    {-# LANGUAGE CPP #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Network
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/network/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  provisional
    -- Portability :  portable
    --
    -- The "Network" interface is a \"higher-level\" interface to
    -- networking facilities, and it is recommended unless you need the
    -- lower-level interface in "Network.Socket".
    --
    -----------------------------------------------------------------------------

    #include "HsNetworkConfig.h"

    #ifdef HAVE_GETADDRINFO
    -- Use IPv6-capable function definitions if the OS supports it.
    #define IPV6_SOCKET_SUPPORT 1
    #endif

    module Network (

    	-- * Basic data types
    	Socket,
            PortID(..),
    	HostName,
    	PortNumber,	-- instance (Eq, Enum, Num, Real, Integral)

    	-- * Initialisation
    	withSocketsDo,  -- :: IO a   -> IO a

    	-- * Server-side connections
    	listenOn,	-- :: PortID -> IO Socket
    	accept,		-- :: Socket -> IO (Handle, HostName, PortNumber)
            sClose,		-- :: Socket -> IO ()

    	-- * Client-side connections
    	connectTo,	-- :: HostName -> PortID -> IO Handle

    	-- * Simple sending and receiving
    	{-$sendrecv-}
    	sendTo,		-- :: HostName -> PortID -> String -> IO ()
    	recvFrom,	-- :: HostName -> PortID -> IO String

    	-- * Miscellaneous
    	socketPort,	-- :: Socket -> IO PortID

    	-- * Networking Issues
    	-- ** Buffering
    	{-$buffering-}

    	-- ** Improving I\/O Performance over sockets
    	{-$performance-}

    	-- ** @SIGPIPE@
    	{-$sigpipe-}

           ) where

    import Control.Monad (liftM)
    import Network.BSD
    import Network.Socket hiding ( accept, socketPort, recvFrom, sendTo, PortNumber )
    import qualified Network.Socket as Socket ( accept )
    import System.IO
    import Prelude
    import qualified Control.Exception as Exception

    -- ---------------------------------------------------------------------------
    -- High Level ``Setup'' functions

    -- If the @PortID@ specifies a unix family socket and the @Hostname@
    -- differs from that returned by @getHostname@ then an error is
    -- raised. Alternatively an empty string may be given to @connectTo@
    -- signalling that the current hostname applies.

    data PortID =
    	  Service String		-- Service Name eg "ftp"
    	| PortNumber PortNumber		-- User defined Port Number
    #if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS) && !defined(_WIN32)
    	| UnixSocket String		-- Unix family socket in file system
    #endif

    -- | Calling 'connectTo' creates a client side socket which is
    -- connected to the given host and port.  The Protocol and socket type is
    -- derived from the given port identifier.  If a port number is given
    -- then the result is always an internet family 'Stream' socket.

    connectTo :: HostName		-- Hostname
    	  -> PortID 		-- Port Identifier
    	  -> IO Handle		-- Connected Socket

    #if defined(IPV6_SOCKET_SUPPORT)
    -- IPv6 and IPv4.

    connectTo hostname (Service serv) = connect' hostname serv

    connectTo hostname (PortNumber port) = connect' hostname (show port)
    #else
    -- IPv4 only.

    connectTo hostname (Service serv) = do
        proto <- getProtocolNumber "tcp"
        bracketOnError
    	(socket AF_INET Stream proto)
    	(sClose)  -- only done if there's an error
    	(\sock -> do
              port	<- getServicePortNumber serv
              he	<- getHostByName hostname
              connect sock (SockAddrInet port (hostAddress he))
              socketToHandle sock ReadWriteMode
     	)

    connectTo hostname (PortNumber port) = do
        proto <- getProtocolNumber "tcp"
        bracketOnError
    	(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
    	)
    #endif

    #if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS) && !defined(_WIN32)
    connectTo _ (UnixSocket path) = do
        bracketOnError
    	(socket AF_UNIX Stream 0)
    	(sClose)
    	(\sock -> do
              connect sock (SockAddrUnix path)
              socketToHandle sock ReadWriteMode
    	)
    #endif

    #if defined(IPV6_SOCKET_SUPPORT)
    connect' :: HostName -> ServiceName -> IO Handle

    connect' host serv = do
        proto <- getProtocolNumber "tcp"
        let hints = defaultHints { addrFlags = [AI_ADDRCONFIG]
                                 , addrProtocol = proto
                                 , addrSocketType = Stream }
        addrs <- getAddrInfo (Just hints) (Just host) (Just serv)
        let addr = head addrs
        bracketOnError
    	(socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr))
    	(sClose)  -- only done if there's an error
    	(\sock -> do
              connect sock (addrAddress addr)
              socketToHandle sock ReadWriteMode
     	)
    #endif

