QueryResponse: Minor simplification of awaitMessage.

1 files changed, 242 insertions, 231 deletions

diff --git a/dht/src/Network/QueryResponse.hs b/dht/src/Network/QueryResponse.hs
index 5fcd1989..f62fbefe 100644
--- a/dht/src/Network/QueryResponse.hs
+++ b/dht/src/Network/QueryResponse.hs
@@ -44,13 +44,17 @@ import DPut
 import DebugTag
 import Data.TableMethods
 
+-- | An inbound packet or condition raised while monitoring a connection.
+data Arrival err addr x
+    = Terminated       -- ^ Virtual message that signals EOF.
+    | ParseError !err  -- ^ A badly-formed message was recieved.
+    | Arrival { arrivedFrom :: !addr , arrivedMsg  :: !x } -- ^ Inbound message.
+
 -- | Three methods are required to implement a datagram based query\/response protocol.
 data TransportA err addr x y = Transport
-    { -- | Blocks until an inbound packet is available. Returns 'Nothing' when
-      -- no more packets are expected due to a shutdown or close event.
-      -- Otherwise, the packet will be parsed as type /x/ and an origin address
-      -- /addr/.  Parse failure is indicated by the type 'err'.
-      awaitMessage :: forall a. (Maybe (Either err (x, addr)) -> IO a) -> IO a
+    { -- | Blocks until an inbound packet is available. Then calls the provided
+      -- continuation with the packet and origin addres or an error condition.
+      awaitMessage :: forall a. (Arrival err addr x -> IO a) -> IO a
       -- | Send an /y/ packet to the given destination /addr/.
     , sendMessage :: addr -> y -> IO ()
       -- | Shutdown and clean up any state related to this 'Transport'.
@@ -75,7 +79,12 @@ layerTransportM ::
         -> TransportA err addr' x' y'
 layerTransportM parse encode tr =
     tr { awaitMessage = \kont ->
-                awaitMessage tr $ \m -> mapM (mapM $ uncurry parse) m >>= kont . fmap join
+                awaitMessage tr $ \case
+                    Terminated     -> kont $ Terminated
+                    ParseError e   -> kont $ ParseError e
+                    Arrival addr x -> parse x addr >>= \case
+                        Left e           -> kont $ ParseError e
+                        Right (x',addr') -> kont $ Arrival addr' x'
        , sendMessage = \addr' msg' -> do
                 (msg,addr) <- encode msg' addr'
                 sendMessage tr addr msg
@@ -104,16 +113,6 @@ layerTransport parse encode tr =
 -- | Paritions a 'Transport' into two higher-level transports.  Note: An 'MVar'
 -- is used to share the same underlying socket, so be sure to fork a thread for
 -- both returned 'Transport's to avoid hanging.
-partitionTransport :: ((b,a) -> Either (x,xaddr) (b,a))
-                      -> ((x,xaddr) -> Maybe (b,a))
-                      -> Transport err a b
-                      -> IO (Transport err xaddr x, Transport err a b)
-partitionTransport parse encodex tr =
-    partitionTransportM (return . parse) (return . encodex) tr
-
--- | Paritions a 'Transport' into two higher-level transports.  Note: An 'MVar'
--- is used to share the same underlying socket, so be sure to fork a thread for
--- both returned 'Transport's to avoid hanging.
