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Networking sample in Haskell

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very basic example to connect/listen/accept on a port.

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  1. import Network.Socket
  2. import Network.BSD
  3. import System.IO (Handle, IOMode(ReadWriteMode), hPutStrLn, hGetLine, hClose)
  4. import Control.Monad (liftM)
  5. import Control.Concurrent (forkIO)
  6. import Control.Exception (finally)
  7.  
  8. connectTo :: String -> Int -> IO Handle
  9. connectTo host port_ = do
  10.       let port = toEnum port_
  11.       sock <- socket AF_INET Stream 0
  12.       addrs <- liftM hostAddresses $ getHostByName host
  13.       if null addrs then error $ "no such host : " ++ host else return ()
  14.       connect sock $ SockAddrInet port (head addrs)
  15.       handle <- socketToHandle sock ReadWriteMode
  16.       return handle
  17.  
  18. listenAt :: Int -> (Handle -> IO ()) -> IO ()
  19. listenAt port_ f = do
  20.       let port = toEnum port_
  21.       lsock <- socket AF_INET Stream 0
  22.       bindSocket lsock $ SockAddrInet port iNADDR_ANY
  23.       listen lsock sOMAXCONN
  24.       loop lsock `finally` sClose lsock
  25.    where
  26.       loop lsock = do
  27.       (sock,SockAddrInet _ _) <- accept lsock
  28.       handle <- socketToHandle sock ReadWriteMode
  29.       f handle
  30.       loop lsock
  31.  
  32. server = withSocketsDo $ do
  33.   listenAt 12345 (\h -> forkIO (do
  34.       putStrLn "connection."
  35.       hPutStrLn h "Hello, and Goodbye!"
  36.    `finally` hClose h) >> return ())
  37.  
  38. client = withSocketsDo $ do
  39.   h <- connectTo "localhost" 12345
  40.   hGetLine h >>= putStrLn
  41.   hClose h

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