path: root/dht/src/Network/BitTorrent/MainlineDHT.hs

{-# LANGUAGE CPP                        #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE DeriveFoldable             #-}
{-# LANGUAGE DeriveFunctor              #-}
{-# LANGUAGE DeriveTraversable          #-}
{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE NamedFieldPuns             #-}
{-# LANGUAGE PatternSynonyms            #-}
{-# LANGUAGE StandaloneDeriving         #-}
{-# LANGUAGE TupleSections              #-}
module Network.BitTorrent.MainlineDHT where

import Control.Applicative
import Control.Arrow
import Control.Concurrent.STM
import Control.Monad
import Crypto.Random
import Data.BEncode                           as BE
import qualified Data.BEncode.BDict           as BE
         ;import Data.BEncode.BDict           (BKey)
import Data.BEncode.Pretty
import Data.BEncode.Types                     (BDict)
import Data.Bits
import Data.Bits.ByteString                   ()
import Data.Bool
import Data.ByteArray                         (ByteArrayAccess)
import qualified Data.ByteString              as B
         ;import Data.ByteString              (ByteString)
import qualified Data.ByteString.Base16       as Base16
import qualified Data.ByteString.Char8        as C8
import Data.ByteString.Lazy                   (toStrict)
import qualified Data.ByteString.Lazy.Char8   as L8
import Data.Char
import Data.Coerce
import Data.Data
import Data.Default
import Data.Digest.CRC32C
import Data.Function                          (fix)
import Data.Hashable
#if MIN_VERSION_iproute(1,7,4)
import Data.IP hiding ( fromSockAddr
#if MIN_VERSION_iproute(1,7,8)
                      , toSockAddr
#endif
                      )
#else
import Data.IP
#endif
import Data.Maybe
import Data.Monoid
import Data.Ord
import qualified Data.Serialize               as S
import Data.Set                               (Set)
import Data.Time.Clock.POSIX                  (POSIXTime, getPOSIXTime)
import Data.Torrent
import Data.Word
import qualified Data.Wrapper.PSQInt          as Int
import Debug.Trace
import Network.BitTorrent.MainlineDHT.Symbols
import Network.Kademlia
import Network.Kademlia.Bootstrap
import Network.Address                        (fromSockAddr,
                                               setPort, sockAddrPort, testIdBit,
                                               toSockAddr, genBucketSample', WantIP(..),
                                               un4map,either4or6,ipFamily)
import Network.BitTorrent.DHT.ContactInfo     as Peers
import Network.Kademlia.Search          (Search (..))
import Network.BitTorrent.DHT.Token           as Token
import qualified Network.Kademlia.Routing          as R
         ;import Network.Kademlia.Routing          (getTimestamp)
import Network.QueryResponse                  as QR
import Network.Socket
import System.IO.Error
import System.IO.Unsafe                       (unsafeInterleaveIO)
import qualified Text.ParserCombinators.ReadP as RP
#ifdef THREAD_DEBUG
import Control.Concurrent.Lifted.Instrument
#else
import Control.Concurrent.Lifted
import GHC.Conc                  (labelThread)
#endif
import qualified Data.Aeson as JSON
         ;import Data.Aeson (FromJSON, ToJSON, (.=))
import Text.Read
import System.Global6
import Control.TriadCommittee
import Data.TableMethods
import DPut
import DebugTag

newtype NodeId = NodeId ByteString
 deriving (Eq,Ord,ByteArrayAccess, Bits, Hashable)

instance BEncode NodeId where
    fromBEncode bval = do
        bs <- fromBEncode bval
        if B.length bs /= 20
            then Left "Invalid length node id."
            else Right $ NodeId bs

    toBEncode (NodeId bs) = toBEncode bs

instance Show NodeId where
    show (NodeId bs) = C8.unpack $ Base16.encode bs

instance S.Serialize NodeId where
    get = NodeId <$> S.getBytes 20
    put (NodeId bs) = S.putByteString bs

instance FiniteBits NodeId where
    finiteBitSize _ = 160

instance Read NodeId where
    readsPrec _ str
        | (bs, xs) <- Base16.decode $ C8.pack str
        , B.length bs == 20
                    = [ (NodeId bs, drop 40 str) ]
        | otherwise = []

zeroID :: NodeId
zeroID = NodeId $ B.replicate 20 0

data NodeInfo = NodeInfo
  { nodeId   :: NodeId
  , nodeIP   :: IP
  , nodePort :: PortNumber
  }
 deriving (Eq,Ord)

instance ToJSON NodeInfo where
    toJSON (NodeInfo nid (IPv4 ip) port)
        = JSON.object [ "node-id" .= show nid
                      , "ipv4" .= show ip
                      , "port" .= (fromIntegral port :: Int)
                      ]
    toJSON (NodeInfo nid (IPv6 ip6) port)
        | Just ip <- un4map ip6
          = JSON.object [ "node-id" .= show nid
                        , "ipv4" .= show ip
                        , "port" .= (fromIntegral port :: Int)
                        ]
        | otherwise
          = JSON.object [ "node-id" .= show nid
                        , "ipv6" .= show ip6
                        , "port" .= (fromIntegral port :: Int)
                        ]
instance FromJSON NodeInfo where
    parseJSON (JSON.Object v) = do
        nidstr <- v JSON..: "node-id"
        ip6str <- v JSON..:? "ipv6"
        ip4str <- v JSON..:? "ipv4"
        portnum <- v JSON..: "port"
        ip <- maybe empty (return . IPv6) (ip6str >>= readMaybe)
              <|> maybe empty (return . IPv4) (ip4str >>= readMaybe)
        let (bs,_) = Base16.decode (C8.pack nidstr)
        guard (B.length bs == 20)
        return $ NodeInfo (NodeId bs) ip (fromIntegral (portnum :: Word16))

hexdigit :: Char -> Bool
hexdigit c = ('0' <= c && c <= '9') || ( 'a' <= c && c <= 'f') || ( 'A' <= c && c <= 'F')

instance Read NodeInfo where
  readsPrec i = RP.readP_to_S $ do
    RP.skipSpaces
    let n = 40 -- characters in node id.
        parseAddr = RP.between (RP.char '(') (RP.char ')') (RP.munch (/=')'))
                      RP.+++ RP.munch (not . isSpace)
        nodeidAt = do hexhash <- sequence $ replicate n (RP.satisfy hexdigit)
                      RP.char '@' RP.+++ RP.satisfy isSpace
                      addrstr <- parseAddr
                      nid <- case Base16.decode $ C8.pack hexhash of
                              (bs,_) | B.length bs==20 -> return (NodeId bs)
                              _                        -> fail "Bad node id."
                      return (nid,addrstr)
    (nid,addrstr) <- ( nodeidAt RP.+++ ( (zeroID,) <$> parseAddr) )
    let raddr = do
            ip <- RP.between (RP.char '[') (RP.char ']')
                         (IPv6 <$> RP.readS_to_P (readsPrec i))
                  RP.+++ (IPv4 <$> RP.readS_to_P (readsPrec i))
            _    <- RP.char ':'
            port <- toEnum <$> RP.readS_to_P (readsPrec i)
            return (ip, port)