 partitionTransportM :: ((b,a) -> IO (Either (x,xaddr) (b,a)))
                       -> ((x,xaddr) -> IO (Maybe (b,a)))
                       -> Transport err a b
@@ -122,22 +121,35 @@ partitionTransportM parse encodex tr = do
     mvar <- newEmptyMVar
     let xtr = tr { awaitMessage = \kont -> fix $ \again -> do
                     awaitMessage tr $ \m -> case m of
-                        Just (Right msg) -> parse msg >>=
-                                                either (kont . Just . Right)
-                                                       (\y -> putMVar mvar (Just y) >> again)
-                        Just (Left e)    -> kont $ Just (Left e)
-                        Nothing          -> putMVar mvar Nothing >> kont Nothing
+                        Arrival adr msg  -> parse (msg,adr) >>= \case
+                            Left (x,xaddr) -> kont $ Arrival xaddr x
+                            Right y        -> putMVar mvar (Just y) >> again
+                        ParseError e     -> kont $ ParseError e
+                        Terminated       -> putMVar mvar Nothing >> kont Terminated
                  , sendMessage = \addr' msg' -> do
                     msg_addr <- encodex (msg',addr')
                     mapM_ (uncurry . flip $ sendMessage tr) msg_addr
                  }
         ytr = Transport
-                { awaitMessage = \kont -> takeMVar mvar >>= kont . fmap Right
+                { awaitMessage = \kont -> takeMVar mvar >>= kont . \case
+                    Nothing        -> Terminated
+                    Just (y,yaddr) -> Arrival yaddr y
                 , sendMessage = sendMessage tr
                 , closeTransport = return ()
                 }
     return (xtr, ytr)
 
+-- | Paritions a 'Transport' into two higher-level transports.  Note: An 'MVar'
+-- is used to share the same underlying socket, so be sure to fork a thread for
+-- both returned 'Transport's to avoid hanging.
+partitionTransport :: ((b,a) -> Either (x,xaddr) (b,a))
+                      -> ((x,xaddr) -> Maybe (b,a))
+                      -> Transport err a b
+                      -> IO (Transport err xaddr x, Transport err a b)
+partitionTransport parse encodex tr =
+    partitionTransportM (return . parse) (return . encodex) tr
+
+
 partitionAndForkTransport ::
                       (dst -> msg -> IO ())
                       -> ((b,a) -> IO (Either (x,xaddr) (b,a)))
@@ -147,12 +159,12 @@ partitionAndForkTransport ::
 partitionAndForkTransport forkedSend parse encodex tr = do
     mvar <- newEmptyMVar
     let xtr = tr { awaitMessage = \kont -> fix $ \again -> do
-                    awaitMessage tr $ \m -> case m of
-                        Just (Right msg) -> parse msg >>=
-                                                either (kont . Just . Right)
-                                                       (\y -> putMVar mvar (Just y) >> again)
-                        Just (Left e)    -> kont $ Just (Left e)
-                        Nothing          -> putMVar mvar Nothing >> kont Nothing
+                    awaitMessage tr $ \case
+                        Arrival a b -> parse (b,a) >>= \case
+                            Left (x,xaddr) -> kont $ Arrival xaddr x
+                            Right (b,a)    -> putMVar mvar (Arrival a b) >> again
+                        ParseError e     -> kont $ ParseError e
+                        Terminated       -> putMVar mvar Terminated >> kont Terminated
                  , sendMessage = \addr' msg' -> do
                     msg_addr <- encodex (msg',addr')
                     case msg_addr of
@@ -161,7 +173,7 @@ partitionAndForkTransport forkedSend parse encodex tr = do
                         Nothing               -> return ()
                  }
         ytr = Transport
-                { awaitMessage   = \kont -> takeMVar mvar >>= kont . fmap Right
+                { awaitMessage   = \kont -> takeMVar mvar >>= kont
                 , sendMessage    = sendMessage tr
                 , closeTransport = return ()
                 }
@@ -173,11 +185,10 @@ partitionAndForkTransport forkedSend parse encodex tr = do
 --                --> Just g, apply g to x and leave that to a different handler
 addHandler :: (err -> IO ()) -> (addr -> x -> IO (Maybe (x -> x))) -> Transport err addr x -> Transport err addr x
 addHandler onParseError f tr = tr
-    { awaitMessage = \kont -> fix $ \eat -> awaitMessage tr $ \m -> do
-        case m of
-            Just (Right (x, addr)) -> f addr x >>= maybe eat (kont . Just . Right . (, addr) . ($ x))
-            Just (Left  e        ) -> onParseError e >> kont (Just $ Left e)
-            Nothing                -> kont $ Nothing
+    { awaitMessage = \kont -> fix $ \eat -> awaitMessage tr $ \case
+        Arrival addr x -> f addr x >>= maybe eat (kont . Arrival addr . ($ x))
+        ParseError e   -> onParseError e >> kont (ParseError e)
+        Terminated     -> kont Terminated
     }
 
 -- | Modify a 'Transport' to invoke an action upon every received packet.
