Apologies if you have received this request for help already. Can anyone tell me why the following code doesn't work as expected? Both the server and client hang. [dom@lhrtba8fd85 simptest]$ server 20000 & [1] 2694 [dom@lhrtba8fd85 simptest]$ client lhrtba8fd85 20000 client: interrupted [1]+ Broken pipe server 20000 [dom@lhrtba8fd85 simptest]$ more log.txt Starting logging Hello world [dom@lhrtba8fd85 simptest]$ So it looks like the hPutStrLn to the server's socket never completes. What's stopping it? On the client side, "Hello world" gets sent but the hGetLine never completes. I guess because the server for some reason can't send. Dominic. module Main(main) where import System import IO import Socket main :: IO () main = do prog <- getProgName args <- getArgs if (length args /= 2) then do putStrLn ("Use: " ++ prog ++ " <host> <port>") exitWith (ExitFailure (-1)) else return () let host = args !! 0 port = read (args !! 1) :: Int in client host (PortNumber (mkPortNumber port)) client :: Hostname -> PortID -> IO () client host port = do sh <- connectTo host port hPutStr sh "Hello world" hFlush sh x <- hGetLine sh putStrLn x module Main (main) where import System import IO import Socket main :: IO () main = do prog <- getProgName args <- getArgs if (length args /= 1) then do putStrLn ("Use: " ++ prog ++ " <port>") exitWith (ExitFailure (-1)) else return () let port = read (args !! 0) :: Int in server (PortNumber (mkPortNumber port)) -- The server function creates a socket to listen on the port and -- loops to log messages. server :: PortID -> IO () server port = do ofh <- openFile "log.txt" WriteMode hPutStrLn ofh "Starting logging" hFlush ofh socket <- listenOn port (sh,host,portid) <- accept socket let loop = do b <- getBuffer sh 16 case b of Full msg -> do hPutStrLn ofh msg hFlush ofh loop Partial msg -> do hPutStrLn ofh msg hFlush ofh hPutStrLn sh "Finishing Logging" hFlush sh hPutStrLn ofh "Finishing logging" hClose ofh in loop data Buffer = Full String | Partial String getBuffer :: Handle -> Int -> IO Buffer getBuffer h n = if (n <= 0) then return (Full "") else do x <- try (hGetChar h) case x of Right c -> do xs <- getBuffer h (n-1) case xs of Full cs -> return (Full (c:cs)) Partial cs -> return (Partial (c:cs)) Left e -> if isEOFError e then return (Partial "") else ioError e ------------------------------------------------------------------------------------------------- 21st century air travel http://www.britishairways.com