOULD possess an 'xml:lang' attribute specifying the natural language of the XML character data.
+</li>
+<li>MAY contain a child element for an application-specific error condition; this element MUST be qualified by an application-defined namespace, and its structure is defined by that namespace (see <a class='info' href='#streams-error-app'>Section&nbsp;4.9.4<span> (</span><span class='info'>Application-Specific Conditions</span><span>)</span></a>).
+</li>
+</ul>
+
+<p>The &lt;text/&gt; element is OPTIONAL.  If included, it MUST be used only to provide descriptive or diagnostic information that supplements the meaning of a defined condition or application-specific condition.  It MUST NOT be interpreted programmatically by an application.  It MUST NOT be used as the error message presented to a human user, but MAY be shown in addition to the error message associated with the defined condition element (and, optionally, the application-specific condition element).
+</p>
+<a name="streams-error-conditions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3"></a><h3>4.9.3.&nbsp;
+Defined Stream Error Conditions</h3>
+
+<p>The following stream-level error conditions are defined.
+</p>
+<a name="streams-error-conditions-bad-format"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.1"></a><h3>4.9.3.1.&nbsp;
+bad-format</h3>
+
+<p>The entity has sent XML that cannot be processed.
+</p>
+<p>(In the following example, the client sends an XMPP message that is not well-formed XML, which alternatively might trigger a &lt;not-well-formed/&gt; stream error (<a class='info' href='#streams-error-conditions-not-well-formed'>Section&nbsp;4.9.3.13<span> (</span><span class='info'>not-well-formed</span><span>)</span></a>).)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message&gt;
+     &lt;body&gt;No closing tag!
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;bad-format
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p>This error can be used instead of the more specific XML-related errors, such as &lt;bad-namespace-prefix/&gt;, &lt;invalid-xml/&gt;, &lt;not-well-formed/&gt;, &lt;restricted-xml/&gt;, and &lt;unsupported-encoding/&gt;.  However, the more specific errors are RECOMMENDED.
+</p>
+<a name="streams-error-conditions-bad-namespace-prefix"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.2"></a><h3>4.9.3.2.&nbsp;
+bad-namespace-prefix</h3>
+
+<p>The entity has sent a namespace prefix that is unsupported, or has sent no namespace prefix on an element that needs such a prefix (see <a class='info' href='#xml-ns'>Section&nbsp;11.2<span> (</span><span class='info'>XML Namespace Names and Prefixes</span><span>)</span></a>).
+</p>
+<p>(In the following example, the client specifies a namespace prefix of "foobar" for the XML stream namespace.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;foobar:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:foobar='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;bad-namespace-prefix
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-conflict"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.3"></a><h3>4.9.3.3.&nbsp;
+conflict</h3>
+
+<p>The server either (1) is closing the existing stream for this entity because a new stream has been initiated that conflicts with the existing stream, or (2) is refusing a new stream for this entity because allowing the new stream would conflict with an existing stream (e.g., because the server allows only a certain number of connections from the same IP address or allows only one server-to-server stream for a given domain pair as a way of helping to ensure in-order processing as described under <a class='info' href='#rules-order'>Section&nbsp;10.1<span> (</span><span class='info'>In-Order Processing</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;conflict
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p>If a client receives a &lt;conflict/&gt; stream error (<a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>), during the resource binding aspect of its reconnection attempt it MUST NOT blindly request the resourcepart it used during the former session but instead MUST choose a different resourcepart; details are provided under <a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>.
+</p>
+<a name="streams-error-conditions-connection-timeout"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.4"></a><h3>4.9.3.4.&nbsp;
+connection-timeout</h3>
+
+<p>One party is closing the stream because it has reason to believe that the other party has permanently lost the ability to communicate over the stream.  The lack of ability to communicate can be discovered using various methods, such as whitespace keepalives as specified under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>, XMPP-level pings as defined in <a class='info' href='#XEP-0199'>[XEP&#8209;0199]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XMPP Ping,&rdquo; June&nbsp;2009.</span><span>)</span></a>, and XMPP Stream Management as defined in <a class='info' href='#XEP-0198'>[XEP&#8209;0198]<span> (</span><span class='info'>Karneges, J., Hildebrand, J., Saint-Andre, P., Forno, F., Cridland, D., and M. Wild, &ldquo;Stream Management,&rdquo; February&nbsp;2011.</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;stream:error&gt;
+     &lt;connection-timeout
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: RFC 3920 specified that the &lt;connection-timeout/&gt; stream error (<a class='info' href='#streams-error-conditions-connection-timeout'>Section&nbsp;4.9.3.4<span> (</span><span class='info'>connection-timeout</span><span>)</span></a>) is to be used if the peer has not generated any traffic over the stream for some period of time. That behavior is no longer recommended; instead, the error SHOULD be used only if the connected client or peer server has not responded to data sent over the stream.
+</p>
+</blockquote>
+
+<a name="streams-error-conditions-host-gone"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.5"></a><h3>4.9.3.5.&nbsp;
+host-gone</h3>
+
+<p>The value of the 'to' attribute provided in the initial stream header corresponds to an FQDN that is no longer serviced by the receiving entity.
+</p>
+<p>(In the following example, the peer specifies a 'to' address of "foo.im.example.com" when connecting to the "im.example.com" server, but the server no longer hosts a service at that address.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='example.net'
+       to='foo.im.example.com'
+       version='1.0'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
+       to='example.net'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;host-gone
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-host-unknown"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.6"></a><h3>4.9.3.6.&nbsp;
+host-unknown</h3>
+
+<p>The value of the 'to' attribute provided in the initial stream header does not correspond to an FQDN that is serviced by the receiving entity.
+</p>
+<p>(In the following example, the peer specifies a 'to' address of "example.org" when connecting to the "im.example.com" server, but the server knows nothing of that address.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='example.net'
+       to='example.org'
+       version='1.0'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
+       to='example.net'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:server'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;host-unknown
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-improper-addressing"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.7"></a><h3>4.9.3.7.&nbsp;
+improper-addressing</h3>
+
+<p>A stanza sent between two servers lacks a 'to' or 'from' attribute, the 'from' or 'to' attribute has no value, or the value violates the rules for XMPP addresses <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>(In the following example, the peer sends a stanza without a 'to' address over a server-to-server stream.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;message from='juliet@im.example.com'&gt;
+     &lt;body&gt;Wherefore art thou?&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;improper-addressing
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-internal-server-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.8"></a><h3>4.9.3.8.&nbsp;
+internal-server-error</h3>
+
+<p>The server has experienced a misconfiguration or other internal error that prevents it from servicing the stream.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:error&gt;
+     &lt;internal-server-error
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-invalid-from"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.9"></a><h3>4.9.3.9.&nbsp;
+invalid-from</h3>
+
+<p>The data provided in a 'from' attribute does not match an authorized JID or validated domain as negotiated (1) between two servers using SASL or Server Dialback, or (2) between a client and a server via SASL authentication and resource binding.
+</p>
+<p>(In the following example, a peer that has authenticated only as "example.net" attempts to send a stanza from an address at "example.org".)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;message from='romeo@example.org' to='juliet@im.example.com'&gt;
+     &lt;body&gt;Neither, fair saint, if either thee dislike.&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;invalid-from
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-invalid-namespace"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.10"></a><h3>4.9.3.10.&nbsp;
+invalid-namespace</h3>
+
+<p>The stream namespace name is something other than "http://etherx.jabber.org/streams" (see <a class='info' href='#xml-ns'>Section&nbsp;11.2<span> (</span><span class='info'>XML Namespace Names and Prefixes</span><span>)</span></a>) or the content namespace declared as the default namespace is not supported (e.g., something other than "jabber:client" or "jabber:server").
+</p>
+<p>(In the following example, the client specifies a namespace of 'http://wrong.namespace.example.org/' for the stream.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://wrong.namespace.example.org/'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;invalid-namespace
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-invalid-xml"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.11"></a><h3>4.9.3.11.&nbsp;
+invalid-xml</h3>
+
+<p>The entity has sent invalid XML over the stream to a server that performs validation (see <a class='info' href='#xml-validation'>Section&nbsp;11.4<span> (</span><span class='info'>Validation</span><span>)</span></a>).
+</p>
+<p>(In the following example, the peer attempts to send an IQ stanza of type "subscribe", but the XML schema defines no such value for the 'type' attribute.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+P: &lt;iq from='example.net'
+       id='l3b1vs75'
+       to='im.example.com'
+       type='subscribe'&gt;
+     &lt;ping xmlns='urn:xmpp:ping'/&gt;
+   &lt;/iq&gt;
+
+S: &lt;stream:error&gt;
+     &lt;invalid-xml
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-not-authorized"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.12"></a><h3>4.9.3.12.&nbsp;
+not-authorized</h3>
+
+<p>The entity has attempted to send XML stanzas or other outbound data before the stream has been authenticated, or otherwise is not authorized to perform an action related to stream negotiation; the receiving entity MUST NOT process the offending data before sending the stream error.
+</p>
+<p>(In the following example, the client attempts to send XML stanzas before authenticating with the server.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+C: &lt;message to='romeo@example.net'&gt;
+     &lt;body&gt;Wherefore art thou?&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;not-authorized
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-not-well-formed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.13"></a><h3>4.9.3.13.&nbsp;
+not-well-formed</h3>
+
+<p>The initiating entity has sent XML that violates the well-formedness rules of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a> or <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>.
+</p>
+<p>(In the following example, the client sends an XMPP message that is not namespace-well-formed.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message&gt;
+     &lt;foo:body&gt;What is this foo?&lt;/foo:body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;not-well-formed
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: In RFC 3920, the name of this error condition was "xml-not-well-formed" instead of "not-well-formed".  The name was changed because the element name &lt;xml-not-well-formed/&gt; violates the constraint from Section 3 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a> that "names beginning with a match to (('X'|'x')('M'|'m')('L'|'l')) are reserved for standardization in this or future versions of this specification".
+</p>
+</blockquote>
+
+<a name="streams-error-conditions-policy-violation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.14"></a><h3>4.9.3.14.&nbsp;
+policy-violation</h3>
+
+<p>The entity has violated some local service policy (e.g., a stanza exceeds a configured size limit); the server MAY choose to specify the policy in the &lt;text/&gt; element or in an application-specific condition element.
+</p>
+<p>(In the following example, the client sends an XMPP message that is too large according to the server's local service policy.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message to='juliet@im.example.com' id='foo'&gt;
+     &lt;body&gt;[ ... the-emacs-manual ... ]&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;policy-violation
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+     &lt;stanza-too-big xmlns='urn:xmpp:errors'/&gt;
+   &lt;/stream:error&gt;
+
+S: &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-remote-connection-failed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.15"></a><h3>4.9.3.15.&nbsp;
+remote-connection-failed</h3>
+
+<p>The server is unable to properly connect to a remote entity that is needed for authentication or authorization (e.g., in certain scenarios related to Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>); this condition is not to be used when the cause of the error is within the administrative domain of the XMPP service provider, in which case the &lt;internal-server-error/&gt; condition is more appropriate.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;remote-connection-failed
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-reset"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.16"></a><h3>4.9.3.16.&nbsp;
+reset</h3>
+
+<p>The server is closing the stream because it has new (typically security-critical) features to offer, because the keys or certificates used to establish a secure context for the stream have expired or have been revoked during the life of the stream (<a class='info' href='#security-certificates-validation-streams'>Section&nbsp;13.7.2.3<span> (</span><span class='info'>Checking of Certificates in Long-Lived Streams</span><span>)</span></a>), because the TLS sequence number has wrapped (<a class='info' href='#tls-rules-renegotiation'>Section&nbsp;5.3.5<span> (</span><span class='info'>TLS Renegotiation</span><span>)</span></a>), etc.  The reset applies to the stream and to any security context established for that stream (e.g., via TLS and SASL), which means that encryption and authentication need to be negotiated again for the new stream (e.g., TLS session resumption cannot be used).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:error&gt;
+     &lt;reset
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-resource-constraint"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.17"></a><h3>4.9.3.17.&nbsp;
+resource-constraint</h3>
+
+<p>The server lacks the system resources necessary to service the stream.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;resource-constraint
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-restricted-xml"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.18"></a><h3>4.9.3.18.&nbsp;
+restricted-xml</h3>
+
+<p>The entity has attempted to send restricted XML features such as a comment, processing instruction, DTD subset, or XML entity reference (see <a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>).
+</p>
+<p>(In the following example, the client sends an XMPP message containing an XML comment.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message to='juliet@im.example.com'&gt;
+     &lt;!--&lt;subject/&gt;--&gt;
+     &lt;body&gt;This message has no subject.&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;restricted-xml
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-see-other-host"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.19"></a><h3>4.9.3.19.&nbsp;
+see-other-host</h3>
+
+<p>The server will not provide service to the initiating entity but is redirecting traffic to another host under the administrative control of the same service provider.  The XML character data of the &lt;see-other-host/&gt; element returned by the server MUST specify the alternate FQDN or IP address at which to connect, which MUST be a valid domainpart or a domainpart plus port number (separated by the ':' character in the form "domainpart:port").  If the domainpart is the same as the source domain, derived domain, or resolved IPv4 or IPv6 address to which the initiating entity originally connected (differing only by the port number), then the initiating entity SHOULD simply attempt to reconnect at that address.  (The format of an IPv6 address MUST follow <a class='info' href='#IPv6-ADDR'>[IPv6&#8209;ADDR]<span> (</span><span class='info'>Kawamura, S. and M. Kawashima, &ldquo;A Recommendation for IPv6 Address Text Representation,&rdquo; August&nbsp;2010.</span><span>)</span></a>, which includes the enclosing the IPv6 address in square brackets '[' and ']' as originally defined by <a class='info' href='#URI'>[URI]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, &ldquo;Uniform Resource Identifier (URI): Generic Syntax,&rdquo; January&nbsp;2005.</span><span>)</span></a>.)  Otherwise, the initiating entity MUST resolve the FQDN specified in the &lt;see-other-host/&gt; element as described under <a class='info' href='#tcp-resolution'>Section&nbsp;3.2<span> (</span><span class='info'>Resolution of Fully Qualified Domain Names</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;see-other-host
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'&gt;
+       [2001:41D0:1:A49b::1]:9222
+     &lt;/see-other-host&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p>When negotiating a stream with the host to which it has been redirected, the initiating entity MUST apply the same policies it would have applied to the original connection attempt (e.g., a policy requiring TLS), MUST specify the same 'to' address on the initial stream header, and MUST verify the identity of the new host using the same reference identifier(s) it would have used for the original connection attempt (in accordance with <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a>).  Even if the receiving entity returns a &lt;see-other-host/&gt; error before the confidentiality and integrity of the stream have been established (thus introducing the possibility of a denial-of-service attack), the fact that the initiating entity needs to verify the identity of the XMPP service based on the same reference identifiers implies that the initiating entity will not connect to a malicious entity.  To reduce the possibility of a denial-of-service attack, (a) the receiving entity SHOULD NOT close the stream with a &lt;see-other-host/&gt; stream error until after the confidentiality and integrity of the stream have been protected via TLS or an equivalent security layer (such as the SASL GSSAPI mechanism), and (b) the receiving entity MAY have a policy of following redirects only if it has authenticated the receiving entity.  In addition, the initiating entity SHOULD abort the connection attempt after a certain number of successive redirects (e.g., at least 2 but no more than 5).
+</p>
+<a name="streams-error-conditions-system-shutdown"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.20"></a><h3>4.9.3.20.&nbsp;
+system-shutdown</h3>
+
+<p>The server is being shut down and all active streams are being closed.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:error&gt;
+     &lt;system-shutdown
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-undefined-condition"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.21"></a><h3>4.9.3.21.&nbsp;
+undefined-condition</h3>
+
+<p>The error condition is not one of those defined by the other conditions in this list; this error condition SHOULD NOT be used except in conjunction with an application-specific condition.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:error&gt;
+     &lt;undefined-condition
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+     &lt;app-error xmlns='http://example.org/ns'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-unsupported-encoding"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.22"></a><h3>4.9.3.22.&nbsp;
+unsupported-encoding</h3>
+
+<p>The initiating entity has encoded the stream in an encoding that is not supported by the server (see <a class='info' href='#xml-encoding'>Section&nbsp;11.6<span> (</span><span class='info'>Character Encoding</span><span>)</span></a>) or has otherwise improperly encoded the stream (e.g., by violating the rules of the <a class='info' href='#UTF-8'>[UTF&#8209;8]<span> (</span><span class='info'>Yergeau, F., &ldquo;UTF-8, a transformation format of ISO 10646,&rdquo; November&nbsp;2003.</span><span>)</span></a> encoding).
+</p>
+<p>(In the following example, the client attempts to encode data using UTF-16 instead of UTF-8.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0' encoding='UTF-16'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;unsupported-encoding
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-unsupported-feature"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.23"></a><h3>4.9.3.23.&nbsp;
+unsupported-feature</h3>
+
+<p>The receiving entity has advertised a mandatory-to-negotiate stream feature that the initiating entity does not support, and has offered no other mandatory-to-negotiate feature alongside the unsupported feature.
+</p>
+<p>(In the following example, the receiving entity requires negotiation of an example feature, but the initiating entity does not support the feature.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;example xmlns='urn:xmpp:example'&gt;
+       &lt;required/&gt;
+     &lt;/example&gt;
+   &lt;/stream:features&gt;
+
+I: &lt;stream:error&gt;
+     &lt;unsupported-feature
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-unsupported-stanza-type"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.24"></a><h3>4.9.3.24.&nbsp;
+unsupported-stanza-type</h3>
+
+<p>The initiating entity has sent a first-level child of the stream that is not supported by the server, either because the receiving entity does not understand the namespace or because the receiving entity does not understand the element name for the applicable namespace (which might be the content namespace declared as the default namespace).
+</p>
+<p>(In the following example, the client attempts to send a first-level child element of &lt;pubsub/&gt; qualified by the 'jabber:client' namespace, but the schema for that namespace defines no such element.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;pubsub xmlns='jabber:client'&gt;
+     &lt;publish node='princely_musings'&gt;
+       &lt;item id='ae890ac52d0df67ed7cfdf51b644e901'&gt;
+         &lt;entry xmlns='http://www.w3.org/2005/Atom'&gt;
+           &lt;title&gt;Soliloquy&lt;/title&gt;
+           &lt;summary&gt;
+To be, or not to be: that is the question:
+Whether 'tis nobler in the mind to suffer
+The slings and arrows of outrageous fortune,
+Or to take arms against a sea of troubles,
+And by opposing end them?
+           &lt;/summary&gt;
+           &lt;link rel='alternate' type='text/html'
+                 href='http://denmark.example/2003/12/13/atom03'/&gt;
+           &lt;id&gt;tag:denmark.example,2003:entry-32397&lt;/id&gt;
+           &lt;published&gt;2003-12-13T18:30:02Z&lt;/published&gt;
+           &lt;updated&gt;2003-12-13T18:30:02Z&lt;/updated&gt;
+         &lt;/entry&gt;
+       &lt;/item&gt;
+     &lt;/publish&gt;
+   &lt;/pubsub&gt;
+
+S: &lt;stream:error&gt;
+     &lt;unsupported-stanza-type
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-conditions-unsupported-version"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.3.25"></a><h3>4.9.3.25.&nbsp;
+unsupported-version</h3>
+
+<p>The 'version' attribute provided by the initiating entity in the stream header specifies a version of XMPP that is not supported by the server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='11.0'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+   &lt;stream:error&gt;
+     &lt;unsupported-version
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-error-app"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.9.4"></a><h3>4.9.4.&nbsp;
+Application-Specific Conditions</h3>
+
+<p>As noted, an application MAY provide application-specific
+        stream error information by including a properly namespaced child in the error element.  The application-specific element SHOULD supplement or further qualify a defined element.  Thus, the &lt;error/&gt; element will contain two or three child elements.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message&gt;
+     &lt;body&gt;
+       My keyboard layout is:
+
+       QWERTYUIOP{}|
+       ASDFGHJKL:"
+       ZXCVBNM&lt;&gt;?
+     &lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+     &lt;not-well-formed
+         xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+     &lt;text xml:lang='en' xmlns='urn:ietf:params:xml:ns:xmpp-streams'&gt;
+       Some special application diagnostic information!
+     &lt;/text&gt;
+     &lt;escape-your-data xmlns='http://example.org/ns'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<a name="streams-example"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.10"></a><h3>4.10.&nbsp;
+Simplified Stream Examples</h3>
+
+<p>This section contains two highly simplified examples of a stream-based connection between a client and a server; these examples are included for the purpose of illustrating the concepts introduced thus far, but the reader needs to be aware that these examples elide many details (see <a class='info' href='#examples'>Section&nbsp;9<span> (</span><span class='info'>Detailed Examples</span><span>)</span></a> for more complete examples).
+</p>
+<p>A basic connection:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+[ ... stream negotiation ... ]
+
+C:   &lt;message from='juliet@im.example.com/balcony'
+              to='romeo@example.net'
+              xml:lang='en'&gt;
+       &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+     &lt;/message&gt;
+
+S:   &lt;message from='romeo@example.net/orchard'
+              to='juliet@im.example.com/balcony'
+              xml:lang='en'&gt;
+       &lt;body&gt;Neither, fair saint, if either thee dislike.&lt;/body&gt;
+     &lt;/message&gt;
+
+C: &lt;/stream:stream&gt;
+
+S: &lt;/stream:stream&gt;
+</pre></div>
+<p>A connection gone bad:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='juliet@im.example.com'
+       to='im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;?xml version='1.0'?&gt;
+   &lt;stream:stream
+       from='im.example.com'
+       id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+[ ... stream negotiation ... ]
+
+C:   &lt;message from='juliet@im.example.com/balcony'
+              to='romeo@example.net'
+              xml:lang='en'&gt;
+       &lt;body&gt;No closing tag!
+     &lt;/message&gt;
+
+S: &lt;stream:error&gt;
+    &lt;not-well-formed
+        xmlns='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+   &lt;/stream:error&gt;
+   &lt;/stream:stream&gt;
+
+</pre></div>
+<p>More detailed examples are provided under <a class='info' href='#examples'>Section&nbsp;9<span> (</span><span class='info'>Detailed Examples</span><span>)</span></a>.
+</p>
+<a name="tls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5"></a><h3>5.&nbsp;
+STARTTLS Negotiation</h3>
+
+<a name="tls-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.1"></a><h3>5.1.&nbsp;
+Fundamentals</h3>
+
+<p>XMPP includes a method for securing the stream from tampering and eavesdropping.  This channel encryption method makes use of the Transport Layer Security <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a> protocol, specifically a "STARTTLS" extension that is modeled after similar extensions for the <a class='info' href='#IMAP'>[IMAP]<span> (</span><span class='info'>Crispin, M., &ldquo;INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,&rdquo; March&nbsp;2003.</span><span>)</span></a>, <a class='info' href='#POP3'>[POP3]<span> (</span><span class='info'>Myers, J. and M. Rose, &ldquo;Post Office Protocol - Version 3,&rdquo; May&nbsp;1996.</span><span>)</span></a>, and <a class='info' href='#ACAP'>[ACAP]<span> (</span><span class='info'>Newman, C. and J. Myers, &ldquo;ACAP -- Application Configuration Access Protocol,&rdquo; November&nbsp;1997.</span><span>)</span></a> protocols as described in <a class='info' href='#USINGTLS'>[USINGTLS]<span> (</span><span class='info'>Newman, C., &ldquo;Using TLS with IMAP, POP3 and ACAP,&rdquo; June&nbsp;1999.</span><span>)</span></a>.  The XML namespace name for the STARTTLS extension is 'urn:ietf:params:xml:ns:xmpp-tls'.
+</p>
+<a name="tls-support"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2"></a><h3>5.2.&nbsp;
+Support</h3>
+
+<p>Support for STARTTLS is REQUIRED in XMPP client and server implementations.  An administrator of a given deployment MAY specify that TLS is mandatory-to-negotiate for client-to-server communication, server-to-server communication, or both.  An initiating entity SHOULD use TLS to secure its stream with the receiving entity before proceeding with SASL authentication.
+</p>
+<a name="tls-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3"></a><h3>5.3.&nbsp;
+Stream Negotiation Rules</h3>
+
+<a name="tls-rules-mtn"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.1"></a><h3>5.3.1.&nbsp;
+Mandatory-to-Negotiate</h3>
+
+<p>If the receiving entity advertises only the STARTTLS feature or if the receiving entity includes the &lt;required/&gt; child element as explained under <a class='info' href='#tls-process-stream'>Section&nbsp;5.4.1<span> (</span><span class='info'>Exchange of Stream Headers and Stream Features</span><span>)</span></a>, the parties MUST consider TLS as mandatory-to-negotiate.  If TLS is mandatory-to-negotiate, the receiving entity SHOULD NOT advertise support for any stream feature except STARTTLS during the initial stage of the stream negotiation process, because further stream features might depend on prior negotiation of TLS given the order of layers in XMPP (e.g., the particular SASL mechanisms offered by the receiving entity will likely depend on whether TLS has been negotiated).
+</p>
+<a name="tls-rules-restart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.2"></a><h3>5.3.2.&nbsp;
+Restart</h3>
+
+<p>After TLS negotiation, the parties MUST restart the stream.
+</p>
+<a name="tls-rules-data"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.3"></a><h3>5.3.3.&nbsp;
+Data Formatting</h3>
+
+<p>During STARTTLS negotiation, the entities MUST NOT send any whitespace as separators between XML elements (i.e., from the last character of the first-level &lt;starttls/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace as sent by the initiating entity, until the last character of the first-level &lt;proceed/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace as sent by the receiving entity).  This prohibition helps to ensure proper security layer byte precision.  Any such whitespace shown in the STARTTLS examples provided in this document is included only for the sake of readability.
+</p>
+<a name="tls-rules-order"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.4"></a><h3>5.3.4.&nbsp;
+Order of TLS and SASL Negotiations</h3>
+
+<p>If the initiating entity chooses to use TLS, STARTTLS negotiation MUST be completed before proceeding to <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>; this order of negotiation is necessary to help safeguard authentication information sent during SASL negotiation, as well as to make it possible to base the use of the SASL EXTERNAL mechanism on a certificate (or other credentials) provided during prior TLS negotiation.
+</p>
+<a name="tls-rules-renegotiation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.5"></a><h3>5.3.5.&nbsp;
+TLS Renegotiation</h3>
+
+<p>The TLS protocol allows either party in a TLS-protected channel to initiate a new handshake that establishes new cryptographic parameters (see <a class='info' href='#TLS-NEG'>[TLS&#8209;NEG]<span> (</span><span class='info'>Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, &ldquo;Transport Layer Security (TLS) Renegotiation Indication Extension,&rdquo; February&nbsp;2010.</span><span>)</span></a>).  The cases most commonly mentioned are:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Refreshing encryption keys.
+</li>
+<li>Wrapping the TLS sequence number as explained in Section 6.1 of <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>.
+</li>
+<li>Protecting client credentials by completing server authentication first and then completing client authentication over the protected channel.
+</li>
+</ol><p>
+        
+</p>
+<p>Because it is relatively inexpensive to establish streams in XMPP, for the first two cases it is preferable to use an XMPP stream reset (as described under <a class='info' href='#streams-error-conditions-reset'>Section&nbsp;4.9.3.16<span> (</span><span class='info'>reset</span><span>)</span></a>) instead of performing TLS renegotiation.
+</p>
+<p>The third case has improved security characteristics when the TLS client (which might be an XMPP server) presents credentials to the TLS server.  If communicating such credentials to an unauthenticated TLS server might leak private information, it can be appropriate to complete TLS negotiation for the purpose of authenticating the TLS server to the TLS client and then attempt TLS renegotiation for the purpose of authenticating the TLS client to the TLS server.  However, this case is extremely rare because the credentials presented by an XMPP server or XMPP client acting as a TLS client are almost always public (i.e., a PKIX certificate), and therefore providing those credentials before authenticating the XMPP server acting as a TLS server would not in general leak private information.
+</p>
+<p>As a result, implementers are encouraged to carefully weigh the costs and benefits of TLS renegotiation before supporting it in their software, and XMPP entities that act as TLS clients are discouraged from attempting TLS renegotiation unless the certificate (or other credential information) sent during TLS negotiation is known to be private.
+</p>
+<p>Support for TLS renegotiation is strictly OPTIONAL.  However, implementations that support TLS renegotiation MUST implement and use the TLS Renegotiation Extension <a class='info' href='#TLS-NEG'>[TLS&#8209;NEG]<span> (</span><span class='info'>Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, &ldquo;Transport Layer Security (TLS) Renegotiation Indication Extension,&rdquo; February&nbsp;2010.</span><span>)</span></a>.
+</p>
+<p>If an entity that does not support TLS renegotiation detects a renegotiation attempt, then it MUST immediately close the underlying TCP connection without returning a stream error (since the violation has occurred at the TLS layer, not the XMPP layer, as described under <a class='info' href='#security-layers'>Section&nbsp;13.3<span> (</span><span class='info'>Order of Layers</span><span>)</span></a>).
+</p>
+<p>If an entity that supports TLS renegotiation detects a TLS renegotiation attempt that does not use the TLS Renegotiation Extension <a class='info' href='#TLS-NEG'>[TLS&#8209;NEG]<span> (</span><span class='info'>Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, &ldquo;Transport Layer Security (TLS) Renegotiation Indication Extension,&rdquo; February&nbsp;2010.</span><span>)</span></a>, then it MUST immediately close the underlying TCP connection without returning a stream error (since the violation has occurred at the TLS layer, not the XMPP layer as described under <a class='info' href='#security-layers'>Section&nbsp;13.3<span> (</span><span class='info'>Order of Layers</span><span>)</span></a>).
+</p>
+<a name="tls-rules-extensions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3.6"></a><h3>5.3.6.&nbsp;
+TLS Extensions</h3>
+
+<p>Either party to a stream MAY include any TLS extension during the TLS negotiation itself.  This is a matter for the TLS layer, not the XMPP layer.
+</p>
+<a name="tls-process"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4"></a><h3>5.4.&nbsp;
+Process</h3>
+
+<a name="tls-process-stream"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.1"></a><h3>5.4.1.&nbsp;
+Exchange of Stream Headers and Stream Features</h3>
+
+<p>The initiating entity resolves the FQDN of the receiving entity as specified under <a class='info' href='#tcp'>Section&nbsp;3<span> (</span><span class='info'>TCP Binding</span><span>)</span></a>, opens a TCP connection to the advertised port at the resolved IP address, and sends an initial stream header to the receiving entity.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The receiving entity MUST send a response stream header to the initiating entity over the TCP connection opened by the initiating entity.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:stream
+     from='im.example.com'
+     id='t7AMCin9zjMNwQKDnplntZPIDEI='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The receiving entity then MUST send stream features to the initiating entity.  If the receiving entity supports TLS, the stream features MUST include an advertisement for support of STARTTLS negotiation, i.e., a &lt;starttls/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace.
+</p>
+<p>If the receiving entity considers STARTTLS negotiation to be mandatory-to-negotiate, the &lt;starttls/&gt; element MUST contain an empty &lt;required/&gt; child element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'&gt;
+       &lt;required/&gt;
+     &lt;/starttls&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<a name="tls-process-initiate"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.2"></a><h3>5.4.2.&nbsp;
+Initiation of STARTTLS Negotiation</h3>
+
+<a name="tls-process-initiate-command"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.2.1"></a><h3>5.4.2.1.&nbsp;
+STARTTLS Command</h3>
+
+<p>In order to begin the STARTTLS negotiation, the initiating entity issues the STARTTLS command (i.e., a &lt;starttls/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace) to instruct the receiving entity that it wishes to begin a STARTTLS negotiation to secure the stream.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>The receiving entity MUST reply with either a &lt;proceed/&gt; element (proceed case) or a &lt;failure/&gt; element (failure case) qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace.
+</p>
+<a name="tls-process-initiate-failure"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.2.2"></a><h3>5.4.2.2.&nbsp;
+Failure Case</h3>
+
+<p>If the failure case occurs, the receiving entity MUST return a &lt;failure/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace, close the XML stream, and terminate the underlying TCP connection.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+
+R: &lt;/stream:stream&gt;
+</pre></div>
+<p>Causes for the failure case include but are not limited to:
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>The initiating entity has sent a malformed STARTTLS command.
+</li>
+<li>The receiving entity did not offer the STARTTLS feature in its stream features.
+</li>
+<li>The receiving entity cannot complete STARTTLS negotiation because of an internal error.
+</li>
+</ol><p>
+          
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: STARTTLS failure is not triggered by TLS errors such as bad_certificate or handshake_failure, which are generated and handled during the TLS negotiation itself as described in <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>If the failure case occurs, the initiating entity MAY attempt to reconnect as explained under <a class='info' href='#tcp-reconnect'>Section&nbsp;3.3<span> (</span><span class='info'>Reconnection</span><span>)</span></a>.
+</p>
+<a name="tls-process-initiate-proceed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.2.3"></a><h3>5.4.2.3.&nbsp;
+Proceed Case</h3>
+
+<p>If the proceed case occurs, the receiving entity MUST return a &lt;proceed/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>The receiving entity MUST consider the TLS negotiation to have begun immediately after sending the closing '&gt;' character of the &lt;proceed/&gt; element to the initiating entity.  The initiating entity MUST consider the TLS negotiation to have begun immediately after receiving the closing '&gt;' character of the &lt;proceed/&gt; element from the receiving entity.
+</p>
+<p>The entities now proceed to TLS negotiation as explained in the next section.
+</p>
+<a name="tls-process-neg"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.3"></a><h3>5.4.3.&nbsp;
+TLS Negotiation</h3>
+
+<a name="tls-process-neg-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.3.1"></a><h3>5.4.3.1.&nbsp;
+Rules</h3>
+
+<p>In order to complete TLS negotiation over the TCP connection, the entities MUST follow the process defined in <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>.
+</p>
+<p>The following rules apply:
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>The entities MUST NOT send any further XML data until the TLS negotiation is complete.
+</li>
+<li>When using any of the mandatory-to-implement (MTI) ciphersuites specified under <a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>, the receiving entity MUST present a certificate.
+</li>
+<li>So that mutual certificate authentication will be possible, the receiving entity SHOULD send a certificate request to the initiating entity, and the initiating entity SHOULD send a certificate to the receiving entity (but for privacy reasons might opt not to send a certificate until after the receiving entity has authenticated to the initiating entity).
+</li>
+<li>The receiving entity SHOULD choose which certificate to present based on the domainpart contained in the 'to' attribute of the initial stream header (in essence, this domainpart is functionally equivalent to the Server Name Indication defined for TLS in <a class='info' href='#TLS-EXT'>[TLS&#8209;EXT]<span> (</span><span class='info'>Eastlake 3rd, D., &ldquo;Transport Layer Security (TLS) Extensions: Extension Definitions,&rdquo; January&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>To determine if the TLS negotiation will succeed, the initiating entity MUST attempt to validate the receiving entity's certificate in accordance with the certificate validation procedures specified under <a class='info' href='#security-certificates-validation'>Section&nbsp;13.7.2<span> (</span><span class='info'>Certificate Validation</span><span>)</span></a>.
+</li>
+<li>If the initiating entity presents a certificate, the receiving entity too MUST attempt to validate the initiating entity's certificate in accordance with the certificate validation procedures specified under <a class='info' href='#security-certificates-validation'>Section&nbsp;13.7.2<span> (</span><span class='info'>Certificate Validation</span><span>)</span></a>.
+</li>
+<li>Following successful TLS negotiation, all further data transmitted by either party MUST be protected with the negotiated algorithms, keys, and secrets (i.e., encrypted, integrity-protected, or both depending on the ciphersuite used).
+</li>
+</ol><p>
+          
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: See <a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a> regarding ciphersuites that MUST be supported for TLS; naturally, other ciphersuites MAY be supported as well.
+</p>
+</blockquote>
+
+<a name="tls-process-neg-failure"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.3.2"></a><h3>5.4.3.2.&nbsp;
+TLS Failure</h3>
+
+<p>If the TLS negotiation results in failure, the receiving entity MUST terminate the TCP connection.
+</p>
+<p>The receiving entity MUST NOT send a closing &lt;/stream&gt; tag before terminating the TCP connection (since the failure has occurred at the TLS layer, not the XMPP layer as described under <a class='info' href='#security-layers'>Section&nbsp;13.3<span> (</span><span class='info'>Order of Layers</span><span>)</span></a>).
+</p>
+<p>The initiating entity MAY attempt to reconnect as explained under <a class='info' href='#tcp-reconnect'>Section&nbsp;3.3<span> (</span><span class='info'>Reconnection</span><span>)</span></a>, with or without attempting TLS negotiation (in accordance with local service policy, user-configured preferences, etc.).
+</p>
+<a name="tls-process-neg-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.4.3.3"></a><h3>5.4.3.3.&nbsp;
+TLS Success</h3>
+
+<p>If the TLS negotiation is successful, then the entities MUST proceed as follows.
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>The initiating entity MUST discard any information transmitted in layers above TCP that it obtained from the receiving entity in an insecure manner before TLS took effect (e.g., the receiving entity's 'from' address or the stream ID and stream features received from the receiving entity).
+</li>
+<li>The receiving entity MUST discard any information transmitted in layers above TCP that it obtained from the initiating entity in an insecure manner before TLS took effect (e.g., the initiating entity's 'from' address).
+</li>
+<li>The initiating entity MUST send a new initial stream header to the receiving entity over the encrypted connection (as specified under <a class='info' href='#streams-negotiation-restart'>Section&nbsp;4.3.3<span> (</span><span class='info'>Restarts</span><span>)</span></a>, the initiating entity MUST NOT send a closing &lt;/stream&gt; tag before sending the new initial stream header, since the receiving entity and initiating entity MUST consider the original stream to be replaced upon success of the TLS negotiation).
+                <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+              
+</li>
+<li>The receiving entity MUST respond with a new response stream header over the encrypted connection (for which it MUST generate a new stream ID instead of reusing the old stream ID).
+                <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:stream
+     from='im.example.com'
+     id='vgKi/bkYME8OAj4rlXMkpucAqe4='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+              
+</li>
+<li>The receiving entity also MUST send stream features to the initiating entity, which MUST NOT include the STARTTLS feature but which SHOULD include the SASL stream feature as described under <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a> (see especially <a class='info' href='#sasl-process-stream'>Section&nbsp;6.4.1<span> (</span><span class='info'>Exchange of Stream Headers and Stream Features</span><span>)</span></a> regarding the few reasons why the SASL stream feature would not be offered here).
+                <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+       &lt;mechanism&gt;EXTERNAL&lt;/mechanism&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1-PLUS&lt;/mechanism&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1&lt;/mechanism&gt;
+       &lt;mechanism&gt;PLAIN&lt;/mechanism&gt;
+     &lt;/mechanisms&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+              
+</li>
+</ol><p>
+          
+</p>
+<a name="sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6"></a><h3>6.&nbsp;
+SASL Negotiation</h3>
+
+<a name="sasl-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.1"></a><h3>6.1.&nbsp;
+Fundamentals</h3>
+
+<p>XMPP includes a method for authenticating a stream by means of an XMPP-specific profile of the Simple Authentication and Security Layer protocol (see <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>).  SASL provides a generalized method for adding authentication support to connection-based protocols, and XMPP uses an XML namespace profile of SASL that conforms to the profiling requirements of <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>.  The XML namespace name for the SASL extension is 'urn:ietf:params:xml:ns:xmpp-sasl'.
+</p>
+<a name="sasl-support"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.2"></a><h3>6.2.&nbsp;
+Support</h3>
+
+<p>Support for SASL negotiation is REQUIRED in XMPP client and server implementations.
+</p>
+<a name="sasl-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3"></a><h3>6.3.&nbsp;
+Stream Negotiation Rules</h3>
+
+<a name="sasl-rules-mtn"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.1"></a><h3>6.3.1.&nbsp;
+Mandatory-to-Negotiate</h3>
+
+<p>The parties to a stream MUST consider SASL as mandatory-to-negotiate.
+</p>
+<a name="sasl-rules-restart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.2"></a><h3>6.3.2.&nbsp;
+Restart</h3>
+
+<p>After SASL negotiation, the parties MUST restart the stream.
+</p>
+<a name="sasl-rules-preferences"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.3"></a><h3>6.3.3.&nbsp;
+Mechanism Preferences</h3>
+
+<p>Any entity that will act as a SASL client or a SASL server MUST
+maintain an ordered list of its preferred SASL mechanisms according to the
+client or server, where the list is ordered according to local policy or user
+configuration (which SHOULD be in order of perceived strength to enable the
+strongest authentication possible).  The initiating entity MUST maintain its
+own preference order independent of the preference order of the receiving
+entity.  A client MUST try SASL mechanisms in its preference order.  For example, if the server offers the ordered list "PLAIN SCRAM-SHA-1 GSSAPI" or "SCRAM-SHA-1 GSSAPI PLAIN" but the client's ordered list is "GSSAPI SCRAM-SHA-1", the client MUST try GSSAPI first and then SCRAM-SHA-1 but MUST NOT try PLAIN (since PLAIN is not on its list).
+</p>
+<a name="sasl-rules-offers"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.4"></a><h3>6.3.4.&nbsp;
+Mechanism Offers</h3>
+
+<p>If the receiving entity considers <a class='info' href='#tls'>TLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> to be mandatory-to-negotiate before it will accept authentication with a particular SASL mechanism, it MUST NOT advertise that mechanism in its list of available SASL mechanisms before TLS negotiation has been completed.
+</p>
+<p>The receiving entity SHOULD offer the SASL EXTERNAL mechanism if both of the following conditions hold:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>During TLS negotiation the initiating entity presented a certificate that is acceptable to the receiving entity for purposes of strong identity verification in accordance with local service policies (e.g., because said certificate is unexpired, is unrevoked, and is anchored to a root trusted by the receiving entity).
+</li>
+<li>The receiving entity expects that the initiating entity will be able to authenticate and authorize as the identity provided in the certificate; in the case of a server-to-server stream, the receiving entity might have such an expectation because a DNS domain name presented in the initiating entity's certificate matches the domain referenced in the 'from' attribute of the initial stream header, where the matching rules of <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> apply; in the case of a client-to-server stream, the receiving entity might have such an expectation because the bare JID presented in the initiating entity's certificate matches a user account that is registered with the server or because other information contained in the initiating entity's certificate matches that of an entity that has permission to use the server for access to an XMPP network.
+</li>
+</ol><p>
+        
+</p>
+<p>However, the receiving entity MAY offer the SASL EXTERNAL mechanism under other circumstances, as well.
+</p>
+<p>When the receiving entity offers the SASL EXTERNAL mechanism, the receiving entity SHOULD list the EXTERNAL mechanism first among its offered SASL mechanisms and the initiating entity SHOULD attempt SASL negotiation using the EXTERNAL mechanism first (this preference will tend to increase the likelihood that the parties can negotiate mutual certificate authentication).
+</p>
+<p><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a> specifies SASL mechanisms that MUST be supported; naturally, other SASL mechanisms MAY be supported as well.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Best practices for the use of SASL in the context of XMPP are described in <a class='info' href='#XEP-0175'>[XEP&#8209;0175]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices for Use of SASL ANONYMOUS,&rdquo; September&nbsp;2009.</span><span>)</span></a> for the ANONYMOUS mechanism and in <a class='info' href='#XEP-0178'>[XEP&#8209;0178]<span> (</span><span class='info'>Saint-Andre, P. and P. Millard, &ldquo;Best Practices for Use of SASL EXTERNAL with Certificates,&rdquo; February&nbsp;2007.</span><span>)</span></a> for the EXTERNAL mechanism.
+</p>
+</blockquote>
+
+<a name="sasl-rules-data"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.5"></a><h3>6.3.5.&nbsp;
+Data Formatting</h3>
+
+<p>The following data formatting rules apply to the SASL negotiation:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>During SASL negotiation, the entities MUST NOT send any whitespace as separators between XML elements (i.e., from the last character of the first-level &lt;auth/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace as sent by the initiating entity, until the last character of the first-level &lt;success/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace as sent by the receiving entity).  This prohibition helps to ensure proper security layer byte precision.  Any such whitespace shown in the SASL examples provided in this document is included only for the sake of readability.
+</li>
+<li>Any XML character data contained within the XML elements MUST be encoded using base 64, where the encoding adheres to the definition in Section 4 of <a class='info' href='#BASE64'>[BASE64]<span> (</span><span class='info'>Josefsson, S., &ldquo;The Base16, Base32, and Base64 Data Encodings,&rdquo; October&nbsp;2006.</span><span>)</span></a> and where the padding bits are set to zero.
+</li>
+<li>As formally specified in the XML schema for the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace under <a class='info' href='#schemas-sasl'>Appendix&nbsp;A.4<span> (</span><span class='info'>SASL Namespace</span><span>)</span></a>, the receiving entity MAY include one or more application-specific child elements inside the &lt;mechanisms/&gt; element to provide information that might be needed by the initiating entity in order to complete successful SASL negotiation using one or more of the offered mechanisms; however, the syntax and semantics of all such elements are out of scope for this specification (see <a class='info' href='#XEP-0233'>[XEP&#8209;0233]<span> (</span><span class='info'>Miller, M., Saint-Andre, P., and J. Hildebrand, &ldquo;Domain-Based Service Names in XMPP SASL Negotiation,&rdquo; June&nbsp;2010.</span><span>)</span></a> for one example).
+</li>
+</ol><p>
+        
+</p>
+<a name="sasl-rules-layers"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.6"></a><h3>6.3.6.&nbsp;
+Security Layers</h3>
+
+<p>Upon successful SASL negotiation that involves negotiation
+        of a security layer, both the initiating entity and the
+        receiving entity MUST discard any application-layer state (i.e, state from the XMPP layer, excluding state from the TLS negotiation or SASL negotiation).
+</p>
+<a name="sasl-rules-username"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.7"></a><h3>6.3.7.&nbsp;
+Simple User Name</h3>
+
+<p>Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify that the authentication identity used in the context of such mechanisms is a "simple user name" (see Section 2 of <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a> as well as <a class='info' href='#SASLPREP'>[SASLPREP]<span> (</span><span class='info'>Zeilenga, K., &ldquo;SASLprep: Stringprep Profile for User Names and Passwords,&rdquo; February&nbsp;2005.</span><span>)</span></a>).  The exact form of the simple user name in any particular mechanism or deployment thereof is a local matter, and a simple user name does not necessarily map to an application identifier such as a JID or JID component (e.g., a localpart).  However, in the absence of local information provided by the server, an XMPP client SHOULD assume that the authentication identity for such a SASL mechanism is a simple user name equal to the localpart of the user's JID.
+</p>
+<a name="sasl-rules-authzid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.8"></a><h3>6.3.8.&nbsp;
+Authorization Identity</h3>
+
+<p>An authorization identity is an OPTIONAL identity included by the initiating entity to specify an identity to act as (see Section 2 of <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>).  In client-to-server streams, it would most likely be used by an administrator to perform some management task on behalf of another user, whereas in server-to-server streams it would most likely be used to specify a particular add-on service at an XMPP service (e.g., a multi-user chat server at conference.example.com that is hosted by the example.com XMPP service).  If the initiating entity wishes to act on behalf of another entity and the selected SASL mechanism supports transmission of an authorization identity, the initiating entity MUST provide an authorization identity during SASL negotiation.  If the initiating entity does not wish to act on behalf of another entity, it MUST NOT provide an authorization identity.
+</p>
+<p>In the case of client-to-server communication, the value of an authorization identity MUST be a bare JID (&lt;localpart@domainpart&gt;) rather than a full JID (&lt;localpart@domainpart/resourcepart&gt;).
+</p>
+<p>In the case of server-to-server communication, the value of an authorization identity MUST be a domainpart only (&lt;domainpart&gt;).
+</p>
+<p>If the initiating entity provides an authorization identity during SASL negotiation, the receiving entity is responsible for verifying that the initiating entity is in fact allowed to assume the specified authorization identity; if not, the receiving entity MUST return an &lt;invalid-authzid/&gt; SASL error as described under <a class='info' href='#sasl-errors-invalid-authzid'>Section&nbsp;6.5.6<span> (</span><span class='info'>invalid-authzid</span><span>)</span></a>.
+</p>
+<a name="sasl-rules-realms"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.9"></a><h3>6.3.9.&nbsp;
+Realms</h3>
+
+<p>The receiving entity MAY include a realm when negotiating certain SASL mechanisms (e.g., both the GSSAPI and DIGEST-MD5 mechanisms allow the authentication exchange to include a realm, though in different ways, whereas the EXTERNAL, SCRAM, and PLAIN mechanisms do not).  If the receiving entity does not communicate a realm, the initiating entity MUST NOT assume that any realm exists.  The realm MUST be used only for the purpose of authentication; in particular, an initiating entity MUST NOT attempt to derive an XMPP domainpart from the realm information provided by the receiving entity.
+</p>
+<a name="sasl-rules-roundtrips"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.3.10"></a><h3>6.3.10.&nbsp;
+Round Trips</h3>
+
+<p><a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a> specifies that a using protocol such as XMPP can define two methods by which the protocol can save round trips where allowed for the SASL mechanism:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>When the SASL client (the XMPP "initiating entity") requests an authentication exchange, it can include "initial response" data with its request if appropriate for the SASL mechanism in use.  In XMPP, this is done by including the initial response as the XML character data of the &lt;auth/&gt; element.
+</li>
+<li>At the end of the authentication exchange, the SASL server (the XMPP "receiving entity") can include "additional data with success" if appropriate for the SASL mechanism in use.  In XMPP, this is done by including the additional data as the XML character data of the &lt;success/&gt; element.
+</li>
+</ol><p>
+        
+</p>
+<p>For the sake of protocol efficiency, it is REQUIRED for clients and servers to support these methods and RECOMMENDED to use them; however, clients and servers MUST support the less efficient modes as well.
+</p>
+<a name="sasl-process"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4"></a><h3>6.4.&nbsp;
+Process</h3>
+
+<p>The process for SASL negotiation is as follows.
+</p>
+<a name="sasl-process-stream"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.1"></a><h3>6.4.1.&nbsp;
+Exchange of Stream Headers and Stream Features</h3>
+
+<p>If SASL negotiation follows successful <a class='info' href='#tls'>STARTTLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>, then the SASL negotiation occurs over the protected stream that has already been negotiated.  If not, the initiating entity resolves the FQDN of the receiving entity as specified under <a class='info' href='#tcp'>Section&nbsp;3<span> (</span><span class='info'>TCP Binding</span><span>)</span></a>, opens a TCP connection to the advertised port at the resolved IP address, and sends an initial stream header to the receiving entity.  In either case, the receiving entity will receive an initial stream from the initiating entity.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>When the receiving entity processes an initial stream header from the initiating entity, it MUST send a response stream header to the initiating entity (for which it MUST generate a unique stream ID. If TLS negotiation has already succeeded, then this stream ID MUST be different from the stream ID sent before TLS negotiation succeeded).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:stream
+     from='im.example.com'
+     id='vgKi/bkYME8OAj4rlXMkpucAqe4='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The receiving entity also MUST send stream features to the initiating entity.  The stream features SHOULD include an advertisement for support of SASL negotiation, i.e., a &lt;mechanisms/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace.  Typically there are only three cases in which support for SASL negotiation would not be advertised here:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>TLS negotiation needs to happen before SASL can be offered (i.e., TLS is required and the receiving entity is responding to the very first initial stream header it has received for this connection attempt).
+</li>
+<li>SASL negotiation is impossible for a server-to-server connection (i.e., the initiating server has not provided a certificate that would enable strong authentication and therefore the receiving server is falling back to weak identity verification using the Server Dialback protocol <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>).
+</li>
+<li>SASL has already been negotiated (i.e., the receiving entity is responding to an initial stream header sent as a stream restart after successful SASL negotiation).
+</li>
+</ul><p>
+        
+</p>
+<p>The &lt;mechanisms/&gt; element MUST contain one &lt;mechanism/&gt; child element for each authentication mechanism the receiving entity offers to the initiating entity.  As noted, the order of &lt;mechanism/&gt; elements in the XML indicates the preference order of the SASL mechanisms according to the receiving entity (which is not necessarily the preference order according to the initiating entity).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+       &lt;mechanism&gt;EXTERNAL&lt;/mechanism&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1-PLUS&lt;/mechanism&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1&lt;/mechanism&gt;
+       &lt;mechanism&gt;PLAIN&lt;/mechanism&gt;
+     &lt;/mechanisms&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<a name="sasl-process-neg-initiate"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.2"></a><h3>6.4.2.&nbsp;
+Initiation</h3>
+
+<p>In order to begin the SASL negotiation, the initiating entity sends an &lt;auth/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace and includes an appropriate value for the 'mechanism' attribute, thus starting the handshake for that particular authentication mechanism.  This element MAY contain XML character data (in SASL terminology, the "initial response") if the mechanism supports or requires it. If the initiating entity needs to send a zero-length initial response, it MUST transmit the response as a single equals sign character ("="), which indicates that the response is present but contains no data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='PLAIN'&gt;AGp1bGlldAByMG0zMG15cjBtMzA=&lt;/auth&gt;
+</pre></div>
+<p>If the initiating entity subsequently sends another &lt;auth/&gt; element and the ongoing authentication handshake has not yet completed, the receiving entity MUST discard the ongoing handshake and MUST process a new handshake for the subsequently requested SASL mechanism.
+</p>
+<a name="sasl-process-neg-challengeresponse"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.3"></a><h3>6.4.3.&nbsp;
+Challenge-Response Sequence</h3>
+
+<p>If necessary, the receiving entity challenges the initiating entity by sending a &lt;challenge/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY contain XML character data (which MUST be generated in accordance with the definition of the SASL mechanism chosen by the initiating entity).
+</p>
+<p>The initiating entity responds to the challenge by sending a &lt;response/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY contain XML character data (which MUST be generated in accordance with the definition of the SASL mechanism chosen by the initiating entity).
+</p>
+<p>If necessary, the receiving entity sends more challenges and the initiating entity sends more responses.
+</p>
+<p>This series of challenge/response pairs continues until one of three things happens:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>The initiating entity aborts the handshake for this authentication mechanism.
+</li>
+<li>The receiving entity reports failure of the handshake.
+</li>
+<li>The receiving entity reports success of the handshake.
+</li>
+</ul><p>
+        
+</p>
+<p>These scenarios are described in the following sections.
+</p>
+<a name="sasl-process-neg-abort"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.4"></a><h3>6.4.4.&nbsp;
+Abort</h3>
+
+<p>The initiating entity aborts the handshake for this authentication mechanism by sending an &lt;abort/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;abort xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/&gt;
+</pre></div>
+<p>Upon receiving an &lt;abort/&gt; element, the receiving entity MUST return a &lt;failure/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace and containing an &lt;aborted/&gt; child element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;aborted/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-process-neg-failure"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.5"></a><h3>6.4.5.&nbsp;
+SASL Failure</h3>
+
+<p>The receiving entity reports failure of the handshake for this authentication mechanism by sending a &lt;failure/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace (the particular cause of failure MUST be communicated in an appropriate child element of the &lt;failure/&gt; element as defined under <a class='info' href='#sasl-errors'>Section&nbsp;6.5<span> (</span><span class='info'>SASL Errors</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;not-authorized/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<p>Where appropriate for the chosen SASL mechanism, the
+        receiving entity SHOULD allow a configurable but reasonable
+        number of retries (at least 2 and no more than 5); this
+        enables the initiating entity (e.g., an end-user client) to
+        tolerate incorrectly provided credentials (e.g., a mistyped password) without being forced to reconnect (which it would if the receiving entity immediately returned a SASL failure and closed the stream).
+</p>
+<p>If the initiating entity attempts a reasonable number of retries with the same SASL mechanism and all attempts fail, it MAY fall back to the next mechanism in its ordered list by sending a new &lt;auth/&gt; request to the receiving entity, thus starting a new handshake for that authentication mechanism.  If all handshakes fail and there are no remaining mechanisms in the initiating entity's list of supported and acceptable mechanisms, the initiating entity SHOULD simply close the stream as described under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a> (instead of waiting for the stream to time out).
+</p>
+<p>If the initiating entity exceeds the number of retries, the receiving entity MUST close the stream with a stream error, which SHOULD be &lt;policy-violation/&gt; (<a class='info' href='#streams-error-conditions-policy-violation'>Section&nbsp;4.9.3.14<span> (</span><span class='info'>policy-violation</span><span>)</span></a>), although some existing implementations send &lt;not-authorized/&gt; (<a class='info' href='#streams-error-conditions-not-authorized'>Section&nbsp;4.9.3.12<span> (</span><span class='info'>not-authorized</span><span>)</span></a>) instead.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: For server-to-server streams, if the receiving entity cannot offer the SASL EXTERNAL mechanism or any other SASL mechanism based on the security context established during TLS negotiation, the receiving entity MAY attempt to complete weak identity verification using the Server Dialback protocol <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>; however, if according to local service policies weak identity verification is insufficient then the receiving entity SHOULD instead close the stream with a &lt;policy-violation/&gt; stream error (<a class='info' href='#streams-error-conditions-policy-violation'>Section&nbsp;4.9.3.14<span> (</span><span class='info'>policy-violation</span><span>)</span></a>) instead of waiting for the stream to time out.
+</p>
+</blockquote>
+
+<a name="sasl-process-neg-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.4.6"></a><h3>6.4.6.&nbsp;
+SASL Success</h3>
+
+<p>Before considering the SASL handshake to be a success, if the initiating entity provided a 'from' attribute on an initial stream header whose confidentiality and integrity were protected via TLS or an equivalent security layer (such as the SASL GSSAPI mechanism) then the receiving entity SHOULD correlate the authentication identity resulting from the SASL negotiation with that 'from' address; if the two identities do not match then the receiving entity SHOULD terminate the connection attempt (however, the receiving entity might have legitimate reasons not to terminate the connection attempt, for example, because it has overridden a connecting client's address to correct the JID format or assign a JID based on information presented in an end-user certificate).
+</p>
+<p>The receiving entity reports success of the handshake by sending a &lt;success/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY contain XML character data (in SASL terminology, "additional data with success") if the chosen SASL mechanism supports or requires it. If the receiving entity needs to send additional data of zero length, it MUST transmit the data as a single equals sign character ("=").
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: For client-to-server streams, the authorization identity communicated during SASL negotiation is used to determine the canonical address for the initiating client according to the receiving server, as described under <a class='info' href='#streams-negotiation-address'>Section&nbsp;4.3.6<span> (</span><span class='info'>Determination of Addresses</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>Upon receiving the &lt;success/&gt; element, the initiating entity MUST initiate a new stream over the existing TCP connection by sending a new initial stream header to the receiving entity (as specified under <a class='info' href='#streams-negotiation-restart'>Section&nbsp;4.3.3<span> (</span><span class='info'>Restarts</span><span>)</span></a>, the initiating entity MUST NOT send a closing &lt;/stream&gt; tag before sending the new initial stream header, since the receiving entity and initiating entity MUST consider the original stream to be replaced upon success of the SASL negotiation).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Upon receiving the new initial stream header from the initiating entity, the receiving entity MUST respond by sending a new response stream header to the initiating entity (for which it MUST generate a new stream ID instead of reusing the old stream ID).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:stream
+     from='im.example.com'
+     id='gPybzaOzBmaADgxKXu9UClbprp0='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>The receiving entity MUST also send stream features, containing any further available features or containing no features (via an empty &lt;features/&gt; element).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+R: &lt;stream:features&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<a name="sasl-errors"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5"></a><h3>6.5.&nbsp;
+SASL Errors</h3>
+
+<p>The syntax of SASL errors is as follows, where the XML data shown within the square brackets '[' and ']' is OPTIONAL.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+  &lt;defined-condition/&gt;
+  [&lt;text xml:lang='langcode'&gt;
+      OPTIONAL descriptive text
+  &lt;/text&gt;]
+&lt;/failure&gt;
+</pre></div>
+<p>The "defined-condition" MUST be one of the SASL-related error conditions defined in the following sections.  However, because additional error conditions might be defined in the future, if an entity receives a SASL error condition that it does not understand then it MUST treat the unknown condition as a generic authentication failure, i.e., as equivalent to &lt;not-authorized/&gt; (<a class='info' href='#sasl-errors-not-authorized'>Section&nbsp;6.5.10<span> (</span><span class='info'>not-authorized</span><span>)</span></a>).
+</p>
+<p>Inclusion of the &lt;text/&gt; element is OPTIONAL, and can be used to provide application-specific information about the error condition, which information MAY be displayed to a human but only as a supplement to the defined condition.
+</p>
+<p>Because XMPP itself defines an application profile of SASL and there is no expectation that more specialized XMPP applications will be built on top of SASL, the SASL error format does not provide extensibility for application-specific error conditions as is done for XML streams (<a class='info' href='#streams-error-app'>Section&nbsp;4.9.4<span> (</span><span class='info'>Application-Specific Conditions</span><span>)</span></a>) and XML stanzas (<a class='info' href='#stanzas-error-app'>Section&nbsp;8.3.4<span> (</span><span class='info'>Application-Specific Conditions</span><span>)</span></a>).
+</p>
+<a name="sasl-errors-aborted"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.1"></a><h3>6.5.1.&nbsp;
+aborted</h3>
+
+<p>The receiving entity acknowledges that the authentication handshake has been aborted by the initiating entity; sent in reply to the &lt;abort/&gt; element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;abort xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;aborted/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-account-disabled"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.2"></a><h3>6.5.2.&nbsp;
+account-disabled</h3>
+
+<p>The account of the initiating entity has been temporarily disabled; sent in reply to an &lt;auth/&gt; element (with or without initial response data) or a &lt;response/&gt; element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='PLAIN'&gt;AGp1bGlldAByMG0zMG15cjBtMzA=&lt;/auth&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;account-disabled/&gt;
+     &lt;text xml:lang='en'&gt;Call 212-555-1212 for assistance.&lt;/text&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-credentials-expired"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.3"></a><h3>6.5.3.&nbsp;
+credentials-expired</h3>
+
+<p>The authentication failed because the initiating entity provided credentials that have expired; sent in reply to a &lt;response/&gt; element or an &lt;auth/&gt; element with initial response data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     [ ... ]
+   &lt;/response&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;credentials-expired/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-encryption-required"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.4"></a><h3>6.5.4.&nbsp;
+encryption-required</h3>
+
+<p>The mechanism requested by the initiating entity cannot be used unless the confidentiality and integrity of the underlying stream are protected (typically via TLS); sent in reply to an &lt;auth/&gt; element (with or without initial response data).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='PLAIN'&gt;AGp1bGlldAByMG0zMG15cjBtMzA=&lt;/auth&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;encryption-required/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-incorrect-encoding"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.5"></a><h3>6.5.5.&nbsp;
+incorrect-encoding</h3>
+
+<p>The data provided by the initiating entity could not be processed because the base 64 encoding is incorrect (e.g., because the encoding does not adhere to the definition in Section 4 of <a class='info' href='#BASE64'>[BASE64]<span> (</span><span class='info'>Josefsson, S., &ldquo;The Base16, Base32, and Base64 Data Encodings,&rdquo; October&nbsp;2006.</span><span>)</span></a>); sent in reply to a &lt;response/&gt; element or an &lt;auth/&gt; element with initial response data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='DIGEST-MD5'&gt;[ ... ]&lt;/auth&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;incorrect-encoding/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-invalid-authzid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.6"></a><h3>6.5.6.&nbsp;
+invalid-authzid</h3>
+
+<p>The authzid provided by the initiating entity is invalid, either because it is incorrectly formatted or because the initiating entity does not have permissions to authorize that ID; sent in reply to a &lt;response/&gt; element or an &lt;auth/&gt; element with initial response data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     [ ... ]
+   &lt;/response&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;invalid-authzid/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-invalid-mechanism"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.7"></a><h3>6.5.7.&nbsp;
+invalid-mechanism</h3>
+
+<p>The initiating entity did not specify a mechanism, or requested a mechanism that is not supported by the receiving entity; sent in reply to an &lt;auth/&gt; element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='CRAM-MD5'/&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;invalid-mechanism/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-malformed-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.8"></a><h3>6.5.8.&nbsp;
+malformed-request</h3>
+
+<p>The request is malformed (e.g., the &lt;auth/&gt; element includes initial response data but the mechanism does not allow that, or the data sent violates the syntax for the specified SASL mechanism); sent in reply to an &lt;abort/&gt;, &lt;auth/&gt;, &lt;challenge/&gt;, or &lt;response/&gt; element.
+</p>
+<p>(In the following example, the XML character data of the &lt;auth/&gt; element contains more than 255 UTF-8-encoded Unicode characters and therefore violates the "token" production for the SASL ANONYMOUS mechanism as specified in <a class='info' href='#ANONYMOUS'>[ANONYMOUS]<span> (</span><span class='info'>Zeilenga, K., &ldquo;Anonymous Simple Authentication and Security Layer (SASL) Mechanism,&rdquo; June&nbsp;2006.</span><span>)</span></a>.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='ANONYMOUS'&gt;[ ... some-long-token ... ]&lt;/auth&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;malformed-request/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-mechanism-too-weak"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.9"></a><h3>6.5.9.&nbsp;
+mechanism-too-weak</h3>
+
+<p>The mechanism requested by the initiating entity is weaker than server policy permits for that initiating entity; sent in reply to an &lt;auth/&gt; element (with or without initial response data).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+         mechanism='PLAIN'&gt;AGp1bGlldAByMG0zMG15cjBtMzA=&lt;/auth&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;mechanism-too-weak/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-errors-not-authorized"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.10"></a><h3>6.5.10.&nbsp;
+not-authorized</h3>
+
+<p>The authentication failed because the initiating entity did not provide proper credentials, or because some generic authentication failure has occurred but the receiving entity does not wish to disclose specific information about the cause of the failure; sent in reply to a &lt;response/&gt; element or an &lt;auth/&gt; element with initial response data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     [ ... ]
+   &lt;/response&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;not-authorized/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: This error condition includes but is not limited to the case of incorrect credentials or a nonexistent username.  In order to discourage directory harvest attacks, no differentiation is made between incorrect credentials and a nonexistent username.
+</p>
+</blockquote>
+
+<a name="sasl-errors-temporary-auth-failure"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.5.11"></a><h3>6.5.11.&nbsp;
+temporary-auth-failure</h3>
+
+<p>The authentication failed because of a temporary error condition within the receiving entity, and it is advisable for the initiating entity to try again later; sent in reply to an &lt;auth/&gt; element or a &lt;response/&gt; element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+I: &lt;response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     [ ... ]
+   &lt;/response&gt;
+
+R: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;temporary-auth-failure/&gt;
+   &lt;/failure&gt;
+</pre></div>
+<a name="sasl-def"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6.6"></a><h3>6.6.&nbsp;
+SASL Definition</h3>
+
+<p>The profiling requirements of <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a> require that the
+following information be supplied by the definition of a using protocol.
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>service name:</dt>
+<dd>"xmpp"
+</dd>
+<dt>initiation sequence:</dt>
+<dd>After the initiating entity provides
+an opening XML stream header and the receiving entity replies in kind, the
+receiving entity provides a list of acceptable authentication methods.  The
+initiating entity chooses one method from the list and sends it to the
+receiving entity as the value of the 'mechanism' attribute possessed by an
+&lt;auth/&gt; element, optionally including an initial response to avoid a
+round trip.
+</dd>
+<dt>exchange sequence:</dt>
+<dd>Challenges and responses are carried
+through the exchange of &lt;challenge/&gt; elements from receiving entity to
+initiating entity and &lt;response/&gt; elements from initiating entity to
+receiving entity.  The receiving entity reports failure by sending a
+&lt;failure/&gt; element and success by sending a &lt;success/&gt; element; the
+initiating entity aborts the exchange by sending an &lt;abort/&gt; element.
+Upon successful negotiation, both sides consider the original XML stream to be
+closed and new stream headers are sent by both entities.
+</dd>
+<dt>security layer negotiation:</dt>
+<dd>The security layer takes
+effect immediately after sending the closing '&gt;' character of the
+&lt;success/&gt; element for the receiving entity, and immediately after
+receiving the closing '&gt;' character of the &lt;success/&gt; element for the
+initiating entity.  The order of layers is first <a class='info' href='#TCP'>[TCP]<span> (</span><span class='info'>Postel, J., &ldquo;Transmission Control Protocol,&rdquo; September&nbsp;1981.</span><span>)</span></a>, then
+<a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>, then <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>, then XMPP.
+</dd>
+<dt>use of the authorization identity:</dt>
+<dd>The authorization
+identity can be used in XMPP to denote the non-default
+&lt;localpart@domainpart&gt; of a client; an empty string is equivalent to an
+absent authorization identity.
+</dd>
+</dl></blockquote>
+
+<a name="bind"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7"></a><h3>7.&nbsp;
+Resource Binding</h3>
+
+<a name="bind-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.1"></a><h3>7.1.&nbsp;
+Fundamentals</h3>
+
+<p>After a client authenticates with a server, it MUST bind a specific resource to the stream so that the server can properly address the client.  That is, there MUST be an XMPP resource associated with the bare JID (&lt;localpart@domainpart&gt;) of the client, so that the address for use over that stream is a full JID of the form &lt;localpart@domainpart/resource&gt; (including the resourcepart).  This ensures that the server can deliver XML stanzas to and receive XML stanzas from the client in relation to entities other than the server itself or the client's account, as explained under <a class='info' href='#rules'>Section&nbsp;10<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: The client could exchange stanzas with the server itself or the client's account before binding a resource since the full JID is needed only for addressing outside the context of the stream negotiated between the client and the server, but this is not commonly done.
+</p>
+</blockquote>
+
+<p>After a client has bound a resource to the stream, it is referred to as a "connected resource".  A server SHOULD allow an entity to maintain multiple connected resources simultaneously, where each connected resource is associated with a distinct XML stream and is differentiated from the other connected resources by a distinct resourcepart.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: A server SHOULD enable the administrator of an XMPP service to limit the number of connected resources in order to prevent certain denial-of-service attacks as described under <a class='info' href='#security-dos'>Section&nbsp;13.12<span> (</span><span class='info'>Denial of Service</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>If, before completing the resource binding step, the client attempts to send an XML stanza to an entity other than the server itself or the client's account, the server MUST NOT process the stanza and MUST close the stream with a &lt;not-authorized/&gt; stream error (<a class='info' href='#streams-error-conditions-not-authorized'>Section&nbsp;4.9.3.12<span> (</span><span class='info'>not-authorized</span><span>)</span></a>).
+</p>
+<p>The XML namespace name for the resource binding extension is 'urn:ietf:params:xml:ns:xmpp-bind'.
+</p>
+<a name="bind-support"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.2"></a><h3>7.2.&nbsp;
+Support</h3>
+
+<p>Support for resource binding is REQUIRED in XMPP client and server implementations.
+</p>
+<a name="bind-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.3"></a><h3>7.3.&nbsp;
+Stream Negotiation Rules</h3>
+
+<a name="bind-rules-mtn"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.3.1"></a><h3>7.3.1.&nbsp;
+Mandatory-to-Negotiate</h3>
+
+<p>The parties to a stream MUST consider resource binding as mandatory-to-negotiate.
+</p>
+<a name="bind-rules-restart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.3.2"></a><h3>7.3.2.&nbsp;
+Restart</h3>
+
+<p>After resource binding, the parties MUST NOT restart the stream.
+</p>
+<a name="bind-feature"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.4"></a><h3>7.4.&nbsp;
+Advertising Support</h3>
+
+<p>Upon sending a new response stream header to the client after successful SASL negotiation, the server MUST include a &lt;bind/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-bind' namespace in the stream features it presents to the client.
+</p>
+<p>The server MUST NOT include the resource binding stream feature until after the client has authenticated, typically by means of successful SASL negotiation.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:stream
+       from='im.example.com'
+       id='gPybzaOzBmaADgxKXu9UClbprp0='
+       to='juliet@im.example.com'
+       version='1.0'
+       xml:lang='en'
+       xmlns='jabber:client'
+       xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;stream:features&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>Upon being informed that resource binding is mandatory-to-negotiate, the client MUST bind a resource to the stream as described in the following sections.
+</p>
+<a name="bind-generation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.5"></a><h3>7.5.&nbsp;
+Generation of Resource Identifiers</h3>
+
+<p>A resourcepart MUST at a minimum be unique among the connected resources for that &lt;localpart@domainpart&gt;.  Enforcement of this policy is the responsibility of the server.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: A resourcepart can be security-critical.  For example, if a malicious entity can guess a client's resourcepart then it might be able to determine if the client (and therefore the controlling principal) is online or offline, thus resulting in a presence leak as described under <a class='info' href='#security-leaks-presence'>Section&nbsp;13.10.2<span> (</span><span class='info'>Presence Information</span><span>)</span></a>.  To prevent that possibility, a client can either (1) generate a random resourcepart on its own or (2) ask the server to generate a resourcepart on its behalf.  One method for ensuring that the resourcepart is random is to generate a Universally Unique Identifier (UUID) as specified in <a class='info' href='#UUID'>[UUID]<span> (</span><span class='info'>Leach, P., Mealling, M., and R. Salz, &ldquo;A Universally Unique IDentifier (UUID) URN Namespace,&rdquo; July&nbsp;2005.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="bind-servergen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.6"></a><h3>7.6.&nbsp;
+Server-Generated Resource Identifier</h3>
+
+<p>A server MUST be able to generate an XMPP resourcepart on behalf of a client.  The resourcepart generated by the server MUST be random (see <a class='info' href='#RANDOM'>[RANDOM]<span> (</span><span class='info'>Eastlake, D., Schiller, J., and S. Crocker, &ldquo;Randomness Requirements for Security,&rdquo; June&nbsp;2005.</span><span>)</span></a>).
+</p>
+<a name="bind-servergen-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.6.1"></a><h3>7.6.1.&nbsp;
+Success Case</h3>
+
+<p>A client requests a server-generated resourcepart by sending an IQ stanza of type "set" (see <a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>) containing an empty &lt;bind/&gt; element qualified by the 'urn:ietf:params:xml:ns:xmpp-bind' namespace.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq id='tn281v37' type='set'&gt;
+    &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Once the server has generated an XMPP resourcepart for the client, it MUST return an IQ stanza of type "result" to the client, which MUST include a &lt;jid/&gt; child element that specifies the full JID for the connected resource as determined by the server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='tn281v37' type='result'&gt;
+    &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+      &lt;jid&gt;
+        juliet@im.example.com/4db06f06-1ea4-11dc-aca3-000bcd821bfb
+      &lt;/jid&gt;
+    &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-servergen-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.6.2"></a><h3>7.6.2.&nbsp;
+Error Cases</h3>
+
+<p>When a client asks the server to generate a resourcepart during resource binding, the following stanza error conditions are defined:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>The account has reached a limit on the number of simultaneous connected resources allowed.
+</li>
+<li>The client is otherwise not allowed to bind a resource to the stream.
+</li>
+</ul><p>
+        
+</p>
+<p>Naturally, it is possible that error conditions not specified here might occur, as described under <a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>.
+</p>
+<a name="bind-servergen-error-resourceconstraint"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.6.2.1"></a><h3>7.6.2.1.&nbsp;
+Resource Constraint</h3>
+
+<p>If the account has reached a limit on the number of simultaneous connected resources allowed, the server MUST return a &lt;resource-constraint/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-resource-constraint'>Section&nbsp;8.3.3.18<span> (</span><span class='info'>resource-constraint</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='tn281v37' type='error'&gt;
+     &lt;error type='wait'&gt;
+       &lt;resource-constraint
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-servergen-error-notallowed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.6.2.2"></a><h3>7.6.2.2.&nbsp;
+Not Allowed</h3>
+
+<p>If the client is otherwise not allowed to bind a resource to the stream, the server MUST return a &lt;not-allowed/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-not-allowed'>Section&nbsp;8.3.3.10<span> (</span><span class='info'>not-allowed</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='tn281v37' type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;not-allowed
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-clientsubmit"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7"></a><h3>7.7.&nbsp;
+Client-Submitted Resource Identifier</h3>
+
+<p>Instead of asking the server to generate a resourcepart on its behalf, a client MAY attempt to submit a resourcepart that it has generated or that the controlling user has provided.
+</p>
+<a name="bind-clientsubmit-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7.1"></a><h3>7.7.1.&nbsp;
+Success Case</h3>
+
+<p>A client asks its server to accept a client-submitted resourcepart by sending an IQ stanza of type "set" containing a &lt;bind/&gt; element with a child &lt;resource/&gt; element containing non-zero-length XML character data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq id='wy2xa82b4' type='set'&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+       &lt;resource&gt;balcony&lt;/resource&gt;
+     &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>The server SHOULD accept the client-submitted resourcepart.  It does so by returning an IQ stanza of type "result" to the client, including a &lt;jid/&gt; child element that specifies the full JID for the connected resource and contains without modification the client-submitted text.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='result'&gt;
+    &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+      &lt;jid&gt;juliet@im.example.com/balcony&lt;/jid&gt;
+    &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Alternatively, in accordance with local service policies the server MAY refuse the client-submitted resourcepart and override it with a resourcepart that the server generates.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='result'&gt;
+    &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+      &lt;jid&gt;
+   juliet@im.example.com/balcony 4db06f06-1ea4-11dc-aca3-000bcd821bfb
+      &lt;/jid&gt;
+    &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-clientsubmit-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7.2"></a><h3>7.7.2.&nbsp;
+Error Cases</h3>
+
+<p>When a client attempts to submit its own XMPP resourcepart during resource binding, the following stanza error conditions are defined in addition to those described under <a class='info' href='#bind-servergen-error'>Section&nbsp;7.6.2<span> (</span><span class='info'>Error Cases</span><span>)</span></a>:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>The provided resourcepart cannot be processed by the server.
+</li>
+<li>The provided resourcepart is already in use.
+</li>
+</ul><p>
+        
+</p>
+<p>Naturally, it is possible that error conditions not specified here might occur, as described under <a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>.
+</p>
+<a name="bind-clientsubmit-error-badrequest"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7.2.1"></a><h3>7.7.2.1.&nbsp;
+Bad Request</h3>
+
+<p>If the provided resourcepart cannot be processed by the server (e.g., because it is of zero length or because it otherwise violates the rules for resourceparts specified in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>), the server can return a &lt;bad-request/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-bad-request'>Section&nbsp;8.3.3.1<span> (</span><span class='info'>bad-request</span><span>)</span></a>) but SHOULD instead process the resourcepart so that it is in conformance.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-clientsubmit-error-conflict"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7.2.2"></a><h3>7.7.2.2.&nbsp;
+Conflict</h3>
+
+<p>If there is a currently connected client whose session
+          has the resourcepart being requested by the newly connecting client, the server MUST do one of the following (which of these the server does is a matter for implementation or local service policy, although suggestions are provided below).
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>Override the resourcepart provided by the newly connecting client with a server-generated resourcepart.
+              
+              This behavior is encouraged, because it simplifies the resource binding process for client implementations.
+</li>
+<li>Disallow the resource binding attempt of the newly
+              connecting client and maintain the session of the
+              currently connected client.
+              
+              This behavior is neither encouraged nor discouraged, despite the fact that it was implicitly encouraged in RFC 3920; however, note that handling of the &lt;conflict/&gt; error is unevenly supported among existing client implementations, which often treat it as an authentication error and have been observed to discard cached credentials when receiving it.
+</li>
+<li>Terminate the session of the currently connected
+              client and allow the resource binding attempt of the
+              newly connecting client.
+              
+              Although this was the traditional behavior of early XMPP
+              server implementations, it is now discouraged because it
+              can lead to a never-ending cycle of two clients
+              effectively disconnecting each other; however, note that
+              this behavior can be appropriate in some deployment
+              scenarios or if the server knows that the currently connected client has a dead connection or broken stream as described under <a class='info' href='#streams-silence'>Section&nbsp;4.6<span> (</span><span class='info'>Handling of Silent Peers</span><span>)</span></a>.
+</li>
+</ol><p>
+          
+</p>
+<p>If the server follows behavior #1, it returns an
+          &lt;iq/&gt; stanza of type "result" to the newly connecting client, where the &lt;jid/&gt; child of the &lt;bind/&gt; element contains XML character data that indicates the full JID of the client, including the resourcepart that was generated by the server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='result'&gt;
+    &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+      &lt;jid&gt;
+   juliet@im.example.com/balcony 4db06f06-1ea4-11dc-aca3-000bcd821bfb
+      &lt;/jid&gt;
+    &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>If the server follows behavior #2, it sends a &lt;conflict/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-conflict'>Section&nbsp;8.3.3.2<span> (</span><span class='info'>conflict</span><span>)</span></a>) in response to the resource binding attempt of the newly connecting client but maintains the XML stream so that the newly connecting client has an opportunity to negotiate a non-conflicting resourcepart (i.e., the newly connecting client needs to choose a different resourcepart before making another attempt to bind a resource).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>If the server follows behavior #3, it returns a &lt;conflict/&gt; stream error (<a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>) to the currently connected client (as described under <a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>) and returns an IQ stanza of type "result" (indicating success) in response to the resource binding attempt of the newly connecting client.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='wy2xa82b4' type='result'&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+       &lt;jid&gt;
+         juliet@im.example.com/balcony
+       &lt;/jid&gt;
+     &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="bind-clientsubmit-retries"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7.7.3"></a><h3>7.7.3.&nbsp;
+Retries</h3>
+
+<p>If an error occurs when a client submits a resourcepart, the server SHOULD allow a configurable but reasonable number of retries (at least 5 and no more than 10); this enables the client to tolerate incorrectly provided resourceparts (e.g., bad data formats or duplicate text strings) without being forced to reconnect.
+</p>
+<p>After the client has reached the retry limit, the server MUST close the stream with a &lt;policy-violation/&gt; stream error (<a class='info' href='#streams-error-conditions-policy-violation'>Section&nbsp;4.9.3.14<span> (</span><span class='info'>policy-violation</span><span>)</span></a>).
+</p>
+<a name="stanzas"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8"></a><h3>8.&nbsp;
+XML Stanzas</h3>
+
+<p>After a client and a server (or two servers) have completed stream negotiation, either party can send XML stanzas.  Three kinds of XML stanza are defined for the 'jabber:client' and 'jabber:server' namespaces: &lt;message/&gt;, &lt;presence/&gt;, and &lt;iq/&gt;.  In addition, there are five common attributes for these stanza types.  These common attributes, as well as the basic semantics of the three stanza types, are defined in this specification; more detailed information regarding the syntax of XML stanzas for instant messaging and presence applications is provided in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>, and for other applications in the relevant XMPP extension specifications.
+</p>
+<p>Support for the XML stanza syntax and semantics defined in this specification is REQUIRED in XMPP client and server implementations.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: A server MUST NOT process a partial stanza and MUST NOT attach meaning to the transmission timing of any part of a stanza (before receipt of the closing tag).
+</p>
+</blockquote>
+
+<a name="stanzas-attributes"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1"></a><h3>8.1.&nbsp;
+Common Attributes</h3>
+
+<p>The following five attributes are common to message, presence, and IQ stanzas.
+</p>
+<a name="stanzas-attributes-to"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.1"></a><h3>8.1.1.&nbsp;
+to</h3>
+
+<p>The 'to' attribute specifies the JID of the intended recipient for the stanza.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message to='romeo@example.net'&gt;
+  &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>For information about server processing of inbound and outbound XML stanzas based on the 'to' address, refer to <a class='info' href='#rules'>Section&nbsp;10<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>.
+</p>
+<a name="stanzas-attributes-to-c2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.1.1"></a><h3>8.1.1.1.&nbsp;
+Client-to-Server Streams</h3>
+
+<p>The following rules apply to inclusion of the 'to' attribute in stanzas sent from a connected client to its server over an XML stream qualified by the 'jabber:client' namespace.
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>A stanza with a specific intended recipient (e.g., a conversation partner, a remote service, the server itself, even another resource associated with the user's bare JID) MUST possess a 'to' attribute whose value is an XMPP address.
+</li>
+<li>A stanza sent from a client to a server for direct processing by the server (e.g., roster processing as described in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a> or presence sent to the server for broadcasting to other entities) MUST NOT possess a 'to' attribute.
+</li>
+</ol><p>
+          
+</p>
+<p>The following rules apply to inclusion of the 'to' attribute in stanzas sent from a server to a connected client over an XML stream qualified by the 'jabber:client' namespace.
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>If the server has received the stanza from another connected client or from a peer server, the server MUST NOT modify the 'to' address before delivering the stanza to the client.
+</li>
+<li>If the server has itself generated the stanza (e.g., a response to an IQ stanza of type "get" or "set", even if the stanza did not include a 'to' address), the stanza MAY include a 'to' address, which MUST be the full JID of the client; however, if the stanza does not include a 'to' address then the client MUST treat it as if the 'to' address were included with a value of the client's full JID.
+</li>
+</ol><p>
+          
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: It is the server's responsibility to deliver only stanzas that are addressed to the client's full JID or the user's bare JID; thus, there is no need for the client to check the 'to' address of incoming stanzas.  However, if the client does check the 'to' address then it is suggested to check at most the bare JID portion (not the full JID), since the 'to' address might be the user's bare JID, the client's current full JID, or even a full JID with a different resourcepart (e.g., in the case of so-called "offline messages" as described in <a class='info' href='#XEP-0160'>[XEP&#8209;0160]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices for Handling Offline Messages,&rdquo; January&nbsp;2006.</span><span>)</span></a>).
+</p>
+</blockquote>
+
+<a name="stanzas-attributes-to-s2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.1.2"></a><h3>8.1.1.2.&nbsp;
+Server-to-Server Streams</h3>
+
+<p>The following rules apply to inclusion of the 'to' attribute in the context of XML streams qualified by the 'jabber:server' namespace (i.e., server-to-server streams).
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>A stanza MUST possess a 'to' attribute whose value is an XMPP address; if a server receives a stanza that does not meet this restriction, it MUST close the stream with an &lt;improper-addressing/&gt; stream error (<a class='info' href='#streams-error-conditions-improper-addressing'>Section&nbsp;4.9.3.7<span> (</span><span class='info'>improper-addressing</span><span>)</span></a>).
+</li>
+<li>The domainpart of the JID contained in the stanza's 'to' attribute MUST match the FQDN of the receiving server (or any validated domain thereof) as communicated via SASL negotiation (see <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>), Server Dialback (see <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>), or similar means; if a server receives a stanza that does not meet this restriction, it MUST close the stream with a &lt;host-unknown/&gt; stream error (<a class='info' href='#streams-error-conditions-host-unknown'>Section&nbsp;4.9.3.6<span> (</span><span class='info'>host-unknown</span><span>)</span></a>) or a &lt;host-gone/&gt; stream error (<a class='info' href='#streams-error-conditions-host-gone'>Section&nbsp;4.9.3.5<span> (</span><span class='info'>host-gone</span><span>)</span></a>).
+</li>
+</ol><p>
+          
+</p>
+<a name="stanzas-attributes-from"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.2"></a><h3>8.1.2.&nbsp;
+from</h3>
+
+<p>The 'from' attribute specifies the JID of the sender.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message from='juliet@im.example.com/balcony'
+         to='romeo@example.net'&gt;
+  &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<a name="stanzas-attributes-from-c2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.2.1"></a><h3>8.1.2.1.&nbsp;
+Client-to-Server Streams</h3>
+
+<p>The following rules apply to the 'from' attribute in the context of XML streams qualified by the 'jabber:client' namespace (i.e., client-to-server streams).
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>When a server receives an XML stanza from a connected client, the server MUST add a 'from' attribute to the stanza or override the 'from' attribute specified by the client, where the value of the 'from' attribute MUST be the full JID (&lt;localpart@domainpart/resource&gt;) determined by the server for the connected resource that generated the stanza (see <a class='info' href='#streams-negotiation-address'>Section&nbsp;4.3.6<span> (</span><span class='info'>Determination of Addresses</span><span>)</span></a>), or the bare JID (&lt;localpart@domainpart&gt;) in the case of subscription-related presence stanzas (see <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>When the server generates a stanza on its own behalf for delivery to the client from the server itself, the stanza MUST include a 'from' attribute whose value is the bare JID (i.e., &lt;domainpart&gt;) of the server as agreed upon during stream negotiation (e.g., based on the 'to' attribute of the initial stream header).
+</li>
+<li>When the server generates a stanza from the server for delivery to the client on behalf of the account of the connected client (e.g., in the context of data storage services provided by the server on behalf of the client), the stanza MUST either (a) not include a 'from' attribute or (b) include a 'from' attribute whose value is the account's bare JID (&lt;localpart@domainpart&gt;).
+</li>
+<li>A server MUST NOT send to the client a stanza without a 'from' attribute if the stanza was not generated by the server on its own behalf (e.g., if it was generated by another client or a peer server and the server is merely delivering it to the client on behalf of some other entity); therefore, when a client receives a stanza that does not include a 'from' attribute, it MUST assume that the stanza is from the user's account on the server.
+</li>
+</ol><p>
+          
+</p>
+<a name="stanzas-attributes-from-s2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.2.2"></a><h3>8.1.2.2.&nbsp;
+Server-to-Server Streams</h3>
+
+<p>The following rules apply to the 'from' attribute in the context of XML streams qualified by the 'jabber:server' namespace (i.e., server-to-server streams).
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>A stanza MUST possess a 'from' attribute whose value is an XMPP address; if a server receives a stanza that does not meet this restriction, it MUST close the stream with an &lt;improper-addressing/&gt; stream error (<a class='info' href='#streams-error-conditions-improper-addressing'>Section&nbsp;4.9.3.7<span> (</span><span class='info'>improper-addressing</span><span>)</span></a>).
+</li>
+<li>The domainpart of the JID contained in the stanza's 'from' attribute MUST match the FQDN of the sending server (or any validated domain thereof) as communicated via SASL negotiation (see <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>), Server Dialback (see <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>), or similar means; if a server receives a stanza that does not meet this restriction, it MUST close the stream with an &lt;invalid-from/&gt; stream error (<a class='info' href='#streams-error-conditions-invalid-from'>Section&nbsp;4.9.3.9<span> (</span><span class='info'>invalid-from</span><span>)</span></a>).
+</li>
+</ol><p>
+          
+</p>
+<p>Enforcement of these rules helps to prevent certain denial-of-service attacks as described under <a class='info' href='#security-dos'>Section&nbsp;13.12<span> (</span><span class='info'>Denial of Service</span><span>)</span></a>.
+</p>
+<a name="stanzas-attributes-id"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.3"></a><h3>8.1.3.&nbsp;
+id</h3>
+
+<p>The 'id' attribute is used by the originating entity to track any response or error stanza that it might receive in relation to the generated stanza from another entity (such as an intermediate server or the intended recipient).
+</p>
+<p>It is up to the originating entity whether the value of the 'id' attribute is unique only within its current stream or unique globally.
+</p>
+<p>For &lt;message/&gt; and &lt;presence/&gt; stanzas, it is RECOMMENDED for the originating entity to include an 'id' attribute; for &lt;iq/&gt; stanzas, it is REQUIRED.
+</p>
+<p>If the generated stanza includes an 'id' attribute then it is REQUIRED for the response or error stanza to also include an 'id' attribute, where the value of the 'id' attribute MUST match that of the generated stanza.
+</p>
+<p>The semantics of IQ stanzas impose additional restrictions as described under <a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>.
+</p>
+<a name="stanzas-attributes-type"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.4"></a><h3>8.1.4.&nbsp;
+type</h3>
+
+<p>The 'type' attribute specifies the purpose or context of the message, presence, or IQ stanza.  The particular allowable values for the 'type' attribute vary depending on whether the stanza is a message, presence, or IQ stanza.  The defined values for message and presence stanzas are specific to instant messaging and presence applications and therefore are defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>, whereas the values for IQ stanzas specify the part of the semantics for all structured request-response exchanges (no matter what the payload) and therefore are specified under <a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>.  The only 'type' value common to all three kinds of stanzas is "error" as described under <a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>.
+</p>
+<a name="stanzas-attributes-lang"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1.5"></a><h3>8.1.5.&nbsp;
+xml:lang</h3>
+
+<p>A stanza SHOULD possess an 'xml:lang' attribute (as defined in Section 2.12 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>) if the stanza contains XML character data that is intended to be presented to a human user (as explained in <a class='info' href='#CHARSETS'>[CHARSETS]<span> (</span><span class='info'>Alvestrand, H., &ldquo;IETF Policy on Character Sets and Languages,&rdquo; January&nbsp;1998.</span><span>)</span></a>, "internationalization is for humans").  The value of the 'xml:lang' attribute specifies the default language of any such human-readable XML character data.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net/orchard' xml:lang='en'&gt;
+  &lt;show&gt;dnd&lt;/show&gt;
+  &lt;status&gt;Wooing Juliet&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>The value of the 'xml:lang' attribute MAY be overridden by the 'xml:lang' attribute of a specific child element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net/orchard' xml:lang='en'&gt;
+  &lt;show&gt;dnd&lt;/show&gt;
+  &lt;status&gt;Wooing Juliet&lt;/status&gt;
+  &lt;status xml:lang='cs'&gt;Dvo&amp;#x0159;&amp;#x00ED;m se Julii&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>If an outbound stanza generated by a client does not possess an 'xml:lang' attribute, the client's server SHOULD add an 'xml:lang' attribute whose value is that specified for the client's output stream as defined under <a class='info' href='#streams-attr-xmllang'>Section&nbsp;4.7.4<span> (</span><span class='info'>xml:lang</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence from='romeo@example.net/orchard'&gt;
+     &lt;show&gt;dnd&lt;/show&gt;
+     &lt;status&gt;Wooing Juliet&lt;/status&gt;
+   &lt;/presence&gt;
+
+S: &lt;presence from='romeo@example.net/orchard'
+             to='juliet@im.example.com'
+             xml:lang='en'&gt;
+     &lt;show&gt;dnd&lt;/show&gt;
+     &lt;status&gt;Wooing Juliet&lt;/status&gt;
+   &lt;/presence&gt;
+</pre></div>
+<p>If an inbound stanza received by a client or server does not possess an 'xml:lang' attribute, an implementation MUST assume that the default language is that specified for the entity's input stream as defined under <a class='info' href='#streams-attr-xmllang'>Section&nbsp;4.7.4<span> (</span><span class='info'>xml:lang</span><span>)</span></a>.
+</p>
+<p>The value of the 'xml:lang' attribute MUST conform to the NMTOKEN datatype (as defined in Section 2.3 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>) and MUST conform to the format defined in <a class='info' href='#LANGTAGS'>[LANGTAGS]<span> (</span><span class='info'>Phillips, A. and M. Davis, &ldquo;Tags for Identifying Languages,&rdquo; September&nbsp;2009.</span><span>)</span></a>.
+</p>
+<p>A server MUST NOT modify or delete 'xml:lang' attributes on stanzas it receives from other entities.
+</p>
+<a name="stanzas-semantics"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.2"></a><h3>8.2.&nbsp;
+Basic Semantics</h3>
+
+<a name="stanzas-semantics-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.2.1"></a><h3>8.2.1.&nbsp;
+Message Semantics</h3>
+
+<p>The &lt;message/&gt; stanza is a "push" mechanism whereby one entity pushes information to another entity, similar to the communications that occur in a system such as email.  All message stanzas will possess a 'to' attribute that specifies the intended recipient of the message (see <a class='info' href='#stanzas-attributes-to'>Section&nbsp;8.1.1<span> (</span><span class='info'>to</span><span>)</span></a> and <a class='info' href='#rules-noto'>Section&nbsp;10.3<span> (</span><span class='info'>No 'to' Address</span><span>)</span></a>), unless the message is being sent to the bare JID of a connected client's account.  Upon receiving a message stanza with a 'to' address, a server SHOULD attempt to route or deliver it to the intended recipient (see <a class='info' href='#rules'>Section&nbsp;10<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a> for general routing and delivery rules related to XML stanzas).
+</p>
+<a name="stanzas-semantics-presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.2.2"></a><h3>8.2.2.&nbsp;
+Presence Semantics</h3>
+
+<p>The &lt;presence/&gt; stanza is a specialized "broadcast" or "publish-subscribe" mechanism, whereby multiple entities receive information (in this case, network availability information) about an entity to which they have subscribed.  In general, a publishing client SHOULD send a presence stanza with no 'to' attribute, in which case the server to which the client is connected will broadcast that stanza to all subscribed entities.  However, a publishing client MAY also send a presence stanza with a 'to' attribute, in which case the server will route or deliver that stanza to the intended recipient.  Although the &lt;presence/&gt; stanza is most often used by XMPP clients, it can also be used by servers, add-on services, and any other kind of XMPP entity.  See <a class='info' href='#rules'>Section&nbsp;10<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a> for general routing and delivery rules related to XML stanzas, and <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a> for rules specific to presence applications.
+</p>
+<a name="stanzas-semantics-iq"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.2.3"></a><h3>8.2.3.&nbsp;
+IQ Semantics</h3>
+
+<p>Info/Query, or IQ, is a "request-response" mechanism, similar in some ways to the Hypertext Transfer Protocol <a class='info' href='#HTTP'>[HTTP]<span> (</span><span class='info'>Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &ldquo;Hypertext Transfer Protocol -- HTTP/1.1,&rdquo; June&nbsp;1999.</span><span>)</span></a>.  The semantics of IQ enable an entity to make a request of, and receive a response from, another entity.  The data content of the request and response is defined by the schema or other structural definition associated with the XML namespace that qualifies the direct child element of the IQ element (see <a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a>), and the interaction is tracked by the requesting entity through use of the 'id' attribute.  Thus, IQ interactions follow a common pattern of structured data exchange such as get/result or set/result (although an error can be returned in reply to a request if appropriate):
+</p><br /><hr class="insert" />
+<a name="figure-5"></a>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+Requesting                  Responding
+  Entity                      Entity
+----------                  ----------
+    |                            |
+    | &lt;iq id='1' type='get'&gt;     |
+    |   [ ... payload ... ]      |
+    | &lt;/iq&gt;                      |
+    | -------------------------&gt; |
+    |                            |
+    | &lt;iq id='1' type='result'&gt;  |
+    |   [ ... payload ... ]      |
+    | &lt;/iq&gt;                      |
+    | &lt;------------------------- |
+    |                            |
+    | &lt;iq id='2' type='set'&gt;     |
+    |   [ ... payload ... ]      |
+    | &lt;/iq&gt;                      |
+    | -------------------------&gt; |
+    |                            |
+    | &lt;iq id='2' type='error'&gt;   |
+    |   [ ... condition ... ]    |
+    | &lt;/iq&gt;                      |
+    | &lt;------------------------- |
+    |                            |
+</pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;5: Semantics of IQ Stanzas&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
+
+<p>To enforce these semantics, the following rules apply:
+</p>
+<p></p>
+<ol class="text">
+<li>The 'id' attribute is REQUIRED for IQ stanzas.
+</li>
+<li>The 'type' attribute is REQUIRED for IQ stanzas.  The value MUST be one of the following; if not, the recipient or an intermediate router MUST return a &lt;bad-request/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-bad-request'>Section&nbsp;8.3.3.1<span> (</span><span class='info'>bad-request</span><span>)</span></a>).
+            
+            
+<ul class="text">
+<li>get -- The stanza requests information, inquires about what data is needed in order to complete further operations, etc.
+</li>
+<li>set -- The stanza provides data that is needed for an operation to be completed, sets new values, replaces existing values, etc.
+</li>
+<li>result -- The stanza is a response to a successful get or set request.
+</li>
+<li>error -- The stanza reports an error that has occurred regarding processing or delivery of a get or set request (see <a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>).
+</li>
+</ul>
+          
+</li>
+<li>An entity that receives an IQ request of type "get" or "set" MUST reply with an IQ response of type "result" or "error".  The response MUST preserve the 'id' attribute of the request (or be empty if the generated stanza did not include an 'id' attribute).
+</li>
+<li>An entity that receives a stanza of type "result" or "error" MUST NOT respond to the stanza by sending a further IQ response of type "result" or "error"; however, the requesting entity MAY send another request (e.g., an IQ of type "set" to provide obligatory information discovered through a get/result pair).
+</li>
+<li>An IQ stanza of type "get" or "set" MUST contain exactly one child element, which specifies the semantics of the particular request.
+</li>
+<li>An IQ stanza of type "result" MUST include zero or one child elements.
+</li>
+<li>An IQ stanza of type "error" MAY include the child element contained in the associated "get" or "set" and MUST include an &lt;error/&gt; child; for details, see <a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>.
+</li>
+</ol>
+
+<a name="stanzas-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3"></a><h3>8.3.&nbsp;
+Stanza Errors</h3>
+
+<p>Stanza-related errors are handled in a manner similar to <a class='info' href='#streams-error'>stream errors<span> (</span><span class='info'>Stream Errors</span><span>)</span></a>.  Unlike stream errors, stanza errors are recoverable; therefore, they do not result in termination of the XML stream and underlying TCP connection.  Instead, the entity that discovers the error condition returns an error stanza, which is a stanza that:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>is of the same kind (message, presence, or IQ) as the generated stanza that triggered the error
+</li>
+<li>has a 'type' attribute set to a value of "error"
+</li>
+<li>typically swaps the 'from' and 'to' addresses of the generated stanza
+</li>
+<li>mirrors the 'id' attribute (if any) of the generated stanza that triggered the error
+</li>
+<li>contains an &lt;error/&gt; child element that specifies the error condition and therefore provides a hint regarding actions that the sender might be able to take in an effort to remedy the error (however, it is not always possible to remedy the error)
+</li>
+</ul><p>
+      
+</p>
+<a name="stanzas-error-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.1"></a><h3>8.3.1.&nbsp;
+Rules</h3>
+
+<p>The following rules apply to stanza errors:
+</p>
+<p></p>
+<ol class="text">
+<li>The receiving or processing entity that detects an error condition in relation to a stanza SHOULD return an error stanza (and MUST do so for IQ stanzas).
+</li>
+<li>The error stanza SHOULD simply swap the 'from' and 'to' addresses from the generated stanza, unless doing so would (1) result in an information leak (see under <a class='info' href='#security-leaks'>Section&nbsp;13.10<span> (</span><span class='info'>Information Leaks</span><span>)</span></a>) or other breach of security, or (2) force the sender of the error stanza to include a malformed JID in the 'from' or 'to' address of the error stanza.
+</li>
+<li>If the generated stanza was &lt;message/&gt; or &lt;presence/&gt; and included an 'id' attribute then it is REQUIRED for the error stanza to also include an 'id' attribute.  If the generated stanza was &lt;iq/&gt; then the error stanza MUST include an 'id' attribute.  In all cases, the value of the 'id' attribute MUST match that of the generated stanza (or be empty if the generated stanza did not include an 'id' attribute).
+</li>
+<li>An error stanza MUST contain an &lt;error/&gt; child element.
+</li>
+<li>The entity that returns an error stanza MAY pass along its JID to the sender of the generated stanza (e.g., for diagnostic or tracking purposes) through the addition of a 'by' attribute to the &lt;error/&gt; child element.
+</li>
+<li>The entity that returns an error stanza MAY include the original XML sent so that the sender can inspect and, if necessary, correct the XML before attempting to resend (however, this is a courtesy only and the originating entity MUST NOT depend on receiving the original payload). Naturally, the entity MUST NOT include the original data if it not well-formed XML, violates the XML restrictions of XMPP (see under <a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>), or is otherwise harmful (e.g., exceeds a size limit).
+</li>
+<li>An &lt;error/&gt; child MUST NOT be included if the 'type' attribute has a value other than "error" (or if there is no 'type' attribute).
+</li>
+<li>An entity that receives an error stanza MUST NOT respond to the stanza with a further error stanza; this helps to prevent looping.
+</li>
+</ol>
+
+<a name="stanzas-error-syntax"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.2"></a><h3>8.3.2.&nbsp;
+Syntax</h3>
+
+<p>The syntax for stanza-related errors is as follows, where XML data shown within the square brackets '[' and ']' is OPTIONAL, 'intended-recipient' is the JID of the entity to which the original stanza was addressed, 'sender' is the JID of the originating entity, and 'error-generator' is the entity that detects the fact that an error has occurred and thus returns an error stanza.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;stanza-kind from='intended-recipient' to='sender' type='error'&gt;
+  [OPTIONAL to include sender XML here]
+  &lt;error [by='error-generator']
+         type='error-type'&gt;
+    &lt;defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    [&lt;text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
+           xml:lang='langcode'&gt;
+      OPTIONAL descriptive text
+    &lt;/text&gt;]
+    [OPTIONAL application-specific condition element]
+  &lt;/error&gt;
+&lt;/stanza-kind&gt;
+</pre></div>
+<p>The "stanza-kind" MUST be one of message, presence, or iq.
+</p>
+<p>The "error-type" MUST be one of the following:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>auth -- retry after providing credentials
+</li>
+<li>cancel -- do not retry (the error cannot be remedied)
+</li>
+<li>continue -- proceed (the condition was only a warning)
+</li>
+<li>modify -- retry after changing the data sent
+</li>
+<li>wait -- retry after waiting (the error is temporary)
+</li>
+</ul><p>
+        
+</p>
+<p>The "defined-condition" MUST correspond to one of the stanza error conditions defined under <a class='info' href='#stanzas-error-conditions'>Section&nbsp;8.3.3<span> (</span><span class='info'>Defined Conditions</span><span>)</span></a>.  However, because additional error conditions might be defined in the future, if an entity receives a stanza error condition that it does not understand then it MUST treat the unknown condition as equivalent to &lt;undefined-condition/&gt; (<a class='info' href='#stanzas-error-conditions-undefined-condition'>Section&nbsp;8.3.3.21<span> (</span><span class='info'>undefined-condition</span><span>)</span></a>).  If the designers of an XMPP protocol extension or the developers of an XMPP implementation need to communicate a stanza error condition that is not defined in this specification, they can do so by defining an application-specific error condition element qualified by an application-specific namespace.
+</p>
+<p>The &lt;error/&gt; element:
+</p>
+<p></p>
+<ul class="text">
+<li>MUST contain a defined condition element.
