Re: [Haskell-cafe] Printing telnet stream to wx widget with conduit

5 Oct 2014


      Awesome!  It works. Thank you very much for looking into it!


Am 05.10.14 13:12, schrieb Michael Snoyman:
...
On Sun, Oct 5, 2014 at 1:14 PM, Tilmann <t_gass@gmx.de 
<mailto: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 <http://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-T...
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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