CDE

Task/Echo-server/Haskell/echo-server.hs

@@ -0,0 +1,25 @@
+module Main where
+import Network (withSocketsDo, accept, listenOn, sClose, PortID(PortNumber))
+import Control.Monad (forever)
+import System.IO (hGetLine, hPutStrLn, hFlush, hClose)
+import System.IO.Error (isEOFError)
+import Control.Concurrent (forkIO)
+import Control.Exception (bracket)
+
+-- For convenience in testing, ensure that the listen socket is closed if the main loop is aborted
+withListenOn port body = bracket (listenOn port) sClose body
+
+echo (handle, host, port) = catch (forever doOneLine) stop where
+  doOneLine = do line <- hGetLine handle
+                 print (host, port, init line)
+                 hPutStrLn handle line
+                 hFlush handle
+  stop error = do putStrLn $ "Closed connection from " ++ show (host, port) ++ " due to " ++ show error
+                  hClose handle
+
+main = withSocketsDo $
+  withListenOn (PortNumber 12321) $ \listener ->
+    forever $ do
+      acc@(_, host, port) <- accept listener
+      putStrLn $ "Accepted connection from " ++ show (host, port)
+      forkIO (echo acc)