+</li>
+<li>MAY contain a &lt;text/&gt; child element containing XML character data that describes the error in more detail; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace and SHOULD possess an 'xml:lang' attribute specifying the natural language of the XML character data.
+</li>
+<li>MAY contain a child element for an application-specific error condition; this element MUST be qualified by an application-specific namespace that defines the syntax and semantics of the element.
+</li>
+</ul>
+
+<p>The &lt;text/&gt; element is OPTIONAL.  If included, it is to be used only to provide descriptive or diagnostic information that supplements the meaning of a defined condition or application-specific condition.  It MUST NOT be interpreted programmatically by an application.  It SHOULD NOT be used as the error message presented to a human user, but MAY be shown in addition to the error message associated with the defined condition element (and, optionally, the application-specific condition element).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: The syntax defined in <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> included a legacy 'code' attribute, whose semantics have been replaced by the defined condition elements; information about mapping defined condition elements to values of the legacy 'code' attribute can be found in <a class='info' href='#XEP-0086'>[XEP&#8209;0086]<span> (</span><span class='info'>Norris, R. and P. Saint-Andre, &ldquo;Error Condition Mappings,&rdquo; February&nbsp;2004.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3"></a><h3>8.3.3.&nbsp;
+Defined Conditions</h3>
+
+<p>The following conditions are defined for use in stanza errors.
+</p>
+<p>The error-type value that is RECOMMENDED for each defined condition is the usual expected type; however, in some circumstances a different type might be more appropriate.
+</p>
+<a name="stanzas-error-conditions-bad-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.1"></a><h3>8.3.3.1.&nbsp;
+bad-request</h3>
+
+<p>The sender has sent a stanza containing XML that does not conform to the appropriate schema or that cannot be processed (e.g., an IQ stanza that includes an unrecognized value of the 'type' attribute, or an element that is qualified by a recognized namespace but that violates the defined syntax for the element); the associated error type SHOULD be "modify".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@im.example.com/balcony'
+       id='zj3v142b'
+       to='im.example.com'
+       type='subscribe'&gt;
+     &lt;ping xmlns='urn:xmpp:ping'/&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq from='im.example.com'
+       id='zj3v142b'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="stanzas-error-conditions-conflict"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.2"></a><h3>8.3.3.2.&nbsp;
+conflict</h3>
+
+<p>Access cannot be granted because an existing resource exists with the same name or address; the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq id='wy2xa82b4' type='set'&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+       &lt;resource&gt;balcony&lt;/resource&gt;
+     &lt;/bind&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='wy2xa82b4' type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="stanzas-error-conditions-feature-not-implemented"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.3"></a><h3>8.3.3.3.&nbsp;
+feature-not-implemented</h3>
+
+<p>The feature represented in the XML stanza is not implemented by the intended recipient or an intermediate server and therefore the stanza cannot be processed (e.g., the entity understands the namespace but does not recognize the element name); the associated error type SHOULD be "cancel" or "modify".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@im.example.com/balcony'
+       id='9u2bax16'
+       to='pubsub.example.com'
+       type='get'&gt;
+     &lt;pubsub xmlns='http://jabber.org/protocol/pubsub'&gt;
+       &lt;subscriptions/&gt;
+     &lt;/pubsub&gt;
+   &lt;/iq&gt;
+
+E: &lt;iq from='pubsub.example.com'
+       id='9u2bax16'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;feature-not-implemented
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+       &lt;unsupported
+           xmlns='http://jabber.org/protocol/pubsub#errors'
+           feature='retrieve-subscriptions'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="stanzas-error-conditions-forbidden"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.4"></a><h3>8.3.3.4.&nbsp;
+forbidden</h3>
+
+<p>The requesting entity does not possess the necessary permissions to perform an action that only certain authorized roles or individuals are allowed to complete (i.e., it typically relates to authorization rather than authentication); the associated error type SHOULD be "auth".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='auth'&gt;
+       &lt;forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<a name="stanzas-error-conditions-gone"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.5"></a><h3>8.3.3.5.&nbsp;
+gone</h3>
+
+<p>The recipient or server can no longer be contacted at this address, typically on a permanent basis (as opposed to the &lt;redirect/&gt; error condition, which is used for temporary addressing failures); the associated error type SHOULD be "cancel" and the error stanza SHOULD include a new address (if available) as the XML character data of the &lt;gone/&gt; element (which MUST be a Uniform Resource Identifier <a class='info' href='#URI'>[URI]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, &ldquo;Uniform Resource Identifier (URI): Generic Syntax,&rdquo; January&nbsp;2005.</span><span>)</span></a> or Internationalized Resource Identifier <a class='info' href='#IRI'>[IRI]<span> (</span><span class='info'>Duerst, M. and M. Suignard, &ldquo;Internationalized Resource Identifiers (IRIs),&rdquo; January&nbsp;2005.</span><span>)</span></a> at which the entity can be contacted, typically an XMPP IRI as specified in <a class='info' href='#XMPP-URI'>[XMPP&#8209;URI]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP),&rdquo; February&nbsp;2008.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message
+       from='juliet@im.example.com/churchyard'
+       id='sj2b371v'
+       to='romeo@example.net'
+       type='chat'&gt;
+     &lt;body&gt;Thy lips are warm.&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;message
+       from='romeo@example.net'
+       id='sj2b371v'
+       to='juliet@im.example.com/churchyard'
+       type='error'&gt;
+     &lt;error by='example.net'
+            type='cancel'&gt;
+       &lt;gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+         xmpp:romeo@afterlife.example.net
+       &lt;/gone&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-internal-server-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.6"></a><h3>8.3.3.6.&nbsp;
+internal-server-error</h3>
+
+<p>The server has experienced a misconfiguration or other
+          internal error that prevents it from processing the stanza;
+          the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;internal-server-error
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<a name="stanzas-error-conditions-item-not-found"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.7"></a><h3>8.3.3.7.&nbsp;
+item-not-found</h3>
+
+<p>The addressed JID or item requested cannot be found; the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence from='userfoo@example.com/bar'
+             id='pwb2n78i'
+             to='nosuchroom@conference.example.org/foo'/&gt;
+
+S: &lt;presence from='nosuchroom@conference.example.org/foo'
+             id='pwb2n78i'
+             to='userfoo@example.com/bar'
+             type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: An application MUST NOT return this error if doing so would provide information about the intended recipient's network availability to an entity that is not authorized to know such information (for a more detailed discussion of presence authorization, refer to the discussion of presence subscriptions in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>); instead it MUST return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>).
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions-jid-malformed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.8"></a><h3>8.3.3.8.&nbsp;
+jid-malformed</h3>
+
+<p>The sending entity has provided (e.g., during resource binding) or communicated (e.g., in the 'to' address of a stanza) an XMPP address or aspect thereof that violates the rules defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>; the associated error type SHOULD be "modify".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='ch@r@cters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='ch@r@cters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error by='muc.example.com'
+            type='modify'&gt;
+       &lt;jid-malformed
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Enforcement of the format for XMPP localparts is primarily the responsibility of the service at which the associated account or entity is located (e.g., the example.com service is responsible for returning &lt;jid-malformed/&gt; errors related to all JIDs of the form &lt;localpart@example.com&gt;), whereas enforcement of the format for XMPP domainparts is primarily the responsibility of the service that seeks to route a stanza to the service identified by that domainpart (e.g., the example.org service is responsible for returning &lt;jid-malformed/&gt; errors related to stanzas that users of that service have to tried send to JIDs of the form &lt;localpart@example.com&gt;).  However, any entity that detects a malformed JID MAY return this error.
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions-not-acceptable"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.9"></a><h3>8.3.3.9.&nbsp;
+not-acceptable</h3>
+
+<p>The recipient or server understands the request but cannot process it because the request does not meet criteria defined by the recipient or server (e.g., a request to subscribe to information that does not simultaneously include configuration parameters needed by the recipient); the associated error type SHOULD be "modify".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message to='juliet@im.example.com' id='yt2vs71m'&gt;
+     &lt;body&gt;[ ... the-emacs-manual ... ]&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;message from='juliet@im.example.com' id='yt2vs71m'&gt;
+     &lt;error type='modify'&gt;
+       &lt;not-acceptable
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-not-allowed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.10"></a><h3>8.3.3.10.&nbsp;
+not-allowed</h3>
+
+<p>The recipient or server does not allow any entity to perform the action (e.g., sending to entities at a blacklisted domain); the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<a name="stanzas-error-conditions-not-authorized"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.11"></a><h3>8.3.3.11.&nbsp;
+not-authorized</h3>
+
+<p>The sender needs to provide credentials before being allowed to perform the action, or has provided improper credentials (the name "not-authorized", which was borrowed from the "401 Unauthorized" error of <a class='info' href='#HTTP'>[HTTP]<span> (</span><span class='info'>Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &ldquo;Hypertext Transfer Protocol -- HTTP/1.1,&rdquo; June&nbsp;1999.</span><span>)</span></a>, might lead the reader to think that this condition relates to authorization, but instead it is typically used in relation to authentication); the associated error type SHOULD be "auth".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'&gt;
+     &lt;error type='auth'&gt;
+       &lt;not-authorized xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<a name="stanzas-error-conditions-policy-violation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.12"></a><h3>8.3.3.12.&nbsp;
+policy-violation</h3>
+
+<p>The entity has violated some local service policy (e.g., a message contains words that are prohibited by the service) and the server MAY choose to specify the policy in the &lt;text/&gt; element or in an application-specific condition element; the associated error type SHOULD be "modify" or "wait" depending on the policy being violated.
+</p>
+<p>(In the following example, the client sends an XMPP message containing words that are forbidden according to the server's local service policy.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message from='romeo@example.net/foo'
+            to='bill@im.example.com'
+            id='vq71f4nb'&gt;
+     &lt;body&gt;%#&amp;@^!!!&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;message from='bill@im.example.com'
+            id='vq71f4nb'
+            to='romeo@example.net/foo'&gt;
+     &lt;error by='example.net' type='modify'&gt;
+       &lt;policy-violation
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-recipient-unavailable"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.13"></a><h3>8.3.3.13.&nbsp;
+recipient-unavailable</h3>
+
+<p>The intended recipient is temporarily unavailable, undergoing maintenance, etc.; the associated error type SHOULD be "wait".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'&gt;
+     &lt;error type='wait'&gt;
+       &lt;recipient-unavailable
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: An application MUST NOT return this error if doing so would provide information about the intended recipient's network availability to an entity that is not authorized to know such information (for a more detailed discussion of presence authorization, refer to the discussion of presence subscriptions in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>); instead it MUST return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>).
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions-redirect"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.14"></a><h3>8.3.3.14.&nbsp;
+redirect</h3>
+
+<p>The recipient or server is redirecting requests for this information to another entity, typically in a temporary fashion (as opposed to the &lt;gone/&gt; error condition, which is used for permanent addressing failures); the associated error type SHOULD be "modify" and the error stanza SHOULD contain the alternate address in the XML character data of the &lt;redirect/&gt; element (which MUST be a URI or IRI with which the sender can communicate, typically an XMPP IRI as specified in <a class='info' href='#XMPP-URI'>[XMPP&#8209;URI]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP),&rdquo; February&nbsp;2008.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;redirect xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+         xmpp:characters@conference.example.org
+       &lt;/redirect&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: An application receiving a stanza-level redirect SHOULD warn a human user of the redirection attempt and request approval before proceeding to communicate with the entity whose address is contained in the XML character data of the &lt;redirect/&gt; element, because that entity might have a different identity or might enforce different security policies.  The end-to-end authentication or signing of XMPP stanzas could help to mitigate this risk, since it would enable the sender to determine if the entity to which it has been redirected has the same identity as the entity it originally attempted to contact.  An application MAY have a policy of following redirects only if it has authenticated the receiving entity.  In addition, an application SHOULD abort the communication attempt after a certain number of successive redirects (e.g., at least 2 but no more than 5).
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions-registration-required"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.15"></a><h3>8.3.3.15.&nbsp;
+registration-required</h3>
+
+<p>The requesting entity is not authorized to access the requested service because prior registration is necessary (examples of prior registration include members-only rooms in XMPP multi-user chat <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2007.</span><span>)</span></a> and gateways to non-XMPP instant messaging services, which traditionally required registration in order to use the gateway <a class='info' href='#XEP-0100'>[XEP&#8209;0100]<span> (</span><span class='info'>Saint-Andre, P. and D. Smith, &ldquo;Gateway Interaction,&rdquo; October&nbsp;2005.</span><span>)</span></a>); the associated error type SHOULD be "auth".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;presence
+       from='juliet@im.example.com/balcony'
+       id='y2bs71v4'
+       to='characters@muc.example.com/JulieC'&gt;
+     &lt;x xmlns='http://jabber.org/protocol/muc'/&gt;
+   &lt;/presence&gt;
+
+E: &lt;presence
+       from='characters@muc.example.com/JulieC'
+       id='y2bs71v4'
+       to='juliet@im.example.com/balcony'&gt;
+     &lt;error type='auth'&gt;
+       &lt;registration-required
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/presence&gt;
+</pre></div>
+<a name="stanzas-error-conditions-remote-server-not-found"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.16"></a><h3>8.3.3.16.&nbsp;
+remote-server-not-found</h3>
+
+<p>A remote server or service specified as part or all of the JID of the intended recipient does not exist or cannot be resolved (e.g., there is no _xmpp-server._tcp DNS SRV record, the A or AAAA fallback resolution fails, or A/AAAA lookups succeed but there is no response on the IANA-registered port 5269); the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message
+       from='romeo@example.net/home'
+       id='ud7n1f4h'
+       to='bar@example.org'
+       type='chat'&gt;
+    &lt;body&gt;yt?&lt;/body&gt;
+   &lt;/message&gt;
+
+E: &lt;message
+       from='bar@example.org'
+       id='ud7n1f4h'
+       to='romeo@example.net/home'
+       type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;remote-server-not-found
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-remote-server-timeout"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.17"></a><h3>8.3.3.17.&nbsp;
+remote-server-timeout</h3>
+
+<p>A remote server or service specified as part or all of the JID of the intended recipient (or needed to fulfill a request) was resolved but communications could not be established within a reasonable amount of time (e.g., an XML stream cannot be established at the resolved IP address and port, or an XML stream can be established but stream negotiation fails because of problems with TLS, SASL, Server Dialback, etc.); the associated error type SHOULD be "wait" (unless the error is of a more permanent nature, e.g., the remote server is found but it cannot be authenticated or it violates security policies).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message
+       from='romeo@example.net/home'
+       id='ud7n1f4h'
+       to='bar@example.org'
+       type='chat'&gt;
+    &lt;body&gt;yt?&lt;/body&gt;
+   &lt;/message&gt;
+
+E: &lt;message
+       from='bar@example.org'
+       id='ud7n1f4h'
+       to='romeo@example.net/home'
+       type='error'&gt;
+     &lt;error type='wait'&gt;
+       &lt;remote-server-timeout
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-resource-constraint"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.18"></a><h3>8.3.3.18.&nbsp;
+resource-constraint</h3>
+
+<p>The server or recipient is busy or lacks the system resources necessary to service the request; the associated error type SHOULD be "wait".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='romeo@example.net/foo'
+       id='kj4vz31m'
+       to='pubsub.example.com'
+       type='get'&gt;
+     &lt;pubsub xmlns='http://jabber.org/protocol/pubsub'&gt;
+       &lt;items node='my_musings'/&gt;
+     &lt;/pubsub&gt;
+   &lt;/iq&gt;
+
+E: &lt;iq from='pubsub.example.com'
+       id='kj4vz31m'
+       to='romeo@example.net/foo'
+       type='error'&gt;
+     &lt;error type='wait'&gt;
+       &lt;resource-constraint
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="stanzas-error-conditions-service-unavailable"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.19"></a><h3>8.3.3.19.&nbsp;
+service-unavailable</h3>
+
+<p>The server or recipient does not currently provide the requested service; the associated error type SHOULD be "cancel".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message from='romeo@example.net/foo'
+            to='juliet@im.example.com'&gt;
+     &lt;body&gt;Hello?&lt;/body&gt;
+   &lt;/message&gt;
+
+S: &lt;message from='juliet@im.example.com/foo'
+            to='romeo@example.net'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;service-unavailable
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: An application MUST return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>) instead of &lt;item-not-found/&gt; (<a class='info' href='#stanzas-error-conditions-item-not-found'>Section&nbsp;8.3.3.7<span> (</span><span class='info'>item-not-found</span><span>)</span></a>) or &lt;recipient-unavailable/&gt; (<a class='info' href='#stanzas-error-conditions-recipient-unavailable'>Section&nbsp;8.3.3.13<span> (</span><span class='info'>recipient-unavailable</span><span>)</span></a>) if sending one of the latter errors would provide information about the intended recipient's network availability to an entity that is not authorized to know such information (for a more detailed discussion of presence authorization, refer to <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p>
+</blockquote>
+
+<a name="stanzas-error-conditions-subscription-required"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.20"></a><h3>8.3.3.20.&nbsp;
+subscription-required</h3>
+
+<p>The requesting entity is not authorized to access the requested service because a prior subscription is necessary (examples of prior subscription include authorization to receive presence information as defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a> and opt-in data feeds for XMPP publish-subscribe as defined in <a class='info' href='#XEP-0060'>[XEP&#8209;0060]<span> (</span><span class='info'>Millard, P., Saint-Andre, P., and R. Meijer, &ldquo;Publish-Subscribe,&rdquo; July&nbsp;2010.</span><span>)</span></a>); the associated error type SHOULD be "auth".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message
+       from='romeo@example.net/orchard'
+       id='pa73b4n7'
+       to='playwright@shakespeare.example.com'
+       type='chat'&gt;
+     &lt;subject&gt;ACT II, SCENE II&lt;/subject&gt;
+     &lt;body&gt;help, I forgot my lines!&lt;/body&gt;
+   &lt;/message&gt;
+
+E: &lt;message
+       from='playwright@shakespeare.example.com'
+       id='pa73b4n7'
+       to='romeo@example.net/orchard'
+       type='error'&gt;
+     &lt;error type='auth'&gt;
+       &lt;subscription-required
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-undefined-condition"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.21"></a><h3>8.3.3.21.&nbsp;
+undefined-condition</h3>
+
+<p>The error condition is not one of those defined by the
+          other conditions in this list; any error type can be
+          associated with this condition, and it SHOULD NOT be used except in conjunction with an application-specific condition.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message
+       from='northumberland@shakespeare.example'
+       id='richard2-4.1.247'
+       to='kingrichard@royalty.england.example'&gt;
+     &lt;body&gt;My lord, dispatch; read o'er these articles.&lt;/body&gt;
+     &lt;amp xmlns='http://jabber.org/protocol/amp'&gt;
+       &lt;rule action='notify'
+             condition='deliver'
+             value='stored'/&gt;
+     &lt;/amp&gt;
+   &lt;/message&gt;
+
+S: &lt;message from='example.org'
+            id='amp1'
+            to='northumberland@example.net/field'
+            type='error'&gt;
+     &lt;amp xmlns='http://jabber.org/protocol/amp'
+          from='kingrichard@example.org'
+          status='error'
+          to='northumberland@example.net/field'&gt;
+       &lt;rule action='error'
+             condition='deliver'
+             value='stored'/&gt;
+     &lt;/amp&gt;
+     &lt;error type='modify'&gt;
+       &lt;undefined-condition
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+       &lt;failed-rules xmlns='http://jabber.org/protocol/amp#errors'&gt;
+         &lt;rule action='error'
+               condition='deliver'
+               value='stored'/&gt;
+       &lt;/failed-rules&gt;
+     &lt;/error&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="stanzas-error-conditions-unexpected-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.3.22"></a><h3>8.3.3.22.&nbsp;
+unexpected-request</h3>
+
+<p>The recipient or server understood the request but was not expecting it at this time (e.g., the request was out of order); the associated error type SHOULD be "wait" or "modify".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='romeo@example.net/foo'
+       id='o6hsv25z'
+       to='pubsub.example.com'
+       type='set'&gt;
+     &lt;pubsub xmlns='http://jabber.org/protocol/pubsub'&gt;
+        &lt;unsubscribe
+            node='my_musings'
+            jid='romeo@example.net'/&gt;
+     &lt;/pubsub&gt;
+   &lt;/iq&gt;
+
+E: &lt;iq from='pubsub.example.com'
+       id='o6hsv25z'
+       to='romeo@example.net/foo'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;unexpected-request
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+       &lt;not-subscribed
+           xmlns='http://jabber.org/protocol/pubsub#errors'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="stanzas-error-app"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3.4"></a><h3>8.3.4.&nbsp;
+Application-Specific Conditions</h3>
+
+<p>As noted, an application MAY provide application-specific stanza error information by including a properly namespaced child within the error element.  Typically, the application-specific element supplements or further qualifies a defined element.  Thus, the &lt;error/&gt; element will contain two or three child elements.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;iq id='ixc3v1b9' type='error'&gt;
+  &lt;error type='modify'&gt;
+    &lt;bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    &lt;too-many-parameters xmlns='http://example.org/ns'/&gt;
+  &lt;/error&gt;
+&lt;/iq&gt;
+</pre></div><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message type='error' id='7h3baci9'&gt;
+  &lt;error type='modify'&gt;
+    &lt;undefined-condition
+          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    &lt;text xml:lang='en'
+          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+      [ ... application-specific information ... ]
+    &lt;/text&gt;
+    &lt;too-many-parameters xmlns='http://example.org/ns'/&gt;
+  &lt;/error&gt;
+&lt;/message&gt;
+</pre></div>
+<p>An entity that receives an application-specific error condition it does not understand MUST ignore that condition but appropriately process the rest of the error stanza.
+</p>
+<a name="stanzas-extended"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.4"></a><h3>8.4.&nbsp;
+Extended Content</h3>
+
+<p>Although the message, presence, and IQ stanzas provide basic semantics for messaging, availability, and request-response interactions, XMPP uses XML namespaces (see <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>) to extend the basic stanza syntax for the purpose of providing additional functionality.
+</p>
+<p>A message or presence stanza MAY contain one or more optional child elements specifying content that extends the meaning of the message (e.g., an XHTML-formatted version of the message body as described in <a class='info' href='#XEP-0071'>[XEP&#8209;0071]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XHTML-IM,&rdquo; September&nbsp;2008.</span><span>)</span></a>), and an IQ stanza of type "get" or "set" MUST contain one such child element.  Such a child element MAY have any name and MUST possess a namespace declaration (other than "jabber:client", "jabber:server", or "http://etherx.jabber.org/streams") that defines the data contained within the child element.  Such a child element is called an "extension element".  An extension element can be included either at the direct child level of the stanza or in any mix of levels.
+</p>
+<p>Similarly, "extension attributes" are allowed.  That is: a stanza itself (i.e., an &lt;iq/&gt;, &lt;message/&gt;, or &lt;presence/&gt; element qualified by the "jabber:client" or "jabber:server" content namespace) or any child element of such a stanza (whether an extension element or a child element qualified by the content namespace) MAY also include one or more attributes qualified by XML namespaces other than the content namespace or the reserved "http://www.w3.org/XML/1998/namespace" namespace (including the so-called "empty namespace" if the attribute is not prefixed as described under <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: For the sake of backward compatibility and maximum interoperability, an entity that generates a stanza SHOULD NOT include such attributes in the stanza itself or in child elements of the stanza that are qualified by the content namespaces "jabber:client" or "jabber:server" (e.g., the &lt;body/&gt; child of the &lt;message/&gt; stanza).
+</p>
+</blockquote>
+
+<p>An extension element or extension attribute is said to be "extended content" and the qualifying namespace for such an element or attribute is said to be an "extended namespace".
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: Although extended namespaces for XMPP are commonly defined by the XMPP Standards Foundation (XSF) and by the IETF, no specification or IETF standards action is necessary to define extended namespaces, and any individual or organization is free to define XMPP extensions.
+</p>
+</blockquote>
+
+<p>To illustrate these concepts, several examples follow.
+</p>
+<p>The following stanza contains one direct child element whose extended namespace is 'jabber:iq:roster':
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;iq from='juliet@capulet.com/balcony'
+    id='h83vxa4c'
+    type='get'&gt;
+ &lt;query xmlns='jabber:iq:roster'/&gt;
+&lt;/iq&gt;
+</pre></div>
+<p>The following stanza contains two direct child elements with two different extended namespaces.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='juliet@capulet.com/balcony'&gt;
+  &lt;c xmlns='http://jabber.org/protocol/caps'
+     hash='sha-1'
+     node='http://code.google.com/p/exodus'
+     ver='QgayPKawpkPSDYmwT/WM94uAlu0='/&gt;
+  &lt;x xmlns='vcard-temp:x:update'&gt;
+    &lt;photo&gt;sha1-hash-of-image&lt;/photo&gt;
+  &lt;/x&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>The following stanza contains two child elements, one of which is qualified by the "jabber:client" or "jabber:server" content namespace and one of which is qualified by an extended namespace; the extension element in turn contains a child element that is qualified by a different extended namespace.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message to='juliet@capulet.com'&gt;
+  &lt;body&gt;Hello?&lt;/body&gt;
+  &lt;html xmlns='http://jabber.org/protocol/xhtml-im'&gt;
+    &lt;body xmlns='http://www.w3.org/1999/xhtml'&gt;
+      &lt;p style='font-weight:bold'&gt;Hello?&lt;/p&gt;
+    &lt;/body&gt;
+  &lt;/html&gt;
+&lt;/message&gt;
+</pre></div>
+<p>It is conventional in the XMPP community for implementations to not generate namespace prefixes for elements that are qualified by extended namespaces (in the XML community, this convention is sometimes called "prefix-free canonicalization").  However, if an implementation generates such namespace prefixes then it MUST include the namespace declaration in the stanza itself or a child element of the stanza, not in the stream header (see <a class='info' href='#streams-ns-other'>Section&nbsp;4.8.4<span> (</span><span class='info'>Other Namespaces</span><span>)</span></a>).
+</p>
+<p>Routing entities (typically servers) SHOULD try to maintain prefixes when serializing XML stanzas for processing, but receiving entities MUST NOT depend on the prefix strings to have any particular value (the allowance for the 'stream' prefix, described under <a class='info' href='#streams-ns-declarations'>Section&nbsp;4.8.5<span> (</span><span class='info'>Namespace Declarations and Prefixes</span><span>)</span></a>, is an exception to this rule, albeit for streams rather than stanzas).
+</p>
+<p>Support for any given extended namespace is OPTIONAL on the part of any implementation.  If an entity does not understand such a namespace, the entity's expected behavior depends on whether the entity is (1) the recipient or (2) a server that is routing or delivering the stanza to the recipient.
+</p>
+<p>If a recipient receives a stanza that contains an element or attribute it does not understand, it MUST NOT attempt to process that XML data and instead MUST proceed as follows.
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>If an intended recipient receives a message stanza whose only child element is qualified by a namespace it does not understand, then depending on the XMPP application it MUST either ignore the entire stanza or return a stanza error, which SHOULD be &lt;service-unavailable/&gt; (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>).
+</li>
+<li>If an intended recipient receives a presence stanza whose only child element is qualified by a namespace it does not understand, then it MUST ignore the child element by treating the presence stanza as if it contained no child element.
+</li>
+<li>If an intended recipient receives a message or presence stanza that contains XML data qualified by a namespace it does not understand, then it MUST ignore the portion of the stanza qualified by the unknown namespace.
+</li>
+<li>If an intended recipient receives an IQ stanza of type "get" or "set" containing a child element qualified by a namespace it does not understand, then the entity MUST return an IQ stanza of type "error" with an error condition of &lt;service-unavailable/&gt;.
+</li>
+</ul><p>
+      
+</p>
+<p>If a server handles a stanza that is intended for delivery to another entity and that contains a child element it does not understand, it MUST route the stanza unmodified to a remote server or deliver the stanza unmodified to a connected client associated with a local account.
+</p>
+<a name="examples"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9"></a><h3>9.&nbsp;
+Detailed Examples</h3>
+
+<p>The detailed examples in this section further illustrate the protocols defined in this specification.
+</p>
+<a name="examples-c2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1"></a><h3>9.1.&nbsp;
+Client-to-Server Examples</h3>
+
+<p>The following examples show the XMPP data flow for a client
+negotiating an XML stream with a server, exchanging XML stanzas, and closing
+the negotiated stream.  The server is "im.example.com", the server requires use
+of TLS, the client authenticates via the SASL SCRAM-SHA-1 mechanism as
+&lt;juliet@im.example.com&gt; with a password of
+  "r0m30myr0m30", and the client binds a client-submitted resource to the stream.  It is assumed that before sending the initial stream header, the client has already resolved an SRV record of _xmpp&#8209;client._tcp.im.example.com and has opened a TCP connection to the advertised port at the resolved IP address.
+</p>
+<a name="examples-c2s-tls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1.1"></a><h3>9.1.1.&nbsp;
+TLS</h3>
+
+<p>Step 1: Client initiates stream to server:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 2: Server responds by sending a response stream header to client:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:stream
+     from='im.example.com'
+     id='t7AMCin9zjMNwQKDnplntZPIDEI='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 3: Server sends stream features to client (only the STARTTLS extension at this point, which is mandatory-to-negotiate):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:features&gt;
+     &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'&gt;
+       &lt;required/&gt;
+     &lt;/starttls&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>Step 4: Client sends STARTTLS command to server:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>Step 5: Server informs client that it is allowed to proceed:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>Step 5 (alt): Server informs client that STARTTLS negotiation has failed, closes the XML stream, and terminates the TCP connection (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+   &lt;/stream:stream&gt;
+</pre></div>
+<p>Step 6: Client and server attempt to complete TLS negotiation over the existing TCP connection (see <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a> for details).
+</p>
+<p>Step 7: If TLS negotiation is successful, client initiates a new stream to server over the TLS-protected TCP connection:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 7 (alt): If TLS negotiation is unsuccessful, server closes TCP connection (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p>
+<a name="examples-c2s-sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1.2"></a><h3>9.1.2.&nbsp;
+SASL</h3>
+
+<p>Step 8: Server responds by sending a stream header to client along with any available stream features:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:stream
+     from='im.example.com'
+     id='vgKi/bkYME8OAj4rlXMkpucAqe4='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;stream:features&gt;
+     &lt;mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1-PLUS&lt;/mechanism&gt;
+       &lt;mechanism&gt;SCRAM-SHA-1&lt;/mechanism&gt;
+       &lt;mechanism&gt;PLAIN&lt;/mechanism&gt;
+     &lt;/mechanisms&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>Step 9: Client selects an authentication mechanism
+          (in this case, SCRAM-SHA-1), including initial response data:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;auth xmlns="urn:ietf:params:xml:ns:xmpp-sasl"
+         mechanism="SCRAM-SHA-1"&gt;
+     biwsbj1qdWxpZXQscj1vTXNUQUF3QUFBQU1BQUFBTlAwVEFBQUFBQUJQVTBBQQ==
+   &lt;/auth&gt;
+</pre></div>
+<p>The decoded base 64 data is "n,,n=juliet,r=oMsTAAwAAAAMAAAANP0TAAAAAABPU0AA".
+</p>
+<p>Step 10: Server sends a challenge:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;challenge xmlns="urn:ietf:params:xml:ns:xmpp-sasl"&gt;
+     cj1vTXNUQUF3QUFBQU1BQUFBTlAwVEFBQUFBQUJQVTBBQWUxMjQ2OTViLTY5Y
+     TktNGRlNi05YzMwLWI1MWIzODA4YzU5ZSxzPU5qaGtZVE0wTURndE5HWTBaaT
+     AwTmpkbUxUa3hNbVV0TkRsbU5UTm1ORE5rTURNeixpPTQwOTY=
+   &lt;/challenge&gt;
+</pre></div>
+<p>The decoded base 64 data is "r=oMsTAAwAAAAMAAAANP0TAAAAAABPU0AAe124695b-69a9-4de6-9c30-b51b3808c59e,s=NjhkYTM0MDgtNGY0Zi00NjdmLTkxMmUtNDlmNTNmNDNkMDMz,i=4096" (line breaks not included in actual data).
+</p>
+<p>Step 11: Client sends a response:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;response xmlns="urn:ietf:params:xml:ns:xmpp-sasl"&gt;
+     Yz1iaXdzLHI9b01zVEFBd0FBQUFNQUFBQU5QMFRBQUFBQUFCUFUwQUFlMTI0N
+     jk1Yi02OWE5LTRkZTYtOWMzMC1iNTFiMzgwOGM1OWUscD1VQTU3dE0vU3ZwQV
+     RCa0gyRlhzMFdEWHZKWXc9
+   &lt;/response&gt;
+</pre></div>
+<p>
+  The decoded base 64 data is "c=biws,r=oMsTAAwAAAAMAAAANP0TAAAAAABPU0
+  AAe124695b-69a9-4de6-9c30-b51b3808c59e,p=UA57tM/
+  SvpATBkH2FXs0WDXvJYw=" (line breaks not included in actual data).
+
+</p>
+<p>Step 12: Server informs client of success, including additional data with success:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     dj1wTk5ERlZFUXh1WHhDb1NFaVc4R0VaKzFSU289
+   &lt;/success&gt;
+</pre></div>
+<p>The decoded base 64 data is "v=pNNDFVEQxuXxCoSEiW8GEZ+1RSo=".
+</p>
+<p>Step 12 (alt): Server returns a SASL error to client (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+     &lt;not-authorized/&gt;
+   &lt;/failure&gt;
+   &lt;/stream&gt;
+</pre></div>
+<p>Step 13: Client initiates a new stream to server:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;stream:stream
+     from='juliet@im.example.com'
+     to='im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<a name="examples-c2s-bind"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1.3"></a><h3>9.1.3.&nbsp;
+Resource Binding</h3>
+
+<p>Step 14: Server responds by sending a stream header to client along with supported features (in this case, resource binding):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;stream:stream
+     from='im.example.com'
+     id='gPybzaOzBmaADgxKXu9UClbprp0='
+     to='juliet@im.example.com'
+     version='1.0'
+     xml:lang='en'
+     xmlns='jabber:client'
+     xmlns:stream='http://etherx.jabber.org/streams'&gt;
+
+S: &lt;stream:features&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/&gt;
+   &lt;/stream:features&gt;
+</pre></div>
+<p>Upon being informed that resource binding is mandatory-to-negotiate, the client needs to bind a resource to the stream; here we assume that the client submits a human-readable text string.
+</p>
+<p>Step 15: Client binds a resource:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq id='yhc13a95' type='set'&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+       &lt;resource&gt;balcony&lt;/resource&gt;
+     &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Step 16: Server accepts submitted resourcepart and informs client of successful resource binding:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='yhc13a95' type='result'&gt;
+     &lt;bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'&gt;
+       &lt;jid&gt;
+         juliet@im.example.com/balcony
+       &lt;/jid&gt;
+     &lt;/bind&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Step 16 (alt): Server returns error to client (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='yhc13a95' type='error'&gt;
+     &lt;error type='cancel'&gt;
+       &lt;conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="examples-c2s-stanzas"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1.4"></a><h3>9.1.4.&nbsp;
+Stanza Exchange</h3>
+
+<p>Now the client is allowed to send XML stanzas over the negotiated stream.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;message from='juliet@im.example.com/balcony'
+            id='ju2ba41c'
+            to='romeo@example.net'
+            type='chat'
+            xml:lang='en'&gt;
+     &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+   &lt;/message&gt;
+</pre></div>
+<p>If necessary, sender's server negotiates XML streams with intended recipient's server (see <a class='info' href='#examples-s2s'>Section&nbsp;9.2<span> (</span><span class='info'>Server-to-Server Examples</span><span>)</span></a>).
+</p>
+<p>The intended recipient replies, and the message is delivered to the client.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+E: &lt;message from='romeo@example.net/orchard'
+            id='ju2ba41c'
+            to='juliet@im.example.com/balcony'
+            type='chat'
+            xml:lang='en'&gt;
+     &lt;body&gt;Neither, fair saint, if either thee dislike.&lt;/body&gt;
+   &lt;/message&gt;
+</pre></div>
+<p>The client can subsequently send and receive an unbounded number of subsequent XML stanzas over the stream.
+</p>
+<a name="examples-c2s-close"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.1.5"></a><h3>9.1.5.&nbsp;
+Close</h3>
+
+<p>Desiring to send no further messages, the client closes its stream to the server but waits for incoming data from the server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;/stream:stream&gt;
+</pre></div>
+<p>Consistent with <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>, the server might send additional data to the client and then closes its stream to the client.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;/stream:stream&gt;
+</pre></div>
+<p>The client now sends a TLS close_notify alert, receives a responding close_notify alert from the server, and then terminates the underlying TCP connection.
+</p>
+<a name="examples-s2s"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.2"></a><h3>9.2.&nbsp;
+Server-to-Server Examples</h3>
+
+<p>The following examples show the data flow for a server negotiating an XML stream with a peer server, exchanging XML stanzas, and closing the negotiated stream.  The initiating server ("Server1") is im.example.com; the receiving server ("Server2") is example.net and it requires use of TLS; im.example.com presents a certificate and authenticates via the SASL EXTERNAL mechanism.  It is assumed that before sending the initial stream header, Server1 has already resolved an SRV record of _xmpp-server._tcp.example.net and has opened a TCP connection to the advertised port at the resolved IP address.  Note how Server1 declares the content namespace "jabber:server" as the default namespace and uses prefixes for stream-related elements, whereas Server2 uses prefix-free canonicalization.
+</p>
+<a name="examples-s2s-tls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.2.1"></a><h3>9.2.1.&nbsp;
+TLS</h3>
+
+<p>Step 1: Server1 initiates stream to Server2:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;stream:stream
+      from='im.example.com'
+      to='example.net'
+      version='1.0'
+      xmlns='jabber:server'
+      xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 2: Server2 responds by sending a response stream header to Server1:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;stream
+      from='example.net'
+      id='hTiXkW+ih9k2SqdGkk/AZi0OJ/Q='
+      to='im.example.com'
+      version='1.0'
+      xmlns='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 3: Server2 sends stream features to Server1 (only the STARTTLS extension at this point, which is mandatory-to-negotiate):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;features xmlns='http://etherx.jabber.org/streams'&gt;
+      &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'&gt;
+        &lt;required/&gt;
+      &lt;/starttls&gt;
+    &lt;/features&gt;
+</pre></div>
+<p>Step 4: Server1 sends the STARTTLS command to Server2:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>Step 5: Server2 informs Server1 that it is allowed to proceed:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+</pre></div>
+<p>Step 5 (alt): Server2 informs Server1 that STARTTLS negotiation has failed, closes the stream, and terminates the TCP connection (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+    &lt;/stream&gt;
+</pre></div>
+<p>Step 6: Server1 and Server2 attempt to complete TLS negotiation via TCP (see <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a> for details).
+</p>
+<p>Step 7: If TLS negotiation is successful, Server1 initiates a new stream to Server2 over the TLS-protected TCP connection:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;stream:stream
+      from='im.example.com'
+      to='example.net'
+      version='1.0'
+      xmlns='jabber:server'
+      xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 7 (alt): If TLS negotiation is unsuccessful, Server2
+        closes the TCP connection (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step).
+</p>
+<a name="examples-s2s-sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.2.2"></a><h3>9.2.2.&nbsp;
+SASL</h3>
+
+<p>Step 8: Server2 sends a response stream header to Server1 along with available stream features (including a preference for the SASL EXTERNAL mechanism):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;stream
+      from='example.net'
+      id='RChdjlgj/TIBcbT9Keu31zDihH4='
+      to='im.example.com'
+      version='1.0'
+      xmlns='http://etherx.jabber.org/streams'&gt;
+
+S2: &lt;features xmlns='http://etherx.jabber.org/streams'&gt;
+      &lt;mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+        &lt;mechanism&gt;EXTERNAL&lt;/mechanism&gt;
+      &lt;/mechanisms&gt;
+    &lt;/features&gt;
+</pre></div>
+<p>Step 9: Server1 selects the EXTERNAL mechanism (including an empty response of "="):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+          mechanism='EXTERNAL'&gt;=&lt;/auth&gt;
+</pre></div>
+<p>Step 10: Server2 returns success:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/&gt;
+</pre></div>
+<p>Step 10 (alt): Server2 informs Server1 of failed authentication (thus, the stream negotiation process ends unsuccessfully and the parties do not move on to the next step):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'&gt;
+      &lt;not-authorized/&gt;
+    &lt;/failure&gt;
+    &lt;/stream&gt;
+</pre></div>
+<p>Step 11: Server1 initiates a new stream to Server2:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;stream:stream
+      from='im.example.com'
+      to='example.net'
+      version='1.0'
+      xmlns='jabber:server'
+      xmlns:stream='http://etherx.jabber.org/streams'&gt;
+</pre></div>
+<p>Step 12: Server2 responds by sending a stream header to Server1 along with any additional features (or, in this case, an empty features element):
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;stream
+      from='example.net'
+      id='MbbV2FeojySpUIP6J91qaa+TWHM='
+      to='im.example.com'
+      version='1.0'
+      xmlns='http://etherx.jabber.org/streams'&gt;
+
+S2: &lt;features xmlns='http://etherx.jabber.org/streams'/&gt;
+</pre></div>
+<a name="examples-s2s-stanzas"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.2.3"></a><h3>9.2.3.&nbsp;
+Stanza Exchange</h3>
+
+<p>Now Server1 is allowed to send XML stanzas to Server2 over the negotiated stream from im.example.com to example.net; here we assume that the transferred stanzas are those shown earlier for client-to-server communication, albeit over a server-to-server stream qualified by the 'jabber:server' namespace.
+</p>
+<p>Server1 sends XML stanza to Server2:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;message from='juliet@im.example.com/balcony'
+             id='ju2ba41c'
+             to='romeo@example.net'
+             type='chat'
+             xml:lang='en'&gt;
+    &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+   &lt;/message&gt;
+</pre></div>
+<a name="examples-s2s-close"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9.2.4"></a><h3>9.2.4.&nbsp;
+Close</h3>
+
+<p>Desiring to send no further messages, Server1 closes its stream to Server2 but waits for incoming data from Server2.  (In practice, the stream would most likely remain open for some time, since Server1 and Server2 do not immediately know if the stream will be needed for further communication.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S1: &lt;/stream:stream&gt;
+</pre></div>
+<p>Consistent with the recommended stream closing handshake, Server2 closes the stream as well:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S2: &lt;/stream&gt;
+</pre></div>
+<p>Server1 now sends a TLS close_notify alert, receives a responding close_notify alert from Server2, and then terminates the underlying TCP connection.
+</p>
+<a name="rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10"></a><h3>10.&nbsp;
+Server Rules for Processing XML Stanzas</h3>
+
+<p>Each server implementation will contain its own logic for processing stanzas it receives.  Such logic determines whether the server needs to route a given stanza to another domain, deliver it to a local entity (typically a connected client associated with a local account), or handle it directly within the server itself.  This section provides general rules for processing XML stanzas.  However, particular XMPP applications MAY specify delivery rules that modify or supplement the following rules (e.g., a set of delivery rules for instant messaging and presence applications is defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p>
+<a name="rules-order"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.1"></a><h3>10.1.&nbsp;
+In-Order Processing</h3>
+
+<p>An XMPP server MUST ensure in-order processing of the stanzas and other XML elements it receives over a given input stream from a connected client or remote server.
+</p>
+<p>In-order processing applies (a) to any XML elements used to negotiate and manage XML streams, and (b) to all uses of XML stanzas, including but not limited to the following:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Stanzas sent by a client to its server or to its own bare JID for direct processing by the server (e.g., in-order processing of a roster get and initial presence as described in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>Stanzas sent by a connected client and intended for delivery to another entity associated with the server (e.g., stanzas addressed from &lt;juliet@im.example.com&gt; to &lt;nurse@im.example.com&gt;).  The server MUST ensure that it delivers stanzas addressed to the intended recipient in the order it receives them over the input stream from the sending client, treating stanzas addressed to the bare JID and the full JID of the intended recipient as equivalent for delivery purposes.
+</li>
+<li>Stanzas sent by a connected client and intended for delivery to an entity located at a remote domain (e.g., stanzas addressed from &lt;juliet@im.example.com&gt; to &lt;romeo@example.net&gt;).  The routing server MUST ensure that it routes stanzas addressed to the intended recipient in the order it receives them over the input stream from the sending client, treating stanzas addressed to the bare JID and the full JID of the intended recipient as equivalent for routing purposes.  To help ensure in-order processing, the routing server MUST route such stanzas over a single output stream to the remote domain, rather than sending some stanzas over one server-to-server stream and other stanzas over another server-to-server stream.
+</li>
+<li>Stanzas routed from one server to another server for delivery to an entity associated with the remote domain (e.g., stanzas addressed from &lt;juliet@im.example.com&gt; to &lt;romeo@example.net&gt; and routed by &lt;im.example.com&gt; over a server-to-server stream to &lt;example.net&gt;).  The delivering server MUST ensure that it delivers stanzas to the intended recipient in the order it receives them over the input stream from the routing server, treating stanzas addressed to the bare JID and the full JID of the intended recipient as equivalent for delivery purposes.
+</li>
+<li>Stanzas sent by one server to another server for direct processing by the server that is hosting the remote domain (e.g., stanzas addressed from &lt;im.example.com&gt; to &lt;example.net&gt;).
+</li>
+</ol><p>
+      
+</p>
+<p>If the server's processing of a particular request could have an effect on its processing of subsequent data it might receive over that input stream (e.g., enforcement of communication policies), it MUST suspend processing of subsequent data until it has processed the request.
+</p>
+<p>In-order processing applies only to a single input stream.  Therefore, a server is not responsible for ensuring the coherence of data it receives across multiple input streams associated with the same local account (e.g., stanzas received over two different input streams from &lt;juliet@im.example.com/balcony&gt; and &lt;juliet@im.example.com/chamber&gt;) or the same remote domain (e.g., two different input streams negotiated by a remote domain; however, a server MAY close the stream with a &lt;conflict/&gt; stream error (<a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>) if a remote server attempts to negotiate more than one stream, as described under <a class='info' href='#streams-error-conditions-conflict'>Section&nbsp;4.9.3.3<span> (</span><span class='info'>conflict</span><span>)</span></a>).
+</p>
+<a name="rules-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.2"></a><h3>10.2.&nbsp;
+General Considerations</h3>
+
+<p>At high level, there are three primary considerations at play in server processing of XML stanzas, which sometimes are at odds but need to be managed in a consistent way:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>It is good to deliver a stanza to the intended recipient if possible.
+</li>
+<li>If a stanza cannot be delivered, it is helpful to inform the sender.
+</li>
+<li>It is bad to facilitate directory harvesting attacks (<a class='info' href='#security-harvesting'>Section&nbsp;13.11<span> (</span><span class='info'>Directory Harvesting</span><span>)</span></a>) and presence leaks (<a class='info' href='#security-leaks-presence'>Section&nbsp;13.10.2<span> (</span><span class='info'>Presence Information</span><span>)</span></a>).
+</li>
+</ol><p>
+      
+</p>
+<p>With regard to possible delivery-related attacks, the following points need to be kept in mind:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>From the perspective of an attacker, there is little if any effective difference between the server's (i) delivering the stanza or storing it offline for later delivery (see <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>) and (ii) silently ignoring it (because an error is not returned immediately in any of those cases); therefore, in scenarios where a server delivers a stanza or places the stanza into offline storage for later delivery, it needs to silently ignore the stanza if that account does not exist.
+</li>
+<li>How a server processes stanzas sent to the bare JID &lt;localpart@domainpart&gt; has implications for directory harvesting, because an attacker could determine whether an account exists if the server responds differently depending on whether there is an account for a given bare JID.
+</li>
+<li>How a server processes stanzas sent to a full JID has implications for presence leaks, because an attacker could send requests to multiple full JIDs and receive different replies depending on whether the user has a device currently online at that full JID.  The use of randomized resourceparts (whether generated by the client or the server as described under <a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>) significantly helps to mitigate this attack, so it is of somewhat lesser concern than the directory harvesting attack.
+</li>
+</ol><p>
+      
+</p>
+<p>Naturally, presence is not leaked if the entity to which a user's server returns an error already knows the user's presence or is authorized to do so (e.g., by means of a presence subscription or directed presence), and a server does not enable a directory harvesting attack if it returns an error to an entity that already knows if a user exists (e.g., because the entity is in the user's contact list); these matters are discussed more fully in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="rules-noto"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.3"></a><h3>10.3.&nbsp;
+No 'to' Address</h3>
+
+<p>If the stanza possesses no 'to' attribute, the server MUST handle it directly on behalf of the entity that sent it, where the meaning of "handle it directly" depends on whether the stanza is message, presence, or IQ.  Because all stanzas received from other servers MUST possess a 'to' attribute, this rule applies only to stanzas received from a local entity (typically a client) that is connected to the server.
+</p>
+<a name="rules-noto-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.3.1"></a><h3>10.3.1.&nbsp;
+Message</h3>
+
+<p>If the server receives a message stanza with no 'to' attribute, it MUST treat the message as if the 'to' address were the bare JID &lt;localpart@domainpart&gt; of the sending entity.
+</p>
+<a name="rules-noto-presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.3.2"></a><h3>10.3.2.&nbsp;
+Presence</h3>
+
+<p>If the server receives a presence stanza with no 'to' attribute, it MUST broadcast it to the entities that are subscribed to the sending entity's presence, if applicable (<a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a> defines the semantics of such broadcasting for presence applications).
+</p>
+<a name="rules-noto-IQ"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.3.3"></a><h3>10.3.3.&nbsp;
+IQ</h3>
+
+<p>If the server receives an IQ stanza with no 'to' attribute, it MUST process the stanza on behalf of the account from which received the stanza, as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the IQ stanza is of type "get" or "set" and the server understands the namespace that qualifies the payload, the server MUST handle the stanza on behalf of the sending entity or return an appropriate error to the sending entity.  Although the meaning of "handle" is determined by the semantics of the qualifying namespace, in general the server will respond to the IQ stanza of type "get" or "set" by returning an appropriate IQ stanza of type "result" or "error", responding as if the server were the bare JID of the sending entity.  As an example, if the sending entity sends an IQ stanza of type "get" where the payload is qualified by the 'jabber:iq:roster' namespace (as described in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>), then the server will return the roster associated with the sending entity's bare JID to the particular resource of the sending entity that requested the roster.
+</li>
+<li>If the IQ stanza is of type "get" or "set" and the server does not understand the namespace that qualifies the payload, the server MUST return an error to the sending entity, which MUST be &lt;service-unavailable/&gt;.
+</li>
+<li>If the IQ stanza is of type "error" or "result", the server MUST handle the error or result in accordance with the payload of the associated IQ stanza or type "get" or "set" (if there is no such associated stanza, the server MUST ignore the error or result stanza).
+</li>
+</ol><p>
+        
+</p>
+<a name="rules-remote"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.4"></a><h3>10.4.&nbsp;
+Remote Domain</h3>
+
+<p>If the domainpart of the JID contained in the 'to' attribute does not match one of the configured FQDNs of the server, the server SHOULD attempt to route the stanza to the remote domain (subject to local service provisioning and security policies regarding inter-domain communication, since such communication is OPTIONAL for any given deployment).  As described in the following sections, there are two possible cases.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: These rules apply only client-to-server streams.  As described under <a class='info' href='#stanzas-attributes-to-s2s'>Section&nbsp;8.1.1.2<span> (</span><span class='info'>Server-to-Server Streams</span><span>)</span></a>, a server MUST NOT accept a stanza over a server-to-server stream if the domainpart of the JID in the 'to' attribute does not match an FQDN serviced by the receiving server.
+</p>
+</blockquote>
+
+<a name="rules-remote-existing"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.4.1"></a><h3>10.4.1.&nbsp;
+Existing Stream</h3>
+
+<p>If a server-to-server stream already exists between the two domains, the sender's server SHOULD attempt to route the stanza to the authoritative server for the remote domain over the existing stream.
+</p>
+<a name="rules-remote-nostream"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.4.2"></a><h3>10.4.2.&nbsp;
+No Existing Stream</h3>
+
+<p>If there exists no server-to-server stream between the two domains, the sender's server will proceed as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Resolve the FQDN of the remote domain (as described under <a class='info' href='#security-reuse-dns'>Section&nbsp;13.9.2<span> (</span><span class='info'>Use of DNS</span><span>)</span></a>).
+</li>
+<li>Negotiate a server-to-server stream between the two domains (as defined under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> and <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>).
+</li>
+<li>Route the stanza to the authoritative server for the remote domain over the newly established stream.
+</li>
+</ol><p>
+        
+</p>
+<a name="rules-remote-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.4.3"></a><h3>10.4.3.&nbsp;
+Error Handling</h3>
+
+<p>If routing of a stanza to the intended recipient's server is unsuccessful, the sender's server MUST return an error to the sender.  If resolution of the remote domain is unsuccessful, the stanza error MUST be &lt;remote-server-not-found/&gt; (<a class='info' href='#stanzas-error-conditions-remote-server-not-found'>Section&nbsp;8.3.3.16<span> (</span><span class='info'>remote-server-not-found</span><span>)</span></a>).  If resolution succeeds but streams cannot be negotiated, the stanza error MUST be &lt;remote-server-timeout/&gt; (<a class='info' href='#stanzas-error-conditions-remote-server-timeout'>Section&nbsp;8.3.3.17<span> (</span><span class='info'>remote-server-timeout</span><span>)</span></a>).
+</p>
+<p>If stream negotiation with the intended recipient's server is successful but the remote server cannot deliver the stanza to the recipient, the remote server MUST return an appropriate error to the sender by way of the sender's server.
+</p>
+<a name="rules-local"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5"></a><h3>10.5.&nbsp;
+Local Domain</h3>
+
+<p>If the domainpart of the JID contained in the 'to' attribute matches one of the configured FQDNs of the server, the server MUST first determine if the FQDN is serviced by the server itself or by a specialized local service.  If the latter, the server MUST route the stanza to that service.  If the former, the server MUST proceed as follows.  However, the server MUST NOT route or "forward" the stanza to another domain, because it is the server's responsibility to process all stanzas for which the domainpart of the 'to' address matches one of the configured FQDNs of the server (among other things, this helps to prevent looping).
+</p>
+<a name="rules-local-domain"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.1"></a><h3>10.5.1.&nbsp;
+domainpart</h3>
+
+<p>If the JID contained in the 'to' attribute is of the form &lt;domainpart&gt;, then the server MUST either (a) handle the stanza as appropriate for the stanza kind or (b) return an error stanza to the sender.
+</p>
+<a name="rules-local-domainresource"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.2"></a><h3>10.5.2.&nbsp;
+domainpart/resourcepart</h3>
+
+<p>If the JID contained in the 'to' attribute is of the form &lt;domainpart/resourcepart&gt;, then the server MUST either (a) handle the stanza as appropriate for the stanza kind or (b) return an error stanza to the sender.
+</p>
+<a name="rules-local-barejid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.3"></a><h3>10.5.3.&nbsp;
+localpart@domainpart</h3>
+
+<p>An address of this type is normally associated with an account on the server.  The following rules provide some general guidelines; more detailed rules in the context of instant messaging and presence applications are provided in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="rules-local-barejid-nosuchuser"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.3.1"></a><h3>10.5.3.1.&nbsp;
+No Such User</h3>
+
+<p>If there is no local account associated with the &lt;localpart@domainpart&gt;, how the stanza is processed depends on the stanza type.
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>For a message stanza, the server MUST either (a) silently ignore the stanza or (b) return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>) to the sender.
+</li>
+<li>For a presence stanza, the server SHOULD ignore the stanza (or behave as described in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>For an IQ stanza, the server MUST return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>) to the sender.
+</li>
+</ul><p>
+          
+</p>
+<a name="rules-local-barejid-userexists"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.3.2"></a><h3>10.5.3.2.&nbsp;
+User Exists</h3>
+
+<p>If the JID contained in the 'to' attribute is of the form &lt;localpart@domainpart&gt;, how the stanza is processed depends on the stanza type.
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>For a message stanza, if there exists at least one connected resource for the account then the server SHOULD deliver it to at least one of the connected resources.  If there exists no connected resource then the server MUST either (a) store the message offline for delivery when the account next has a connected resource or (b) return a &lt;service-unavailable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>).
+</li>
+<li>For a presence stanza, if there exists at least one connected resource that has sent initial presence (i.e., has a "presence session" as defined in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>) then the server SHOULD deliver it to such resources.  If there exists no connected resource then the server SHOULD ignore the stanza (or behave as described in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>For an IQ stanza, the server MUST handle it directly on behalf of the intended recipient.
+</li>
+</ul><p>
+          
+</p>
+<a name="rules-local-fulljid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10.5.4"></a><h3>10.5.4.&nbsp;
+localpart@domainpart/resourcepart</h3>
+
+<p>If the JID contained in the 'to' attribute is of the form &lt;localpart@domainpart/resourcepart&gt; and the user exists but there is no connected resource that exactly matches the full JID, the stanza SHOULD be processed as if the JID were of the form &lt;localpart@domainpart&gt; as described under <a class='info' href='#rules-local-barejid-userexists'>Section&nbsp;10.5.3.2<span> (</span><span class='info'>User Exists</span><span>)</span></a>.
+</p>
+<p>If the JID contained in the 'to' attribute is of the form &lt;localpart@domainpart/resourcepart&gt;, the user exists, and there is a connected resource that exactly matches the full JID, the server MUST deliver the stanza to that connected resource.
+</p>
+<a name="xml"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11"></a><h3>11.&nbsp;
+XML Usage</h3>
+
+<a name="xml-restrictions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.1"></a><h3>11.1.&nbsp;
+XML Restrictions</h3>
+
+<p>XMPP defines a class of data objects called XML streams as well as the behavior of computer programs that process XML streams.  XMPP is an application profile or restricted form of the Extensible Markup Language <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>, and a complete XML stream (including start and end stream tags) is a conforming XML document.
+</p>
+<p>However, XMPP does not deal with XML documents but with XML streams.  Because XMPP does not require the parsing of arbitrary and complete XML documents, there is no requirement that XMPP needs to support the full feature set of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>.  Furthermore, XMPP uses XML to define protocol data structures and extensions for the purpose of structured interactions between network entities and therefore adheres to the recommendations provided in <a class='info' href='#XML-GUIDE'>[XML&#8209;GUIDE]<span> (</span><span class='info'>Hollenbeck, S., Rose, M., and L. Masinter, &ldquo;Guidelines for the Use of Extensible Markup Language (XML) within IETF Protocols,&rdquo; January&nbsp;2003.</span><span>)</span></a> regarding restrictions on the use of XML in IETF protocols.  As a result, the following features of XML are prohibited in XMPP:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>comments (as defined in Section 2.5 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>)
+</li>
+<li>processing instructions (Section 2.6 therein)
+</li>
+<li>internal or external DTD subsets (Section 2.8 therein)
+</li>
+<li>internal or external entity references (Section 4.2 therein) with the exception of the predefined entities (Section 4.6 therein)
+</li>
+</ul><p>
+      
+</p>
+<p>An XMPP implementation MUST behave as follows with regard to these features:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>An XMPP implementation MUST NOT inject characters matching such features into an XML stream.
+</li>
+<li>If an XMPP implementation receives characters matching such features over an XML stream, it MUST close the stream with a stream error, which SHOULD be &lt;restricted-xml/&gt; (<a class='info' href='#streams-error-conditions-restricted-xml'>Section&nbsp;4.9.3.18<span> (</span><span class='info'>restricted-xml</span><span>)</span></a>), although some existing implementations send &lt;bad-format/&gt; (<a class='info' href='#streams-error-conditions-bad-format'>Section&nbsp;4.9.3.1<span> (</span><span class='info'>bad-format</span><span>)</span></a>) instead.
+</li>
+</ol><p>
+      
+</p>
+<a name="xml-ns"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.2"></a><h3>11.2.&nbsp;
+XML Namespace Names and Prefixes</h3>
+
+<p>XML namespaces (see <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>) are used within XMPP streams to create strict boundaries of data ownership.  The basic function of namespaces is to separate different vocabularies of XML elements that are structurally mixed together.  Ensuring that XMPP streams are namespace-aware enables any allowable XML to be structurally mixed with any data element within XMPP.  XMPP-specific rules for XML namespace names and prefixes are defined under <a class='info' href='#streams-ns'>Section&nbsp;4.8<span> (</span><span class='info'>XML Namespaces</span><span>)</span></a> for XML streams and <a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a> for XML stanzas.
+</p>
+<a name="xml-wellformed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.3"></a><h3>11.3.&nbsp;
+Well-Formedness</h3>
+
+<p>In XML, there are two varieties of well-formedness:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>"XML-well-formedness" in accordance with the definition of "well-formed" from Section 2.1 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>.
+</li>
+<li>"Namespace-well-formedness" in accordance with the definition of "namespace-well-formed" from Section 7 of <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;Namespaces in XML 1.0 (Third Edition),&rdquo; December&nbsp;2009.</span><span>)</span></a>.
+</li>
+</ul><p>
+      
+</p>
+<p>The following rules apply:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>An XMPP entity MUST NOT generate data that is not XML-well-formed.
+</li>
+<li>An XMPP entity MUST NOT accept data that is not XML-well-formed; instead it MUST close the stream over which the data was received with a &lt;not-well-formed/&gt; stream error (<a class='info' href='#streams-error-conditions-not-well-formed'>Section&nbsp;4.9.3.13<span> (</span><span class='info'>not-well-formed</span><span>)</span></a>).
+</li>
+<li>An XMPP entity MUST NOT generate data that is not namespace-well-formed.
+</li>
+<li>An XMPP entity MUST NOT accept data that is not namespace-well-formed (in particular, an XMPP server MUST NOT route or deliver data that is not namespace-well-formed); instead it MUST return either a &lt;not-acceptable/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-not-acceptable'>Section&nbsp;8.3.3.9<span> (</span><span class='info'>not-acceptable</span><span>)</span></a>) or close the stream with a &lt;not-well-formed/&gt; stream error (<a class='info' href='#streams-error-conditions-not-well-formed'>Section&nbsp;4.9.3.13<span> (</span><span class='info'>not-well-formed</span><span>)</span></a>), where it is preferable to close the stream with a stream error because accepting such data can open an entity to certain denial-of-service attacks.
+</li>
+</ol><p>
+      
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: Because these restrictions were underspecified in <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a>, it is possible that implementations based on that specification will send data that does not comply with these restrictions.
+</p>
+</blockquote>
+
+<a name="xml-validation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.4"></a><h3>11.4.&nbsp;
+Validation</h3>
+
+<p>A server is not responsible for ensuring that XML data delivered to a connected client or routed to a peer server is valid, in accordance with the definition of "valid" provided in Section 2.8 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>.  An implementation MAY choose to accept or send only data that has been explicitly validated against the schemas provided in this document, but such behavior is OPTIONAL.  Clients are advised not to rely on the ability to send data that does not conform to the schemas, and SHOULD ignore any non-conformant elements or attributes on the incoming XML stream.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: The terms "valid" and "well-formed" are distinct in XML.
+</p>
+</blockquote>
+
+<a name="xml-declaration"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.5"></a><h3>11.5.&nbsp;
+Inclusion of XML Declaration</h3>
+
+<p>Before sending a stream header, an implementation SHOULD send an XML declaration (matching the "XMLDecl" production from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).  Applications MUST follow the rules provided in <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a> regarding the format of the XML declaration and the circumstances under which the XML declaration is included.
+</p>
+<p>Because external markup declarations are prohibited in XMPP (as described under <a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>), the standalone document declaration (matching the "SDDecl" production from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>) would have no meaning and therefore MUST NOT be included in an XML declaration sent over an XML stream.  If an XMPP entity receives an XML declaration containing a standalone document declaration set to a value of "no", the entity MUST either ignore the standalone document declaration or close the stream with a stream error, which SHOULD be &lt;restricted-xml/&gt; (<a class='info' href='#streams-error-conditions-restricted-xml'>Section&nbsp;4.9.3.18<span> (</span><span class='info'>restricted-xml</span><span>)</span></a>).
+</p>
+<a name="xml-encoding"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.6"></a><h3>11.6.&nbsp;
+Character Encoding</h3>
+
+<p>Implementations MUST support the UTF-8 transformation of Universal Character Set <a class='info' href='#UCS2'>[UCS2]<span> (</span><span class='info'>International Organization for Standardization, &ldquo;Information Technology - Universal Multiple-octet coded Character Set (UCS) - Amendment 2: UCS Transformation Format 8 (UTF-8),&rdquo; October&nbsp;1996.</span><span>)</span></a> characters, as needed for conformance with <a class='info' href='#CHARSETS'>[CHARSETS]<span> (</span><span class='info'>Alvestrand, H., &ldquo;IETF Policy on Character Sets and Languages,&rdquo; January&nbsp;1998.</span><span>)</span></a> and as defined in <a class='info' href='#UTF-8'>[UTF&#8209;8]<span> (</span><span class='info'>Yergeau, F., &ldquo;UTF-8, a transformation format of ISO 10646,&rdquo; November&nbsp;2003.</span><span>)</span></a>.  Implementations MUST NOT attempt to use any other encoding.  If one party to an XML stream detects that the other party has attempted to send XML data with an encoding other than UTF-8, it MUST close the stream with a stream error, which SHOULD be &lt;unsupported-encoding/&gt; (<a class='info' href='#streams-error-conditions-unsupported-encoding'>Section&nbsp;4.9.3.22<span> (</span><span class='info'>unsupported-encoding</span><span>)</span></a>), although some existing implementations send &lt;bad-format/&gt; (<a class='info' href='#streams-error-conditions-bad-format'>Section&nbsp;4.9.3.1<span> (</span><span class='info'>bad-format</span><span>)</span></a>) instead.
+</p>
+<p>Because it is mandatory for an XMPP implementation to support all and only the UTF-8 encoding and because UTF-8 always has the same byte order, an implementation MUST NOT send a byte order mark ("BOM") at the beginning of the data stream.  If an entity receives the <a class='info' href='#UNICODE'>[UNICODE]<span> (</span><span class='info'>The Unicode Consortium, &ldquo;The Unicode Standard, Version 6.0,&rdquo; 2010.</span><span>)</span></a> character U+FEFF anywhere in an XML stream (including as the first character of the stream), it MUST interpret that character as a zero width no-break space, not as a byte order mark.
+</p>
+<a name="xml-whitespace"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.7"></a><h3>11.7.&nbsp;
+Whitespace</h3>
+
+<p>Except where explicitly disallowed (e.g., during <a class='info' href='#tls'>TLS negotiation<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> and <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>), either entity MAY send whitespace as separators between XML stanzas or between any other first-level elements sent over the stream.  One common use for sending such whitespace is explained under <a class='info' href='#streams-close'>Section&nbsp;4.4<span> (</span><span class='info'>Closing a Stream</span><span>)</span></a>.
+</p>
+<a name="xml-versions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11.8"></a><h3>11.8.&nbsp;
+XML Versions</h3>
+
+<p>XMPP is an application profile of XML 1.0.  A future version of XMPP might be defined in terms of higher versions of XML, but this specification defines XMPP only in terms of XML 1.0.
+</p>
+<a name="i18n"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.12"></a><h3>12.&nbsp;
+Internationalization Considerations</h3>
+
+<p>As specified under <a class='info' href='#xml-encoding'>Section&nbsp;11.6<span> (</span><span class='info'>Character Encoding</span><span>)</span></a>, XML streams MUST be encoded in UTF-8.
+</p>
+<p>As specified under <a class='info' href='#streams-attr'>Section&nbsp;4.7<span> (</span><span class='info'>Stream Attributes</span><span>)</span></a>, an XML stream SHOULD include an 'xml:lang' attribute specifying the default language for any XML character data that is intended to be presented to a human user.  As specified under <a class='info' href='#stanzas-attributes-lang'>Section&nbsp;8.1.5<span> (</span><span class='info'>xml:lang</span><span>)</span></a>, an XML stanza SHOULD include an 'xml:lang' attribute if the stanza contains XML character data that is intended to be presented to a human user.  A server SHOULD apply the default 'xml:lang' attribute to stanzas it routes or delivers on behalf of connected entities, and MUST NOT modify or delete 'xml:lang' attributes on stanzas it receives from other entities.
+</p>
+<p>Internationalization of XMPP addresses is specified in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="security"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13"></a><h3>13.&nbsp;
+Security Considerations</h3>
+
+<a name="security-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.1"></a><h3>13.1.&nbsp;
+Fundamentals</h3>
+
+<p>XMPP technologies are typically deployed using a decentralized client-server architecture.  As a result, several paths are possible when two XMPP entities need to communicate:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Both entities are servers.  In this case, the entities can establish a direct server-to-server stream between themselves.
+</li>
+<li>One entity is a server and the other entity is a client whose account is hosted on that server.  In this case, the entities can establish a direct client-to-server stream between themselves.
+</li>
+<li>Both entities are clients whose accounts are hosted on the same server.  In this case, the entities cannot establish a direct stream between themselves, but there is only one intermediate entity between them, whose policies they might understand and in which they might have some level of trust (e.g., the server might require the use of Transport Layer Security for all client connections).
+</li>
+<li>Both entities are clients but their accounts are hosted on different servers.  In this case, the entities cannot establish a direct stream between themselves and there are two intermediate entities between them; each client might have some trust in the server that hosts its account but might know nothing about the policies of the server to which the other client connects.
+</li>
+</ol><p>
+      
+</p>
+<p>This specification covers only the security of a direct XML stream between two servers or between a client and a server (cases #1 and #2), where each stream can be considered a single "hop" along a communication path.  The goal of security for a multi-hop path (cases #3 and #4), although very desirable, is out of scope for this specification.
+</p>
+<p>In accordance with <a class='info' href='#SEC-GUIDE'>[SEC&#8209;GUIDE]<span> (</span><span class='info'>Rescorla, E. and B. Korver, &ldquo;Guidelines for Writing RFC Text on Security Considerations,&rdquo; July&nbsp;2003.</span><span>)</span></a>, this specification covers communication security (confidentiality, data integrity, and peer entity authentication), non-repudiation, and systems security (unauthorized usage, inappropriate usage, and denial of service).  We also discuss common security issues such as information leaks, firewalls, and directory harvesting, as well as best practices related to the reuse of technologies such as base 64, DNS, cryptographic hash functions, SASL, TLS, UTF-8, and XML.
+</p>
+<a name="security-threats"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.2"></a><h3>13.2.&nbsp;
+Threat Model</h3>
+
+<p>The threat model for XMPP is in essence the standard "Internet Threat Model" described in <a class='info' href='#SEC-GUIDE'>[SEC&#8209;GUIDE]<span> (</span><span class='info'>Rescorla, E. and B. Korver, &ldquo;Guidelines for Writing RFC Text on Security Considerations,&rdquo; July&nbsp;2003.</span><span>)</span></a>.  Attackers are assumed to be interested in and capable of launching the following attacks against unprotected XMPP systems:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Eavesdropping
+</li>
+<li>Sniffing passwords
+</li>
+<li>Breaking passwords through dictionary attacks
+</li>
+<li>Discovering usernames through directory harvesting attacks
+</li>
+<li>Replaying, inserting, deleting, or modifying stanzas
+</li>
+<li>Spoofing users
+</li>
+<li>Gaining unauthorized entry to a server or account
+</li>
+<li>Using a server or account inappropriately
+</li>
+<li>Denying service to other entities
+</li>
+<li>Subverting communication streams through man-in-the-middle attacks
+</li>
+<li>Gaining control over on-path servers
+</li>
+</ul><p>
+      
+</p>
+<p>Where appropriate, the following sections describe methods for protecting against these threats.
+</p>
+<a name="security-layers"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.3"></a><h3>13.3.&nbsp;
+Order of Layers</h3>
+
+<p>The order of layers in which protocols MUST be stacked is as follows:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>TCP
+</li>
+<li>TLS
+</li>
+<li>SASL
+</li>
+<li>XMPP
+</li>
+</ol><p>
+      
+</p>
+<p>This order has important security implications, as described throughout these security considerations.
+</p>
+<p>Within XMPP, XML stanzas are further ordered on top of XML streams, as described under <a class='info' href='#streams'>Section&nbsp;4<span> (</span><span class='info'>XML Streams</span><span>)</span></a>.
+</p>
+<a name="security-confidentiality"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.4"></a><h3>13.4.&nbsp;
+Confidentiality and Integrity</h3>
+
+<p>The use of Transport Layer Security (TLS) with appropriate ciphersuites provides a reliable mechanism to ensure the confidentiality and integrity of data exchanged between a client and a server or between two servers.  Therefore, TLS can help to protect against eavesdropping, password sniffing, man-in-the-middle attacks, and stanza replays, insertion, deletion, and modification over an XML stream.  XMPP clients and servers MUST support TLS as defined under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: The confidentiality and integrity of a stream can be protected by methods other than TLS, e.g., by means of a SASL mechanism that involves negotiation of a security layer.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Security Warning: The use of TLS in XMPP applies to a single stream.  Because XMPP is typically deployed using a distributed client-server architecture (as explained under <a class='info' href='#arch-network'>Section&nbsp;2.5<span> (</span><span class='info'>Distributed Network of Clients and Servers</span><span>)</span></a>), a stanza might traverse multiple streams, and not all of those streams might be TLS-protected.  For example, a stanza sent from a client with a session at one server (e.g., &lt;romeo@example.net/orchard&gt;) and intended for delivery to a client with a session at another server (e.g., &lt;juliet@example.com/balcony&gt;) will traverse three streams: (1) the stream from the sender's client to its server, (2) the stream from the sender's server to the recipient's server, and (3) the stream from the recipient's server to the recipient's client.  Furthermore, the stanza will be processed as cleartext within the sender's server and the recipient's server.  Therefore, even if the stream from the sender's client to its server is protected, the confidentiality and integrity of a stanza sent over that protected stream cannot be guaranteed when the stanza is processed by the sender's server, sent from the sender's server to the recipient's server, processed by the recipient's server, or sent from the recipient's server to the recipient's client.  Only a robust technology for end-to-end encryption could ensure the confidentiality and integrity of a stanza as it traverses all of the "hops" along a communication path (e.g., a technology that meets the requirements defined in <a class='info' href='#E2E-REQS'>[E2E&#8209;REQS]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Requirements for End-to-End Encryption in the Extensible Messaging and Presence Protocol (XMPP),&rdquo; March&nbsp;2010.</span><span>)</span></a>).  Unfortunately, the XMPP community has so far failed to produce an end-to-end encryption technology that might be suitable for widespread implementation and deployment, and definition of such a technology is out of scope for this document.
+</p>
+</blockquote>
+
+<a name="security-authentication"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.5"></a><h3>13.5.&nbsp;
+Peer Entity Authentication</h3>
+
+<p>The use of the Simple Authentication and Security Layer (SASL) for authentication provides a reliable mechanism for peer entity authentication.  Therefore, SASL helps to protect against user spoofing, unauthorized usage, and man-in-the middle attacks.  XMPP clients and servers MUST support SASL as defined under <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>.
+</p>
+<a name="security-strong"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.6"></a><h3>13.6.&nbsp;
+Strong Security</h3>
+
+<p><a class='info' href='#STRONGSEC'>[STRONGSEC]<span> (</span><span class='info'>Schiller, J., &ldquo;Strong Security Requirements for Internet Engineering Task Force Standard Protocols,&rdquo; August&nbsp;2002.</span><span>)</span></a> defines "strong security" and its importance to communication over the Internet.  For the purpose of XMPP communication over client-to-server and server-to-server streams, the term "strong security" refers to the use of security technologies that provide both mutual authentication and integrity checking (e.g., a combination of TLS encryption and SASL authentication using appropriate SASL mechanisms).
+</p>
+<p>Implementations MUST support strong security.  Service provisioning SHOULD use strong security.
+</p>
+<p>An implementation SHOULD make it possible for an end user or service administrator to provision a deployment with specific trust anchors for the certificate presented by a connecting entity (either client or server); when an application is thus provisioned, it MUST NOT use a generic PKI trust store to authenticate the connecting entity.  More detailed rules and guidelines regarding certificate validation are provided in the next section.
+</p>
+<p>The initial stream and the response stream MUST be secured separately, although security in both directions MAY be established via mechanisms that provide mutual authentication.
+</p>
+<a name="security-certificates"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7"></a><h3>13.7.&nbsp;
+Certificates</h3>
+
+<p>Channel encryption of an XML stream using Transport Layer Security as described under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>, and in some cases also authentication as described under <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>, is commonly based on a PKIX certificate presented by the receiving entity (or, in the case of mutual certificate authentication, both the receiving entity and the initiating entity).  This section describes best practices regarding the generation of PKIX certificates to be presented by XMPP entities and the verification of PKIX certificates presented by XMPP entities.
+</p>
+<p>In general, the following sections rely on and extend the rules and guidelines provided in the <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a> profile of <a class='info' href='#X509'>[X509]<span> (</span><span class='info'>International Telecommunications Union, &ldquo;Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks,&rdquo; March&nbsp;2000.</span><span>)</span></a>, and in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a>.  The reader is referred to those specifications for a detailed understanding of PKIX certificates and their use in TLS.
+</p>
+<a name="security-certificates-generation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1"></a><h3>13.7.1.&nbsp;
+Certificate Generation</h3>
+
+<a name="security-certificates-generation-general"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.1"></a><h3>13.7.1.1.&nbsp;
+General Considerations</h3>
+
+<p>The following rules apply to end entity public key certificates that are issued to XMPP servers or clients:
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>The certificate MUST conform to <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a>.
+</li>
+<li>The certificate MUST NOT contain a basicConstraints extension with the cA boolean set to TRUE.
+</li>
+<li>The subject field MUST NOT be null.
+</li>
+<li>The signatureAlgorithm SHOULD be the PKCS #1 version 1.5 signature algorithm with SHA-256 as defined by <a class='info' href='#PKIX-ALGO'>[PKIX&#8209;ALGO]<span> (</span><span class='info'>Jonsson, J. and B. Kaliski, &ldquo;Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,&rdquo; February&nbsp;2003.</span><span>)</span></a>, or a stronger algorithm if available.
+</li>
+<li>The certificate SHOULD include an Authority Information Access (AIA) extension that specifies the address of an Online Certificate Status Protocol <a class='info' href='#OCSP'>[OCSP]<span> (</span><span class='info'>Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, &ldquo;X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP,&rdquo; June&nbsp;1999.</span><span>)</span></a> responder (if not, a relying party would need to fall back on the use of Certificate Revocation Lists (CRLs) as described in <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a>).
+</li>
+</ol><p>
+          
+</p>
+<p>The following rules apply to certification authority (CA) certificates that are used by issuers of XMPP end entity certificates:
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>The certificate MUST conform to <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a>.
+</li>
+<li>The certificate MUST contain a keyUsage extension with the digitalSignature bit set.
+</li>
+<li>The subject field MUST NOT be null.
+</li>
+<li>The signatureAlgorithm SHOULD be the PKCS #1 version 1.5
+signature algorithm with SHA-256 as defined by <a class='info' href='#PKIX-ALGO'>[PKIX&#8209;ALGO]<span> (</span><span class='info'>Jonsson, J. and B. Kaliski, &ldquo;Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,&rdquo; February&nbsp;2003.</span><span>)</span></a>, or a
+stronger algorithm if available.
+</li>
+<li>For issuers of public key certificates, the issuer's certificate MUST contain a basicConstraints extension with the cA boolean set to TRUE.
+</li>
+</ol><p>
+          
+</p>
+<a name="security-certificates-generation-server"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.2"></a><h3>13.7.1.2.&nbsp;
+Server Certificates</h3>
+
+<a name="security-certificates-generation-server-rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.2.1"></a><h3>13.7.1.2.1.&nbsp;
+Rules</h3>
+
+<p>In a PKIX certificate to be presented by an XMPP server (i.e., a "server certificate"), the certificate SHOULD include one or more XMPP addresses (i.e., domainparts) associated with XMPP services hosted at the server.  The rules and guidelines defined in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> apply to XMPP server certificates, with the following XMPP-specific considerations:
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>Support for the DNS-ID identifier type <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a> is REQUIRED in XMPP client and server software implementations.  Certification authorities that issue XMPP-specific certificates MUST support the DNS-ID identifier type.  XMPP service providers SHOULD include the DNS-ID identifier type in certificate requests.
+</li>
+<li>Support for the SRV-ID identifier type <a class='info' href='#PKIX-SRV'>[PKIX&#8209;SRV]<span> (</span><span class='info'>Santesson, S., &ldquo;Internet X.509 Public Key Infrastructure Subject Alternative Name for Expression of Service Name,&rdquo; August&nbsp;2007.</span><span>)</span></a> is REQUIRED for XMPP client and server software implementations (for verification purposes XMPP client implementations need to support only the "_xmpp-client" service type, whereas XMPP server implementations need to support both the "_xmpp-client" and "_xmpp-server" service types).  Certification authorities that issue XMPP-specific certificates SHOULD support the SRV-ID identifier type.  XMPP service providers SHOULD include the SRV-ID identifier type in certificate requests.
+</li>
+<li>Support for the XmppAddr identifier type (specified under <a class='info' href='#security-certificates-generation-xmppaddr'>Section&nbsp;13.7.1.4<span> (</span><span class='info'>XmppAddr Identifier Type</span><span>)</span></a>) is encouraged in XMPP client and server software implementations for the sake of backward-compatibility, but is no longer encouraged in certificates issued by certification authorities or requested by XMPP service providers.
+</li>
+<li>DNS domain names in server certificates MAY contain the wildcard character '*' as the complete left-most label within the identifier.
+</li>
+</ul><p>
+            
+</p>
+<a name="security-certificates-generation-server-examples"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.2.2"></a><h3>13.7.1.2.2.&nbsp;
+Examples</h3>
+
+<p>For our first (relatively simple) example, consider a company called "Example Products, Inc."  It hosts an XMPP service at "im.example.com" (i.e., user addresses at the service are of the form "user@im.example.com"), and SRV lookups for the xmpp-client and xmpp-server services at "im.example.com" yield one machine, called "x.example.com", as follows:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+_xmpp-client._tcp.im.example.com. 400 IN SRV 20 0 5222 x.example.com
+_xmpp-server._tcp.im.example.com. 400 IN SRV 20 0 5269 x.example.com
+</pre></div>
+<p>The certificate presented by x.example.com contains the following representations:
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>An otherName type of SRVName (id-on-dnsSRV) containing an IA5String (ASCII) string of "_xmpp-client.im.example.com"
+</li>
+<li>An otherName type of SRVName (id-on-dnsSRV) containing an IA5String (ASCII) string of "_xmpp-server.im.example.com"
+</li>
+<li>A dNSName containing an ASCII string of "im.example.com"
+</li>
+<li>An otherName type of XmppAddr (id-on-xmppAddr) containing a UTF-8 string of "im.example.com"
+</li>
+<li>A CN containing an ASCII string of "Example Products, Inc."
+</li>
+</ul><p>
+            
+</p>
+<p>For our second (more complex) example, consider an ISP called "Example Internet Services".  It hosts an XMPP service at "example.net" (i.e., user addresses at the service are of the form "user@example.net"), but SRV lookups for the xmpp-client and xmpp-server services at "example.net" yield two machines ("x1.example.net" and "x2.example.net"), as follows:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+_xmpp-client._tcp.example.net. 68400 IN SRV 20 0 5222 x1.example.net.
+_xmpp-client._tcp.example.net. 68400 IN SRV 20 0 5222 x2.example.net.
+_xmpp-server._tcp.example.net. 68400 IN SRV 20 0 5269 x1.example.net.
+_xmpp-server._tcp.example.net. 68400 IN SRV 20 0 5269 x2.example.net.
+</pre></div>
+<p>Example Internet Services also hosts chatrooms at chat.example.net, and provides an xmpp-server SRV record for that service as well (thus enabling entities from remote domains to access that service).  It also might provide other such services in the future, so it wishes to represent a wildcard in its certificate to handle such growth.
+</p>
+<p>The certificate presented by either x1.example.net or x2.example.net contains the following representations:
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>An otherName type of SRVName (id-on-dnsSRV) containing an IA5String (ASCII) string of "_xmpp-client.example.net"
+</li>
+<li>An otherName type of SRVName (id-on-dnsSRV) containing an IA5String (ASCII) string of "_xmpp-server.example.net"
+</li>
+<li>An otherName type of SRVName (id-on-dnsSRV) containing an IA5String (ASCII) string of "_xmpp-server.chat.example.net"
+</li>
+<li>A dNSName containing an ASCII string of "example.net"
+</li>
+<li>A dNSName containing an ASCII string of "*.example.net"
+</li>
+<li>An otherName type of XmppAddr (id-on-xmppAddr) containing a UTF-8 string of "example.net"
+</li>
+<li>An otherName type of XmppAddr (id-on-xmppAddr) containing a UTF-8 string of "chat.example.net"
+</li>
+<li>A CN containing an ASCII string of "Example Internet Services"
+</li>
+</ul><p>
+            
+</p>
+<a name="security-certificates-generation-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.3"></a><h3>13.7.1.3.&nbsp;
+Client Certificates</h3>
+
+<p>In a PKIX certificate to be presented by an XMPP client controlled by a human user (i.e., a "client certificate"), it is RECOMMENDED for the certificate to include one or more JIDs associated with an XMPP user.  If included, a JID MUST be represented as an XmppAddr as specified under <a class='info' href='#security-certificates-generation-xmppaddr'>Section&nbsp;13.7.1.4<span> (</span><span class='info'>XmppAddr Identifier Type</span><span>)</span></a>.
+</p>
+<a name="security-certificates-generation-xmppaddr"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.1.4"></a><h3>13.7.1.4.&nbsp;
+XmppAddr Identifier Type</h3>
+
+<p>The XmppAddr identifier type is a UTF8String within an otherName entity inside the subjectAltName, using the <a class='info' href='#ASN.1'>[ASN.1]<span> (</span><span class='info'>CCITT, &ldquo;Recommendation X.208: Specification of Abstract Syntax Notation One (ASN.1),&rdquo; 1988.</span><span>)</span></a> Object Identifier "id-on-xmppAddr" specified below.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
+        dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
+
+id-on  OBJECT IDENTIFIER ::= { id-pkix 8 }  -- other name forms
+
+id-on-xmppAddr  OBJECT IDENTIFIER ::= { id-on 5 }
+
+XmppAddr ::= UTF8String
+</pre></div>
+<p>As an alternative to the "id-on-xmppAddr" notation, this Object Identifier MAY be represented in dotted display format (i.e., "1.3.6.1.5.5.7.8.5") or in the Uniform Resource Name notation specified in <a class='info' href='#URN-OID'>[URN&#8209;OID]<span> (</span><span class='info'>Mealling, M., &ldquo;A URN Namespace of Object Identifiers,&rdquo; February&nbsp;2001.</span><span>)</span></a> (i.e., "urn:oid:1.3.6.1.5.5.7.8.5").
+</p>
+<p>Thus for example the JID &lt;juliet@im.example.com&gt; as included in a certificate could be formatted in any of the following three ways:
+</p>
+<p>
+            </p>
+<blockquote class="text"><dl>
+<dt>id-on-xmppAddr:</dt>
+<dd>subjectAltName=otherName:id-on-xmppAddr;UTF8:juliet@im.example.com
+</dd>
+<dt>dotted display format:</dt>
+<dd>subjectAltName=otherName:1.3.6.1.5.5.7.8.5;UTF8:juliet@im.example.com
+</dd>
+<dt>URN notation:</dt>
+<dd>subjectAltName=otherName:urn:oid:1.3.6.1.5.5.7.8.5;UTF8:juliet@im.example.com
+</dd>
+</dl></blockquote><p>
+          
+</p>
+<p>Use of the "id-on-xmppAddr" format is RECOMMENDED in the generation of certificates, but all three formats MUST be supported for the purpose of certificate validation.
+</p>
+<p>The "id-on-xmppAddr" object identifier MAY be used in conjunction with the extended key usage extension specified in Section 4.2.1.12 of <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a> in order to explicitly define and limit the intended use of a certificate to the XMPP network.
+</p>
+<a name="security-certificates-validation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2"></a><h3>13.7.2.&nbsp;
+Certificate Validation</h3>
+
+<p>When an XMPP entity is presented with a server certificate or client certificate by a peer for the purpose of encryption or authentication of XML streams as described under <a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a> and <a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>, the entity MUST attempt to validate the certificate to determine if the certificate will be considered a "trusted certificate", i.e., a certificate that is acceptable for encryption and/or authentication in accordance with the XMPP entity's local service policies or configured settings.
+</p>
+<p>For both server certificates and client certificates, the validating entity MUST do the following:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Attempt to verify the integrity of the certificate.
+</li>
+<li>Attempt to verify that the certificate has been properly signed by the issuing Certificate Authority.
+</li>
+<li>Attempt to validate the full certification path.
+</li>
+<li>Check the rules for end entity public key certificates and certification authority certificates specified under <a class='info' href='#security-certificates-generation-general'>Section&nbsp;13.7.1.1<span> (</span><span class='info'>General Considerations</span><span>)</span></a> for the general case and under either <a class='info' href='#security-certificates-generation-server'>Section&nbsp;13.7.1.2<span> (</span><span class='info'>Server Certificates</span><span>)</span></a> or <a class='info' href='#security-certificates-generation-client'>Section&nbsp;13.7.1.3<span> (</span><span class='info'>Client Certificates</span><span>)</span></a> for XMPP server or client certificates, respectively.
+</li>
+<li>Check certificate revocation messages via Certificate Revocation Lists (CRLs), the Online Certificate Status Protocol <a class='info' href='#OCSP'>[OCSP]<span> (</span><span class='info'>Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, &ldquo;X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP,&rdquo; June&nbsp;1999.</span><span>)</span></a>, or both.
+</li>
+</ol><p>
+        
+</p>
+<p>If any of those validation attempts fail, the validating entity MUST unilaterally terminate the session.
+</p>
+<p>The following sections describe the additional identity verification rules that apply to server-to-server and client-to-server streams.
+</p>
+<p>Once the identity of the stream peer has been validated, the validating entity SHOULD also correlate the validated identity with the 'from' address (if any) of the stream header it received from the peer.  If the two identities do not match, the validating entity SHOULD terminate the connection attempt (however, there might be good reasons why the identities do not match, as described under <a class='info' href='#streams-attr-from'>Section&nbsp;4.7.1<span> (</span><span class='info'>from</span><span>)</span></a>).
+</p>
+<a name="security-certificates-validation-server"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.1"></a><h3>13.7.2.1.&nbsp;
+Server Certificates</h3>
+
+<p>For server certificates, the rules and guidelines defined in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> apply, with the proviso that the XmppAddr identifier specified under <a class='info' href='#security-certificates-generation-xmppaddr'>Section&nbsp;13.7.1.4<span> (</span><span class='info'>XmppAddr Identifier Type</span><span>)</span></a> is allowed as a reference identifier.
+</p>
+<p>The identities to be checked are set as follows:
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>The initiating entity sets the source domain of its reference
+     identifiers to the 'to' address it communicates in the initial stream
+     header; i.e., this is the identity it expects the receiving entity to
+     provide in a PKIX certificate.
+</li>
+<li>The receiving entity sets the source domain of its reference
+     identifiers to the 'from' address communicated by the initiating
+     entity in the initial stream header; i.e., this is the identity that
+     the initiating entity is trying to assert.
+</li>
+</ul><p>
+          
+</p>
+<p>
+  In the case of server-to-server communication, the matching procedure
+  described in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> can be performed by an application server
+  (receiving entity) when verifying an incoming server-to-server
+  connection from a peer server (initiating entity).  In this case, the
+  receiving entity verifies the identity of the initiating entity and
+  uses as the source domain of its reference identifiers the DNS domain
+  name asserted by the initiating entity in the 'from' attribute of the
+  initial stream header.  However, the matching procedure described in
+  <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a> remains unchanged and is applied in the same way.
+
+</p>
+<a name="security-certificates-validation-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.2"></a><h3>13.7.2.2.&nbsp;
+Client Certificates</h3>
+
+<p>When an XMPP server validates a certificate presented by a client, there are three possible cases, as discussed in the following sections.
+</p>
+<p>The identities to be checked are set as follows:
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>
+     The client sets the source domain of its reference identifiers to
+     the 'to' address it communicates in the initial stream header;
+     i.e., this is the identity it expects the server to provide in a
+     PKIX certificate.
+
+</li>
+<li>
+     The server sets the bare JID of its reference identifiers to the
+     'from' address communicated by the initiating entity in the
+     initial stream header; i.e., this is the identity that the client
+     is trying to assert.
+
+</li>
+</ul><p>
+          
+</p>
+<a name="security-certificates-validation-client-case1"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.2.1"></a><h3>13.7.2.2.1.&nbsp;
+Case #1</h3>
+
+<p>If the client certificate appears to be certified by a certification path terminating in a trust anchor (as described in Section 6.1 of <a class='info' href='#PKIX'>[PKIX]<span> (</span><span class='info'>Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,&rdquo; May&nbsp;2008.</span><span>)</span></a>), the server MUST check the certificate for any instances of the XmppAddr as described under <a class='info' href='#security-certificates-generation-xmppaddr'>Section&nbsp;13.7.1.4<span> (</span><span class='info'>XmppAddr Identifier Type</span><span>)</span></a>.  There are three possible sub-cases:
+</p>
+<p>
+              </p>
+<blockquote class="text"><dl>
+<dt>Sub-Case #1:</dt>
+<dd>The server finds one XmppAddr for which the domainpart of the represented JID matches one of the configured FQDNs of the server; the server SHOULD use this represented JID as the validated identity of the client.
+</dd>
+<dt>Sub-Case #2:</dt>
+<dd>The server finds more than one XmppAddr for which the domainpart of the represented JID matches one of the configured FQDNs of the server; the server SHOULD use one of these represented JIDs as the validated identity of the client, choosing among them based on the bare JID contained in the 'from' address of the initial stream header (if any), based on the domainpart contained in the 'to' address of the initial stream header, or in accordance with local service policies (such as a lookup in a user database based on other information contained in the client certificate).
+</dd>
+<dt>Sub-Case #3:</dt>
+<dd>The server finds no XmppAddrs, or finds at least one XmppAddr but the domainpart of the represented JID does not match one of the configured FQDNs of the server; the server MUST NOT use the represented JID (if any) as the validated identity of the client but instead MUST validate the identity of the client using other means in accordance with local service policies (such as a lookup in a user database based on other information contained in the client certificate).  If the identity cannot be so validated, the server MAY abort the validation process and terminate the TLS negotiation.
+</dd>
+</dl></blockquote><p>
+            
+</p>
+<a name="security-certificates-validation-client-case2"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.2.2"></a><h3>13.7.2.2.2.&nbsp;
+Case #2</h3>
+
+<p>If the client certificate is certified by a Certificate Authority not known to the server, the server MUST proceed as under Case #1, Sub-Case #3.
+</p>
+<a name="security-certificates-validation-client-case3"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.2.3"></a><h3>13.7.2.2.3.&nbsp;
+Case #3</h3>
+
+<p>If the client certificate is self-signed, the server MUST proceed as under Case #1, Sub-Case #3.
+</p>
+<a name="security-certificates-validation-streams"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.3"></a><h3>13.7.2.3.&nbsp;
+Checking of Certificates in Long-Lived Streams</h3>
+
+<p>Because XMPP uses long-lived XML streams, it is possible that a certificate presented during stream negotiation might expire or be revoked while the stream is still live (this is especially relevant in the context of server-to-server streams).  Therefore, each party to a long-lived stream SHOULD:
+</p>
+<p>
+            </p>
+<ol class="text">
+<li>Cache the expiration date of the certificate presented by the other party and any certificates on which that certificate depends (such as a root or intermediate certificate for a certification authority), and close the stream when any such certificate expires, with a stream error of &lt;reset/&gt; (<a class='info' href='#streams-error-conditions-reset'>Section&nbsp;4.9.3.16<span> (</span><span class='info'>reset</span><span>)</span></a>).
+</li>
+<li>Periodically query the Online Certificate Status Protocol <a class='info' href='#OCSP'>[OCSP]<span> (</span><span class='info'>Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, &ldquo;X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP,&rdquo; June&nbsp;1999.</span><span>)</span></a> responder listed in the Authority Information Access (AIA) extension of the certificate presented by the other party and any certificates on which that certificate depends (such as a root or intermediate certificate for a certification authority), and close the stream if any such certificate has been revoked, with a stream error of &lt;reset/&gt; (<a class='info' href='#streams-error-conditions-reset'>Section&nbsp;4.9.3.16<span> (</span><span class='info'>reset</span><span>)</span></a>).  It is RECOMMENDED to query the OSCP responder at or near the time communicated via the nextUpdate field received in the OCSP response or, if the nextUpdate field is not set, to query every 24 hours.
+</li>
+</ol><p>
+          
+</p>
+<p>After the stream is closed, the initiating entity from the closed stream will need to reconnect and the receiving entity will need to authenticate the initiating entity based on whatever certificate it presents during negotiation of the new stream.
+</p>
+<a name="security-certificates-validation-extensions"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.7.2.4"></a><h3>13.7.2.4.&nbsp;
+Use of Certificates in XMPP Extensions</h3>
+
+<p>Certificates MAY be used in extensions to XMPP for the purpose of application-layer encryption or authentication above the level of XML streams (e.g., for end-to-end encryption).  Such extensions will define their own certificate handling rules.  At a minimum, such extensions are encouraged to remain consistent with the rules defined in this specification, specifying additional rules only when necessary.
+</p>
+<a name="security-mti"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.8"></a><h3>13.8.&nbsp;
+Mandatory-to-Implement TLS and SASL Technologies</h3>
+
+<p>The following TLS ciphersuites and SASL mechanisms are mandatory-to-implement (naturally, implementations MAY support other ciphersuites and mechanisms as well).  For security considerations related to TLS ciphersuites, see <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a> and <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>.  For security considerations related to SASL mechanisms, see <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a>, <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>, and specifications for particular SASL mechanisms such as <a class='info' href='#SCRAM'>[SCRAM]<span> (</span><span class='info'>Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, &ldquo;Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-API Mechanisms,&rdquo; July&nbsp;2010.</span><span>)</span></a>, <a class='info' href='#DIGEST-MD5'>[DIGEST&#8209;MD5]<span> (</span><span class='info'>Leach, P. and C. Newman, &ldquo;Using Digest Authentication as a SASL Mechanism,&rdquo; May&nbsp;2000.</span><span>)</span></a>, and <a class='info' href='#PLAIN'>[PLAIN]<span> (</span><span class='info'>Zeilenga, K., &ldquo;The PLAIN Simple Authentication and Security Layer (SASL) Mechanism,&rdquo; August&nbsp;2006.</span><span>)</span></a>.
+</p>
+<a name="security-mti-auth"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.8.1"></a><h3>13.8.1.&nbsp;
+For Authentication Only</h3>
+
+<p>For authentication only, servers and clients MUST support
+        the SASL Salted Challenge Response Authentication Mechanism
+        <a class='info' href='#SCRAM'>[SCRAM]<span> (</span><span class='info'>Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, &ldquo;Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-API Mechanisms,&rdquo; July&nbsp;2010.</span><span>)</span></a> -- in particular, the SCRAM-SHA-1 and SCRAM-SHA-1-PLUS variants.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Even though it is possible to complete authentication only without confidentiality, it is RECOMMENDED for servers and clients to protect the stream with TLS before attempting authentication with SASL, both to help protect the information exchanged during SASL negotiation and to help prevent certain downgrade attacks as described under <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a> and <a class='info' href='#security-reuse-tls'>Section&nbsp;13.9.5<span> (</span><span class='info'>Use of TLS</span><span>)</span></a>.  Even if TLS is used, implementations SHOULD also enforce channel binding as described under <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: The SCRAM-SHA-1 or SASL-SCRAM-SHA-1-PLUS variants of the SCRAM mechanism replace the SASL DIGEST-MD5 mechanism as XMPP's mandatory-to-implement password-based method for authentication only.  For backward-compatibility with existing deployed infrastructure, implementations are encouraged to continue supporting the DIGEST-MD5 mechanism as specified in <a class='info' href='#DIGEST-MD5'>[DIGEST&#8209;MD5]<span> (</span><span class='info'>Leach, P. and C. Newman, &ldquo;Using Digest Authentication as a SASL Mechanism,&rdquo; May&nbsp;2000.</span><span>)</span></a>; however, there are known interoperability issues with DIGEST-MD5 that make it impractical in the long term.
+</p>
+</blockquote>
+
+<a name="security-mti-conf"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.8.2"></a><h3>13.8.2.&nbsp;
+For Confidentiality Only</h3>
+
+<p>For confidentiality only, servers MUST support TLS with the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Because a connection with confidentiality only has weaker security properties than a connection with both confidentiality and authentication, it is RECOMMENDED for servers and clients to prefer connections with both qualities (e.g., by protecting the stream with TLS before attempting authentication with SASL).  In practice, confidentiality only is employed merely for server-to-server connections when the peer server does not present a trusted certificate and the servers use Server Dialback <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a> for weak identity verification, but TLS with confidentiality only is still desirable to protect the connection against casual eavesdropping.
+</p>
+</blockquote>
+
+<a name="security-mti-bothpass"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.8.3"></a><h3>13.8.3.&nbsp;
+For Confidentiality and Authentication with Passwords</h3>
+
+<p>For both confidentiality and authentication with passwords, servers and clients MUST implement TLS with the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite plus SASL SCRAM, in particular the SCRAM&#8209;SHA&#8209;1 and SCRAM&#8209;SHA&#8209;1&#8209;PLUS variants (with SCRAM&#8209;SHA1&#8209;PLUS being preferred, as described under <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a>).
+</p>
+<p>As further explained in the following Security Warning, in certain circumstances a server MAY offer TLS with the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite plus SASL PLAIN when it is not possible to offer more secure alternatives; in addition, clients SHOULD implement PLAIN over TLS in order to maximize interoperability with servers that are not able to deploy more secure alternatives.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: In practice, many
+        servers offer, and many clients use, TLS plus SASL PLAIN.  The
+        SCRAM-SHA-1 and especially SCRAM-SHA-1-PLUS variants of the
+        SCRAM mechanism are strongly preferred over the PLAIN
+        mechanism because of their superior security properties
+        (including for SCRAM-SHA-1-PLUS the ability to enforce channel
+        binding as described under
+        <a class='info' href='#security-reuse-sasl'>Section&nbsp;13.9.4<span> (</span><span class='info'>Use of SASL</span><span>)</span></a>).  A client SHOULD treat
+        TLS plus SASL PLAIN as a technology of last resort to be used
+        only when interacting with a server that does not offer SCRAM
+        (or other alternatives that are more secure than TLS plus SASL
+        PLAIN), MUST prefer more secure mechanisms (e.g., EXTERNAL,
+        SCRAM-SHA-1-PLUS, SCRAM-SHA-1, or the older DIGEST-MD5
+        mechanism) to the PLAIN mechanism, and MUST NOT use the PLAIN
+        mechanism if the stream does not at a minimum have
+        confidentiality and integrity protection via TLS with full
+        certificate validation as described under
+        <a class='info' href='#security-certificates-validation-server'>Section&nbsp;13.7.2.1<span> (</span><span class='info'>Server Certificates</span><span>)</span></a>.  A
+        server MUST NOT offer SASL PLAIN if the confidentiality and
+        integrity of the stream are not protected via TLS or an
+        equivalent security layer.  A server SHOULD NOT offer TLS plus
+        SASL PLAIN unless it is unable to offer some variant of SASL
+        SCRAM (or other alternatives that are more secure than TLS
+        plus SASL PLAIN), e.g., because the XMPP service depends for
+        authentication purposes on a database or directory that is not
+        under the control of the XMPP administrators, such as
+        Pluggable Authentication Modules (PAM), an Lightweight
+        Directory Access Protocol (LDAP) directory <a class='info' href='#LDAP'>[LDAP]<span> (</span><span class='info'>Zeilenga, K., &ldquo;Lightweight Directory Access Protocol (LDAP): Technical Specification Road Map,&rdquo; June&nbsp;2006.</span><span>)</span></a>, or an Authentication, Authorization, and Accounting (AAA) key management protocol (for guidance, refer to <a class='info' href='#AAA'>[AAA]<span> (</span><span class='info'>Housley, R. and B. Aboba, &ldquo;Guidance for Authentication, Authorization, and Accounting (AAA) Key Management,&rdquo; July&nbsp;2007.</span><span>)</span></a>). However, offering TLS plus SASL PLAIN even when the server supports more secure alternatives might be appropriate if the server needs to enable interoperability with an installed base of clients that do not yet support SCRAM or other alternatives that are more secure than TLS plus SASL PLAIN.
+</p>
+</blockquote>
+
+<a name="security-mti-bothnopass"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.8.4"></a><h3>13.8.4.&nbsp;
+For Confidentiality and Authentication without Passwords</h3>
+
+<p>For both confidentiality and authentication without passwords, servers MUST and clients SHOULD implement TLS with the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite plus the SASL EXTERNAL mechanism (see Appendix A of <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>) with PKIX certificates.
+</p>
+<a name="security-reuse"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9"></a><h3>13.9.&nbsp;
+Technology Reuse</h3>
+
+<a name="security-reuse-base64"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.1"></a><h3>13.9.1.&nbsp;
+Use of Base 64 in SASL</h3>
+
+<p>Both the client and the server MUST verify any base 64 data received during <a class='info' href='#sasl'>SASL negotiation<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>.  An implementation MUST reject (not ignore) any characters that are not explicitly allowed by the base 64 alphabet; this helps to guard against creation of a covert channel that could be used to "leak" information.
+</p>
+<p>An implementation MUST NOT break on invalid input and MUST reject any sequence of base 64 characters containing the pad ('=') character if that character is included as something other than the last character of the data (e.g., "=AAA" or "BBBB=CCC"); this helps to guard against buffer overflow attacks and other attacks on the implementation.
+</p>
+<p>While base 64 encoding visually hides otherwise easily recognized information (such as passwords), it does not provide any computational confidentiality.
+</p>
+<p>All uses of base 64 encoding MUST follow the definition in Section 4 of <a class='info' href='#BASE64'>[BASE64]<span> (</span><span class='info'>Josefsson, S., &ldquo;The Base16, Base32, and Base64 Data Encodings,&rdquo; October&nbsp;2006.</span><span>)</span></a> and padding bits MUST be set to zero.
+</p>
+<a name="security-reuse-dns"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.2"></a><h3>13.9.2.&nbsp;
+Use of DNS</h3>
+
+<p>XMPP typically relies on the Domain Name System
+        (specifically <a class='info' href='#DNS-SRV'>[DNS&#8209;SRV]<span> (</span><span class='info'>Gulbrandsen, A., Vixie, P., and L. Esibov, &ldquo;A DNS RR for specifying the location of services (DNS SRV),&rdquo; February&nbsp;2000.</span><span>)</span></a> records) to resolve a
+        fully qualified domain name to an IP address before a client connects to a server or before a peer server connects to another server.  Before attempting to negotiate an XML stream, the initiating entity MUST NOT proceed until it has resolved the DNS domain name of the receiving entity as specified under <a class='info' href='#tcp'>Section&nbsp;3<span> (</span><span class='info'>TCP Binding</span><span>)</span></a> (although it is not necessary to resolve the DNS domain name before each connection attempt, because DNS resolution results can be temporarily cached in accordance with time-to-live values). However, in the absence of a secure DNS option (e.g., as provided by <a class='info' href='#DNSSEC'>[DNSSEC]<span> (</span><span class='info'>Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, &ldquo;DNS Security Introduction and Requirements,&rdquo; March&nbsp;2005.</span><span>)</span></a>), a malicious attacker with access to the DNS server data, or able to cause spoofed answers to be cached in a recursive resolver, can potentially cause the initiating entity to connect to any XMPP server chosen by the attacker.  Deployment and validation of server certificates help to prevent such attacks.
+</p>
+<a name="security-reuse-hash"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.3"></a><h3>13.9.3.&nbsp;
+Use of Hash Functions</h3>
+
+<p>XMPP itself does not directly mandate the use of any particular cryptographic hash function.  However, technologies on which XMPP depends (e.g., TLS and particular SASL mechanisms), as well as various XMPP extensions, might make use of cryptographic hash functions.  Those who implement XMPP technologies or who develop XMPP extensions are advised to closely monitor the state of the art regarding attacks against cryptographic hash functions in Internet protocols as they relate to XMPP.  For helpful guidance, refer to <a class='info' href='#HASHES'>[HASHES]<span> (</span><span class='info'>Hoffman, P. and B. Schneier, &ldquo;Attacks on Cryptographic Hashes in Internet Protocols,&rdquo; November&nbsp;2005.</span><span>)</span></a>.
+</p>
+<a name="security-reuse-sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.4"></a><h3>13.9.4.&nbsp;
+Use of SASL</h3>
+
+<p>Because the initiating entity chooses an acceptable SASL mechanism from the list presented by the receiving entity, the initiating entity depends on the receiving entity's list for authentication.  This dependency introduces the possibility of a downgrade attack if an attacker can gain control of the channel and therefore present a weak list of mechanisms.  To mitigate this attack, the parties SHOULD protect the channel using TLS before attempting SASL negotiation and either perform full certificate validation as described under <a class='info' href='#security-certificates-validation-server'>Section&nbsp;13.7.2.1<span> (</span><span class='info'>Server Certificates</span><span>)</span></a> or use a SASL mechanism that provides channel bindings, such as SCRAM-SHA-1-PLUS.  (Protecting the channel via TLS with full certificate validation can help to ensure the confidentiality and integrity of the information exchanged during SASL negotiation.)
+</p>
