[noPoll] Websocket disconnect issues
Francis Brosnan Blázquez
francis.brosnan en aspl.es
Jue Abr 21 09:30:20 CEST 2016
Hello Rahul,
Thanks for reporting. I'm reviewing the issue. I'll let you know
something,
Best Regards,
>
>
> Hello,
>
>
>
> I have some more debug information regarding this issue.
>
>
>
> To confirm the conjecture that the next two bytes may not always be
> immediately available,
>
> I made a local modification as shown below and ran the test again
> waiting for next failure.
>
> Instead of immediately aborting the connection when this situation
> occurs, I poll the connection
>
> for a short duration to see if the next two bytes appear subsequently,
> and then abort the connection anyway.
>
>
>
> } else if (msg->payload_size == 126) {
>
> /* get extended 2 bytes length as unsigned 16 bit
>
> unsigned integer */
>
> bytes = __nopoll_conn_receive (conn, buffer + 2, 2);
>
> if (bytes != 2) {
>
> int i;
>
> nopoll_log (conn->ctx, NOPOLL_LEVEL_CRITICAL, "Failed to
> get next 2 bytes to read header from the wire (read %d, %d), failed to
> received content, shutting down id=%d the connection", bytes, errno,
> conn->id);
>
> for (i = 0; i < 100; i++) {
>
> bytes = __nopoll_conn_receive (conn, buffer + 2, 2);
>
> if (bytes == 2) {
>
> nopoll_log (conn->ctx, NOPOLL_LEVEL_CRITICAL,
> "Finally got next 2 bytes to read header from the wire after %d tries,
> shutting down anyway id=%d the connection", i, conn->id);
>
> break;
>
> }
>
> nopoll_sleep(10); // 10 ms sleep
>
> }
>
> nopoll_msg_unref (msg);
>
> nopoll_conn_shutdown (conn);
>
> return NULL;
>
> } /* end if */
>
>
>
> The above is just a local change to confirm the root cause.
>
>
>
> I reproduced the disconnection bug again and from the logs, you can
> see that only one byte was available initially
>
> and after a very short duration we do get the remaining bytes.
>
>
>
> The relevant log lines look like:
>
>
>
> nopoll_conn.c:2798 Failed to get next 2 bytes to read header from the
> wire (read 1, 0), failed to received content, shutting down id=2 the
> connection
>
> nopoll_conn.c:2802 Finally got next 2 bytes to read header from the
> wire after 5 tries, shutting down anyway id=2 the connection
>
>
>
> I think, not getting next 2 (or 4 bytes) should not be treated as an
> error situation, but rather treated as
>
> full message not yet available just like when waiting for the first
> two bytes of the message. The call is supposed to be
>
> non-blocking so we of course cannot poll like the test code snippet
> above.
>
>
>
> Do let me know if you need any further info.
>
> This issue is very critical to move forward with our current
> application.
>
>
>
> Regards,
>
>
>
> Rahul
>
>
>
>
>
>
> From: nopoll-bounces en lists.aspl.es
> [mailto:nopoll-bounces en lists.aspl.es] On Behalf Of Kale, Rahul
> Sent: Tuesday, April 19, 2016 6:33 PM
> To: nopoll en lists.aspl.es
> Subject: [noPoll] Websocket disconnect issues
>
>
>
>
>
>
>
> Hello,
>
>
>
> I have been trying to track down a random websocket disconnection
> issue that we are facing.
>
> In our application, after some random number of hours of a good
> websocket connection that is
>
> transferring data back and forth, the connection suddenly breaks. We
> are using noPoll only
>
> for the client side of a WebSocket connection. The server side is
> Apache frontend with
>
> node app backend.
>
>
>
> After eliminating all other probable causes, I enabled noPoll debug
> logs and was finally able
>
> to catch the error which causes a disconnect:
>
>
>
> nopoll_conn.c:2797 Failed to get next 2 bytes to read header from the
> wire, failed to received content, shutting down id=2 the connection
>
>
>
> Reproducing this is difficult since it takes anything from a couple of
> hours to a couple of days
>
> but eventually it happens. My debugging efforts at narrowing this down
> is thus taking quite a while.
>
>
>
> We are using secure web sockets (wss://).
>
>
>
> Looking at the code, it seems that in the noPoll library, we expect
> the next two bytes of
>
> the websocket header to be always available if we read the first two
> bytes.
>
> I think that over TCP (and possibly even more so over TLS)
>
> this may not always be guaranteed. The socket is non-blocking and it
> may occasionally
>
> have a pattern that 4 bytes are split over two (or more) TCP segments.
>
>
>
> For reading first two bytes noPoll library seems to be buffering if
> data is not available.
>
> For correctness, should this be done for subsequent parts of the
> header too?
>
> Of course, I am not an expert here so could you analyze and let me
> know what is could
>
> be the root cause? What should be my next steps?
>
>
>
> I have already verified that this is not due to http(s) server error.
> I did a TCP dump
>
> and confirmed that when this happens, the first FIN is sent by the
> client (noPoll) to the http server.
>
>
>
>
>
> Regards,
>
>
>
> Rahul
>
>
>
> Rahul Kale
>
>
>
> IP Video Systems
>
> Barco, Inc
>
> 1287 Anvilwood Ave
>
> Sunnyvale, CA 94089
>
>
>
> Tel +1 408 400 4238
>
>
>
> This message is subject to the following terms and conditions: MAIL
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>
>
>
> This message is subject to the following terms and conditions: MAIL
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--
Francis Brosnan Blázquez - ASPL
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