Re: [Linphone-developers] ortp: using port used by other process

[Petr Kuba]

Hello Simon,
thank you for your quick response.

Yes, we are setting explicitly the port using rtp_session_set_local_addr().

Our application is a media server which can open many rtp streams. We 
use a pool (range) of ports which are used iteratively for rtp streams.
The problem appears when two instances of the server are run 
simultaneously (which can be sometimes useful). In this case we need to 
detect that we are trying to open a socket which is already in use and 
report an error. SO_REUSEADDR seems to be dangerous in this case.

We don't want to use random ports because with large number of ports 
(e.g. more than 1000) the pool is faster. We just need to get informed 
about error in some specific cases (such as two instances running with 
the same pool).

According to what I found out about close() the socket should become 
available again after some (unspecified) time so with large enough pool 
I believe this should not be a problem. BTW have you considered calling 
shutdown() and receiving FD_CLOSE before calling close()? It looks like 
it might help a little bit (but I might be wrong).

Do you think that it would be possible at least to make use SO_REUSEADDR 
configurable?


BTW, one more (very minor from our point of view) problem we met while 
inspecting this problem:

When calling rtp_session_set_local_addr() for the first time 
session->rtp.socket seems to have uninitialized (random) value. It 
causes calling of the following code at the beginning of 
rtp_session_set_local_addr() which is probably not desired:

        /* don't rebind, but close before*/
        rtp_session_release_sockets(session);

Regards,
Petr


Simon Morlat wrote:
> Hello,
>
> Are you setting explicitely the port using rtp_session_set_local_addr() ?
> In lastest version of oRTP, if rtp_session_set_local_addr() is used, 
> SO_REUSEADDR is used to allow the socket to be reused later (after close()).
> If rtp_session_set_local_addr() is NOT used, then a random port is choosen by 
> oRTP, and in this case SO_REUSEADDR is not used to avoid binding on a busy 
> port.
> Does it solve your problem ?
>
> Simon
>
> Le Thursday 19 March 2009 13:36:38 Petr Kuba, vous avez écrit :
> > Hello,
> >
> > We met the following problem with ortp in our application: if the local
> > port we want to use is already used by some other process no error is
> > reported. Therefore we do not hear any audio without being informed
> > about the problem.
> >
> > We believe that this is caused by the following line in the
> > create_and_bind() function:
> >
> > err = setsockopt (sock, SOL_SOCKET, SO_REUSEADDR,
> >                 (SOCKET_OPTION_VALUE)&optval, sizeof (optval));
> >
> > The create_and_bind() function is called from the
> > rtp_session_set_local_addr() function.
> >
> > We met this problem in ortp 0.13.1 (under Windows XP) but after quick
> > check it looks like the same would happen with 0.15.0.
> >
> > Could you explain us why SO_REUSEADDR option is used and suggest some
> > way to detect problems? Our idea is to make use of SO_REUSEADDR
> > configurable.
> >
> > Thanks,
> > Petr

--
   Petr Kuba, Project Manager
   OptimSys, s.r.o
   address@hidden
   Tel: +420 541 143 065
   Fax: +420 541 143 066
   http://www.optimsys.cz