+<p>The SASL framework itself does not provide a method for binding SASL authentication to a security layer providing confidentiality and integrity protection that was negotiated at a lower layer (e.g., TLS).  Such a binding is known as a "channel binding" (see <a class='info' href='#CHANNEL'>[CHANNEL]<span> (</span><span class='info'>Williams, N., &ldquo;On the Use of Channel Bindings to Secure Channels,&rdquo; November&nbsp;2007.</span><span>)</span></a>).  Some SASL mechanisms provide channel bindings, which in the case of XMPP would typically be a binding to TLS (see <a class='info' href='#CHANNEL-TLS'>[CHANNEL&#8209;TLS]<span> (</span><span class='info'>Altman, J., Williams, N., and L. Zhu, &ldquo;Channel Bindings for TLS,&rdquo; July&nbsp;2010.</span><span>)</span></a>).  If a SASL mechanism provides a channel binding (e.g., this is true of <a class='info' href='#SCRAM'>[SCRAM]<span> (</span><span class='info'>Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, &ldquo;Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-API Mechanisms,&rdquo; July&nbsp;2010.</span><span>)</span></a>), then XMPP entities using that mechanism SHOULD prefer the channel binding variant (e.g., preferring "SCRAM-SHA-1-PLUS" over "SCRAM-SHA-1").  If a SASL mechanism does not provide a channel binding, then the mechanism cannot provide a way to verify that the source and destination end points to which the lower layer's security is bound are equivalent to the end points that SASL is authenticating; furthermore, if the end points are not identical, then the lower layer's security cannot be trusted to protect data transmitted between the SASL-authenticated entities.  In such a situation, a SASL security layer SHOULD be negotiated that effectively ignores the presence of the lower-layer security.
+</p>
+<p>Many deployed XMPP services authenticate client connections by means of passwords.  It is well known that most human users choose relatively weak passwords.  Although service provisioning is out of scope for this document, XMPP servers that allow password-based authentication SHOULD enforce minimal criteria for password strength to help prevent dictionary attacks.  Because all password-based authentication mechanisms are susceptible to password guessing attacks, XMPP servers MUST limit the number of retries allowed during SASL authentication, as described under <a class='info' href='#sasl-process-neg-failure'>Section&nbsp;6.4.5<span> (</span><span class='info'>SASL Failure</span><span>)</span></a>.
+</p>
+<p>Some SASL mechanisms (e.g., <a class='info' href='#ANONYMOUS'>[ANONYMOUS]<span> (</span><span class='info'>Zeilenga, K., &ldquo;Anonymous Simple Authentication and Security Layer (SASL) Mechanism,&rdquo; June&nbsp;2006.</span><span>)</span></a>) do not provide strong peer entity authentication of the client to the server.  Service administrators are advised to enable such mechanisms with caution.  Best practices for the use of the SASL ANONYMOUS mechanism in XMPP are described in <a class='info' href='#XEP-0175'>[XEP&#8209;0175]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices for Use of SASL ANONYMOUS,&rdquo; September&nbsp;2009.</span><span>)</span></a>.
+</p>
+<a name="security-reuse-tls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.5"></a><h3>13.9.5.&nbsp;
+Use of TLS</h3>
+
+<p>Implementations of TLS typically support multiple versions of the Transport Layer Security protocol as well as the older Secure Sockets Layer (SSL) protocol.  Because of known security vulnerabilities, XMPP servers and clients MUST NOT request, offer, or use SSL 2.0.  For further details, see Appendix E.2 of <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a> along with <a class='info' href='#TLS-SSL2'>[TLS&#8209;SSL2]<span> (</span><span class='info'>Turner, S. and T. Polk, &ldquo;Prohibiting Secure Sockets Layer (SSL) Version 2.0,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>To prevent man-in-the-middle attacks, the TLS client (which might be an XMPP client or an XMPP server) MUST verify the certificate of the TLS server and MUST check its understanding of the server FQDN against the server's identity as presented in the TLS Certificate message as described under <a class='info' href='#security-certificates-validation-server'>Section&nbsp;13.7.2.1<span> (</span><span class='info'>Server Certificates</span><span>)</span></a> (for further details, see <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>Support for TLS renegotiation is strictly OPTIONAL.  However, implementations that support TLS renegotiation MUST implement and use the TLS Renegotiation Extension <a class='info' href='#TLS-NEG'>[TLS&#8209;NEG]<span> (</span><span class='info'>Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, &ldquo;Transport Layer Security (TLS) Renegotiation Indication Extension,&rdquo; February&nbsp;2010.</span><span>)</span></a>.  Further details are provided under <a class='info' href='#tls-rules-renegotiation'>Section&nbsp;5.3.5<span> (</span><span class='info'>TLS Renegotiation</span><span>)</span></a>.
+</p>
+<a name="security-reuse-utf8"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.6"></a><h3>13.9.6.&nbsp;
+Use of UTF-8</h3>
+
+<p>The use of UTF-8 makes it possible to transport non-ASCII characters, and thus enables character "spoofing" scenarios, in which a displayed value appears to be something other than it is.  Furthermore, there are known attack scenarios related to the decoding of UTF-8 data.  On both of these points, refer to <a class='info' href='#UTF-8'>[UTF&#8209;8]<span> (</span><span class='info'>Yergeau, F., &ldquo;UTF-8, a transformation format of ISO 10646,&rdquo; November&nbsp;2003.</span><span>)</span></a> for more information.
+</p>
+<a name="security-reuse-xml"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.9.7"></a><h3>13.9.7.&nbsp;
+Use of XML</h3>
+
+<p>Because XMPP is an application profile of the Extensible Markup Language <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>, many of the security considerations described in <a class='info' href='#XML-MEDIA'>[XML&#8209;MEDIA]<span> (</span><span class='info'>Murata, M., St. Laurent, S., and D. Kohn, &ldquo;XML Media Types,&rdquo; January&nbsp;2001.</span><span>)</span></a> and <a class='info' href='#XML-GUIDE'>[XML&#8209;GUIDE]<span> (</span><span class='info'>Hollenbeck, S., Rose, M., and L. Masinter, &ldquo;Guidelines for the Use of Extensible Markup Language (XML) within IETF Protocols,&rdquo; January&nbsp;2003.</span><span>)</span></a> also apply to XMPP.  Several aspects of XMPP mitigate the risks described there, such as the prohibitions specified under <a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a> and the lack of external references to style sheets or transformations, but these mitigating factors are by no means comprehensive.
+</p>
+<a name="security-leaks"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.10"></a><h3>13.10.&nbsp;
+Information Leaks</h3>
+
+<a name="security-leaks-ipaddress"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.10.1"></a><h3>13.10.1.&nbsp;
+IP Addresses</h3>
+
+<p>A client's IP address and method of access MUST NOT be made public by a server (e.g., as typically occurs in <a class='info' href='#IRC'>[IRC]<span> (</span><span class='info'>Kalt, C., &ldquo;Internet Relay Chat: Architecture,&rdquo; April&nbsp;2000.</span><span>)</span></a>).
+</p>
+<a name="security-leaks-presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.10.2"></a><h3>13.10.2.&nbsp;
+Presence Information</h3>
+
+<p>One of the core aspects of XMPP is presence: information about the network availability of an XMPP entity (i.e., whether the entity is currently online or offline).  A "presence leak" occurs when an entity's network availability is inadvertently and involuntarily revealed to a second entity that is not authorized to know the first entity's network availability.
+</p>
+<p>Although presence is discussed more fully in <a class='info' href='#XMPP-IM'>[XMPP&#8209;IM]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; March&nbsp;2011.</span><span>)</span></a>, it is important to note that an XMPP server MUST NOT leak presence.  In particular at the core XMPP level, real-time addressing and network availability is associated with a specific connected resource; therefore, any disclosure of a connected resource's full JID comprises a presence leak.  To help prevent such a presence leak, a server MUST NOT return different stanza errors depending on whether a potential attacker sends XML stanzas to the entity's bare JID (&lt;localpart@domainpart&gt;) or full JID (&lt;localpart@domainpart/resourcepart&gt;).
+</p>
+<a name="security-harvesting"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.11"></a><h3>13.11.&nbsp;
+Directory Harvesting</h3>
+
+<p>If a server generates an error stanza in response to receiving a stanza for a user account that does not exist, using the &lt;service-unavailable/&gt; stanza error condition (<a class='info' href='#stanzas-error-conditions-service-unavailable'>Section&nbsp;8.3.3.19<span> (</span><span class='info'>service-unavailable</span><span>)</span></a>) can help protect against directory harvesting attacks, since this is the same error condition that is returned if, for instance, the namespace of an IQ child element is not understood, or if "offline message storage" (<a class='info' href='#XEP-0160'>[XEP&#8209;0160]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices for Handling Offline Messages,&rdquo; January&nbsp;2006.</span><span>)</span></a>) or message forwarding is not enabled for a domain.  However, subtle differences in the exact XML of error stanzas, as well as in the timing with which such errors are returned, can enable an attacker to determine the network presence of a user when more advanced blocking technologies are not used (see for instance <a class='info' href='#XEP-0016'>[XEP&#8209;0016]<span> (</span><span class='info'>Millard, P. and P. Saint-Andre, &ldquo;Privacy Lists,&rdquo; February&nbsp;2007.</span><span>)</span></a> and <a class='info' href='#XEP-0191'>[XEP&#8209;0191]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Simple Communications Blocking,&rdquo; February&nbsp;2007.</span><span>)</span></a>).  Therefore, a server that exercises a higher level of caution might not return any error at all in response to certain kinds of received stanzas, so that a non-existent user appears to behave like a user that has no interest in conversing with the sender.
+</p>
+<a name="security-dos"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.12"></a><h3>13.12.&nbsp;
+Denial of Service</h3>
+
+<p><a class='info' href='#DOS'>[DOS]<span> (</span><span class='info'>Handley, M., Rescorla, E., and IAB, &ldquo;Internet Denial-of-Service Considerations,&rdquo; December&nbsp;2006.</span><span>)</span></a> defines denial of service as follows:
+</p>
+<p>
+        </p>
+<blockquote class="text"><dl>
+<dt></dt>
+<dd>A denial-of-service (DoS) attack is an attack in which one or more machines target a victim and attempt to prevent the victim from doing useful work. The victim can be a network server, client or router, a network link or an entire network, an individual Internet user or a company doing business using the Internet, an Internet Service Provider (ISP), country, or any combination of or variant on these.
+</dd>
+</dl></blockquote><p>
+      
+</p>
+<p>Some considerations discussed in this document help to prevent denial-of-service attacks (e.g., the mandate that a server MUST NOT process XML stanzas from clients that have not yet provided appropriate authentication credentials and MUST NOT process XML stanzas from peer servers whose identity it has not either authenticated via SASL or weakly verified via Server Dialback).
+</p>
+<p>In addition, <a class='info' href='#XEP-0205'>[XEP&#8209;0205]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices to Discourage Denial of Service Attacks,&rdquo; January&nbsp;2009.</span><span>)</span></a> provides a detailed discussion of potential denial-of-service attacks against XMPP systems along with best practices for preventing such attacks.  The recommendations include:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>A server implementation SHOULD enable a server administrator to limit the number of TCP connections that it will accept from a given IP address at any one time.  If an entity attempts to connect but the maximum number of TCP connections has been reached, the receiving server MUST NOT allow the new connection to proceed.
+</li>
+<li>A server implementation SHOULD enable a server administrator to limit the number of TCP connection attempts that it will accept from a given IP address in a given time period.  If an entity attempts to connect but the maximum number of connection attempts has been reached, the receiving server MUST NOT allow the new connection to proceed.
+</li>
+<li>A server implementation SHOULD enable a server administrator to limit the number of connected resources it will allow an account to bind at any one time.  If a client attempts to bind a resource but it has already reached the configured number of allowable resources, the receiving server MUST return a &lt;resource-constraint/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-resource-constraint'>Section&nbsp;8.3.3.18<span> (</span><span class='info'>resource-constraint</span><span>)</span></a>).
+</li>
+<li>A server implementation SHOULD enable a server administrator to limit the size of stanzas it will accept from a connected client or peer server (where "size" is inclusive of all XML markup as defined in Section 2.4 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>, from the opening "&lt;" character of the stanza to the closing "&gt;" character).  A deployed server's maximum stanza size MUST NOT be smaller than 10000 bytes, which reflects a reasonable compromise between the benefits of expressiveness for originating entities and the costs of stanza processing for servers.  A server implementation SHOULD NOT blindly set 10000 bytes as the value for all deployments but instead SHOULD enable server administrators to set their own limits.  If a connected resource or peer server sends a stanza that violates the upper limit, the receiving server MUST either return a &lt;policy-violation/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-policy-violation'>Section&nbsp;8.3.3.12<span> (</span><span class='info'>policy-violation</span><span>)</span></a>), thus allowing the sender to recover, or close the stream with a &lt;policy-violation/&gt; stream error (<a class='info' href='#streams-error-conditions-policy-violation'>Section&nbsp;4.9.3.14<span> (</span><span class='info'>policy-violation</span><span>)</span></a>).
+</li>
+<li>A server implementation SHOULD enable a server administrator to limit the number of XML stanzas that a connected client is allowed to send to distinct recipients within a given time period.  If a connected client sends too many stanzas to distinct recipients in a given time period, the receiving server SHOULD NOT process the stanza and instead SHOULD return a &lt;policy-violation/&gt; stanza error (<a class='info' href='#stanzas-error-conditions-policy-violation'>Section&nbsp;8.3.3.12<span> (</span><span class='info'>policy-violation</span><span>)</span></a>).
+</li>
+<li>A server implementation SHOULD enable a server administrator to limit the amount of bandwidth it will allow a connected client or peer server to use in a given time period.
+</li>
+<li>A server implementation MAY enable a server administrator to limit the types of stanzas (based on the extended content "payload") that it will allow a connected resource or peer server send over an active connection.  Such limits and restrictions are a matter of deployment policy.
+</li>
+<li>A server implementation MAY refuse to route or deliver any stanza that it considers to be abusive, with or without returning an error to the sender.
+</li>
+</ol><p>
+      
+</p>
+<p>For more detailed recommendations regarding denial-of-service attacks in XMPP systems, refer to <a class='info' href='#XEP-0205'>[XEP&#8209;0205]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices to Discourage Denial of Service Attacks,&rdquo; January&nbsp;2009.</span><span>)</span></a>.
+</p>
+<a name="security-firewalls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.13"></a><h3>13.13.&nbsp;
+Firewalls</h3>
+
+<p>Although DNS SRV records can instruct connecting entities to use TCP ports other than 5222 (client-to-server) and 5269 (server-to-server), communication using XMPP typically occurs over those ports, which are registered with the IANA (see <a class='info' href='#iana'>Section&nbsp;14<span> (</span><span class='info'>IANA Considerations</span><span>)</span></a>).  Use of these well-known ports allows administrators to easily enable or disable XMPP activity through existing and commonly deployed firewalls.
+</p>
+<a name="security-federation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.14"></a><h3>13.14.&nbsp;
+Interdomain Federation</h3>
+
+<p>The term "federation" is commonly used to describe communication between two servers.
+</p>
+<p>Because service provisioning is a matter of policy, it is OPTIONAL for any given server to support federation.  If a particular server enables federation, it SHOULD enable strong security as previously described to ensure both authentication and confidentiality; compliant implementations SHOULD support TLS and SASL for this purpose.
+</p>
+<p>Before RFC 3920 defined TLS plus SASL EXTERNAL with certificates for encryption and authentication of server-to-server streams, the only method for weak identity verification of a peer server was Server Dialback as defined in <a class='info' href='#XEP-0220'>[XEP&#8209;0220]<span> (</span><span class='info'>Miller, J., Saint-Andre, P., and P. Hancke, &ldquo;Server Dialback,&rdquo; March&nbsp;2010.</span><span>)</span></a>.  Even when <a class='info' href='#DNSSEC'>[DNSSEC]<span> (</span><span class='info'>Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, &ldquo;DNS Security Introduction and Requirements,&rdquo; March&nbsp;2005.</span><span>)</span></a> is used, Server Dialback provides only weak identity verification and provides no confidentiality or integrity.  At the time of writing, Server Dialback is still the most widely used technique for some level of assurance over server-to-server streams.  This reality introduces the possibility of a downgrade attack from TLS + SASL EXTERNAL to Server Dialback if an attacker can gain control of the channel and therefore convince the initiating server that the receiving server does not support TLS or does not have an appropriate certificate.  To help prevent this attack, the parties SHOULD protect the channel using TLS before proceeding, even if the presented certificates are self-signed or otherwise untrusted.
+</p>
+<a name="security-nonrepudiation"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13.15"></a><h3>13.15.&nbsp;
+Non-Repudiation</h3>
+
+<p>Systems that provide both peer entity authentication and data integrity have the potential to enable an entity to prove to a third party that another entity intended to send particular data.  Although XMPP systems can provide both peer entity authentication and data integrity, XMPP was never designed to provide non-repudiation.
+</p>
+<a name="iana"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14"></a><h3>14.&nbsp;
+IANA Considerations</h3>
+
+<p>The following subsections update the registrations provided in <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a>.  This section is to be interpreted according to <a class='info' href='#IANA-GUIDE'>[IANA&#8209;GUIDE]<span> (</span><span class='info'>Narten, T. and H. Alvestrand, &ldquo;Guidelines for Writing an IANA Considerations Section in RFCs,&rdquo; May&nbsp;2008.</span><span>)</span></a>.
+</p>
+<a name="iana-ns-tls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.1"></a><h3>14.1.&nbsp;
+XML Namespace Name for TLS Data</h3>
+
+<p>A URN sub-namespace for STARTTLS negotiation data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows.  (This namespace name adheres to the format defined in <a class='info' href='#XML-REG'>[XML&#8209;REG]<span> (</span><span class='info'>Mealling, M., &ldquo;The IETF XML Registry,&rdquo; January&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>URI:</dt>
+<dd>urn:ietf:params:xml:ns:xmpp-tls
+</dd>
+<dt>Specification:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Description:</dt>
+<dd>This is the XML namespace name for STARTTLS negotiation data in the Extensible Messaging and Presence Protocol (XMPP) as defined by RFC 6120.
+</dd>
+<dt>Registrant Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+</dl></blockquote>
+
+<a name="iana-ns-sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.2"></a><h3>14.2.&nbsp;
+XML Namespace Name for SASL Data</h3>
+
+<p>A URN sub-namespace for SASL negotiation data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows.  (This namespace name adheres to the format defined in <a class='info' href='#XML-REG'>[XML&#8209;REG]<span> (</span><span class='info'>Mealling, M., &ldquo;The IETF XML Registry,&rdquo; January&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>URI:</dt>
+<dd>urn:ietf:params:xml:ns:xmpp-sasl
+</dd>
+<dt>Specification:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Description:</dt>
+<dd>This is the XML namespace name for SASL negotiation data in the Extensible Messaging and Presence Protocol (XMPP) as defined by RFC 6120.
+</dd>
+<dt>Registrant Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+</dl></blockquote>
+
+<a name="iana-ns-streams"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.3"></a><h3>14.3.&nbsp;
+XML Namespace Name for Stream Errors</h3>
+
+<p>A URN sub-namespace for stream error data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows.  (This namespace name adheres to the format defined in <a class='info' href='#XML-REG'>[XML&#8209;REG]<span> (</span><span class='info'>Mealling, M., &ldquo;The IETF XML Registry,&rdquo; January&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>URI:</dt>
+<dd>urn:ietf:params:xml:ns:xmpp-streams
+</dd>
+<dt>Specification:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Description:</dt>
+<dd>This is the XML namespace name for stream error data in the Extensible Messaging and Presence Protocol (XMPP) as defined by RFC 6120.
+</dd>
+<dt>Registrant Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+</dl></blockquote>
+
+<a name="iana-ns-bind"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.4"></a><h3>14.4.&nbsp;
+XML Namespace Name for Resource Binding</h3>
+
+<p>A URN sub-namespace for resource binding in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows.  (This namespace name adheres to the format defined in <a class='info' href='#XML-REG'>[XML&#8209;REG]<span> (</span><span class='info'>Mealling, M., &ldquo;The IETF XML Registry,&rdquo; January&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>URI:</dt>
+<dd>urn:ietf:params:xml:ns:xmpp-bind
+</dd>
+<dt>Specification:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Description:</dt>
+<dd>This is the XML namespace name for resource binding in the Extensible Messaging and Presence Protocol (XMPP) as defined by RFC 6120.
+</dd>
+<dt>Registrant Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+</dl></blockquote>
+
+<a name="iana-ns-stanzas"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.5"></a><h3>14.5.&nbsp;
+XML Namespace Name for Stanza Errors</h3>
+
+<p>A URN sub-namespace for stanza error data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows.  (This namespace name adheres to the format defined in <a class='info' href='#XML-REG'>[XML&#8209;REG]<span> (</span><span class='info'>Mealling, M., &ldquo;The IETF XML Registry,&rdquo; January&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p></p>
+<blockquote class="text"><dl>
+<dt>URI:</dt>
+<dd>urn:ietf:params:xml:ns:xmpp-stanzas
+</dd>
+<dt>Specification:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Description:</dt>
+<dd>This is the XML namespace name for stanza error data in the Extensible Messaging and Presence Protocol (XMPP) as defined by RFC 6120.
+</dd>
+<dt>Registrant Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+</dl></blockquote>
+
+<a name="iana-gssapi"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.6"></a><h3>14.6.&nbsp;
+GSSAPI Service Name</h3>
+
+<p>The IANA has registered "xmpp" as a <a class='info' href='#GSS-API'>[GSS&#8209;API]<span> (</span><span class='info'>Linn, J., &ldquo;Generic Security Service Application Program Interface Version 2, Update 1,&rdquo; January&nbsp;2000.</span><span>)</span></a> service name, as defined under <a class='info' href='#sasl-def'>Section&nbsp;6.6<span> (</span><span class='info'>SASL Definition</span><span>)</span></a>.
+</p>
+<a name="iana-ports"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.14.7"></a><h3>14.7.&nbsp;
+Port Numbers and Service Names</h3>
+
+<p>The IANA has registered "xmpp-client" and "xmpp-server" as keywords for <a class='info' href='#TCP'>[TCP]<span> (</span><span class='info'>Postel, J., &ldquo;Transmission Control Protocol,&rdquo; September&nbsp;1981.</span><span>)</span></a> ports 5222 and 5269, respectively.  In accordance with <a class='info' href='#IANA-PORTS'>[IANA&#8209;PORTS]<span> (</span><span class='info'>Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, &ldquo;Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Transport Protocol Port Number and Service Name Registry,&rdquo; February&nbsp;2011.</span><span>)</span></a>, this document updates the existing registration, as follows.
+</p>
+<p>
+        </p>
+<blockquote class="text"><dl>
+<dt>Service Name:</dt>
+<dd>xmpp-client
+</dd>
+<dt>Transport Protocol:</dt>
+<dd>TCP
+</dd>
+<dt>Description:</dt>
+<dd>A service offering support for connections by XMPP client applications
+</dd>
+<dt>Registrant:</dt>
+<dd>IETF XMPP Working Group
+</dd>
+<dt>Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+<dt>Reference:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Port Number:</dt>
+<dd>5222
+</dd>
+</dl></blockquote><p>
+      
+</p>
+<p>
+        </p>
+<blockquote class="text"><dl>
+<dt>Service Name:</dt>
+<dd>xmpp-server
+</dd>
+<dt>Transport Protocol:</dt>
+<dd>TCP
+</dd>
+<dt>Description:</dt>
+<dd>A service offering support for connections by XMPP server applications
+</dd>
+<dt>Registrant:</dt>
+<dd>IETF XMPP Working Group
+</dd>
+<dt>Contact:</dt>
+<dd>IESG &lt;iesg@ietf.org&gt;
+</dd>
+<dt>Reference:</dt>
+<dd>RFC 6120
+</dd>
+<dt>Port Number:</dt>
+<dd>5269
+</dd>
+</dl></blockquote><p>
+      
+</p>
+<a name="conformance"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.15"></a><h3>15.&nbsp;
+Conformance Requirements</h3>
+
+<p>This section describes a protocol feature set that summarizes the conformance requirements of this specification.  This feature set is appropriate for use in software certification, interoperability testing, and implementation reports.  For each feature, this section provides the following information:
+</p>
+<p>
+      </p>
+<ul class="text">
+<li>A human-readable name
+</li>
+<li>An informational description
+</li>
+<li>A reference to the particular section of this document that normatively defines the feature
+</li>
+<li>Whether the feature applies to the Client role, the Server
+        role, or both (where "N/A" signifies that the feature is not
+        applicable to the specified role)
+</li>
+<li>Whether the feature MUST or SHOULD be implemented, where the capitalized terms are to be understood as described in <a class='info' href='#KEYWORDS'>[KEYWORDS]<span> (</span><span class='info'>Bradner, S., &ldquo;Key words for use in RFCs to Indicate Requirement Levels,&rdquo; March&nbsp;1997.</span><span>)</span></a>
+</li>
+</ul><p>
+    
+</p>
+<p>The feature set specified here attempts to adhere to the concepts and formats proposed by Larry Masinter within the IETF's NEWTRK Working Group in 2005, as captured in <a class='info' href='#INTEROP'>[INTEROP]<span> (</span><span class='info'>Masinter, L., &ldquo;Formalizing IETF Interoperability Reporting,&rdquo; October&nbsp;2005.</span><span>)</span></a>.  Although this feature set is more detailed than called for by <a class='info' href='#REPORTS'>[REPORTS]<span> (</span><span class='info'>Dusseault, L. and R. Sparks, &ldquo;Guidance on Interoperation and Implementation Reports for Advancement to Draft Standard,&rdquo; September&nbsp;2009.</span><span>)</span></a>, it provides a suitable basis for the generation of implementation reports to be submitted in support of advancing this specification from Proposed Standard to Draft Standard in accordance with <a class='info' href='#PROCESS'>[PROCESS]<span> (</span><span class='info'>Bradner, S., &ldquo;The Internet Standards Process -- Revision 3,&rdquo; October&nbsp;1996.</span><span>)</span></a>.
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>bind-gen
+</dd>
+<dt>Description:</dt>
+<dd>Generate a random resource on demand.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#bind-servergen'>Section&nbsp;7.6<span> (</span><span class='info'>Server-Generated Resource Identifier</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>bind-mtn
+</dd>
+<dt>Description:</dt>
+<dd>Consider resource binding as mandatory-to-negotiate.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#bind-rules-mtn'>Section&nbsp;7.3.1<span> (</span><span class='info'>Mandatory-to-Negotiate</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>bind-restart
+</dd>
+<dt>Description:</dt>
+<dd>Do not restart the stream after negotiation of resource binding.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#bind-rules-restart'>Section&nbsp;7.3.2<span> (</span><span class='info'>Restart</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>bind-support
+</dd>
+<dt>Description:</dt>
+<dd>Support binding of client resources to an authenticated stream.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#bind'>Section&nbsp;7<span> (</span><span class='info'>Resource Binding</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>sasl-correlate
+</dd>
+<dt>Description:</dt>
+<dd>When authenticating a stream peer using SASL, correlate the authentication identifier resulting from SASL negotiation with the 'from' address (if any) of the stream header it received from the peer.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sasl-process-neg-success'>Section&nbsp;6.4.6<span> (</span><span class='info'>SASL Success</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>sasl-errors
+</dd>
+<dt>Description:</dt>
+<dd>Support SASL errors during the negotiation process.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sasl-errors'>Section&nbsp;6.5<span> (</span><span class='info'>SASL Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>sasl-mtn
+</dd>
+<dt>Description:</dt>
+<dd>Consider SASL as mandatory-to-negotiate.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sasl-rules-mtn'>Section&nbsp;6.3.1<span> (</span><span class='info'>Mandatory-to-Negotiate</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>sasl-restart
+</dd>
+<dt>Description:</dt>
+<dd>Initiate or handle a stream restart after SASL negotiation.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sasl-rules-restart'>Section&nbsp;6.3.2<span> (</span><span class='info'>Restart</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>sasl-support
+</dd>
+<dt>Description:</dt>
+<dd>Support the Simple Authentication and Security Layer for stream authentication.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sasl'>Section&nbsp;6<span> (</span><span class='info'>SASL Negotiation</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>security-mti-auth-scram
+</dd>
+<dt>Description:</dt>
+<dd>Support the SASL SCRAM mechanism for authentication only (this implies support for both the SCRAM&#8209;SHA&#8209;1 and SCRAM&#8209;SHA&#8209;1&#8209;PLUS variants).
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>security-mti-both-external
+</dd>
+<dt>Description:</dt>
+<dd>Support TLS with SASL EXTERNAL for confidentiality and authentication.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>security-mti-both-plain
+</dd>
+<dt>Description:</dt>
+<dd>Support TLS using the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite plus the SASL PLAIN mechanism for confidentiality and authentication.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server MAY.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>security-mti-both-scram
+</dd>
+<dt>Description:</dt>
+<dd>Support TLS using the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite plus the SCRAM-SHA-1 and SCRAM-SHA-1-PLUS variants of the SASL SCRAM mechanism for confidentiality and authentication.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>security-mti-confidentiality
+</dd>
+<dt>Description:</dt>
+<dd>Support TLS using the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite for confidentiality only.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-mti'>Section&nbsp;13.8<span> (</span><span class='info'>Mandatory-to-Implement TLS and SASL Technologies</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-from
+</dd>
+<dt>Description:</dt>
+<dd>Support the common 'from' attribute for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-from'>Section&nbsp;8.1.2<span> (</span><span class='info'>from</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-from-stamp
+</dd>
+<dt>Description:</dt>
+<dd>Stamp or rewrite the 'from' address of all stanzas received from connected clients.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-from-c2s'>Section&nbsp;8.1.2.1<span> (</span><span class='info'>Client-to-Server Streams</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-from-validate
+</dd>
+<dt>Description:</dt>
+<dd>Validate the 'from' address of all stanzas received from peer servers.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-from-s2s'>Section&nbsp;8.1.2.2<span> (</span><span class='info'>Server-to-Server Streams</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-id
+</dd>
+<dt>Description:</dt>
+<dd>Support the common 'id' attribute for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-id'>Section&nbsp;8.1.3<span> (</span><span class='info'>id</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-to
+</dd>
+<dt>Description:</dt>
+<dd>Support the common 'to' attribute for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-to'>Section&nbsp;8.1.1<span> (</span><span class='info'>to</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-to-validate
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that all stanzas received from peer servers include a 'to' address.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-to'>Section&nbsp;8.1.1<span> (</span><span class='info'>to</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-type
+</dd>
+<dt>Description:</dt>
+<dd>Support the common 'type' attribute for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-type'>Section&nbsp;8.1.4<span> (</span><span class='info'>type</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-attribute-xmllang
+</dd>
+<dt>Description:</dt>
+<dd>Support the common 'xml:lang' attribute for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-attributes-lang'>Section&nbsp;8.1.5<span> (</span><span class='info'>xml:lang</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-error
+</dd>
+<dt>Description:</dt>
+<dd>Generate and handle stanzas of type "error" for all stanza kinds.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-error-child
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that stanzas of type "error" include an &lt;error/&gt; child element.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-error-id
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that stanzas of type "error" preserve the 'id' provided in the triggering stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-error-reply
+</dd>
+<dt>Description:</dt>
+<dd>Do not reply to a stanza of type "error" with another stanza of type "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-error'>Section&nbsp;8.3<span> (</span><span class='info'>Stanza Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-extension
+</dd>
+<dt>Description:</dt>
+<dd>Correctly process XML data qualified by an unsupported XML namespace, where "correctly process" means to ignore that portion of the stanza in the case of a message or presence stanza and return an error in the case of an IQ stanza (for the intended recipient), and to route or deliver the stanza (for a routing entity such as a server).
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-extended'>Section&nbsp;8.4<span> (</span><span class='info'>Extended Content</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-iq-child
+</dd>
+<dt>Description:</dt>
+<dd>Include exactly one child element in an &lt;iq/&gt; stanza of type "get" or "set", zero or one child elements in an &lt;iq/&gt; stanza of type "result", and one or two child elements in an &lt;iq/&gt; stanza of type "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-iq-id
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that all &lt;iq/&gt; stanzas include an 'id' attribute.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-iq-reply
+</dd>
+<dt>Description:</dt>
+<dd>Reply to an &lt;iq/&gt; stanza of type "get" or "set" with an &lt;iq/&gt; stanza of type "result" or "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-iq-type
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that all &lt;iq/&gt; stanzas include a 'type' attribute whose value is "get", "set", "result", or "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-kind-iq
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;iq/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-iq'>Section&nbsp;8.2.3<span> (</span><span class='info'>IQ Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-kind-message
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;message/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-message'>Section&nbsp;8.2.1<span> (</span><span class='info'>Message Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stanza-kind-presence
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;presence/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#stanzas-semantics-presence'>Section&nbsp;8.2.2<span> (</span><span class='info'>Presence Semantics</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-initial-from
+</dd>
+<dt>Description:</dt>
+<dd>Include a 'from' attribute in the initial stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-from'>Section&nbsp;4.7.1<span> (</span><span class='info'>from</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-initial-lang
+</dd>
+<dt>Description:</dt>
+<dd>Include an 'xml:lang' attribute in the initial stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-xmllang'>Section&nbsp;4.7.4<span> (</span><span class='info'>xml:lang</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-initial-to
+</dd>
+<dt>Description:</dt>
+<dd>Include a 'to' attribute in the initial stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-to'>Section&nbsp;4.7.2<span> (</span><span class='info'>to</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-response-from
+</dd>
+<dt>Description:</dt>
+<dd>Include a 'from' attribute in the response stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-from'>Section&nbsp;4.7.1<span> (</span><span class='info'>from</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-response-id
+</dd>
+<dt>Description:</dt>
+<dd>Include an 'id' attribute in the response stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-id'>Section&nbsp;4.7.3<span> (</span><span class='info'>id</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-response-id-unique
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that the 'id' attribute in the response stream header is unique within the context of the receiving entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-id'>Section&nbsp;4.7.3<span> (</span><span class='info'>id</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-attribute-response-to
+</dd>
+<dt>Description:</dt>
+<dd>Include a 'to' attribute in the response stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-attr-to'>Section&nbsp;4.7.2<span> (</span><span class='info'>to</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-error-generate
+</dd>
+<dt>Description:</dt>
+<dd>Generate a stream error (followed by a closing stream tag and termination of the TCP connection) upon detecting a stream-related error condition.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-error'>Section&nbsp;4.9<span> (</span><span class='info'>Stream Errors</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-fqdn-resolution
+</dd>
+<dt>Description:</dt>
+<dd>Resolve FQDNs before opening a TCP connection to the receiving entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tcp-resolution'>Section&nbsp;3.2<span> (</span><span class='info'>Resolution of Fully Qualified Domain Names</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-negotiation-complete
+</dd>
+<dt>Description:</dt>
+<dd>Do not consider the stream negotiation process to be complete until the receiving entity sends a stream features advertisement that is empty or that contains only voluntary-to-negotiate features.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-negotiation-complete'>Section&nbsp;4.3.5<span> (</span><span class='info'>Completion of Stream Negotiation</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-negotiation-features
+</dd>
+<dt>Description:</dt>
+<dd>Send stream features after sending a response stream header.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-negotiation-features'>Section&nbsp;4.3.2<span> (</span><span class='info'>Stream Features Format</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-negotiation-restart
+</dd>
+<dt>Description:</dt>
+<dd>Consider the previous stream to be replaced upon negotiation of a stream feature that necessitates a stream restart, and send or receive a new initial stream header after negotiation of such a stream feature.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-negotiation-restart'>Section&nbsp;4.3.3<span> (</span><span class='info'>Restarts</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-reconnect
+</dd>
+<dt>Description:</dt>
+<dd>Reconnect with exponential backoff if a TCP connection is terminated unexpectedly.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tcp-reconnect'>Section&nbsp;3.3<span> (</span><span class='info'>Reconnection</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>stream-tcp-binding
+</dd>
+<dt>Description:</dt>
+<dd>Bind an XML stream to a TCP connection.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tcp'>Section&nbsp;3<span> (</span><span class='info'>TCP Binding</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>tls-certs
+</dd>
+<dt>Description:</dt>
+<dd>Check the identity specified in a certificate that is presented during TLS negotiation.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-certificates-validation'>Section&nbsp;13.7.2<span> (</span><span class='info'>Certificate Validation</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>tls-mtn
+</dd>
+<dt>Description:</dt>
+<dd>Consider TLS as mandatory-to-negotiate if STARTTLS is the only feature advertised or if the STARTTLS feature advertisement includes an empty &lt;required/&gt; element.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tls-rules-mtn'>Section&nbsp;5.3.1<span> (</span><span class='info'>Mandatory-to-Negotiate</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>tls-restart
+</dd>
+<dt>Description:</dt>
+<dd>Initiate or handle a stream restart after TLS negotiation.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tls-rules-restart'>Section&nbsp;5.3.2<span> (</span><span class='info'>Restart</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>tls-support
+</dd>
+<dt>Description:</dt>
+<dd>Support Transport Layer Security for stream encryption.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#tls'>Section&nbsp;5<span> (</span><span class='info'>STARTTLS Negotiation</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>tls-correlate
+</dd>
+<dt>Description:</dt>
+<dd>When validating a certificate presented by a stream peer during TLS negotiation, correlate the validated identity with the 'from' address (if any) of the stream header it received from the peer.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#security-certificates-validation'>Section&nbsp;13.7.2<span> (</span><span class='info'>Certificate Validation</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-namespace-content-client
+</dd>
+<dt>Description:</dt>
+<dd>Support 'jabber:client' as a content namespace.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-ns-content'>Section&nbsp;4.8.2<span> (</span><span class='info'>Content Namespace</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-namespace-content-server
+</dd>
+<dt>Description:</dt>
+<dd>Support 'jabber:server' as a content namespace.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-ns-content'>Section&nbsp;4.8.2<span> (</span><span class='info'>Content Namespace</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-namespace-streams-declaration
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that there is a namespace declaration for the 'http://etherx.jabber.org/streams' namespace.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-ns-stream'>Section&nbsp;4.8.1<span> (</span><span class='info'>Stream Namespace</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-namespace-streams-prefix
+</dd>
+<dt>Description:</dt>
+<dd>Ensure that all elements qualified by the 'http://etherx.jabber.org/streams' namespace are prefixed by the prefix (if any) defined in the namespace declaration.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#streams-ns-stream'>Section&nbsp;4.8.1<span> (</span><span class='info'>Stream Namespace</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-restriction-comment
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept XML comments.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-restriction-dtd
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept internal or external DTD subsets.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-restriction-pi
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept XML processing instructions.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-restriction-ref
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept internal or external entity references with the exception of the predefined entities.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-restrictions'>Section&nbsp;11.1<span> (</span><span class='info'>XML Restrictions</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-wellformed-xml
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept data that is not XML-well-formed.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-wellformed'>Section&nbsp;11.3<span> (</span><span class='info'>Well-Formedness</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>xml-wellformed-ns
+</dd>
+<dt>Description:</dt>
+<dd>Do not generate or accept data that is not namespace-well-formed.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#xml-wellformed'>Section&nbsp;11.3<span> (</span><span class='info'>Well-Formedness</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<a name="rfc.references"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.16"></a><h3>16.&nbsp;
+References</h3>
+
+<a name="rfc.references1"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>16.1.&nbsp;Normative References</h3>
+<table width="99%" border="0">
+<tr><td class="author-text" valign="top"><a name="BASE64">[BASE64]</a></td>
+<td class="author-text">Josefsson, S., &ldquo;<a href="http://tools.ietf.org/html/rfc4648">The Base16, Base32, and Base64 Data Encodings</a>,&rdquo; RFC&nbsp;4648, October&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4648.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="CHANNEL">[CHANNEL]</a></td>
+<td class="author-text">Williams, N., &ldquo;<a href="http://tools.ietf.org/html/rfc5056">On the Use of Channel Bindings to Secure Channels</a>,&rdquo; RFC&nbsp;5056, November&nbsp;2007 (<a href="http://www.rfc-editor.org/rfc/rfc5056.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="CHANNEL-TLS">[CHANNEL-TLS]</a></td>
+<td class="author-text">Altman, J., Williams, N., and L. Zhu, &ldquo;<a href="http://tools.ietf.org/html/rfc5929">Channel Bindings for TLS</a>,&rdquo; RFC&nbsp;5929, July&nbsp;2010 (<a href="http://www.rfc-editor.org/rfc/rfc5929.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="CHARSETS">[CHARSETS]</a></td>
+<td class="author-text"><a href="mailto:Harald.T.Alvestrand@uninett.no">Alvestrand, H.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2277">IETF Policy on Character Sets and Languages</a>,&rdquo; BCP&nbsp;18, RFC&nbsp;2277, January&nbsp;1998 (<a href="http://www.rfc-editor.org/rfc/rfc2277.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2277.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2277.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DNS-CONCEPTS">[DNS-CONCEPTS]</a></td>
+<td class="author-text">Mockapetris, P., &ldquo;<a href="http://tools.ietf.org/html/rfc1034">Domain names - concepts and facilities</a>,&rdquo; STD&nbsp;13, RFC&nbsp;1034, November&nbsp;1987 (<a href="http://www.rfc-editor.org/rfc/rfc1034.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DNS-SRV">[DNS-SRV]</a></td>
+<td class="author-text"><a href="mailto:arnt@troll.no">Gulbrandsen, A.</a>, Vixie, P., and <a href="mailto:levone@microsoft.com">L. Esibov</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2782">A DNS RR for specifying the location of services (DNS SRV)</a>,&rdquo; RFC&nbsp;2782, February&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2782.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IPv6-ADDR">[IPv6-ADDR]</a></td>
+<td class="author-text">Kawamura, S. and M. Kawashima, &ldquo;<a href="http://tools.ietf.org/html/rfc5952">A Recommendation for IPv6 Address Text Representation</a>,&rdquo; RFC&nbsp;5952, August&nbsp;2010 (<a href="http://www.rfc-editor.org/rfc/rfc5952.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="KEYWORDS">[KEYWORDS]</a></td>
+<td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>,&rdquo; BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997 (<a href="http://www.rfc-editor.org/rfc/rfc2119.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2119.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2119.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="LANGMATCH">[LANGMATCH]</a></td>
+<td class="author-text">Phillips, A. and M. Davis, &ldquo;<a href="http://tools.ietf.org/html/rfc4647">Matching of Language Tags</a>,&rdquo; BCP&nbsp;47, RFC&nbsp;4647, September&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4647.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="LANGTAGS">[LANGTAGS]</a></td>
+<td class="author-text">Phillips, A. and M. Davis, &ldquo;<a href="http://tools.ietf.org/html/rfc5646">Tags for Identifying Languages</a>,&rdquo; BCP&nbsp;47, RFC&nbsp;5646, September&nbsp;2009 (<a href="http://www.rfc-editor.org/rfc/rfc5646.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="OCSP">[OCSP]</a></td>
+<td class="author-text"><a href="mailto:mmyers@verisign.com">Myers, M.</a>, <a href="mailto:rankney@erols.com">Ankney, R.</a>, <a href="mailto:ambarish@valicert.com">Malpani, A.</a>, <a href="mailto:galperin@mycfo.com">Galperin, S.</a>, and <a href="mailto:cadams@entrust.com">C. Adams</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2560">X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP</a>,&rdquo; RFC&nbsp;2560, June&nbsp;1999 (<a href="http://www.rfc-editor.org/rfc/rfc2560.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PKIX">[PKIX]</a></td>
+<td class="author-text">Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, &ldquo;<a href="http://tools.ietf.org/html/rfc5280">Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</a>,&rdquo; RFC&nbsp;5280, May&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5280.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PKIX-ALGO">[PKIX-ALGO]</a></td>
+<td class="author-text">Jonsson, J. and B. Kaliski, &ldquo;<a href="http://tools.ietf.org/html/rfc3447">Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1</a>,&rdquo; RFC&nbsp;3447, February&nbsp;2003 (<a href="http://www.rfc-editor.org/rfc/rfc3447.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PKIX-SRV">[PKIX-SRV]</a></td>
+<td class="author-text">Santesson, S., &ldquo;<a href="http://tools.ietf.org/html/rfc4985">Internet X.509 Public Key Infrastructure Subject Alternative Name for Expression of Service Name</a>,&rdquo; RFC&nbsp;4985, August&nbsp;2007 (<a href="http://www.rfc-editor.org/rfc/rfc4985.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PLAIN">[PLAIN]</a></td>
+<td class="author-text">Zeilenga, K., &ldquo;<a href="http://tools.ietf.org/html/rfc4616">The PLAIN Simple Authentication and Security Layer (SASL) Mechanism</a>,&rdquo; RFC&nbsp;4616, August&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4616.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="RANDOM">[RANDOM]</a></td>
+<td class="author-text">Eastlake, D., Schiller, J., and S. Crocker, &ldquo;<a href="http://tools.ietf.org/html/rfc4086">Randomness Requirements for Security</a>,&rdquo; BCP&nbsp;106, RFC&nbsp;4086, June&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4086.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SASL">[SASL]</a></td>
+<td class="author-text">Melnikov, A. and K. Zeilenga, &ldquo;<a href="http://tools.ietf.org/html/rfc4422">Simple Authentication and Security Layer (SASL)</a>,&rdquo; RFC&nbsp;4422, June&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4422.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SCRAM">[SCRAM]</a></td>
+<td class="author-text">Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, &ldquo;<a href="http://tools.ietf.org/html/rfc5802">Salted Challenge Response Authentication Mechanism (SCRAM) SASL and GSS-API Mechanisms</a>,&rdquo; RFC&nbsp;5802, July&nbsp;2010 (<a href="http://www.rfc-editor.org/rfc/rfc5802.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="STRONGSEC">[STRONGSEC]</a></td>
+<td class="author-text">Schiller, J., &ldquo;<a href="http://tools.ietf.org/html/rfc3365">Strong Security Requirements for Internet Engineering Task Force Standard Protocols</a>,&rdquo; BCP&nbsp;61, RFC&nbsp;3365, August&nbsp;2002 (<a href="http://www.rfc-editor.org/rfc/rfc3365.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TCP">[TCP]</a></td>
+<td class="author-text">Postel, J., &ldquo;<a href="http://tools.ietf.org/html/rfc793">Transmission Control Protocol</a>,&rdquo; STD&nbsp;7, RFC&nbsp;793, September&nbsp;1981 (<a href="http://www.rfc-editor.org/rfc/rfc793.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS">[TLS]</a></td>
+<td class="author-text">Dierks, T. and E. Rescorla, &ldquo;<a href="http://tools.ietf.org/html/rfc5246">The Transport Layer Security (TLS) Protocol Version 1.2</a>,&rdquo; RFC&nbsp;5246, August&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5246.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-CERTS">[TLS-CERTS]</a></td>
+<td class="author-text">Saint-Andre, P. and J. Hodges, &ldquo;<a href="http://tools.ietf.org/html/rfc6125">Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)</a>,&rdquo; RFC&nbsp;6125, March&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-NEG">[TLS-NEG]</a></td>
+<td class="author-text">Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, &ldquo;<a href="http://tools.ietf.org/html/rfc5746">Transport Layer Security (TLS) Renegotiation Indication Extension</a>,&rdquo; RFC&nbsp;5746, February&nbsp;2010 (<a href="http://www.rfc-editor.org/rfc/rfc5746.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-SSL2">[TLS-SSL2]</a></td>
+<td class="author-text">Turner, S. and T. Polk, &ldquo;<a href="http://tools.ietf.org/html/rfc6176">Prohibiting Secure Sockets Layer (SSL) Version 2.0</a>,&rdquo; RFC&nbsp;6176, March&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="UCS2">[UCS2]</a></td>
+<td class="author-text">International Organization for Standardization, &ldquo;Information Technology - Universal Multiple-octet coded Character Set (UCS) - Amendment 2: UCS Transformation Format 8 (UTF-8),&rdquo; ISO&nbsp;Standard 10646-1 Addendum 2, October&nbsp;1996.</td></tr>
+<tr><td class="author-text" valign="top"><a name="UNICODE">[UNICODE]</a></td>
+<td class="author-text">The Unicode Consortium, &ldquo;<a href="http://www.unicode.org/versions/Unicode6.0.0/">The Unicode Standard, Version 6.0</a>,&rdquo; 2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="UTF-8">[UTF-8]</a></td>
+<td class="author-text">Yergeau, F., &ldquo;<a href="http://tools.ietf.org/html/rfc3629">UTF-8, a transformation format of ISO 10646</a>,&rdquo; STD&nbsp;63, RFC&nbsp;3629, November&nbsp;2003 (<a href="http://www.rfc-editor.org/rfc/rfc3629.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="URI">[URI]</a></td>
+<td class="author-text"><a href="mailto:timbl@w3.org">Berners-Lee, T.</a>, <a href="mailto:fielding@gbiv.com">Fielding, R.</a>, and <a href="mailto:LMM@acm.org">L. Masinter</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>,&rdquo; STD&nbsp;66, RFC&nbsp;3986, January&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc3986.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3986.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3986.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="X509">[X509]</a></td>
+<td class="author-text">International Telecommunications Union, &ldquo;Information technology - Open Systems Interconnection - The Directory:
+Public-key and attribute certificate frameworks,&rdquo; ITU-T&nbsp;Recommendation X.509, ISO&nbsp;Standard 9594-8, March&nbsp;2000.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML">[XML]</a></td>
+<td class="author-text">Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;<a href="http://www.w3.org/TR/2008/REC-xml-20081126">Extensible Markup Language (XML) 1.0 (Fifth Edition)</a>,&rdquo; World Wide Web Consortium Recommendation&nbsp;REC-xml-20081126, November&nbsp;2008 (<a href="http://www.w3.org/TR/2008/REC-xml-20081126">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-GUIDE">[XML-GUIDE]</a></td>
+<td class="author-text"><a href="mailto:shollenbeck@verisign.com">Hollenbeck, S.</a>, <a href="mailto:mrose@dbc.mtview.ca.us">Rose, M.</a>, and <a href="mailto:LMM@acm.org">L. Masinter</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3470">Guidelines for the Use of Extensible Markup Language (XML) within IETF Protocols</a>,&rdquo; BCP&nbsp;70, RFC&nbsp;3470, January&nbsp;2003 (<a href="http://www.rfc-editor.org/rfc/rfc3470.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3470.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3470.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-MEDIA">[XML-MEDIA]</a></td>
+<td class="author-text">Murata, M., St. Laurent, S., and D. Kohn, &ldquo;<a href="http://tools.ietf.org/html/rfc3023">XML Media Types</a>,&rdquo; RFC&nbsp;3023, January&nbsp;2001 (<a href="http://www.rfc-editor.org/rfc/rfc3023.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-NAMES">[XML-NAMES]</a></td>
+<td class="author-text">Thompson, H., Hollander, D., Layman, A., Bray, T., and R. Tobin, &ldquo;<a href="http://www.w3.org/TR/2009/REC-xml-names-20091208">Namespaces in XML 1.0 (Third Edition)</a>,&rdquo; World Wide Web Consortium Recommendation&nbsp;REC-xml-names-20091208, December&nbsp;2009 (<a href="http://www.w3.org/TR/2009/REC-xml-names-20091208">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-ADDR">[XMPP-ADDR]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc6122">Extensible Messaging and Presence Protocol (XMPP): Address Format</a>,&rdquo; RFC&nbsp;6122, March&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-IM">[XMPP-IM]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc6121">Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence</a>,&rdquo; RFC&nbsp;6121, March&nbsp;2011.</td></tr>
+</table>
+
+<a name="rfc.references2"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>16.2.&nbsp;Informative References</h3>
+<table width="99%" border="0">
+<tr><td class="author-text" valign="top"><a name="AAA">[AAA]</a></td>
+<td class="author-text">Housley, R. and B. Aboba, &ldquo;<a href="http://tools.ietf.org/html/rfc4962">Guidance for Authentication, Authorization, and Accounting (AAA) Key Management</a>,&rdquo; BCP&nbsp;132, RFC&nbsp;4962, July&nbsp;2007 (<a href="http://www.rfc-editor.org/rfc/rfc4962.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="ABNF">[ABNF]</a></td>
+<td class="author-text">Crocker, D. and P. Overell, &ldquo;<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>,&rdquo; STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5234.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="ACAP">[ACAP]</a></td>
+<td class="author-text"><a href="mailto:chris.newman@innosoft.com">Newman, C.</a> and <a href="mailto:jgmyers@netscape.com">J. Myers</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2244">ACAP -- Application Configuration Access Protocol</a>,&rdquo; RFC&nbsp;2244, November&nbsp;1997 (<a href="http://www.rfc-editor.org/rfc/rfc2244.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="ANONYMOUS">[ANONYMOUS]</a></td>
+<td class="author-text">Zeilenga, K., &ldquo;<a href="http://tools.ietf.org/html/rfc4505">Anonymous Simple Authentication and Security Layer (SASL) Mechanism</a>,&rdquo; RFC&nbsp;4505, June&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4505.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="ASN.1">[ASN.1]</a></td>
+<td class="author-text">CCITT, &ldquo;Recommendation X.208: Specification of Abstract Syntax Notation One (ASN.1),&rdquo; 1988.</td></tr>
+<tr><td class="author-text" valign="top"><a name="DIGEST-MD5">[DIGEST-MD5]</a></td>
+<td class="author-text">Leach, P. and C. Newman, &ldquo;<a href="http://tools.ietf.org/html/rfc2831">Using Digest Authentication as a SASL Mechanism</a>,&rdquo; RFC&nbsp;2831, May&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2831.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DNSSEC">[DNSSEC]</a></td>
+<td class="author-text">Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, &ldquo;<a href="http://tools.ietf.org/html/rfc4033">DNS Security Introduction and Requirements</a>,&rdquo; RFC&nbsp;4033, March&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4033.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DNS-TXT">[DNS-TXT]</a></td>
+<td class="author-text"><a href="mailto:rosenbaum@lkg.dec.com">Rosenbaum, R.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc1464">Using the Domain Name System To Store Arbitrary String Attributes</a>,&rdquo; RFC&nbsp;1464, May&nbsp;1993 (<a href="http://www.rfc-editor.org/rfc/rfc1464.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DOS">[DOS]</a></td>
+<td class="author-text">Handley, M., Rescorla, E., and IAB, &ldquo;<a href="http://tools.ietf.org/html/rfc4732">Internet Denial-of-Service Considerations</a>,&rdquo; RFC&nbsp;4732, December&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4732.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="E2E-REQS">[E2E-REQS]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;Requirements for End-to-End Encryption in the Extensible Messaging and Presence Protocol (XMPP),&rdquo; Work in&nbsp;Progress, March&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="EMAIL-ARCH">[EMAIL-ARCH]</a></td>
+<td class="author-text">Crocker, D., &ldquo;<a href="http://tools.ietf.org/html/rfc5598">Internet Mail Architecture</a>,&rdquo; RFC&nbsp;5598, July&nbsp;2009 (<a href="http://www.rfc-editor.org/rfc/rfc5598.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="ETHERNET">[ETHERNET]</a></td>
+<td class="author-text">&ldquo;Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications,&rdquo; IEEE&nbsp;Standard 802.3, September&nbsp;1998.</td></tr>
+<tr><td class="author-text" valign="top"><a name="GSS-API">[GSS-API]</a></td>
+<td class="author-text"><a href="mailto:jlinn@rsasecurity.com">Linn, J.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2743">Generic Security Service Application Program Interface Version 2, Update 1</a>,&rdquo; RFC&nbsp;2743, January&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2743.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="HASHES">[HASHES]</a></td>
+<td class="author-text">Hoffman, P. and B. Schneier, &ldquo;<a href="http://tools.ietf.org/html/rfc4270">Attacks on Cryptographic Hashes in Internet Protocols</a>,&rdquo; RFC&nbsp;4270, November&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4270.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="HTTP">[HTTP]</a></td>
+<td class="author-text"><a href="mailto:fielding@ics.uci.edu">Fielding, R.</a>, <a href="mailto:jg@w3.org">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com">Mogul, J.</a>, <a href="mailto:frystyk@w3.org">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com">Leach, P.</a>, and <a href="mailto:timbl@w3.org">T. Berners-Lee</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>,&rdquo; RFC&nbsp;2616, June&nbsp;1999 (<a href="http://www.rfc-editor.org/rfc/rfc2616.txt">TXT</a>, <a href="http://www.rfc-editor.org/rfc/rfc2616.ps">PS</a>, <a href="http://www.rfc-editor.org/rfc/rfc2616.pdf">PDF</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2616.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2616.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IANA-GUIDE">[IANA-GUIDE]</a></td>
+<td class="author-text">Narten, T. and H. Alvestrand, &ldquo;<a href="http://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>,&rdquo; BCP&nbsp;26, RFC&nbsp;5226, May&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5226.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IANA-PORTS">[IANA-PORTS]</a></td>
+<td class="author-text">Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, &ldquo;Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Transport Protocol Port Number and Service Name Registry,&rdquo; Work in&nbsp;Progress, February&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="IMAP">[IMAP]</a></td>
+<td class="author-text">Crispin, M., &ldquo;<a href="http://tools.ietf.org/html/rfc3501">INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1</a>,&rdquo; RFC&nbsp;3501, March&nbsp;2003 (<a href="http://www.rfc-editor.org/rfc/rfc3501.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IMP-REQS">[IMP-REQS]</a></td>
+<td class="author-text"><a href="mailto:mday@alum.mit.edu">Day, M.</a>, <a href="mailto:sonuag@microsoft.com">Aggarwal, S.</a>, and <a href="mailto:jesse@intonet.com">J. Vincent</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2779">Instant Messaging / Presence Protocol Requirements</a>,&rdquo; RFC&nbsp;2779, February&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2779.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="INTEROP">[INTEROP]</a></td>
+<td class="author-text">Masinter, L., &ldquo;Formalizing IETF Interoperability Reporting,&rdquo; Work in&nbsp;Progress, October&nbsp;2005.</td></tr>
+<tr><td class="author-text" valign="top"><a name="IRC">[IRC]</a></td>
+<td class="author-text">Kalt, C., &ldquo;<a href="http://tools.ietf.org/html/rfc2810">Internet Relay Chat: Architecture</a>,&rdquo; RFC&nbsp;2810, April&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2810.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IRI">[IRI]</a></td>
+<td class="author-text">Duerst, M. and M. Suignard, &ldquo;<a href="http://tools.ietf.org/html/rfc3987">Internationalized Resource Identifiers (IRIs)</a>,&rdquo; RFC&nbsp;3987, January&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc3987.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="LDAP">[LDAP]</a></td>
+<td class="author-text">Zeilenga, K., &ldquo;<a href="http://tools.ietf.org/html/rfc4510">Lightweight Directory Access Protocol (LDAP): Technical Specification Road Map</a>,&rdquo; RFC&nbsp;4510, June&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4510.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="LINKLOCAL">[LINKLOCAL]</a></td>
+<td class="author-text">Cheshire, S., Aboba, B., and E. Guttman, &ldquo;<a href="http://tools.ietf.org/html/rfc3927">Dynamic Configuration of IPv4 Link-Local Addresses</a>,&rdquo; RFC&nbsp;3927, May&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc3927.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="MAILBOXES">[MAILBOXES]</a></td>
+<td class="author-text"><a href="mailto:dcrocker@imc.org">Crocker, D.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2142">MAILBOX NAMES FOR COMMON SERVICES, ROLES AND FUNCTIONS</a>,&rdquo; RFC&nbsp;2142, May&nbsp;1997 (<a href="http://www.rfc-editor.org/rfc/rfc2142.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2142.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2142.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="POP3">[POP3]</a></td>
+<td class="author-text"><a href="mailto:jgm+@cmu.edu">Myers, J.</a> and <a href="mailto:mrose@dbc.mtview.ca.us">M. Rose</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc1939">Post Office Protocol - Version 3</a>,&rdquo; STD&nbsp;53, RFC&nbsp;1939, May&nbsp;1996 (<a href="http://www.rfc-editor.org/rfc/rfc1939.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PROCESS">[PROCESS]</a></td>
+<td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2026">The Internet Standards Process -- Revision 3</a>,&rdquo; BCP&nbsp;9, RFC&nbsp;2026, October&nbsp;1996 (<a href="http://www.rfc-editor.org/rfc/rfc2026.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="REPORTS">[REPORTS]</a></td>
+<td class="author-text">Dusseault, L. and R. Sparks, &ldquo;<a href="http://tools.ietf.org/html/rfc5657">Guidance on Interoperation and Implementation Reports for Advancement to Draft Standard</a>,&rdquo; BCP&nbsp;9, RFC&nbsp;5657, September&nbsp;2009 (<a href="http://www.rfc-editor.org/rfc/rfc5657.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="REST">[REST]</a></td>
+<td class="author-text">Fielding, R., &ldquo;<a href="http://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation.pdf">Architectural Styles and the Design of Network-based Software Architectures</a>,&rdquo; &nbsp;2000.</td></tr>
+<tr><td class="author-text" valign="top"><a name="RFC3920">[RFC3920]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P., Ed.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3920">Extensible Messaging and Presence Protocol (XMPP): Core</a>,&rdquo; RFC&nbsp;3920, October&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3920.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3920.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3920.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="RFC3921">[RFC3921]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P., Ed.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3921">Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence</a>,&rdquo; RFC&nbsp;3921, October&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3921.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3921.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3921.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SASLPREP">[SASLPREP]</a></td>
+<td class="author-text">Zeilenga, K., &ldquo;<a href="http://tools.ietf.org/html/rfc4013">SASLprep: Stringprep Profile for User Names and Passwords</a>,&rdquo; RFC&nbsp;4013, February&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4013.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SEC-TERMS">[SEC-TERMS]</a></td>
+<td class="author-text">Shirey, R., &ldquo;<a href="http://tools.ietf.org/html/rfc4949">Internet Security Glossary, Version 2</a>,&rdquo; RFC&nbsp;4949, August&nbsp;2007 (<a href="http://www.rfc-editor.org/rfc/rfc4949.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SMTP">[SMTP]</a></td>
+<td class="author-text">Klensin, J., &ldquo;<a href="http://tools.ietf.org/html/rfc5321">Simple Mail Transfer Protocol</a>,&rdquo; RFC&nbsp;5321, October&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5321.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SEC-GUIDE">[SEC-GUIDE]</a></td>
+<td class="author-text">Rescorla, E. and B. Korver, &ldquo;<a href="http://tools.ietf.org/html/rfc3552">Guidelines for Writing RFC Text on Security Considerations</a>,&rdquo; BCP&nbsp;72, RFC&nbsp;3552, July&nbsp;2003 (<a href="http://www.rfc-editor.org/rfc/rfc3552.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-EXT">[TLS-EXT]</a></td>
+<td class="author-text">Eastlake 3rd, D., &ldquo;<a href="http://tools.ietf.org/html/rfc6066">Transport Layer Security (TLS) Extensions: Extension Definitions</a>,&rdquo; RFC&nbsp;6066, January&nbsp;2011 (<a href="http://www.rfc-editor.org/rfc/rfc6066.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-RESUME">[TLS-RESUME]</a></td>
+<td class="author-text">Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, &ldquo;<a href="http://tools.ietf.org/html/rfc5077">Transport Layer Security (TLS) Session Resumption without Server-Side State</a>,&rdquo; RFC&nbsp;5077, January&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5077.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="URN-OID">[URN-OID]</a></td>
+<td class="author-text">Mealling, M., &ldquo;<a href="http://tools.ietf.org/html/rfc3061">A URN Namespace of Object Identifiers</a>,&rdquo; RFC&nbsp;3061, February&nbsp;2001 (<a href="http://www.rfc-editor.org/rfc/rfc3061.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="USINGTLS">[USINGTLS]</a></td>
+<td class="author-text"><a href="mailto:chris.newman@innosoft.com">Newman, C.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2595">Using TLS with IMAP, POP3 and ACAP</a>,&rdquo; RFC&nbsp;2595, June&nbsp;1999 (<a href="http://www.rfc-editor.org/rfc/rfc2595.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="UUID">[UUID]</a></td>
+<td class="author-text"><a href="mailto:paulle@microsoft.com">Leach, P.</a>, <a href="mailto:michael@refactored-networks.com">Mealling, M.</a>, and <a href="mailto:rsalz@datapower.com">R. Salz</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc4122">A Universally Unique IDentifier (UUID) URN Namespace</a>,&rdquo; RFC&nbsp;4122, July&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4122.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc4122.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc4122.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0001">[XEP-0001]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0001.html">XMPP Extension Protocols</a>,&rdquo; XSF XEP&nbsp;0001, March&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0016">[XEP-0016]</a></td>
+<td class="author-text">Millard, P. and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0016.html">Privacy Lists</a>,&rdquo; XSF XEP&nbsp;0016, February&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0045">[XEP-0045]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0045.html">Multi-User Chat</a>,&rdquo; XSF XEP&nbsp;0045, July&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0060">[XEP-0060]</a></td>
+<td class="author-text"><a href="mailto:">Millard, P.</a>, <a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, and <a href="mailto:ralphm@ik.nu">R. Meijer</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0060.html">Publish-Subscribe</a>,&rdquo; XSF XEP&nbsp;0060, July&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0071">[XEP-0071]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0071.html">XHTML-IM</a>,&rdquo; XSF XEP&nbsp;0071, September&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0077">[XEP-0077]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0077.html">In-Band Registration</a>,&rdquo; XSF XEP&nbsp;0077, September&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0086">[XEP-0086]</a></td>
+<td class="author-text"><a href="mailto:rob@cataclysm.cx">Norris, R.</a> and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0086.html">Error Condition Mappings</a>,&rdquo; XSF XEP&nbsp;0086, February&nbsp;2004.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0100">[XEP-0100]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a> and <a href="mailto:dizzyd@jabber.org">D. Smith</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0100.html">Gateway Interaction</a>,&rdquo; XSF XEP&nbsp;0100, October&nbsp;2005.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0114">[XEP-0114]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0114.html">Jabber Component Protocol</a>,&rdquo; XSF XEP&nbsp;0114, March&nbsp;2005.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0124">[XEP-0124]</a></td>
+<td class="author-text"><a href="mailto:ian.paterson@clientside.co.uk">Paterson, I.</a>, <a href="mailto:dizzyd@jabber.org">Smith, D.</a>, and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0124.html">Bidirectional-streams Over Synchronous HTTP (BOSH)</a>,&rdquo; XSF XEP&nbsp;0124, July&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0138">[XEP-0138]</a></td>
+<td class="author-text"><a href="mailto:jhildebr@cisco.com">Hildebrand, J.</a> and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0138.html">Stream Compression</a>,&rdquo; XSF XEP&nbsp;0138, May&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0156">[XEP-0156]</a></td>
+<td class="author-text"><a href="mailto:jhildebrand@jabber.com">Hildebrand, J.</a> and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0156.html">Discovering Alternative XMPP Connection Methods</a>,&rdquo; XSF XEP&nbsp;0156, June&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0160">[XEP-0160]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0160.html">Best Practices for Handling Offline Messages</a>,&rdquo; XSF XEP&nbsp;0160, January&nbsp;2006.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0174">[XEP-0174]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0174.html">Link-Local Messaging</a>,&rdquo; XSF XEP&nbsp;0174, November&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0175">[XEP-0175]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0175.html">Best Practices for Use of SASL ANONYMOUS</a>,&rdquo; XSF XEP&nbsp;0175, September&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0178">[XEP-0178]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a> and <a href="mailto:">P. Millard</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0178.html">Best Practices for Use of SASL EXTERNAL with Certificates</a>,&rdquo; XSF XEP&nbsp;0178, February&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0191">[XEP-0191]</a></td>
+<td class="author-text"><a href="mailto:">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0191.html">Simple Communications Blocking</a>,&rdquo; XSF XEP&nbsp;0191, February&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0198">[XEP-0198]</a></td>
+<td class="author-text"><a href="mailto:justin@affinix.com">Karneges, J.</a>, <a href="mailto:jhildebr@cisco.com">Hildebrand, J.</a>, <a href="mailto:">Saint-Andre, P.</a>, <a href="mailto:fabio.forno@gmail.com">Forno, F.</a>, Cridland, D., and M. Wild, &ldquo;<a href="http://xmpp.org/extensions/xep-0198.html">Stream Management</a>,&rdquo; XSF XEP&nbsp;0198, February&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0199">[XEP-0199]</a></td>
+<td class="author-text"><a href="mailto:">Saint-Andre, P.</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0199.html">XMPP Ping</a>,&rdquo; XSF XEP&nbsp;0199, June&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0205">[XEP-0205]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0205.html">Best Practices to Discourage Denial of Service Attacks</a>,&rdquo; XSF XEP&nbsp;0205, January&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0206">[XEP-0206]</a></td>
+<td class="author-text"><a href="mailto:ian.paterson@clientside.co.uk">Paterson, I.</a> and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0206.html">XMPP Over BOSH</a>,&rdquo; XSF XEP&nbsp;0206, July&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0220">[XEP-0220]</a></td>
+<td class="author-text"><a href="mailto:jer@jabber.org">Miller, J.</a>, <a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, and <a href="mailto:">P. Hancke</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0220.html">Server Dialback</a>,&rdquo; XSF XEP&nbsp;0220, March&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0225">[XEP-0225]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0225.html">Component Connections</a>,&rdquo; XSF XEP&nbsp;0225, October&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0233">[XEP-0233]</a></td>
+<td class="author-text"><a href="mailto:linuxwolf@outer-planes.net">Miller, M.</a>, <a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, and <a href="mailto:jhildebr@cisco.com">J. Hildebrand</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0233.html">Domain-Based Service Names in XMPP SASL Negotiation</a>,&rdquo; XSF XEP&nbsp;0233, June&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0288">[XEP-0288]</a></td>
+<td class="author-text"><a href="mailto:">Hancke, P.</a> and <a href="mailto:dave.cridland@isode.com">D. Cridland</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0288.html">Bidirectional Server-to-Server Connections</a>,&rdquo; XSF XEP&nbsp;0288, October&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-FRAG">[XML-FRAG]</a></td>
+<td class="author-text">Grosso, P. and D. Veillard, &ldquo;<a href="http://www.w3.org/TR/2001/CR-xml-fragment-20010212">XML Fragment Interchange</a>,&rdquo; World Wide Web Consortium CR&nbsp;CR-xml-fragment-20010212, February&nbsp;2001 (<a href="http://www.w3.org/TR/2001/CR-xml-fragment-20010212">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-REG">[XML-REG]</a></td>
+<td class="author-text">Mealling, M., &ldquo;<a href="http://tools.ietf.org/html/rfc3688">The IETF XML Registry</a>,&rdquo; BCP&nbsp;81, RFC&nbsp;3688, January&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3688.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-SCHEMA">[XML-SCHEMA]</a></td>
+<td class="author-text">Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech, &ldquo;<a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028">XML Schema Part 1: Structures Second Edition</a>,&rdquo; World Wide Web Consortium Recommendation&nbsp;REC-xmlschema-1-20041028, October&nbsp;2004 (<a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-URI">[XMPP-URI]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc5122">Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP)</a>,&rdquo; RFC&nbsp;5122, February&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5122.txt">TXT</a>).</td></tr>
+</table>
+
+<a name="schema"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A"></a><h3>Appendix A.&nbsp;
+XML Schemas</h3>
+
+<p>The following schemas formally define various namespaces used in this document, in conformance with <a class='info' href='#XML-SCHEMA'>[XML&#8209;SCHEMA]<span> (</span><span class='info'>Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech, &ldquo;XML Schema Part 1: Structures Second Edition,&rdquo; October&nbsp;2004.</span><span>)</span></a>.  Because validation of XML streams and stanzas is optional, these schemas are not normative and are provided for descriptive purposes only.
+</p>
+<a name="schemas-stream"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.1"></a><h3>A.1.&nbsp;
+Stream Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='http://etherx.jabber.org/streams'
+    xmlns='http://etherx.jabber.org/streams'
+    elementFormDefault='unqualified'&gt;
+
+  &lt;xs:import namespace='jabber:client'/&gt;
+  &lt;xs:import namespace='jabber:server'/&gt;
+  &lt;xs:import namespace='urn:ietf:params:xml:ns:xmpp-sasl'/&gt;
+  &lt;xs:import namespace='urn:ietf:params:xml:ns:xmpp-streams'/&gt;
+  &lt;xs:import namespace='urn:ietf:params:xml:ns:xmpp-tls'/&gt;
+
+  &lt;xs:element name='stream'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence xmlns:client='jabber:client'
+                   xmlns:server='jabber:server'&gt;
+        &lt;xs:element ref='features'
+                    minOccurs='0'
+                    maxOccurs='1'/&gt;
+        &lt;xs:any namespace='urn:ietf:params:xml:ns:xmpp-tls'
+                minOccurs='0'
+                maxOccurs='1'/&gt;
+        &lt;xs:any namespace='urn:ietf:params:xml:ns:xmpp-sasl'
+                minOccurs='0'
+                maxOccurs='1'/&gt;
+        &lt;xs:any namespace='##other'
+                minOccurs='0'
+                maxOccurs='unbounded'
+                processContents='lax'/&gt;
+        &lt;xs:choice minOccurs='0' maxOccurs='1'&gt;
+          &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+            &lt;xs:element ref='client:message'/&gt;
+            &lt;xs:element ref='client:presence'/&gt;
+            &lt;xs:element ref='client:iq'/&gt;
+          &lt;/xs:choice&gt;
+          &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+            &lt;xs:element ref='server:message'/&gt;
+            &lt;xs:element ref='server:presence'/&gt;
+            &lt;xs:element ref='server:iq'/&gt;
+          &lt;/xs:choice&gt;
+        &lt;/xs:choice&gt;
+        &lt;xs:element ref='error' minOccurs='0' maxOccurs='1'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='from' type='xs:string' use='optional'/&gt;
+      &lt;xs:attribute name='id' type='xs:string' use='optional'/&gt;
+      &lt;xs:attribute name='to' type='xs:string' use='optional'/&gt;
+      &lt;xs:attribute name='version' type='xs:decimal' use='optional'/&gt;
+      &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+      &lt;xs:anyAttribute namespace='##other' processContents='lax'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='features'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:any namespace='##other'
+                minOccurs='0'
+                maxOccurs='unbounded'
+                processContents='lax'/&gt;
+      &lt;/xs:sequence&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='error'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence  xmlns:err='urn:ietf:params:xml:ns:xmpp-streams'&gt;
+        &lt;xs:group   ref='err:streamErrorGroup'/&gt;
+        &lt;xs:element ref='err:text'
+                    minOccurs='0'
+                    maxOccurs='1'/&gt;
+        &lt;xs:any     namespace='##other'
+                    minOccurs='0'
+                    maxOccurs='1'
+                    processContents='lax'/&gt;
+      &lt;/xs:sequence&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-streamerror"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2"></a><h3>A.2.&nbsp;
+Stream Error Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='urn:ietf:params:xml:ns:xmpp-streams'
+    xmlns='urn:ietf:params:xml:ns:xmpp-streams'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='bad-format' type='empty'/&gt;
+  &lt;xs:element name='bad-namespace-prefix' type='empty'/&gt;
+  &lt;xs:element name='conflict' type='empty'/&gt;
+  &lt;xs:element name='connection-timeout' type='empty'/&gt;
+  &lt;xs:element name='host-gone' type='empty'/&gt;
+  &lt;xs:element name='host-unknown' type='empty'/&gt;
+  &lt;xs:element name='improper-addressing' type='empty'/&gt;
+  &lt;xs:element name='internal-server-error' type='empty'/&gt;
+  &lt;xs:element name='invalid-from' type='empty'/&gt;
+  &lt;xs:element name='invalid-id' type='empty'/&gt;
+  &lt;xs:element name='invalid-namespace' type='empty'/&gt;
+  &lt;xs:element name='invalid-xml' type='empty'/&gt;
+  &lt;xs:element name='not-authorized' type='empty'/&gt;
+  &lt;xs:element name='not-well-formed' type='empty'/&gt;
+  &lt;xs:element name='policy-violation' type='empty'/&gt;
+  &lt;xs:element name='remote-connection-failed' type='empty'/&gt;
+  &lt;xs:element name='reset' type='empty'/&gt;
+  &lt;xs:element name='resource-constraint' type='empty'/&gt;
+  &lt;xs:element name='restricted-xml' type='empty'/&gt;
+  &lt;xs:element name='see-other-host' type='xs:string'/&gt;
+  &lt;xs:element name='system-shutdown' type='empty'/&gt;
+  &lt;xs:element name='undefined-condition' type='empty'/&gt;
+  &lt;xs:element name='unsupported-encoding' type='empty'/&gt;
+  &lt;xs:element name='unsupported-stanza-type' type='empty'/&gt;
+  &lt;xs:element name='unsupported-version' type='empty'/&gt;
+
+  &lt;xs:group name='streamErrorGroup'&gt;
+    &lt;xs:choice&gt;
+      &lt;xs:element ref='bad-format'/&gt;
+      &lt;xs:element ref='bad-namespace-prefix'/&gt;
+      &lt;xs:element ref='conflict'/&gt;
+      &lt;xs:element ref='connection-timeout'/&gt;
+      &lt;xs:element ref='host-gone'/&gt;
+      &lt;xs:element ref='host-unknown'/&gt;
+      &lt;xs:element ref='improper-addressing'/&gt;
+      &lt;xs:element ref='internal-server-error'/&gt;
+      &lt;xs:element ref='invalid-from'/&gt;
+      &lt;xs:element ref='invalid-id'/&gt;
+      &lt;xs:element ref='invalid-namespace'/&gt;
+      &lt;xs:element ref='invalid-xml'/&gt;
+      &lt;xs:element ref='not-authorized'/&gt;
+      &lt;xs:element ref='not-well-formed'/&gt;
+      &lt;xs:element ref='policy-violation'/&gt;
+      &lt;xs:element ref='remote-connection-failed'/&gt;
+      &lt;xs:element ref='reset'/&gt;
+      &lt;xs:element ref='resource-constraint'/&gt;
+      &lt;xs:element ref='restricted-xml'/&gt;
+      &lt;xs:element ref='see-other-host'/&gt;
+      &lt;xs:element ref='system-shutdown'/&gt;
+      &lt;xs:element ref='undefined-condition'/&gt;
+      &lt;xs:element ref='unsupported-encoding'/&gt;
+      &lt;xs:element ref='unsupported-stanza-type'/&gt;
+      &lt;xs:element ref='unsupported-version'/&gt;
+    &lt;/xs:choice&gt;
+  &lt;/xs:group&gt;
+
+  &lt;xs:element name='text'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='empty'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:enumeration value=''/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-starttls"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3"></a><h3>A.3.&nbsp;
+STARTTLS Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='urn:ietf:params:xml:ns:xmpp-tls'
+    xmlns='urn:ietf:params:xml:ns:xmpp-tls'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='starttls'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:choice minOccurs='0' maxOccurs='1'&gt;
+        &lt;xs:element name='required' type='empty'/&gt;
+      &lt;/xs:choice&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='proceed' type='empty'/&gt;
+
+  &lt;xs:element name='failure' type='empty'/&gt;
+
+  &lt;xs:simpleType name='empty'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:enumeration value=''/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-sasl"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.4"></a><h3>A.4.&nbsp;
+SASL Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='urn:ietf:params:xml:ns:xmpp-sasl'
+    xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='mechanisms'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:element name='mechanism'
+                    minOccurs='1'
+                    maxOccurs='unbounded'
+                    type='xs:NMTOKEN'/&gt;
+        &lt;xs:any namespace='##other'
+                minOccurs='0'
+                maxOccurs='unbounded'
+                processContents='lax'/&gt;
+      &lt;/xs:sequence&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='abort' type='empty'/&gt;
+
+  &lt;xs:element name='auth'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute name='mechanism'
+                        type='xs:NMTOKEN'
+                        use='required'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='challenge' type='xs:string'/&gt;
+
+  &lt;xs:element name='response' type='xs:string'/&gt;
+
+  &lt;xs:element name='success' type='xs:string'/&gt;
+
+  &lt;xs:element name='failure'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:choice minOccurs='0'&gt;
+          &lt;xs:element name='aborted' type='empty'/&gt;
+          &lt;xs:element name='account-disabled' type='empty'/&gt;
+          &lt;xs:element name='credentials-expired' type='empty'/&gt;
+          &lt;xs:element name='encryption-required' type='empty'/&gt;
+          &lt;xs:element name='incorrect-encoding' type='empty'/&gt;
+          &lt;xs:element name='invalid-authzid' type='empty'/&gt;
+          &lt;xs:element name='invalid-mechanism' type='empty'/&gt;
+          &lt;xs:element name='malformed-request' type='empty'/&gt;
+          &lt;xs:element name='mechanism-too-weak' type='empty'/&gt;
+          &lt;xs:element name='not-authorized' type='empty'/&gt;
+          &lt;xs:element name='temporary-auth-failure' type='empty'/&gt;
+        &lt;/xs:choice&gt;
+        &lt;xs:element ref='text' minOccurs='0' maxOccurs='1'/&gt;
+      &lt;/xs:sequence&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='text'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='empty'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:enumeration value=''/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.5"></a><h3>A.5.&nbsp;
+Client Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='jabber:client'
+    xmlns='jabber:client'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:import
+      namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+
+  &lt;xs:element name='message'&gt;
+     &lt;xs:complexType&gt;
+        &lt;xs:sequence&gt;
+          &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+            &lt;xs:element ref='subject'/&gt;
+            &lt;xs:element ref='body'/&gt;
+            &lt;xs:element ref='thread'/&gt;
+          &lt;/xs:choice&gt;
+          &lt;xs:any     namespace='##other'
+                      minOccurs='0'
+                      maxOccurs='unbounded'
+                      processContents='lax'/&gt;
+          &lt;xs:element ref='error'
+                      minOccurs='0'/&gt;
+        &lt;/xs:sequence&gt;
+        &lt;xs:attribute name='from'
+                      type='xs:string'
+                      use='optional'/&gt;
+        &lt;xs:attribute name='id'
+                      type='xs:NMTOKEN'
+                      use='optional'/&gt;
+        &lt;xs:attribute name='to'
+                      type='xs:string'
+                      use='optional'/&gt;
+        &lt;xs:attribute name='type'
+                      use='optional'
+                      default='normal'&gt;
+          &lt;xs:simpleType&gt;
+            &lt;xs:restriction base='xs:NMTOKEN'&gt;
+              &lt;xs:enumeration value='chat'/&gt;
+              &lt;xs:enumeration value='error'/&gt;
+              &lt;xs:enumeration value='groupchat'/&gt;
+              &lt;xs:enumeration value='headline'/&gt;
+              &lt;xs:enumeration value='normal'/&gt;
+            &lt;/xs:restriction&gt;
+          &lt;/xs:simpleType&gt;
+        &lt;/xs:attribute&gt;
+        &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+     &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='body'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='subject'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='thread'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:NMTOKEN'&gt;
+          &lt;xs:attribute name='parent'
+                        type='xs:NMTOKEN'
+                        use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='presence'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+          &lt;xs:element ref='show'/&gt;
+          &lt;xs:element ref='status'/&gt;
+          &lt;xs:element ref='priority'/&gt;
+        &lt;/xs:choice&gt;
+        &lt;xs:any     namespace='##other'
+                    minOccurs='0'
+                    maxOccurs='unbounded'
+                    processContents='lax'/&gt;
+        &lt;xs:element ref='error'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='from'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='id'
+                    type='xs:NMTOKEN'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='to'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='type' use='optional'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='error'/&gt;
+            &lt;xs:enumeration value='probe'/&gt;
+            &lt;xs:enumeration value='subscribe'/&gt;
+            &lt;xs:enumeration value='subscribed'/&gt;
+            &lt;xs:enumeration value='unavailable'/&gt;
+            &lt;xs:enumeration value='unsubscribe'/&gt;
+            &lt;xs:enumeration value='unsubscribed'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+      &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='show'&gt;
+    &lt;xs:simpleType&gt;
+      &lt;xs:restriction base='xs:NMTOKEN'&gt;
+        &lt;xs:enumeration value='away'/&gt;
+        &lt;xs:enumeration value='chat'/&gt;
+        &lt;xs:enumeration value='dnd'/&gt;
+        &lt;xs:enumeration value='xa'/&gt;
+      &lt;/xs:restriction&gt;
+    &lt;/xs:simpleType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='status'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='string1024'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='string1024'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:minLength value='1'/&gt;
+      &lt;xs:maxLength value='1024'/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+  &lt;xs:element name='priority' type='xs:byte'/&gt;
+
+  &lt;xs:element name='iq'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:any     namespace='##other'
+                    minOccurs='0'
+                    maxOccurs='1'
+                    processContents='lax'/&gt;
+        &lt;xs:element ref='error'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='from'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='id'
+                    type='xs:NMTOKEN'
+                    use='required'/&gt;
+      &lt;xs:attribute name='to'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='type' use='required'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='error'/&gt;
+            &lt;xs:enumeration value='get'/&gt;
+            &lt;xs:enumeration value='result'/&gt;
+            &lt;xs:enumeration value='set'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+      &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='error'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+        &lt;xs:group ref='err:stanzaErrorGroup'/&gt;
+        &lt;xs:element ref='err:text'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='by'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='type' use='required'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='auth'/&gt;
+            &lt;xs:enumeration value='cancel'/&gt;
+            &lt;xs:enumeration value='continue'/&gt;
+            &lt;xs:enumeration value='modify'/&gt;
+            &lt;xs:enumeration value='wait'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-server"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.6"></a><h3>A.6.&nbsp;
+Server Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='jabber:server'
+    xmlns='jabber:server'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:import
+      namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+
+  &lt;xs:element name='message'&gt;
+     &lt;xs:complexType&gt;
+        &lt;xs:sequence&gt;
+          &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+            &lt;xs:element ref='subject'/&gt;
+            &lt;xs:element ref='body'/&gt;
+            &lt;xs:element ref='thread'/&gt;
+          &lt;/xs:choice&gt;
+          &lt;xs:any namespace='##other'
+                  minOccurs='0'
+                  maxOccurs='unbounded'
+                  processContents='lax'/&gt;
+          &lt;xs:element ref='error'
+                      minOccurs='0'/&gt;
+        &lt;/xs:sequence&gt;
+        &lt;xs:attribute name='from'
+                      type='xs:string'
+                      use='required'/&gt;
+        &lt;xs:attribute name='id'
+                      type='xs:NMTOKEN'
+                      use='optional'/&gt;
+        &lt;xs:attribute name='to'
+                      type='xs:string'
+                      use='required'/&gt;
+        &lt;xs:attribute name='type'
+                      use='optional'
+                      default='normal'&gt;
+          &lt;xs:simpleType&gt;
+            &lt;xs:restriction base='xs:NMTOKEN'&gt;
+              &lt;xs:enumeration value='chat'/&gt;
+              &lt;xs:enumeration value='error'/&gt;
+              &lt;xs:enumeration value='groupchat'/&gt;
+              &lt;xs:enumeration value='headline'/&gt;
+              &lt;xs:enumeration value='normal'/&gt;
+            &lt;/xs:restriction&gt;
+          &lt;/xs:simpleType&gt;
+        &lt;/xs:attribute&gt;
+        &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+     &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='body'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='subject'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='thread'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:NMTOKEN'&gt;
+          &lt;xs:attribute name='parent'
+                        type='xs:NMTOKEN'
+                        use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='subject'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:NMTOKEN'&gt;
+          &lt;xs:attribute name='parent'
+                        type='xs:NMTOKEN'
+                        use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='presence'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:choice minOccurs='0' maxOccurs='unbounded'&gt;
+          &lt;xs:element ref='show'/&gt;
+          &lt;xs:element ref='status'/&gt;
+          &lt;xs:element ref='priority'/&gt;
+        &lt;/xs:choice&gt;
+        &lt;xs:any     namespace='##other'
+                    minOccurs='0'
+                    maxOccurs='unbounded'
+                    processContents='lax'/&gt;
+        &lt;xs:element ref='error'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='from'
+                    type='xs:string'
+                    use='required'/&gt;
+      &lt;xs:attribute name='id'
+                    type='xs:NMTOKEN'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='to'
+                    type='xs:string'
+                    use='required'/&gt;
+      &lt;xs:attribute name='type' use='optional'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='error'/&gt;
+            &lt;xs:enumeration value='probe'/&gt;
+            &lt;xs:enumeration value='subscribe'/&gt;
+            &lt;xs:enumeration value='subscribed'/&gt;
+            &lt;xs:enumeration value='unavailable'/&gt;
+            &lt;xs:enumeration value='unsubscribe'/&gt;
+            &lt;xs:enumeration value='unsubscribed'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+      &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='show'&gt;
+    &lt;xs:simpleType&gt;
+      &lt;xs:restriction base='xs:NMTOKEN'&gt;
+        &lt;xs:enumeration value='away'/&gt;
+        &lt;xs:enumeration value='chat'/&gt;
+        &lt;xs:enumeration value='dnd'/&gt;
+        &lt;xs:enumeration value='xa'/&gt;
+      &lt;/xs:restriction&gt;
+    &lt;/xs:simpleType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='status'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='string1024'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='string1024'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:minLength value='1'/&gt;
+      &lt;xs:maxLength value='1024'/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+  &lt;xs:element name='priority' type='xs:byte' default='0'/&gt;
+
+  &lt;xs:element name='iq'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:any namespace='##other'
+                minOccurs='0'
+                maxOccurs='1'
+                processContents='lax'/&gt;
+        &lt;xs:element ref='error'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='from'
+                    type='xs:string'
+                    use='required'/&gt;
+      &lt;xs:attribute name='id'
+                    type='xs:NMTOKEN'
+                    use='required'/&gt;
+      &lt;xs:attribute name='to'
+                    type='xs:string'
+                    use='required'/&gt;
+      &lt;xs:attribute name='type' use='required'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='error'/&gt;
+            &lt;xs:enumeration value='get'/&gt;
+            &lt;xs:enumeration value='result'/&gt;
+            &lt;xs:enumeration value='set'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+      &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='error'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+        &lt;xs:group ref='err:stanzaErrorGroup'/&gt;
+        &lt;xs:element ref='err:text'
+                    minOccurs='0'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='by'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='type' use='required'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='auth'/&gt;
+            &lt;xs:enumeration value='cancel'/&gt;
+            &lt;xs:enumeration value='continue'/&gt;
+            &lt;xs:enumeration value='modify'/&gt;
+            &lt;xs:enumeration value='wait'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-bind"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.7"></a><h3>A.7.&nbsp;
+Resource Binding Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='urn:ietf:params:xml:ns:xmpp-bind'
+    xmlns='urn:ietf:params:xml:ns:xmpp-bind'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='bind'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:choice&gt;
+        &lt;xs:element name='resource' type='resourceType'/&gt;
+        &lt;xs:element name='jid' type='fullJIDType'/&gt;
+      &lt;/xs:choice&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='fullJIDType'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:minLength value='8'/&gt;
+      &lt;xs:maxLength value='3071'/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+  &lt;xs:simpleType name='resourceType'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:minLength value='1'/&gt;
+      &lt;xs:maxLength value='1023'/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="schemas-stanzaerror"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.8"></a><h3>A.8.&nbsp;
+Stanza Error Namespace</h3>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='urn:ietf:params:xml:ns:xmpp-stanzas'
+    xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='bad-request' type='empty'/&gt;
+  &lt;xs:element name='conflict' type='empty'/&gt;
+  &lt;xs:element name='feature-not-implemented' type='empty'/&gt;
+  &lt;xs:element name='forbidden' type='empty'/&gt;
+  &lt;xs:element name='gone' type='xs:string'/&gt;
+  &lt;xs:element name='internal-server-error' type='empty'/&gt;
+  &lt;xs:element name='item-not-found' type='empty'/&gt;
+  &lt;xs:element name='jid-malformed' type='empty'/&gt;
+  &lt;xs:element name='not-acceptable' type='empty'/&gt;
+  &lt;xs:element name='not-allowed' type='empty'/&gt;
+  &lt;xs:element name='not-authorized' type='empty'/&gt;
+  &lt;xs:element name='policy-violation' type='empty'/&gt;
+  &lt;xs:element name='recipient-unavailable' type='empty'/&gt;
+  &lt;xs:element name='redirect' type='xs:string'/&gt;
+  &lt;xs:element name='registration-required' type='empty'/&gt;
+  &lt;xs:element name='remote-server-not-found' type='empty'/&gt;
+  &lt;xs:element name='remote-server-timeout' type='empty'/&gt;
+  &lt;xs:element name='resource-constraint' type='empty'/&gt;
+  &lt;xs:element name='service-unavailable' type='empty'/&gt;
+  &lt;xs:element name='subscription-required' type='empty'/&gt;
+  &lt;xs:element name='undefined-condition' type='empty'/&gt;
+  &lt;xs:element name='unexpected-request' type='empty'/&gt;
+
+  &lt;xs:group name='stanzaErrorGroup'&gt;
+    &lt;xs:choice&gt;
+      &lt;xs:element ref='bad-request'/&gt;
+      &lt;xs:element ref='conflict'/&gt;
+      &lt;xs:element ref='feature-not-implemented'/&gt;
+      &lt;xs:element ref='forbidden'/&gt;
+      &lt;xs:element ref='gone'/&gt;
+      &lt;xs:element ref='internal-server-error'/&gt;
+      &lt;xs:element ref='item-not-found'/&gt;
+      &lt;xs:element ref='jid-malformed'/&gt;
+      &lt;xs:element ref='not-acceptable'/&gt;
+      &lt;xs:element ref='not-authorized'/&gt;
+      &lt;xs:element ref='not-allowed'/&gt;
+      &lt;xs:element ref='policy-violation'/&gt;
+      &lt;xs:element ref='recipient-unavailable'/&gt;
+      &lt;xs:element ref='redirect'/&gt;
+      &lt;xs:element ref='registration-required'/&gt;
+      &lt;xs:element ref='remote-server-not-found'/&gt;
+      &lt;xs:element ref='remote-server-timeout'/&gt;
+      &lt;xs:element ref='resource-constraint'/&gt;
+      &lt;xs:element ref='service-unavailable'/&gt;
+      &lt;xs:element ref='subscription-required'/&gt;
+      &lt;xs:element ref='undefined-condition'/&gt;
+      &lt;xs:element ref='unexpected-request'/&gt;
+    &lt;/xs:choice&gt;
+  &lt;/xs:group&gt;
+
+  &lt;xs:element name='text'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:simpleContent&gt;
+        &lt;xs:extension base='xs:string'&gt;
+          &lt;xs:attribute ref='xml:lang' use='optional'/&gt;
+        &lt;/xs:extension&gt;
+      &lt;/xs:simpleContent&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:simpleType name='empty'&gt;
+    &lt;xs:restriction base='xs:string'&gt;
+      &lt;xs:enumeration value=''/&gt;
+    &lt;/xs:restriction&gt;
+  &lt;/xs:simpleType&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="contact"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.B"></a><h3>Appendix B.&nbsp;
+Contact Addresses</h3>
+
+<p>Consistent with <a class='info' href='#MAILBOXES'>[MAILBOXES]<span> (</span><span class='info'>Crocker, D., &ldquo;MAILBOX NAMES FOR COMMON SERVICES, ROLES AND FUNCTIONS,&rdquo; May&nbsp;1997.</span><span>)</span></a>, organization that offer XMPP services are encouraged to provide an Internet mailbox of "XMPP" for inquiries related to that service, where the host portion of the resulting mailto URI is the organization's domain, not the domain of the XMPP service itself (e.g., the XMPP service might be offered at im.example.com but the Internet mailbox would be &lt;xmpp@example.com&gt;).
+</p>
+<a name="provisioning"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.C"></a><h3>Appendix C.&nbsp;
+Account Provisioning</h3>
+
+<p>Account provisioning is out of scope for this specification.
+      Possible methods for account provisioning include account
+      creation by a server administrator and in-band account
+      registration using the 'jabber:iq:register' namespace as
+      documented in <a class='info' href='#XEP-0077'>[XEP&#8209;0077]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;In-Band Registration,&rdquo; September&nbsp;2009.</span><span>)</span></a>.  An XMPP server
+      implementation or administrative function MUST ensure that any
+      JID assigned during account provisioning (including localpart,
+      domainpart, resourcepart, and separator characters) conforms to
+      the canonical format for XMPP addresses defined in
+      <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="diffs"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.D"></a><h3>Appendix D.&nbsp;
+Differences from RFC 3920</h3>
+
+<p>Based on consensus derived from implementation and deployment experience as well as formal interoperability testing, the following substantive modifications were made from RFC 3920 (in addition to numerous changes of an editorial nature).
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Moved specification of the XMPP address format to a separate document.
+</li>
+<li>Recommended or mandated use of the 'from' and 'to' attributes on stream headers.
+</li>
+<li>More fully specified the stream closing handshake.
+</li>
+<li>Specified the recommended stream reconnection algorithm.
+</li>
+<li>Changed the name of the &lt;xml-not-well-formed/&gt; stream error condition to &lt;not-well-formed/&gt; for compliance with the XML specification.
+</li>
+<li>Removed the unnecessary and unused &lt;invalid-id/&gt; stream error (see RFC 3920 for historical documentation).
+</li>
+<li>Specified return of the &lt;restricted-xml/&gt; stream error in response to receipt of prohibited XML features.
+</li>
+<li>More completely specified the format and handling of the &lt;see-other-host/&gt; stream error, including consistency with RFC 3986 and RFC 5952 with regard to IPv6 addresses (e.g., enclosing the IPv6 address in square brackets '[' and ']').
+</li>
+<li>Specified that the SASL SCRAM mechanism is a mandatory-to-implement technology for client-to-server streams.
+</li>
+<li>Specified that TLS plus the SASL PLAIN mechanism is a mandatory-to-implement technology for client-to-server streams.
+</li>
+<li>Specified that support for the SASL EXTERNAL mechanism is required for servers but only recommended for clients (since end-user X.509 certificates are difficult to obtain and not yet widely deployed).
+</li>
+<li>Removed the hard two-connection rule for server-to-server streams.
+</li>
+<li>More clearly specified the certificate profile for both public key certificates and issuer certificates.
+</li>
+<li>Added the &lt;reset/&gt; stream error (<a class='info' href='#streams-error-conditions-reset'>Section&nbsp;4.9.3.16<span> (</span><span class='info'>reset</span><span>)</span></a>) condition to handle expired/revoked certificates or the addition of security-critical features to an existing stream.
+</li>
+<li>Added the &lt;account-disabled/&gt;, &lt;credentials-expired/&gt;, &lt;encryption-required/&gt;, and &lt;malformed-request/&gt; SASL error conditions to handle error flows mistakenly left out of RFC 3920 or discussed in RFC 4422 but not in RFC 2222.
+</li>
+<li>Removed the unused &lt;payment-required/&gt; stanza error.
+</li>
+<li>Removed the unnecessary requirement for escaping of characters that map to certain predefined entities, since they do not need to be escaped in XML.
+</li>
+<li>Clarified the process of DNS SRV lookups and fallbacks.
+</li>
+<li>Clarified the handling of SASL security layers.
+</li>
+<li>Clarified that a SASL simple user name is the localpart, not the bare JID.
+</li>
+<li>Clarified the stream negotiation process and associated flow chart.
+</li>
+<li>Clarified the handling of stream features.
+</li>
+<li>Added a 'by' attribute to the &lt;error/&gt; element for stanza errors so that the entity that has detected the error can include its JID for diagnostic or tracking purposes.
+</li>
+<li>Clarified the handling of data that violates the well-formedness definitions for XML 1.0 and XML namespaces.
+</li>
+<li>Specified the security considerations in more detail, especially with regard to presence leaks and denial-of-service attacks.
+</li>
+<li>Moved documentation of the Server Dialback protocol from this specification to a separate specification maintained by the XMPP Standards Foundation.
+</li>
+</ul><p>
+      
+</p>
+<a name="intro-ack"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.E"></a><h3>Appendix E.&nbsp;
+Acknowledgements</h3>
+
+<p>This document is an update to, and derived from, RFC 3920.  This document would have been impossible without the work of the contributors and commenters acknowledged there.
+</p>
+<p>Hundreds of people have provided implementation feedback, bug reports, requests for clarification, and suggestions for improvement since publication of RFC 3920.  Although the document editor has endeavored to address all such feedback, he is solely responsible for any remaining errors and ambiguities.
+</p>
+<p>Special thanks are due to Kevin Smith, Matthew Wild, Dave Cridland, Philipp Hancke, Waqas Hussain, Florian Zeitz, Ben Campbell, Jehan Pages, Paul Aurich, Justin Karneges, Kurt Zeilenga, Simon Josefsson, Ralph Meijer, Curtis King, and others for their comments during Working Group Last Call.
+</p>
+<p>Thanks also to Yaron Sheffer and Elwyn Davies for their reviews on behalf of the Security Directorate and the General Area Review Team, respectively.
+</p>
+<p>The Working Group chairs were Ben Campbell and Joe Hildebrand.  The responsible Area Director was Gonzalo Camarillo.
+</p>
+<a name="rfc.authors"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>Author's Address</h3>
+<table width="99%" border="0" cellpadding="0" cellspacing="0">
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Peter Saint-Andre</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Cisco</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">1899 Wyknoop Street, Suite 600</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Denver, CO  80202</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">USA</td></tr>
+<tr><td class="author" align="right">Phone:&nbsp;</td>
+<td class="author-text">+1-303-308-3282</td></tr>
+<tr><td class="author" align="right">EMail:&nbsp;</td>
+<td class="author-text"><a href="mailto:psaintan@cisco.com">psaintan@cisco.com</a></td></tr>
+</table>
+</body></html>
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+
+<table border="0" cellpadding="0" cellspacing="2" width="30" align="right">
+    <tr>
+        <td class="RFCbug">
+                <span class="RFC">&nbsp;RFC&nbsp;</span><br /><span class="hotText">&nbsp;6121&nbsp;</span>
+        </td>
+    </tr>
+    <tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a><br /></td></tr>
+</table>
+<table summary="layout" width="66%" border="0" cellpadding="0" cellspacing="0"><tr><td><table summary="layout" width="100%" border="0" cellpadding="2" cellspacing="1">
+<tr><td class="header">Internet Engineering Task Force (IETF)</td><td class="header">P. Saint-Andre</td></tr>
+<tr><td class="header">Request for Comments: 6121</td><td class="header">Cisco</td></tr>
+<tr><td class="header">Obsoletes: <a href='http://tools.ietf.org/html/rfc3921'>3921</a></td><td class="header">March 2011</td></tr>
+<tr><td class="header">Category: Standards Track</td><td class="header">&nbsp;</td></tr>
+<tr><td class="header">ISSN: 2070-1721</td><td class="header">&nbsp;</td></tr>
+</table></td></tr></table>
+<h1><br />Extensible Messaging and Presence Protocol
+    (XMPP): Instant&nbsp;Messaging&nbsp;and&nbsp;Presence</h1>
+
+<h3>Abstract</h3>
+
+<p>This document defines extensions to core features of the Extensible Messaging and Presence Protocol (XMPP) that provide basic instant messaging (IM) and presence functionality in conformance with the requirements in RFC 2779.  This document obsoletes RFC 3921.
+</p>
+<h3>Status of This Memo</h3>
+<p>
+This is an Internet Standards Track document.</p>
+<p>
+This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p>
+<p>
+Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6121.</p>
+
+<h3>Copyright Notice</h3>
+<p>
+Copyright (c) 2011 IETF Trust and the persons identified as the
+document authors.  All rights reserved.</p>
+<p>
+This document is subject to BCP 78 and the IETF Trust's Legal
+Provisions Relating to IETF Documents
+(http://trustee.ietf.org/license-info) in effect on the date of
+publication of this document.  Please review these documents
+carefully, as they describe your rights and restrictions with respect
+to this document. Code Components extracted from this document must
+include Simplified BSD License text as described in Section 4.e of
+the Trust Legal Provisions and are provided without warranty as
+described in the Simplified BSD License.</p>
+<a name="toc"></a><hr />
+
+<table border="0" cellpadding="0" cellspacing="2" width="30" align="right">
+    <tr>
+        <td class="RFCbug">
+                <span class="RFC">&nbsp;RFC&nbsp;</span><br /><span class="hotText">&nbsp;6121&nbsp;</span>
+        </td>
+    </tr>
+    <tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a><br /></td></tr>
+</table>
+<h3>Table of Contents</h3>
+<p class="toc">
+<a href="#intro">1.</a>&nbsp;
+Introduction<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-overview">1.1.</a>&nbsp;
+Overview<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-history">1.2.</a>&nbsp;
+History<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-requirements">1.3.</a>&nbsp;
+Requirements<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-summary">1.4.</a>&nbsp;
+Functional Summary<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#intro-terms">1.5.</a>&nbsp;
+Terminology<br />
+<a href="#roster">2.</a>&nbsp;
+Managing the Roster<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax">2.1.</a>&nbsp;
+Syntax and Semantics<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-ver">2.1.1.</a>&nbsp;
+Ver Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items">2.1.2.</a>&nbsp;
+Roster Items<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-approved">2.1.2.1.</a>&nbsp;
+Approved Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-ask">2.1.2.2.</a>&nbsp;
+Ask Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-jid">2.1.2.3.</a>&nbsp;
+JID Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-name">2.1.2.4.</a>&nbsp;
+Name Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-subscription">2.1.2.5.</a>&nbsp;
+Subscription Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-items-group">2.1.2.6.</a>&nbsp;
+Group Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-actions-get">2.1.3.</a>&nbsp;
+Roster Get<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-actions-result">2.1.4.</a>&nbsp;
+Roster Result<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-actions-set">2.1.5.</a>&nbsp;
+Roster Set<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-syntax-actions-push">2.1.6.</a>&nbsp;
+Roster Push<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-login">2.2.</a>&nbsp;
+Retrieving the Roster on Login<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-add">2.3.</a>&nbsp;
+Adding a Roster Item<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-add-request">2.3.1.</a>&nbsp;
+Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-add-success">2.3.2.</a>&nbsp;
+Success Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-add-errors">2.3.3.</a>&nbsp;
+Error Cases<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-update">2.4.</a>&nbsp;
+Updating a Roster Item<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-update-request">2.4.1.</a>&nbsp;
+Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-update-success">2.4.2.</a>&nbsp;
+Success Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-update-error">2.4.3.</a>&nbsp;
+Error Cases<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-delete">2.5.</a>&nbsp;
+Deleting a Roster Item<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-delete-request">2.5.1.</a>&nbsp;
+Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-delete-success">2.5.2.</a>&nbsp;
+Success Case<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-delete-error">2.5.3.</a>&nbsp;
+Error Cases<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-versioning">2.6.</a>&nbsp;
+Roster Versioning<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-versioning-feature">2.6.1.</a>&nbsp;
+Stream Feature<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-versioning-request">2.6.2.</a>&nbsp;
+Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#roster-versioning-success">2.6.3.</a>&nbsp;
+Success Case<br />
+<a href="#sub">3.</a>&nbsp;
+Managing Presence Subscriptions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request">3.1.</a>&nbsp;
+Requesting a Subscription<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-gen">3.1.1.</a>&nbsp;
+Client Generation of Outbound Subscription Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-outbound">3.1.2.</a>&nbsp;
+Server Processing of Outbound Subscription Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-inbound">3.1.3.</a>&nbsp;
+Server Processing of Inbound Subscription Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-handle">3.1.4.</a>&nbsp;
+Client Processing of Inbound Subscription Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-approvalout">3.1.5.</a>&nbsp;
+Server Processing of Outbound Subscription Approval<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-request-approvalin">3.1.6.</a>&nbsp;
+Server Processing of Inbound Subscription Approval<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-cancel">3.2.</a>&nbsp;
+Canceling a Subscription<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-cancel-gen">3.2.1.</a>&nbsp;
+Client Generation of Subscription Cancellation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-cancel-outbound">3.2.2.</a>&nbsp;
+Server Processing of Outbound Subscription Cancellation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-cancel-inbound">3.2.3.</a>&nbsp;
+Server Processing of Inbound Subscription Cancellation<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-unsub">3.3.</a>&nbsp;
+Unsubscribing<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-unsub-gen">3.3.1.</a>&nbsp;
+Client Generation of Unsubscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-unsub-outbound">3.3.2.</a>&nbsp;
+Server Processing of Outbound Unsubscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-unsub-inbound">3.3.3.</a>&nbsp;
+Server Processing of Inbound Unsubscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-preapproval">3.4.</a>&nbsp;
+Pre-Approving a Subscription Request<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-preapproval-gen">3.4.1.</a>&nbsp;
+Client Generation of Subscription Pre-Approval<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#sub-preapproval-proc">3.4.2.</a>&nbsp;
+Server Processing of Subscription Pre-Approval<br />
+<a href="#presence">4.</a>&nbsp;
+Exchanging Presence Information<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-fundamentals">4.1.</a>&nbsp;
+Presence Fundamentals<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-initial">4.2.</a>&nbsp;
+Initial Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-initial-gen">4.2.1.</a>&nbsp;
+Client Generation of Initial Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-initial-outbound">4.2.2.</a>&nbsp;
+Server Processing of Outbound Initial Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-initial-inbound">4.2.3.</a>&nbsp;
+Server Processing of Inbound Initial Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-initial-client">4.2.4.</a>&nbsp;
+Client Processing of Initial Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-probe">4.3.</a>&nbsp;
+Presence Probes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-probe-outbound">4.3.1.</a>&nbsp;
+Server Generation of Outbound Presence Probe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-probe-inbound">4.3.2.</a>&nbsp;
+Server Processing of Inbound Presence Probe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-probe-inbound-id">4.3.2.1.</a>&nbsp;
+Handling of the 'id' Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-broadcast">4.4.</a>&nbsp;
+Subsequent Presence Broadcast<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-broadcast-gen">4.4.1.</a>&nbsp;
+Client Generation of Subsequent Presence Broadcast<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-broadcast-outbound">4.4.2.</a>&nbsp;
+Server Processing of Subsequent Outbound Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-broadcast-inbound">4.4.3.</a>&nbsp;
+Server Processing of Subsequent Inbound Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-broadcast-client">4.4.4.</a>&nbsp;
+Client Processing of Subsequent Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-unavailable">4.5.</a>&nbsp;
+Unavailable Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-unavailable-gen">4.5.1.</a>&nbsp;
+Client Generation of Unavailable Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-unavailable-outbound">4.5.2.</a>&nbsp;
+Server Processing of Outbound Unavailable Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-unavailable-inbound">4.5.3.</a>&nbsp;
+Server Processing of Inbound Unavailable Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-unavailable-client">4.5.4.</a>&nbsp;
+Client Processing of Unavailable Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed">4.6.</a>&nbsp;
+Directed Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-considerations">4.6.1.</a>&nbsp;
+General Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-gen">4.6.2.</a>&nbsp;
+Client Generation of Directed Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-outbound">4.6.3.</a>&nbsp;
+Server Processing of Outbound Directed Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-inbound">4.6.4.</a>&nbsp;
+Server Processing of Inbound Directed Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-client">4.6.5.</a>&nbsp;
+Client Processing of Inbound Directed Presence<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-directed-probe">4.6.6.</a>&nbsp;
+Server Processing of Presence Probes<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax">4.7.</a>&nbsp;
+Presence Syntax<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax-type">4.7.1.</a>&nbsp;
+Type Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax-children">4.7.2.</a>&nbsp;
+Child Elements<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax-children-show">4.7.2.1.</a>&nbsp;
+Show Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax-children-status">4.7.2.2.</a>&nbsp;
+Status Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-syntax-children-priority">4.7.2.3.</a>&nbsp;
+Priority Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#presence-extended">4.7.3.</a>&nbsp;
+Extended Content<br />
+<a href="#message">5.</a>&nbsp;
+Exchanging Messages<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-chat">5.1.</a>&nbsp;
+One-to-One Chat Sessions<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax">5.2.</a>&nbsp;
+Message Syntax<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-to">5.2.1.</a>&nbsp;
+To Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-type">5.2.2.</a>&nbsp;
+Type Attribute<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-body">5.2.3.</a>&nbsp;
+Body Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-subject">5.2.4.</a>&nbsp;
+Subject Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-thread">5.2.5.</a>&nbsp;
+Thread Element<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#message-syntax-extended">5.3.</a>&nbsp;
+Extended Content<br />
+<a href="#iq">6.</a>&nbsp;
+Exchanging IQ Stanzas<br />
+<a href="#session">7.</a>&nbsp;
+A Sample Session<br />
+<a href="#rules">8.</a>&nbsp;
+Server Rules for Processing XML Stanzas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-general">8.1.</a>&nbsp;
+General Considerations<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-noto">8.2.</a>&nbsp;
+No 'to' Address<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-remote">8.3.</a>&nbsp;
+Remote Domain<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local">8.4.</a>&nbsp;
+Local Domain<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart">8.5.</a>&nbsp;
+Local User<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-nosuchuser">8.5.1.</a>&nbsp;
+No Such User<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-barejid">8.5.2.</a>&nbsp;
+localpart@domainpart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-barejid-resource">8.5.2.1.</a>&nbsp;
+Available or Connected Resources<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-barejid-noresource">8.5.2.2.</a>&nbsp;
+No Available or Connected Resources<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-fulljid">8.5.3.</a>&nbsp;
+localpart@domainpart/resourcepart<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-fulljid-match">8.5.3.1.</a>&nbsp;
+Resource Matches<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-localpart-fulljid-nomatch">8.5.3.2.</a>&nbsp;
+No Resource Matches<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rules-local-message">8.5.4.</a>&nbsp;
+Summary of Message Delivery Rules<br />
+<a href="#uri">9.</a>&nbsp;
+Handling of URIs<br />
+<a href="#i18n">10.</a>&nbsp;
+Internationalization Considerations<br />
+<a href="#security">11.</a>&nbsp;
+Security Considerations<br />
+<a href="#conformance">12.</a>&nbsp;
+Conformance Requirements<br />
+<a href="#rfc.references1">13.</a>&nbsp;
+References<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references1">13.1.</a>&nbsp;
+Normative References<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references2">13.2.</a>&nbsp;
+Informative References<br />
+<a href="#substates">Appendix&nbsp;A.</a>&nbsp;
+Subscription States<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-defined">A.1.</a>&nbsp;
+Defined States<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-out">A.2.</a>&nbsp;
