On Thu, 1 Oct 2020, Andriy Gelman wrote:
On Thu, 01. Oct 22:00, Zhao Zhili wrote:
On 10/1/20 4:15 AM, Martin Storsjö wrote:
> On Wed, 30 Sep 2020, Zhao Zhili wrote:
>
> > Hi Martin,
> >
> > On 9/30/20 5:41 PM, Martin Storsjö wrote:
> > > In listen mode with UDP transport, once the sender has sent
> > > the TEARDOWN and closed the connection, poll will indicate that
> > > one can read from the connection (indicating that the socket has
> > > reached EOF and should be closed by the receiver as well). In this
> > > case, parse_rtsp_message won't try to parse the command (because
> > > it's no longer in state STREAMING), but previously just returned
> > > zero.
> > >
> > > Prior to f6161fccf8c5720ceac1ed1df8ba60ff8fed69f5, this caused
> > > udp_read_packet to return zero, which is treated as EOF by
> > > read_packet. But after that commit, udp_read_packet would continue
> > > if parse_rtsp_message didn't return an explicit error code.
> > >
> > > To keep the original behaviour from before that commit, more
> > > explicitly return an error in parse_rtsp_message when in the wrong
> > > state.
> > >
> > > Fixes: #8840
> > > ---
> > > libavformat/rtsp.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
> > > index 5d8491b74b..ad12f2ae98 100644
> > > --- a/libavformat/rtsp.c
> > > +++ b/libavformat/rtsp.c
> > > @@ -1970,7 +1970,7 @@ static int parse_rtsp_message(AVFormatContext *s)
> > > av_log(s, AV_LOG_WARNING,
> > > "Unable to answer to TEARDOWN\n");
> > > } else
> > > - return 0;
> > > + return AVERROR_EOF;
> >
> > Does the else part needs the same fix?
>
> Which else part do you refer to? The else above (with the warning)? Yes
> that bit looks a bit odd to me as well - your patch 2/2 looks like a
> good fix for that.
I mean the else below, especially
/* XXX: parse message */
if (rt->state != RTSP_STATE_STREAMING)
return 0;
I did some tests with the rtsp server from:
https://github.com/revmischa/rtsp-server
This point can be reached with rt->state = RTSP_STATE_IDLE when the
initial_pause option is set:
./ffmpeg -initial_pause 1 -i rtsp://127.0.0.1/abc -f null -
Then it seems changing the return value in the above code would lead to
unintended results.
Thanks for testing this.
Indeed, I'd rather treat that as a separate case. The listen mode is not
very widely used, and this issue can be traced back to a regression, so
that can be easily fixed in that context.
For the other case you're pointing out, I don't have a concrete bug (the
UDP mode seems to require waiting for a long timeout at the end though,
but changing this return statement to return an error doesn't seem to
help), and the normal non-listen mode code can be used in a huge variety
of cases, many that aren't very easy to test (e.g. the code used to
support RealRTSP, but I'm not sure if there's any publicly available test
clips/servers for that any longer - multimediawiki used to list some, but
I tested them last time close to a decade ago, and then there might have
been zero or one of them still responding). So for that code, I'd tread
much more carefully...
// Martin
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