    -- | Creates the server side socket which has been bound to the
    -- specified port.
    --
    -- NOTE: To avoid the \"Address already in use\"
    -- problems popped up several times on the GHC-Users mailing list we
    -- set the 'ReuseAddr' socket option on the listening socket.  If you
    -- don't want this behaviour, please use the lower level
    -- 'Network.Socket.listen' instead.

    listenOn :: PortID 	-- ^ Port Identifier
    	 -> IO Socket	-- ^ Connected Socket

    #if defined(IPV6_SOCKET_SUPPORT)
    -- IPv6 and IPv4.

    listenOn (Service serv) = listen' serv

    listenOn (PortNumber port) = listen' (show port)
    #else
    -- IPv4 only.

    listenOn (Service serv) = do
        proto <- getProtocolNumber "tcp"
        bracketOnError
            (socket AF_INET Stream proto)
    	(sClose)
    	(\sock -> do
    	    port    <- getServicePortNumber serv
    	    setSocketOption sock ReuseAddr 1
    	    bindSocket sock (SockAddrInet port iNADDR_ANY)
    	    listen sock maxListenQueue
    	    return sock
    	)

    listenOn (PortNumber port) = do
        proto <- getProtocolNumber "tcp"
        bracketOnError
        	(socket AF_INET Stream proto)
    	(sClose)
    	(\sock -> do
    	    setSocketOption sock ReuseAddr 1
    	    bindSocket sock (SockAddrInet port iNADDR_ANY)
    	    listen sock maxListenQueue
    	    return sock
    	)
    #endif

    #if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS) && !defined(_WIN32)
    listenOn (UnixSocket path) =
        bracketOnError
        	(socket AF_UNIX Stream 0)
    	(sClose)
    	(\sock -> do
    	    setSocketOption sock ReuseAddr 1
    	    bindSocket sock (SockAddrUnix path)
    	    listen sock maxListenQueue
    	    return sock
    	)
    #endif

    #if defined(IPV6_SOCKET_SUPPORT)
    listen' :: ServiceName -> IO Socket

    listen' serv = do
        proto <- getProtocolNumber "tcp"
        let hints = defaultHints { addrFlags = [AI_ADDRCONFIG, AI_PASSIVE]
                                 , addrProtocol = proto }
        addrs <- getAddrInfo (Just hints) Nothing (Just serv)
        let addr = head addrs
        bracketOnError
            (socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr))
    	(sClose)
    	(\sock -> do
    	    setSocketOption sock ReuseAddr 1
    	    bindSocket sock (addrAddress addr)
    	    listen sock maxListenQueue
    	    return sock
    	)
    #endif

    -- -----------------------------------------------------------------------------
    -- accept

    -- | Accept a connection on a socket created by 'listenOn'.  Normal
    -- I\/O opertaions (see "System.IO") can be used on the 'Handle'
    -- returned to communicate with the client.
    -- Notice that although you can pass any Socket to Network.accept,
    -- only sockets of either AF_UNIX, AF_INET, or AF_INET6 will work
    -- (this shouldn't be a problem, though). When using AF_UNIX, HostName
    -- will be set to the path of the socket and PortNumber to -1.
    --
    accept :: Socket 		-- ^ Listening Socket
           -> IO (Handle,
    	      HostName,
    	      PortNumber)	-- ^ Triple of: read\/write 'Handle' for
    				-- communicating with the client,
    			 	-- the 'HostName' of the peer socket, and
    				-- the 'PortNumber' of the remote connection.
    accept sock@(MkSocket _ AF_INET _ _ _) = do
     ~(sock', (SockAddrInet port haddr)) <- Socket.accept sock
     peer <- Exception.catchJust Exception.ioErrors
    	  (do
    	     (HostEntry peer _ _ _) <- getHostByAddr AF_INET haddr
    	     return peer
    	  )
    	  (\e -> inet_ntoa haddr)
    		-- if getHostByName fails, we fall back to the IP address
     handle <- socketToHandle sock' ReadWriteMode
     return (handle, peer, port)
    #if defined(IPV6_SOCKET_SUPPORT)
    accept sock@(MkSocket _ AF_INET6 _ _ _) = do
     (sock', addr) <- Socket.accept sock
     (Just peer, _) <- getNameInfo [] True False addr
     handle <- socketToHandle sock' ReadWriteMode
     (PortNumber port) <- socketPort sock'
     return (handle, peer, port)
    #endif
    #if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS) && !defined(_WIN32)
    accept sock@(MkSocket _ AF_UNIX _ _ _) = do
     ~(sock', (SockAddrUnix path)) <- Socket.accept sock
     handle <- socketToHandle sock' ReadWriteMode
     return (handle, path, -1)
    #endif
    accept sock@(MkSocket _ family _ _ _) =
      error $ "Sorry, address family " ++ (show family) ++ " is not supported!"

