[Haskell-cafe] a tiny HTTP server.. that doesn't work

[Corey O'Connor]

Thanks for the input!

The sClose on line 21 is actually never called: the "dispatch_on_request"
loops forever.
The sClose implied by Network.HTTP.close on line 34 is called, but (in
theory) after the "ErrorClosed" error is produced. This error comes from
the "receiveHTTP" on line 37. Which should occur before the
Network.HTTP.close.

The reasoning of "client side has already closed the connection" makes
sense, but I would imagine the client (JMeter in this case) would wait for
a response before closing the connection. JMeter does receive a reply in
the failure cases. Which is the reply formed on line 23.

Curiously: If the Network.HTTP.close is removed the server does not fail,
but some requests takes several seconds to process. I presume the ordering
of effects is then correct, but without the explicit close the close occurs
only a GC time.

Cheers,
Corey


-Corey O'Connor
coreyoconnor at gmail.com
http://corebotllc.com/


On Mon, Oct 21, 2013 at 1:57 PM, Jeremy Shaw <jeremy at n-heptane.com> wrote:

> my hypothesis is that you are getting 'ErrorClosed' when calling
> 'sClose' because the client side has already beat you to the punch.
> But that is just a hypothesis.
>
> - jeremy
>
> On Mon, Oct 21, 2013 at 3:34 PM, Corey O'Connor <coreyoconnor at gmail.com>
> wrote:
> > I attempted to write a tiny HTTP server using only Haskell Platform
> > packages:
> >
> > * https://github.com/coreyoconnor/tiny-http-hp
> >
> > Which works... Unless the threaded runtime is used.
> >
> > When compiled using the threaded runtime and run with +RTS -N this server
> > fails to reply correctly to ~3% of requests. The expectation is that the
> > reply will be exactly the request body. However, 3% of the time the HTTP
> > request fails to be parsed due to an "ErrorClosed"
> >
> > The server then executes:
> >
> > *
> https://github.com/coreyoconnor/tiny-http-hp/blob/master/TinyHttp.hs#L23
> >
> > which responds to the client. The client receives the response correctly
> > most of the time.
> >
> > My current hypothesis is that some aspect of lazy IO is not playing nice.
> > The connection is being closed before the request can be completely
> parsed.
> >
> > Is this correct? What am I missing?
> >
> > I know there are other HTTP server packages that could be used. However,
> the
> > exercise was to build a HTTP server using only Haskell Platform packages.
> >
> > Below is the main body of the code:
> >
> >
> > main = withSocketsDo $ do
> >
> >     http_socket <- listenOn $ PortNumber 9090
> >
> >     dispatch_on_accept http_socket $ either handle_failed_request
> > handle_valid_request
> >
> >     sClose http_socket
> >
> >
> >
> > handle_failed_request failure = return $ Response (4,0,0) "Bad Request"
> > [mkHeader HdrConnection "close"]
> >
> >                                                   (encodeUtf8 $ pack $
> show
> > failure)
> >
> >
> > handle_valid_request request = do
> >
> >     let request_body = rqBody request
> >
> >     return $ Response (2,0,0) "OK" [mkHeader HdrConnection "close"]
> >
> >                       (encodeUtf8 $ pack $ show request_body)
> >
> >
> > dispatch_on_accept http_socket handler = forever $ accept http_socket >>=
> > forkIO . httpHandler . fst
> >
> >     where
> >         httpHandler client_socket = bracket (socketConnection "client" 0
> > client_socket)
> >
> >                                             Network.HTTP.close
> >
> >                                             client_interact
> >         client_interact :: HandleStream BS.ByteString -> IO ()
> >
> >         client_interact byte_stream = receiveHTTP byte_stream >>= handler
> >>>= respondHTTP byte_stream
> >
> >
> > -Corey O'Connor
> > coreyoconnor at gmail.com
> > http://corebotllc.com/
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
>
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