@hackage websockets0.1.2.5

A library for creating WebSocket-capable servers, where the implemented protocol is defined here: http://is.gd/eSdLB.

This library is only tested with Chromium >=7 and Firefox >=4 and is a work in progress.

How do you use this library? Here's how:

• Get a Handle to your connected client.

• Perform the initial handshake with shakeHands (or getRequest and putResponse).

• Send and receive strict bytestrings with putFrame and getFrame.

And here's a short example of a server that accepts clients, greets them with a welcome message, checks for disconnects and replies to all messages by echoing them back with an appended meow:

import Network.WebSockets (shakeHands, getFrame, putFrame)
import Network (listenOn, PortID(PortNumber), accept, withSocketsDo)
import System.IO (Handle, hClose)
import qualified Data.ByteString as B (append, null)
import Data.ByteString.UTF8 (fromString) -- this is from utf8-string
import Control.Monad (forever)
import Control.Concurrent (forkIO)

main :: IO ()
main = withSocketsDo $ do
  socket <- listenOn (PortNumber 12345)
  putStrLn "Listening on port 12345."
  forever $ do
    (h, _, _) <- accept socket
    forkIO (talkTo h)


talkTo :: Handle -> IO ()
talkTo h = do
  request <- shakeHands h
  case request of
    Left error -> putStrLn error
    Right rqst -> do
      putFrame h (fromString "滴水之恩当以涌泉相报")
      putStrLn "Shook hands, sent welcome message."
      talkLoop h

  hClose h
  putStrLn "Client quit, closed handle."


talkLoop :: Handle -> IO ()
talkLoop h = do
  msg <- getFrame h
  if B.null msg
     then return ()
     else do
       putFrame h $ B.append msg (fromString ", MEOW!")
       talkLoop h

The example above will suffice if you wish to accept any WebSocket-capable client, regardless of its origin or target. It won't suffice if you have to filter the incoming clients by the contents of their requests. For that, you can use getRequest and putResponse, which allow you to inspect the request details before you send back a response, if any.

If you have any suggestions, bug reports and/or fixes, feel free to send them to mailto:sinisa@bidin.cc.