[noPoll] Fixed -- Re: Websocket disconnect issues
Francis Brosnan Blázquez
francis.brosnan en aspl.es
Jue Abr 21 10:51:33 CEST 2016
Hello Rahul,
I've updated noPoll sources to reproduce the problem you described
(test_30)
and added needed updates to make it work (svn revision 262):
https://github.com/ASPLes/nopoll
Check them to see if they fixes your issue,
Best Regards,
> 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
> > DISCLAIMER
> >
> >
> > This message is subject to the following terms and conditions: MAIL
> > DISCLAIMER
>
>
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--
Francis Brosnan Blázquez - ASPL
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