+Server Processing of Outbound Presence Subscription Stanzas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-out-subscribe">A.2.1.</a>&nbsp;
+Subscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-out-unsubscribe">A.2.2.</a>&nbsp;
+Unsubscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-out-subscribed">A.2.3.</a>&nbsp;
+Subscribed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-out-unsubscribed">A.2.4.</a>&nbsp;
+Unsubscribed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-in">A.3.</a>&nbsp;
+Server Processing of Inbound Presence Subscription Stanzas<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-in-subscribe">A.3.1.</a>&nbsp;
+Subscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-in-unsubscribe">A.3.2.</a>&nbsp;
+Unsubscribe<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-in-subscribed">A.3.3.</a>&nbsp;
+Subscribed<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#substates-in-unsubscribed">A.3.4.</a>&nbsp;
+Unsubscribed<br />
+<a href="#blocking">Appendix&nbsp;B.</a>&nbsp;
+Blocking Communication<br />
+<a href="#vcard">Appendix&nbsp;C.</a>&nbsp;
+vCards<br />
+<a href="#schema">Appendix&nbsp;D.</a>&nbsp;
+XML Schema for jabber:iq:roster<br />
+<a href="#diffs">Appendix&nbsp;E.</a>&nbsp;
+Differences From RFC 3921<br />
+<a href="#acks">Appendix&nbsp;F.</a>&nbsp;
+Acknowledgements<br />
+</p>
+<br clear="all" />
+
+<a name="intro"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1"></a><h3>1.&nbsp;
+Introduction</h3>
+
+<a name="intro-overview"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.1"></a><h3>1.1.&nbsp;
+Overview</h3>
+
+<p>The Extensible Messaging and Presence Protocol (XMPP) is an application profile of the Extensible Markup Language <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a> that enables the near-real-time exchange of structured yet extensible data between any two or more network entities.  The core features of XMPP defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> provide the building blocks for many types of near-real-time applications, which can be layered on top of the core by sending application-specific data qualified by particular XML namespaces (refer to <a class='info' href='#XML-NAMES'>[XML&#8209;NAMES]<span> (</span><span class='info'>Bray, T., Hollander, D., and A. Layman, &ldquo;Namespaces in XML,&rdquo; January&nbsp;1999.</span><span>)</span></a>).  This document defines XMPP extensions that provide the basic functionality expected of an instant messaging (IM) and presence application as described in <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a>.
+</p>
+<a name="intro-history"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.2"></a><h3>1.2.&nbsp;
+History</h3>
+
+<p>The basic syntax and semantics of XMPP were developed originally within the Jabber open-source community, mainly in 1999.  In late 2002, the XMPP Working Group was chartered with developing an adaptation of the core Jabber protocol that would be suitable as an IETF IM and presence technology in accordance with <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a>.  In October 2004, <a class='info' href='#RFC3920'>[RFC3920]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; October&nbsp;2004.</span><span>)</span></a> and <a class='info' href='#RFC3921'>[RFC3921]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; October&nbsp;2004.</span><span>)</span></a> were published, representing the most complete definition of XMPP at that time.
+</p>
+<p>Since 2004 the Internet community has gained extensive implementation and deployment experience with XMPP, including formal interoperability testing carried out under the auspices of the XMPP Standards Foundation (XSF).  This document incorporates comprehensive feedback from software developers and service providers, including a number of backward-compatible modifications summarized under <a class='info' href='#diffs'>Appendix&nbsp;E<span> (</span><span class='info'>Differences From RFC 3921</span><span>)</span></a>.  As a result, this document reflects the rough consensus of the Internet community regarding the IM and presence features of XMPP 1.0, thus obsoleting RFC 3921.
+</p>
+<a name="intro-requirements"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.3"></a><h3>1.3.&nbsp;
+Requirements</h3>
+
+<p>Traditionally, IM applications have combined the following factors:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>The central point of focus is a list of one's contacts or "buddies" (in XMPP this list is called a "roster").
+</li>
+<li>The purpose of using such an application is to exchange relatively brief text messages with particular contacts in close to real time -- often relatively large numbers of such messages in rapid succession, in the form of a one-to-one "chat session" as described under <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a>.
+</li>
+<li>The catalyst for exchanging messages is "presence" -- i.e., information about the network availability of particular contacts (thus knowing who is online and available for a one-to-one chat session).
+</li>
+<li>Presence information is provided only to contacts that one has authorized by means of an explicit agreement called a "presence subscription".
+</li>
+</ol><p>
+      
+</p>
+<p>Thus at a high level this document assumes that a user needs to be able to complete the following use cases:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>Manage items in one's contact list
+</li>
+<li>Exchange messages with one's contacts
+</li>
+<li>Exchange presence information with one's contacts
+</li>
+<li>Manage presence subscriptions to and from one's contacts
+</li>
+</ul><p>
+      
+</p>
+<p>Detailed definitions of these functionality areas are contained in RFC 2779 <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a>, and the interested reader is referred to that document regarding in-depth requirements.  Although the XMPP IM and presence extensions specified herein meet the requirements of RFC 2779, they were not designed explicitly with that specification in mind, since the base protocol evolved through an open development process within the Jabber open-source community before RFC 2779 was written.  Although XMPP protocol extensions addressing many other functionality areas have been defined in the XMPP Standards Foundation's XEP series (e.g., multi-user text chat as specified in <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2008.</span><span>)</span></a>), such extensions are not specified in this document because they are not mandated by RFC 2779.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: RFC 2779 stipulates that presence services must be separable from IM services and vice-versa; i.e., it must be possible to use the protocol to provide a presence service, a messaging service, or both.  Although the text of this document assumes that implementations and deployments will want to offer a unified IM and presence service, it is not mandatory for an XMPP service to offer both a presence service and a messaging service, and the protocol makes it possible to offer separate and distinct services for presence and for messaging.  (For example, a presence-only service could return a &lt;service-unavailable/&gt; stanza error if a client attempts to send a &lt;message/&gt; stanza.)
+</p>
+</blockquote>
+
+<a name="intro-summary"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.4"></a><h3>1.4.&nbsp;
+Functional Summary</h3>
+
+<p>This non-normative section provides a developer-friendly, functional summary of XMPP-based IM and presence features; consult the sections that follow for a normative definition of these features.
+</p>
+<p><a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> specifies how an XMPP client connects to an XMPP server.  In particular, it specifies the preconditions that need to be fulfilled before a client is allowed to send XML stanzas (the basic unit of meaning in XMPP) to other entities on an XMPP network.  These preconditions comprise negotiation of the XML stream and include exchange of XML stream headers, optional channel encryption via Transport Layer Security <a class='info' href='#TLS'>[TLS]<span> (</span><span class='info'>Dierks, T. and E. Rescorla, &ldquo;The Transport Layer Security (TLS) Protocol Version 1.2,&rdquo; August&nbsp;2008.</span><span>)</span></a>, mandatory authentication via Simple Authentication and Security Layer <a class='info' href='#SASL'>[SASL]<span> (</span><span class='info'>Melnikov, A. and K. Zeilenga, &ldquo;Simple Authentication and Security Layer (SASL),&rdquo; June&nbsp;2006.</span><span>)</span></a>, and binding of a resource to the stream for client addressing.  The reader is referred to <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> for details regarding these preconditions, and knowledge of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> is assumed herein.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: <a class='info' href='#RFC3921'>[RFC3921]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; October&nbsp;2004.</span><span>)</span></a> specified one additional precondition: formal establishment of an instant messaging and presence session.  Implementation and deployment experience has shown that this additional step is unnecessary.  However, for backward compatibility an implementation MAY still offer that feature.  This enables older software to connect while letting newer software save a round trip.
+</p>
+</blockquote>
+
+<p>Upon fulfillment of the preconditions specified in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, an XMPP client has a long-lived XML stream with an XMPP server, which enables the user controlling that client to send and receive a potentially unlimited number of XML stanzas over the stream.  Such a stream can be used to exchange messages, share presence information, and engage in structured request-response interactions in close to real time.  After negotiation of the XML stream, the typical flow for an instant messaging and presence session is as follows:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>Retrieve one's roster.  (See <a class='info' href='#roster-login'>Section&nbsp;2.2<span> (</span><span class='info'>Retrieving the Roster on Login</span><span>)</span></a>.)
+</li>
+<li>Send initial presence to the server for broadcast to all subscribed contacts, thus "going online" from the perspective of XMPP communication.  (See <a class='info' href='#presence-initial'>Section&nbsp;4.2<span> (</span><span class='info'>Initial Presence</span><span>)</span></a>.)
+</li>
+<li>Exchange messages, manage presence subscriptions, perform roster
+updates, and in general process and generate other XML stanzas with particular
+semantics throughout the life of the session.  (See Sections <a class='info' href='#message'>5<span> (</span><span class='info'>Exchanging Messages</span><span>)</span></a>, <a class='info' href='#sub'>3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>,
+<a class='info' href='#roster'>2<span> (</span><span class='info'>Managing the Roster</span><span>)</span></a>, and <a class='info' href='#iq'>6<span> (</span><span class='info'>Exchanging IQ Stanzas</span><span>)</span></a>.)
+</li>
+<li>Terminate the session when desired by sending unavailable presence and closing the underlying XML stream. (See <a class='info' href='#presence-unavailable'>Section&nbsp;4.5<span> (</span><span class='info'>Unavailable Presence</span><span>)</span></a>.)
+</li>
+</ol><p>
+      
+</p>
+<a name="intro-terms"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.1.5"></a><h3>1.5.&nbsp;
+Terminology</h3>
+
+<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 <a class='info' href='#KEYWORDS'>[KEYWORDS]<span> (</span><span class='info'>Bradner, S., &ldquo;Key words for use in RFCs to Indicate Requirement Levels,&rdquo; March&nbsp;1997.</span><span>)</span></a>.
+</p>
+<p>This document inherits the terminology defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>The terms "automated client" and "interactive client" are to be understood in the sense defined in <a class='info' href='#TLS-CERTS'>[TLS&#8209;CERTS]<span> (</span><span class='info'>Saint-Andre, P. and J. Hodges, &ldquo;Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>For convenience, this document employs the term "user" to refer to the owner of an XMPP account; however, account owners need not be humans and can be bots, devices, or other automated applications.
+</p>
+<p>Several other terms, such as "interested resource", are defined within the body of this document.
+</p>
+<p>Following the "XML Notation" used in <a class='info' href='#IRI'>[IRI]<span> (</span><span class='info'>Duerst, M. and M. Suignard, &ldquo;Internationalized Resource Identifiers (IRIs),&rdquo; January&nbsp;2005.</span><span>)</span></a> to represent characters that cannot be rendered in ASCII-only documents, some examples in this document use the form "&amp;#x...." as a notational device to represent <a class='info' href='#UNICODE'>[UNICODE]<span> (</span><span class='info'>The Unicode Consortium, &ldquo;The Unicode Standard, Version 6.0,&rdquo; 2010.</span><span>)</span></a> characters (e.g., the string "&amp;#x0159;" stands for the Unicode character LATIN SMALL LETTER R WITH CARON); this form is definitely not to be sent over the wire in XMPP systems.
+</p>
+<p>In examples, lines have been wrapped for improved readability, "[...]" means elision, and the following prepended strings are used (these prepended strings are not to be sent over the wire):
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>C: = client
+</li>
+<li>CC: = contact's client
+</li>
+<li>CS: = contact's server
+</li>
+<li>S: = server
+</li>
+<li>UC: = user's client
+</li>
+<li>US: = user's server
+</li>
+</ul><p>
+      
+</p>
+<p>Readers need to be aware that the examples are not exhaustive
+      and that, in examples for some protocol flows, the alternate
+      steps shown would not necessarily be triggered by the exact data
+      sent in the previous step; in all cases, the protocol definitions specified in this document or in normatively referenced documents rule over any examples provided here.  All examples are fictional and the information exchanged (e.g., usernames and passwords) does not represent any existing users or servers.
+</p>
+<a name="roster"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2"></a><h3>2.&nbsp;
+Managing the Roster</h3>
+
+<p>In XMPP, a user's roster contains any number of specific contacts.  A user's roster is stored by the user's server on the user's behalf so that the user can access roster information from any device.  When the user adds items to the roster or modifies existing items, if an error does not occur then the server SHOULD store that data unmodified if at all possible and MUST return the data it has stored when an authorized client requests the roster.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Because the user's roster can contain confidential data, the server MUST restrict access to this data so that only authorized entities (typically limited to the account owner) are able to retrieve, modify, or delete it.
+</p>
+</blockquote>
+
+<p>RFC 3921 assumed that the only place where a user stores their roster is the server where the user's account is registered and at which the user authenticates for access to the XMPP network.  This specification removes that strict coupling of roster storage to account registration and network authentication, with the result that a user could store their roster at another location, or could have multiple rosters that are stored in multiple locations.  However, in the absence of implementation and deployment experience with a more flexible roster storage model, this specification retains the terminology of RFC 3921 by using the terms "client" and "server" (and "the roster" instead of "a roster"), rather than coining a new term for "a place where a user stores a roster".  Future documents might provide normative rules for non-server roster storage or for the management of multiple rosters, but such rules are out of scope for this document.
+</p>
+<a name="roster-syntax"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1"></a><h3>2.1.&nbsp;
+Syntax and Semantics</h3>
+
+<p>Rosters are managed using &lt;iq/&gt; stanzas (see Section 8.2.3 of
+<a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>), specifically by means of a &lt;query/&gt; child element qualified by the 'jabber:iq:roster' namespace.  The detailed syntax and semantics are defined in the following sections.
+</p>
+<a name="roster-syntax-ver"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.1"></a><h3>2.1.1.&nbsp;
+Ver Attribute</h3>
+
+<p>The 'ver' attribute is a string that identifies a particular version of the roster information.  The value MUST be generated only by the server and MUST be treated by the client as opaque.  The server can use any appropriate method for generating the version ID, such as a hash of the roster data or a strictly increasing sequence number.
+</p>
+<p>Inclusion of the 'ver' attribute is RECOMMENDED.
+</p>
+<p>Use of the 'ver' attribute is described more fully under <a class='info' href='#roster-versioning'>Section&nbsp;2.6<span> (</span><span class='info'>Roster Versioning</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: The 'ver' attribute of the &lt;query/&gt; element was not defined in RFC 3921 and is newly defined in this specification.
+</p>
+</blockquote>
+
+<a name="roster-syntax-items"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2"></a><h3>2.1.2.&nbsp;
+Roster Items</h3>
+
+<p>The &lt;query/&gt; element inside a <a class='info' href='#roster-syntax-actions-set'>roster set<span> (</span><span class='info'>Roster Set</span><span>)</span></a> contains one &lt;item/&gt; child, and a <a class='info' href='#roster-syntax-actions-result'>roster result<span> (</span><span class='info'>Roster Result</span><span>)</span></a> typically contains multiple &lt;item/&gt; children.  Each &lt;item/&gt; element describes a unique "roster item" (sometimes also called a "contact").
+</p>
+<p>The syntax of the &lt;item/&gt; element is described in the following sections.
+</p>
+<a name="roster-syntax-items-approved"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.1"></a><h3>2.1.2.1.&nbsp;
+Approved Attribute</h3>
+
+<p>The boolean 'approved' attribute with a value of "true" is used to signal subscription pre-approval as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a> (the default is "false", in accordance with <a class='info' href='#XML-DATATYPES'>[XML&#8209;DATATYPES]<span> (</span><span class='info'>Biron, P. and A. Malhotra, &ldquo;XML Schema Part 2: Datatypes Second Edition,&rdquo; October&nbsp;2004.</span><span>)</span></a>).
+</p>
+<p>A server SHOULD include the 'approved' attribute to inform the client of subscription pre-approvals.  A client MUST NOT include the 'approved' attribute in the roster sets it sends to the server, but instead MUST use presence stanzas of type "subscribed" and "unsubscribed" to manage pre-approvals as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: The 'approved' attribute of the &lt;item/&gt; element was not defined in RFC 3921 and is newly defined in this specification.
+</p>
+</blockquote>
+
+<a name="roster-syntax-items-ask"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.2"></a><h3>2.1.2.2.&nbsp;
+Ask Attribute</h3>
+
+<p>The 'ask' attribute of the &lt;item/&gt; element with a value of "subscribe" is used to signal various subscription sub-states that include a "Pending Out" aspect as described under <a class='info' href='#sub-request-outbound'>Section&nbsp;3.1.2<span> (</span><span class='info'>Server Processing of Outbound Subscription Request</span><span>)</span></a>.
+</p>
+<p>A server SHOULD include the 'ask' attribute to inform the client of "Pending Out" sub-states.  A client MUST NOT include the 'ask' attribute in the roster sets it sends to the server, but instead MUST use presence stanzas of type "subscribe" and "unsubscribe" to manage such sub-states as described under <a class='info' href='#sub-request-outbound'>Section&nbsp;3.1.2<span> (</span><span class='info'>Server Processing of Outbound Subscription Request</span><span>)</span></a>.
+</p>
+<a name="roster-syntax-items-jid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.3"></a><h3>2.1.2.3.&nbsp;
+JID Attribute</h3>
+
+<p>The 'jid' attribute of the &lt;item/&gt; element specifies the Jabber Identifier (JID) that uniquely identifies the roster item.
+</p>
+<p>The 'jid' attribute is REQUIRED whenever a client or server adds, updates, deletes, or returns a roster item.
+</p>
+<a name="roster-syntax-items-name"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.4"></a><h3>2.1.2.4.&nbsp;
+Name Attribute</h3>
+
+<p>The 'name' attribute of the &lt;item/&gt; element specifies the "handle" to be associated with the JID, as determined by the user (not the contact).  Although the value of the 'name' attribute MAY have meaning to a human user, it is opaque to the server.  However, the 'name' attribute MAY be used by the server for matching purposes within the context of various XMPP extensions (one possible comparison method is that described for XMPP resourceparts in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p>
+<p>It is OPTIONAL for a client to include the 'name' attribute when adding or updating a roster item.
+</p>
+<a name="roster-syntax-items-subscription"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.5"></a><h3>2.1.2.5.&nbsp;
+Subscription Attribute</h3>
+
+<p>The state of the presence subscription is captured in the 'subscription' attribute of the &lt;item/&gt; element.  The defined subscription-related values are:
+</p>
+<p>
+            </p>
+<blockquote class="text"><dl>
+<dt>none:</dt>
+<dd>the user does not have a subscription to the contact's presence, and the contact does not have a subscription to the user's presence; this is the default value, so if the subscription attribute is not included then the state is to be understood as "none"
+</dd>
+<dt>to:</dt>
+<dd>the user has a subscription to the contact's presence, but the contact does not have a subscription to the user's presence
+</dd>
+<dt>from:</dt>
+<dd>the contact has a subscription to the user's presence, but the user does not have a subscription to the contact's presence
+</dd>
+<dt>both:</dt>
+<dd>the user and the contact have subscriptions to each other's presence (also called a "mutual subscription")
+</dd>
+</dl></blockquote><p>
+          
+</p>
+<p>In a <a class='info' href='#roster-syntax-actions-result'>roster result<span> (</span><span class='info'>Roster Result</span><span>)</span></a>, the client MUST ignore values of the 'subscription' attribute other than "none", "to", "from", or "both".
+</p>
+<p>In a <a class='info' href='#roster-syntax-actions-push'>roster push<span> (</span><span class='info'>Roster Push</span><span>)</span></a>, the client MUST ignore values of the 'subscription' attribute other than "none", "to", "from", "both", or "remove".
+</p>
+<p>In a <a class='info' href='#roster-syntax-actions-set'>roster set<span> (</span><span class='info'>Roster Set</span><span>)</span></a>, the 'subscription' attribute MAY be included with a value of "remove", which indicates that the item is to be removed from the roster; in a roster set the server MUST ignore all values of the 'subscription' attribute other than "remove".
+</p>
+<p>Inclusion of the 'subscription' attribute is OPTIONAL.
+</p>
+<a name="roster-syntax-items-group"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.2.6"></a><h3>2.1.2.6.&nbsp;
+Group Element</h3>
+
+<p>The &lt;group/&gt; child element specifies a category or "bucket" into which the roster item is to be grouped by a client.  An &lt;item/&gt; element MAY contain more than one &lt;group/&gt; element, which means that roster groups are not exclusive.  Although the XML character data of the &lt;group/&gt; element MAY have meaning to a human user, it is opaque to the server.  However, the &lt;group/&gt; element MAY be used by the server for matching purposes within the context of various XMPP extensions (one possible comparison method is that described for XMPP resourceparts in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p>
+<p>It is OPTIONAL for a client to include the &lt;group/&gt; element when adding or updating a roster item.  If a <a class='info' href='#roster-syntax-actions-set'>roster set<span> (</span><span class='info'>Roster Set</span><span>)</span></a> includes no &lt;group/&gt; element, then the item is to be interpreted as being affiliated with no group.
+</p>
+<a name="roster-syntax-actions-get"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.3"></a><h3>2.1.3.&nbsp;
+Roster Get</h3>
+
+<p>A "roster get" is a client's request for the server to return the roster; syntactically it is an IQ stanza of type "get" sent from client to server and containing a &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace, where the &lt;query/&gt; element MUST NOT contain any &lt;item/&gt; child elements.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='bv1bs71f'
+       type='get'&gt;
+    &lt;query xmlns='jabber:iq:roster'/&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>The expected outcome of sending a roster get is for the server to return a roster result.
+</p>
+<a name="roster-syntax-actions-result"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.4"></a><h3>2.1.4.&nbsp;
+Roster Result</h3>
+
+<p>A "roster result" is the server's response to a roster get; syntactically it is an IQ stanza of type "result" sent from server to client and containing a &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace.
+</p>
+<p>The &lt;query/&gt; element in a roster result contains one &lt;item/&gt; element for each contact and therefore can contain more than one &lt;item/&gt; element.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='bv1bs71f'
+       to='juliet@example.com/chamber'
+       type='result'&gt;
+    &lt;query xmlns='jabber:iq:roster' ver='ver7'&gt;
+      &lt;item jid='nurse@example.com'/&gt;
+      &lt;item jid='romeo@example.net'/&gt;
+    &lt;/query&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>If the roster exists but there are no contacts in the roster, then the server MUST return an IQ-result containing a child &lt;query/&gt; element that in turn contains no &lt;item/&gt; children (i.e., the server MUST NOT return an empty &lt;iq/&gt; stanza of type "error").
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='bv1bs71f'
+       to='juliet@example.com/chamber'
+       type='result'&gt;
+    &lt;query xmlns='jabber:iq:roster' ver='ver9'/&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>If the roster does not exist, then the server MUST return a stanza error with a condition of &lt;item-not-found/&gt;.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='bv1bs71f'
+       to='juliet@example.com/chamber'
+       type='error'&gt;
+    &lt;error type='cancel'&gt;
+      &lt;item-not-found
+          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    &lt;/error&gt;
+  &lt;/iq&gt;
+</pre></div>
+<a name="roster-syntax-actions-set"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.5"></a><h3>2.1.5.&nbsp;
+Roster Set</h3>
+
+<p>A "roster set" is a client's request for the server to modify (i.e., create, update, or delete) a roster item; syntactically it is an IQ stanza of type "set" sent from client to server and containing a &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace.
+</p>
+<p>The following rules apply to roster sets:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The &lt;query/&gt; element MUST contain one and only one &lt;item/&gt; element.
+</li>
+<li>The server MUST ignore any value of the 'subscription' attribute other than "remove" (see <a class='info' href='#roster-syntax-items-subscription'>Section&nbsp;2.1.2.5<span> (</span><span class='info'>Subscription Attribute</span><span>)</span></a>).
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Traditionally, the IQ stanza of the roster set included no 'to' address, with the result that all roster sets were sent from an authenticated resource (full JID) of the account whose roster was being updated.  Furthermore, RFC 3921 required a server to perform special-case checking of roster sets to ignore the 'to' address; however, this specification has removed that special-casing, which means that a roster set might include a 'to' address other than that of the sender.  Therefore, the entity that processes a roster set MUST verify that the sender of the roster set is authorized to update the roster, and if not return a &lt;forbidden/&gt; error.
+</p>
+</blockquote>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='rs1'
+       type='set'&gt;
+    &lt;query xmlns='jabber:iq:roster'&gt;
+      &lt;item jid='nurse@example.com'/&gt;
+    &lt;/query&gt;
+  &lt;/iq&gt;
+</pre></div>
+<a name="roster-syntax-actions-push"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.1.6"></a><h3>2.1.6.&nbsp;
+Roster Push</h3>
+
+<p>A "roster push" is a newly created, updated, or deleted roster item that is sent from the server to the client; syntactically it is an IQ stanza of type "set" sent from server to client and containing a &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace.
+</p>
+<p>The following rules apply to roster pushes:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The &lt;query/&gt; element in a roster push MUST contain one and only one &lt;item/&gt; element.
+</li>
+<li>A receiving client MUST ignore the stanza unless it has no 'from' attribute (i.e., implicitly from the bare JID of the user's account) or it has a 'from' attribute whose value matches the user's bare JID &lt;user@domainpart&gt;.
+</li>
+</ol><p>
+        
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='a78b4q6ha463'
+       to='juliet@example.com/chamber'
+       type='set'&gt;
+    &lt;query xmlns='jabber:iq:roster'&gt;
+      &lt;item jid='nurse@example.com'/&gt;
+    &lt;/query&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>As mandated by the semantics of the IQ stanza as defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, each resource that receives a roster push from the server is supposed to reply with an IQ stanza of type "result" or "error" (however, it is known that many existing clients do not reply to roster pushes).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='a78b4q6ha463'
+       type='result'/&gt;
+
+C: &lt;iq from='juliet@example.com/chamber'
+       id='a78b4q6ha463'
+       type='result'/&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Traditionally, a roster push included no 'from' address, with the result that all roster pushes were sent implicitly from the bare JID of the account itself.  However, this specification allows entities other than the user's server to maintain roster information, which means that a roster push might include a 'from' address other than the bare JID of the user's account.  Therefore, the client MUST check the 'from' address to verify that the sender of the roster push is authorized to update the roster.  If the client receives a roster push from an unauthorized entity, it MUST NOT process the pushed data; in addition, the client can either return a stanza error of &lt;service-unavailable/&gt; error or refuse to return a stanza error at all (the latter behavior overrides a MUST-level requirement from <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> for the purpose of preventing a presence leak).
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: There is no error case for client processing of roster pushes; if the server receives an IQ of type "error" in response to a roster push then it SHOULD ignore the error.
+</p>
+</blockquote>
+
+<a name="roster-login"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.2"></a><h3>2.2.&nbsp;
+Retrieving the Roster on Login</h3>
+
+<p>Upon authenticating with a server and binding a resource (thus becoming a connected resource as defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>), a client SHOULD request the roster before sending initial presence (however, because receiving the roster is not necessarily desirable for all resources, e.g., a connection with limited bandwidth, the client's request for the roster is not mandatory).  After a connected resource sends initial presence (see <a class='info' href='#presence-initial'>Section&nbsp;4.2<span> (</span><span class='info'>Initial Presence</span><span>)</span></a>), it is referred to as an "available resource".  If a connected resource or available resource requests the roster, it is referred to as an "interested resource".  The server MUST send roster pushes to all interested resources.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Presence subscription requests are sent to available resources, whereas the roster pushes associated with subscription state changes are sent to interested resources.  Therefore, if a resource wishes to receive both subscription requests and roster pushes, it MUST both send initial presence and request the roster.
+</p>
+</blockquote>
+
+<p>A client requests the roster by sending a roster get over its stream with the server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='hu2bac18'
+       type='get'&gt;
+     &lt;query xmlns='jabber:iq:roster'/&gt;
+   &lt;/iq&gt;
+</pre></div><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='hu2bac18'
+       to='juliet@example.com/balcony'
+       type='result'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver11'&gt;
+       &lt;item jid='romeo@example.net'
+             name='Romeo'
+             subscription='both'&gt;
+         &lt;group&gt;Friends&lt;/group&gt;
+       &lt;/item&gt;
+       &lt;item jid='mercutio@example.com'
+             name='Mercutio'
+             subscription='from'/&gt;
+       &lt;item jid='benvolio@example.net'
+             name='Benvolio'
+             subscription='both'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>If the server cannot process the roster get, it MUST return an appropriate stanza error as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> (such as &lt;service-unavailable/&gt; if the roster namespace is not supported or &lt;internal-server-error/&gt; if the server experiences trouble processing or returning the roster).
+</p>
+<a name="roster-add"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.3"></a><h3>2.3.&nbsp;
+Adding a Roster Item</h3>
+
+<a name="roster-add-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.3.1"></a><h3>2.3.1.&nbsp;
+Request</h3>
+
+<p>At any time, a client can add an item to the roster.  This is done by sending a roster set containing a new item.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='ph1xaz53'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="roster-add-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.3.2"></a><h3>2.3.2.&nbsp;
+Success Case</h3>
+
+<p>If the server can successfully process the roster set for the new item (i.e., if no error occurs), it MUST create the item in the user's roster and proceed as follows.
+</p>
+<p>The server MUST return an IQ stanza of type "result" to the connected resource that sent the roster set.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq id='ph1xaz53'
+       to='juliet@example.com/balcony'
+       type='result'/&gt;
+</pre></div>
+<p>The server MUST also send a roster push containing the new roster item to all of the user's interested resources, including the resource that generated the roster set.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq to='juliet@example.com/balcony'
+       id='a78b4q6ha463'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver13'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'
+             subscription='none'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq to='juliet@example.com/chamber'
+       id='x81g3bdy4n19'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver13'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'
+             subscription='none'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>As mandated by the semantics of the IQ stanza as defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, each resource that receives a roster push from the server is supposed to reply with an IQ stanza of type "result" or "error" (however, it is known that many existing clients do not reply to roster pushes).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='a78b4q6ha463'
+       type='result'/&gt;
+
+C: &lt;iq from='juliet@example.com/chamber'
+       id='x81g3bdy4n19'
+       type='result'/&gt;
+</pre></div>
+<a name="roster-add-errors"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.3.3"></a><h3>2.3.3.&nbsp;
+Error Cases</h3>
+
+<p>If the server cannot successfully process the roster set, it MUST return a stanza error.  The following error cases are defined.  Naturally, other stanza errors can occur, such as &lt;internal-server-error/&gt; if the server experiences an internal problem with processing the roster get, or even &lt;not-allowed/&gt; if the server only allows roster modifications by means of a non-XMPP method such as a web interface.
+</p>
+<p>The server MUST return a &lt;forbidden/&gt; stanza error to the client if the sender of the roster set is not authorized to update the roster (where typically only an authenticated resource of the account itself is authorized).
+</p>
+<p>The server MUST return a &lt;bad-request/&gt; stanza error to the client if the roster set contains any of the following violations:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The &lt;query/&gt; element contains more than one &lt;item/&gt; child element.
+</li>
+<li>The &lt;item/&gt; element contains more than one &lt;group/&gt; element, but there are duplicate groups (one possible comparison method for determining duplicates is that described for XMPP resourceparts in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+</ol><p>
+        
+</p>
+<p>The server MUST return a &lt;not-acceptable/&gt; stanza error to the client if the roster set contains any of the following violations:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>The length of the 'name' attribute is greater than a server-configured limit.
+</li>
+<li>The XML character data of the &lt;group/&gt; element is of zero length (to remove an item from all groups, the client instead needs to exclude any &lt;group/&gt; element from the roster set).
+</li>
+<li>The XML character data of the &lt;group/&gt; element is larger than a server-configured limit.
+</li>
+</ol><p>
+        
+</p>
+<p>Error: Roster set initiated by unauthorized entity
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='ix7s53v2'
+       to='romeo@example.net'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='ix7s53v2'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+    &lt;error type='auth'&gt;
+      &lt;forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    &lt;/error&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>Error: Roster set contains more than one item
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='nw83vcj4'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+       &lt;item jid='mother@example.com'
+             name='Mom'&gt;
+         &lt;group&gt;Family&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='nw83vcj4'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+    &lt;error type='modify'&gt;
+      &lt;bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+    &lt;/error&gt;
+  &lt;/iq&gt;
+</pre></div>
+<p>Error: Roster set contains item with oversized handle
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='yl491b3d'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='[ ... some-very-long-handle ... ]'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='yl491b3d'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Error: Roster set contains duplicate groups
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='tk3va749'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='tk3va749'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Error: Roster set contains empty group
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='fl3b486u'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'&gt;
+         &lt;group&gt;&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='fl3b486u'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Error: Roster set contains oversized group name
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='qh3b4v19'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             name='Nurse'&gt;
+         &lt;group&gt;[ ... some-very-long-group-name ... ]&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='qh3b4v19'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: Some servers return a &lt;not-allowed/&gt; stanza error to the client if the value of the &lt;item/&gt; element's 'jid' attribute matches the bare JID &lt;localpart@domainpart&gt; of the user's account.
+</p>
+</blockquote>
+
+<a name="roster-update"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.4"></a><h3>2.4.&nbsp;
+Updating a Roster Item</h3>
+
+<a name="roster-update-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.4.1"></a><h3>2.4.1.&nbsp;
+Request</h3>
+
+<p>Updating an existing roster item is done in the same way as adding a new roster item, i.e., by sending a roster set to the server.  Because a roster item is atomic, the item MUST be updated exactly as provided in the roster set.
+</p>
+<p>There are several reasons why a client might update a roster item:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Adding a group
+</li>
+<li>Deleting a group
+</li>
+<li>Changing the handle
+</li>
+<li>Deleting the handle
+</li>
+</ol><p>
+        
+</p>
+<p>Consider a roster item that is defined as follows:
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+    &lt;item jid='romeo@example.net'
+          name='Romeo'&gt;
+      &lt;group&gt;Friends&lt;/group&gt;
+    &lt;/item&gt;
+</pre></div>
+<p>The user who has this item in her roster might want to add the item to another group.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='di43b2x9'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='romeo@example.net'
+             name='Romeo'&gt;
+         &lt;group&gt;Friends&lt;/group&gt;
+         &lt;group&gt;Lovers&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>Sometime later, the user might want to remove the item from the original group.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='lf72v157'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='romeo@example.net'
+             name='Romeo'&gt;
+         &lt;group&gt;Lovers&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>The user might want to remove the item from all groups.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='ju4b62a5'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='romeo@example.net'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>The user might also want to change the handle for the item.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='gb3sv487'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='romeo@example.net'
+             name='MyRomeo'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>The user might then want to remove the handle altogether.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='o3bx66s5'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='romeo@example.net'
+             name=''/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Including an empty 'name' attribute is equivalent to including no 'name' attribute; both actions set the name to the empty string.
+</p>
+</blockquote>
+
+<a name="roster-update-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.4.2"></a><h3>2.4.2.&nbsp;
+Success Case</h3>
+
+<p>As with adding a roster item, if the roster item can be successfully processed then the server MUST update the item in the user's roster, send a roster push to all of the user's interested resources, and send an IQ result to the initiating resource; details are provided under <a class='info' href='#roster-add'>Section&nbsp;2.3<span> (</span><span class='info'>Adding a Roster Item</span><span>)</span></a>.
+</p>
+<a name="roster-update-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.4.3"></a><h3>2.4.3.&nbsp;
+Error Cases</h3>
+
+<p>The error cases described under <a class='info' href='#roster-add-errors'>Section&nbsp;2.3.3<span> (</span><span class='info'>Error Cases</span><span>)</span></a> also apply to updating a roster item.
+</p>
+<a name="roster-delete"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.5"></a><h3>2.5.&nbsp;
+Deleting a Roster Item</h3>
+
+<a name="roster-delete-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.5.1"></a><h3>2.5.1.&nbsp;
+Request</h3>
+
+<p>At any time, a client can delete an item from his or her roster by sending a roster set and specifying a value of "remove" for the 'subscription' attribute.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='hm4hs97y'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='nurse@example.com'
+             subscription='remove'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="roster-delete-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.5.2"></a><h3>2.5.2.&nbsp;
+Success Case</h3>
+
+<p>As with adding a roster item, if the server can successfully process the roster set then it MUST update the item in the user's roster, send a roster push to all of the user's interested resources (with the 'subscription' attribute set to a value of "remove"), and send an IQ result to the initiating resource; details are provided under <a class='info' href='#roster-add'>Section&nbsp;2.3<span> (</span><span class='info'>Adding a Roster Item</span><span>)</span></a>.
+</p>
+<p>In addition, the user's server might need to generate one or more subscription-related presence stanzas, as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the user has a presence subscription to the contact, then the user's server MUST send a presence stanza of type "unsubscribe" to the contact (in order to unsubscribe from the contact's presence).
+</li>
+<li>If the contact has a presence subscription to the user, then the user's server MUST send a presence stanza of type "unsubscribed" to the contact (in order to cancel the contact's subscription to the user).
+</li>
+<li>If the presence subscription is mutual, then the user's server MUST send both a presence stanza of type "unsubscribe" and a presence stanza of type "unsubscribed" to the contact.
+</li>
+</ol><p>
+        
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;presence from='juliet@example.com'
+             id='lm3ba81g'
+             to='nurse@example.com'
+             type='unsubscribe'/&gt;
+
+S: &lt;presence from='juliet@example.com'
+             id='xb2c1v4k'
+             to='nurse@example.com'
+             type='unsubscribed'/&gt;
+</pre></div>
+<a name="roster-delete-error"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.5.3"></a><h3>2.5.3.&nbsp;
+Error Cases</h3>
+
+<p>If the value of the 'jid' attribute specifies an item that is not in the roster, then the server MUST return an &lt;item-not-found/&gt; stanza error.
+</p>
+<p>Error: Roster item not found
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='juliet@example.com/balcony'
+       id='uj4b1ca8'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster'&gt;
+       &lt;item jid='[ ... non-existent-jid ... ]'
+             subscription='remove'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq id='uj4b1ca8'
+       to='juliet@example.com/balcony'
+       type='error'&gt;
+     &lt;error type='modify'&gt;
+       &lt;item-not-found
+           xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+     &lt;/error&gt;
+   &lt;/iq&gt;
+</pre></div>
+<a name="roster-versioning"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.6"></a><h3>2.6.&nbsp;
+Roster Versioning</h3>
+
+<a name="roster-versioning-feature"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.6.1"></a><h3>2.6.1.&nbsp;
+Stream Feature</h3>
+
+<p>If a server supports roster versioning, then it MUST advertise the following stream feature during stream negotiation.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;ver xmlns='urn:xmpp:features:rosterver'/&gt;
+</pre></div>
+<p>  The roster versioning stream feature is merely informative and
+  therefore is never mandatory-to-negotiate.
+</p>
+<a name="roster-versioning-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.6.2"></a><h3>2.6.2.&nbsp;
+Request</h3>
+
+<p>If a client supports roster versioning and the server to which it has connected advertises support for roster versioning as described in the foregoing section, then the client SHOULD include the 'ver' element in its request for the roster. If the server does not advertise support for roster versioning, the client MUST NOT include the 'ver' attribute. If the client includes the 'ver' attribute in its roster get, it sets the attribute's value to the version ID associated with its last cache of the roster.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+C: &lt;iq from='romeo@example.net/home'
+       id='r1h3vzp7'
+       to='romeo@example.net'
+       type='get'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver14'/&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>If the client has not yet cached the roster or the cache is lost or corrupted, but the client wishes to bootstrap the use of roster versioning, it MUST set the 'ver' attribute to the empty string (i.e., ver="").
+</p>
+<p>Naturally, if the client does not support roster versioning or does not wish to bootstrap the use of roster versioning, it will not include the 'ver' attribute.
+</p>
+<a name="roster-versioning-success"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.2.6.3"></a><h3>2.6.3.&nbsp;
+Success Case</h3>
+
+<p>Whether or not the roster has been modified since the version ID enumerated by the client, the server MUST either return the complete roster as described under <a class='info' href='#roster-syntax-actions-result'>Section&nbsp;2.1.4<span> (</span><span class='info'>Roster Result</span><span>)</span></a> (including a 'ver' attribute that signals the latest version) or return an empty IQ-result (thus indicating that any roster modifications will be sent via roster pushes, as described below). In general, unless returning the complete roster would (1) use less bandwidth than sending individual roster pushes to the client (e.g., if the roster contains only a few items) or (2) the server cannot associate the version ID with any previous version it has on file, the server SHOULD send an empty IQ-result and then send the modifications (if any) via roster pushes.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq from='romeo@example.net'
+       id='r1h3vzp7'
+       to='romeo@example.net/home'
+       type='result'/&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: This empty IQ-result is different from an empty &lt;query/&gt; element, thus disambiguating this usage from an empty roster.
+</p>
+</blockquote>
+
+<p>If roster versioning is enabled and the roster has not been modified since the version ID enumerated by the client, the server will simply not send any roster pushes to the client (until and unless some relevant event triggers a roster push during the lifetime of the client's session).
+</p>
+<p>If the roster has been modified since the version ID enumerated by the client, the server MUST then send one roster push to the client for each roster item that has been modified since the version ID enumerated by the client. (We call a roster push that is sent for purposes of roster version synchronization an "interim roster push".)
+</p>
+<p></p>
+<blockquote class="text">
+<p>Definition: A "roster modification" is any change to the roster data that would result in a roster push to a connected client. Therefore, internal states related to roster processing within the server that would not result in a roster push to a connected client do not necessitate a change to the version.
+</p>
+</blockquote>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+S: &lt;iq from='romeo@example.net'
+       id='ah382g67'
+       to='romeo@example.net/home'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver34'&gt;
+       &lt;item jid='tybalt@example.org' subscription='remove'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq from='romeo@example.net'
+       id='b2gs90j5'
+       to='romeo@example.net/home'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver42'&gt;
+       &lt;item jid='bill@example.org' subscription='both'/&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq from='romeo@example.net'
+       id='c73gs419'
+       to='romeo@example.net/home'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver72'&gt;
+       &lt;item jid='nurse@example.org'
+             name='Nurse'
+             subscription='to'&gt;
+         &lt;group&gt;Servants&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+
+S: &lt;iq from='romeo@example.net'
+       id='dh361f35'
+       to='romeo@example.net/home'
+       type='set'&gt;
+     &lt;query xmlns='jabber:iq:roster' ver='ver96'&gt;
+       &lt;item jid='juliet@example.org'
+             name='Juliet'
+             subscription='both'&gt;
+         &lt;group&gt;VIPs&lt;/group&gt;
+       &lt;/item&gt;
+     &lt;/query&gt;
+   &lt;/iq&gt;
+</pre></div>
+<p>These "interim roster pushes" can be understood as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Imagine that the client had an active presence session for the entire time between its cached roster version (say, "ver14") and the new roster version (say, "ver96").
+</li>
+<li>During that time, the client might have received roster pushes related to various roster versions (which might have been, say, "ver51" and "ver79"). However, some of those roster pushes might have contained intermediate updates to the same roster item (e.g., modifications to the subscription state for bill@example.org from "none" to "to" and from "to" to "both").
+</li>
+<li>The interim roster pushes would not include all of the intermediate steps, only the final result of all modifications applied to each item while the client was in fact offline (which might have been, say, "ver34", "ver42", "ver72", and "ver96").
+</li>
+</ol><p>
+        
+</p>
+<p>The client MUST handle an "interim roster push" in the same way it handles any roster push (indeed, from the client's perspective it cannot tell the difference between an "interim" roster push and a "live" roster push and therefore it has no way of knowing when it has received all of the interim roster pushes).  When requesting the roster after reconnection, the client SHOULD request the version associated with the last roster push it received during its previous session, not the version associated with the roster result it received at the start of its previous session.
+</p>
+<p>When roster versioning is enabled, the server MUST include the updated roster version with each roster push. Roster pushes MUST occur in order of modification and the version contained in a roster push MUST be unique.  Even if the client has not included the 'ver' attribute in its roster gets or sets, the server SHOULD include the 'ver' attribute on all roster pushes and results that it sends to the client.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Guidelines and more detailed examples for roster versioning are provided in <a class='info' href='#XEP-0237'>[XEP&#8209;0237]<span> (</span><span class='info'>Saint-Andre, P. and D. Cridland, &ldquo;Roster Versioning,&rdquo; March&nbsp;2010.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="sub"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3"></a><h3>3.&nbsp;
+Managing Presence Subscriptions</h3>
+
+<p>In order to protect the privacy of XMPP users, presence information is disclosed only to other entities that a user has approved.  When a user has agreed that another entity is allowed to view its presence, the entity is said to have a "subscription" to the user's presence.  An entity that has a subscription to a user's presence or to which a user has a presence subscription is called a "contact" (in this document the term "contact" is also used in a less strict sense to refer to a potential contact or any item in a user's roster).
+</p>
+<p>In XMPP, a subscription lasts across presence sessions; indeed, it lasts until the contact unsubscribes or the user cancels the previously granted subscription.  (This model is different from that used for presence subscriptions in the Session Initiation Protocol (SIP), as defined in <a class='info' href='#SIP-PRES'>[SIP&#8209;PRES]<span> (</span><span class='info'>Rosenberg, J., &ldquo;A Presence Event Package for the Session Initiation Protocol (SIP),&rdquo; August&nbsp;2004.</span><span>)</span></a>.)
+</p>
+<p>Subscriptions are managed within XMPP by sending presence stanzas containing specially defined attributes ("subscribe", "unsubscribe", "subscribed", and "unsubscribed").
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: When a server processes or generates an outbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed", the server MUST stamp the outgoing presence stanza with the bare JID &lt;localpart@domainpart&gt; of the sending entity, not the full JID &lt;localpart@domainpart/resourcepart&gt;.  Enforcement of this rule simplifies the presence subscription model and helps to prevent presence leaks; for information about presence leaks, refer to the security considerations of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<p>Subscription states are reflected in the rosters of both the user and the contact.  This section does not cover every possible case related to presence subscriptions, and mainly narrates the protocol flows for bootstrapping a mutual subscription between a user and a contact.  Complete details regarding subscription states can be found under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>.
+</p>
+<a name="sub-request"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1"></a><h3>3.1.&nbsp;
+Requesting a Subscription</h3>
+
+<p>A "subscription request" is a request from a user for authorization to permanently subscribe to a contact's presence information; syntactically it is a presence stanza whose 'type' attribute has a value of "subscribe".  A subscription request is generated by a user's client, processed by the (potential) contact's server, and acted on by the contact via the contact's client.  The workflow is described in the following sections.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Presence subscription requests are sent to available resources, whereas the roster pushes associated with subscription state changes are sent to interested resources.  Therefore, if a resource wishes to receive both subscription requests and roster pushes, it MUST both send initial presence and request the roster.
+</p>
+</blockquote>
+
+<a name="sub-request-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.1"></a><h3>3.1.1.&nbsp;
+Client Generation of Outbound Subscription Request</h3>
+
+<p>A user's client generates a subscription request by sending a presence stanza of type "subscribe" and specifying a 'to' address of the potential contact's bare JID &lt;contact@domainpart&gt;.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence id='xk3h1v69'
+              to='juliet@example.com'
+              type='subscribe'/&gt;
+</pre></div>
+<p>When a user sends a presence subscription request to a potential instant messaging and presence contact, the value of the 'to' attribute MUST be a bare JID &lt;contact@domainpart&gt; rather than a full JID &lt;contact@domainpart/resourcepart&gt;, since the desired result is for the user to receive presence from all of the contact's resources, not merely the particular resource specified in the 'to' attribute.  Use of bare JIDs also simplifies subscription processing, presence probes, and presence notifications by the user's server and the contact's server.
+</p>
+<p>For tracking purposes, a client SHOULD include an 'id' attribute in a presence subscription request.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Many XMPP clients prompt the user for information about the potential contact (e.g., "handle" and desired roster group) when generating an outbound presence subscription request and therefore send a roster set before sending the outbound presence subscription request.  This behavior is OPTIONAL, because a client MAY instead wait until receiving the initial roster push from the server before uploading user-provided information about the contact.  A server MUST process a roster set and outbound presence subscription request in either order (i.e., in whatever order generated by the client).
+</p>
+</blockquote>
+
+<a name="sub-request-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.2"></a><h3>3.1.2.&nbsp;
+Server Processing of Outbound Subscription Request</h3>
+
+<p>Upon receiving the outbound presence subscription request, the user's server MUST proceed as follows.
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Before processing the request, the user's server MUST check the syntax of the JID contained in the 'to' attribute (however, it is known that some existing implementations do not perform this check).  If the JID is of the form &lt;contact@domainpart/resourcepart&gt; instead of &lt;contact@domainpart&gt;, the user's server SHOULD treat it as if the request had been directed to the contact's bare JID and modify the 'to' address accordingly.  The server MAY also verify that the JID adheres to the format defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a> and possibly return a &lt;jid-malformed/&gt; stanza error.
+</li>
+<li>If the potential contact is hosted on the same server as the
+user, then the server MUST adhere to the rules specified under <a class='info' href='#sub-request-inbound'>Section&nbsp;3.1.3<span> (</span><span class='info'>Server Processing of Inbound Subscription Request</span><span>)</span></a> when processing the subscription request and delivering it to the (local) contact.
+</li>
+<li>If the potential contact is hosted on a remote server, subject to local service policies the user's server MUST then route the stanza to that remote domain in accordance with core XMPP stanza processing rules.  (This can result in returning an appropriate stanza error to the user, such as &lt;remote-server-timeout/&gt;.)
+</li>
+</ol><p>
+        
+</p>
+<p>As mentioned, before locally delivering or remotely routing the presence subscription request, the user's server MUST stamp the outbound subscription request with the bare JID &lt;user@domainpart&gt; of the user.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='romeo@example.net'
+              id='xk3h1v69'
+              to='juliet@example.com'
+              type='subscribe'/&gt;
+</pre></div>
+<p>If the presence subscription request cannot be locally delivered or remotely routed (e.g., because the request is malformed, the local contact does not exist, the remote server does not exist, an attempt to contact the remote server times out, or any other error is determined or experienced by the user's server), then the user's server MUST return an appropriate error stanza to the user.  An example follows.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com'
+              id='xk3h1v69'
+              to='romeo@example.net'
+              type='error'&gt;
+      &lt;error type='modify'&gt;
+        &lt;remote-server-not-found
+            xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/&gt;
+      &lt;/error&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>After locally delivering or remotely routing the presence subscription request, the user's server MUST then send a roster push to all of the user's interested resources, containing the potential contact with a subscription state of "none" and with notation that the subscription is pending (via an 'ask' attribute whose value is "subscribe").
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='b89c5r7ib574'
+        to='romeo@example.net/foo'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item ask='subscribe'
+              jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+US: &lt;iq id='b89c5r7ib575'
+        to='romeo@example.net/bar'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item ask='subscribe'
+              jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<p>If a remote contact does not approve or deny the subscription request within some configurable amount of time, the user's server SHOULD resend the subscription request to the contact based on an implementation-specific algorithm (e.g., whenever a new resource becomes available for the user, or after a certain amount of time has elapsed); this helps to recover from transient, silent errors that might have occurred when the original subscription request was routed to the remote domain.  When doing so, it is RECOMMENDED for the server to include an 'id' attribute so that it can track responses to the resent subscription request.
+</p>
+<a name="sub-request-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.3"></a><h3>3.1.3.&nbsp;
+Server Processing of Inbound Subscription Request</h3>
+
+<p>Before processing the inbound presence subscription request, the contact's server SHOULD check the syntax of the JID contained in the 'to' attribute.  If the JID is of the form &lt;contact@domainpart/resourcepart&gt; instead of &lt;contact@domainpart&gt;, the contact's server SHOULD treat it as if the request had been directed to the contact's bare JID and modify the 'to' address accordingly.  The server MAY also verify that the JID adheres to the format defined in <a class='info' href='#XMPP-ADDR'>[XMPP&#8209;ADDR]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Address Format,&rdquo; March&nbsp;2011.</span><span>)</span></a> and possibly return a &lt;jid-malformed/&gt; stanza error.
+</p>
+<p>When processing the inbound presence subscription request, the contact's server MUST adhere to the following rules:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Above all, the contact's server MUST NOT automatically approve subscription requests on the contact's behalf -- unless the contact has (a) pre-approved subscription requests from the user as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>, (b) configured its account to automatically approve subscription requests, or (c) accepted an agreement with its service provider that allows automatic approval (for instance, via an employment agreement within an enterprise deployment).  Instead, if a subscription request requires approval then the contact's server MUST deliver that request to the contact's available resource(s) for approval or denial by the contact.
+</li>
+<li>If the contact exists and the user already has a subscription to the contact's presence, then the contact's server MUST auto-reply on behalf of the contact by sending a presence stanza of type "subscribed" from the contact's bare JID to the user's bare JID.  Likewise, if the contact previously sent a presence stanza of type "subscribed" and the contact's server treated that as indicating "pre-approval" for the user's presence subscription (see <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>), then the contact's server SHOULD also auto-reply on behalf of the contact.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com'
+              id='xk3h1v69'
+              to='romeo@example.net'
+              type='subscribed'/&gt;
+</pre></div>
+            
+</li>
+<li>Otherwise, if there is at least one available resource associated with the contact when the subscription request is received by the contact's server, then the contact's server MUST send that subscription request to all available resources in accordance with <a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>.
+            
+            As a way of acknowledging receipt of the presence subscription request, the contact's server MAY send a presence stanza of type "unavailable" from the bare JID of the contact to the bare JID of the user (the user's client MUST NOT assume that this acknowledgement provides presence information about the contact, since it comes from the contact's bare JID and is received before the subscription request has been approved).
+</li>
+<li>Otherwise, if the contact has no available resources when the subscription request is received by the contact's server, then the contact's server MUST keep a record of the complete presence stanza comprising the subscription request, including any extended content contained therein (see Section 8.4 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>), and then deliver the request when the contact next has an available resource.  The contact's server MUST continue to deliver the subscription request whenever the contact creates an available resource, until the contact either approves or denies the request.  (The contact's server MUST NOT deliver more than one subscription request from any given user when the contact next has an available resource; e.g., if the user sends multiple subscription requests to the contact while the contact is offline, the contact's server SHOULD store only one of those requests, such as the first request or last request, and MUST deliver only one of the requests when the contact next has an available resource; this helps to prevent "subscription request spam".)
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: Until and unless the contact approves the subscription request as described under <a class='info' href='#sub-request-handle'>Section&nbsp;3.1.4<span> (</span><span class='info'>Client Processing of Inbound Subscription Request</span><span>)</span></a>, the contact's server MUST NOT add an item for the user to the contact's roster.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Security Warning: The mandate for the contact's server to store the complete stanza of the presence subscription request introduces the possibility of an application resource exhaustion attack (see Section 2.1.2 of <a class='info' href='#DOS'>[DOS]<span> (</span><span class='info'>Handley, M., Rescorla, E., and IAB, &ldquo;Internet Denial-of-Service Considerations,&rdquo; December&nbsp;2006.</span><span>)</span></a>), for example, by a rogue server or a coordinated group of users (e.g., a botnet) against the contact's server or particular contact.  Server implementers are advised to consider the possibility of such attacks and provide tools for counteracting it, such as enabling service administrators to set limits on the number or size of inbound presence subscription requests that the server will store in aggregate or for any given contact.
+</p>
+</blockquote>
+
+<a name="sub-request-handle"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.4"></a><h3>3.1.4.&nbsp;
+Client Processing of Inbound Subscription Request</h3>
+
+<p>When an interactive client receives a subscription request, it MUST present the request to the natural person controlling the client (i.e., the "contact") for approval, unless the contact has explicitly configured the client to automatically approve or deny some or all subscription requests as described above.  An automated client that is not controlled by a natural person will have its own application-specific rules for approving or denying subscription requests.
+</p>
+<p>A client approves a subscription request by sending a presence stanza of type "subscribed", which is processed as described under <a class='info' href='#sub-request-approvalout'>Section&nbsp;3.1.5<span> (</span><span class='info'>Server Processing of Outbound Subscription Approval</span><span>)</span></a> for the contact's server and <a class='info' href='#sub-request-approvalin'>Section&nbsp;3.1.6<span> (</span><span class='info'>Server Processing of Inbound Subscription Approval</span><span>)</span></a> for the user's server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence id='h4v1c4kj'
+              to='romeo@example.net'
+              type='subscribed'/&gt;
+</pre></div>
+<p>A client denies a subscription request by sending a presence stanza of type "unsubscribed", which is processed as described under <a class='info' href='#sub-cancel'>Section&nbsp;3.2<span> (</span><span class='info'>Canceling a Subscription</span><span>)</span></a> for both the contact's server and the user's server.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence id='tb2m1b59'
+              to='romeo@example.net'
+              type='unsubscribed'/&gt;
+</pre></div>
+<p>For tracking purposes, a client SHOULD include an 'id' attribute in a subscription approval or subscription denial; this 'id' attribute MUST NOT mirror the 'id' attribute of the subscription request.
+</p>
+<a name="sub-request-approvalout"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.5"></a><h3>3.1.5.&nbsp;
+Server Processing of Outbound Subscription Approval</h3>
+
+<p>When the contact's client sends the subscription approval, the contact's server MUST stamp the outbound stanza with the bare JID &lt;contact@domainpart&gt; of the contact and locally deliver or remotely route the stanza to the user.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com'
+              id='h4v1c4kj'
+              to='romeo@example.net'
+              type='subscribed'/&gt;
+</pre></div>
+<p>The contact's server then MUST send an updated roster push to all of the contact's interested resources, with the 'subscription' attribute set to a value of "from". (Here we assume that the contact does not already have a subscription to the user; if that were the case, the 'subscription' attribute would be set to a value of "both", as explained under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;iq id='a78b4q6ha463'
+        to='juliet@example.com/balcony'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='from'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+CS: &lt;iq id='x81g3bdy4n19'
+        to='juliet@example.com/chamber'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='from'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<p>From the perspective of the contact, there now exists a subscription from the user, which is why the 'subscription' attribute is set to a value of "from".  (Here we assume that the contact does not already have a subscription to the user; if that were the case, the 'subscription' attribute would be set to a value of "both", as explained under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>.)
+</p>
+<p>The contact's server MUST then also send current presence to the user from each of the contact's available resources.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com/balcony'
+              id='pw72bc5j'
+              to='romeo@example.net'/&gt;
+
+CS: &lt;presence from='juliet@example.com/chamber'
+              id='ux31da4q'
+              to='romeo@example.net'/&gt;
+</pre></div>
+<p>In order to subscribe to the user's presence, the contact would then need to send a subscription request to the user.  (XMPP clients will often automatically send the subscription request instead of requiring the contact to initiate the subscription request, since it is assumed that the desired end state is a mutual subscription.)  Naturally, when the contact sends a subscription request to the user, the subscription states will be different from those shown in the foregoing examples (see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>) and the roles will be reversed.
+</p>
+<a name="sub-request-approvalin"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.1.6"></a><h3>3.1.6.&nbsp;
+Server Processing of Inbound Subscription Approval</h3>
+
+<p>When the user's server receives a subscription approval, it MUST first check if the contact is in the user's roster with subscription='none' or subscription='from' and the 'ask' flag set to "subscribe" (i.e., a subscription state of "None + Pending Out", "None + Pending Out+In", or "From + Pending Out"; see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>).  If this check is successful, then the user's server MUST:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Deliver the inbound subscription approval to all of the user's interested resources (this helps to give the user's client(s) proper context regarding the subscription approval so that they can differentiate between a roster push originated by another of the user's resources and a subscription approval received from the contact).  This MUST occur before sending the roster push described in the next step.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com'
+              id='h4v1c4kj'
+              to='romeo@example.net'
+              type='subscribed'/&gt;
+</pre></div>
+            
+</li>
+<li>Initiate a roster push to all of the user's interested resources, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "to" (if the subscription state was "None + Pending Out" or "None + Pending Out+In") or "both" (if the subscription state was "From + Pending Out").
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='b89c5r7ib576'
+        to='romeo@example.net/foo'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='to'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+US: &lt;iq id='b89c5r7ib577'
+        to='romeo@example.net/bar'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='to'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+
+            
+</li>
+<li>The user's server MUST also deliver the available presence stanza received from each of the contact's available resources to each of the user's available resources.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+[ ... to resource1 ... ]
+
+US: &lt;presence from='juliet@example.com/balcony'
+              id='pw72bc5j'
+              to='romeo@example.net'/&gt;
+
+[ ... to resource2 ... ]
+
+US: &lt;presence from='juliet@example.com/balcony'
+              id='pw72bc5j'
+              to='romeo@example.net'/&gt;
+
+[ ... to resource1 ... ]
+
+US: &lt;presence from='juliet@example.com/chamber'
+              id='ux31da4q'
+              to='romeo@example.net'/&gt;
+
+[ ... to resource2 ... ]
+
+US: &lt;presence from='juliet@example.com/chamber'
+              id='ux31da4q'
+              to='romeo@example.net'/&gt;
+</pre></div>
+            
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: If the user's account has no available resources when the inbound subscription approval notification is received, the user's server MAY keep a record of the notification (ideally the complete presence stanza) and then deliver the notification when the account next has an available resource.  This behavior provides more complete signaling to the user regarding the reasons for the roster change that occurred while the user was offline.
+</p>
+</blockquote>
+
+<p>Otherwise -- that is, if the user does not exist, if the contact is not in the user's roster, or if the contact is in the user's roster with a subscription state other than those described in the foregoing check -- then the user's server MUST silently ignore the subscription approval notification by not delivering it to the user, not modifying the user's roster, and not generating a roster push to the user's interested resources.
+</p>
+<p>From the perspective of the user, there now exists a subscription to the contact's presence (which is why the 'subscription' attribute is set to a value of "to").
+</p>
+<a name="sub-cancel"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2"></a><h3>3.2.&nbsp;
+Canceling a Subscription</h3>
+
+<a name="sub-cancel-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.1"></a><h3>3.2.1.&nbsp;
+Client Generation of Subscription Cancellation</h3>
+
+<p>If a contact would like to cancel a subscription that it has previously granted to a user, to cancel a subscription pre-approval (<a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>), or to deny a subscription request, it sends a presence stanza of type "unsubscribed".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence id='ij5b1v7g'
+              to='romeo@example.net'
+              type='unsubscribed'/&gt;
+</pre></div>
+<a name="sub-cancel-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.2"></a><h3>3.2.2.&nbsp;
+Server Processing of Outbound Subscription Cancellation</h3>
+
+<p>Upon receiving the outbound subscription cancellation, the contact's server MUST proceed as follows.
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the user's bare JID is not yet in the contact's roster or is in the contact's roster with a state of "None", "None + Pending Out", or "To", the contact's server SHOULD NOT route or deliver the presence stanza of type "unsubscribed" to the user and MUST NOT send presence notifications of type "unavailable" to the user as described below.
+</li>
+<li>If the user's bare JID is in the contact's roster with a state of "None", "None + Pending Out", or "To" and the 'approved' flag is set to "true" (thus signaling a subscription pre-approval as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>), the contact's server MUST remove the pre-approval and MUST NOT route or deliver the presence stanza of type "unsubscribed" to the user.
+</li>
+<li>Otherwise, as shown in the following examples, the contact's server MUST route or deliver both presence notifications of type "unavailable" and presence stanzas of type "unsubscribed" to the user and MUST send a roster push to the contact.
+</li>
+</ol><p>
+        
+</p>
+<p>While the user is still subscribed to the contact's presence (i.e., before the contact's server routes or delivers the presence stanza of type "unsubscribed" to the user), the contact's server MUST send a presence stanza of type "unavailable" from all of the contact's online resources to the user.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com/balcony'
+              id='i8bsg3h3'
+              type='unavailable'/&gt;
+
+CS: &lt;presence from='juliet@example.com/chamber'
+              id='bvx2c9mk'
+              type='unavailable'/&gt;
+</pre></div>
+<p>Then the contact's server MUST route or deliver the presence stanza of type "unsubscribed" to the user, making sure to stamp the outbound subscription cancellation with the bare JID &lt;contact@domainpart&gt; of the contact.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com'
+              id='ij5b1v7g'
+              to='romeo@example.net'
+              type='unsubscribed'/&gt;
+</pre></div>
+<p>The contact's server then MUST send a roster push with the updated roster item to all of the contact's interested resources, where the subscription state is now either "none" or "to" (see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;iq id='pw3f2v175b34'
+        to='juliet@example.com/balcony'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+CS: &lt;iq id='zu2y3f571v35'
+        to='juliet@example.com/chamber'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<a name="sub-cancel-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.2.3"></a><h3>3.2.3.&nbsp;
+Server Processing of Inbound Subscription Cancellation</h3>
+
+<p>When the user's server receives the inbound subscription cancellation, it MUST first check if the contact is in the user's roster with subscription='to' or subscription='both' (see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>).  If this check is successful, then the user's server MUST:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Deliver the inbound subscription cancellation to all of the user's interested resources (this helps to give the user's client(s) proper context regarding the subscription cancellation so that they can differentiate between a roster push originated by another of the user's resources and a subscription cancellation received from the contact).  This MUST occur before sending the roster push described in the next step.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com'
+              id='ij5b1v7g'
+              to='romeo@example.net'
+              type='unsubscribed'/&gt;
+</pre></div>
+            
+</li>
+<li>Initiate a roster push to all of the user's interested resources, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "none" (if the subscription state was "To" or "To + Pending In") or "from" (if the subscription state was "Both").
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='h37h3u1bv400'
+        to='romeo@example.net/foo'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+US: &lt;iq id='h37h3u1bv401'
+        to='romeo@example.net/bar'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+
+            
+</li>
+</ol><p>
+        
+</p>
+<p>The user's server MUST also deliver the inbound presence stanzas of type "unavailable".
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: If the user's account has no available resources when the inbound unsubscribed notification is received, the user's server MAY keep a record of the notification (ideally the complete presence stanza) and then deliver the notification when the account next has an available resource.  This behavior provides more complete signaling to the user regarding the reasons for the roster change that occurred while the user was offline.
+</p>
+</blockquote>
+
+<p>Otherwise -- that is, if the user does not exist, if the contact is not in the user's roster, or if the contact is in the user's roster with a subscription state other than those described in the foregoing check -- then the user's server MUST silently ignore the unsubscribed notification by not delivering it to the user, not modifying the user's roster, and not generating a roster push to the user's interested resources.
+</p>
+<a name="sub-unsub"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.3"></a><h3>3.3.&nbsp;
+Unsubscribing</h3>
+
+<a name="sub-unsub-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.3.1"></a><h3>3.3.1.&nbsp;
+Client Generation of Unsubscribe</h3>
+
+<p>If a user would like to unsubscribe from a contact's presence, it sends a presence stanza of type "unsubscribe".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence id='ul4bs71n'
+              to='juliet@example.com'
+              type='unsubscribe'/&gt;
+</pre></div>
+<a name="sub-unsub-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.3.2"></a><h3>3.3.2.&nbsp;
+Server Processing of Outbound Unsubscribe</h3>
+
+<p>Upon receiving the outbound unsubscribe, the user's server MUST proceed as follows.
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the contact is hosted on the same server as the user, then
+the server MUST adhere to the rules specified under <a class='info' href='#sub-unsub-inbound'>Section&nbsp;3.3.3<span> (</span><span class='info'>Server Processing of Inbound Unsubscribe</span><span>)</span></a> when processing the subscription request.
+</li>
+<li>If the contact is hosted on a remote server, subject to local service policies the user's server MUST then route the stanza to that remote domain in accordance with core XMPP stanza processing rules.  (This can result in returning an appropriate stanza error to the user, such as &lt;remote-server-timeout/&gt;.)
+</li>
+</ol><p>
+        
+</p>
+<p>As mentioned, before locally delivering or remotely routing the unsubscribe, the user's server MUST stamp the stanza with the bare JID &lt;user@domainpart&gt; of the user.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='romeo@example.net'
+              id='ul4bs71n'
+              to='juliet@example.com'
+              type='unsubscribe'/&gt;
+</pre></div>
+<p>The user's server then MUST send a roster push with the updated roster item to all of the user's interested resources, where the subscription state is now either "none" or "from" (see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='h37h3u1bv402'
+        to='romeo@example.net/foo'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+US: &lt;iq to='romeo@example.net/bar'
+        type='set'
+        id='h37h3u1bv403'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<a name="sub-unsub-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.3.3"></a><h3>3.3.3.&nbsp;
+Server Processing of Inbound Unsubscribe</h3>
+
+<p>When the contact's server receives the unsubscribe notification, it MUST first check if the user's bare JID is in the contact's roster with subscription='from' or subscription='both' (i.e., a subscription state of "From", "From + Pending Out", or "Both"; see <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>).  If this check is successful, then the contact's server MUST:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>Deliver the inbound unsubscribe to all of the contact's interested resources (this helps to give the contact's client(s) proper context regarding the unsubscribe so that they can differentiate between a roster push originated by another of the contact's resources and an unsubscribe received from the user).  This MUST occur before sending the roster push described in the next step.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='romeo@example.net'
+              id='ul4bs71n'
+              to='juliet@example.com'
+              type='unsubscribe'/&gt;
+</pre></div>
+            
+</li>
+<li>Initiate a roster push to all of the contact's interested resources, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none" (if the subscription state was "From" or "From + Pending Out") or "to" (if the subscription state was "Both").
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;iq id='tn2b5893g1s4'
+        to='juliet@example.com/balcony'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+
+CS: &lt;iq id='sp3b56n27hrp'
+        to='juliet@example.com/chamber'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='romeo@example.net'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+            
+</li>
+<li>Generate an outbound presence stanza of type "unavailable" from each of the contact's available resources to the user.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com/balcony'
+              id='o5v91w49'
+              to='romeo@example.net'
+              type='unavailable'/&gt;
+
+CS: &lt;presence from='juliet@example.com/chamber'
+              id='n6b1c37k'
+              to='romeo@example.net'
+              type='unavailable'/&gt;
+</pre></div>
+            
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: If the contact's account has no available resources when the inbound unsubscribe notification is received, the contact's server MAY keep a record of the notification (ideally the complete presence stanza) and then deliver the notification when the account next has an available resource.  This behavior provides more complete signaling to the user regarding the reasons for the roster change that occurred while the user was offline.
+</p>
+</blockquote>
+
+<p>Otherwise -- that is, if the contact does not exist, if the user is not in the contact's roster, or if the user's bare JID is in the contact's roster with a subscription state other than those described in the foregoing check -- then the contact's server MUST silently ignore the unsubscribe stanza by not delivering it to the contact, not modifying the contact's roster, and not generating a roster push to the contact's interested resources.  However, if the contact's server is keeping track of an inbound presence subscription request from the user to the contact but the user is not yet in the contact's roster (functionally equivalent to a subscription state of "None + Pending In" where the contact never added the user to the contact's roster), then the contact's server MUST simply remove any record of the inbound presence subscription request (it cannot remove the user from the contact's roster because the user was never added to the contact's roster).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: The user's client MUST NOT depend on receiving the unavailable presence notification from the contact, since it MUST consider its presence subscription to the contact, and its presence information about the contact, to be null and void when it sends the presence stanza of type "unsubscribe" or when it receives the roster push triggered by the unsubscribe request.
+</p>
+</blockquote>
+
+<a name="sub-preapproval"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.4"></a><h3>3.4.&nbsp;
+Pre-Approving a Subscription Request</h3>
+
+<p>If a user has not received a subscription request from a contact, the user can "pre-approve" such a request so that it will be automatically approved by the user's server.
+</p>
+<p>Support for subscription pre-approvals is OPTIONAL on the part of clients and servers.  If a server supports subscription pre-approvals, then it MUST advertise the following stream feature during stream negotiation.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;sub xmlns='urn:xmpp:features:pre-approval'/&gt;
+</pre></div>
+<p>The subscription pre-approval stream feature is merely informative and therefore is never mandatory-to-negotiate.
+</p>
+<a name="sub-preapproval-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.4.1"></a><h3>3.4.1.&nbsp;
+Client Generation of Subscription Pre-Approval</h3>
+
+<p>If the server to which a client connects has advertised support for subscription pre-approvals, the client MAY generate a subscription pre-approval by sending a presence stanza of type "subscribed" to the contact.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence id='pg81vx64'
+              to='juliet@example.com'
+              type='subscribed'/&gt;
+</pre></div>
+<p>If the server does not advertise support for subscription pre-approvals, the client MUST NOT attempt to pre-approve subscription requests from potential or actual contacts.
+</p>
+<a name="sub-preapproval-proc"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.3.4.2"></a><h3>3.4.2.&nbsp;
+Server Processing of Subscription Pre-Approval</h3>
+
+<p>Upon receiving the presence stanza of type "subscribed", the user's server MUST proceed as follows if it supports subscription pre-approvals.
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the contact is in the user's roster with a state of "Both", "From", or "From + Pending Out", the user's server MUST silently ignore the stanza.
+</li>
+<li>If the contact is in the user's roster with a state of "To + Pending In", "None + Pending In", or "None + Pending Out+In", the user's server MUST handle the stanza as a normal subscription approval (see under <a class='info' href='#sub-request-approvalout'>Section&nbsp;3.1.5<span> (</span><span class='info'>Server Processing of Outbound Subscription Approval</span><span>)</span></a>) by updating the existing roster item to a state of "Both", "From", or "From + Pending Out" (respectively), pushing the modified roster item to all of the user's interested resources, and routing the presence stanza of type "subscribed" to the contact.
+</li>
+<li>If the contact is in the user's roster with a state of "To", "None", or "None + Pending Out", the user's server MUST note the subscription pre-approval by setting the 'approved' flag to a value of "true", then push the modified roster item to all of the user's interested resources.  However, the user's server MUST NOT route the presence stanza of type "subscribed" to the contact.
+</li>
+<li>If the contact is not yet in the user's roster, the user's server MUST create a roster item for the contact with a state of "None" and set the 'approved' flag to a value of "true", then push the roster item to all of the user's interested resources.  However, the user's server MUST NOT route the presence stanza of type "subscribed" to the contact.
+</li>
+</ol><p>
+        
+</p>
+<p>An example of the roster push follows.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='h3bs81vs763f'
+        to='romeo@example.net/bar'
+        type='set'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item approved='true'
+              jid='juliet@example.com'
+              subscription='none'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<p>When the 'approved' flag is set to "true", the user's server MUST NOT deliver a presence stanza of type "subscribe" from the contact to the user, but instead MUST automatically respond to such a stanza on behalf of the user by returning a presence stanza of type "subscribed" from the bare JID of the user to the bare JID of the contact.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: It is a matter of implementation or local service policy whether the server maintains a record of the subscription approval after it has received a presence subscription request from the contact.  If the server does not maintain such a record, upon receiving the subscription request it will not include the 'approved' attribute in the roster item for the contact (i.e., in subsequent roster pushes and roster results).  If the server maintains such a record, it will always include the 'approved' attribute (set to "true") in the roster item for the contact, until and unless the user sends a presence stanza of type "unsubscribed" to the contact (or removes the contact from the roster entirely).
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: A client can cancel a pre-approval by sending a presence stanza of type "unsubscribed", as described more fully under <a class='info' href='#sub-cancel'>Section&nbsp;3.2<span> (</span><span class='info'>Canceling a Subscription</span><span>)</span></a>.  In this case, the user's server would send a roster push to all of the user's interested resources with the 'approved' attribute removed.  (Alternatively, the client can simply remove the roster item entirely.)
+</p>
+</blockquote>
+
+<a name="presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4"></a><h3>4.&nbsp;
+Exchanging Presence Information</h3>
+
+<a name="presence-fundamentals"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.1"></a><h3>4.1.&nbsp;
+Presence Fundamentals</h3>
+
+<p>The concept of presence refers to an entity's availability for communication over a network.  At the most basic level, presence is a boolean "on/off" variable that signals whether an entity is available or unavailable for communication (the terms "online" and "offline" are also used).  In XMPP, an entity's availability is signaled when its client generates a &lt;presence/&gt; stanza with no 'type' attribute, and an entity's lack of availability is signaled when its client generates a &lt;presence/&gt; stanza whose 'type' attribute has a value of "unavailable".
+</p>
+<p>XMPP presence typically follows a "publish-subscribe" or "observer" pattern, wherein an entity sends presence to its server, and its server then broadcasts that information to all of the entity's contacts who have a subscription to the entity's presence (in the terminology of <a class='info' href='#IMP-MODEL'>[IMP&#8209;MODEL]<span> (</span><span class='info'>Day, M., Rosenberg, J., and H. Sugano, &ldquo;A Model for Presence and Instant Messaging,&rdquo; February&nbsp;2000.</span><span>)</span></a>, an entity that generates presence is a "presentity" and the entities that receive presence are "subscribers").  A client generates presence for broadcast to all subscribed entities by sending a presence stanza to its server with no 'to' address, where the presence stanza has either no 'type' attribute or a 'type' attribute whose value is "unavailable".  This kind of presence is called "broadcast presence".  (A client can also send "directed presence", i.e., a presence stanza with a 'to' address; this is less common but is sometimes used to send presence to entities that are not subscribed to the user's presence; see <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a>.)
+</p>
+<p>After a client completes the preconditions specified in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, it can establish a "presence session" at its server by sending <a class='info' href='#presence-initial'>initial presence<span> (</span><span class='info'>Initial Presence</span><span>)</span></a>, where the presence session is terminated by sending <a class='info' href='#presence-unavailable'>unavailable presence<span> (</span><span class='info'>Unavailable Presence</span><span>)</span></a>.  For the duration of its presence session, a connected resource (in the terminology of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>) is said to be an "available resource".
+</p>
+<p>In XMPP, applications that combine messaging and presence functionality, the default type of communication for which presence signals availability is messaging; however, it is not necessary for XMPP applications to combine messaging and presence functionality, and they can provide standalone presence features without messaging (in addition, XMPP servers do not require information about network availability in order to successfully route message and IQ stanzas).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Informational Note: In the examples that follow, the user is &lt;juliet@example.com&gt;, she has two available resources ("balcony" and "chamber"), and she has three contacts in her roster with a subscription state of "from" or "both": &lt;romeo@example.net&gt;, &lt;mercutio@example.com&gt;, and &lt;benvolio@example.net&gt;.
+</p>
+</blockquote>
+
+<a name="presence-initial"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2"></a><h3>4.2.&nbsp;
+Initial Presence</h3>
+
+<a name="presence-initial-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2.1"></a><h3>4.2.1.&nbsp;
+Client Generation of Initial Presence</h3>
+
+<p>After completing the preconditions described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> (REQUIRED) and requesting the roster (RECOMMENDED), a client signals its availability for communication by sending "initial presence" to its server, i.e., a presence stanza with no 'to' address (indicating that it is meant to be broadcast by the server on behalf of the client) and no 'type' attribute (indicating the user's availability).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence/&gt;
+</pre></div>
+<p>The initial presence stanza MAY contain the &lt;priority/&gt; element, the &lt;show/&gt; element, and one or more instances of the &lt;status/&gt; element, as well as extended content; details are provided under <a class='info' href='#presence-syntax'>Section&nbsp;4.7<span> (</span><span class='info'>Presence Syntax</span><span>)</span></a>.
+</p>
+<a name="presence-initial-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2.2"></a><h3>4.2.2.&nbsp;
+Server Processing of Outbound Initial Presence</h3>
+
+<p>Upon receiving initial presence from a client, the user's server MUST send the initial presence stanza from the full JID &lt;user@domainpart/resourcepart&gt; of the user to all contacts that are subscribed to the user's presence; such contacts are those for which a JID is present in the user's roster with the 'subscription' attribute set to a value of "from" or "both".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'/&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='mercutio@example.com'/&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='benvolio@example.net'/&gt;
+</pre></div>
+<p>The user's server MUST also broadcast initial presence from the user's newly available resource to all of the user's available resources, including the resource that generated the presence notification in the first place (i.e., an entity is implicitly subscribed to its own presence).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+[... to the "balcony" resource ...]
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='juliet@example.com'/&gt;
+
+[... to the "chamber" resource ...]
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='juliet@example.com'/&gt;
+</pre></div>
+<p>In the absence of presence information about the user's contacts, the user's server MUST also send presence probes to the user's contacts on behalf of the user as specified under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.
+</p>
+<a name="presence-initial-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2.3"></a><h3>4.2.3.&nbsp;
+Server Processing of Inbound Initial Presence</h3>
+
+<p>Upon receiving presence from the user, the contact's server MUST deliver the user's presence stanza to all of the contact's available resources.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+[ ... to resource1 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'/&gt;
+
+[ ... to resource2 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'/&gt;
+</pre></div>
+<a name="presence-initial-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.2.4"></a><h3>4.2.4.&nbsp;
+Client Processing of Initial Presence</h3>
+
+<p>When the contact's client receives presence from the user, the following behavior is suggested for interactive clients:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the user's bare JID is in the contact's roster, display the presence information in an appropriate roster interface.
+</li>
+<li>If the user is not in the contact's roster but the contact and the user are actively exchanging message or IQ stanzas, display the presence information in the user interface for that communication session (see also <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a> and <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a>).
+</li>
+<li>Otherwise, ignore the presence information and do not display it to the contact.
+</li>
+</ol><p>
+        
+</p>
+<a name="presence-probe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3"></a><h3>4.3.&nbsp;
+Presence Probes</h3>
+
+<p>A "presence probe" is a request for a contact's current presence information, sent on behalf of a user by the user's server; syntactically it is a presence stanza whose 'type' attribute has a value of "probe".  In the context of presence subscriptions, the value of the 'from' address MUST be the bare JID of the subscribed user and the value of the 'to' address MUST be the bare JID of the contact to which the user is subscribed, since presence subscriptions are based on the bare JID.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com'
+              id='ign291v5'
+              to='romeo@example.net'
+              type='probe'/&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: RFC 3921 specified that probes are sent from the full JID, not the bare JID (a rule that was changed because subscriptions are based on the bare JID).  Some existing implementations send from the full JID instead of the bare JID.
+</p>
+</blockquote>
+
+<p>Probes can also be sent by an entity that has received presence outside the context of a presence subscription, typically when the contact has sent directed presence as described under <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a>; in this case the value of the 'from' or 'to' address can be a full JID instead of a bare JID.  See <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a> for a complete discussion.
+</p>
+<p>Presence probes SHOULD NOT be sent by a client, because in general a client will not need to send them since the task of gathering presence from a user's contacts is managed by the user's server.  However, if a user's client generates an outbound presence probe then the user's server SHOULD route the probe (if the contact is at another server) or process the probe (if the contact is at the same server) and MUST NOT use its receipt of the presence probe from a connected client as the sole cause for returning a stanza or stream error to the client.
+</p>
+<a name="presence-probe-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.1"></a><h3>4.3.1.&nbsp;
+Server Generation of Outbound Presence Probe</h3>
+
+<p>When a server needs to discover the availability of a user's contact, it sends a presence probe from the bare JID &lt;user@domainpart&gt; of the user to the bare JID &lt;contact@domainpart&gt; of the contact.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Although presence probes are intended for sending to contacts (i.e., entities to which a user is subscribed), a server MAY send a presence probe to the full JID of an entity from which the user has received presence information during the current session.
+</p>
+</blockquote>
+
+<p>The user's server SHOULD send a presence probe whenever the user starts a new presence session by sending initial presence; however, the server MAY choose not to send the probe at that point if it has what it deems to be reliable and up-to-date presence information about the user's contacts (e.g., because the user has another available resource or because the user briefly logged off and on before the new presence session began).  In addition, a server MAY periodically send a presence probe to a contact if it has not received presence information or other traffic from the contact in some configurable amount of time; this can help to prevent "ghost" contacts who appear to be online but in fact are not.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com'
+              id='ign291v5'
+              to='romeo@example.net'
+              type='probe'/&gt;
+
+US: &lt;presence from='juliet@example.com'
+              id='xv291f38'
+              to='mercutio@example.com'
+              type='probe'/&gt;
+</pre></div>
+<p>Naturally, the user's server does not need to send a presence probe to a contact if the contact's account resides on the same server as the user, since the server possesses the contact's information locally.
+</p>
+<a name="presence-probe-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.2"></a><h3>4.3.2.&nbsp;
+Server Processing of Inbound Presence Probe</h3>
+
+<p>Upon receiving a presence probe to the contact's bare JID from the user's server on behalf of the user, the contact's server MUST reply as follows:
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the contact account does not exist or the user's bare JID is in the contact's roster with a subscription state other than "From", "From + Pending Out", or "Both" (as explained under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>), then the contact's server SHOULD return a presence stanza of type "unsubscribed" in response to the presence probe (this will trigger a protocol flow for canceling the user's subscription to the contact as described under <a class='info' href='#sub-cancel'>Section&nbsp;3.2<span> (</span><span class='info'>Canceling a Subscription</span><span>)</span></a>; however, this MUST NOT result in cancellation of a subscription pre-approval as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>).  Here the 'from' address MUST be the bare JID of the contact, since specifying a full JID would constitute a presence leak as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='mercutio@example.com'
+              id='xv291f38'
+              to='juliet@example.com'
+              type='unsubscribed'/&gt;
+</pre></div>
+             However, if a server receives a presence probe from a configured domain of the server itself or another such trusted service, it MAY provide presence information about the user to that entity.
+            
+</li>
+<li>Else, if the contact has moved temporarily or permanently to another address, then the server SHOULD return a presence stanza of type "error" with a stanza error condition of &lt;redirect/&gt; (temporary) or &lt;gone/&gt; (permanent) that includes the new address of the contact.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='mercutio@example.com'
+              id='xv291f38'
+              to='juliet@example.com'
+              type='error'&gt;
+      &lt;error type='modify'&gt;
+        &lt;gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'&gt;
+          xmpp:la-mer@example.com
+        &lt;/gone&gt;
+      &lt;/error&gt;
+    &lt;/presence&gt;
+</pre></div>
+            
+</li>
+<li>Else, if the contact has no available resources, then the server SHOULD reply to the presence probe by sending to the user a presence stanza of type "unavailable" (although sending unavailable presence here is preferable because it results in a deterministic answer to the probe, it is not mandatory because it can greatly increase the number of presence notifications generated by the contact's server).  Here the 'from' address is the bare JID because there is no available resource associated with the contact.
+            
+            If appropriate in accordance with local security policies this presence notification MAY include the full XML of the last unavailable presence stanza that the server received from the contact (including the 'id' of the original stanza), but if not then the presence notification SHOULD simply indicate that the contact is unavailable without any of the details originally provided.  In any case, the presence notification returned to the probing entity SHOULD include information about the time when the last unavailable presence stanza was generated (formatted using the XMPP delayed delivery extension <a class='info' href='#DELAY'>[DELAY]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Delayed Delivery,&rdquo; September&nbsp;2009.</span><span>)</span></a>).
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='mercutio@example.com'
+              id='xv291f38'
+              to='juliet@example.com'
+              type='unavailable'&gt;
+      &lt;delay xmlns='urn:xmpp:delay'
+             stamp='2002-09-10T23:41:07Z'/&gt;
+    &lt;/presence&gt;
+</pre></div>
+            
+</li>
+<li>Else, if the contact has at least one available resource, then the server MUST reply to the presence probe by sending to the user the full XML of the last presence stanza with no 'to' attribute received by the server from each of the contact's available resources.  Here the 'from' addresses are the full JIDs of each available resource.
+              <div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='romeo@example.net/foo'
+              id='hzf1v27k'
+              to='juliet@example.com'/&gt;
+
+CS: &lt;presence from='romeo@example.net/bar'
+              id='ps6t1fu3'
+              to='juliet@example.com'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+</pre></div>
+            
+</li>
+</ol><p>
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: By "full XML" is meant the complete stanza from the opening &lt;presence&gt; tag to the closing &lt;/presence&gt; tag, including all elements and attributes whether qualified by the content namespace or extended namespaces; however, in accordance with <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, the contact's server will need to transform the content namespace from 'jabber:client' to 'jabber:server' if it sends the complete stanza over a server-to-server stream.
+</p>
+</blockquote>
+
+<p>If the contact's server receives a presence probe addressed to a full JID of the contact, the server MUST NOT return presence information about any resource except the resource specified by the 'to' address of the probe.  Rules #1 and #2 for a bare JID probe apply equally to the case of a full JID probe.  If there is a resource matching the full JID and the probing entity has authorization via a presence subscription to see the contact's presence, then the server MUST return an available presence notification, which SHOULD communicate only the fact that the resource is available (not detailed information such as the &lt;show/&gt;, &lt;status/&gt;, &lt;priority/&gt;, or presence extensions).
+</p>
+<p>
+          </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='romeo@example.net/bar'
+              to='lobby@chat.example.com'/&gt;
+</pre></div><p>
+
+        
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: See <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a> regarding rules that supplement the foregoing for handling of directed presence.
+</p>
+</blockquote>
+
+<a name="presence-probe-inbound-id"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.3.2.1"></a><h3>4.3.2.1.&nbsp;
+Handling of the 'id' Attribute</h3>
+
+<p>The handling of the 'id' attribute in relation to
+          presence probes was unspecified in RFC 3921. Although the
+          pattern of "send a probe and receive a reply" might seem
+          like a request-response protocol similar to the XMPP
+          &lt;iq/&gt; stanza, in fact it is not because the response
+          to a probe might consist of multiple presence stanzas (one
+          for each available resource currently active for the
+          contact).  For this reason, if the contact currently has
+          available resources then the contact's server SHOULD
+          preserve the 'id' attribute of the contact's original
+          presence stanza (if any) when sending those presence
+          notifications to the probing entity. By contrast, if the contact currently has no available resources, the probing entity is not authorized (via presence subscription) to see the contact's presence, or an error occurs in relation to the probe, then the contact's server SHOULD mirror the 'id' of the user's presence probe when replying to the probing entity.
+</p>
+<p>The following examples illustrate the difference.
+</p>
+<p>In the first scenario, Juliet sends presence from her "chamber" resource.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence from='juliet@example.com/chamber' id='pres1'&gt;
+      &lt;show&gt;dnd&lt;/show&gt;
+      &lt;status&gt;busy!&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div><p>
+
+          
+</p>
+<p>She also sends presence from her "balcony" resource.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence from='juliet@example.com/balcony' id='pres2'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;stepped away&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div><p>
+
+          
+</p>
+<p>Romeo's server then sends a probe to Juliet.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='romeo@example.net' id='probe1' type='probe'/&gt;
+</pre></div><p>
+
+          
+</p>
+<p>Juliet's server then sends both of her presence notifications to Romeo, preserving the 'id' attributes included in the stanzas that her client has sent.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com/chamber' id='pres1'&gt;
+      &lt;show&gt;dnd&lt;/show&gt;
+      &lt;status&gt;busy!&lt;/status&gt;
+    &lt;/presence&gt;
+
+CS: &lt;presence from='juliet@example.com/balcony' id='pres2'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;stepped away&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div><p>
+
+          
+</p>
+<p>In the second scenario, Juliet is offline when Romeo's server sends a probe.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='romeo@example.net'
+              id='probe2'
+              type='probe'/&gt;
+</pre></div><p>
+
+          
+</p>
+<p>Juliet's server replies with an unavailable notification, mirroring the 'id' of Rome's presence probe because there is no 'id' to preserve from an available notification that her client has sent.
+            </p>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence from='juliet@example.com'
+              id='probe2'
+              type='unavailable'/&gt;
+</pre></div><p>
+
+          
+</p>
+<a name="presence-broadcast"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4"></a><h3>4.4.&nbsp;
+Subsequent Presence Broadcast</h3>
+
+<a name="presence-broadcast-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4.1"></a><h3>4.4.1.&nbsp;
+Client Generation of Subsequent Presence Broadcast</h3>
+
+<p>After sending initial presence, at any time during its session the user's client can update its availability for broadcast by sending a presence stanza with no 'to' address and no 'type' attribute.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>The presence broadcast MAY contain the &lt;priority/&gt; element, the &lt;show/&gt; element, and one or more instances of the &lt;status/&gt; element, as well as extended content; details are provided under <a class='info' href='#presence-syntax'>Section&nbsp;4.7<span> (</span><span class='info'>Presence Syntax</span><span>)</span></a>.
+</p>
+<p>However, a user SHOULD send a presence update only to broadcast information that is relevant to the user's availability for communication or the communication capabilities of the resource.  Information that is not relevant in this way might be of interest to the user's contacts but SHOULD be sent via other means, such as the "publish-subscribe" method described in <a class='info' href='#XEP-0163'>[XEP&#8209;0163]<span> (</span><span class='info'>Saint-Andre, P. and K. Smith, &ldquo;Personal Eventing Protocol,&rdquo; July&nbsp;2010.</span><span>)</span></a>.
+</p>
+<a name="presence-broadcast-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4.2"></a><h3>4.4.2.&nbsp;
+Server Processing of Subsequent Outbound Presence</h3>
+
+<p>Upon receiving a presence stanza expressing updated availability, the user's server MUST broadcast the full XML of that presence stanza to the contacts who are in the user's roster with a subscription type of "from" or "both".
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: RFC 3921 specified that the user's server would check to make sure that it had not received a presence error from the contact before sending subsequent presence notifications. That rule has been removed because this specification uses presence stanzas of type "unsubscribe" (not "error") to solve subscription synchronization problems, in part because such stanzas change the contact's subscription state in the user's roster to either "none" or "to" (see <a class='info' href='#sub-unsub'>Section&nbsp;3.3<span> (</span><span class='info'>Unsubscribing</span><span>)</span></a> and <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>), thus obviating the need for the error check.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: If the subscription type is "both", some existing server implementations send subsequent presence notifications to a contact only if the contact is online according to the user's server (that is, if the user's server never received a positive indication that the contact is online in response to the presence probe it sent to the contact, the user's server does not send subsequent presence notifications from the user to the contact).  This behavior is perceived to save bandwidth, since most presence subscriptions are bidirectional and many contacts will not be online at any given time.
+</p>
+</blockquote>
+<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='benvolio@example.net'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='mercutio@example.com'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: See <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a> regarding rules that supplement the foregoing for handling of directed presence.
+</p>
+</blockquote>
+
+<p>The user's server MUST also send the presence stanza to all of the user's available resources (including the resource that generated the presence notification in the first place).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com/balcony'
+              to='juliet@example.com/chamber'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='juliet@example.com/balcony'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+</pre></div>
+<a name="presence-broadcast-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4.3"></a><h3>4.4.3.&nbsp;
+Server Processing of Subsequent Inbound Presence</h3>
+
+<p>Upon receiving presence from the user, the contact's server MUST deliver the user's presence stanza to all of the contact's available resources.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+[ ... to resource1 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+
+[ ... to resource2 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+    &lt;/presence&gt;
+</pre></div>
+<a name="presence-broadcast-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.4.4"></a><h3>4.4.4.&nbsp;
+Client Processing of Subsequent Presence</h3>
+
+<p>From the perspective of the contact's client, there is no significant difference between initial presence broadcast and subsequent presence, so the contact's client follows the rules for processing of inbound presence defined under <a class='info' href='#presence-broadcast-inbound'>Section&nbsp;4.4.3<span> (</span><span class='info'>Server Processing of Subsequent Inbound Presence</span><span>)</span></a>.
+</p>
+<a name="presence-unavailable"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5"></a><h3>4.5.&nbsp;
+Unavailable Presence</h3>
+
+<a name="presence-unavailable-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5.1"></a><h3>4.5.1.&nbsp;
+Client Generation of Unavailable Presence</h3>
+
+<p>Before ending its presence session with a server, the user's client SHOULD gracefully become unavailable by sending "unavailable presence", i.e., a presence stanza that possesses no 'to' attribute and that possesses a 'type' attribute whose value is "unavailable".
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence type='unavailable'/&gt;
+</pre></div>
+<p>Optionally, the unavailable presence stanza MAY contain one or more &lt;status/&gt; elements specifying the reason why the user is no longer available.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>However, the unavailable presence stanza MUST NOT contain the &lt;priority/&gt; element or the &lt;show/&gt; element, since these elements apply only to available resources.
+</p>
+<a name="presence-unavailable-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5.2"></a><h3>4.5.2.&nbsp;
+Server Processing of Outbound Unavailable Presence</h3>
+
+<p>The user's server MUST NOT depend on receiving unavailable presence from an available resource, since the resource might become unavailable ungracefully (e.g., the resource's XML stream might be closed with or without a stream error for any of the reasons described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p>
+<p>If an available resource becomes unavailable for any reason (either gracefully or ungracefully), the user's server MUST broadcast unavailable presence to all contacts that are in the user's roster with a subscription type of "from" or "both".
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: RFC 3921 specified that the user's server would check to make sure that it had not received a presence error from the contact before sending unavailable presence notifications. That rule has been removed because this specification uses presence stanzas of type "unsubscribe" (not "error") to solve subscription synchronization problems, in part because such stanzas change the contact's subscription state in the user's roster to either "none" or "to" (see <a class='info' href='#sub-unsub'>Section&nbsp;3.3<span> (</span><span class='info'>Unsubscribing</span><span>)</span></a> and <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>), thus obviating the need for the error check.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Even if the user's server does not broadcast the user's subsequent presence notifications to contacts who are offline (as described under <a class='info' href='#presence-broadcast-outbound'>Section&nbsp;4.4.2<span> (</span><span class='info'>Server Processing of Subsequent Outbound Presence</span><span>)</span></a>), it MUST broadcast the user's unavailable presence notification; if it did not do so, the last presence received by the contact's server would be the user's initial presence for the presence session, with the result that the contact would consider the user to be online.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: See <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a> regarding rules that supplement the foregoing for handling of directed presence.
+</p>
+</blockquote>
+
+<p>If the unavailable notification was gracefully received from the client, then the server MUST broadcast the full XML of the presence stanza.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='benvolio@example.net'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence from='juliet@example.com/balcony'
+              to='mercutio@example.com'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>The user's server MUST also send the unavailable notification to all of the user's available resources (as well as to the resource that generated the unavailable presence in the first place).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence from='juliet@example.com/balcony'
+              to='juliet@example.com/chamber'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>If the server detects that the user has gone offline ungracefully, then the server MUST generate the unavailable presence broadcast on the user's behalf.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: Any presence stanza with no 'type' attribute and no 'to' attribute that the client sends after the server broadcasts or generates an unavailable presence notification MUST be routed or delivered by the user's server to all subscribers (i.e., MUST be treated as equivalent to initial presence for a new presence session).
+</p>
+</blockquote>
+
+<a name="presence-unavailable-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5.3"></a><h3>4.5.3.&nbsp;
+Server Processing of Inbound Unavailable Presence</h3>
+
+<p>Upon receiving an unavailable notification from the user, the contact's server MUST deliver the user's presence stanza to all of the contact's available resources.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+[ ... to resource1 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+
+[ ... to resource2 ... ]
+
+CS: &lt;presence from='juliet@example.com/balcony'
+              to='romeo@example.net'
+              type='unavailable'&gt;
+      &lt;status&gt;going on vacation&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: If the contact's server does not broadcast subsequent presence notifications to users who are offline (as described under <a class='info' href='#presence-broadcast-outbound'>Section&nbsp;4.4.2<span> (</span><span class='info'>Server Processing of Subsequent Outbound Presence</span><span>)</span></a>), it MUST also update its internal representation of which entities are online by noting that the user is unavailable.
+</p>
+</blockquote>
+
+<a name="presence-unavailable-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.5.4"></a><h3>4.5.4.&nbsp;
+Client Processing of Unavailable Presence</h3>
+
+<p>From the perspective of the contact's client, there is no significant difference between available presence broadcast and unavailable presence broadcast, so in general the contact's client follows the rules for processing of inbound presence defined under <a class='info' href='#presence-broadcast-inbound'>Section&nbsp;4.4.3<span> (</span><span class='info'>Server Processing of Subsequent Inbound Presence</span><span>)</span></a>.
+</p>
+<p>However, if the contact receives an unavailable notification from the bare JID of the user (rather than the full JID of a particular available resource), the contact's client SHOULD treat the unavailable notification as applying to all resources.
+</p>
+<a name="presence-directed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6"></a><h3>4.6.&nbsp;
+Directed Presence</h3>
+
+<p>This section supplements the rules for client and server processing of presence notifications and presence probes, but only for the special case of directed presence.
+</p>
+<a name="presence-directed-considerations"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.1"></a><h3>4.6.1.&nbsp;
