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- using hFlush does *not* seem to cure the problem??

That's worrying, and it perhaps indicates that there's another problem somewhere. I just tried a small test and hFlush does appear to do the right thing, so do you think you could boil down your example to something small that demonstrates the problem? Does it happen only on Windows, or Un*x too?

Windows only, of course!-) On Solaris, I never even noticed there might be a problem (it seems to work even without acknowledgment or hFlush..). I append my current test MyNetwork module - server and client are the main functions of the respective apps, nothing else going on, so it's very small, but for modified copies of some of the Network code (for use on windows, you'll want to change to the other definition of whatsWrong and uncomment c_getLastError). On solaris (ghc version 5.04), this seems to work as shown. On win2k (ghc version 5.04), with error reporting on, I get: $ ./server.exe & [1] 1388 tcp: 6 $ ./client.exe huhuadsfas tcp: 6 CLIENT: huhuadsfas WSAGetLastError: 10054 Fail: failed Action: hGetLine Handle: {loc=,type=duplex (read-write),binary=True,buffering=line} Reason: No error File: [1]+ Exit 1 ./server.exe (on win98, not even the tcp number would be correct, hence the hardcoded 6). The 10054 error from the hGetLine is the "Connection reset by peer."-message I mentioned earlier. So it seems that on windows, when the client terminates, the connection goes down and the server fails when trying to get the message. Whereas on solaris, the message gets through anyway. Uncommenting the hFlush in the client makes no difference whatsoever. Uncomment the acknowledgement in client and server instead, and it works like a charm (although it does require an asymmetry between the two processes - I have to know which one lives longer..). Over to you, Claus ------------------------------------------ module MyNetwork where import System(system,getArgs) import IO(hPutStrLn ,hGetLine ,hClose ,hFlush ,hSetBuffering ,BufferMode(..) ,IOMode(..) ,Handle) import Control.Exception as Exception import Foreign import Foreign.C import Network hiding (listenOn,connectTo) import Network.BSD(getProtocolNumber,getHostByName,hostAddress) import Network.Socket(Family(..) ,SocketType(..) ,SockAddr(..) ,SocketOption(..) ,socket ,sClose ,setSocketOption ,bindSocket ,listen ,connect ,socketToHandle ,iNADDR_ANY ,maxListenQueue ) server :: IO () server = withSocketsDo $ do s <- listenOn $ PortNumber 9000 loop s where loop s = do l <- getInput s putStrLn $ "SERVER: "++l loop s getInput s = do (h,host,portnr) <- accept s hSetBuffering h LineBuffering l <- whatsWrong $ hGetLine h -- hPutStrLn h "<ack>" -- hClose h -- not a good idea? return l client :: IO () client = withSocketsDo $ do args <- getArgs h <- connectTo "localhost" $ PortNumber 9000 hSetBuffering h LineBuffering let l = unwords args putStrLn $ "CLIENT: "++l hPutStrLn h l -- hFlush h -- hGetLine h -- wait for acknowledgement return () {- only for winsock foreign import stdcall unsafe "WSAGetLastError" c_getLastError :: IO CInt -} {- -- does this exist? foreign import ccall unsafe "getWSErrorDescr" c_getWSError :: CInt -> IO (Ptr CChar) -} whatsWrong act = act {- whatsWrong act = Exception.catch act (\e-> do errCode <- c_getLastError -- perr <- c_getWSError errCode -- err <- peekCString perr putStrLn $ "WSAGetLastError: "++show errCode throw e) -} listenOn :: PortID -- ^ Port Identifier -> IO Socket -- ^ Connected Socket listenOn (PortNumber port) = do proto <- getProtocolNumber "tcp" putStrLn $ "tcp: "++show proto let proto = 6 -- bug in ghc's getProtocolNumber.. bracketOnError (whatsWrong (socket AF_INET Stream proto)) (sClose) (\sock -> do setSocketOption sock ReuseAddr 1 bindSocket sock (SockAddrInet port iNADDR_ANY) listen sock maxListenQueue return sock ) bracketOnError :: IO a -- ^ computation to run first (\"acquire resource\") -> (a -> IO b) -- ^ computation to run last (\"release resource\") -> (a -> IO c) -- ^ computation to run in-between -> IO c -- returns the value from the in-between computation bracketOnError before after thing = block (do a <- before r <- Exception.catch (unblock (thing a)) (\e -> do { after a; throw e }) return r ) connectTo :: HostName -- Hostname -> PortID -- Port Identifier -> IO Handle -- Connected Socket connectTo hostname (PortNumber port) = do proto <- getProtocolNumber "tcp" putStrLn $ "tcp: "++show proto let proto = 6 -- bug in ghc's getProtocolNumber.. bracketOnError (whatsWrong (socket AF_INET Stream proto)) (sClose) -- only done if there's an error (\sock -> do he <- getHostByName hostname connect sock (SockAddrInet port (hostAddress he)) socketToHandle sock ReadWriteMode )