    (ip,port) <- case RP.readP_to_S raddr addrstr of
                    [] -> fail "Bad address."
                    ((ip,port),_):_ -> return (ip,port)
    return $ NodeInfo nid ip port



-- The Hashable instance depends only on the IP address and port number.  It is
-- used to compute the announce token.
instance Hashable NodeInfo where
  hashWithSalt s ni = hashWithSalt s (nodeIP ni , nodePort ni)
  {-# INLINE hashWithSalt #-}


instance Show NodeInfo where
    showsPrec _ (NodeInfo nid ip port) =
        shows nid . ('@' :) . showsip . (':' :) . shows port
     where
        showsip
            | IPv4 ip4 <- ip                          = shows ip4
            | IPv6 ip6 <- ip , Just ip4 <- un4map ip6 = shows ip4
            | otherwise                               = ('[' :) . shows ip . (']' :)

{-

-- | KRPC 'compact list' compatible encoding: contact information for
-- nodes is encoded as a 26-byte string. Also known as "Compact node
-- info" the 20-byte Node ID in network byte order has the compact
-- IP-address/port info concatenated to the end.
  get = NodeInfo <$> (NodeId <$> S.getBytes 20 ) <*> S.get <*> S.get
-}

getNodeInfo4 :: S.Get NodeInfo
getNodeInfo4 = NodeInfo <$> (NodeId <$> S.getBytes 20)
                        <*> (IPv4 <$> S.get)
                        <*> S.get

putNodeInfo4 :: NodeInfo -> S.Put
putNodeInfo4 (NodeInfo (NodeId nid) ip port)
    | IPv4 ip4 <- ip                          = put4 ip4
    | IPv6 ip6 <- ip , Just ip4 <- un4map ip6 = put4 ip4
    | otherwise                               = return ()
 where
    put4 ip4 = S.putByteString nid >> S.put ip4 >> S.put port

getNodeInfo6 :: S.Get NodeInfo
getNodeInfo6 = NodeInfo <$> (NodeId <$> S.getBytes 20)
                        <*> (IPv6 <$> S.get)
                        <*> S.get

putNodeInfo6 :: NodeInfo -> S.Put
putNodeInfo6 (NodeInfo (NodeId nid) (IPv6 ip) port)
               = S.putByteString nid >> S.put ip >> S.put port
putNodeInfo6 _ = return ()


-- | TODO: This should depend on the bind address to support IPv4-only. For
-- now, in order to support dual-stack listen, we're going to assume IPv6 is
-- wanted and map IPv4 addresses accordingly.
nodeAddr :: NodeInfo -> SockAddr
nodeAddr (NodeInfo _ ip port) =
    case ip of
        IPv4 ip4 -> setPort port $ toSockAddr (ipv4ToIPv6 ip4)
        IPv6 ip6 -> setPort port $ toSockAddr ip6

nodeInfo :: NodeId -> SockAddr -> Either String NodeInfo
nodeInfo nid saddr
    | Just ip <- fromSockAddr saddr
    , Just port <- sockAddrPort saddr = Right $ NodeInfo nid ip port
    | otherwise                       = Left "Address family not supported."

-- | Types of RPC errors.
data ErrorCode
    -- | Some error doesn't fit in any other category.
  = GenericError

    -- | Occurs when server fail to process procedure call.
  | ServerError

    -- | Malformed packet, invalid arguments or bad token.
  | ProtocolError

    -- | Occurs when client trying to call method server don't know.
  | MethodUnknown
    deriving (Show, Read, Eq, Ord, Bounded, Typeable, Data)

-- | According to the table:
-- <http://bittorrent.org/beps/bep_0005.html#errors>
instance Enum ErrorCode where
  fromEnum GenericError  = 201
  fromEnum ServerError   = 202
  fromEnum ProtocolError = 203
  fromEnum MethodUnknown = 204
  {-# INLINE fromEnum #-}
  toEnum 201 = GenericError
  toEnum 202 = ServerError
  toEnum 203 = ProtocolError
  toEnum 204 = MethodUnknown
  toEnum _   = GenericError
  {-# INLINE toEnum #-}

instance BEncode ErrorCode where
  toBEncode = toBEncode . fromEnum
  {-# INLINE toBEncode #-}
  fromBEncode b = toEnum <$> fromBEncode b
  {-# INLINE fromBEncode #-}

data Error = Error
    { errorCode    :: !ErrorCode  -- ^ The type of error.
    , errorMessage :: !ByteString -- ^ Human-readable text message.
    } deriving ( Show, Eq, Ord, Typeable, Data, Read )

newtype TransactionId = TransactionId ByteString
 deriving (Eq, Ord, Show, BEncode)

newtype Method = Method ByteString
 deriving (Eq, Ord, Show, BEncode)

data Message a = Q { msgOrigin   :: NodeId
                   , msgID       :: TransactionId
                   , qryPayload  :: a
                   , qryMethod   :: Method
                   , qryReadOnly :: Bool }

               | R { msgOrigin      :: NodeId
                   , msgID          :: TransactionId
                   , rspPayload     :: Either Error a
                   , rspReflectedIP :: Maybe SockAddr }

showBE :: BValue -> String
showBE bval = L8.unpack (showBEncode bval)

instance BE.BEncode (Message BValue) where
    toBEncode m = encodeMessage m
                  {-
                  in case m of
                        Q {} -> trace ("encoded(query): "++showBE r) r
                        R {} -> trace ("encoded(response): "++showBE r) r -}
    fromBEncode bval = decodeMessage bval
                       {-
                       in case r of
                            Left e -> trace (show e) r
                            Right (Q {}) -> trace ("decoded(query): "++showBE bval) r
                            Right (R {}) -> trace ("decoded(response): "++showBE bval) r -}

