5.2. Socket: The high-level networking interface

The Socket interface is a ``higher-level'' interface to sockets, and it is what we recommend. Please tell us if the facilities it offers are inadequate to your task! The interface is relatively modest:

data Socket     -- instance of: Eq, Show

data PortID =
      Service String        -- Service Name eg "ftp"
    | PortNumber PortNumber -- User defined Port Number
    | UnixSocket String     -- Unix family socket in file system,
                            -- not available con Cygwin/Mingw
type Hostname    = String

connectTo       :: Hostname -> PortID -> IO Handle
listenOn        :: PortID -> IO Socket

accept		:: Socket -> IO (Handle, HostName, PortNumber)

sendTo          :: Hostname -> PortID -> String -> IO ()
recvFrom        :: Hostname -> PortID -> IO String

socketPort      :: Socket -> IO PortID

withSocketsDo   :: IO a -> IO a

data PortNumber -- instance of Eq, Ord, Enum, Num, Real, Integral, Show
mkPortNumber    :: Int -> PortNumber

5.2.1. Buffering

The Handle returned by connectTo and accept is unbuffered by default. To improve performance when shifting large amounts of data, it is wise to enable block buffering on the Handle with IO.hSetBuffering. For really fast I/O, it might also be worth looking at the hGetBuf and hPutBuf family of functions in IOExts (see Section 4.14).

5.2.2. SIGPIPE

On Unix, when reading from a socket and the writing 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 (Section 7.2):

5.2.3. Sockets on Windows

On Windows, you need to initialise WinSock before trying to use sockets, i.e.

main = withSocketDo $ do {...}