[Haskell-cafe] hGetLine problem

[Michael Walter]

Hello again,

this test program should do the relevant parts for the bug -- on
Windows it works fine, though, I'll have to check at home whether it's
reproducable using it.

- Michael

module Test where

import Control.Concurrent
import Network
import System.IO

mainLoop socket = do
	(handle, _, _) <- accept socket
	forkIO $ do
		line <- hGetLine handle
		putStrLn line 
		hPutStrLn handle "HTTP/1.0 200 OK\r"
		hPutStrLn handle "Content-Type: text/html\r"
		hPutStrLn handle "\r"
		hPutStrLn handle "Test\r"
		hClose handle
	mainLoop socket

main = withSocketsDo $ listenOn (PortNumber 8000) >>= mainLoop



On Thu, 9 Dec 2004 11:44:16 -0500, Michael Walter
<michael.walter at gmail.com> wrote:
> I'll do so at lunch break/from home tonight.
> 
> Thanks,
> Michael
> 
> 
> 
> 
> On Thu, 9 Dec 2004 16:19:20 +0000, Jules Bean <jules at jellybean.co.uk> wrote:
> >
> > On 9 Dec 2004, at 15:30, Michael Walter wrote:
> > > I continued toying with my toy web server, and I'm "sometimes" getting
> > > "Invalid argument" errors in hGetLine for a handle I retrieved from
> > > Network.listenOn.
> > >
> >
> > My first guess would be that hGetLine would return invalid argument if
> > it was called on a handle which represents a file which is now closed.
> > However, testing in GHCI suggests that returns "illegal operation
> > (handle is closed)". Could be different for network sockets, I suppose.
> >
> >
> >
> > > "Sometimes", because it works fine in the browser, except when I
> > > reload very frequently -- maybe it's related to some concurrency
> > > issues (I'm using forkIO to spawn off the handler process from the
> > > main server loop). When I wanted to benchmark the server using "ab"
> > > (Apache Benchmark), it didn't even "survive" one request but Fail'ed
> > > using that error message - "<handle: n>: hGetLine: Invalid argument".
> > >
> > > I tried adjusting the buffering mode.
> > >
> > > Do you have any ideas?
> > >
> >
> > Sounds like a double-close error or something like that. Hard to say
> > without seeing the code. Can you make a minimal example?
> >
> > Jules
> >
> >
>