+General Considerations</h3>
+
+<p>In general, a client sends directed presence when it wishes to share availability information with an entity that is not subscribed to its presence, typically on a temporary basis.  Common uses of directed presence include casual one-to-one chat sessions as described under <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a> and multi-user chat rooms as described in <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2008.</span><span>)</span></a>.
+</p>
+<p>The temporary relationship established by sharing directed presence with another entity is secondary to the permanent relationship established through a presence subscription.  Therefore, the acts of creating, modifying, or canceling a presence subscription MUST take precedence over the rules specified in the following subsections.  For example, if a user shares directed presence with a contact but then adds the contact to the user's roster by completing the presence subscription "handshake", the user's server MUST treat the contact just as it would any normal subscriber as described under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>, for example, by sending subsequent presence broadcasts to the contact.  As another example, if the user then cancels the contact's subscription to the user's presence, the user's server MUST handle the cancellation just as it normally would as described under <a class='info' href='#sub-cancel'>Section&nbsp;3.2<span> (</span><span class='info'>Canceling a Subscription</span><span>)</span></a>, which includes sending unavailable presence to the contact even if the user has sent directed presence to the contact.
+</p>
+<p>XMPP servers typically implement directed presence by keeping a list of the entities (bare JIDs or full JIDs) to which a user has sent directed presence during the user's current session for a given resource (full JID), then clearing the list when the user goes offline (e.g., by sending a broadcast presence stanza of type "unavailable").  The server MUST remove from the directed presence list (or its functional equivalent) any entity to which the user sends directed unavailable presence and SHOULD remove any entity that sends unavailable presence to the user.
+</p>
+<a name="presence-directed-gen"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.2"></a><h3>4.6.2.&nbsp;
+Client Generation of Directed Presence</h3>
+
+<p>As noted, directed presence is a client-generated presence stanza with a 'to' attribute whose value is the bare JID or full JID of the other entity and with either no 'type' attribute (indicating availability) or a 'type' attribute whose value is "unavailable".
+</p>
+<a name="presence-directed-outbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.3"></a><h3>4.6.3.&nbsp;
+Server Processing of Outbound Directed Presence</h3>
+
+<p>When the user's server receives a directed presence stanza, it SHOULD process it according to the following rules.
+</p>
+<p>
+          </p>
+<ol class="text">
+<li>If the user sends directed available or unavailable presence to a contact that is in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast (i.e., during the user's presence session), the user's server MUST locally deliver or remotely route the full XML of that presence stanza but SHOULD NOT otherwise modify the contact's status regarding presence broadcast (i.e., it SHOULD include the contact's JID in any subsequent presence broadcasts initiated by the user).
+</li>
+<li>If the user sends directed presence to an entity that is not in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast (i.e., during the user's presence session), the user's server MUST locally deliver or remotely route the full XML of that presence stanza to the entity but MUST NOT modify the contact's status regarding available presence broadcast (i.e., it MUST NOT include the entity's JID in any subsequent broadcasts of available presence initiated by the user); however, if the available resource from which the user sent the directed presence becomes unavailable, the user's server MUST route that unavailable presence to the entity (if the user has not yet sent directed unavailable presence to that entity).
+</li>
+<li>If the user sends directed presence without first sending initial presence or after having sent unavailable presence broadcast (i.e., the resource is connected but not available), the user's server MUST treat the entity to which the user sends directed presence as in case #2 above.
+</li>
+</ol><p>
+        
+</p>
+<a name="presence-directed-inbound"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.4"></a><h3>4.6.4.&nbsp;
+Server Processing of Inbound Directed Presence</h3>
+
+<p>From the perspective of the contact's server, there is no
+significant difference between presence broadcast and directed presence, so the
+contact's server follows the rules for processing of inbound presence defined
+under Sections <a class='info' href='#presence-probe-inbound'>4.3.2<span> (</span><span class='info'>Server Processing of Inbound Presence Probe</span><span>)</span></a>, <a class='info' href='#presence-broadcast-inbound'>4.4.3<span> (</span><span class='info'>Server Processing of Subsequent Inbound Presence</span><span>)</span></a>, and <a class='info' href='#presence-unavailable-inbound'>4.5.3<span> (</span><span class='info'>Server Processing of Inbound Unavailable Presence</span><span>)</span></a>.
+</p>
+<a name="presence-directed-client"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.5"></a><h3>4.6.5.&nbsp;
+Client Processing of Inbound Directed Presence</h3>
+
+<p>From the perspective of the contact's client, there is no significant difference between presence broadcast and directed presence, so the contact's client follows the rules for processing of inbound presence defined under <a class='info' href='#presence-broadcast-inbound'>Section&nbsp;4.4.3<span> (</span><span class='info'>Server Processing of Subsequent Inbound Presence</span><span>)</span></a>.
+</p>
+<a name="presence-directed-probe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.6.6"></a><h3>4.6.6.&nbsp;
+Server Processing of Presence Probes</h3>
+
+<p>If a user's client has sent directed presence to another entity (e.g., a one-to-one chat partner or a multi-user chat room), after some time the entity or its server might want to know if the client is still online.  This scenario is especially common in the case of multi-user chat rooms, in which the user might be a participant for a long period of time.  If the user's client goes offline without the chat room being informed (either by the client or the client's server), the user's representation in the room might become a "ghost" that appears to be participating but that in fact is no longer present in the room.  To detect such "ghosts", some multi-user chat room implementations send presence probes to users that have joined the room.
+</p>
+<p>In the case of directed presence, the probing entity SHOULD send the probe from the JID that received directed presence (whether a full JID or a bare JID).  The probe SHOULD be sent to the user's full JID, not the user's bare JID without a resourcepart, because the temporary "authorization" involved with directed presence is based on the full JID from which the user sent directed presence to the probing entity.  When the user's server receives a probe, it MUST first apply any logic associated with presence subscriptions as described under <a class='info' href='#presence-probe-inbound'>Section&nbsp;4.3.2<span> (</span><span class='info'>Server Processing of Inbound Presence Probe</span><span>)</span></a>.  If the probing entity does not have a subscription to the user's presence, then the server MUST check if the user has sent directed presence to the entity during its current session; if so, the server SHOULD answer the probe with only mere presence of type "available" or "unavailable" (i.e., not including child elements) and only for that full JID (i.e., not for any other resources that might be currently associated with the user's bare JID).
+</p>
+<a name="presence-syntax"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7"></a><h3>4.7.&nbsp;
+Presence Syntax</h3>
+
+<a name="presence-syntax-type"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.1"></a><h3>4.7.1.&nbsp;
+Type Attribute</h3>
+
+<p>The absence of a 'type' attribute signals that the relevant entity is available for communication (see <a class='info' href='#presence-initial'>Section&nbsp;4.2<span> (</span><span class='info'>Initial Presence</span><span>)</span></a> and <a class='info' href='#presence-broadcast'>Section&nbsp;4.4<span> (</span><span class='info'>Subsequent Presence Broadcast</span><span>)</span></a>).
+</p>
+<p>A 'type' attribute with a value of "unavailable" signals that the relevant entity is not available for communication (see <a class='info' href='#presence-unavailable'>Section&nbsp;4.5<span> (</span><span class='info'>Unavailable Presence</span><span>)</span></a>).
+</p>
+<p>The XMPP presence stanza is also used to negotiate and manage subscriptions to the presence of other entities.  These tasks are completed via presence stanzas of type "subscribe", "unsubscribe", "subscribed", and "unsubscribed" as described under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>.
+</p>
+<p>If a user and contact are associated with different XMPP servers, those servers also use a special presence stanza of type "probe" in order to determine the availability of the entity on the peer server; details are provided under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.  Clients SHOULD NOT send presence stanzas of type "probe".
+</p>
+<p>The values of the 'type' attribute can be summarized as follows:
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>error -- An error has occurred regarding processing of a previously sent presence stanza; if the presence stanza is of type "error", it MUST include an &lt;error/&gt; child element (refer to <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</li>
+<li>probe -- A request for an entity's current presence; SHOULD be generated only by a server on behalf of a user.
+</li>
+<li>subscribe -- The sender wishes to subscribe to the recipient's presence.
+</li>
+<li>subscribed -- The sender has allowed the recipient to receive their presence.
+</li>
+<li>unavailable -- The sender is no longer available for communication.
+</li>
+<li>unsubscribe -- The sender is unsubscribing from the receiver's presence.
+</li>
+<li>unsubscribed -- The subscription request has been denied or a previously granted subscription has been canceled.
+</li>
+</ul><p>
+        
+</p>
+<p>If the value of the 'type' attribute is not one of the foregoing values, the recipient or an intermediate router SHOULD return a stanza error of &lt;bad-request/&gt;.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: There is no default value for the 'type' attribute of the &lt;presence/&gt; element.
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: There is no value of "available" for the 'type' attribute of the &lt;presence/&gt; element.
+</p>
+</blockquote>
+
+<a name="presence-syntax-children"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.2"></a><h3>4.7.2.&nbsp;
+Child Elements</h3>
+
+<p>In accordance with the default namespace declaration, a presence stanza is qualified by the 'jabber:client' or 'jabber:server' namespace, which defines certain child elements of presence stanzas, in particular the &lt;show/&gt;, &lt;status/&gt;, and &lt;priority/&gt; elements.  These child elements are used to provide more detailed information about an entity's availability.  Typically these child elements are included only if the presence stanza possesses no 'type' attribute, although exceptions are noted in the text that follows.
+</p>
+<a name="presence-syntax-children-show"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.2.1"></a><h3>4.7.2.1.&nbsp;
+Show Element</h3>
+
+<p>The OPTIONAL &lt;show/&gt; element specifies the particular availability sub-state of an entity or a specific resource thereof.  A presence stanza MUST NOT contain more than one &lt;show/&gt; element.  There are no attributes defined for the &lt;show/&gt; element.  The &lt;show/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).  The XML character data of the &lt;show/&gt; element is not meant for presentation to a human user.  The XML character data MUST be one of the following (additional availability states could be defined through extended content elements):
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>away -- The entity or resource is temporarily away.
+</li>
+<li>chat -- The entity or resource is actively interested in chatting.
+</li>
+<li>dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
+</li>
+<li>xa -- The entity or resource is away for an extended period (xa = "eXtended Away").
+</li>
+</ul><p>
+          
+</p>
+<p>If no &lt;show/&gt; element is provided, the entity is assumed to be online and available.
+</p>
+<p>Any specialized processing of availability states by recipients and intermediate routers is up to the implementation (e.g., incorporation of availability states into stanza routing and delivery logic).
+</p>
+<a name="presence-syntax-children-status"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.2.2"></a><h3>4.7.2.2.&nbsp;
+Status Element</h3>
+
+<p>The OPTIONAL &lt;status/&gt; element contains human-readable XML character data specifying a natural-language description of an entity's availability.  It is normally used in conjunction with the show element to provide a detailed description of an availability state (e.g., "In a meeting") when the presence stanza has no 'type' attribute.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net/orchard'
+          xml:lang='en'&gt;
+  &lt;show&gt;dnd&lt;/show&gt;
+  &lt;status&gt;Wooing Juliet&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>There are no attributes defined for the &lt;status/&gt; element, with the exception of the 'xml:lang' attribute inherited from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>.  The &lt;status/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).  Multiple instances of the &lt;status/&gt; element MAY be included, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which from the sender's perspective can include the XML stream header as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net/orchard'
+          id='jx62vs97'
+          xml:lang='en'&gt;
+  &lt;show&gt;dnd&lt;/show&gt;
+  &lt;status&gt;Wooing Juliet&lt;/status&gt;
+  &lt;status xml:lang='cs'&gt;Dvo&amp;#x0159;&amp;#x00ED;m se Julii&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>A presence stanza of type "unavailable" MAY also include a &lt;status/&gt; element to provide detailed information about why the entity is going offline.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net/orchard'
+          id='oy6sb241'
+          type='unavailable'
+          xml:lang='en'&gt;
+  &lt;status&gt;Busy IRL&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>The &lt;status/&gt; child MAY also be sent in a subscription-related presence stanza (i.e., type "subscribe", "subscribed", "unsubscribe", or "unsubscribed") to provide a description of the action.  An interactive client MAY present this &lt;status/&gt; information to a human user (see <a class='info' href='#security'>Section&nbsp;11<span> (</span><span class='info'>Security Considerations</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net'
+          id='uc51xs63'
+          to='nurse@example.com'
+          type='subscribe'&gt;
+  &lt;status&gt;Hi, Juliet told me to add you to my buddy list.&lt;/status&gt;
+&lt;/presence&gt;
+</pre></div>
+<a name="presence-syntax-children-priority"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.2.3"></a><h3>4.7.2.3.&nbsp;
+Priority Element</h3>
+
+<p>The OPTIONAL &lt;priority/&gt; element contains non-human-readable XML character data that specifies the priority level of the resource.  The value MUST be an integer between -128 and +127.  A presence stanza MUST NOT contain more than one &lt;priority/&gt; element.  There are no attributes defined for the &lt;priority/&gt; element.  The &lt;priority/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence xml:lang='en'&gt;
+  &lt;show&gt;dnd&lt;/show&gt;
+  &lt;status&gt;Wooing Juliet&lt;/status&gt;
+  &lt;status xml:lang='cs'&gt;Dvo&amp;#x0159;&amp;#x00ED;m se Julii&lt;/status&gt;
+  &lt;priority&gt;1&lt;/priority&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>If no priority is provided, the processing server or client MUST consider the priority to be zero ("0").
+</p>
+<p>The client's server MAY override the priority value
+          provided by the client (e.g., in order to impose a message
+          handling rule of delivering a message intended for the
+          account's bare JID to all of the account's available
+          resources). If the server does so, it MUST communicate the modified priority value when it echoes the client's presence back to itself and sends the presence notification to the user's contacts (because this modified priority value is typically the default value of zero, communicating the modified priority value can be done by not including the &lt;priority/&gt; child element).
+</p>
+<p>For information regarding the semantics of priority values in stanza processing within instant messaging and presence applications, refer to <a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>.
+</p>
+<a name="presence-extended"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.4.7.3"></a><h3>4.7.3.&nbsp;
+Extended Content</h3>
+
+<p>As described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, an XML stanza MAY contain any child element that is qualified by a namespace other than the default namespace; this applies to the presence stanza as well.
+</p>
+<p>(In the following example, the presence stanza includes entity capabilities information as defined in <a class='info' href='#XEP-0115'>[XEP&#8209;0115]<span> (</span><span class='info'>Hildebrand, J., Saint-Andre, P., and R. Tron&#xE7;on, &ldquo;Entity Capabilities,&rdquo; February&nbsp;2008.</span><span>)</span></a>.)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;presence from='romeo@example.net'&gt;
+  &lt;c xmlns='http://jabber.org/protocol/caps'
+     hash='sha-1'
+     node='http://psi-im.org'
+     ver='q07IKJEyjvHSyhy//CH0CxmKi8w='/&gt;
+&lt;/presence&gt;
+</pre></div>
+<p>Any extended content included in a presence stanza SHOULD represent aspects of an entity's availability for communication or provide information about communication-related capabilities.
+</p>
+<a name="message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5"></a><h3>5.&nbsp;
+Exchanging Messages</h3>
+
+<p>Once a client has authenticated with a server and bound a resource to an XML stream as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, an XMPP server will route XML stanzas to and from that client.  One kind of stanza that can be exchanged is &lt;message/&gt; (if, that is, messaging functionality is enabled on the server).  Exchanging messages is a basic use of XMPP and occurs when a user generates a message stanza that is addressed to another entity.  As defined under <a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>, the sender's server is responsible for delivering the message to the intended recipient (if the recipient is on the same local server) or for routing the message to the recipient's server (if the recipient is on a remote server).  Thus a message stanza is used to "push" information to another entity.
+</p>
+<a name="message-chat"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.1"></a><h3>5.1.&nbsp;
+One-to-One Chat Sessions</h3>
+
+<p>In practice, instant messaging activity between human users tends to occur in the form of a conversational burst that we call a "chat session": the exchange of multiple messages between two parties in relatively rapid succession within a relatively brief period of time.
+</p>
+<p>When a human user intends to engage in such a chat session with a contact (rather than sending a single message to which no reply is expected), the message type generated by the user's client SHOULD be "chat" and the contact's client SHOULD preserve that message type in subsequent replies.   The user's client also SHOULD include a &lt;thread/&gt; element with its initial message, which the contact's client SHOULD also preserve during the life of the chat session (see <a class='info' href='#message-syntax-thread'>Section&nbsp;5.2.5<span> (</span><span class='info'>Thread Element</span><span>)</span></a>).
+</p>
+<p>The user's client SHOULD address the initial message in a chat session to the bare JID &lt;contact@domainpart&gt; of the contact (rather than attempting to guess an appropriate full JID &lt;contact@domainpart/resourcepart&gt; based on the &lt;show/&gt;, &lt;status/&gt;, or &lt;priority/&gt; value of any presence notifications it might have received from the contact).  Until and unless the user's client receives a reply from the contact, it SHOULD send any further messages to the contact's bare JID.  The contact's client SHOULD address its replies to the user's full JID &lt;user@domainpart/resourcepart&gt; as provided in the 'from' address of the initial message.  Once the user's client receives a reply from the contact's full JID, it SHOULD address its subsequent messages to the contact's full JID as provided in the 'from' address of the contact's replies, thus "locking in" on that full JID.  A client SHOULD "unlock" after having received a &lt;message/&gt; or &lt;presence/&gt; stanza from any other resource controlled by the peer (or a presence stanza from the locked resource); as a result, it SHOULD address its next message(s) in the chat session to the bare JID of the peer (thus "unlocking" the previous "lock") until it receives a message from one of the peer's full JIDs.
+</p>
+<p>When two parties engage in a chat session but do not share presence with each other based on a presence subscription, they SHOULD send directed presence to each other so that either party can easily discover if the peer goes offline during the course of the chat session.  However, a client MUST provide a way for a user to disable such presence sharing globally or to enable it only with particular entities.  Furthermore, a party SHOULD send directed unavailable presence to the peer when it has reason to believe that the chat session is over (e.g., if, after some reasonable amount of time, no subsequent messages have been exchanged between the parties).
+</p>
+<p>An example of a chat session is provided under <a class='info' href='#session'>Section&nbsp;7<span> (</span><span class='info'>A Sample Session</span><span>)</span></a>.
+</p>
+<a name="message-syntax"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2"></a><h3>5.2.&nbsp;
+Message Syntax</h3>
+
+<p>The following sections describe the syntax of the &lt;message/&gt; stanza.
+</p>
+<a name="message-syntax-to"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2.1"></a><h3>5.2.1.&nbsp;
+To Attribute</h3>
+
+<p>An instant messaging client specifies an intended recipient for a message by providing the JID of the intended recipient in the 'to' attribute of the &lt;message/&gt; stanza.
+</p>
+<p>If the message is being sent outside the context of any existing chat session or received message, the value of the 'to' address SHOULD be of the form &lt;localpart@domainpart&gt; rather than of the form &lt;localpart@domainpart/resourcepart&gt; (see <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    id='ktx72v49'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>If the message is being sent in reply to a message previously received from an address of the form &lt;localpart@domainpart/resourcepart&gt; (e.g., within the context of a one-to-one chat session as described under <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a>), the value of the 'to' address SHOULD be of the form &lt;localpart@domainpart/resourcepart&gt; rather than of the form &lt;localpart@domainpart&gt; unless the sender has knowledge (e.g., via presence) that the intended recipient's resource is no longer available.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='romeo@example.net/orchard'
+    id='sl3nx51f'
+    to='juliet@example.com/balcony'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;body&gt;Neither, fair saint, if either thee dislike.&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<a name="message-syntax-type"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2.2"></a><h3>5.2.2.&nbsp;
+Type Attribute</h3>
+
+<p>Common uses of the message stanza in instant messaging applications include: single messages; messages sent in the context of a one-to-one chat session; messages sent in the context of a multi-user chat room; alerts, notifications, or other information to which no reply is expected; and errors.  These uses are differentiated via the 'type' attribute.  Inclusion of the 'type' attribute is RECOMMENDED.  If included, the 'type' attribute MUST have one of the following values:
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>chat -- The message is sent in the context of a one-to-one chat session.  Typically an interactive client will present a message of type "chat" in an interface that enables one-to-one chat between the two parties, including an appropriate conversation history.  Detailed recommendations regarding one-to-one chat sessions are provided under <a class='info' href='#message-chat'>Section&nbsp;5.1<span> (</span><span class='info'>One-to-One Chat Sessions</span><span>)</span></a>.
+</li>
+<li>error -- The message is generated by an entity that experiences an error when processing a message received from another entity (for details regarding stanza error syntax, refer to <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).  A client that receives a message of type "error" SHOULD present an appropriate interface informing the original sender regarding the nature of the error.
+</li>
+<li>groupchat -- The message is sent in the context of a multi-user chat environment (similar to that of <a class='info' href='#IRC'>[IRC]<span> (</span><span class='info'>Kalt, C., &ldquo;Internet Relay Chat: Architecture,&rdquo; April&nbsp;2000.</span><span>)</span></a>).  Typically a receiving client will present a message of type "groupchat" in an interface that enables many-to-many chat between the parties, including a roster of parties in the chatroom and an appropriate conversation history.  For detailed information about XMPP-based groupchat, refer to <a class='info' href='#XEP-0045'>[XEP&#8209;0045]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Multi-User Chat,&rdquo; July&nbsp;2008.</span><span>)</span></a>.
+</li>
+<li>headline -- The message provides an alert, a notification, or other transient information to which no reply is expected (e.g., news headlines, sports updates, near-real-time market data, or syndicated content).  Because no reply to the message is expected, typically a receiving client will present a message of type "headline" in an interface that appropriately differentiates the message from standalone messages, chat messages, and groupchat messages (e.g., by not providing the recipient with the ability to reply).  If the 'to' address is the bare JID, the receiving server SHOULD deliver the message to all of the recipient's available resources with non-negative presence priority and MUST deliver the message to at least one of those resources; if the 'to' address is a full JID and there is a matching resource, the server MUST deliver the message to that resource; otherwise the server MUST either silently ignore the message or return an error (see <a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>).
+</li>
+<li>normal -- The message is a standalone message that is sent outside the context of a one-to-one conversation or groupchat, and to which it is expected that the recipient will reply.  Typically a receiving client will present a message of type "normal" in an interface that enables the recipient to reply, but without a conversation history.  The default value of the 'type' attribute is "normal".
+</li>
+</ul><p>
+      
+</p>
+<p>An IM application SHOULD support all of the foregoing message types.  If an application receives a message with no 'type' attribute or the application does not understand the value of the 'type' attribute provided, it MUST consider the message to be of type "normal" (i.e., "normal" is the default).
+</p>
+<p>Guidelines for server handling of different message types is provided under <a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>.
+</p>
+<p>Although the 'type' attribute is OPTIONAL, it is considered polite to mirror the type in any replies to a message; furthermore, some specialized applications (e.g., a multi-user chat service) MAY at their discretion enforce the use of a particular message type (e.g., type='groupchat').
+</p>
+<a name="message-syntax-body"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2.3"></a><h3>5.2.3.&nbsp;
+Body Element</h3>
+
+<p>The &lt;body/&gt; element contains human-readable XML character data that specifies the textual contents of the message; this child element is normally included but is OPTIONAL.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    id='b4vs9km4'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>There are no attributes defined for the &lt;body/&gt; element, with the exception of the 'xml:lang' attribute.  Multiple instances of the &lt;body/&gt; element MAY be included in a message stanza for the purpose of providing alternate versions of the same body, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which from the sender's perspective can include the XML stream header as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    id='z94nb37h'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+  &lt;body xml:lang='cs'&gt;
+     Pro&amp;#x010D;e&amp;#x017D; jsi ty, Romeo?
+   &lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>The &lt;body/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).
+</p>
+<a name="message-syntax-subject"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2.4"></a><h3>5.2.4.&nbsp;
+Subject Element</h3>
+
+<p>The &lt;subject/&gt; element contains human-readable XML character data that specifies the topic of the message.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    id='c8xg3nf8'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;subject&gt;I implore you!&lt;/subject&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>There are no attributes defined for the &lt;subject/&gt; element, with the exception of the 'xml:lang' attribute inherited from <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>.  Multiple instances of the &lt;subject/&gt; element MAY be included for the purpose of providing alternate versions of the same subject, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which from the sender's perspective can include the XML stream header as described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    id='jk3v47gw'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;subject&gt;I implore you!&lt;/subject&gt;
+  &lt;subject xml:lang='cs'&gt;
+    &amp;#x00DA;p&amp;#x011B;nliv&amp;#x011B; pros&amp;#x00ED;m!
+  &lt;/subject&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+  &lt;body xml:lang='cs'&gt;
+     Pro&amp;#x010D;e&amp;#x017E; jsi ty, Romeo?
+   &lt;/body&gt;
+&lt;/message&gt;
+</pre></div>
+<p>The &lt;subject/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).
+</p>
+<a name="message-syntax-thread"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.2.5"></a><h3>5.2.5.&nbsp;
+Thread Element</h3>
+
+<p>The primary use of the XMPP &lt;thread/&gt; element is to uniquely identify a conversation thread or "chat session" between two entities instantiated by &lt;message/&gt; stanzas of type 'chat'.  However, the XMPP &lt;thread/&gt; element MAY also be used to uniquely identify an analogous thread between two entities instantiated by &lt;message/&gt; stanzas of type 'headline' or 'normal', or among multiple entities in the context of a multi-user chat room instantiated by &lt;message/&gt; stanzas of type 'groupchat'. It MAY also be used for &lt;message/&gt; stanzas not related to a human conversation, such as a game session or an interaction between plugins.  The &lt;thread/&gt; element is not used to identify individual messages, only conversations or messaging sessions.
+</p>
+<p>The inclusion of the &lt;thread/&gt; element is OPTIONAL.  Because the &lt;thread/&gt; element identifies the particular conversation thread to which a message belongs, a message stanza MUST NOT contain more than one &lt;thread/&gt; element.
+</p>
+<p>The &lt;thread/&gt; element MAY possess a 'parent' attribute that identifies another thread of which the current thread is an offshoot or child.  The 'parent' attribute MUST conform to the syntax of the &lt;thread/&gt; element itself and its value MUST be different from the XML character data of the &lt;thread/&gt; element on which the 'parent' attribute is included.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: The ability to specify both a parent thread and a child thread introduces the possibility of conflicts between thread identifiers for overlapping threads.  For example, one &lt;thread/&gt; element might contain XML character data of "foo" and a 'parent' attribute whose value is "bar", a second &lt;thread/&gt; element might contain XML character data of "bar" and a 'parent' attribute whose value is "baz", and a third &lt;thread/&gt; element might contain XML character data of "baz" and a 'parent' attribute whose value is once again "foo".  It is up to the implementation how it will treat conflicts between such overlapping thread identifiers (e.g., whether it will "chain together" thread identifiers by showing "foo" as both a parent and grandchild of "baz" in a multi-level user interface, or whether it will show only one level of dependency at a time).
+</p>
+</blockquote>
+
+<p>The value of the &lt;thread/&gt; element is not human-readable and MUST be treated as opaque by entities; no semantic meaning can be derived from it, and only exact comparisons can be made against it.  The value of the &lt;thread/&gt; element MUST uniquely identify the conversation thread either between the conversation partners or more generally (one way to ensure uniqueness is by generating a universally unique identifier (UUID) as described in <a class='info' href='#UUID'>[UUID]<span> (</span><span class='info'>Leach, P., Mealling, M., and R. Salz, &ldquo;A Universally Unique IDentifier (UUID) URN Namespace,&rdquo; July&nbsp;2005.</span><span>)</span></a>).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: An application that generates a ThreadID MUST ensure that it does not reveal identifying information about the entity (e.g., the MAC address of the device on which the XMPP application is running).
+</p>
+</blockquote>
+
+<p>The &lt;thread/&gt; element MUST NOT contain mixed content (as defined in Section 3.2.2 of <a class='info' href='#XML'>[XML]<span> (</span><span class='info'>Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;Extensible Markup Language (XML) 1.0 (Fifth Edition),&rdquo; November&nbsp;2008.</span><span>)</span></a>).
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;subject&gt;I implore you!&lt;/subject&gt;
+  &lt;subject xml:lang='cs'&gt;
+    &amp;#x00DA;p&amp;#x011B;nliv&amp;#x011B; pros&amp;#x00ED;m!
+  &lt;/subject&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+  &lt;body xml:lang='cs'&gt;
+     Pro&amp;#x010D;e&amp;#x017E; jsi ty, Romeo?
+  &lt;/body&gt;
+  &lt;thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'&gt;
+    0e3141cd80894871a68e6fe6b1ec56fa
+  &lt;/thread&gt;
+&lt;/message&gt;
+</pre></div>
+<p>For detailed recommendations regarding use of the &lt;thread/&gt; element, refer to <a class='info' href='#XEP-0201'>[XEP&#8209;0201]<span> (</span><span class='info'>Saint-Andre, P., Paterson, I., and K. Smith, &ldquo;Best Practices for Message Threads,&rdquo; November&nbsp;2010.</span><span>)</span></a>.
+</p>
+<a name="message-syntax-extended"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.5.3"></a><h3>5.3.&nbsp;
+Extended Content</h3>
+
+<p>As described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, an XML stanza MAY contain any child element that is qualified by a namespace other than the default namespace; this applies to the message stanza as well.  Guidelines for handling extended content on the part of both routing servers and end recipients are provided in Section 8.4 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<p>(In the following example, the message stanza includes an XHTML-formatted version of the message as defined in <a class='info' href='#XEP-0071'>[XEP&#8209;0071]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XHTML-IM,&rdquo; September&nbsp;2008.</span><span>)</span></a>).)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;message
+    from='juliet@example.com/balcony'
+    to='romeo@example.net'
+    type='chat'
+    xml:lang='en'&gt;
+  &lt;body&gt;Wherefore art thou, Romeo?&lt;/body&gt;
+  &lt;html xmlns='http://jabber.org/protocol/xhtml-im'&gt;
+    &lt;body xmlns='http://www.w3.org/1999/xhtml'&gt;
+      &lt;p&gt;Wherefore &lt;span style='font-style: italic'&gt;art&lt;/span&gt;
+      thou, &lt;span style='color:red'&gt;Romeo&lt;/span&gt;?&lt;/p&gt;
+    &lt;/body&gt;
+  &lt;/html&gt;
+&lt;/message&gt;
+</pre></div>
+<a name="iq"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.6"></a><h3>6.&nbsp;
+Exchanging IQ Stanzas</h3>
+
+<p>As described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, IQ stanzas provide a structured request-response mechanism.  The basic semantics of that mechanism (e.g., that the 'id' attribute is mandatory) are defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, whereas the specific semantics needed to complete particular use cases are defined in all instances by the extended namespace that qualifies the direct child element of an IQ stanza of type "get" or "set".  The 'jabber:client' and 'jabber:server' namespaces do not define any children of IQ stanzas other than the &lt;error/&gt; element common to all stanza types.  This document defines one such extended namespace, for <a class='info' href='#roster'>Managing the Roster<span> (</span><span class='info'>Managing the Roster</span><span>)</span></a>.  However, an IQ stanza MAY contain structured information qualified by any extended namespace.
+</p>
+<a name="session"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.7"></a><h3>7.&nbsp;
+A Sample Session</h3>
+
+<p>The examples in this section illustrate a possible instant messaging and presence session.  The user is &lt;romeo@example.net&gt;, he has an available resource whose resourcepart is "orchard", and he has the following individuals in his roster:
+</p>
+<p>
+      </p>
+<ul class="text">
+<li>&lt;juliet@example.com&gt; (subscription="both" and she has two available resources, "chamber" and "balcony")
+</li>
+<li>&lt;benvolio@example.net&gt; (subscription="to")
+</li>
+<li>&lt;mercutio@example.org&gt; (subscription="from")
+</li>
+</ul><p>
+    
+</p>
+<p>First, the user completes the preconditions (stream establishment, TLS and SASL negotiation, and resource binding) described in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>; those protocol flows are not reproduced here.
+</p>
+<p>Next, the user requests his roster.
+</p>
+<p>Example 1: User requests current roster from server
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;iq from='romeo@example.net/orchard'
+        id='hf61v3n7'
+        type='get'&gt;
+      &lt;query xmlns='jabber:iq:roster'/&gt;
+    &lt;/iq&gt;
+</pre></div>
+<p>Example 2: User receives roster from server
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;iq id='hf61v3n7'
+        to='romeo@example.net/orchard'
+        type='result'&gt;
+      &lt;query xmlns='jabber:iq:roster'&gt;
+        &lt;item jid='juliet@example.com'
+              name='Juliet'
+              subscription='both'&gt;
+          &lt;group&gt;Friends&lt;/group&gt;
+        &lt;/item&gt;
+        &lt;item jid='benvolio@example.org'
+              name='Benvolio'
+              subscription='to'/&gt;
+        &lt;item jid='mercutio@example.org'
+              name='Mercutio'
+              subscription='from'/&gt;
+      &lt;/query&gt;
+    &lt;/iq&gt;
+</pre></div>
+<p>Now the user begins a presence session.
+</p>
+<p>Example 3: User sends initial presence
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence/&gt;
+</pre></div>
+<p>Example 4: User's server sends presence probes to contacts with subscription="to" and subscription="both" on behalf of the user
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence
+        from='romeo@example.net'
+        to='juliet@example.com'
+        type='probe'/&gt;
+
+US: &lt;presence
+        from='romeo@example.net'
+        to='benvolio@example.org'
+        type='probe'/&gt;
+</pre></div>
+<p>Example 5: User's server sends initial presence to contacts with subscription="from" and subscription="both" on behalf of the user's available resource, as well as to user
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'/&gt;
+
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='mercutio@example.org'/&gt;
+
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='romeo@example.net'/&gt;
+</pre></div>
+<p>Example 6: Contacts' servers reply to presence probe on behalf of all available resources
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence
+        from='juliet@example.com/balcony'
+        to='romeo@example.net'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;be right back&lt;/status&gt;
+      &lt;priority&gt;0&lt;/priority&gt;
+    &lt;/presence&gt;
+
+CS: &lt;presence
+        from='juliet@example.com/chamber'
+        to='romeo@example.net'&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+
+CS: &lt;presence
+        from='benvolio@example.org/pda'
+        to='romeo@example.net'
+        xml:lang='en'&gt;
+      &lt;show&gt;dnd&lt;/show&gt;
+      &lt;status&gt;gallivanting&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Example 7: Contacts' servers deliver user's initial presence to all available resources
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'/&gt;
+
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'/&gt;
+
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='mercutio@example.org'/&gt;
+</pre></div>
+<p>Example 8: User sends directed presence to another user not in his roster
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence
+        from='romeo@example.net/orchard'
+        to='nurse@example.com'
+        xml:lang='en'&gt;
+      &lt;show&gt;dnd&lt;/show&gt;
+      &lt;status&gt;courting Juliet&lt;/status&gt;
+      &lt;priority&gt;0&lt;/priority&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Now the user engages in a chat session with one of his contacts.
+</p>
+<p>Example 9: A threaded conversation
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;message
+        from='juliet@example.com/balcony'
+        to='romeo@example.net'
+        type='chat'
+        xml:lang='en'&gt;
+      &lt;body&gt;My ears have not yet drunk a hundred words&lt;/body&gt;
+      &lt;thread&gt;e0ffe42b28561960c6b12b944a092794b9683a38&lt;/thread&gt;
+    &lt;/message&gt;
+
+CC: &lt;message
+        from='juliet@example.com/balcony'
+        to='romeo@example.net'
+        type='chat'
+        xml:lang='en'&gt;
+      &lt;body&gt;Of that tongue's utterance, yet I know the sound:&lt;/body&gt;
+      &lt;thread&gt;e0ffe42b28561960c6b12b944a092794b9683a38&lt;/thread&gt;
+    &lt;/message&gt;
+
+CC: &lt;message
+        from='juliet@example.com/balcony'
+        to='romeo@example.net'
+        type='chat'
+        xml:lang='en'&gt;
+      &lt;body&gt;Art thou not Romeo, and a Montague?&lt;/body&gt;
+      &lt;thread&gt;e0ffe42b28561960c6b12b944a092794b9683a38&lt;/thread&gt;
+    &lt;/message&gt;
+
+UC: &lt;message
+        from='romeo@example.net/orchard'
+        to='juliet@example.com/balcony'
+        type='chat'
+        xml:lang='en'&gt;
+      &lt;body&gt;Neither, fair saint, if either thee dislike.&lt;/body&gt;
+      &lt;thread&gt;e0ffe42b28561960c6b12b944a092794b9683a38&lt;/thread&gt;
+    &lt;/message&gt;
+
+CC: &lt;message
+        from='juliet@example.com/balcony'
+        to='romeo@example.net/orchard'
+        type='chat'
+        xml:lang='en'&gt;
+      &lt;body&gt;How cam'st thou hither, tell me, and wherefore?&lt;/body&gt;
+      &lt;thread&gt;e0ffe42b28561960c6b12b944a092794b9683a38&lt;/thread&gt;
+    &lt;/message&gt;
+</pre></div>
+<p>And so on.
+</p>
+<p>The user can also send subsequent presence broadcast.
+</p>
+<p>Example 10: User sends updated available presence for broadcast
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Example 11: User's server broadcasts updated presence to the contacts who have a subscription of type "both" or "from" (but not to the entity to which the user sent directed presence)
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='mercutio@example.org'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Example 12: Contacts' servers deliver updated presence
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+
+CS: &lt;presence
+        from='romeo@example.net/orchard'
+        to='mercutio@example.org'
+        xml:lang='en'&gt;
+      &lt;show&gt;away&lt;/show&gt;
+      &lt;status&gt;I shall return!&lt;/status&gt;
+      &lt;priority&gt;1&lt;/priority&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Example 13: One of the contact's resources broadcasts unavailable notification
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CC: &lt;presence from='juliet@example.com/chamber' type='unavailable'/&gt;
+</pre></div>
+<p>Example 14: Contact's server sends unavailable notification to user
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+CS: &lt;presence
+        from='juliet@example.com/chamber'
+        to='romeo@example.net'
+        type='unavailable'/&gt;
+</pre></div>
+<p>Now the user ends his presence session.
+</p>
+<p>Example 15: User sends unavailable notification
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;presence type='unavailable' xml:lang='en'&gt;
+      &lt;status&gt;gone home&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Example 16: User's server broadcasts unavailable notification to contacts as well as to the entity to whom the user sent directed presence
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='juliet@example.com'
+        type='unavailable'
+        xml:lang='en'&gt;
+      &lt;status&gt;gone home&lt;/status&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='mercutio@example.org'
+        type='unavailable'
+        xml:lang='en'&gt;
+      &lt;status&gt;gone home&lt;/status&gt;
+    &lt;/presence&gt;
+
+US: &lt;presence
+        from='romeo@example.net/orchard'
+        to='nurse@example.com'
+        type='unavailable'
+        xml:lang='en'&gt;
+      &lt;status&gt;gone home&lt;/status&gt;
+    &lt;/presence&gt;
+</pre></div>
+<p>Finally the user closes his stream and the server responds in kind.
+</p>
+<p>Example 17: User closes stream
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+UC: &lt;/stream:stream&gt;
+</pre></div>
+<p>Example 18: User's server closes stream
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+US: &lt;/stream:stream&gt;
+</pre></div>
+<p>THE END
+</p>
+<a name="rules"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8"></a><h3>8.&nbsp;
+Server Rules for Processing XML Stanzas</h3>
+
+<p>Basic server rules for processing XML stanzas are defined in
+    <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, and the reader is referred to that specification for underlying rules and security implications.  This section defines supplementary rules for XMPP instant messaging and presence servers.
+</p>
+<p>Some delivery rules defined in this section specify the use of "offline storage", i.e., the server's act of storing a message stanza on behalf of the user and then delivering it when the user next becomes available.  For recommendations regarding offline message storage, refer to <a class='info' href='#XEP-0160'>[XEP&#8209;0160]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Best Practices for Handling Offline Messages,&rdquo; January&nbsp;2006.</span><span>)</span></a>.
+</p>
+<a name="rules-general"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.1"></a><h3>8.1.&nbsp;
+General Considerations</h3>
+
+<p><a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> discusses general considerations for stanza delivery, in particular the tradeoffs between (i) providing an acceptable level of service regarding stanza delivery and (ii) preventing directory harvesting attacks and presence leaks.  However, the concept of a directory harvesting attack does not apply if a contact is known to and trusted by a user (because the contact is in the user's roster as described under <a class='info' href='#roster'>Section&nbsp;2<span> (</span><span class='info'>Managing the Roster</span><span>)</span></a>).  Similarly, the concept of a presence leak does not apply if a contact is authorized to know a user's presence (by means of a presence subscription as described under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>) or if the user has voluntarily sent presence to an entity (by means of directed presence as described under <a class='info' href='#presence-directed'>Section&nbsp;4.6<span> (</span><span class='info'>Directed Presence</span><span>)</span></a>).  Therefore, in cases where the following sections guard against directory harvesting attacks and presence leaks by providing an alternative of (a) silently ignoring a stanza or (b) returning an error, a server SHOULD return an error if the originating entity is in the user's roster (when the error would reveal whether the user's account exists) or is authorized to receive presence from the user or has received directed presence from the user (when the error would reveal the presence of a user's resource).
+</p>
+<p></p>
+<blockquote class="text">
+<p>Security Warning: All of the stanza processing rules described below are defined with the understanding that they will be applied subject to enforcement of relevant privacy and security policies, such as those deployed by means of <a class='info' href='#XEP-0016'>[XEP&#8209;0016]<span> (</span><span class='info'>Millard, P. and P. Saint-Andre, &ldquo;Privacy Lists,&rdquo; February&nbsp;2007.</span><span>)</span></a> or <a class='info' href='#XEP-0191'>[XEP&#8209;0191]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Simple Communications Blocking,&rdquo; February&nbsp;2007.</span><span>)</span></a>.  The conformance language (MUST, SHOULD, etc.) in the following sections is not meant to override any such local service policies.
+</p>
+</blockquote>
+
+<a name="rules-noto"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.2"></a><h3>8.2.&nbsp;
+No 'to' Address</h3>
+
+<p>If the stanza possesses no 'to' attribute, the rules defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> apply.
+</p>
+<a name="rules-remote"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.3"></a><h3>8.3.&nbsp;
+Remote Domain</h3>
+
+<p>If the domainpart of the address contained in the 'to' attribute of an outbound stanza does not match a configured domain of the server itself, then the rules provided in Section 10.4 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> apply.
+</p>
+<p></p>
+<blockquote class="text">
+<p>Interoperability Note: RFC 3921 specified how to use the _im._xmpp and _pres._xmpp SRV records <a class='info' href='#IMP-SRV'>[IMP&#8209;SRV]<span> (</span><span class='info'>Peterson, J., &ldquo;Address Resolution for Instant Messaging and Presence,&rdquo; August&nbsp;2004.</span><span>)</span></a> as a fallback method for discovering whether a remote instant messaging and presence service communicates via XMPP.  Because those SRV records have not been widely deployed, this document no longer specifies their use, and new implementations are not encouraged.
+</p>
+</blockquote>
+
+<a name="rules-local"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.4"></a><h3>8.4.&nbsp;
+Local Domain</h3>
+
+<p>If the domainpart of the JID contained in the 'to' attribute matches one of the configured domains of the server, the domain is serviced by the server itself (not by a specialized local service), and the JID is of the form &lt;domainpart&gt; or &lt;domainpart/resourcepart&gt;, the rules defined in <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> apply.
+</p>
+<a name="rules-localpart"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5"></a><h3>8.5.&nbsp;
+Local User</h3>
+
+<p>If the 'to' address specifies a bare JID &lt;localpart@domainpart&gt; or full JID &lt;localpart@domainpart/resourcepart&gt; where the domainpart of the JID matches a configured domain that is serviced by the server itself, the server MUST proceed as follows.
+</p>
+<a name="rules-localpart-nosuchuser"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.1"></a><h3>8.5.1.&nbsp;
+No Such User</h3>
+
+<p>If the user account identified by the 'to' attribute does not exist, how the stanza is processed depends on the stanza type.
+</p>
+<p>
+          </p>
+<ul class="text">
+<li>For an IQ stanza, the server MUST return a &lt;service-unavailable/&gt; stanza error to the sender.
+</li>
+<li>For a message stanza, the server MUST either (a) silently ignore the message or (b) return a &lt;service-unavailable/&gt; stanza error to the sender.
+</li>
+<li>For a presence stanza with no 'type' attribute or a 'type' attribute of "unavailable", the server MUST silently ignore the stanza.
+</li>
+<li>For a presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed", the server MUST silently ignore the stanza.
+</li>
+<li>For a presence stanza of type "probe", the server MUST either (a) silently ignore the stanza or (b) return a presence stanza of type "unsubscribed".
+</li>
+</ul><p>
+        
+</p>
+<a name="rules-localpart-barejid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2"></a><h3>8.5.2.&nbsp;
+localpart@domainpart</h3>
+
+<p>If the JID contained in the 'to' attribute is of the form &lt;localpart@domainpart&gt;, then the server MUST adhere to the following rules.
+</p>
+<a name="rules-localpart-barejid-resource"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.1"></a><h3>8.5.2.1.&nbsp;
+Available or Connected Resources</h3>
+
+<p>If there is at least one available resource or connected resource, how the stanza is processed depends on the stanza type.
+</p>
+<a name="rules-localpart-barejid-resource-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.1.1"></a><h3>8.5.2.1.1.&nbsp;
+Message</h3>
+
+<p>For a message stanza of type "normal":
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>If all of the available resources have a negative presence priority then the server SHOULD either (a) store the message offline for later delivery or (b) return a stanza error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</li>
+<li>If there is one available resource with a non-negative presence priority then the server MUST deliver the message to that resource.
+</li>
+<li>If there is more than one resource with a non-negative presence priority then the server MUST either (a) deliver the message to the "most available" resource or resources (according to the server's implementation-specific algorithm, e.g., treating the resource or resources with the highest presence priority as "most available") or (b) deliver the message to all of the non-negative resources.
+</li>
+</ul><p>
+            
+</p>
+<p>For a message stanza of type "chat":
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>If the only available resource has a negative presence priority then the server SHOULD either (a) store the message offline for later delivery or (b) return a stanza error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</li>
+<li>If the only available resource has a non-negative presence priority then the server MUST deliver the message to that resource.
+</li>
+<li>If there is more than one resource with a non-negative presence priority then the server MUST either (a) deliver the message to the "most available" resource or resources (according to the server's implementation-specific algorithm, e.g., treating the resource or resources with the highest presence priority as "most available") or (b) deliver the message to all of the non-negative resources that have opted in to receive chat messages.
+</li>
+</ul><p>
+            
+</p>
+<p>For a message stanza of type "groupchat", the server MUST NOT deliver the stanza to any of the available resources but instead MUST return a stanza error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</p>
+<p>For a message stanza of type "headline":
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>If the only available resource has a negative presence priority then the server MUST silently ignore the stanza.
+</li>
+<li>If the only available resource has a non-negative presence priority then the server MUST deliver the message to that resource.
+</li>
+<li>If there is more than one resource with a non-negative presence priority then the server MUST deliver the message to all of the non-negative resources.
+</li>
+</ul><p>
+            
+</p>
+<p>For a message stanza of type "error", the server MUST silently ignore the message.
+</p>
+<p>However, for any message type the server MUST NOT deliver the stanza to any available resource with a negative priority; if the only available resource has a negative priority, the server SHOULD handle the message as if there were no available resources or connected resources as described under <a class='info' href='#rules-localpart-barejid-noresource'>Section&nbsp;8.5.2.2<span> (</span><span class='info'>No Available or Connected Resources</span><span>)</span></a>.
+</p>
+<p>In all cases, the server MUST NOT rewrite the 'to' attribute (i.e., it MUST leave it as &lt;localpart@domainpart&gt; rather than change it to &lt;localpart@domainpart/resourcepart&gt;).
+</p>
+<a name="rules-localpart-barejid-resource-pres"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.1.2"></a><h3>8.5.2.1.2.&nbsp;
+Presence</h3>
+
+<p>For a presence stanza with no type or of type "unavailable", the server MUST deliver it to all available resources.
+</p>
+<p>For a presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed", the server MUST adhere to the rules defined under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a> and summarized under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>.
+</p>
+<p>For a presence stanza of type "probe", the server MUST handle it directly as described under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.
+</p>
+<p>In all cases, the server MUST NOT rewrite the 'to' attribute (i.e., it MUST leave it as &lt;localpart@domainpart&gt; rather than change it to &lt;localpart@domainpart/resourcepart&gt;).
+</p>
+<a name="rules-localpart-barejid-resource-iq"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.1.3"></a><h3>8.5.2.1.3.&nbsp;
+IQ</h3>
+
+<p>For an IQ stanza, the server itself MUST reply on behalf of the user with either an IQ result or an IQ error, and MUST NOT deliver the IQ stanza to any of the user's available resources.  Specifically, if the semantics of the qualifying namespace define a reply that the server can provide on behalf of the user, then the server MUST reply to the stanza on behalf of the user by returning either an IQ stanza of type "result" or an IQ stanza of type "error" that is appropriate to the original payload; if not, then the server MUST reply with a &lt;service-unavailable/&gt; stanza error.
+</p>
+<a name="rules-localpart-barejid-noresource"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.2"></a><h3>8.5.2.2.&nbsp;
+No Available or Connected Resources</h3>
+
+<p>If there are no available resources or connected resources associated with the user, how the stanza is processed depends on the stanza type.
+</p>
+<a name="rules-localpart-barejid-noresource-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.2.1"></a><h3>8.5.2.2.1.&nbsp;
+Message</h3>
+
+<p>For a message stanza of type "normal" or "chat", the server SHOULD either (a) add the message to offline storage or (b) return a stanza error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</p>
+<p>For a message stanza of type "groupchat", the server MUST return an error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</p>
+<p>For a message stanza of type "headline" or "error", the server MUST silently ignore the message.
+</p>
+<a name="rules-localpart-barejid-noresource-pres"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.2.2"></a><h3>8.5.2.2.2.&nbsp;
+Presence</h3>
+
+<p>For a presence stanza with no type or of type "unavailable", the server SHOULD silently ignore the stanza by not storing it for later delivery and not replying to it on behalf of the user.
+</p>
+<p>For a presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed", the server MUST adhere to the rules defined under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a> and summarized under <a class='info' href='#substates'>Appendix&nbsp;A<span> (</span><span class='info'>Subscription States</span><span>)</span></a>.
+</p>
+<p>For a presence stanza of type "probe", the server MUST handle it directly as described under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.
+</p>
+<a name="rules-localpart-barejid-noresource-iq"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.2.2.3"></a><h3>8.5.2.2.3.&nbsp;
+IQ</h3>
+
+<p>For an IQ stanza, the server itself MUST reply on behalf of the user with either an IQ result or an IQ error.  Specifically, if the semantics of the qualifying namespace define a reply that the server can provide on behalf of the user, then the server MUST reply to the stanza on behalf of the user by returning either an IQ stanza of type "result" or an IQ stanza of type "error" that is appropriate to the original payload; if not, then the server MUST reply with a &lt;service-unavailable/&gt; stanza error.
+</p>
+<a name="rules-localpart-fulljid"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3"></a><h3>8.5.3.&nbsp;
+localpart@domainpart/resourcepart</h3>
+
+<p>If the domainpart of the JID contained in the 'to' attribute of an inbound stanza matches one of the configured domains of the server itself and the JID contained in the 'to' attribute is of the form &lt;localpart@domainpart/resourcepart&gt;, then the server MUST adhere to the following rules.
+</p>
+<a name="rules-localpart-fulljid-match"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3.1"></a><h3>8.5.3.1.&nbsp;
+Resource Matches</h3>
+
+<p>If an available resource or connected resource exactly matches the full JID, how the stanza is processed depends on the stanza type.
+</p>
+<p>
+            </p>
+<ul class="text">
+<li>For an IQ stanza of type "get" or "set", if the intended recipient does not share presence with the requesting entity either by means of a presence subscription of type "both" or "from" or by means of directed presence, then the server SHOULD NOT deliver the IQ stanza but instead SHOULD return a &lt;service-unavailable/&gt; stanza error to the requesting entity.  This policy helps to prevent presence leaks (see <a class='info' href='#security'>Section&nbsp;11<span> (</span><span class='info'>Security Considerations</span><span>)</span></a>).
+</li>
+<li>For an IQ stanza of type "result" or "error", the server MUST deliver the stanza to the resource.
+</li>
+<li>For a message stanza, the server MUST deliver the stanza to the resource.
+</li>
+<li>For a presence stanza with no 'type' attribute or a 'type' attribute of "unavailable", the server MUST deliver the stanza to the resource.
+</li>
+<li>For a presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed", the server MUST follow the guidelines provided under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>.
+</li>
+<li>For a presence stanza of type "probe", the server MUST follow the guidelines provided under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.
+</li>
+</ul><p>
+          
+</p>
+<a name="rules-localpart-fulljid-nomatch"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3.2"></a><h3>8.5.3.2.&nbsp;
+No Resource Matches</h3>
+
+<p>If no available resource or connected resource exactly matches the full JID, how the stanza is processed depends on the stanza type.
+</p>
+<a name="rules-local-fulljid-nomatch-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3.2.1"></a><h3>8.5.3.2.1.&nbsp;
+Message</h3>
+
+<p>For a message stanza of type "normal", "groupchat", or "headline", the server MUST either (a) silently ignore the stanza or (b) return an error stanza to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</p>
+<p>For a message stanza of type "chat":
+</p>
+<p>
+              </p>
+<ul class="text">
+<li>If there is no available or connected resource, the server MUST either (a) store the message offline for later delivery or (b) return an error stanza to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</li>
+<li>If all of the available resources have a negative presence priority then the server SHOULD (a) store the message offline for later delivery or (b) return a stanza error to the sender, which SHOULD be &lt;service-unavailable/&gt;.
+</li>
+<li>If there is one available resource with a non-negative presence priority then the server MUST deliver the message to that resource.
+</li>
+<li>If there is more than one resource with a non-negative presence priority then the server MUST either (a) deliver the message to the "most available" resource or resources (according to the server's implementation-specific algorithm, e.g., treating the resource or resources with the highest presence priority as "most available") or (b) deliver the message to all of the non-negative resources that have opted in to receive chat messages.
+</li>
+</ul><p>
+            
+</p>
+<p>For a message stanza of type "error", the server MUST silently ignore the stanza.
+</p>
+<a name="rules-localpart-fulljid-nomatch-presence"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3.2.2"></a><h3>8.5.3.2.2.&nbsp;
+Presence</h3>
+
+<p>For a presence stanza with no 'type' attribute or a 'type' attribute of "unavailable", the server MUST silently ignore the stanza.
+</p>
+<p>For a presence stanza of type "subscribe", the server MUST follow the guidelines provided under <a class='info' href='#sub-request-inbound'>Section&nbsp;3.1.3<span> (</span><span class='info'>Server Processing of Inbound Subscription Request</span><span>)</span></a>.
+</p>
+<p>For a presence stanza of type "subscribed", "unsubscribe", or "unsubscribed", the server MUST ignore the stanza.
+</p>
+<p>For a presence stanza of type "probe", the server MUST follow the guidelines provided under <a class='info' href='#presence-probe'>Section&nbsp;4.3<span> (</span><span class='info'>Presence Probes</span><span>)</span></a>.
+</p>
+<a name="rules-localpart-fulljid-nomatch-iq"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.3.2.3"></a><h3>8.5.3.2.3.&nbsp;
+IQ</h3>
+
+<p>For an IQ stanza, the server MUST return a &lt;service-unavailable/&gt; stanza error to the sender.
+</p>
+<a name="rules-local-message"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.8.5.4"></a><h3>8.5.4.&nbsp;
+Summary of Message Delivery Rules</h3>
+
+<p>The following table summarizes the message (not stanza) delivery rules described earlier in this section.  The left column shows various combinations of conditions (non-existent account, no active resources, only one resource and it has a negative presence priority, only one resource and it has a non-negative presence priority, or more than one resource and each one has a non-negative presence priority) and 'to' addresses (bare JID, full JID matching an available resource, or full JID matching no available resource).  The subsequent columns list the four primary message types (normal, chat, groupchat, or headline) along with six possible delivery options: storing the message offline (O), bouncing the message with a stanza error (E), silently ignoring the message (S), delivering the message to the resource specified in the 'to' address (D), delivering the message to the "most available" resource or resources according to the server's implementation-specific algorithm, e.g., treating the resource or resources with the highest presence priority as "most available" (M), or delivering the message to all resources with non-negative presence priority (A -- where for chat messages "all resources" can mean the set of resources that have explicitly opted in to receiving every chat message).  The '/' character stands for "exclusive or".  The server SHOULD observe the rules given in section 8.1 when choosing which action to take for a particular message.
+</p>
+<p>Table 1: Message Delivery Rules
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++----------------------------------------------------------+
+| Condition        | Normal | Chat  | Groupchat | Headline |
++----------------------------------------------------------+
+| ACCOUNT DOES NOT EXIST                                   |
+|  bare            |  S/E   |  S/E  |     E     |    S     |
+|  full            |  S/E   |  S/E  |    S/E    |   S/E    |
++----------------------------------------------------------+
+| ACCOUNT EXISTS, BUT NO ACTIVE RESOURCES                  |
+|  bare            |  O/E   |  O/E  |     E     |    S     |
+|  full (no match) |  S/E   |  O/E  |    S/E    |   S/E    |
++----------------------------------------------------------+
+| 1+ NEGATIVE RESOURCES BUT ZERO NON-NEGATIVE RESOURCES    |
+|  bare            |  O/E   |  O/E  |     E     |    S     |
+|  full match      |   D    |   D   |     D     |    D     |
+|  full no match   |  S/E   |  O/E  |    S/E    |   S/E    |
++----------------------------------------------------------+
+| 1 NON-NEGATIVE RESOURCE                                  |
+|  bare            |   D    |   D   |     E     |    D     |
+|  full match      |   D    |   D   |     D     |    D     |
+|  full no match   |  S/E   |   D   |    S/E    |   S/E    |
++----------------------------------------------------------+
+| 1+ NON-NEGATIVE RESOURCES                                |
+|  bare            |  M/A   |  M/A* |     E     |    A     |
+|  full match      |   D    |  D/A* |     D     |    D     |
+|  full no match   |  S/E   |  M/A* |    S/E    |   S/E    |
++----------------------------------------------------------+
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>* For messages of type "chat", a server SHOULD NOT act in accordance with option (A) unless clients can explicitly opt in to receiving all chat messages; however, methods for opting in are outside the scope of this specification.
+</p>
+</blockquote>
+
+<a name="uri"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.9"></a><h3>9.&nbsp;
+Handling of URIs</h3>
+
+<p>The addresses of XMPP entities as used in communication over an XMPP network (e.g., in the 'from' and 'to' addresses of an XML stanza) MUST NOT be prepended with a Uniform Resource Identifier <a class='info' href='#URI'>[URI]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, &ldquo;Uniform Resource Identifier (URI): Generic Syntax,&rdquo; January&nbsp;2005.</span><span>)</span></a> scheme.
+</p>
+<p>However, an application that is external to XMPP itself (e.g., a page on the World Wide Web) might need to identify an XMPP entity either as a URI or as an Internationalized Resource Identifier <a class='info' href='#IRI'>[IRI]<span> (</span><span class='info'>Duerst, M. and M. Suignard, &ldquo;Internationalized Resource Identifiers (IRIs),&rdquo; January&nbsp;2005.</span><span>)</span></a>, and an XMPP client might need to interact with such an external application (for example, an XMPP client might be invoked by clicking a link provided on a web page).  In the context of such interactions, XMPP clients are encouraged to handle addresses that are encoded as "xmpp:" URIs and IRIs as specified in <a class='info' href='#XMPP-URI'>[XMPP&#8209;URI]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP),&rdquo; February&nbsp;2008.</span><span>)</span></a> and further described in <a class='info' href='#XEP-0147'>[XEP&#8209;0147]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;XMPP URI Scheme Query Components,&rdquo; September&nbsp;2006.</span><span>)</span></a>.  Although XMPP clients are also encouraged to handle addresses that are encoded as "im:" URIs as specified in <a class='info' href='#CPIM'>[CPIM]<span> (</span><span class='info'>Peterson, J., &ldquo;Common Profile for Instant Messaging (CPIM),&rdquo; August&nbsp;2004.</span><span>)</span></a> and "pres:" URIs as specified in <a class='info' href='#CPP'>[CPP]<span> (</span><span class='info'>Peterson, J., &ldquo;Common Profile for Presence (CPP),&rdquo; August&nbsp;2004.</span><span>)</span></a>, they can do so by removing the "im:" or "pres:" scheme and entrusting address resolution to the server as specified under <a class='info' href='#rules-remote'>Section&nbsp;8.3<span> (</span><span class='info'>Remote Domain</span><span>)</span></a>.
+</p>
+<a name="i18n"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.10"></a><h3>10.&nbsp;
+Internationalization Considerations</h3>
+
+<p>For internationalization considerations, refer to the relevant section of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p>
+<a name="security"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.11"></a><h3>11.&nbsp;
+Security Considerations</h3>
+
+<p>Core security considerations for XMPP are provided in Section 13 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, including discussion of channel encryption, authentication, information leaks, denial-of-service attacks, and interdomain federation.
+</p>
+<p>Section 13.1 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a> outlines the architectural roles of clients and servers in typical deployments of XMPP, and discusses the security properties associated with those roles.  These roles have an impact on the security of instant messages, presence subscriptions, and presence notifications as described in this document.  In essence, an XMPP user registers (or has provisioned) an account on an XMPP server and therefore places some level of trust in the server to complete various tasks on the user's behalf, enforce security policies, etc.  Thus it is the server's responsibility to:
+</p>
+<p>
+      </p>
+<ol class="text">
+<li>Preferably mandate the use of channel encryption for communication with local clients and remote servers.
+</li>
+<li>Authenticate any client that wishes to access the user's account.
+</li>
+<li>Process XML stanzas to and from clients that have authenticated as the user (specifically with regard to instant messaging and presence functionality, store the user's roster, process inbound and outbound subscription requests and responses, generate and handle presence probes, broadcast outbound presence notifications, route outbound messages, and deliver inbound messages and presence notifications).
+</li>
+</ol><p>
+    
+</p>
+<p>As discussed in Sections 13.1 and 13.4 of <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>, even if the server fulfills the foregoing responsibilities, the client does not have any assurance that stanzas it might exchange with other clients (whether on the same server or a remote server) are protected for all hops along the XMPP communication path, or within the server itself.  It is the responsibility of the client to use an appropriate technology for encryption and signing of XML stanzas if it wishes to ensure end-to-end confidentiality and integrity of its communications.
+</p>
+<p>Additional considerations that apply only to instant messaging and presence applications of XMPP are defined in several places within this document; specifically:
+</p>
+<p>
+      </p>
+<ul class="text">
+<li>When a server processes an inbound presence stanza of type "probe" whose intended recipient is a user associated with one of the server's configured domains, the server MUST NOT reveal the user's presence if the sender is an entity that is not authorized to receive that information as determined by presence subscriptions (see <a class='info' href='#presence'>Section&nbsp;4<span> (</span><span class='info'>Exchanging Presence Information</span><span>)</span></a>).
+</li>
+<li>A user's server MUST NOT leak the user's network availability to entities who are not authorized to know the user's presence.  In XMPP itself, authorization takes the form of an explicit subscription from a contact to the user (as described under <a class='info' href='#sub'>Section&nbsp;3<span> (</span><span class='info'>Managing Presence Subscriptions</span><span>)</span></a>).  However, some XMPP deployments might consider an entity to be authorized if there is an existing trust relationship between the entity and the user who is generating presence information (as an example, a corporate deployment of XMPP might automatically add the user's presence information to a private directory of employees if the organization mandates the sharing of presence information as part of an employment agreement).
+</li>
+<li>When a server processes an outbound presence stanza with no type or of type "unavailable", it MUST follow the rules defined under <a class='info' href='#presence'>Section&nbsp;4<span> (</span><span class='info'>Exchanging Presence Information</span><span>)</span></a> in order to ensure that such presence information is not sent to entities that are not authorized to know such information.
+</li>
+<li>A client MAY ignore the &lt;status/&gt; element when contained in a presence stanza of type "subscribe", "unsubscribe", "subscribed", or "unsubscribed"; this can help prevent "presence subscription spam".
+</li>
+</ul><p>
+    
+</p>
+<a name="conformance"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.12"></a><h3>12.&nbsp;
+Conformance Requirements</h3>
+
+<p>This section describes a protocol feature set that summarizes the conformance requirements of this specification.  This feature set is appropriate for use in software certification, interoperability testing, and implementation reports.  For each feature, this section provides the following information:
+</p>
+<p>
+      </p>
+<ul class="text">
+<li>A human-readable name
+</li>
+<li>An informational description
+</li>
+<li>A reference to the particular section of this document that normatively defines the feature
+</li>
+<li>Whether the feature applies to the Client role, the Server role, or both (where "N/A" signifies that the feature is not applicable to the specified role)
+</li>
+<li>Whether the feature MUST or SHOULD be implemented, where the capitalized terms are to be understood as described in <a class='info' href='#KEYWORDS'>[KEYWORDS]<span> (</span><span class='info'>Bradner, S., &ldquo;Key words for use in RFCs to Indicate Requirement Levels,&rdquo; March&nbsp;1997.</span><span>)</span></a>
+</li>
+</ul><p>
+    
+</p>
+<p>The feature set specified here attempts to adhere to the concepts and formats proposed by Larry Masinter within the IETF's NEWTRK Working Group in 2005, as captured in <a class='info' href='#INTEROP'>[INTEROP]<span> (</span><span class='info'>Masinter, L., &ldquo;Formalizing IETF Interoperability Reporting,&rdquo; October&nbsp;2005.</span><span>)</span></a>.  Although this feature set is more detailed than called for by <a class='info' href='#REPORTS'>[REPORTS]<span> (</span><span class='info'>Dusseault, L. and R. Sparks, &ldquo;Guidance on Interoperation and Implementation Reports for Advancement to Draft Standard,&rdquo; September&nbsp;2009.</span><span>)</span></a>, it provides a suitable basis for the generation of implementation reports to be submitted in support of advancing this specification from Proposed Standard to Draft Standard in accordance with <a class='info' href='#PROCESS'>[PROCESS]<span> (</span><span class='info'>Bradner, S., &ldquo;The Internet Standards Process -- Revision 3,&rdquo; October&nbsp;1996.</span><span>)</span></a>.
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>message-body
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;body/&gt; child element of the &lt;message/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#message-syntax-body'>Section&nbsp;5.2.3<span> (</span><span class='info'>Body Element</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server N/A.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>message-subject
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;subject/&gt; child element of the &lt;message/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#message-syntax-subject'>Section&nbsp;5.2.4<span> (</span><span class='info'>Subject Element</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server N/A.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>message-thread
+</dd>
+<dt>Description:</dt>
+<dd>Support the &lt;thread/&gt; child element of the &lt;message/&gt; stanza.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#message-syntax-thread'>Section&nbsp;5.2.5<span> (</span><span class='info'>Thread Element</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server N/A.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>message-type-support
+</dd>
+<dt>Description:</dt>
+<dd>Support reception of messages of type "normal", "chat", "groupchat", "headline", and "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#message-syntax-type'>Section&nbsp;5.2.2<span> (</span><span class='info'>Type Attribute</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server N/A.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>message-type-deliver
+</dd>
+<dt>Description:</dt>
+<dd>Appropriately deliver messages of type "normal", "chat", "groupchat", "headline", and "error".
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#rules'>Section&nbsp;8<span> (</span><span class='info'>Server Rules for Processing XML Stanzas</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server SHOULD.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-notype
+</dd>
+<dt>Description:</dt>
+<dd>Treat a presence stanza with no 'type' attribute as indicating availability.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#presence-syntax-type'>Section&nbsp;4.7.1<span> (</span><span class='info'>Type Attribute</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-probe
+</dd>
+<dt>Description:</dt>
+<dd>Send and receive presence stanzas with a 'type' attribute of "probe" for the discovery of presence information.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#presence-syntax-type'>Section&nbsp;4.7.1<span> (</span><span class='info'>Type Attribute</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client N/A, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-sub-approval
+</dd>
+<dt>Description:</dt>
+<dd>Treat an outbound presence stanza of type "subscribed" as the act of approving a presence subscription request previously received from another entity, and treat an inbound presence stanza of type "subscribed" as a subscription approval from another entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sub-request'>Section&nbsp;3.1<span> (</span><span class='info'>Requesting a Subscription</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-sub-cancel
+</dd>
+<dt>Description:</dt>
+<dd>Treat an outbound presence stanza of type "unsubscribed" as the act of denying a subscription request received from another entity or canceling a subscription approval previously granted to another entity, and treat an inbound presence stanza of type "unsubscribed" as an subscription denial or cancellation from another entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sub-cancel'>Section&nbsp;3.2<span> (</span><span class='info'>Canceling a Subscription</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-sub-preapproval
+</dd>
+<dt>Description:</dt>
+<dd>Treat an outbound presence stanza of type "subscribed" in certain circumstances as the act of pre-approving a subscription request received from another entity; this includes support for the 'approved' attribute of the &lt;item/&gt; element within the 'jabber:iq:roster' namespace.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MAY, Server MAY.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-sub-request
+</dd>
+<dt>Description:</dt>
+<dd>Treat an outbound presence stanza of type "subscribe" as the act of requesting a subscription to the presence information of another entity, and treat an inbound presence stanza of type "subscribe" as a presence subscription request from another entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sub-request'>Section&nbsp;3.1<span> (</span><span class='info'>Requesting a Subscription</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-sub-unsubscribe
+</dd>
+<dt>Description:</dt>
+<dd>Treat an outbound presence stanza of type "unsubscribe" as the act of unsubscribing from another entity, and treat an inbound presence stanza of type "unsubscribe" as an unsubscribe notification from another entity.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#sub-unsub'>Section&nbsp;3.3<span> (</span><span class='info'>Unsubscribing</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>presence-unavailable
+</dd>
+<dt>Description:</dt>
+<dd>Treat a presence stanza with a 'type' attribute of "unavailable" as indicating lack of availability.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#presence-syntax-type'>Section&nbsp;4.7.1<span> (</span><span class='info'>Type Attribute</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>roster-get
+</dd>
+<dt>Description:</dt>
+<dd>Treat an IQ stanza of type "get" containing an empty &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace as a request to retrieve the roster information associated with an account on a server.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#roster-syntax-actions-get'>Section&nbsp;2.1.3<span> (</span><span class='info'>Roster Get</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>roster-set
+</dd>
+<dt>Description:</dt>
+<dd>Treat an IQ stanza of type "set" containing a &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace as a request to add or update the item contained in the &lt;query/&gt; element.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#roster-syntax-actions-set'>Section&nbsp;2.1.5<span> (</span><span class='info'>Roster Set</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>roster-push
+</dd>
+<dt>Description:</dt>
+<dd>Send a roster push to each interested resource whenever the server-side representation of the roster information materially changes, or handle such a push when received from the server.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#roster-syntax-actions-push'>Section&nbsp;2.1.6<span> (</span><span class='info'>Roster Push</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client MUST, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<p>
+      </p>
+<blockquote class="text"><dl>
+<dt>Feature:</dt>
+<dd>roster-version
+</dd>
+<dt>Description:</dt>
+<dd>Treat the 'ver' attribute of the &lt;query/&gt; element qualified by the 'jabber:iq:roster' namespace as an identifier of the particular version of roster information being sent or received.
+</dd>
+<dt>Section:</dt>
+<dd><a class='info' href='#roster-syntax-ver'>Section&nbsp;2.1.1<span> (</span><span class='info'>Ver Attribute</span><span>)</span></a>
+</dd>
+<dt>Roles:</dt>
+<dd>Client SHOULD, Server MUST.
+</dd>
+</dl></blockquote><p>
+    
+</p>
+<a name="rfc.references"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.13"></a><h3>13.&nbsp;
+References</h3>
+
+<a name="rfc.references1"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>13.1.&nbsp;Normative References</h3>
+<table width="99%" border="0">
+<tr><td class="author-text" valign="top"><a name="DELAY">[DELAY]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0203.html">Delayed Delivery</a>,&rdquo; XSF XEP&nbsp;0203, September&nbsp;2009.</td></tr>
+<tr><td class="author-text" valign="top"><a name="KEYWORDS">[KEYWORDS]</a></td>
+<td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>,&rdquo; BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997 (<a href="http://www.rfc-editor.org/rfc/rfc2119.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2119.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2119.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML">[XML]</a></td>
+<td class="author-text">Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J., and T. Bray, &ldquo;<a href="http://www.w3.org/TR/2008/REC-xml-20081126">Extensible Markup Language (XML) 1.0 (Fifth Edition)</a>,&rdquo; World Wide Web Consortium Recommendation&nbsp;REC&#8209;xml&#8209;20081126, November&nbsp;2008 (<a href="http://www.w3.org/TR/2008/REC-xml-20081126">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-NAMES">[XML-NAMES]</a></td>
+<td class="author-text"><a href="mailto:tbray@textuality.com">Bray, T.</a>, <a href="mailto:dmh@corp.hp.com">Hollander, D.</a>, and <a href="mailto:andrewl@microsoft.com">A. Layman</a>, &ldquo;<a href="http://www.w3.org/TR/REC-xml-names">Namespaces in XML</a>,&rdquo; W3C&nbsp;REC-xml-names, January&nbsp;1999.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-CORE">[XMPP-CORE]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc6120">Extensible Messaging and Presence Protocol (XMPP): Core</a>,&rdquo; RFC&nbsp;6120, March&nbsp;2011.</td></tr>
+</table>
+
+<a name="rfc.references2"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>13.2.&nbsp;Informative References</h3>
+<table width="99%" border="0">
+<tr><td class="author-text" valign="top"><a name="CPIM">[CPIM]</a></td>
+<td class="author-text">Peterson, J., &ldquo;<a href="http://tools.ietf.org/html/rfc3860">Common Profile for Instant Messaging (CPIM)</a>,&rdquo; RFC&nbsp;3860, August&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3860.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="CPP">[CPP]</a></td>
+<td class="author-text">Peterson, J., &ldquo;<a href="http://tools.ietf.org/html/rfc3859">Common Profile for Presence (CPP)</a>,&rdquo; RFC&nbsp;3859, August&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3859.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="DOS">[DOS]</a></td>
+<td class="author-text">Handley, M., Rescorla, E., and IAB, &ldquo;<a href="http://tools.ietf.org/html/rfc4732">Internet Denial-of-Service Considerations</a>,&rdquo; RFC&nbsp;4732, December&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4732.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IMP-MODEL">[IMP-MODEL]</a></td>
+<td class="author-text"><a href="mailto:mday@alum.mit.edu">Day, M.</a>, <a href="mailto:jdrosen@dynamicsoft.com">Rosenberg, J.</a>, and <a href="mailto:suga@flab.fujitsu.co.jp">H. Sugano</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2778">A Model for Presence and Instant Messaging</a>,&rdquo; RFC&nbsp;2778, February&nbsp;2000.</td></tr>
+<tr><td class="author-text" valign="top"><a name="IMP-REQS">[IMP-REQS]</a></td>
+<td class="author-text"><a href="mailto:mday@alum.mit.edu">Day, M.</a>, <a href="mailto:sonuag@microsoft.com">Aggarwal, S.</a>, and <a href="mailto:jesse@intonet.com">J. Vincent</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2779">Instant Messaging / Presence Protocol Requirements</a>,&rdquo; RFC&nbsp;2779, February&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2779.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IMP-SRV">[IMP-SRV]</a></td>
+<td class="author-text">Peterson, J., &ldquo;<a href="http://tools.ietf.org/html/rfc3861">Address Resolution for Instant Messaging and Presence</a>,&rdquo; RFC&nbsp;3861, August&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3861.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="INTEROP">[INTEROP]</a></td>
+<td class="author-text">Masinter, L., &ldquo;Formalizing IETF Interoperability Reporting,&rdquo; Work in&nbsp;Progress, October&nbsp;2005.</td></tr>
+<tr><td class="author-text" valign="top"><a name="IRC">[IRC]</a></td>
+<td class="author-text">Kalt, C., &ldquo;<a href="http://tools.ietf.org/html/rfc2810">Internet Relay Chat: Architecture</a>,&rdquo; RFC&nbsp;2810, April&nbsp;2000 (<a href="http://www.rfc-editor.org/rfc/rfc2810.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="IRI">[IRI]</a></td>
+<td class="author-text">Duerst, M. and M. Suignard, &ldquo;<a href="http://tools.ietf.org/html/rfc3987">Internationalized Resource Identifiers (IRIs)</a>,&rdquo; RFC&nbsp;3987, January&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc3987.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="PROCESS">[PROCESS]</a></td>
+<td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2026">The Internet Standards Process -- Revision 3</a>,&rdquo; BCP&nbsp;9, RFC&nbsp;2026, October&nbsp;1996 (<a href="http://www.rfc-editor.org/rfc/rfc2026.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="REPORTS">[REPORTS]</a></td>
+<td class="author-text">Dusseault, L. and R. Sparks, &ldquo;<a href="http://tools.ietf.org/html/rfc5657">Guidance on Interoperation and Implementation Reports for Advancement to Draft Standard</a>,&rdquo; BCP&nbsp;9, RFC&nbsp;5657, September&nbsp;2009 (<a href="http://www.rfc-editor.org/rfc/rfc5657.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="RFC3920">[RFC3920]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P., Ed.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3920">Extensible Messaging and Presence Protocol (XMPP): Core</a>,&rdquo; RFC&nbsp;3920, October&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3920.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3920.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3920.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="RFC3921">[RFC3921]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P., Ed.</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc3921">Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence</a>,&rdquo; RFC&nbsp;3921, October&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3921.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc3921.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc3921.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SASL">[SASL]</a></td>
+<td class="author-text">Melnikov, A. and K. Zeilenga, &ldquo;<a href="http://tools.ietf.org/html/rfc4422">Simple Authentication and Security Layer (SASL)</a>,&rdquo; RFC&nbsp;4422, June&nbsp;2006 (<a href="http://www.rfc-editor.org/rfc/rfc4422.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="SIP-PRES">[SIP-PRES]</a></td>
+<td class="author-text">Rosenberg, J., &ldquo;<a href="http://tools.ietf.org/html/rfc3856">A Presence Event Package for the Session Initiation Protocol (SIP)</a>,&rdquo; RFC&nbsp;3856, August&nbsp;2004 (<a href="http://www.rfc-editor.org/rfc/rfc3856.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS">[TLS]</a></td>
+<td class="author-text">Dierks, T. and E. Rescorla, &ldquo;<a href="http://tools.ietf.org/html/rfc5246">The Transport Layer Security (TLS) Protocol Version 1.2</a>,&rdquo; RFC&nbsp;5246, August&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5246.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="TLS-CERTS">[TLS-CERTS]</a></td>
+<td class="author-text">Saint-Andre, P. and J. Hodges, &ldquo;<a href="http://tools.ietf.org/html/rfc6125">Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)</a>,&rdquo; RFC&nbsp;6125, March&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="UNICODE">[UNICODE]</a></td>
+<td class="author-text">The Unicode Consortium, &ldquo;<a href="http://www.unicode.org/versions/Unicode6.0.0/">The Unicode Standard, Version 6.0</a>,&rdquo; 2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="URI">[URI]</a></td>
+<td class="author-text">Berners-Lee, T., Fielding, R., and L. Masinter, &ldquo;<a href="http://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>,&rdquo; STD&nbsp;66, RFC&nbsp;3986, January&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc3986.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="UUID">[UUID]</a></td>
+<td class="author-text"><a href="mailto:paulle@microsoft.com">Leach, P.</a>, <a href="mailto:michael@refactored-networks.com">Mealling, M.</a>, and <a href="mailto:rsalz@datapower.com">R. Salz</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc4122">A Universally Unique IDentifier (UUID) URN Namespace</a>,&rdquo; RFC&nbsp;4122, July&nbsp;2005 (<a href="http://www.rfc-editor.org/rfc/rfc4122.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc4122.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc4122.xml">XML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0016">[XEP-0016]</a></td>
+<td class="author-text">Millard, P. and <a href="mailto:stpeter@jabber.org">P. Saint-Andre</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0016.html">Privacy Lists</a>,&rdquo; XSF XEP&nbsp;0016, February&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0045">[XEP-0045]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0045.html">Multi-User Chat</a>,&rdquo; XSF XEP&nbsp;0045, July&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0054">[XEP-0054]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0054.html">vcard-temp</a>,&rdquo; XSF XEP&nbsp;0054, July&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0071">[XEP-0071]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0071.html">XHTML-IM</a>,&rdquo; XSF XEP&nbsp;0071, September&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0115">[XEP-0115]</a></td>
+<td class="author-text"><a href="mailto:jhildebrand@jabber.com">Hildebrand, J.</a>, <a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, and <a href="mailto:public@el-tramo.be">R. Tron&#xE7;on</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0115.html">Entity Capabilities</a>,&rdquo; XSF XEP&nbsp;0115, February&nbsp;2008.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0147">[XEP-0147]</a></td>
+<td class="author-text"><a href="mailto:">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0147.html">XMPP URI Scheme Query Components</a>,&rdquo; XSF XEP&nbsp;0147, September&nbsp;2006.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0160">[XEP-0160]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0160.html">Best Practices for Handling Offline Messages</a>,&rdquo; XSF XEP&nbsp;0160, January&nbsp;2006.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0163">[XEP-0163]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a> and <a href="mailto:kevin@kismith.co.uk">K. Smith</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0163.html">Personal Eventing Protocol</a>,&rdquo; XSF XEP&nbsp;0163, July&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0191">[XEP-0191]</a></td>
+<td class="author-text"><a href="mailto:">Saint-Andre, P.</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0191.html">Simple Communications Blocking</a>,&rdquo; XSF XEP&nbsp;0191, February&nbsp;2007.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0201">[XEP-0201]</a></td>
+<td class="author-text"><a href="mailto:stpeter@jabber.org">Saint-Andre, P.</a>, <a href="mailto:ian.paterson@clientside.co.uk">Paterson, I.</a>, and <a href="mailto:kevin@kismith.co.uk">K. Smith</a>, &ldquo;<a href="http://www.xmpp.org/extensions/xep-0201.html">Best Practices for Message Threads</a>,&rdquo; XSF XEP&nbsp;0201, November&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XEP-0237">[XEP-0237]</a></td>
+<td class="author-text"><a href="mailto:">Saint-Andre, P.</a> and <a href="mailto:dave.cridland@isode.com">D. Cridland</a>, &ldquo;<a href="http://xmpp.org/extensions/xep-0237.html">Roster Versioning</a>,&rdquo; XSF XEP&nbsp;0237, March&nbsp;2010.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-DATATYPES">[XML-DATATYPES]</a></td>
+<td class="author-text">Biron, P. and A. Malhotra, &ldquo;<a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">XML Schema Part 2: Datatypes Second Edition</a>,&rdquo; W3C&nbsp;REC-xmlschema-2, October&nbsp;2004 (<a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XML-SCHEMA">[XML-SCHEMA]</a></td>
+<td class="author-text">Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech, &ldquo;<a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028">XML Schema Part 1: Structures Second Edition</a>,&rdquo; World Wide Web Consortium Recommendation&nbsp;REC-xmlschema-1-20041028, October&nbsp;2004 (<a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028">HTML</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-ADDR">[XMPP-ADDR]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc6122">Extensible Messaging and Presence Protocol (XMPP): Address Format</a>,&rdquo; RFC&nbsp;6122, March&nbsp;2011.</td></tr>
+<tr><td class="author-text" valign="top"><a name="XMPP-URI">[XMPP-URI]</a></td>
+<td class="author-text">Saint-Andre, P., &ldquo;<a href="http://tools.ietf.org/html/rfc5122">Internationalized Resource Identifiers (IRIs) and Uniform Resource Identifiers (URIs) for the Extensible Messaging and Presence Protocol (XMPP)</a>,&rdquo; RFC&nbsp;5122, February&nbsp;2008 (<a href="http://www.rfc-editor.org/rfc/rfc5122.txt">TXT</a>).</td></tr>
+<tr><td class="author-text" valign="top"><a name="VCARD">[VCARD]</a></td>
+<td class="author-text"><a href="mailto:frank_dawson@lotus.com">Dawson, F.</a> and <a href="mailto:howes@netscape.com">T. Howes</a>, &ldquo;<a href="http://tools.ietf.org/html/rfc2426">vCard MIME Directory Profile</a>,&rdquo; RFC&nbsp;2426, September&nbsp;1998 (<a href="http://xml.resource.org/public/rfc/html/rfc2426.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2426.xml">XML</a>).</td></tr>
+</table>
+
+<a name="substates"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A"></a><h3>Appendix A.&nbsp;
+Subscription States</h3>
+
+<p>This section provides detailed information about subscription states and server processing of subscription-related presence stanzas (i.e., presence stanzas of type "subscribe", "subscribed", "unsubscribe", and "unsubscribed").
+</p>
+<a name="substates-defined"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.1"></a><h3>A.1.&nbsp;
+Defined States</h3>
+
+<p>There are four primary subscription states (these states are described from the perspective of the user, not the contact):
+</p>
+<p>
+        </p>
+<blockquote class="text"><dl>
+<dt>None:</dt>
+<dd>The user does not have a subscription to the contact's presence, and the contact does not have a subscription to the user's presence.
+</dd>
+<dt>To:</dt>
+<dd>The user has a subscription to the contact's presence, but the contact does not have a subscription to the user's presence.
+</dd>
+<dt>From:</dt>
+<dd>The contact has a subscription to the user's presence, but the user does not have a subscription to the contact's presence.
+</dd>
+<dt>Both:</dt>
+<dd>Both the user and the contact have subscriptions to each other's presence (i.e., the union of 'from' and 'to').
+</dd>
+</dl></blockquote><p>
+      
+</p>
+<p></p>
+<blockquote class="text">
+<p>Implementation Note: For the purpose of processing subscription-related presence stanzas as described in the following sections, a subscription state of "None" includes the case of the contact not being in the user's roster at all, i.e., an unknown entity from the perspective of the user's roster.
+</p>
+</blockquote>
+
+<p>The foregoing states are supplemented by various sub-states related to pending inbound and outbound subscriptions, thus yielding nine possible subscription states:
+</p>
+<p>
+        </p>
+<ol class="text">
+<li>"None" = Contact and user are not subscribed to each other, and neither has requested a subscription from the other; this is reflected in the user's roster by subscription='none'.
+</li>
+<li>"None + Pending Out" = Contact and user are not subscribed to each other, and user has sent contact a subscription request but contact has not replied yet; this is reflected in the user's roster by subscription='none' and ask='subscribe'.
+</li>
+<li>"None + Pending In" = Contact and user are not subscribed to each other, and contact has sent user a subscription request but user has not replied yet. This state might or might not be reflected in the user's roster, as follows: if the user has created a roster item for the contact then the server MUST maintain that roster item and also note the existence of the inbound presence subscription request, whereas if the user has not created a roster item for the contact then the user's server MUST note the existence of the inbound presence subscription request but MUST NOT create a roster item for the contact (instead, the server MUST wait until the user has approved the subscription request before adding the contact to the user's roster).
+</li>
+<li>"None + Pending Out+In" = Contact and user are not subscribed to each other, contact has sent user a subscription request but user has not replied yet, and user has sent contact a subscription request but contact has not replied yet; this is reflected in the user's roster by subscription='none' and ask='subscribe'.
+</li>
+<li>"To" = User is subscribed to contact (one-way); this is reflected in the user's roster by subscription='to'.
+</li>
+<li>"To + Pending In" = User is subscribed to contact, and contact has sent user a subscription request but user has not replied yet; this is reflected in the user's roster by subscription='to'.
+</li>
+<li>"From" = Contact is subscribed to user (one-way); this is reflected in the user's roster by subscription='from'.
+</li>
+<li>"From + Pending Out" = Contact is subscribed to user, and user has sent contact a subscription request but contact has not replied yet; this is reflected in the user's roster by subscription='from' and ask='subscribe'.
+</li>
+<li>"Both" = User and contact are subscribed to each other
+          (two-way); this is reflected in the user's roster by
+          subscription='both'.
+</li>
+</ol><p>
+      
+</p>
+<a name="substates-out"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2"></a><h3>A.2.&nbsp;
+Server Processing of Outbound Presence Subscription Stanzas</h3>
+
+<p>Outbound presence subscription stanzas enable the user to manage his or her subscription to the contact's presence (via the "subscribe" and "unsubscribe" types), and to manage the contact's access to the user's presence (via the "subscribed" and "unsubscribed" types).
+</p>
+<p>The following rules apply to outbound routing of the stanza as well as changes to the user's roster.  (These rules are described from the perspective of the user, not the contact.  In addition, "S.N." stands for SHOULD NOT and "M.N." stands for MUST NOT.)
+</p>
+<a name="substates-out-subscribe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2.1"></a><h3>A.2.1.&nbsp;
+Subscribe</h3>
+
+<p>Table 2: Processing of outbound "subscribe" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++------------------------------------------------------------------+
+|  EXISTING STATE          |  ROUTE?   |  NEW STATE                |
++------------------------------------------------------------------+
+|  "None"                  |  MUST [1] |  "None + Pending Out"     |
+|  "None + Pending Out"    |  MUST     |  no state change          |
+|  "None + Pending In"     |  MUST [1] |  "None + Pending Out+In"  |
+|  "None + Pending Out+In" |  MUST     |  no state change          |
+|  "To"                    |  MUST     |  no state change          |
+|  "To + Pending In"       |  MUST     |  no state change          |
+|  "From"                  |  MUST [1] |  "From + Pending Out"     |
+|  "From + Pending Out"    |  MUST     |  no state change          |
+|  "Both"                  |  MUST     |  no state change          |
++------------------------------------------------------------------+
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>[1] A state change to "pending out" includes setting the 'ask' flag to a value of "subscribe" in the user's roster.
+</p>
+</blockquote>
+
+<a name="substates-out-unsubscribe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2.2"></a><h3>A.2.2.&nbsp;
+Unsubscribe</h3>
+
+<p>Table 3: Processing of outbound "unsubscribe" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++-----------------------------------------------------------------+
+|  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
++-----------------------------------------------------------------+
+|  "None"                  |  MUST    |  no state change          |
+|  "None + Pending Out"    |  MUST    |  "None"                   |
+|  "None + Pending In"     |  MUST    |  no state change          |
+|  "None + Pending Out+In" |  MUST    |  "None + Pending In"      |
+|  "To"                    |  MUST    |  "None"                   |
+|  "To + Pending In"       |  MUST    |  "None + Pending In"      |
+|  "From"                  |  MUST    |  no state change          |
+|  "From + Pending Out"    |  MUST    |  "From"                   |
+|  "Both"                  |  MUST    |  "From"                   |
++-----------------------------------------------------------------+
+</pre></div>
+<a name="substates-out-subscribed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2.3"></a><h3>A.2.3.&nbsp;
+Subscribed</h3>
+
+<p>Table 4: Processing of outbound "subscribed" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++-----------------------------------------------------------------+
+|  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
++-----------------------------------------------------------------+
+|  "None"                  |  M.N.    |  pre-approval [1]         |
+|  "None + Pending Out"    |  M.N.    |  pre-approval [1]         |
+|  "None + Pending In"     |  MUST    |  "From"                   |
+|  "None + Pending Out+In" |  MUST    |  "From + Pending Out"     |
+|  "To"                    |  M.N.    |  pre-approval [1]         |
+|  "To + Pending In"       |  MUST    |  "Both"                   |
+|  "From"                  |  M.N.    |  no state change          |
+|  "From + Pending Out"    |  M.N.    |  no state change          |
+|  "Both"                  |  M.N.    |  no state change          |
++-----------------------------------------------------------------+
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>[1] Detailed information regarding subscription pre-approval is provided under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="substates-out-unsubscribed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.2.4"></a><h3>A.2.4.&nbsp;
+Unsubscribed</h3>
+
+<p>Table 5: Processing of outbound "unsubscribed" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++-----------------------------------------------------------------+
+|  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
++-----------------------------------------------------------------+
+|  "None"                  |  S.N.    |  no state change [1]      |
+|  "None + Pending Out"    |  S.N.    |  no state change [1]      |
+|  "None + Pending In"     |  MUST    |  "None"                   |
+|  "None + Pending Out+In" |  MUST    |  "None + Pending Out"     |
+|  "To"                    |  S.N.    |  no state change [1]      |
+|  "To + Pending In"       |  MUST    |  "To"                     |
+|  "From"                  |  MUST    |  "None"                   |
+|  "From + Pending Out"    |  MUST    |  "None + Pending Out"     |
+|  "Both"                  |  MUST    |  "To"                     |
++-----------------------------------------------------------------+
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>[1] This event can result in cancellation of a subscription pre-approval, as described under <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>.
+</p>
+</blockquote>
+
+<a name="substates-in"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3"></a><h3>A.3.&nbsp;
+Server Processing of Inbound Presence Subscription Stanzas</h3>
+
+<p>Inbound presence subscription stanzas request a subscription-related action from the user (via the "subscribe" type), inform the user of subscription-related actions taken by the contact (via the "unsubscribe" type), or enable the user to manage the contact's access to the user's presence information (via the "subscribed" and "unsubscribed" types).
+</p>
+<p>The following rules apply to delivery of the inbound stanza as well as changes to the user's roster.  (These rules for server processing of inbound presence subscription stanzas are described from the perspective of the user, not the contact.  In addition, "S.N." stands for SHOULD NOT.)
+</p>
+<a name="substates-in-subscribe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3.1"></a><h3>A.3.1.&nbsp;
+Subscribe</h3>
+
+<p>Table 6: Processing of inbound "subscribe" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++------------------------------------------------------------------+
+|  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
++------------------------------------------------------------------+
+|  "None"                  |  MUST [1]  |  "None + Pending In"     |
+|  "None + Pending Out"    |  MUST      |  "None + Pending Out+In" |
+|  "None + Pending In"     |  S.N.      |  no state change         |
+|  "None + Pending Out+In" |  S.N.      |  no state change         |
+|  "To"                    |  MUST      |  "To + Pending In"       |
+|  "To + Pending In"       |  S.N.      |  no state change         |
+|  "From"                  |  S.N. [2]  |  no state change         |
+|  "From + Pending Out"    |  S.N. [2]  |  no state change         |
+|  "Both"                  |  S.N. [2]  |  no state change         |
++------------------------------------------------------------------+
+</pre></div>
+<p></p>
+<blockquote class="text">
+<p>[1] If the user previously sent presence of type "subscribed" as described under <a class='info' href='#substates-out-subscribed'>Appendix&nbsp;A.2.3<span> (</span><span class='info'>Subscribed</span><span>)</span></a> and <a class='info' href='#sub-preapproval'>Section&nbsp;3.4<span> (</span><span class='info'>Pre-Approving a Subscription Request</span><span>)</span></a>, then the server MAY auto-reply with "subscribed" and change the state to "From" rather than "None + Pending In".
+</p>
+</blockquote>
+
+<p></p>
+<blockquote class="text">
+<p>[2] Server SHOULD auto-reply with "subscribed".
+</p>
+</blockquote>
+
+<a name="substates-in-unsubscribe"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3.2"></a><h3>A.3.2.&nbsp;
+Unsubscribe</h3>
+
+<p>When the user's server receives a presence stanza of type "unsubscribe" for the user from the contact, if the stanza results in a subscription state change from the user's perspective then the user's server MUST change the state, MUST deliver the presence stanza from the contact to the user, and SHOULD auto-reply by sending a presence stanza of type "unsubscribed" to the contact on behalf of the user.  Otherwise the user's server MUST NOT change the state and (because there is no state change) SHOULD NOT deliver the stanza.  These rules are summarized in the following table.
+</p>
+<p>Table 7: Processing of inbound "unsubscribe" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++------------------------------------------------------------------+
+|  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
++------------------------------------------------------------------+
+|  "None"                  |  S.N.      |  no state change         |
+|  "None + Pending Out"    |  S.N.      |  no state change         |
+|  "None + Pending In"     |  MUST [1]  |  "None"                  |
+|  "None + Pending Out+In" |  MUST [1]  |  "None + Pending Out"    |
+|  "To"                    |  S.N.      |  no state change         |
+|  "To + Pending In"       |  MUST [1]  |  "To"                    |
+|  "From"                  |  MUST [1]  |  "None"                  |
+|  "From + Pending Out"    |  MUST [1]  |  "None + Pending Out"    |
+|  "Both"                  |  MUST [1]  |  "To"                    |
++------------------------------------------------------------------+
+</pre></div>
+<p>[1] Server SHOULD auto-reply with "unsubscribed".
+</p>
+<a name="substates-in-subscribed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3.3"></a><h3>A.3.3.&nbsp;
+Subscribed</h3>
+
+<p>When the user's server receives a presence stanza of type "subscribed" for the user from the contact, if there is no pending outbound request for access to the contact's presence information, then it MUST NOT change the subscription state and (because there is no state change) SHOULD NOT deliver the stanza to the user.  If there is a pending outbound request for access to the contact's presence information and the inbound presence stanza of type "subscribed" results in a subscription state change, then the user's server MUST change the subscription state and MUST deliver the stanza to the user.  If the user already is subscribed to the contact's presence information, the inbound presence stanza of type "subscribed" does not result in a subscription state change; therefore the user's server MUST NOT change the subscription state and (because there is no state change) SHOULD NOT deliver the stanza to the user.  These rules are summarized in the following table.
+</p>
+<p>Table 8: Processing of inbound "subscribed" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++------------------------------------------------------------------+
+|  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
++------------------------------------------------------------------+
+|  "None"                  |  S.N.      |  no state change         |
+|  "None + Pending Out"    |  MUST      |  "To"                    |
+|  "None + Pending In"     |  S.N.      |  no state change         |
+|  "None + Pending Out+In" |  MUST      |  "To + Pending In"       |
+|  "To"                    |  S.N.      |  no state change         |
+|  "To + Pending In"       |  S.N.      |  no state change         |
+|  "From"                  |  S.N.      |  no state change         |
+|  "From + Pending Out"    |  MUST      |  "Both"                  |
+|  "Both"                  |  S.N.      |  no state change         |
++------------------------------------------------------------------+
+</pre></div>
+<a name="substates-in-unsubscribed"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.A.3.4"></a><h3>A.3.4.&nbsp;
+Unsubscribed</h3>
+
+<p>When the user's server receives a presence stanza of type "unsubscribed" for the user from the contact, if there is a pending outbound request for access to the contact's presence information or if the user currently is subscribed to the contact's presence information, then the user's server MUST change the subscription state and MUST deliver the stanza to the user.  Otherwise, the user's server MUST NOT change the subscription state and (because there is no state change) SHOULD NOT deliver the stanza.  These rules are summarized in the following table.
+</p>
+<p>Table 9: Processing of inbound "unsubscribed" stanzas
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
++------------------------------------------------------------------+
+|  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
++------------------------------------------------------------------+
+|  "None"                  |  S.N.      |  no state change         |
+|  "None + Pending Out"    |  MUST      |  "None"                  |
+|  "None + Pending In"     |  S.N.      |  no state change         |
+|  "None + Pending Out+In" |  MUST      |  "None + Pending In"     |
+|  "To"                    |  MUST      |  "None"                  |
+|  "To + Pending In"       |  MUST      |  "None + Pending In"     |
+|  "From"                  |  S.N.      |  no state change         |
+|  "From + Pending Out"    |  MUST      |  "From"                  |
+|  "Both"                  |  MUST      |  "From"                  |
++------------------------------------------------------------------+
+</pre></div>
+<a name="blocking"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.B"></a><h3>Appendix B.&nbsp;
+Blocking Communication</h3>
+
+<p>Sections 2.3.5 and 5.4.10 of <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a> require that a compliant instant messaging and presence technology needs to enable a user to block communications from selected users.  Protocols for doing so are specified in <a class='info' href='#XEP-0016'>[XEP&#8209;0016]<span> (</span><span class='info'>Millard, P. and P. Saint-Andre, &ldquo;Privacy Lists,&rdquo; February&nbsp;2007.</span><span>)</span></a> and <a class='info' href='#XEP-0191'>[XEP&#8209;0191]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Simple Communications Blocking,&rdquo; February&nbsp;2007.</span><span>)</span></a>.
+</p>
+<a name="vcard"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.C"></a><h3>Appendix C.&nbsp;
+vCards</h3>
+
+<p>Sections 3.1.3 and 4.1.4 of <a class='info' href='#IMP-REQS'>[IMP&#8209;REQS]<span> (</span><span class='info'>Day, M., Aggarwal, S., and J. Vincent, &ldquo;Instant Messaging / Presence Protocol Requirements,&rdquo; February&nbsp;2000.</span><span>)</span></a> require that it be possible to retrieve out-of-band contact information for other users (e.g., telephone number or email address).  An XML representation of the vCard specification defined in <a class='info' href='#VCARD'>RFC 2426<span> (</span><span class='info'>Dawson, F. and T. Howes, &ldquo;vCard MIME Directory Profile,&rdquo; September&nbsp;1998.</span><span>)</span></a> [VCARD] is in common use within the XMPP community to provide such information but is out of scope for this specification (documentation of this protocol is contained in <a class='info' href='#XEP-0054'>[XEP&#8209;0054]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;vcard-temp,&rdquo; July&nbsp;2008.</span><span>)</span></a>).
+</p>
+<a name="schema"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.D"></a><h3>Appendix D.&nbsp;
+XML Schema for jabber:iq:roster</h3>
+
+<p>The following schema formally defines the 'jabber:iq:roster' namespace used in this document, in conformance with <a class='info' href='#XML-SCHEMA'>[XML&#8209;SCHEMA]<span> (</span><span class='info'>Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech, &ldquo;XML Schema Part 1: Structures Second Edition,&rdquo; October&nbsp;2004.</span><span>)</span></a>.  Because validation of XML streams and stanzas is optional, this schema is not normative and is provided for descriptive purposes only.  For schemas defining core XMPP namespaces, refer to <a class='info' href='#XMPP-CORE'>[XMPP&#8209;CORE]<span> (</span><span class='info'>Saint-Andre, P., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Core,&rdquo; March&nbsp;2011.</span><span>)</span></a>.
+</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
+&lt;?xml version='1.0' encoding='UTF-8'?&gt;
+
+&lt;xs:schema
+    xmlns:xs='http://www.w3.org/2001/XMLSchema'
+    targetNamespace='jabber:iq:roster'
+    xmlns='jabber:iq:roster'
+    elementFormDefault='qualified'&gt;
+
+  &lt;xs:element name='query'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:element ref='item'
+                    minOccurs='0'
+                    maxOccurs='unbounded'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='ver'
+                    type='xs:string'
+                    use='optional'/&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='item'&gt;
+    &lt;xs:complexType&gt;
+      &lt;xs:sequence&gt;
+        &lt;xs:element ref='group'
+                    minOccurs='0'
+                    maxOccurs='unbounded'/&gt;
+      &lt;/xs:sequence&gt;
+      &lt;xs:attribute name='approved'
+                    type='xs:boolean'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='ask'
+                    use='optional'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='subscribe'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+      &lt;xs:attribute name='jid'
+                    type='xs:string'
+                    use='required'/&gt;
+      &lt;xs:attribute name='name'
+                    type='xs:string'
+                    use='optional'/&gt;
+      &lt;xs:attribute name='subscription'
+                    use='optional'
+                    default='none'&gt;
+        &lt;xs:simpleType&gt;
+          &lt;xs:restriction base='xs:NMTOKEN'&gt;
+            &lt;xs:enumeration value='both'/&gt;
+            &lt;xs:enumeration value='from'/&gt;
+            &lt;xs:enumeration value='none'/&gt;
+            &lt;xs:enumeration value='remove'/&gt;
+            &lt;xs:enumeration value='to'/&gt;
+          &lt;/xs:restriction&gt;
+        &lt;/xs:simpleType&gt;
+      &lt;/xs:attribute&gt;
+    &lt;/xs:complexType&gt;
+  &lt;/xs:element&gt;
+
+  &lt;xs:element name='group' type='xs:string'/&gt;
+
+&lt;/xs:schema&gt;
+</pre></div>
+<a name="diffs"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.E"></a><h3>Appendix E.&nbsp;
+Differences From RFC 3921</h3>
+
+<p>Based on consensus derived from implementation and deployment experience as well as formal interoperability testing, the following substantive modifications were made from <a class='info' href='#RFC3921'>[RFC3921]<span> (</span><span class='info'>Saint-Andre, P., Ed., &ldquo;Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,&rdquo; October&nbsp;2004.</span><span>)</span></a> (in addition to numerous changes of an editorial nature).
+</p>
+<p>
+        </p>
+<ul class="text">
+<li>The protocol for session establishment was determined to be unnecessary and therefore the content previously defined in Section 3 of RFC 3921 was removed.  However, for the sake of backward-compatibility server implementations are encouraged to advertise support for the feature, even though session establishment is a "no-op".
+</li>
+<li>In order to more seamlessly repair lack of synchronization in subscription states between rosters located at different servers, clarified and modified error handling related to presence subscription requests, presence probes and presence notifications.
+</li>
+<li>Changed the 'from' address for presence probes so that it is the bare JID, not the full JID.
+</li>
+<li>Adjusted and clarified stanza delivery rules based on implementation and deployment experience.
+</li>
+<li>Explicitly specified that a server is allowed to deliver a message stanza of type "normal" or "chat" to all resources if it has a method for allowing resources to opt in to such behavior.
+</li>
+<li>Allowed a server to use its own algorithm for determining the "most available" resource for the purpose of message delivery, but mentioned the recommended algorithm from RFC 3921 (based on presence priority) as one possible algorithm.
+</li>
+<li>Added optional versioning of roster information to save bandwidth in cases where the roster has not changed (or has changed very little) between sessions; the relevant protocol interactions were originally described in <a class='info' href='#XEP-0237'>[XEP&#8209;0237]<span> (</span><span class='info'>Saint-Andre, P. and D. Cridland, &ldquo;Roster Versioning,&rdquo; March&nbsp;2010.</span><span>)</span></a>.
+</li>
+<li>Added optional server support for pre-approved presence subscriptions via presence stanzas of type "subscribed", including a new 'approved' attribute that can be set to "true" (for a pre-approved subscription) or "false" (the default).
+</li>
+<li>Added optional 'parent' attribute to &lt;thread/&gt; element.
+</li>
+<li>Moved the protocol for communications blocking (specified in Section 10 of RFC 3921) back to <a class='info' href='#XEP-0016'>[XEP&#8209;0016]<span> (</span><span class='info'>Millard, P. and P. Saint-Andre, &ldquo;Privacy Lists,&rdquo; February&nbsp;2007.</span><span>)</span></a>, from which it was originally taken.
+</li>
+<li>Recommended returning presence unavailable in response to probes.
+</li>
+<li>Clarified handling of presence probes sent to full JIDs.
+</li>
+<li>Explicitly specified that the default value for the presence &lt;priority/&gt; element is zero.
+</li>
+<li>Removed recommendation to support the "_im" and "_pres" SRV records.
+</li>
+</ul><p>
+      
+</p>
+<a name="acks"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<a name="rfc.section.F"></a><h3>Appendix F.&nbsp;
+Acknowledgements</h3>
+
+<p>This document is an update to, and derived from, RFC 3921.  This document would have been impossible without the work of the contributors and commenters acknowledged there.
+</p>
+<p>Hundreds of people have provided implementation feedback, bug reports, requests for clarification, and suggestions for improvement since publication of RFC 3921.  Although the document editor has endeavored to address all such feedback, he is solely responsible for any remaining errors and ambiguities.
+</p>
+<p>Some of the text about roster versioning was borrowed from <a class='info' href='#XEP-0237'>[XEP&#8209;0237]<span> (</span><span class='info'>Saint-Andre, P. and D. Cridland, &ldquo;Roster Versioning,&rdquo; March&nbsp;2010.</span><span>)</span></a>, and some of the text about message threads was borrowed from <a class='info' href='#XEP-0201'>[XEP&#8209;0201]<span> (</span><span class='info'>Saint-Andre, P., Paterson, I., and K. Smith, &ldquo;Best Practices for Message Threads,&rdquo; November&nbsp;2010.</span><span>)</span></a>.
+</p>
+<p>Special thanks are due to Kevin Smith, Matthew Wild, Dave Cridland, Waqas Hussain, Philipp Hancke, Florian Zeitz, Jonas Lindberg, Jehan Pages, Tory Patnoe, and others for their comments during Working Group Last Call.
+</p>
+<p>Thanks also to Richard Barnes for his review on behalf of the Security Directorate.
+</p>
+<p>The Working Group chairs were Ben Campbell and Joe Hildebrand.  The responsible Area Director was Gonzalo Camarillo.
+</p>
+<a name="rfc.authors"></a><br /><hr />
+<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
+<h3>Author's Address</h3>
+<table width="99%" border="0" cellpadding="0" cellspacing="0">
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Peter Saint-Andre</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Cisco</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">1899 Wyknoop Street, Suite 600</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">Denver, CO  80202</td></tr>
+<tr><td class="author-text">&nbsp;</td>
+<td class="author-text">USA</td></tr>
+<tr><td class="author" align="right">Phone:&nbsp;</td>
+<td class="author-text">+1-303-308-3282</td></tr>
+<tr><td class="author" align="right">EMail:&nbsp;</td>
+<td class="author-text"><a href="mailto:psaintan@cisco.com">psaintan@cisco.com</a></td></tr>
+</table>
+</body></html>
diff --git a/examples/dhtd.hs b/examples/dhtd.hs
index 837cb210..219221e5 100644
--- a/examples/dhtd.hs
+++ b/examples/dhtd.hs
@@ -21,11 +21,12 @@ module Main where
 import Control.Arrow
 import Control.Applicative
 import Control.Concurrent.STM
-import Control.DeepSeq
 import Control.Exception
 import Control.Monad
+import Control.Monad.Trans.Resource (runResourceT)
 import Data.Bool
 import Data.Char
+import Data.Function
 import Data.Hashable
 import Data.List
 import qualified Data.IntMap.Strict as IntMap
@@ -53,6 +54,8 @@ import qualified Data.HashMap.Strict as HashMap
 import qualified Data.Vector as V
 import qualified Data.Text as T
 import qualified Data.Text.Encoding as T
+import System.Posix.Signals
+
 