decodeMessage :: BValue -> Either String (Message BValue)
decodeMessage = fromDict $ do
    key <- lookAhead (field (req "y"))
    let _ = key :: BKey
    f <- case key of
        "q" -> do a <- field (req "a")
                  g <- either fail return $ flip fromDict a $ do
                    who <- field (req "id")
                    ro  <- fromMaybe False <$> optional (field (req "ro"))
                    return $ \meth tid -> Q who tid a meth ro
                  meth <- field (req "q")
                  return $ g meth
        "r" -> do ip <- do
                        ipstr <- optional (field (req "ip"))
                        mapM (either fail return . decodeAddr) ipstr
                  vals <- field (req "r")
                  either fail return $ flip fromDict vals $ do
                    who <- field (req "id")
                    return $ \tid -> R who tid (Right vals) ip
        "e" -> do (ecode,emsg) <- field (req "e")
                  ip <- do
                        ipstr <- optional (field (req "ip"))
                        mapM (either fail return . decodeAddr) ipstr
                  -- FIXME:Spec does not give us the NodeId of the sender.
                  --       Using 'zeroID' as place holder.
                  --       We should ignore the msgOrigin for errors in 'updateRouting'.
                  --       We should consider making msgOrigin a Maybe value.
                  return $ \tid -> R zeroID tid (Left (Error ecode emsg)) ip
        _   -> fail $ "Mainline message is not a query, response, or an error: "
                        ++ show key
    tid <- field (req "t")
    return $ f (tid :: TransactionId)


encodeMessage :: Message BValue -> BValue
encodeMessage (Q origin tid a meth ro)
    = case a of
        BDict args -> encodeQuery tid meth (BDict $ genericArgs origin ro `BE.union` args)
        _          -> encodeQuery tid meth a -- XXX: Not really a valid query.
encodeMessage (R origin tid v ip)
    = case v of
        Right (BDict vals) -> encodeResponse tid (BDict $ genericArgs origin False `BE.union` vals) ip
        Left  err          -> encodeError tid err


encodeAddr :: SockAddr -> ByteString
encodeAddr = either encode4 encode6 . either4or6
 where
    encode4 (SockAddrInet port addr)
              = S.runPut (S.putWord32host addr >> S.putWord16be (fromIntegral port))

    encode6 (SockAddrInet6 port _ addr _)
              = S.runPut (S.put addr >> S.putWord16be (fromIntegral port))
    encode6 _ = B.empty

decodeAddr :: ByteString -> Either String SockAddr
decodeAddr bs = S.runGet g bs
 where
    g | (B.length bs == 6) = flip SockAddrInet <$> S.getWord32host <*> (fromIntegral <$> S.getWord16be)
      | otherwise          = do host <- S.get -- TODO: Is this right?
                                port <- fromIntegral <$> S.getWord16be
                                return $ SockAddrInet6 port 0 host 0

genericArgs :: BEncode a => a -> Bool -> BDict
genericArgs nodeid ro =
       "id" .=! nodeid
    .: "ro" .=? bool Nothing (Just (1 :: Int)) ro
    .: endDict

encodeError :: BEncode a => a -> Error -> BValue
encodeError tid (Error ecode emsg) = encodeAny tid "e" (ecode,emsg) id

encodeResponse :: (BEncode tid, BEncode vals) =>
                  tid -> vals -> Maybe SockAddr -> BValue
encodeResponse tid rvals rip =
    encodeAny tid "r" rvals ("ip" .=? (BString . encodeAddr <$> rip) .:)

encodeQuery :: (BEncode args, BEncode tid, BEncode method) =>
               tid -> method -> args -> BValue
encodeQuery tid qmeth qargs = encodeAny tid "q" qmeth ("a" .=! qargs .:)

encodeAny ::
    (BEncode tid, BEncode a) =>
    tid -> BKey -> a -> (BDict -> BDict) -> BValue
encodeAny tid key val aux = toDict $
    aux $  key .=! val
        .: "t" .=! tid
        .: "y" .=! key
        .: endDict


showPacket :: ([L8.ByteString] -> [L8.ByteString]) -> SockAddr -> L8.ByteString -> ByteString -> String
showPacket f addr flow bs = L8.unpack $ L8.unlines es
 where
    es = map (L8.append prefix) (f $ L8.lines pp)

    prefix = L8.pack (either show show $ either4or6 addr) <> flow

    pp = either L8.pack showBEncode $ BE.decode bs

-- Add detailed printouts for every packet.
addVerbosity :: Transport err SockAddr ByteString -> Transport err SockAddr ByteString
addVerbosity tr =
    tr { awaitMessage = \kont -> awaitMessage tr $ \m -> do
            case m of
                Arrival addr msg -> dput XBitTorrent (showPacket id addr " --> " msg)
                _                -> return ()
            kont m
       , sendMessage = \addr msg -> do
            dput XBitTorrent (showPacket id addr " <-- " msg)
            sendMessage tr addr msg
       }


showParseError :: ByteString -> SockAddr -> String -> String
showParseError bs addr err = showPacket (L8.pack err :) addr " --> " bs

parsePacket :: ByteString -> SockAddr -> Either String (Message BValue, NodeInfo)
parsePacket bs addr = left (showParseError bs addr) $ do
    pkt <- BE.decode bs
    -- TODO: Error packets do not include a valid msgOrigin.
    --       The BE.decode method is using 'zeroID' as a placeholder.
    ni <- nodeInfo (msgOrigin pkt) addr
    return (pkt, ni)

encodePacket :: Message BValue -> NodeInfo -> (ByteString, SockAddr)
encodePacket msg ni = ( toStrict $ BE.encode msg
                      , nodeAddr ni )

classify :: Message BValue -> MessageClass String Method TransactionId NodeInfo (Message BValue)
classify (Q { msgID = tid, qryMethod = meth }) = IsQuery meth tid
classify (R { msgID = tid                   }) = IsResponse tid

encodeResponsePayload :: BEncode a => TransactionId -> NodeInfo -> NodeInfo -> a -> Message BValue
encodeResponsePayload tid self dest b = R (nodeId self) tid (Right $ BE.toBEncode b) (Just $ nodeAddr dest)

