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

[Michael Snoyman]

On Sun, Oct 5, 2014 at 1:14 PM, Tilmann <t_gass at 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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