 import Announcer
 import Crypto.Tox -- (zeros32,SecretKey,PublicKey, generateSecretKey, toPublic, encodeSecret, decodeSecret, userKeys)
@@ -60,8 +63,6 @@ import Network.UPNP as UPNP
 import Network.Address hiding (NodeId, NodeInfo(..))
 import Network.QueryResponse
 import Network.StreamServer
-import Network.Kademlia
-import Network.Kademlia.Bootstrap
 import Network.Kademlia.Search
 import qualified Network.BitTorrent.MainlineDHT as Mainline
 import qualified Network.Tox as Tox
@@ -71,6 +72,7 @@ import qualified Data.Aeson as J
 import qualified Data.ByteString.Lazy as L
 import qualified Data.ByteString.Char8 as B
 import Control.Concurrent.Tasks
+import Control.Monad.Trans.Control
 import System.IO.Error
 import qualified Data.Serialize as S
 import Network.BitTorrent.DHT.ContactInfo as Peers
@@ -88,6 +90,13 @@ import Data.Typeable
 import Roster
 import OnionRouter
 
+-- Presence imports.
+import ConsoleWriter
+import Presence
+import XMPPServer
+import Connection
+
+
 showReport :: [(String,String)] -> String
 showReport kvs = showColumns $ map (\(x,y)->[x,y]) kvs
 