encodeQueryPayload :: BEncode a =>
    Method -> Bool -> TransactionId -> NodeInfo -> NodeInfo -> a -> Message BValue
encodeQueryPayload meth isReadonly tid self dest b = Q (nodeId self) tid (BE.toBEncode b) meth isReadonly

errorPayload :: TransactionId -> NodeInfo -> NodeInfo -> Error -> Message a
errorPayload tid self dest e = R (nodeId self) tid (Left e) (Just $ nodeAddr dest)

decodePayload :: BEncode a => Message BValue -> Either String a
decodePayload msg = BE.fromBEncode $ qryPayload msg

type Handler = MethodHandler String TransactionId NodeInfo (Message BValue)

handler :: ( BEncode a
           , BEncode b
           ) =>
           (NodeInfo -> a -> IO b) -> Maybe Handler
handler f = Just $ MethodHandler decodePayload encodeResponsePayload f


handlerE :: ( BEncode a
            , BEncode b
            ) =>
            (NodeInfo -> a -> IO (Either Error b)) -> Maybe Handler
handlerE f = Just $ MethodHandler decodePayload enc f
 where
    enc tid self dest (Left e)  = errorPayload  tid self dest e
    enc tid self dest (Right b) = encodeResponsePayload tid self dest b

type AnnounceSet = Set (InfoHash, PortNumber)

data SwarmsDatabase = SwarmsDatabase
    { contactInfo   :: !( TVar PeerStore     ) -- ^ Published by other nodes.
    , sessionTokens :: !( TVar SessionTokens ) -- ^ Query session IDs.
    , announceInfo  :: !( TVar AnnounceSet   ) -- ^ To publish by this node.
    }

newSwarmsDatabase :: IO SwarmsDatabase
newSwarmsDatabase = do
    toks <- nullSessionTokens
    atomically
        $ SwarmsDatabase <$> newTVar def
                    <*> newTVar toks
                    <*> newTVar def

data Routing = Routing
    { tentativeId :: NodeInfo
    , committee4  :: TriadCommittee NodeId SockAddr
    , committee6  :: TriadCommittee NodeId SockAddr
    , refresher4  :: BucketRefresher NodeId NodeInfo TransactionId
    , refresher6  :: BucketRefresher NodeId NodeInfo TransactionId
    }

sched4 :: Routing -> TVar (Int.PSQ POSIXTime)
sched4 Routing { refresher4 = BucketRefresher { refreshQueue } } = refreshQueue

sched6 :: Routing -> TVar (Int.PSQ POSIXTime)
sched6 Routing { refresher6 = BucketRefresher { refreshQueue } } = refreshQueue

routing4 :: Routing -> TVar (R.BucketList NodeInfo)
routing4 Routing { refresher4 = BucketRefresher { refreshBuckets } } = refreshBuckets

routing6 :: Routing -> TVar (R.BucketList NodeInfo)
routing6 Routing { refresher6 = BucketRefresher { refreshBuckets } } = refreshBuckets

traced :: Show tid => TableMethods t tid -> TableMethods t tid
traced (TableMethods ins del lkup)
            = TableMethods (\tid mvar t -> trace ("insert "++show tid) $ ins tid mvar t)
                           (\tid t -> trace ("del "++show tid) $ del tid t)
                           (\tid t -> trace ("lookup "++show tid) $ lkup tid t)


type MainlineClient = Client String Method TransactionId NodeInfo (Message BValue)

-- | Like 'nodeInfo' but falls back to 'iNADDR_ANY' for nodeIP' and 'nodePort'.
mkNodeInfo :: NodeId -> SockAddr -> NodeInfo
mkNodeInfo nid addr = NodeInfo
    { nodeId   = nid
    , nodeIP   = fromMaybe (toEnum 0) $ fromSockAddr addr
    , nodePort = fromMaybe 0 $ sockAddrPort addr
    }

newClient :: SwarmsDatabase
    -> SockAddr -- ^ Tentative IP address for this node (the bind address is suitable).
    -> Transport String SockAddr ByteString -- ^ UDP transport
    -> IO ( MainlineClient
          , Routing
          , [NodeInfo] -> [NodeInfo] -> IO ()
          , [NodeInfo] -> [NodeInfo] -> IO ()
          , IO ()
          )
newClient swarms addr udp = do
    nid <- NodeId <$> getRandomBytes 20
    let tentative_info = mkNodeInfo nid addr
    tentative_info6 <-
        maybe tentative_info
              (\ip6 -> tentative_info { nodeId = fromMaybe (nodeId tentative_info)
                                                    $ bep42 (toSockAddr ip6) (nodeId tentative_info)
                                      , nodeIP = IPv6 ip6
                                      })
            <$> global6
    addr4 <- atomically $ newTChan
    addr6 <- atomically $ newTChan
    mkrouting <- atomically $ do
        -- We defer initializing the refreshSearch and refreshPing until we
        -- have a client to send queries with.
        let nullPing = const $ return False
        tbl4 <- newTVar $ R.nullTable (comparing nodeId) (\s -> hashWithSalt s . nodeId) tentative_info R.defaultBucketCount
        refresher4 <- newBucketRefresher tbl4 nullSearch nullPing
        tbl6 <- newTVar $ R.nullTable (comparing nodeId) (\s -> hashWithSalt s . nodeId) tentative_info6 R.defaultBucketCount
        refresher6 <- newBucketRefresher tbl6 nullSearch nullPing
        let updateIPVote tblvar addrvar a = do
                bkts <- readTVar tblvar
                case bep42 a (nodeId $ R.thisNode bkts) of
                    Just nid -> do
                        let tbl = R.nullTable (comparing nodeId)
                                              (\s -> hashWithSalt s . nodeId)
                                              (mkNodeInfo nid a)
                                              (R.defaultBucketCount)
                        writeTVar tblvar tbl
                        writeTChan addrvar $ Just (a,map fst $ concat $ R.toList bkts)
                    Nothing -> return ()
        committee4 <- newTriadCommittee $ updateIPVote tbl4 addr4
        committee6 <- newTriadCommittee $ updateIPVote tbl6 addr6
        return $ \client ->
            -- Now we have a client, so tell the BucketRefresher how to search and ping.
            let updIO r = updateRefresherIO (nodeSearch client) (ping client) r
            in Routing tentative_info committee4 committee6 (updIO refresher4) (updIO refresher6)
    map_var <- atomically $ newTVar (0, mempty)

    let routing = mkrouting outgoingClient

        net = onInbound (updateRouting outgoingClient routing)
              $ layerTransport parsePacket encodePacket
              $ udp