@@ -201,12 +212,186 @@ forkListener :: String -> Transport err addr x -> IO (IO ())
 forkListener name client = do
     thread_id <- forkIO $ do
         myThreadId >>= flip labelThread ("listener."++name)
-        fix $ \loop -> awaitMessage client $ maybe (return ()) (const loop)
+        fix $ \loop -> awaitMessage client $ \case
+            Terminated -> return ()
+            _          -> loop
         dput XMisc $ "Listener died: " ++ name
     return $ do
         closeTransport client
         -- killThread thread_id
 
+-- * Implementing a query\/response 'Client'.
+
+-- | These methods indicate what should be done upon various conditions.  Write
+-- to a log file, make debug prints, or simply ignore them.
+--
+--   [ /addr/ ]  Address of remote peer.
+--
+--   [ /x/ ]     Incoming or outgoing packet.
+--
+--   [ /meth/ ]  Method id of incoming or outgoing request.
+--
+--   [ /tid/ ]   Transaction id for outgoing packet.
+--
+--   [ /err/ ]   Error information, typically a 'String'.
+data ErrorReporter addr x meth tid err = ErrorReporter
+    { -- | Incoming: failed to parse packet.
+      reportParseError :: err -> IO ()
+      -- | Incoming: no handler for request.
+    , reportMissingHandler :: meth -> addr -> x -> IO ()
+      -- | Incoming: unable to identify request.
+    , reportUnknown :: addr -> x -> err -> IO ()
+    }
+
+ignoreErrors :: ErrorReporter addr x meth tid err
+ignoreErrors = ErrorReporter
+    { reportParseError = \_ -> return ()
+    , reportMissingHandler = \_ _ _ -> return ()
+    , reportUnknown = \_ _ _ -> return ()
+    }
+
+logErrors :: ( Show addr
+               , Show meth
+               ) => ErrorReporter addr x meth tid String
+logErrors = ErrorReporter
+    { reportParseError = \err -> dput XMisc err
+    , reportMissingHandler = \meth addr x -> dput XMisc $ show addr ++ " --> Missing handler ("++show meth++")"
+    , reportUnknown = \addr x err -> dput XMisc $ show addr ++ " --> " ++ err
+    }
+
+printErrors :: ( Show addr
+               , Show meth
+               ) => Handle -> ErrorReporter addr x meth tid String
+printErrors h = ErrorReporter
+    { reportParseError = \err -> hPutStrLn h err
+    , reportMissingHandler = \meth addr x -> hPutStrLn h $ show addr ++ " --> Missing handler ("++show meth++")"
+    , reportUnknown = \addr x err -> hPutStrLn h $ show addr ++ " --> " ++ err
+    }
+
+-- Change the /err/ type for an 'ErrorReporter'.
+instance Contravariant (ErrorReporter addr x meth tid) where
+    -- contramap :: (t5 -> t4) -> ErrorReporter t3 t2 t1 t t4 -> ErrorReporter t3 t2 t1 t t5
+    contramap f (ErrorReporter pe mh unk)
+        = ErrorReporter (\e -> pe (f e))
+                        mh
+                        (\addr x e -> unk addr x (f e))
+
+-- | An incoming message can be classified into three cases.
+data MessageClass err meth tid addr x
+    = IsQuery meth tid                                    -- ^ An unsolicited query is handled based on it's /meth/ value.  Any response
+                                                          -- should include the provided /tid/ value.
+    | IsResponse tid                                      -- ^ A response to a outgoing query we associated with a /tid/ value.
+    | IsUnsolicited (addr -> addr -> IO (Maybe (x -> x))) -- ^ Transactionless informative packet.  The io action will be invoked
+                                                          -- with the source and destination address of a message.  If it handles the
+                                                          -- message, it should return Nothing. Otherwise, it should return a transform
+                                                          -- (usually /id/) to apply before the next handler examines it.