@@ -146,21 +155,6 @@ data DHTAnnouncable nid = forall dta tok ni r.
     , qresultAddr :: dta -> nid
     }
 
-data DHTLink = forall status linkid params.
-                ( Show status
-                , Show linkid
-                , Typeable status
-                , Typeable linkid
-                , Typeable params
-                ) => DHTLink
-    { linkInit    :: params -> IO (Either String status)
-    , linkParamParser :: [String] -> Either String params
-    , linkStatus  :: IO (Either String status)
-    , showLinkStatus :: status -> String
-    , linkNewPipe :: String -> linkid -> IO (Either String status)
-    , linkUnPipe  :: linkid -> IO (Either String status)
-    }
-
 data DHTSearch nid ni = forall addr tok r. DHTSearch
     { searchThread     :: ThreadId
     , searchState      :: SearchState nid addr tok ni r
@@ -191,7 +185,6 @@ data DHT = forall nid ni. ( Show     ni
     , dhtPing          :: Map.Map String (DHTPing ni)
     , dhtQuery         :: Map.Map String (DHTQuery nid ni)
     , dhtAnnouncables  :: Map.Map String (DHTAnnouncable nid)
-    , dhtLinks         :: Map.Map String DHTLink
     , dhtParseId       :: String -> Either String nid
     , dhtSearches      :: TVar (Map.Map (String,nid) (DHTSearch nid ni))
     , dhtFallbackNodes :: IO [ni]
@@ -375,6 +368,8 @@ reportSearchResults meth h DHTSearch{searchShowTok,searchState,searchResults} =
         ns'           = map showN ns
     reportResult meth id (const Nothing) id h (Right (ns',rs, Just ()))
 