        -- Paranoid: It's safe to define /net/ and /client/ to be mutually
        -- recursive since 'updateRouting' does not invoke 'awaitMessage' which
        -- which was modified by 'onInbound'.  However, I'm going to avoid the
        -- mutual reference just to be safe.
        outgoingClient = client { clientNet = net { awaitMessage = pure . ($ Terminated) } }

        dispatch = DispatchMethods
            { classifyInbound = classify -- :: x -> MessageClass err meth tid addr x
            , lookupHandler   = handlers -- :: meth -> Maybe (MethodHandler err tid addr x)
            , tableMethods    = mapT     -- :: TransactionMethods tbl tid x
            }

        handlers :: Method -> Maybe Handler
        handlers ( Method "ping"          ) = handler pingH
        handlers ( Method "find_node"     ) = handler $ findNodeH routing
        handlers ( Method "get_peers"     ) = handler $ getPeersH routing swarms
        handlers ( Method "announce_peer" ) = handlerE $ announceH swarms
        handlers ( Method meth            ) = Just $ defaultHandler meth

        mapT = transactionMethods mapMethods gen

        gen :: Word16 -> (TransactionId, Word16)
        gen cnt = (TransactionId $ S.encode cnt, cnt+1)

        client = Client
            { clientNet           = addHandler (handleMessage client) net
            , clientDispatcher    = dispatch
            , clientErrorReporter = ignoreErrors -- printErrors stderr
            , clientPending       = map_var
            , clientAddress       = \maddr -> atomically $ do
                let var = case flip prefer4or6 Nothing <$> maddr of
                            Just Want_IP6 -> routing6 routing
                            _             -> routing4 routing
                R.thisNode <$> readTVar var
            , clientResponseId    = return
            }

    fork $ fix $ \again -> do
        myThreadId >>= flip labelThread "addr4"
        x <- atomically (readTChan addr4)
        forM_ x $ \(addr, ns) -> do
            dput XBitTorrent $ "External IPv4: "++show (addr, length ns)
            forM_ ns $ \n -> do
                dput XBitTorrent $ "Change IP, ping: "++show n
                ping outgoingClient n
            -- TODO: trigger bootstrap ipv4
            again
    fork $ fix $ \again -> do
        myThreadId >>= flip labelThread "addr6"
        x <- atomically (readTChan addr6)
        forM_ x $ \(addr,ns) -> do
            dput XBitTorrent $ "External IPv6: "++show (addr, length ns)
            forM_ ns $ \n -> do
                dput XBitTorrent $ "Change IP, ping: "++show n
                ping outgoingClient n
            -- TODO: trigger bootstrap ipv6
            again


    refresh_thread4 <- forkPollForRefresh $ refresher4 routing
    refresh_thread6 <- forkPollForRefresh $ refresher6 routing

    gc_peers <- forkAnnouncedInfohashesGC (contactInfo swarms)

    return (client, routing, bootstrap (refresher4 routing), bootstrap (refresher6 routing)
           , do killThread refresh_thread4 -- TODO: Better termination mechanism.
                killThread refresh_thread6 -- TODO: Better termination mechanism.
                atomically $ writeTChan addr4 Nothing -- Terminate "addr4" thread.
                atomically $ writeTChan addr6 Nothing -- Terminate "addr6" thread.
                killThread gc_peers
                )

-- Note that you should call .put() every hour for content that you want to
-- keep alive, since nodes may discard data nodes older than 2 hours. (source:
-- https://www.npmjs.com/package/bittorrent-dht)
--
-- This function will discard records between 3 and 6 hours old.
forkAnnouncedInfohashesGC :: TVar PeerStore -> IO ThreadId
forkAnnouncedInfohashesGC vpeers = fork $ do
    myThreadId >>= flip labelThread "gc:bt-peers"
    fix $ \loop -> do
        cutoff <- getPOSIXTime
        threadDelay 10800000000 -- 3 hours
        atomically $ modifyTVar' vpeers $ deleteOlderThan cutoff
        loop

-- | Modifies a purely random 'NodeId' to one that is related to a given
-- routable address in accordance with BEP 42.
--
-- Test vectors from the spec:
--
-- IP           rand  example node ID
-- ============ ===== ==========================================
-- 124.31.75.21   1   5fbfbf f10c5d6a4ec8a88e4c6ab4c28b95eee4 01
-- 21.75.31.124  86   5a3ce9 c14e7a08645677bbd1cfe7d8f956d532 56
-- 65.23.51.170  22   a5d432 20bc8f112a3d426c84764f8c2a1150e6 16
-- 84.124.73.14  65   1b0321 dd1bb1fe518101ceef99462b947a01ff 41
-- 43.213.53.83  90   e56f6c bf5b7c4be0237986d5243b87aa6d5130 5a
bep42 :: SockAddr -> NodeId -> Maybe NodeId
bep42 addr0 (NodeId r)
 | let addr = either id id $ either4or6 addr0 -- unmap 4mapped SockAddrs
 , Just ip <- fmap S.encode (fromSockAddr addr :: Maybe IPv4)
              <|> fmap S.encode (fromSockAddr addr :: Maybe IPv6)
    = genBucketSample' retr (NodeId $ crc $ applyMask ip) (3,0x07,0)
 | otherwise
    = Nothing
 where
    ip4mask = "\x03\x0f\x3f\xff" :: ByteString
    ip6mask = "\x01\x03\x07\x0f\x1f\x3f\x7f\xff" :: ByteString
    nbhood_select = B.last r .&. 7
    retr n = pure $ B.drop (B.length r - n) r
    crc = S.encode . crc32c . B.pack
    applyMask ip = case B.zipWith (.&.) msk ip of
                    (b:bs) -> (b .|. shiftL nbhood_select 5) : bs
                    bs     -> bs
        where msk | B.length ip == 4  =  ip4mask
                  | otherwise         =  ip6mask



defaultHandler :: ByteString -> Handler
defaultHandler meth = MethodHandler decodePayload errorPayload returnError
 where
    returnError :: NodeInfo -> BValue -> IO Error
    returnError _ _ = return $ Error MethodUnknown ("Unknown method " <> meth)