+    | IsUnknown err                                       -- ^ None of the above.
+
+-- | Handler for an inbound query of type /x/ from an address of type _addr_.
+data MethodHandler err tid addr x = forall a b. MethodHandler
+    { -- | Parse the query into a more specific type for this method.
+      methodParse :: x -> Either err a
+      -- | Serialize the response for transmission, given a context /ctx/ and the origin
+      -- and destination addresses.
+    , methodSerialize :: tid -> addr -> addr -> b -> x
+      -- | Fully typed action to perform upon the query.  The remote origin
+      -- address of the query is provided to the handler.
+    , methodAction :: addr -> a -> IO b
+    }
+      -- | See also 'IsUnsolicited' which likely makes this constructor unnecessary.
+    | forall a. NoReply
+    { -- | Parse the query into a more specific type for this method.
+      methodParse :: x -> Either err a
+      -- | Fully typed action to perform upon the query.  The remote origin
+      -- address of the query is provided to the handler.
+    , noreplyAction :: addr -> a -> IO ()
+    }
+
+-- | To dispatch responses to our outbound queries, we require three
+-- primitives.  See the 'transactionMethods' function to create these
+-- primitives out of a lookup table and a generator for transaction ids.
+--
+-- The type variable /d/ is used to represent the current state of the
+-- transaction generator and the table of pending transactions.
+data TransactionMethods d qid addr x = TransactionMethods
+    {
+      -- | Before a query is sent, this function stores an 'MVar' to which the
+      -- response will be written too.  The returned /qid/ is a transaction id
+      -- that can be used to forget the 'MVar' if the remote peer is not
+      -- responding.
+      dispatchRegister :: POSIXTime -- time of expiry
+                          -> (Maybe x -> IO ()) -- callback upon response (or timeout)
+                          -> addr
+                          -> d
+                          -> STM (qid, d)
+      -- | This method is invoked when an incoming packet /x/ indicates it is
+      -- a response to the transaction with id /qid/.  The returned IO action
+      -- will write the packet to the correct 'MVar' thus completing the
+      -- dispatch.
+    , dispatchResponse :: qid -> x -> d -> STM (d, IO ())
+      -- | When a timeout interval elapses, this method is called to remove the
+      -- transaction from the table.
+    , dispatchCancel :: qid -> d -> STM d
+    }
+
+-- | A set of methods necessary for dispatching incoming packets.
+data DispatchMethods tbl err meth tid addr x = DispatchMethods
+    { -- | Classify an inbound packet as a query or response.
+      classifyInbound :: x -> MessageClass err meth tid addr x
+      -- | Lookup the handler for a inbound query.
+    , lookupHandler :: meth -> Maybe (MethodHandler err tid addr x)
+      -- | Methods for handling incoming responses.
+    , tableMethods :: TransactionMethods tbl tid addr x
+    }
+
+-- | All inputs required to implement a query\/response client.
+data Client err meth tid addr x = forall tbl. Client
+    { -- | The 'Transport' used to dispatch and receive packets.
+      clientNet :: Transport err addr x
+      -- | Methods for handling inbound packets.
+    , clientDispatcher :: DispatchMethods tbl err meth tid addr x
+      -- | Methods for reporting various conditions.
+    , clientErrorReporter :: ErrorReporter addr x meth tid err
+      -- | State necessary for routing inbound responses and assigning unique
+      -- /tid/ values for outgoing queries.
+    , clientPending :: TVar tbl
+      -- | An action yielding this client\'s own address.  It is invoked once
+      -- on each outbound and inbound packet.  It is valid for this to always
+      -- return the same value.
+      --
+      -- The argument, if supplied, is the remote address for the transaction.
+      -- This can be used to maintain consistent aliases for specific peers.
+    , clientAddress :: Maybe addr -> IO addr
+      -- | Transform a query /tid/ value to an appropriate response /tid/
+      -- value.  Normally, this would be the identity transformation, but if
+      -- /tid/ includes a unique cryptographic nonce, then it should be
+      -- generated here.
