Hi, The problem is not with the haskell, but with telnet, which uses line buffered output itself. Try the following: module Main(main) where import IO import Network main = do socket <- listenOn (PortNumber 15151) (handle,hostName,_) <- accept socket hSetBuffering handle (BlockBuffering (Just 4096)) putStr ("Accepted: "++hostName++"\n") c <- hGetLine handle putStrLn (show c) telnet to this, type a line and hit return ... should print the line. Regards, Keean Schupke George Russell wrote:

The attached short program (compile with "ghc VServer.hs -o v -package net") is supposed to set up a server on port 15151, wait for a connection, read the first character from the connection, and print it out. Unfortunately if I test it, by running it, and starting up "telnet [machine] 15151" somewhere else, and then type some random text, EG "foo[RETURN]", it does not work. It looks as if the problem is that VServer.hs issues the command hSetBuffering handle (BlockBuffering (Just 4096)) on the connection, because when I change it to hSetBuffering handle NoBuffering the program works.

However this is not what I want to do!! Because setting NoBuffering on the handle is going to mean that when the Server *outputs* something, it will potentially be done very expensively character by character. How do I get block buffering on the Server's output, but not have input to the server held up?

The same thing seems to happen with client Handles by the way.

------------------------------------------------------------------------

-- Test program for server using GHC Socket library. module Main(main) where

import IO import Network

main = do socket <- listenOn (PortNumber 15151) (handle,hostName,_) <- accept socket hSetBuffering handle (BlockBuffering (Just 4096)) putStr ("Accepted: "++hostName++"\n") c <- hGetChar handle putStrLn (show c)

George Russell wrote:

The attached short program (compile with "ghc VServer.hs -o v -package net") is supposed to set up a server on port 15151, wait for a connection, read the first character from the connection, and print it out. Unfortunately if I test it, by running it, and starting up "telnet [machine] 15151" somewhere else, and then type some random text, EG "foo[RETURN]", it does not work. It looks as if the problem is that VServer.hs issues the command hSetBuffering handle (BlockBuffering (Just 4096)) on the connection, because when I change it to hSetBuffering handle NoBuffering the program works.

However this is not what I want to do!! Because setting NoBuffering on the handle is going to mean that when the Server *outputs* something, it will potentially be done very expensively character by character. How do I get block buffering on the Server's output, but not have input to the server held up?

Try using the low-level accept function in Network.Socket, calling socketToHandle twice to get separate read/write streams, e.g. accept2 :: Socket -> IO (Handle, Handle, HostName, PortNumber) accept2 sock = do ~(sock', (SockAddrInet port haddr)) <- Network.Socket.accept sock (HostEntry peer _ _ _) <- getHostByAddr AF_INET haddr handle'r <- socketToHandle sock' ReadMode handle'w <- socketToHandle sock' WriteMode return (handle'r, handle'w, peer, port) [This is untested, so I may have overlooked something.] More generally, many of the higher-level I/O functions have been over-simplified to the point where they're unsuitable for real-world use. -- Glynn Clements