mainlineKademlia :: MainlineClient
                    -> TriadCommittee NodeId SockAddr
                    -> BucketRefresher NodeId NodeInfo TransactionId
                    -> Kademlia NodeId NodeInfo
mainlineKademlia client committee refresher
    = Kademlia quietInsertions
               mainlineSpace
               (vanillaIO (refreshBuckets refresher) $ ping client)
                   { tblTransition = \tr -> do
                        io1 <- transitionCommittee committee tr
                        io2 <- touchBucket refresher tr
                        return $ do
                            io1 >> io2
                            {-  noisy (timestamp updates are currently reported as transitions to Accepted)
                            dput XBitTorrent $ unwords
                                [ show (transitionedTo tr)
                                , show (transitioningNode tr)
                                ] -}
                   }


mainlineSpace :: R.KademliaSpace NodeId NodeInfo
mainlineSpace = R.KademliaSpace
    { R.kademliaLocation = nodeId
    , R.kademliaTestBit  = testIdBit
    , R.kademliaXor      = xor
    , R.kademliaSample   = genBucketSample'
    }

transitionCommittee :: TriadCommittee NodeId SockAddr -> RoutingTransition NodeInfo -> STM (IO ())
transitionCommittee committee (RoutingTransition ni Stranger) = do
    delVote committee (nodeId ni)
    return $ do
        dput XBitTorrent $ "delVote "++show (nodeId ni)
transitionCommittee committee _ = return $ return ()

updateRouting :: MainlineClient -> Routing -> NodeInfo -> Message BValue -> IO ()
updateRouting client routing naddr msg = do
    case prefer4or6 naddr Nothing of
        Want_IP4 -> go (committee4 routing) (refresher4 routing)
        Want_IP6 -> go (committee6 routing) (refresher6 routing)
 where
    go committee refresher = do
        self <- atomically $ R.thisNode <$> readTVar (refreshBuckets refresher)
        when (nodeIP self /= nodeIP naddr) $ do
            case msg of
                R { rspReflectedIP = Just sockaddr }
                    -> do
                        -- dput XBitTorrent $ "External: "++show (nodeId naddr,sockaddr)
                        atomically $ addVote committee (nodeId naddr) sockaddr
                _   -> return ()
            insertNode (mainlineKademlia client committee refresher) naddr

data Ping = Ping deriving Show

-- Pong is the same as Ping.
type Pong = Ping
pattern Pong = Ping

instance BEncode Ping where
  toBEncode Ping = toDict endDict
  fromBEncode _  = pure Ping

wantList :: WantIP -> [ByteString]
wantList Want_IP4  = ["ip4"]
wantList Want_IP6  = ["ip6"]
wantList Want_Both = ["ip4","ip6"]

instance BEncode WantIP where
    toBEncode w = toBEncode $ wantList w
    fromBEncode bval = do
        wants <- fromBEncode bval
        let _ = wants :: [ByteString]
        case (elem "ip4" wants, elem "ip6" wants) of
             (True,True)  -> Right Want_Both
             (True,False) -> Right Want_IP4
             (False,True) -> Right Want_IP6
             _            -> Left "Unrecognized IP type."

data FindNode = FindNode NodeId (Maybe WantIP)

instance BEncode FindNode where
  toBEncode (FindNode nid iptyp) = toDict   $ target_key .=! nid
                                              .: want_key .=? iptyp
                                              .: endDict
  fromBEncode                    = fromDict $ FindNode  <$>! target_key
                                                        <*>? want_key

data NodeFound = NodeFound
    { nodes4 :: [NodeInfo]
    , nodes6 :: [NodeInfo]
    }

instance BEncode NodeFound where
  toBEncode (NodeFound ns ns6) = toDict $
       nodes_key .=?
        (if Prelude.null ns then Nothing
                            else Just (S.runPut (mapM_ putNodeInfo4 ns)))
    .: nodes6_key .=?
        (if Prelude.null ns6 then Nothing
                             else Just (S.runPut (mapM_ putNodeInfo6 ns6)))
    .: endDict

  fromBEncode bval = NodeFound <$> ns4 <*> ns6
   where
    opt ns = fromMaybe [] <$> optional ns
    ns4 = opt $ fromDict (binary getNodeInfo4 nodes_key) bval
    ns6 = opt $ fromDict (binary getNodeInfo6 nodes6_key) bval

binary :: S.Get a -> BKey -> BE.Get [a]
binary get k = field (req k) >>= either (fail . format) return .
    S.runGet (many get)
  where
    format str = "fail to deserialize " ++ show k ++ " field: " ++ str

pingH :: NodeInfo -> Ping -> IO Pong
pingH _ Ping = return Pong

prefer4or6 :: NodeInfo -> Maybe WantIP -> WantIP
prefer4or6 addr iptyp = fromMaybe (ipFamily $ nodeIP addr) iptyp

findNodeH :: Routing -> NodeInfo -> FindNode -> IO NodeFound
findNodeH routing addr (FindNode node iptyp) = do
    let preferred = prefer4or6 addr iptyp

    (append4,append6) <- atomically $ do
        ni4 <- R.thisNode <$> readTVar (routing4 routing)
        ni6 <- R.thisNode <$> readTVar (routing6 routing)
        return $ case ipFamily (nodeIP addr) of
            Want_IP4 -> (id, (++ [ni6]))
            Want_IP6 -> ((++ [ni4]), id)
    ks  <- bool (return []) (go append4 $ routing4 routing) (preferred /= Want_IP6)
    ks6 <- bool (return []) (go append6 $ routing6 routing) (preferred /= Want_IP4)
    return $ NodeFound ks ks6
 where
    go f var = f . R.kclosest mainlineSpace k node <$> atomically (readTVar var)

    k = R.defaultK


data GetPeers = GetPeers InfoHash (Maybe WantIP)

instance BEncode GetPeers where
  toBEncode (GetPeers ih iptyp)
              = toDict   $ info_hash_key .=! ih
                        .: want_key .=? iptyp
                        .: endDict
  fromBEncode = fromDict $ GetPeers <$>! info_hash_key <*>? want_key


data GotPeers = GotPeers
  { -- | If the queried node has no peers for the infohash, returned
    -- the K nodes in the queried nodes routing table closest to the
    -- infohash supplied in the query.
    peers        :: [PeerAddr]

