[Live-devel] UDP sockets don't use ReceivingInterfaceAddr?

[Patrick White]

In a word.. nevermind.

Oops.. got my logic backwards.. Yes, the port number is always 0 for RTP UDP 
unicast... and that's why the if never happens and ReceivingInterfaceAddr is 
never used.  With your added bit about multicast using a !0 port number, and 
thinking through all the logic reasoning, I can see now why it is done this 
way -- it is the only way to control which adapter multicast traffic goes 
out. ..And I can also see now that it would be unwise (not wrong, just 
unwise) to change the code, so I won't :)

Sorry about any confusion.. trying to juggle too many closely related logic 
threads at once and wires got crossed in the 'ol noggin.

later,
patbob

On Tuesday 24 February 2009 8:32 am, Patrick White wrote:
> > >I'm trying to use ReceivingInterfaceAddr & SendingInterfaceAddr to
> > > control which interface RTSP/RTP traffic is going in and out on.
> > >In setupDatagramSocket(), there is the line:
> > >     if (port.num() == 0) addr = ReceivingInterfaceAddr;
> > >This line is just prior to the bind() call.  So.. UDP ports are only
> > > bound to a particular interface if portnum is also 0.  Because of this,
> > > all the UDP sockets used for RTP traffic are bound to IP_ADDRANY.
> > >Is there a particular reason for this?  Is it a multicast thing or
> > > something?
> >
> > Yes, I think so.  I think the intention was that you would want to
> > create a datagram socket with an initial non-zero port number only
> > for multicast streams, in which case you probably wouldn't want to
> > bind() to something other than INADDR_ANY.  But I'm not sure.
> >
> > But anyway, if you're really doing this for unicast RTSP/RTP, then
> > you shouldn't run into this issue, because - in this case - the port
> > number should be 0 when the socket is created, I think.
>
> We're doing unicast, and the port number is never 0 through this code --
> it's always 6970+, so the adapter assignment can never happen.
>
> By default, ReceivingInterfaceAddr is 0 (IP_ADDRANY), which is also what
> addr is by default, so normally this assignment makes no difference.  I've
> tried it with unicast RTP and it works fine.  It should also work fine with
> multicast, restricting the outbound traffic to a particular adapter, but I
> don't have any way to test multicast anything at the current time.
>
> I figured I'd ask before committing the change, just in case you or someone
> else knows why it needs to be this way.  Since we're trying to push as many
> changes as we can back into your library, I don't want to push back bugs if
> we can help it.
>
> > >Can I change it to make it always set addr from ReceivingInterfaceAddr?
> >
> > This is Open Source; you can change it to whatever you want :-)  I
> > can't guarantee that it will work, though.
>
> The change works fine for us.. and yes, we have the source so we can change
> it.
>
> thanks,
> patbob
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