+    , clientResponseId :: tid -> IO tid
+    }
+
+-- | These four parameters are required to implement an outgoing query.  A
+-- peer-to-peer algorithm will define a 'MethodSerializer' for every 'MethodHandler' that
+-- might be returned by 'lookupHandler'.
+data MethodSerializer tid addr x meth a b = MethodSerializer
+    { -- | Returns the microseconds to wait for a response to this query being
+      -- sent to the given address.  The /addr/ may also be modified to add
+      -- routing information.
+      methodTimeout :: addr -> STM (addr,Int)
+      -- | A method identifier used for error reporting.  This needn't be the
+      -- same as the /meth/ argument to 'MethodHandler', but it is suggested.
+    , method :: meth
+      -- | Serialize the outgoing query /a/ into a transmittable packet /x/.
+      -- The /addr/ arguments are, respectively, our own origin address and the
+      -- destination of the request.  The /tid/ argument is useful for attaching
+      -- auxiliary notations on all outgoing packets.
+    , wrapQuery :: tid -> addr -> addr -> a -> x
+      -- | Parse an inbound packet /x/ into a response /b/ for this query.
+    , unwrapResponse :: x -> b
+    }
+
+microsecondsDiff :: Int -> POSIXTime
+microsecondsDiff us = fromIntegral us / 1000000
+
 asyncQuery_ :: Client err meth tid addr x
               -> MethodSerializer tid addr x meth a b
               -> a
@@ -276,64 +461,6 @@ sendQuery c@(Client net d err pending whoami _) meth q addr0 = do
             atomically $ readTVar pending >>= dispatchCancel (tableMethods d) tid >>= writeTVar pending
             return Nothing
 
--- * Implementing a query\/response 'Client'.
-
--- | All inputs required to implement a query\/response client.
-data Client err meth tid addr x = forall tbl. Client
-    { -- | The 'Transport' used to dispatch and receive packets.
-      clientNet :: Transport err addr x
-      -- | Methods for handling inbound packets.
-    , clientDispatcher :: DispatchMethods tbl err meth tid addr x
-      -- | Methods for reporting various conditions.
-    , clientErrorReporter :: ErrorReporter addr x meth tid err
-      -- | State necessary for routing inbound responses and assigning unique
-      -- /tid/ values for outgoing queries.
-    , clientPending :: TVar tbl
-      -- | An action yielding this client\'s own address.  It is invoked once
-      -- on each outbound and inbound packet.  It is valid for this to always
-      -- return the same value.
-      --
-      -- The argument, if supplied, is the remote address for the transaction.
-      -- This can be used to maintain consistent aliases for specific peers.
-    , clientAddress :: Maybe addr -> IO addr
-      -- | Transform a query /tid/ value to an appropriate response /tid/
-      -- value.  Normally, this would be the identity transformation, but if
-      -- /tid/ includes a unique cryptographic nonce, then it should be
-      -- generated here.
-    , clientResponseId :: tid -> IO tid
-    }
-
--- | An incoming message can be classified into three cases.
-data MessageClass err meth tid addr x
-    = IsQuery meth tid                                    -- ^ An unsolicited query is handled based on it's /meth/ value.  Any response
-                                                          -- should include the provided /tid/ value.
-    | IsResponse tid                                      -- ^ A response to a outgoing query we associated with a /tid/ value.
-    | IsUnsolicited (addr -> addr -> IO (Maybe (x -> x))) -- ^ Transactionless informative packet.  The io action will be invoked
-                                                          -- with the source and destination address of a message.  If it handles the
-                                                          -- message, it should return Nothing. Otherwise, it should return a transform
-                                                          -- (usually /id/) to apply before the next handler examines it.
-    | IsUnknown err                                       -- ^ None of the above.
-
--- | Handler for an inbound query of type /x/ from an address of type _addr_.
-data MethodHandler err tid addr x = forall a b. MethodHandler
-    { -- | Parse the query into a more specific type for this method.
-      methodParse :: x -> Either err a
-      -- | Serialize the response for transmission, given a context /ctx/ and the origin
-      -- and destination addresses.