  , nodes        :: NodeFound

    -- | The token value is a required argument for a future
    -- announce_peer query.
  , grantedToken :: Token
  } -- deriving (Show, Eq, Typeable)

nodeIsIPv6 :: NodeInfo -> Bool
nodeIsIPv6 (NodeInfo _ (IPv6 _) _) = True
nodeIsIPv6 _                       = False

instance BEncode GotPeers where
  toBEncode GotPeers { nodes = NodeFound ns4 ns6, ..} = toDict $
       nodes_key  .=? (if null ns4 then Nothing
                                   else Just $ S.runPut (mapM_ putNodeInfo4 ns4))
    .: nodes6_key .=? (if null ns6 then Nothing
                                   else Just $ S.runPut (mapM_ putNodeInfo4 ns6))
    .: token_key .=! grantedToken
    .: peers_key .=! map S.encode peers
    .: endDict

  fromBEncode = fromDict $ do
    ns4 <- fromMaybe [] <$> optional (binary getNodeInfo4 nodes_key)        -- "nodes"
    ns6 <- fromMaybe [] <$> optional (binary getNodeInfo6 nodes6_key)       -- "nodes6"
    -- TODO: BEP 42...
    --
    -- Once enforced, responses to get_peers requests whose node ID does not
    -- match its external IP should be considered to not contain a token and
    -- thus not be eligible as storage target.  Implementations should take
    -- care that they find the closest set of nodes which return a token and
    -- whose IDs matches their IPs before sending a store request to those
    -- nodes.
    --
    -- Sounds like something to take care of at peer-search time, so I'll
    -- ignore it for now.
    tok <- field    (req    token_key)                                      -- "token"
    ps <- fromMaybe [] <$> optional (field (req peers_key) >>= decodePeers) -- "values"
    pure $ GotPeers ps (NodeFound ns4 ns6) tok
     where
       decodePeers = either fail pure . mapM S.decode

getPeersH :: Routing -> SwarmsDatabase -> NodeInfo -> GetPeers -> IO GotPeers
getPeersH routing (SwarmsDatabase peers toks _) naddr (GetPeers ih iptyp) = do
    ps <- do
        tm <- getTimestamp
        atomically $ do
          (ps,store') <- Peers.freshPeers ih tm <$> readTVar peers
          writeTVar peers store'
          return ps
    -- Filter peer results to only a single address family, IPv4 or IPv6, as
    -- per BEP 32.
    let notboth  = iptyp >>= \case Want_Both -> Nothing
                                   specific  -> Just specific
        selected = prefer4or6 naddr notboth
        ps'      = filter ( (== selected) . ipFamily . peerHost ) ps
    tok <- grantToken toks naddr
    ns <- findNodeH routing naddr (FindNode (coerce ih) iptyp)
    return $ GotPeers ps' ns tok

-- | Announce that the peer, controlling the querying node, is
-- downloading a torrent on a port.
data Announce = Announce
  { -- | If set, the 'port' field should be ignored and the source
    -- port of the UDP packet should be used as the peer's port
    -- instead. This is useful for peers behind a NAT that may not
    -- know their external port, and supporting uTP, they accept
    -- incoming connections on the same port as the DHT port.
    impliedPort :: Bool

    -- | infohash of the torrent;
  , topic    :: InfoHash

    -- | some clients announce the friendly name of the torrent here.
  , announcedName :: Maybe ByteString

    -- | the port /this/ peer is listening;
  , port     :: PortNumber

    -- TODO: optional boolean "seed" key

    -- | received in response to a previous get_peers query.
  , sessionToken :: Token

  } deriving (Show, Eq, Typeable)

mkAnnounce :: PortNumber -> InfoHash -> Token -> Announce
mkAnnounce portnum info token = Announce
    { topic = info
    , port = portnum
    , sessionToken = token
    , announcedName = Nothing
    , impliedPort = False
    }


instance BEncode Announce where
  toBEncode Announce {..} = toDict $
       implied_port_key .=? flagField impliedPort
    .: info_hash_key    .=! topic
    .: name_key         .=? announcedName
    .: port_key         .=! port
    .: token_key        .=! sessionToken
    .: endDict
    where
      flagField flag = if flag then Just (1 :: Int) else Nothing

  fromBEncode = fromDict $ do
    Announce <$> (boolField <$> optional (field (req implied_port_key)))
             <*>! info_hash_key
             <*>? name_key
             <*>! port_key
             <*>! token_key
    where
      boolField = maybe False (/= (0 :: Int))



-- | The queried node must verify that the token was previously sent
-- to the same IP address as the querying node. Then the queried node
-- should store the IP address of the querying node and the supplied
-- port number under the infohash in its store of peer contact
-- information.
data Announced = Announced
  deriving (Show, Eq, Typeable)

instance BEncode Announced where
  toBEncode   _ = toBEncode Ping
  fromBEncode _ = pure  Announced

announceH :: SwarmsDatabase -> NodeInfo -> Announce -> IO (Either Error Announced)
announceH (SwarmsDatabase peers toks _) naddr announcement = do
  checkToken toks naddr (sessionToken announcement)
    >>= bool (Left  <$> return (Error ProtocolError "invalid parameter: token"))
             (Right <$> go)
 where
    go = atomically $ do
        modifyTVar' peers
            $ insertPeer (topic announcement) (announcedName announcement)
            $ PeerAddr
                { peerId = Nothing
                -- Avoid storing IPv4-mapped addresses.
                , peerHost = case nodeIP naddr of
                    IPv6 ip6 | Just ip4 <- un4map ip6 -> IPv4 ip4
                    a                                 -> a
                , peerPort = if impliedPort announcement
                                then nodePort naddr
                                else port announcement
                }
        return Announced

isReadonlyClient :: MainlineClient -> Bool
isReadonlyClient client = False -- TODO

mainlineAsync :: ( BEncode xqry
                 , BEncode xrsp
                 ) => Method
                  -> (xrsp -> rsp)
                  -> (qry -> xqry)
                  -> MainlineClient
                  -> qry
                  -> NodeInfo
                  -> (TransactionId -> QR.Result rsp -> IO ())
                  -> IO TransactionId
mainlineAsync meth unwrap msg client nid addr withResult = do
    asyncQuery client serializer (msg nid) addr $ \qid reply -> do
        withResult qid $ case reply of
            Success (Right x) -> Success x
            Success (Left e)  -> Canceled -- TODO: Do something with parse errors.
            Canceled          -> Canceled
            TimedOut          -> TimedOut
 where
    serializer = MethodSerializer
        { methodTimeout  = \ni -> return (ni, 5000000)
        , method         = meth
        , wrapQuery      = encodeQueryPayload meth (isReadonlyClient client)
        , unwrapResponse = (>>= either (Left . Error GenericError . C8.pack)
                                       (Right . unwrap)
                                       . BE.fromBEncode)
                           . rspPayload
        }


