Re: [FFmpeg-devel] [PATCH v2 2/3] avformat/udp: Fix IP_MULTICAST_TTL for BSD compatibility

[lance.lmwang@gmail.com]

On Sat, Feb 05, 2022 at 10:59:55AM +0100, Marton Balint wrote:
> 
> 
> On Sat, 5 Feb 2022, lance.lmwang@gmail.com wrote:
> 
> > From: Limin Wang <lance.lmwang@gmail.com>
> > 
> > Suggested by zhilizhao, vlc project has solved the compatibility by
> > the same way, so I borrowed the comments from vlc project.
> > 
> > Fix #ticket9449
> > 
> > Signed-off-by: Limin Wang <lance.lmwang@gmail.com>
> > ---
> > libavformat/udp.c | 15 +++++++++++++--
> > 1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavformat/udp.c b/libavformat/udp.c
> > index 3dc79eb..34488d6 100644
> > --- a/libavformat/udp.c
> > +++ b/libavformat/udp.c
> > @@ -164,6 +164,10 @@ static int udp_set_multicast_ttl(int sockfd, int mcastTTL,
> > {
> >     int protocol, cmd;
> > 
> > +    /* There is some confusion in the world whether IP_MULTICAST_TTL
> > +     * takes a byte or an int as an argument.
> > +     * BSD seems to indicate byte so we are going with that and use
> > +     * int as a fallback to be safe */
> 
> The code does the opposite. Tries int and falls back to byte. Either change
> code or change comment.

Yes, good catch, so vlc use wrong comments. I'll change comments like below.
+     * BSD seems to indicate byte so we are going with that and tries
+     * int and falls back to byte to be safe */

> 
> Regards,
> Marton
> 
> >     switch (addr->sa_family) {
> > #ifdef IP_MULTICAST_TTL
> >         case AF_INET:
> > @@ -183,8 +187,15 @@ static int udp_set_multicast_ttl(int sockfd, int mcastTTL,
> >     }
> > 
> >     if (setsockopt(sockfd, protocol, cmd, &mcastTTL, sizeof(mcastTTL)) < 0) {
> > -        ff_log_net_error(logctx, AV_LOG_ERROR, "setsockopt");
> > -        return ff_neterrno();
> > +        /* BSD compatibility */
> > +        unsigned char ttl;
> > +
> > +        ff_log_net_error(logctx, AV_LOG_DEBUG, "setsockopt");
> > +        ttl = (unsigned char)(( mcastTTL > 255 ) ? 255 : mcastTTL);
> > +        if (setsockopt(sockfd, protocol, cmd, &ttl, sizeof(ttl)) < 0) {
> > +            ff_log_net_error(logctx, AV_LOG_ERROR, "setsockopt");
> > +            return ff_neterrno();
> > +        }
> >     }
> > 
> >     return 0;
> > -- 
> > 1.8.3.1
> > 
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-- 
Thanks,
Limin Wang
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