-    , methodSerialize :: tid -> addr -> addr -> b -> x
-      -- | Fully typed action to perform upon the query.  The remote origin
-      -- address of the query is provided to the handler.
-    , methodAction :: addr -> a -> IO b
-    }
-      -- | See also 'IsUnsolicited' which likely makes this constructor unnecessary.
-    | forall a. NoReply
-    { -- | Parse the query into a more specific type for this method.
-      methodParse :: x -> Either err a
-      -- | Fully typed action to perform upon the query.  The remote origin
-      -- address of the query is provided to the handler.
-    , noreplyAction :: addr -> a -> IO ()
-    }
-
 contramapAddr :: (a -> b) -> MethodHandler err tid b x -> MethodHandler err tid a x
 contramapAddr f (MethodHandler p s a)
     = MethodHandler
@@ -343,7 +470,6 @@ contramapAddr f (MethodHandler p s a)
 contramapAddr f (NoReply p a)
     = NoReply p (\addr arg -> a (f addr) arg)
 
-
 -- | Attempt to invoke a 'MethodHandler' upon a given inbound query.  If the
 -- parse is successful, the returned IO action will construct our reply if
 -- there is one.  Otherwise, a parse err is returned.
@@ -358,65 +484,6 @@ dispatchQuery (MethodHandler unwrapQ wrapR f) tid self x addr =
 dispatchQuery (NoReply unwrapQ f) tid self x addr =
     fmap (\a -> f addr a >> return Nothing) $ unwrapQ x
 
--- | These four parameters are required to implement an outgoing query.  A
--- peer-to-peer algorithm will define a 'MethodSerializer' for every 'MethodHandler' that
--- might be returned by 'lookupHandler'.
-data MethodSerializer tid addr x meth a b = MethodSerializer
-    { -- | Returns the microseconds to wait for a response to this query being
-      -- sent to the given address.  The /addr/ may also be modified to add
-      -- routing information.
-      methodTimeout :: addr -> STM (addr,Int)
-      -- | A method identifier used for error reporting.  This needn't be the
-      -- same as the /meth/ argument to 'MethodHandler', but it is suggested.
-    , method :: meth
-      -- | Serialize the outgoing query /a/ into a transmittable packet /x/.
-      -- The /addr/ arguments are, respectively, our own origin address and the
-      -- destination of the request.  The /tid/ argument is useful for attaching
-      -- auxiliary notations on all outgoing packets.
-    , wrapQuery :: tid -> addr -> addr -> a -> x
-      -- | Parse an inbound packet /x/ into a response /b/ for this query.
-    , unwrapResponse :: x -> b
-    }
-
-
--- | To dispatch responses to our outbound queries, we require three
--- primitives.  See the 'transactionMethods' function to create these
--- primitives out of a lookup table and a generator for transaction ids.
---
--- The type variable /d/ is used to represent the current state of the
--- transaction generator and the table of pending transactions.
-data TransactionMethods d qid addr x = TransactionMethods
-    {
-      -- | Before a query is sent, this function stores an 'MVar' to which the
-      -- response will be written too.  The returned /qid/ is a transaction id
-      -- that can be used to forget the 'MVar' if the remote peer is not
-      -- responding.
-      dispatchRegister :: POSIXTime -- time of expiry
-                          -> (Maybe x -> IO ()) -- callback upon response (or timeout)
-                          -> addr
-                          -> d
-                          -> STM (qid, d)
-      -- | This method is invoked when an incoming packet /x/ indicates it is
-      -- a response to the transaction with id /qid/.  The returned IO action
-      -- will write the packet to the correct 'MVar' thus completing the
-      -- dispatch.
-    , dispatchResponse :: qid -> x -> d -> STM (d, IO ())
-      -- | When a timeout interval elapses, this method is called to remove the
-      -- transaction from the table.
-    , dispatchCancel :: qid -> d -> STM d
-    }
-
--- | Construct 'TransactionMethods' methods out of 3 lookup table primitives and a
--- function for generating unique transaction ids.