+data ConnectionManager = forall status k. ConnectionManager { typedManager :: Connection.Manager status k }
+
 data Session = Session
     { netname           :: String
     , dhts              :: Map.Map String DHT
@@ -384,9 +379,10 @@ data Session = Session
     , toxkeys           :: TVar Tox.AnnouncedKeys
     , userkeys          :: TVar [(SecretKey,PublicKey)]
     , roster            :: Roster
+    , connectionManager :: ConnectionManager
     , onionRouter       :: OnionRouter
     , announcer         :: Announcer
-    , signalQuit        :: MVar ()
+    , signalQuit        :: IO ()
     }
 
 exceptionsToClient :: ClientHandle -> IO () -> IO ()
@@ -481,7 +477,7 @@ clientSession s@Session{..} sock cnum h = do
 
         ("stop", _) -> do hPutClient h "Terminating DHT Daemon."
                           hCloseClient h
-                          putMVar signalQuit ()
+                          signalQuit
 
         ("throw", er) -> cmd0 $ do
                             throwIO $ userError er
@@ -633,7 +629,6 @@ clientSession s@Session{..} sock cnum h = do
                 hPutClientChunk h $ "trampolines: " ++ show (IntMap.size ts) ++ "\n"
                 hPutClient h $ showColumns $ ["","responses","timeouts"]:r
 
-
         ("g", s) | Just DHT{..} <- Map.lookup netname dhts
                     -> cmd0 $ do
                         -- arguments: method
@@ -901,46 +896,29 @@ clientSession s@Session{..} sock cnum h = do
                             mkentry (k :-> Down tm) = [ show cnt, show k, show (now - tm) ]
                                 where Just (_,(cnt,_)) = MM.lookup' k (Tox.keyAssoc keydb)
                         hPutClient h $ showColumns entries
-        ("c", s) | "" <- strp s -> cmd0 $ do
-                        let combinedLinkMap = Map.unions $map (dhtLinks . snd) (Map.toList dhts)
-                        -- TODO: list all connections
-                        let connections =  [[{-TODO-}]]
-                        hPutClient h $ showColumns connections
-        ("c", s) -> cmd0 $ do
-                        let combinedLinkMap = Map.unions $map (dhtLinks . snd) (Map.toList dhts)
-                        -- form new connection according of type corresponding to parameter
-                        let ws = words s
-                        result
-                          <- case ws of
-                              (linktype:rest)
-                                -> case (Map.lookup (head ws) combinedLinkMap) of
-                                    Nothing -> return . Left $ "I don't know a '" ++ head ws ++ "' link type."
-                                    Just l@(DHTLink
-                                              { linkInit        {- :: params   -> IO (Either String status) -}
-                                              , linkParamParser {- :: [String] -> Either String params      -}
-                                              , showLinkStatus  {- :: status   -> String                    -}
-                                              }) -> case linkParamParser rest of
-                                                        Left er -> return $ Left er
-                                                        Right params -> fmap showLinkStatus <$> linkInit params
-                              _ -> return $ Left "parse error"
-                        case result of
-                            Left er -> hPutClient h er
-                            Right statusstr -> hPutClient h statusstr
+
+        ("c", s) | "" <- strp s -> cmd0 $ join $ atomically $ do
+            ConnectionManager mgr <- return connectionManager
+            cmap <- connections mgr
+            cs <- Map.toList <$> mapM connStatus cmap
+            let mkrow = Connection.showKey mgr *** Connection.showStatus mgr
+                rs    = map mkrow cs
+            return $ do
+            hPutClient h $ showReport rs
 
         ("help", s) | Just DHT{..} <- Map.lookup netname dhts
                     -> cmd0 $ do
             let tolist :: a -> [a]
                 tolist = (:[])
 
-                dhtkeys, announcables, links, ks, allcommands :: [[String]]
+                dhtkeys, announcables, ks, allcommands :: [[String]]
                 dhtkeys = map tolist $ Map.keys dhts
                 queries = map (tolist . ("s "++)) $ Map.keys dhtQuery
                 xs = map (tolist . ("x "++)) $ Map.keys dhtQuery
                 gs = map (tolist . ("g "++)) $ Map.keys dhtQuery
                 announcables = map (tolist . ("p "++)) $ Map.keys dhtAnnouncables
-                links = map (tolist . ("c "++)) $ Map.keys dhtLinks
                 ks = [["k gen"],["k public"],["k secret"]]
-                allcommands = sortBy (comparing head) $ concat [sessionCommands, dhtkeys, announcables, links, ks, queries, gs,xs]
+                allcommands = sortBy (comparing (take 1)) $ concat [sessionCommands, dhtkeys, announcables, ks, queries, gs,xs]
 
             hPutClient h ("Available commands:\n" ++ showColumns allcommands)
 
@@ -957,27 +935,36 @@ readExternals nodeAddr vars = do
     return $ filter (not . unspecified) as
 
 data Options = Options
-    { portbt  :: String
-    , porttox :: String
-    , ip6bt   :: Bool
-    , ip6tox  :: Bool
-    , dhtkey  :: Maybe SecretKey
+    { portbt    :: String
+    , porttox   :: String
+    , ip6bt     :: Bool
+    , ip6tox    :: Bool
+    , dhtkey    :: Maybe SecretKey
+    -- | Currently only relevant to XMPP server code.
+    --
+    --   [ 0 ] Don't log XMPP stanzas.
+    --
+    --   [ 1 ] Log non-ping stanzas.
+    --
+    --   [ 2 ] Log all stanzas, even pings.
+    , verbosity :: Int
     }
  deriving (Eq,Show)
 
 sensibleDefaults :: Options
 sensibleDefaults = Options
-    { portbt  = "6881"
-    , porttox = "33445"
-    , ip6bt   = True
-    , ip6tox  = True
-    , dhtkey  = Nothing
+    { portbt    = "6881"
+    , porttox   = "33445"
+    , ip6bt     = True
+    , ip6tox    = True
+    , dhtkey    = Nothing
+    , verbosity = 1
     }
 
 -- bt=<port>,tox=<port>
 -- -4
 parseArgs :: [String] -> Options -> Options
-parseArgs []          opts         = opts
+parseArgs []                  opts = opts
 parseArgs ("--dhtkey":k:args) opts = parseArgs args opts
     { dhtkey = decodeSecret $ B.pack k }
 parseArgs ("-4":args) opts         = parseArgs args opts
@@ -996,7 +983,7 @@ noArgPing f [] x = f x
 noArgPing _ _  _ = return Nothing
 
 main :: IO ()
-main = do
+main = runResourceT $ liftBaseWith $ \resT -> do
     args <- getArgs
     let opts = parseArgs args sensibleDefaults
     print opts
@@ -1010,6 +997,18 @@ main = do
 
     announcer <- forkAnnouncer
 
+    -- XMPP initialization
+    cw        <- newConsoleWriter
+    serverVar <- atomically $ newEmptyTMVar
+    state     <- newPresenceState cw serverVar
+
+    -- XMPP stanza handling
+    sv    <- resT $ xmppServer (presenceHooks state (verbosity opts))
+    -- We now have a server object but it's not ready to use until
+    -- we put it into the 'server' field of our /state/ record.
+
+    conns <- xmppConnections sv
+
     (quitBt,btdhts,btips,baddrs) <- case portbt opts of
         "" -> return (return (), Map.empty,return [],[])
         p  -> do
@@ -1080,9 +1079,6 @@ main = do
                                                               , qresultAddr = const $ Mainline.zeroID
                                                               })]
 
-                    , dhtLinks = Map.fromList
-                                    [ {- TODO -}
-                                    ]
                     , dhtSecretKey = return Nothing
                     , dhtBootstrap = case wantip of
                                         Want_IP4 -> btBootstrap4
@@ -1262,9 +1258,6 @@ main = do
 
                                                                , announceInterval = 8
                                                                })]
-                    , dhtLinks = Map.fromList
-                                    [ {- TODO -}
-                                    ]
                     , dhtSecretKey = return $ Just $ transportSecret (Tox.toxCryptoKeys tox)
                     , dhtBootstrap = case wantip of
                                         Want_IP4 -> toxStrap4
@@ -1283,8 +1276,11 @@ main = do
 
     let dhts = Map.union btdhts toxdhts
 
-    waitForSignal <- do
-        signalQuit <- newEmptyMVar
+    (waitForSignal, checkQuit) <- do
+        signalQuit <- atomically $ newTVar False
+        let quitCommand = atomically $ writeTVar signalQuit True
+        installHandler sigTERM (CatchOnce (atomically $ writeTVar signalQuit True)) Nothing
+        installHandler sigINT (CatchOnce (atomically $ writeTVar signalQuit True)) Nothing
         let defaultToxData = do
                 toxids <- atomically $ newTVar []
                 rster <- newRoster
@@ -1296,20 +1292,22 @@ main = do
         let session = clientSession0 $ Session
                 { netname           = concat $ take 1 $ Map.keys dhts -- initial default DHT
                 , dhts              = dhts  -- all DHTs
-                , signalQuit        = signalQuit
+                , signalQuit        = quitCommand
                 , swarms            = swarms
                 , cryptosessions    = netCryptoSessionsState
                 , toxkeys           = keysdb
                 , userkeys          = toxids
                 , roster            = rstr
+                , connectionManager = ConnectionManager conns
                 , onionRouter       = orouter
                 , externalAddresses = liftM2 (++) btips toxips
                 , announcer         = announcer
                 }
         srv <- streamServer (withSession session) (SockAddrUnix "dht.sock")
-        return $ do
-            () <- takeMVar signalQuit
-            quitListening srv
+        return ( do atomically $ readTVar signalQuit >>= check
+                    quitListening srv
+               , readTVar signalQuit >>= check
+               )
 
 
     forM_ (Map.toList dhts)
@@ -1331,6 +1329,25 @@ main = do
             bootstrap btSaved fallbackNodes
         return ()
 
+    atomically $ do
+        putTMVar serverVar  (sv,conns) -- Okay, now it's ready. :)
+                                       -- FIXME: This is error prone.
+
+    forkIO $ do
+        myThreadId >>= flip labelThread "XMPP.stanzas"
+        let console = cwPresenceChan <$> consoleWriter state
+        fix $ \loop -> do
+        what <- atomically
+            $ orElse (do (client,stanza) <- maybe retry takeTMVar console
+                         return $ do informClientPresence0 state Nothing client stanza
+                                     loop)
+                     (checkQuit >> return (return ()))
+        what
+
+    hPutStrLn stderr "Started XMPP server."
+
+    -- Wait for DHT and XMPP threads to finish.
+    -- Use ResourceT to clean-up XMPP server.
     waitForSignal
 
     stopAnnouncer announcer
diff --git a/g b/g
new file mode 100755
index 00000000..a48efef2
--- /dev/null
+++ b/g
@@ -0,0 +1,25 @@
+#!/bin/bash
+warn="-freverse-errors -fwarn-unused-imports -Wmissing-signatures -fdefer-typed-holes"
+exts="-XOverloadedStrings -XRecordWildCards"
+defs="-DBENCODE_AESON -DTHREAD_DEBUG"
+hide="-hide-package crypto-random -hide-package crypto-api -hide-package crypto-numbers -hide-package cryptohash -hide-package prettyclass"
+
+root=${0%/*}
+cd "$root"
+
+me=${0##*/}
+me=${me%.*}
+ghc                                  \
+    $hide                            \
+    $exts                            \
+    $defs                            \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    -iArchive                        \
+    -isrc                            \
+    -icryptonite-backport            \
+    build/b/Presence/monitortty.o    \
+    build/b/cbits/cryptonite_salsa.o \
+    build/b/cbits/cryptonite_xsalsa.o\
+    $warn                            \
+    "$@"
diff --git a/gi b/gi
new file mode 100755
index 00000000..8101348e
--- /dev/null
+++ b/gi
@@ -0,0 +1,14 @@
+#!/bin/bash
+args="-fwarn-unused-imports"
+
+root=${0%/*}
+cd "$root"
+
+me=g
+ghci                                 \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    -iArchive                        \
+    build/b/Presence/monitortty.o    \
+    $args                            \
+    "$@"
diff --git a/graphdeps b/graphdeps
new file mode 100755
index 00000000..4ee6939a
--- /dev/null
+++ b/graphdeps
@@ -0,0 +1,19 @@
+#!/bin/bash
+
+args="-r Todo"
+
+graphmod $args "$@"         \
+          -i . -i Presence  \
+          Presence/main.hs  \
+ | awk 'BEGIN{n=1;}
+        !/label="Main"/{print;}
+        /label="Main"/{if(n==1) print;n=n+1;}' \
+   | sed '2isize="13,8!"; ratio=fill;' \
+ > modules.dot
+
+fgnode="$(sed -n '/label="FGConsole"/{s#\(.*\)\[.*#\1#; p}' modules.dot)"
+
+cat modules.dot | sed '3'i$fgnode'->monitortty;\
+monitortty[label="monitortty.c"];' | dot -Tsvg > modules.svg
+
+
diff --git a/modules.svg b/modules.svg
new file mode 100644
index 00000000..32e85a40
--- /dev/null
+++ b/modules.svg
@@ -0,0 +1,337 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.26.3 (20100126.1600)
+ -->
+<!-- Title: G Pages: 1 -->
+<svg width="933pt" height="576pt"
+ viewBox="0.00 0.00 932.73 576.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph1" class="graph" transform="scale(0.654088 0.654088) rotate(0) translate(4 876.615)">
+<title>G</title>
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+<path fill="none" stroke="black" d="M429.334,-396.558C396.917,-356.878 319.091,-261.617 281.718,-215.87"/>
+<polygon fill="black" stroke="black" points="284.267,-213.459 275.23,-207.929 278.846,-217.887 284.267,-213.459"/>
+</g>
+<!-- u14 -->
+<g id="node28" class="node"><title>u14</title>
+<ellipse fill="none" stroke="black" cx="444" cy="-190.511" rx="45.1673" ry="18"/>
+<text text-anchor="middle" x="444" y="-186.411" font-family="Times Roman,serif" font-size="14.00">Render</text>
+</g>
+<!-- u13&#45;&gt;u14 -->
+<g id="edge66" class="edge"><title>u13&#45;&gt;u14</title>
+<path fill="none" stroke="black" d="M444,-396.18C444,-357.114 444,-265.433 444,-218.809"/>
+<polygon fill="black" stroke="black" points="447.5,-218.781 444,-208.781 440.5,-218.781 447.5,-218.781"/>
+</g>
+<!-- u12 -->
+<g id="node8" class="node"><title>u12</title>
+<ellipse fill="none" stroke="black" cx="782" cy="-190.511" rx="86.1654" ry="18"/>
+<text text-anchor="middle" x="782" y="-186.411" font-family="Times Roman,serif" font-size="14.00">GetHostByAddr</text>
+</g>
+<!-- u11&#45;&gt;u12 -->
+<g id="edge62" class="edge"><title>u11&#45;&gt;u12</title>
+<path fill="none" stroke="black" d="M782,-396.18C782,-357.114 782,-265.433 782,-218.809"/>
+<polygon fill="black" stroke="black" points="785.5,-218.781 782,-208.781 778.5,-218.781 785.5,-218.781"/>
+</g>
+<!-- u11&#45;&gt;u10 -->
+<g id="edge60" class="edge"><title>u11&#45;&gt;u10</title>
+<path fill="none" stroke="black" d="M764.935,-397.094C745.163,-376.519 712.091,-340.86 687,-307.511 664.706,-277.878 642.405,-241.466 628.204,-217.209"/>
+<polygon fill="black" stroke="black" points="631.223,-215.438 623.175,-208.547 625.169,-218.952 631.223,-215.438"/>
+</g>
+<!-- u2 -->
+<g id="node16" class="node"><title>u2</title>
+<ellipse fill="none" stroke="black" cx="1050" cy="-190.511" rx="111.181" ry="18"/>
+<text text-anchor="middle" x="1050" y="-186.411" font-family="Times Roman,serif" font-size="14.00">ByteStringOperators</text>
+</g>
+<!-- u11&#45;&gt;u2 -->
+<g id="edge58" class="edge"><title>u11&#45;&gt;u2</title>
+<path fill="none" stroke="black" d="M802.585,-397.306C849.801,-357.841 966.027,-260.697 1020.69,-215.009"/>
+<polygon fill="black" stroke="black" points="1023.18,-217.493 1028.6,-208.394 1018.69,-212.122 1023.18,-217.493"/>
+</g>
+<!-- u9&#45;&gt;u10 -->
+<g id="edge56" class="edge"><title>u9&#45;&gt;u10</title>
+<path fill="none" stroke="black" d="M610.246,-396.18C610.769,-357.114 611.997,-265.433 612.621,-218.809"/>
+<polygon fill="black" stroke="black" points="616.121,-218.827 612.755,-208.781 609.122,-218.733 616.121,-218.827"/>
+</g>
+<!-- u9&#45;&gt;u7 -->
+<g id="edge54" class="edge"><title>u9&#45;&gt;u7</title>
+<path fill="none" stroke="black" d="M575.027,-401.554C529.583,-383.885 448.757,-349.568 387,-307.511 346.975,-280.253 307.082,-240.56 283.225,-215.137"/>
+<polygon fill="black" stroke="black" points="285.722,-212.682 276.353,-207.735 280.592,-217.445 285.722,-212.682"/>
+</g>
+<!-- u9&#45;&gt;u2 -->
+<g id="edge52" class="edge"><title>u9&#45;&gt;u2</title>
+<path fill="none" stroke="black" d="M647.388,-402.369C700.07,-384.633 798.482,-349.179 877,-307.511 929.408,-279.698 985.5,-239.639 1019.15,-214.351"/>
+<polygon fill="black" stroke="black" points="1021.35,-217.081 1027.21,-208.257 1017.12,-211.499 1021.35,-217.081"/>
+</g>
+<!-- u8 -->
+<g id="node12" class="node"><title>u8</title>
+<ellipse fill="none" stroke="black" cx="756" cy="-672.511" rx="39.1069" ry="18"/>
+<text text-anchor="middle" x="756" y="-668.411" font-family="Times Roman,serif" font-size="14.00">XMPP</text>
+</g>
+<!-- u8&#45;&gt;u17 -->
+<g id="edge50" class="edge"><title>u8&#45;&gt;u17</title>
+<path fill="none" stroke="black" d="M737.933,-656.328C709.311,-630.691 653.37,-580.584 619.98,-550.677"/>
+<polygon fill="black" stroke="black" points="622.194,-547.961 612.41,-543.896 617.524,-553.175 622.194,-547.961"/>
+</g>
+<!-- u8&#45;&gt;u16 -->
+<g id="edge48" class="edge"><title>u8&#45;&gt;u16</title>
+<path fill="none" stroke="black" d="M756,-654.315C756,-629.397 756,-584.404 756,-554.998"/>
+<polygon fill="black" stroke="black" points="759.5,-554.936 756,-544.936 752.5,-554.936 759.5,-554.936"/>
+</g>
+<!-- u8&#45;&gt;u13 -->
+<g id="edge46" class="edge"><title>u8&#45;&gt;u13</title>
+<path fill="none" stroke="black" d="M717.738,-668.663C662.059,-661.059 558.838,-639.087 499,-577.511 462.878,-540.339 450.455,-478.656 446.2,-442.778"/>
+<polygon fill="black" stroke="black" points="449.649,-442.107 445.124,-432.527 442.687,-442.838 449.649,-442.107"/>
+</g>
+<!-- u8&#45;&gt;u11 -->
+<g id="edge44" class="edge"><title>u8&#45;&gt;u11</title>
+<path fill="none" stroke="black" d="M776.789,-657.038C797.565,-640.149 828.204,-611.002 841,-577.511 853.214,-545.542 851.135,-533.198 841,-500.511 834.014,-477.978 818.857,-456.105 805.655,-440.057"/>
+<polygon fill="black" stroke="black" points="808.132,-437.567 798.983,-432.223 802.802,-442.106 808.132,-437.567"/>
+</g>
+<!-- u8&#45;&gt;u9 -->
+<g id="edge42" class="edge"><title>u8&#45;&gt;u9</title>
+<path fill="none" stroke="black" d="M721.477,-663.99C660.787,-648.237 539.105,-612.923 515,-577.511 495.743,-549.221 501.122,-531.793 515,-500.511 527.185,-473.043 552.959,-450.619 574.589,-435.564"/>
+<polygon fill="black" stroke="black" points="576.586,-438.439 582.942,-429.963 572.687,-432.625 576.586,-438.439"/>
+</g>
+<!-- u8&#45;&gt;u7 -->
+<g id="edge40" class="edge"><title>u8&#45;&gt;u7</title>
+<path fill="none" stroke="black" d="M716.818,-671.159C610.215,-666.578 319.04,-647.749 261,-577.511 216.241,-523.345 244.622,-299.347 256.505,-219.195"/>
+<polygon fill="black" stroke="black" points="260.031,-219.283 258.063,-208.872 253.11,-218.238 260.031,-219.283"/>
+</g>
+<!-- u8&#45;&gt;u3 -->
+<g id="edge38" class="edge"><title>u8&#45;&gt;u3</title>
+<path fill="none" stroke="black" d="M776.785,-657.179C799.362,-639.756 835.478,-609.554 860,-577.511 893.106,-534.252 919.483,-476 933.337,-442.124"/>
+<polygon fill="black" stroke="black" points="936.585,-443.426 937.068,-432.843 930.09,-440.816 936.585,-443.426"/>
+</g>
+<!-- u8&#45;&gt;u2 -->
+<g id="edge36" class="edge"><title>u8&#45;&gt;u2</title>
+<path fill="none" stroke="black" d="M783.348,-659.313C842.428,-629.028 980.699,-548.146 1031,-432.511 1062.27,-360.626 1058.13,-265.44 1053.53,-218.766"/>
+<polygon fill="black" stroke="black" points="1057,-218.348 1052.46,-208.776 1050.04,-219.091 1057,-218.348"/>
+</g>
+<!-- u4 -->
+<g id="node14" class="node"><title>u4</title>
+<ellipse fill="none" stroke="black" cx="1221" cy="-672.511" rx="39.1069" ry="18"/>
+<text text-anchor="middle" x="1221" y="-668.411" font-family="Times Roman,serif" font-size="14.00">UTmp</text>
+</g>
+<!-- u5 -->
+<g id="node20" class="node"><title>u5</title>
+<ellipse fill="none" stroke="black" cx="1241" cy="-526.511" rx="59.065" ry="18"/>
+<text text-anchor="middle" x="1241" y="-522.411" font-family="Times Roman,serif" font-size="14.00">BitSyntax</text>
+</g>
+<!-- u4&#45;&gt;u5 -->
+<g id="edge32" class="edge"><title>u4&#45;&gt;u5</title>
+<path fill="none" stroke="black" d="M1223.49,-654.315C1226.91,-629.397 1233.07,-584.404 1237.1,-554.998"/>
+<polygon fill="black" stroke="black" points="1240.59,-555.318 1238.48,-544.936 1233.65,-554.368 1240.59,-555.318"/>
+</g>
+<!-- u1 -->
+<g id="node17" class="node"><title>u1</title>
+<ellipse fill="none" stroke="black" cx="1064" cy="-526.511" rx="62.0391" ry="18"/>
+<text text-anchor="middle" x="1064" y="-522.411" font-family="Times Roman,serif" font-size="14.00">ConfigFiles</text>
+</g>
+<!-- u1&#45;&gt;u3 -->
+<g id="edge30" class="edge"><title>u1&#45;&gt;u3</title>
+<path fill="none" stroke="black" d="M1045.51,-509.256C1025.43,-490.512 993.177,-460.409 970.424,-439.173"/>
+<polygon fill="black" stroke="black" points="972.802,-436.605 963.103,-432.341 968.026,-441.722 972.802,-436.605"/>
+</g>
+<!-- u1&#45;&gt;u2 -->
+<g id="edge28" class="edge"><title>u1&#45;&gt;u2</title>
+<path fill="none" stroke="black" d="M1064.39,-508.418C1064.84,-483.297 1065.36,-436.436 1064,-396.511 1061.84,-332.846 1055.93,-258.304 1052.52,-218.664"/>
+<polygon fill="black" stroke="black" points="1056.01,-218.335 1051.65,-208.677 1049.03,-218.943 1056.01,-218.335"/>
+</g>
+<!-- u0 -->
+<g id="node18" class="node"><title>u0</title>
+<ellipse fill="none" stroke="black" cx="974" cy="-844.511" rx="34.2406" ry="18"/>
+<text text-anchor="middle" x="974" y="-840.411" font-family="Times Roman,serif" font-size="14.00">Main</text>
+</g>
+<!-- u0&#45;&gt;u6 -->
+<g id="edge18" class="edge"><title>u0&#45;&gt;u6</title>
+<path fill="none" stroke="black" d="M939.803,-843.856C806.714,-840.826 324.082,-825.222 190,-756.511 164.653,-743.522 143.663,-718.347 130.211,-698.93"/>
+<polygon fill="black" stroke="black" points="133.034,-696.854 124.572,-690.478 127.211,-700.739 133.034,-696.854"/>
+</g>
+<!-- u0&#45;&gt;u18 -->
+<g id="edge24" class="edge"><title>u0&#45;&gt;u18</title>
+<path fill="none" stroke="black" d="M942.708,-836.902C891.962,-823.966 789.213,-795.269 708,-756.511 579.32,-695.099 441.178,-595.552 380.987,-550.28"/>
+<polygon fill="black" stroke="black" points="382.771,-547.241 372.682,-544.005 378.551,-552.826 382.771,-547.241"/>
+</g>
+<!-- u0&#45;&gt;u8 -->
+<g id="edge22" class="edge"><title>u0&#45;&gt;u8</title>
+<path fill="none" stroke="black" d="M955.035,-829.548C916.417,-799.078 828.516,-729.725 783.574,-694.266"/>
+<polygon fill="black" stroke="black" points="785.722,-691.503 775.703,-688.056 781.386,-696.998 785.722,-691.503"/>
+</g>
+<!-- u0&#45;&gt;u7 -->
+<g id="edge20" class="edge"><title>u0&#45;&gt;u7</title>
+<path fill="none" stroke="black" d="M940.012,-842.777C860.903,-837.764 659.438,-819.328 505,-756.511 371.977,-702.404 305.122,-703.387 236,-577.511 170.19,-457.665 224.521,-284.432 249.798,-217.926"/>
+<polygon fill="black" stroke="black" points="253.082,-219.138 253.441,-208.55 246.557,-216.603 253.082,-219.138"/>
+</g>
+<!-- u0&#45;&gt;u4 -->
+<g id="edge16" class="edge"><title>u0&#45;&gt;u4</title>
+<path fill="none" stroke="black" d="M1004.62,-836.63C1045.64,-824.834 1118.93,-799.278 1168,-756.511 1185.88,-740.929 1199.84,-717.845 1208.94,-699.817"/>
+<polygon fill="black" stroke="black" points="1212.29,-700.929 1213.49,-690.402 1205.99,-697.885 1212.29,-700.929"/>
+</g>
+<!-- u0&#45;&gt;u3 -->
+<g id="edge14" class="edge"><title>u0&#45;&gt;u3</title>
+<path fill="none" stroke="black" d="M972.73,-826.309C968.045,-759.149 951.703,-524.925 945.99,-443.037"/>
+<polygon fill="black" stroke="black" points="949.475,-442.69 945.287,-432.958 942.492,-443.177 949.475,-442.69"/>
+</g>
+<!-- u0&#45;&gt;u2 -->
+<g id="edge12" class="edge"><title>u0&#45;&gt;u2</title>
+<path fill="none" stroke="black" d="M988.643,-827.967C1022.67,-788.265 1106.34,-683.028 1135,-577.511 1171.28,-443.966 1098.05,-281.324 1065.02,-217.784"/>
+<polygon fill="black" stroke="black" points="1068.04,-216.005 1060.27,-208.799 1061.85,-219.276 1068.04,-216.005"/>
+</g>
+<!-- u0&#45;&gt;u1 -->
+<g id="edge10" class="edge"><title>u0&#45;&gt;u1</title>
+<path fill="none" stroke="black" d="M979.097,-826.502C994.067,-773.607 1037.99,-618.418 1056.08,-554.507"/>
+<polygon fill="black" stroke="black" points="1059.49,-555.291 1058.85,-544.715 1052.76,-553.384 1059.49,-555.291"/>
+</g>
+<!-- u19 -->
+<g id="node23" class="node"><title>u19</title>
+<ellipse fill="none" stroke="black" cx="1339" cy="-672.511" rx="55.0898" ry="18"/>
+<text text-anchor="middle" x="1339" y="-668.411" font-family="Times Roman,serif" font-size="14.00">MultiMap</text>
+</g>
+<!-- u0&#45;&gt;u19 -->
+<g id="edge26" class="edge"><title>u0&#45;&gt;u19</title>
+<path fill="none" stroke="black" d="M1007.95,-842.09C1068.01,-836.318 1194.7,-817.311 1280,-756.511 1300.48,-741.91 1316.32,-717.873 1326.4,-699.244"/>
+<polygon fill="black" stroke="black" points="1329.52,-700.827 1331.01,-690.337 1323.3,-697.607 1329.52,-700.827"/>
+</g>
+<!-- u15 -->
+<g id="node27" class="node"><title>u15</title>
+<ellipse fill="none" stroke="black" cx="444" cy="-78.5106" rx="38.9134" ry="18"/>
+<text text-anchor="middle" x="444" y="-74.4106" font-family="Times Roman,serif" font-size="14.00">Token</text>
+</g>
+<!-- u14&#45;&gt;u15 -->
+<g id="edge68" class="edge"><title>u14&#45;&gt;u15</title>
+<path fill="none" stroke="black" d="M444,-172.016C444,-154.239 444,-127.129 444,-106.669"/>
+<polygon fill="black" stroke="black" points="447.5,-106.661 444,-96.661 440.5,-106.661 447.5,-106.661"/>
+</g>
+</g>
+</svg>
diff --git a/nalias.hs b/nalias.hs
new file mode 100644
index 00000000..fa1b6f71
--- /dev/null
+++ b/nalias.hs
@@ -0,0 +1,70 @@
+import Network.Socket
+import qualified Network.BSD as BSD
+import ControlMaybe
+import Control.Exception ({-evaluate,-}handle,SomeException(..),bracketOnError,ErrorCall(..))
+import System.IO.Error (isDoesNotExistError)
+import System.Endian
+import Data.List (nub)
+import qualified Data.Text as Text
+import GetHostByAddr (getHostByAddr)
+import Control.Concurrent
+import Control.Concurrent.STM
+import Control.Monad
+import System.Environment
+
+unmap6mapped4 addr@(SockAddrInet6 port _ (0,0,0xFFFF,a) _) =
+    SockAddrInet port (toBE32 a)
+unmap6mapped4 addr = addr
+
+make6mapped4 addr@(SockAddrInet6 {}) = addr
+make6mapped4 addr@(SockAddrInet port a) = SockAddrInet6 port 0 (0,0,0xFFFF,fromBE32 a) 0
+
+
+reverseResolve addr = 
+    handleIO_ (return []) $ do
+        ent <- getHostByAddr (unmap6mapped4 addr) --  AF_UNSPEC addr
+        let names = BSD.hostName ent : BSD.hostAliases ent
+        return $ map Text.pack $ nub names
+
+forwardResolve addrtext = do
+    r <- atomically newEmptyTMVar
+    mvar <- atomically newEmptyTMVar
+    rt <- forkOS $ resolver r mvar
+    tt <- forkIO $ timer r rt
+    atomically $ putTMVar mvar tt
+    atomically $ readTMVar r
+ where
+    resolver r mvar = do
+      xs <- handle (\e -> let _ = isDoesNotExistError e in return [])
+            $ do fmap (map $ make6mapped4 . addrAddress) $ 
+                  getAddrInfo (Just $ defaultHints { addrFlags = [ AI_CANONNAME, AI_V4MAPPED ]})
+                    (Just $ Text.unpack $ strip_brackets addrtext)
+                    (Just "5269")
+      did <- atomically $ tryPutTMVar r (nub xs)
+      when did $ do
+      tt <- atomically $ readTMVar mvar
+      throwTo tt (ErrorCall "Interrupted delay")
+      return ()
+    timer r rt = do
+      handle (\(ErrorCall _)-> return ()) $ do
+      threadDelay 2000000
+      did <- atomically $ tryPutTMVar r []
+      when did $ do
+      putStrLn $ "timeout resolving: "++show addrtext
+      killThread rt
+    strip_brackets s = 
+      case Text.uncons s of
+          Just ('[',t) -> Text.takeWhile (/=']') t
+          _            -> s
+
+main = do
+    args <- getArgs
+    forM args $ \arg -> do
+    putStrLn $ arg ++ ":"
+    let targ = Text.pack arg
+    addrs <- forwardResolve targ
+    putStrLn $ "  forward: " ++ show addrs
+    forM addrs $ \addr -> do
+        names <- reverseResolve addr
+        putStrLn $ "  reverse "++show addr++": "++show names
+    return ()
diff --git a/nalias2.hs b/nalias2.hs
new file mode 100644
index 00000000..609f2ec6
--- /dev/null
+++ b/nalias2.hs
@@ -0,0 +1,18 @@
+import System.Environment
+import Control.Monad
+import qualified Data.Text as Text
+
+import DNSCache
+
+main = do
+    dns <- newDNSCache
+    args <- getArgs
+    forM args $ \arg -> do
+    putStrLn $ arg ++ ":"
+    let targ = Text.pack arg
+    addrs <- forwardResolve dns targ
+    putStrLn $ "  forward: " ++ show addrs
+    forM addrs $ \addr -> do
+        names <- reverseResolve dns addr
+        putStrLn $ "  reverse "++show addr++": "++show names
+    return ()
diff --git a/p b/p
new file mode 100755
index 00000000..1ed6e374
--- /dev/null
+++ b/p
@@ -0,0 +1,28 @@
+#!/bin/bash
+warn="-freverse-errors -fwarn-unused-imports -Wmissing-signatures -fdefer-typed-holes"
+exts="-XOverloadedStrings -XRecordWildCards"
+defs="-DBENCODE_AESON -DTHREAD_DEBUG"
+hide="-hide-package crypto-random -hide-package crypto-api -hide-package crypto-numbers -hide-package cryptohash -hide-package prettyclass"
+opts="-rtsopts -hisuf p_hi -osuf p_o -prof -fprof-auto -fprof-auto-exported"
+
+root=${0%/*}
+cd "$root"
+
+me=${0##*/}
+me=${me%.*}
+set -x
+ghc                                  \
+    $opts                            \
+    $hide                            \
+    $exts                            \
+    $defs                            \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    -iArchive                        \
+    -isrc                            \
+    -icryptonite-backport            \
+    build/b/Presence/monitortty.o    \
+    build/b/cbits/cryptonite_salsa.o \
+    build/b/cbits/cryptonite_xsalsa.o\
+    $warn                            \
+    "$@"
diff --git a/presence.cabal.bak b/presence.cabal.bak
new file mode 100644
index 00000000..81ca59b2
--- /dev/null
+++ b/presence.cabal.bak
@@ -0,0 +1,156 @@
+name: presence
+version: 0.0.1
+cabal-version: >=1.10
+build-type: Simple
+license: AllRightsReserved
+synopsis: XMPP Server which detects unix logins
+description: When users login to your localhost, their presence is detected and announced
+             to connected xmpp clients.  presence is a modern XMPP variant of the old Unix Talk
+             program. Eventually, this will be expanded to become a peer-to-peer service allowing
+             xmpp instant messaging between separate computers as well. And somewhere down the
+             road, extended again to make use of Jingle to facilitate VOIP.
+author: Joe Crayne
+data-dir: ""
+
+library
+    cpp-options: -DRENDERFLUSH
+    c-sources: Presence/monitortty.c
+    hs-source-dirs: . Presence
+    ghc-options: -O2 -fwarn-unused-binds
+    hs-source-dirs: . Presence
+    build-depends:
+        base,
+        binary,
+        blaze-builder,
+        bytestring,
+        conduit (>=1.0.4),
+        conduit-extra,
+        containers,
+        cpu,
+        deepseq,
+        directory,
+        filepath,
+        hinotify,
+        mtl,
+        network,
+        process,
+        random,
+        resourcet,
+        stm,
+        template-haskell,
+        text (>=0.11.2.0),
+        time,
+        transformers,
+        unix,
+        void,
+        xml-conduit,
+        xml-types
+    exposed-modules:
+        ByteStringOperators,
+        ClientState,
+        ConfigFiles,
+        ConnectionKey,
+        ConsoleWriter,
+        Control.Concurrent.STM.StatusCache,
+        Control.Concurrent.STM.UpdateStream,
+        ControlMaybe,
+        Data.BitSyntax,
+        DNSCache,
+        EventUtil,
+        FGConsole,
+        GetHostByAddr,
+        LocalPeerCred,
+        LockedChan,
+        Logging,
+        Nesting,
+        Paths,
+        PeerResolve,
+        Server,
+        SockAddr,
+        SocketLike,
+        TraversableT,
+        UTmp,
+        XMPPServer
+ 
+executable presence
+    main-is: xmppServer.hs
+    buildable: True
+    cpp-options: -DRENDERFLUSH
+    hs-source-dirs: .
+    ghc-options: -O2 -fwarn-unused-binds -threaded
+    build-depends:
+        base, presence,
+        bytestring,
+        containers,
+        cpu,
+        mtl,
+        network,
+        resourcet,
+        stm,
+        text (>=0.11.2.0),
+        transformers,
+        unix,
+        xml-types
+ 
+executable whosocket
+    main-is: whosocket.hs
+    hs-source-dirs: .
+    cpp-options: -DRENDERFLUSH
+    ghc-options: -O2 -fwarn-unused-binds -threaded
+    build-depends:
+        base, presence,
+        bytestring,
+        cpu,
+        directory,
+        network,
+        unix
+
+executable nalias2
+    main-is: nalias2.hs
+    hs-source-dirs: .
+    ghc-options: -O2 -fwarn-unused-binds -threaded
+    build-depends: base, presence, text (>=0.11.2.0)
+
+executable consolation
+    main-is: consolation.hs
+    hs-source-dirs: .
+    ghc-options: -O2 -fwarn-unused-binds -threaded
+    cpp-options: -DRENDERFLUSH
+    build-depends:
+        base, presence,
+        bytestring,
+        containers,
+        cpu,
+        mtl,
+        network,
+        resourcet,
+        stm,
+        text (>=0.11.2.0),
+        transformers,
+        unix,
+        xml-types
+    main-is: xmppServer.hs
+
+executable pwrite
+    main-is: pwrite.hs
+    hs-source-dirs: .
+    ghc-options: -O2 -fwarn-unused-binds -threaded
+    build-depends:
+        base,
+        presence,
+        text (>=0.11.2.0),
+        unix
+
+-- [ ] ConduitServer.hs:main = mainC
+-- [ ] Control/Concurrent/STM/StatusCache.hs:-- > main = do q <- atomically $ Cache.new (== '(') (==')')
+-- [ ] Control/Concurrent/STM/UpdateStream.hs:-- > main = do
+-- [ ] Presence/Server.hs:-- > main = runResourceT $ do
+-- [ ] Presence/main.hs:main = do
+-- [x] consolation.hs:main = do
+-- [ ] nalias.hs:main = do
+-- [x] nalias2.hs:main = do
+-- [x] pwrite.hs:main = do
+-- [ ] simplechat.hs:main = do
+-- [ ] test-server.hs:main = do
+-- [x] whosocket.hs:main = do
+-- [x] xmppServer.hs:main = runResourceT $ do
diff --git a/presence.service b/presence.service
new file mode 100644
index 00000000..85f20cda
--- /dev/null
+++ b/presence.service
@@ -0,0 +1,11 @@
+[Unit]
+Description=XMPP Daemon
+
+[Service]
+ExecStart=/usr/local/bin/presence
+StandardOutput=journal
+StandardError=journal
+Restart=always
+
+[Install]
+WantedBy=multi-user.target
diff --git a/pwrite.hs b/pwrite.hs
new file mode 100644
index 00000000..bad6af06
--- /dev/null
+++ b/pwrite.hs
@@ -0,0 +1,105 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE OverloadedStrings #-}
+import System.Environment
+import System.Posix.Files ( getFileStatus, fileMode )
+import Data.Bits          ( (.&.) )
+import Data.Text          ( Text )
+import qualified Data.Text    as Text
+import qualified Data.Text.IO as Text
+import Control.Applicative
+import Control.Monad
+import Data.Maybe
+import XMPPServer
+import Data.Monoid
+
+-- Transforms a string of form language[_territory][.codeset][@modifier]
+-- typically used in LC_ locale variables into the BCP 47
+-- language codes used in xml:lang attributes.
+toBCP47 :: [Char] -> [Char]
+toBCP47 lang = map hyphen $ takeWhile (/='.') lang
+ where hyphen '_' = '-'
+       hyphen  c  =  c
+
+
+#if MIN_VERSION_base(4,6,0)
+#else
+lookupEnv k = fmap (lookup k) getEnvironment
+#endif
+
+getPreferedLang :: IO Text
+getPreferedLang = do
+    lang <- do
+        lc_all <- lookupEnv "LC_ALL"
+        lc_messages <- lookupEnv "LC_MESSAGES"
+        lang <- lookupEnv "LANG"
+        return $ lc_all `mplus` lc_messages `mplus` lang
+    return $ maybe "en" (Text.pack . toBCP47) lang
+
+cimatch :: Text -> Text -> Bool
+cimatch w t = Text.toLower w == Text.toLower t
+
+cimatches :: Text -> [Text] -> [Text]
+cimatches w ts = dropWhile (not . cimatch w) ts
+
+-- rfc4647 lookup of best match language tag
+lookupLang :: [Text] -> [Text] -> Maybe Text
+lookupLang (w:ws) tags
+    | Text.null w = lookupLang ws tags
+    | otherwise   = case cimatches w tags of
+                        (t:_) -> Just t
+                        []    -> lookupLang (reduce w:ws) tags
+ where
+    reduce w = Text.concat $ reverse nopriv
+        where
+            rparts = reverse . init $ Text.groupBy (\_ c -> c/='-') w
+            nopriv = dropWhile ispriv rparts
+            ispriv t = Text.length t == 2 && Text.head t == '-'
+
+lookupLang [] tags | "" `elem` tags = Just ""
+                   | otherwise      = listToMaybe $ tags
+
+
+messageText :: Stanza -> IO Text
+messageText msg = do
+    pref <- getPreferedLang
+    let m = msgLangMap (stanzaType msg)
+        key = lookupLang [pref] (map fst m)
+        choice = do
+            k <- key
+            lookup k m
+    flip (maybe $ return "") choice $ \choice -> do
+    let subj = fmap ("Subject: " <>) $ msgSubject choice
+        ts = catMaybes [subj, msgBody choice]
+    return $ Text.intercalate "\n\n" ts
+
+crlf :: Text -> Text
+crlf t = Text.unlines $ map cr (Text.lines t)
+ where
+    cr t | Text.last t == '\r'  = t
+         | otherwise            = t <> "\r"
+
+deliverTerminalMessage ::
+    forall t t1. t -> Text -> t1 -> Stanza -> IO Bool
+deliverTerminalMessage cw tty utmp msg = do
+    mode <- fmap fileMode (getFileStatus $ Text.unpack tty)
+    let mesgy = mode .&. 0o020 /= 0 -- verify mode g+w
+    if not mesgy then return False else do
+    text <- do
+        t <- messageText msg
+        return $ Text.unpack
+            $ case stanzaFrom msg of
+                Just from -> "\r\n" <> from <> " says...\r\n" <> crlf t <> "\r\n"
+                Nothing -> crlf t <> "\r\n"
+    writeFile (Text.unpack tty) text
+    return True -- return True if a message was delivered
+
+main = do
+    args <- getArgs
+    let mas = (,) <$> listToMaybe args <*> listToMaybe (drop 1 args)
+    flip (maybe $ putStrLn "pwrite user tty") mas $ \(usr,tty) -> do
+    bod <- Text.getContents
+    stanza <- makeMessage "jabber:client" "nobody" (Text.pack usr) bod
+    b <- deliverTerminalMessage () (Text.pack tty) () stanza
+    when b $ putStrLn "delivered."
+    return ()
diff --git a/simplechat.hs b/simplechat.hs
new file mode 100644
index 00000000..bf592db3
--- /dev/null
+++ b/simplechat.hs
@@ -0,0 +1,66 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+import Data.HList.TypeEqGeneric1()
+import Data.HList.TypeCastGeneric1()
+import ByteStringOperators
+
+import Data.ByteString.Lazy.Char8 as L 
+    ( ByteString
+    , hPutStrLn
+    , init )
+import System.IO 
+    ( Handle
+    )
+import Control.Concurrent (forkIO)
+import Control.Concurrent.Chan
+import Data.HList
+
+import Server
+
+
+startCon socket st  = do
+    let chan = hOccursFst st
+        nr = hOccursFst st :: ConnId
+        hdl = hOccursFst st :: Handle
+        quit = writeChan chan (nr,Nothing)
+        broadcast msg = writeChan chan (nr,Just msg)
+    chan' <- dupChan chan
+    reader <- forkIO $ fix $ \loop -> do
+        (nr', line) <- readChan chan'
+        case ( line, nr==nr') of
+          ( Nothing   , True  ) -> Prelude.putStrLn "quit-client."
+          ( Just msg  , False ) -> hPutStrLn hdl msg >> loop
+          _                     -> loop
+
+    hPutStrLn hdl "Hi, what's your name?"
+    line <- getPacket hdl
+    let name = L.init line
+    Prelude.putStrLn $ "readFst: " ++ show line
+    hPutStrLn hdl ("Welcome, " <++> name <++> "!")
+    broadcast ("--> " <++> name <++> " entered.")
+
+    return (name .*. ConnectionFinalizer quit .*. st)
+
+doCon st bs cont = do
+    let hdl = hOccursFst st :: Handle 
+        nr = hOccursFst st :: ConnId
+        chan = hOccursFst st
+        broadcast msg = writeChan chan (nr,Just msg)
+        name = hHead st
+    Prelude.putStrLn $ "read: " ++ show bs
+    case bs of
+     "quit\n" -> hPutStrLn hdl "Bye!"
+     _      -> do
+        broadcast (name <++> ": " <++> L.init bs)
+        cont ()
+
+
+main = do
+    (chan :: Chan (ConnId, Maybe ByteString)) <- newChan
+    doServer (5222 .*. chan .*. HNil)
+             doCon
+             startCon
+    getLine
+
+
diff --git a/stack.yaml b/stack.yaml
new file mode 100644
index 00000000..e2280624
--- /dev/null
+++ b/stack.yaml
@@ -0,0 +1,35 @@
+# This file was automatically generated by stack init
+# For more information, see: http://docs.haskellstack.org/en/stable/yaml_configuration.html
+
+# Specifies the GHC version and set of packages available (e.g., lts-3.5, nightly-2015-09-21, ghc-7.10.2)
+resolver: lts-5.4
+
+# Local packages, usually specified by relative directory name
+packages:
+- '.'
+# Packages to be pulled from upstream that are not in the resolver (e.g., acme-missiles-0.3)
+extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+flags: {}
+
+# Extra package databases containing global packages
+extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: >= 1.0.0
+
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor
diff --git a/t b/t
new file mode 100755
index 00000000..22b21361
--- /dev/null
+++ b/t
@@ -0,0 +1,14 @@
+#!/bin/bash
+args="-threaded -fwarn-unused-imports -rtsopts -DRENDERFLUSH -optP-include -optPdist/build/autogen/cabal_macros.h"
+
+root=${0%/*}
+cd "$root"
+
+me=${0##*/}
+me=${me%.*}
+ghc                                  \
+    -hidir build/$me -odir build/$me \
+    -iPresence                       \
+    $args                            \
+    Presence/monitortty.c            \
+    "$@"
diff --git a/test-server.hs b/test-server.hs
new file mode 100644
index 00000000..795a8190
--- /dev/null
+++ b/test-server.hs
@@ -0,0 +1,541 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Main where
+
+import Debug.Trace
+import Control.Exception (evaluate) -- ,handle,SomeException(..),bracketOnError)
+import Control.Exception ({-evaluate,-}handle,SomeException(..),bracketOnError,ErrorCall(..))
+import System.IO.Error (ioeGetErrorType)
+import Server
+import Control.Monad
+import Control.Monad.Trans.Resource
+import Control.Monad.IO.Class
+import Control.Monad.STM
+import Control.Monad.Fix
+import Control.Concurrent (threadDelay,forkOS,forkIO)
+import Control.Concurrent.STM.TMVar
+import Control.Concurrent.STM.TChan
+import Network.Socket
+import System.Process.Internals
+import System.Process
+import Data.Char
+import System.IO hiding (isEOF)
+import System.Posix.Signals hiding (Ignore)
+
+
+makeGots sv = do
+    let chan = serverEvent sv
+    gotchan <- atomically $ dupTChan chan
+    forkIO $ do
+        fix $ \loop -> do
+        (k,e) <- atomically $ readTChan chan
+        case e of
+            Connection pingflag read write -> todo
+            EOF -> todo   
+        loop
+    return gotchan
+
+isConnection (_,Connection {}) = True
+isConnection _              = False
+isPending want (_,HalfConnection got) | got/=want = True
+isPending _ _                                     = False
+isRead str (_,Got r) | r==str = True
+isRead _   _                  = False
+isEOF (_,EOF) = True
+isEOF _       = False
+
+-- localhost port = SockAddrInet port 127
+localhost port = SockAddrInet6 port 0 (0,0,0,1) 0
+
+withServer f = runResourceT $ do
+    sv <- server
+    result <- liftIO $ f sv
+    release (serverReleaseKey sv)
+    return result
+
+writeToPort port str = do
+    s <- readProcess "/usr/bin/socat" ["-","TCP6:localhost:"++show port] str
+    reverse s `seq` return ()
+
+connectToPort port = do
+    (inp,outp,err,p) <-
+        runInteractiveProcess "/usr/bin/socat" 
+                              ["-","TCP6:localhost:"++show port]
+                              Nothing
+                              Nothing 
+    hSetBuffering inp NoBuffering
+    hSetBuffering outp NoBuffering
+    hSetBuffering err NoBuffering
+    forkOS $ do putStrLn $ "SOCAT-ConnectToPort:"++show (port,(inp,outp,err))
+                hGetContents err >>= putStrLn
+    return (inp,outp,err,p)
+
+listenOnPort port = do
+    putStrLn $ "socat - TCP6-LISTEN:"++show port++",fork"
+    (inp,outp,err,p) <-
+        runInteractiveProcess "/usr/bin/socat" 
+                              ["-","TCP6-LISTEN:"++show port++",fork"]
+                              Nothing
+                              Nothing 
+    hSetBuffering inp NoBuffering
+    hSetBuffering outp NoBuffering
+    hSetBuffering err NoBuffering
+    forkOS $ do { putStrLn "SOCAT-listenOnPort:"; hGetContents err >>= putStrLn }
+    -- forkOS $ do { putStrLn "SOCAT-listenOnPort:"; hGetContents outp >>= putStrLn }
+    return (inp,outp,err,p)
+
+stopListening (inp,outp,err,p) = do
+    {-
+    forkOS $ do
+        o <- hGetContents outp
+        void $ evaluate (length o)
+    forkOS $ do
+        e <- hGetContents err
+        void $ evaluate (length e)
+    threadDelay 1000000
+    hClose inp
+    threadDelay 1000000
+    forkOS $ do
+        threadDelay 100000
+        mapM_ hClose [outp,err]
+    -}
+    withProcessHandle p $ \p -> do
+        case p of
+            OpenHandle pid -> trace ("interrupting: "++show pid)
+                                $ signalProcess sigINT pid
+            _ -> return ()
+        return (p,())
+    {-
+    threadDelay 500000
+    terminateProcess p
+    -}
+    e <- waitForProcess p
+    putStrLn $ "SOCAT-LISTEN exit: "++show e
+
+
+
+chanContents ch = do
+        x  <- atomically $ do
+            bempty <- isEmptyTChan ch
+            if bempty
+                then return Nothing
+                else fmap Just $ readTChan ch
+        maybe (return [])
+              (\x -> do
+                xs <- chanContents ch
+                return (x:xs))
+              x
+
+control sv = atomically . putTMVar (serverCommand sv)
+
+testListen = do
+    let send con str = do hPutStr con str
+                          hFlush con
+                          threadDelay 100000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server SockAddr
+            events = serverEvent sv
+            params :: ConnectionParameters SockAddr
+            params = connectionDefaults (return . snd)
+        control sv (Listen 39242 params)
+        h1@(con1,con2,_,_)<- connectToPort 39242
+        send con1 "Joe was here"
+        control sv (Ignore 39242)
+        threadDelay 500000
+        stopListening h1
+        threadDelay 500000
+        return events
+    e <- chanContents events
+    putStrLn $ "testListen: "++ show e
+    return $
+        and [ length e == 3
+            , isConnection $ e !! 0
+            , isRead "Joe was here" $ e !! 1
+            , isEOF $ e !! 2 
+            ]
+
+
+testReplace = do
+    let send con str = do hPutStrLn con str
+                          hFlush con
+                          threadDelay 100000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = connectionDefaults (const $ return ())
+        control sv (Listen 39242 params)
+        h1@(con1,_,_,_)<- connectToPort 39242
+        send con1 "Joe was here"
+        h2@(con2,_,_,_) <- connectToPort 39242
+        send con2 "Jim also"
+        send con1 "What?"
+        threadDelay 500000
+        stopListening h1 -- misnomer
+        stopListening h2 -- misnomer
+        threadDelay 500000
+        return events
+    e <- chanContents events
+    -- [([::ffff:127.0.0.1]:43722,Connection)
+    -- ,([::ffff:127.0.0.1]:43722,Got "Joe was here\n")
+    -- ,([::ffff:127.0.0.1]:43723,Connection)
+    -- ,([::ffff:127.0.0.1]:43723,Got "Jim also\n")
+    -- ,([::ffff:127.0.0.1]:43722,Got "What?\n")
+    -- ,([::ffff:127.0.0.1,EOF)]:43722
+    -- ,([::ffff:127.0.0.1,EOF)]:43723]
+    -- putStrLn $ show e
+    putStrLn $ "testReplace: "++ show e
+    return $  case e of
+                [(_,Connection {})
+                 ,(_,Got "Joe was here\n")
+                 ,(_,EOF)
+                 ,(_,Connection {})
+                 ,(_,Got "Jim also\n")
+                 ,(_,EOF)] 
+                  -> True
+                _ -> False
+
+testPendingOut = do
+    let send con str = do hPutStr con str
+                          hFlush con
+                          threadDelay 100000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server SockAddr
+            events = serverEvent sv
+            params :: ConnectionParameters SockAddr
+            params = (connectionDefaults (return . snd))
+                     { duplex = False }
+        control sv (Listen 39249 params)
+        h1@(con1,con2,_,_)<- connectToPort 39249
+        send con1 "Joe was here"
+        stopListening h1
+        threadDelay 500000
+        return events
+
+    e <- chanContents events
+    putStrLn $ "testPendingOut: "++ show e
+    return $
+        and [ length e == 3
+            , isPending Out $ e !! 0
+            , isRead "Joe was here" $ e !! 1
+            , isEOF $ e !! 2 
+            ]
+
+testReplacePendingOut = do
+    let send con str = do hPutStrLn con str
+                          hFlush con
+                          threadDelay 100000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { duplex = False }
+        control sv (Ignore 39242)
+        control sv (Listen 39242 params)
+        threadDelay 500000
+        h1@(con1,_,_,_) <- connectToPort 39242
+        send con1 "Joe was here"
+        h2@(con2,_,_,_) <- connectToPort 39242
+        send con2 "Jim also"
+        send con1 "What?"
+        threadDelay 500000
+        control sv (Ignore 39242)
+        threadDelay 500000
+        stopListening h1 -- misnomer
+        stopListening h2 -- misnomer
+        threadDelay 500000
+        return events
+    e <- chanContents events
+    putStrLn $ "testReplacePendingOut: "++ show e
+    return $  case e of
+                [ (_,HalfConnection In)
+                 ,(_,Got "Joe was here\n")
+                 ,(_,EOF)
+                 ,(_,HalfConnection In)
+                 ,(_,Got "Jim also\n")
+                 ,(_,EOF)] 
+                  -> True
+                _ -> False
+
+testReplacePendingIn = do
+    let send con str = do hPutStrLn con str
+                          hFlush con
+                          threadDelay 100000
+    (events,socat) <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { duplex = False }
+        threadDelay 500000
+        socat <- listenOnPort 39242
+        threadDelay 500000
+        control sv (Connect (localhost 39242) params)
+        control sv (Connect (localhost 39242) params)
+        return (events,socat)
+    threadDelay 500000
+    stopListening socat
+    threadDelay 500000
+    e <- chanContents events
+    putStrLn $ "testReplacePendingIn: "++ show e
+    return $ e==[((),HalfConnection Out)
+                ,((),EOF)
+                ,((),HalfConnection Out)
+                ,((),EOF)]
+
+testPromotePendingOut = do
+    putStrLn "----------- testPromotePendingOut"
+    hFlush stdout
+    let send con str = do hPutStr con str
+                          hFlush con
+                          threadDelay 100000
+    (events,s,socat) <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { duplex = False }
+        control sv (Ignore 39244)
+        threadDelay 500000
+        control sv (Listen 39244 params)
+        socat <- listenOnPort 39243
+        h@(con1,con2,_,_) <- connectToPort 39244
+        putStrLn $ "connected to 39244, Sending Joe was here"
+        send con1 "Joe was here"
+        threadDelay 500000
+        putStrLn $ "Connecting to 39243"
+        control sv (Connect (localhost 39243) params)
+        threadDelay 500000
+        putStrLn $ "probably connected to 39243"
+        control sv (Send () "and jim")
+        putStrLn $ "connected to 39244, Sending Joe was here twice"
+        hFlush stdout
+        send con1 "Joe was here twice"
+        threadDelay 500000
+        s <- fmap (take 7) $ hGetContents ((\(_,x,_,_)->x) socat)
+        last s `seq` threadDelay 500000
+        stopListening h -- misnomer
+        threadDelay 50000
+        return (events,s,socat)
+    stopListening socat
+    threadDelay 500000
+    e <- chanContents events
+    putStrLn $ "testPromotePendingOut: "++ show (s,e)
+    -- testPromotePendingOut: ("and jim",[HalfConnection () In,((),Got "Joe was here"),((),Read () "Joe was here twice",((),EOF)]),Connection)
+    --
+    return . and $
+        [ s== "and jim"
+        , e== [ ((),HalfConnection In)
+              , ((),Got "Joe was here")
+              , ((),Connection {})
+              , ((),Got "Joe was here twice")
+              , ((),EOF) ]
+        ]
+
+testPromotePendingIn = do
+    putStrLn "----------- testPromotePendingIn"
+    hFlush stdout
+    let send con str = do handle (\e -> putStrLn . show $ ioeGetErrorType e) $ do
+                            hPutStrLn con str
+                            hFlush con
+                            threadDelay 500000
+    (events,socat,s) <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { duplex = False }
+
+        -- Outgoing connection
+        socat <- listenOnPort 39248
+        threadDelay 500000
+        putStrLn $ "Connecting to 39248..."
+        control sv (Connect (localhost 39248) params)
+        threadDelay 1000000
+        putStrLn $ "...probably connected to 39248"
+        control sv (Send () "and jim")
+        threadDelay 1000000
+
+        s <- fmap (take 7) $ hGetContents ((\(_,x,_,_)->x) socat)
+        length s `seq` threadDelay 500000
+
+        control sv (Listen 39247 params)
+        threadDelay 500000
+        h@(con1,con2,_,_) <- connectToPort 39247
+        send con1 "howdy!"
+        h2@(con1',con2',_,_) <- connectToPort 39247
+        threadDelay 500000
+        send con1' "what?"
+        threadDelay 1000000
+        hClose con1
+        hClose con1'
+        threadDelay 1000000
+        stopListening socat
+        threadDelay 1000000
+
+        return (events,socat,s)
+    e <- chanContents events
+    putStrLn $ "testPromotePendingIn: "++ show (s,e)
+    -- testPromotePendingIn: ("and jim",[HalfConnection () Out,((),((),Got "howdy!\n"),((),EOF (),HalfConnection () In,Read () "what?\n",EOF (),EOF)]),Connection)
+    -- ("and jim",[HalfConnection () Out,((),((),Got "howdy!\n"),((),HalfConnection () In,Read () "what?\n",EOF (),EOF)]),Connection)
+    return . and $
+        [ s == "and jim"
+        , e == [ ((),HalfConnection Out)
+                ,((),Connection {})
+                ,((),Got "howdy!\n")
+                ,((),EOF)
+                ,((),HalfConnection In)
+                ,((),Got "what?\n")
+                ,((),EOF)]
+        ]
+
+testPing = do
+    putStrLn "----------- testPing"
+    let send con str = do handle (\e -> putStrLn . show $ ioeGetErrorType e) $ do
+                            hPutStrLn con str
+                            hFlush con
+                            threadDelay 500000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { pingInterval = 2000
+                     , timeout = 1000 }
+        control sv (Listen 32957 params)
+        threadDelay 500000
+        socat@(h,_,_,_) <- connectToPort 32957
+
+        -- putStrLn $ "sending hey you!"
+        send h "hey you!"
+        -- putStrLn $ "delay"
+        threadDelay 3500000 -- ping timeout
+        -- putStrLn $ "sending what?"
+        send h "what?" -- lost due to timeout
+        -- putStrLn $ "delay-2"
+        threadDelay 500000
+        -- putStrLn $ "close h"
+        hClose h
+
+        threadDelay 500000
+        socat@(h,_,_,_) <- connectToPort 32957
+        send h "try 2: hey you!"
+        threadDelay 2500000 -- ping warning
+        send h "try 2: what?"
+        threadDelay 1000000 -- no warning or timeout
+        send h "try 2: yes."
+        stopListening socat
+        threadDelay 1000000
+        return events
+    
+    e <- chanContents events
+    putStrLn $ "testPing: "++show e
+    -- testPing: [((),Connection <STM action> <IO action> <function>)
+{-
+,((),Got "hey you!\n")
+,((),RequiresPing)
+,((),RequiresPing)
+,((),Got "what?\n")
+,((),EOF)
+,((),Connection <STM action> <IO action> <function>)
+,((),Got "try 2: hey you!\n")
+,((),RequiresPing)
+,((),Got "try 2: what?\n")
+,((),Got "try 2: yes.\n")
+,((),EOF)]
+testPing: [((),Connection <STM action> <IO action> <function>)
+,((),Got "hey you!\n")
+,((),RequiresPing)
+,((),Got "what?\n")
+,((),RequiresPing)
+,((),EOF)
+,((),Connection <STM action> <IO action> <function>)
+,((),Got "try 2: hey you!\n")
+,((),RequiresPing)
+,((),Got "try 2: what?\n")
+,((),RequiresPing)]
+testPing: [((),Connection <STM action> <IO action> <function>)
+,((),Got "hey you!\n")
+,((),RequiresPing)
+,((),Got "what?\n")
+,((),RequiresPing)
+,((),EOF)
+,((),Connection <STM action> <IO action> <function>)
+,((),Got "try 2: hey you!\n")
+,((),RequiresPing)
+,((),Got "try 2: what?\n")
+,((),Got "try 2: yes.\n")
+,((),EOF)]
+
+-}
+
+    return $ e == [((),Connection {})
+                  ,((),Got "hey you!\n")
+                  ,((),RequiresPing)
+                  ,((),EOF)
+                  ,((),Connection {})
+                  ,((),Got "try 2: hey you!\n")
+                  ,((),RequiresPing)
+                  ,((),Got "try 2: what?\n")
+                  ,((),Got "try 2: yes.\n")
+                  ,((),EOF)]
+
+testDisabledPing = do
+    let send con str = do hPutStrLn con str
+                          hFlush con
+                          threadDelay 500000
+    events <- withServer $ \sv -> do
+        let _ = sv :: Server ()
+            events = serverEvent sv
+            params = (connectionDefaults (const $ return ()))
+                     { pingInterval = 0 
+                     , timeout = 0 }
+        control sv (Listen 32958 params)
+        threadDelay 500000
+        socat@(h,_,_,_) <- connectToPort 32958
+
+        send h "hey you!"
+        threadDelay 3500000 -- ping timeout
+        send h "what?" -- lost due to timeout
+        threadDelay 500000
+        hClose h
+
+        threadDelay 500000
+        socat@(h,_,_,_) <- connectToPort 32958
+        send h "try 2: hey you!"
+        threadDelay 2500000 -- ping warning
+        send h "try 2: what?"
+        threadDelay 1000000 -- no warning or timeout
+        send h "try 2: yes."
+        stopListening socat
+        threadDelay 5000000
+        return events
+    
+    e <- chanContents events
+    putStrLn $ "testDisabledPing: "++show e
+    return $ e == [((),Connection {})
+                  ,((),Got "hey you!\n")
+                  ,((),Got "what?\n")
+                  ,((),EOF)
+                  ,((),Connection {})
+                  ,((),Got "try 2: hey you!\n")
+                  ,((),Got "try 2: what?\n")
+                  ,((),Got "try 2: yes.\n")
+                  ,((),EOF)]
+main = do
+    result1 <- testListen
+    result2 <- testReplace
+    result3 <- testPendingOut
+    result4 <- testReplacePendingOut
+    threadDelay 100000
+    result5 <- testReplacePendingIn
+    result6 <- testPromotePendingOut
+    result7 <- testPromotePendingIn
+    result8 <- testPing
+    result9 <- testDisabledPing
+    let passOrFail str True  = putStrLn $ str ++ ": passed"
+        passOrFail str False = putStrLn $ str ++ ": failed"
+    passOrFail "testListen" result1
+    passOrFail "testReplace" result2
+    passOrFail "testPendingOut" result3
+    passOrFail "testReplacePendingOut" result4
+    passOrFail "testReplacePendingIn" result5
+    passOrFail "testPromotePendingOut" result6
+    passOrFail "testPromotePendingIn" result7
+    passOrFail "testPing" result8
+    passOrFail "testDisabledPing" result9
+    return ()
diff --git a/whosocket.hs b/whosocket.hs
new file mode 100644
index 00000000..f84e3178
--- /dev/null
+++ b/whosocket.hs
@@ -0,0 +1,60 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TupleSections     #-}
+module Main where
+
+import LocalPeerCred
+import ControlMaybe
+import UTmp
+import ByteStringOperators
+
+import System.Directory
+import Data.Char
+import System.Posix.Types
+import System.Posix.Files
+import qualified Data.ByteString.Lazy.Char8 as L 
+    ( unpack
+    , pack
+    , take
+    , putStrLn
+    )
+import Data.List (groupBy)
+import Data.Maybe (listToMaybe,mapMaybe,catMaybes)
+
+import Network.Socket
+import System.Environment
+import Control.Arrow (first)
+import System.Endian
+
+usage = do
+    putStrLn $ "whosocket numeric-address port"
+
+main = do
+    args <- getArgs
+    case (args??0,args??1) of
+        (Just addr_str,Just port_str) -> whosocket addr_str port_str
+        _                             -> usage
+
+whosocket :: HostName -> ServiceName -> IO ()
+whosocket addr_str port_str = do
+    info <- getAddrInfo (Just $ defaultHints { addrFlags = [ AI_NUMERICHOST ] }) 
+                        (Just addr_str) 
+                        (Just port_str)
+    let addr = head $ map addrAddress info
+    r <- getLocalPeerCred' addr
+    putStrLn $ "r{"++show addr++"} = " ++ show r
+
+    us <- UTmp.users
+    let filterTTYs (_,tty,pid) = 
+            if L.take 3 tty == "tty"
+              then Just (tty,pid)
+              else Nothing
+        tty_pids = mapMaybe filterTTYs us
+
+    tty <- maybe (return Nothing)
+                 (fmap fst . uncurry (identifyTTY tty_pids))
+                 r
+    putStrLn $ "uid = " ++ show (fmap fst r)
+    L.putStrLn $ "tty = " <++?> tty
+
+    return ()
+
diff --git a/xmppServer.hs b/xmppServer.hs
new file mode 100644
index 00000000..b0a53e8b
--- /dev/null
+++ b/xmppServer.hs
@@ -0,0 +1,47 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE LambdaCase #-}
+import Control.Concurrent
+import Control.Concurrent.STM
+import Control.Monad.Fix
+import Control.Monad.IO.Class
+import Control.Monad.Trans.Resource (runResourceT)
+import Data.Monoid
+import System.Environment
+import System.Posix.Signals
+
+import ConsoleWriter
+import Presence
+import XMPPServer
+
+main :: IO ()
+main = runResourceT $ do
+    args <- liftIO getArgs
+    let verbosity = getSum $ flip foldMap args $ \case
+            ('-':xs) -> Sum $ length (filter (=='-') xs)
+            _        -> mempty
+    cw    <- liftIO newConsoleWriter
+    state <- liftIO $ newPresenceState cw
+    sv    <- xmppServer (presenceHooks state verbosity)
+    liftIO $ do
+    atomically $ putTMVar (server state) sv
+
+    quitVar <- newEmptyTMVarIO
+    installHandler sigTERM (CatchOnce (atomically $ putTMVar quitVar True)) Nothing
+    installHandler sigINT (CatchOnce (atomically $ putTMVar quitVar True)) Nothing
+
+    forkIO $ do
+        let console = cwPresenceChan $ consoleWriter state
+        fix $ \loop -> do
+        what <- atomically
+            $ orElse (do (client,stanza) <- takeTMVar console
+                         return $ do informClientPresence0 state Nothing client stanza
+                                     loop)
+                     (do readTMVar quitVar
+                         return $ return ())
+        what
+
+    quitMessage <- atomically $ takeTMVar quitVar
+
+    putStrLn "goodbye."
+    return ()