What is happening is that the socket is closed after the accept
but before the hGetLine, so the handle is invalid (there is no
socket any more)... This is correct behaviour when the client
closes the connection whilst you are writing to it...
The answer is just to catch the exception.
Keean.
Michael Walter wrote:
Yep - this program "sometimes" fails for me with such an error message:
Fail: <socket: 8>: hGetLine: invalid argument (Invalid argument)
If I omit the forkIO and do synchronous processing, I noticed that
Apache Benchmark connects a second time but closes the connection
immediately. When I added a `catch` \e -> mainLoop socket at the end
of the main loop, it worked fine.
But when I reintroduced the forkIO, it seemed to be "hanging" in the
main process's accept (when the fork failed with above's error
message).
Any ideas?
Confusingly yours,
Michael
On Thu, 9 Dec 2004 14:29:10 -0500, Michael Walter
<[EMAIL PROTECTED]> wrote:
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
<[EMAIL PROTECTED]> wrote:
I'll do so at lunch break/from home tonight.
Thanks,
Michael
On Thu, 9 Dec 2004 16:19:20 +0000, Jules Bean <[EMAIL PROTECTED]> 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
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