mainlineSend :: ( BEncode xqry
                , BEncode xrsp
                ) => Method
                  -> (xrsp -> rsp)
                  -> (qry -> xqry)
                  -> MainlineClient
                  -> qry
                  -> NodeInfo
                  -> IO (QR.Result rsp)
mainlineSend meth unwrap msg client nid addr = do
    reply <- sendQuery client serializer (msg nid) addr
    return $ case reply of
        Success (Right x) -> Success x
        Success (Left e)  -> Canceled -- TODO: Do something with parse errors.
        Canceled          -> Canceled
        TimedOut          -> TimedOut
 where
    serializer = MethodSerializer
        { methodTimeout  = \ni -> return (ni, 5000000)
        , method         = meth
        , wrapQuery      = encodeQueryPayload meth (isReadonlyClient client)
        , unwrapResponse = (>>= either (Left . Error GenericError . C8.pack)
                                       (Right . unwrap)
                                       . BE.fromBEncode)
                           . rspPayload
        }

ping :: MainlineClient -> NodeInfo -> IO Bool
ping client addr =
    fromMaybe False . resultToMaybe
    <$> mainlineSend (Method "ping") (\Pong -> True) (const Ping) client () addr

-- searchQuery        :: ni -> IO (Maybe [ni], [r], tok))
getNodes :: MainlineClient -> NodeId -> NodeInfo -> IO (QR.Result ([NodeInfo],[NodeInfo],Maybe ()))
getNodes = mainlineSend (Method "find_node") unwrapNodes $ flip FindNode (Just Want_Both)

asyncGetNodes :: MainlineClient -> NodeId -> NodeInfo -> (TransactionId -> QR.Result ([NodeInfo],[NodeInfo],Maybe ()) -> IO ())
                                -> IO TransactionId
asyncGetNodes = mainlineAsync (Method "find_node") unwrapNodes $ flip FindNode (Just Want_Both)

unwrapNodes :: NodeFound -> ([NodeInfo], [NodeInfo], Maybe ())
unwrapNodes (NodeFound ns4 ns6) = (ns4++ns6, ns4++ns6, Just ())

getPeers :: MainlineClient -> NodeId -> NodeInfo -> IO (QR.Result ([NodeInfo],[PeerAddr],Maybe Token))
getPeers = mainlineSend (Method "get_peers") unwrapPeers $ flip GetPeers (Just Want_Both) . coerce

asyncGetPeers :: MainlineClient -> NodeId -> NodeInfo -> (TransactionId -> QR.Result ([NodeInfo],[PeerAddr],Maybe Token) -> IO ())
                                -> IO TransactionId
asyncGetPeers = mainlineAsync (Method "get_peers") unwrapPeers $ flip GetPeers (Just Want_Both) . coerce

unwrapPeers :: GotPeers -> ([NodeInfo], [PeerAddr], Maybe Token)
unwrapPeers (GotPeers ps (NodeFound ns4 ns6) tok) = (ns4++ns6, ps, Just tok)

nullTransactionId :: TransactionId
nullTransactionId = TransactionId B.empty

nullSearch :: Search NodeId (IP, PortNumber) tok NodeInfo r TransactionId
nullSearch = Search
    { searchSpace       = mainlineSpace
    , searchNodeAddress = nodeIP &&& nodePort
    , searchQuery       = \_ _ f -> f nullTransactionId Canceled >> return nullTransactionId
    , searchQueryCancel = \_ _ -> return ()
    , searchAlpha       = 8
    , searchK           = 16
    }

mainlineSearch :: MainlineClient
                  -> (MainlineClient -> NodeId -> NodeInfo
                      -> (TransactionId -> QR.Result ([NodeInfo], [r], Maybe tok) -> IO ()) -> IO TransactionId)
                  -> Search NodeId (IP, PortNumber) tok NodeInfo r TransactionId
mainlineSearch client qry = Search
    { searchSpace       = mainlineSpace
    , searchNodeAddress = nodeIP &&& nodePort
    , searchQuery       = qry client
    , searchQueryCancel = cancelQuery client
    , searchAlpha       = 8
    , searchK           = 16
    }

nodeSearch :: MainlineClient -> Search NodeId (IP, PortNumber) () NodeInfo NodeInfo TransactionId
nodeSearch client = mainlineSearch client asyncGetNodes

peerSearch :: MainlineClient -> Search NodeId (IP, PortNumber) Token NodeInfo PeerAddr TransactionId
peerSearch client = mainlineSearch client asyncGetPeers

-- | List of bootstrap nodes maintained by different bittorrent
-- software authors.
bootstrapNodes :: WantIP -> IO [NodeInfo]
bootstrapNodes want = unsafeInterleaveIO $ do
    let wellknowns =
          [ "router.bittorrent.com:6881" -- by BitTorrent Inc.

            -- doesn't work at the moment (use git blame)  of commit
          , "dht.transmissionbt.com:6881" -- by Transmission project

          , "router.utorrent.com:6881"
          ]
    nss <- forM wellknowns $ \hostAndPort -> do
        e <- resolve want hostAndPort
        case e of
            Left  _        -> return []
            Right sockaddr -> either (const $ return [])
                                     (return . (: []))
                                     $ nodeInfo zeroID sockaddr
    return $ concat nss

-- | Resolve either a numeric network address or a hostname to a
-- numeric IP address of the node.
resolve :: WantIP -> String -> IO (Either IOError SockAddr)
resolve want hostAndPort = do
    let hints = defaultHints { addrSocketType = Datagram
                             , addrFamily = case want of
                                  Want_IP4 -> AF_INET
                                  _        -> AF_INET6
                             }
        (rport,rhost) = span (/= ':') $ reverse hostAndPort
        (host,port) = case rhost of
                        []     -> (hostAndPort, Nothing)
                        (_:hs) -> (reverse hs, Just (reverse rport))
    tryIOError $ do
        -- getAddrInfo throws exception on empty list, so this
        --  pattern matching never fails.
        info : _ <- getAddrInfo (Just hints) (Just host) port
        return $ addrAddress info


announce :: MainlineClient -> Announce -> NodeInfo -> IO (Maybe Announced)
announce client msg addr =
    resultToMaybe <$> mainlineSend (Method "announce_peer") id (\() -> msg) client () addr