[racket] WebSocket server dropping connections

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Mon Feb 7 10:19:20 EST 2011

I don't know much about Chrome 10, but is it possible that it has
dropped support for the old framing mode? The WebSocket implementation
supports both old and new, but defaults to old because that's what a
lot of browsers (used to) default to.

Look at framing-mode in the documentation.

It is unlikely that they are being garbage collected, because it uses
the same "connection manager" machinery as the Web server, that
retains references to the ports.


2011/2/6 Jakub Piotr Cłapa <jpc-ml at zenburn.net>:
> I am using the WebSocket server and having problems with connections
> dropping unexpectedly. I am connecting from Chrome 10 (dev channel).
> In the connection handler I register callbacks (which get asynchronously
> called in other threads) and use ws-send! in them.
> The callback looks like this:
> #v+
> (define ((event-sender name [ws (current-websocket)]) obj key old new)
>  (if (ws-conn-closed? ws)
>      (begin
>        (eprintf "~a.~a: conn closed\n" (object-name obj) key)
>        (remove-current-observer))
>      (parameterize ([current-websocket ws])
>        (try
>         (send-json! (list "changed" (symbol->string name) (symbol->string
> key)
>                           (if (void? old) #\null old) new))
>         (eprintf "send failed for websocket: ~a\n" (debug-ws ws))))))
> (define (debug-ws ws)
>  (append (for/list ([i (in-range 5)]) (unsafe-vector-ref ws i))
>          (list (port-closed? (unsafe-vector-ref ws 3))
>                (port-closed? (unsafe-vector-ref ws 4)))))
> #v-
> The ws-conn-closed? returns #f. The debug-ws uses unsafe ops to extract tcp
> ports. Both report closed at this point.
> I pasted my server initialization code below. None of the logging statements
> get executed in the dropped connection case.
> My only guess is that the connection threads get garbage collected while
> waiting on the tcp input-port.
> #v+
> (define (handle-handshake bs hs)
>  (define origin
>    (header-value (headers-assq* #"Origin" hs)))
>  (values
>   (list (make-header #"Sec-WebSocket-Origin" origin)
>         (make-header #"Sec-WebSocket-Location"
>                      #"ws://localhost:8080/"))
>   #f))
> (define (handle-connection sock state)
>  (parameterize ([current-websocket sock])
>    (log-info (format "client connected: ~s" (debug-ws (current-websocket))))
>    (with-handlers ([exn:fail:network? (exn-handler (λ (msg) (log-debug
> msg)))]
>                    [exn:fail? (exn-handler (λ (msg) (log-error msg)))]
>                    [(λ (exn) #t) (λ (exn) (log-error (format "WTF?: ~s"
> exn)) (raise exn))])
>      (let loop ()
>        (let ([m (ws-recv (current-websocket))])
>          (cond
>            [(eof-object? m)
>             (log-info (format "client disconnected: ~s" (debug-ws
> (current-websocket))))]
>            [else
>             (log-debug (format "message received: ~a" m))
>             (let ([msg (try (json->jsexpr m)
>                             (raise-proto-error "malformed ws message: ~s"
> m))])
>               (handle-request msg)
>               (loop))]))))
>    (log-info "exiting from handle-client")
>    (remove-observers!)))
> (define (start-server)
>  (ws-serve handle-connection
>            #:port 8080
>            #:conn-headers handle-handshake))
> #v-
> --
> regards,
> Jakub Piotr Cłapa
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Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93

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