-transactionMethods ::
-    TableMethods t tid  -- ^ Table methods to lookup values by /tid/.
-    -> (g -> (tid,g))   -- ^ Generate a new unique /tid/ value and update the generator state /g/.
-    -> TransactionMethods (g,t (Maybe x -> IO ())) tid addr x
-transactionMethods methods generate = transactionMethods' id id methods generate
-
-microsecondsDiff :: Int -> POSIXTime
-microsecondsDiff us = fromIntegral us / 1000000
-
 -- | Like 'transactionMethods' but allows extra information to be stored in the
 -- table of pending transactions.  This also enables multiple 'Client's to
 -- share a single transaction table.
@@ -439,69 +506,13 @@ transactionMethods' store load (TableMethods insert delete lookup) generate = Tr
             Nothing -> return ((g,t), return ())
     }
 
--- | A set of methods necessary for dispatching incoming packets.
-data DispatchMethods tbl err meth tid addr x = DispatchMethods
-    { -- | Classify an inbound packet as a query or response.
-      classifyInbound :: x -> MessageClass err meth tid addr x
-      -- | Lookup the handler for a inbound query.
-    , lookupHandler :: meth -> Maybe (MethodHandler err tid addr x)
-      -- | Methods for handling incoming responses.
-    , tableMethods :: TransactionMethods tbl tid addr x
-    }
-
--- | These methods indicate what should be done upon various conditions.  Write
--- to a log file, make debug prints, or simply ignore them.
---
---   [ /addr/ ]  Address of remote peer.
---
---   [ /x/ ]     Incoming or outgoing packet.
---
---   [ /meth/ ]  Method id of incoming or outgoing request.
---
---   [ /tid/ ]   Transaction id for outgoing packet.
---
---   [ /err/ ]   Error information, typically a 'String'.
-data ErrorReporter addr x meth tid err = ErrorReporter
-    { -- | Incoming: failed to parse packet.
-      reportParseError :: err -> IO ()
-      -- | Incoming: no handler for request.
-    , reportMissingHandler :: meth -> addr -> x -> IO ()
-      -- | Incoming: unable to identify request.
-    , reportUnknown :: addr -> x -> err -> IO ()
-    }
-
-ignoreErrors :: ErrorReporter addr x meth tid err
-ignoreErrors = ErrorReporter
-    { reportParseError = \_ -> return ()
-    , reportMissingHandler = \_ _ _ -> return ()
-    , reportUnknown = \_ _ _ -> return ()
-    }
-
-logErrors :: ( Show addr
-               , Show meth
-               ) => ErrorReporter addr x meth tid String
-logErrors = ErrorReporter
-    { reportParseError = \err -> dput XMisc err
-    , reportMissingHandler = \meth addr x -> dput XMisc $ show addr ++ " --> Missing handler ("++show meth++")"
-    , reportUnknown = \addr x err -> dput XMisc $ show addr ++ " --> " ++ err
-    }
-
-printErrors :: ( Show addr
-               , Show meth
-               ) => Handle -> ErrorReporter addr x meth tid String
-printErrors h = ErrorReporter
-    { reportParseError = \err -> hPutStrLn h err
-    , reportMissingHandler = \meth addr x -> hPutStrLn h $ show addr ++ " --> Missing handler ("++show meth++")"
-    , reportUnknown = \addr x err -> hPutStrLn h $ show addr ++ " --> " ++ err
-    }
-
--- Change the /err/ type for an 'ErrorReporter'.
-instance Contravariant (ErrorReporter addr x meth tid) where
-    -- contramap :: (t5 -> t4) -> ErrorReporter t3 t2 t1 t t4 -> ErrorReporter t3 t2 t1 t t5
-    contramap f (ErrorReporter pe mh unk)
-        = ErrorReporter (\e -> pe (f e))
-                        mh
-                        (\addr x e -> unk addr x (f e))
+-- | Construct 'TransactionMethods' methods out of 3 lookup table primitives and a
+-- function for generating unique transaction ids.
+transactionMethods ::
+    TableMethods t tid  -- ^ Table methods to lookup values by /tid/.
