On Sun, Oct 5, 2014 at 1:14 PM, Tilmann <t_gass@gmx.de> wrote:

Hi,
I have this little program that works 'sometimes'. It is supposed to connect to a server via telnet and print the incoming text to a wx textwidget. Usually I get an error message: ChessGui: <socket: 22>: hGetBufSome: illegal operation (handle is closed), but I acutally saw it working a few times...
The whole thing is a bit out of my Haskell-league, so I´m a bit lost now. Any help is very appreciated!

Best regards,
Tilmann

module Main where

import Control.Concurrent (forkIO, killThread)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Control.Monad.Trans.Resource
import Data.Conduit
import qualified Data.Conduit.Binary as CB
import qualified Data.ByteString.Char8 as BS
import Network (connectTo, PortID (..))
import System.IO
import Graphics.UI.WX
import Graphics.UI.WX.Types
import Graphics.UI.WXCore.WxcDefs

main = start gui

gui = do
f <- frame []
t <- textCtrlEx f (wxTE_MULTILINE .+. wxTE_RICH2) [font := fontFixed]
e <- entry f []
set f [layout := boxed "console" (grid 5 5 [[floatLeft $ expand $ hstretch $ widget t]
,[expand $ hstretch $ widget e]])]
telnet "freechess.org" 5000 t

telnet :: String -> Int -> TextCtrl() -> IO ()
telnet host port t = runResourceT $ do
(releaseSock, hsock) <- allocate (connectTo host $ PortNumber $ fromIntegral port) hClose
liftIO $ mapM_ (`hSetBuffering` LineBuffering) [ hsock ]
liftIO $ forkIO $ CB.sourceHandle hsock $$ (sink' t)
return ()

I don't know anything about wxwidgets, but I *do* see a problem here. You're using `allocate` to say "when this ResourceT block exits, call hClose on the Socket". You then take the socket and pass it to a new thread. That new thread tries to continue using that Socket, but the first thread's ResourceT block exits immediately, closing the Socket. You may want to instead try using resourceForkIO[1].

On a separate note, your usage of mapM_ isn't necessary in this case. You can make do with:

liftIO $ hSetBuffering hsock LineBuffering

[1] http://haddocks.fpcomplete.com/fp/7.8/20140916-162/resourcet/Control-Monad-Trans-Resource.html#v:resourceForkIO

sink' :: TextCtrl () -> Sink BS.ByteString IO ()
sink' textCtrl = do
mstr <- await
case mstr of
Nothing -> return ()
Just str -> do
text' <- liftIO $ (get textCtrl text)
liftIO $ set textCtrl [text := text' ++ BS.unpack str ]
sink' textCtrl

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