    -- -----------------------------------------------------------------------------
    -- sendTo/recvFrom

    {-$sendrecv
    Send and receive data from\/to the given host and port number.  These
    should normally only be used where the socket will not be required for
    further calls. Also, note that due to the use of 'hGetContents' in 'recvFrom'
    the socket will remain open (i.e. not available) even if the function already
    returned. Their use is strongly discouraged except for small test-applications
    or invocations from the command line.
    -}

    sendTo :: HostName 	-- Hostname
           -> PortID	-- Port Number
           -> String	-- Message to send
           -> IO ()
    sendTo h p msg = do
      s <- connectTo h p
      hPutStr s msg
      hClose s

    recvFrom :: HostName 	-- Hostname
    	 -> PortID	-- Port Number
    	 -> IO String	-- Received Data

    #if defined(IPV6_SOCKET_SUPPORT)
    recvFrom host port = do
        proto <- getProtocolNumber "tcp"
        let hints = defaultHints { addrFlags = [AI_ADDRCONFIG]
                                 , addrProtocol = proto
                                 , addrSocketType = Stream }
        allowed <- map addrAddress `liftM` getAddrInfo (Just hints) (Just host)
                                                       Nothing
        s <- listenOn port
        let waiting = do
            (s', addr) <- Socket.accept s
            if not (addr `oneOf` allowed)
             then sClose s' >> waiting
             else socketToHandle s' ReadMode >>= hGetContents
        waiting
      where
        a@(SockAddrInet _ ha) `oneOf` ((SockAddrInet _ hb):bs)
            | ha == hb = True
            | otherwise = a `oneOf` bs
        a@(SockAddrInet6 _ _ ha _) `oneOf` ((SockAddrInet6 _ _ hb _):bs)
            | ha == hb = True
            | otherwise = a `oneOf` bs
        _ `oneOf` _ = False
    #else
    recvFrom host port = do
     ip  <- getHostByName host
     let ipHs = hostAddresses ip
     s   <- listenOn port
     let
      waiting = do
         ~(s', SockAddrInet _ haddr)  <-  Socket.accept s
         he <- getHostByAddr AF_INET haddr
         if not (any (`elem` ipHs) (hostAddresses he))
          then do
             sClose s'
             waiting
          else do
    	h <- socketToHandle s' ReadMode
            msg <- hGetContents h
            return msg

     message <- waiting
     return message
    #endif

    -- ---------------------------------------------------------------------------
    -- Access function returning the port type/id of socket.

    -- | Returns the 'PortID' associated with a given socket.
    socketPort :: Socket -> IO PortID
    socketPort s = do
        sockaddr <- getSocketName s
        return (portID sockaddr)
      where
       portID sa =
        case sa of
         SockAddrInet port _      -> PortNumber port
    #if defined(IPV6_SOCKET_SUPPORT)
         SockAddrInet6 port _ _ _ -> PortNumber port
    #endif
    #if !defined(mingw32_HOST_OS) && !defined(cygwin32_HOST_OS) && !defined(_WIN32)
         SockAddrUnix path	      -> UnixSocket path
    #endif

    -- ---------------------------------------------------------------------------
    -- Utils

    #if __GLASGOW_HASKELL__ < 606
    -- Like bracket, but only performs the final action if there was an
    -- exception raised by the middle bit.
    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 =
      Exception.block (do
        a <- before
        r <- Exception.catch
               (Exception.unblock (thing a))
               (\e -> do { after a; Exception.throw e })
        return r
     )
    #else
    bracketOnError = Exception.bracketOnError
    #endif

    -----------------------------------------------------------------------------
    -- Extra documentation

    {-$buffering

    The 'Handle' returned by 'connectTo' and 'accept' is block-buffered by
    default.  For an interactive application you may want to set the
    buffering mode on the 'Handle' to
    'LineBuffering' or 'NoBuffering', like so:

    > h <- connectTo host port
    > hSetBuffering h LineBuffering
    -}

    {-$performance

    For really fast I\/O, it might be worth looking at the 'hGetBuf' and
    'hPutBuf' family of functions in "System.IO".
    -}

    {-$sigpipe

    On Unix, when writing to a socket and the reading end is
    closed by the remote client, the program is normally sent a
    @SIGPIPE@ signal by the operating system.  The
    default behaviour when a @SIGPIPE@ is received is
    to terminate the program silently, which can be somewhat confusing
    if you haven't encountered this before.  The solution is to
    specify that @SIGPIPE@ is to be ignored, using
    the POSIX library:

    >  import Posix
    >  main = do installHandler sigPIPE Ignore Nothing; ...
    -}