+    -> (g -> (tid,g))   -- ^ Generate a new unique /tid/ value and update the generator state /g/.
+    -> TransactionMethods (g,t (Maybe x -> IO ())) tid addr x
+transactionMethods methods generate = transactionMethods' id id methods generate
 
 -- | Handle a single inbound packet and then invoke the given continuation.
 -- The 'forkListener' function is implemented by passing this function to 'fix'
@@ -559,14 +570,14 @@ sockAddrFamily _                       = AF_CAN -- SockAddrCan constructor depre
 -- | Packets with an empty payload may trigger EOF exception.
 -- 'udpTransport' uses this function to avoid throwing in that
 -- case.
-ignoreEOF :: Socket -> MVar () -> a -> IOError -> IO (Maybe a)
+ignoreEOF :: Socket -> MVar () -> Arrival e a x -> IOError -> IO (Arrival e a x)
 ignoreEOF sock isClosed def e = do
     done <- tryReadMVar isClosed
     case done of
         Just () -> do close sock
                       dput XMisc "Closing UDP socket."
-                      pure Nothing
-        _ -> if isEOFError e then pure $ Just def
+                      pure Terminated
+        _ -> if isEOFError e then pure def
                              else throwIO e
 
 -- | Hard-coded maximum packet size for incoming UDP Packets received via
@@ -585,13 +596,6 @@ saferSendTo sock bs saddr = void (B.sendTo sock bs saddr)
             then return ()
             else throw e
 
--- | A 'udpTransport' uses a UDP socket to send and receive 'ByteString's.  The
--- argument is the listen-address for incoming packets.  This is a useful
--- low-level 'Transport' that can be transformed for higher-level protocols
--- using 'layerTransport'.
-udpTransport :: Show err => SockAddr -> IO (Transport err SockAddr ByteString)
-udpTransport bind_address = fst <$> udpTransport' bind_address
-
 -- | Like 'udpTransport' except also returns the raw socket (for broadcast use).
 udpTransport' :: Show err => SockAddr -> IO (Transport err SockAddr ByteString, Socket)
 udpTransport' bind_address = do
@@ -604,8 +608,8 @@ udpTransport' bind_address = do
   isClosed <- newEmptyMVar
   let tr = Transport {
       awaitMessage = \kont -> do
-        r <- handle (ignoreEOF sock isClosed $ Right (B.empty, SockAddrInet 0 0)) $ do
-                Just . Right <$!> B.recvFrom sock udpBufferSize
+        r <- handle (ignoreEOF sock isClosed $ Arrival (SockAddrInet 0 0) B.empty) $ do
+                uncurry (flip Arrival) <$!> B.recvFrom sock udpBufferSize
         kont $! r
     , sendMessage = case family of
         AF_INET6 -> \case
@@ -638,13 +642,20 @@ udpTransport' bind_address = do
     }
   return (tr, sock)
 
+-- | A 'udpTransport' uses a UDP socket to send and receive 'ByteString's.  The
+-- argument is the listen-address for incoming packets.  This is a useful
+-- low-level 'Transport' that can be transformed for higher-level protocols
+-- using 'layerTransport'.
+udpTransport :: Show err => SockAddr -> IO (Transport err SockAddr ByteString)
+udpTransport bind_address = fst <$> udpTransport' bind_address
+
 chanTransport :: (addr -> TChan (x, addr)) -> addr -> TChan (x, addr) -> TVar Bool -> Transport err addr x
 chanTransport chanFromAddr self achan aclosed = Transport
     { awaitMessage = \kont -> do
-        x <- atomically $ (Just <$> readTChan achan)
+        x <- atomically $ (uncurry (flip Arrival) <$> readTChan achan)
                             `orElse`
-                          (readTVar aclosed >>= check >> return Nothing)
-        kont $ Right <$> x
+                          (readTVar aclosed >>= check >> return Terminated)
+        kont x
     , sendMessage = \them bs -> do
         atomically $ writeTChan (chanFromAddr them) (bs,self)
     , closeTransport = atomically $ writeTVar aclosed True