Re: [Haskell-cafe] enumerators: exception that can't be catched

29 Aug 2013

      Hi,

Thank you for the reply.

Unlikely it is the case (if I understand it correctly). The exception is
thrown by "enumSocket", I added traces to prove that. And it is
propagated to
"runWithSocket" ( http://hackage.haskell.org/packages/archive/websockets/0.7.4.0/doc/html/src/... ), so that "Data.Enumerator.run" returns "Left". So actually it is not an IO exception, but it is thrown via "throwError".

Looks like I don't have other options except to reimplement websockets
protocol myself :(

Thanks,
Yuras

On Tue, 2013-08-27 at 15:40 -0400, Ben Doyle wrote:
...
This is partially guesswork, but the code to catchWSError looks
dubious:
catchWsError :: WebSockets p a
             -> (SomeException -> WebSockets p a)
             -> WebSockets p a
  catchWsError act c = WebSockets $ do
      env <- ask
      let it  = peelWebSockets env $ act
          cit = peelWebSockets env . c
      lift $ it `E.catchError` cit
    where
      peelWebSockets env = flip runReaderT env . unWebSockets
Look at `cit`. It runs the recovery function, then hands the underlying Iteratee the existing environment. That's fine if `act` is at fault, but there are Iteratee- and IO-ish things in WebSocketsEnv---if one of `envSink` or `envSendBuilder` is causing the exception, it'll just get re-thrown after `E.catchError`. (I think. That's the guesswork part.)
So check how `envSendBuilder` is built up, and see if there's a way it could throw an exception on client disconnect.
On Tue, Aug 27, 2013 at 10:28 AM, Yuras Shumovich
 wrote:
        Hello,
I'm debugging an issue in "websockets" package,
        https://github.com/jaspervdj/websockets/issues/42
I'm not familiar with "enumerator" package (websockets are
        based on it),
        so I'm looking for help. The exception is throws inside
        "enumSocket"
        enumerator using
        "throwError" ( http://hackage.haskell.org/packages/archive/network-enumerator/0.1.5/doc/htm... ), but I can't catch it with "catchError". It is propagated to "run" function:
           <interactive>: recv: resource vanished (Connection reset by
        peer)
The question is: how is it possible? could it be a bug in
        "enumerator"
        package?
Thanks,
        Yuras
_______________________________________________
        Haskell-Cafe mailing list
        Haskell-Cafe@haskell.org
        http://www.haskell.org/mailman/listinfo/haskell-cafe