Webrtcbin does not add peer-reflexive ice candidates

[Trey Hutcheson]

Stun can be difficult. In our lab, sometimes the outbound stun requests
from the remote peer (the browser) fail because of snat exhaustion, or
simply by rate limiting of the stun server. When this happens, the only
candidate to make it to our side is an mDNS candidate.

I'd like to confirm your assertion that the peer reflexive candidate is
added internally by libnice, but I'm using the rust gstreamer bindings (and
the libnice crate is out of date and doesn't expose many of the c
functions) and mostly opaque to me. I can, however, confirm that the remote
side successfully establishes a connected pair, but the local side
(webrtcbin) never advances the ice-connection-state
beyond GST_WEBRTC_ICE_CONNECTION_STATE_CHECKING.

On Tue, Oct 6, 2020 at 1:52 PM Olivier Crête <olivier.crete at collabora.com>
wrote:

> Hi,
>
> The peer reflexive candidates already get added internally inside libnice,
> the "new-remote-candidate" signal is just there for debugging and logging
> at the application level.
>
> So in theory, if you already set the remote credentials, I believe it
> should work. That said, this is a bit of code that has move quite a bit in
> the last few libnice releases. And there may very well be a bug in there.
>
> In practice, I expect you'd always at least get a "host" candidate from
> the other side.
>
> Olivier
>
> On Tue, 2020-10-06 at 13:10 -0500, Trey Hutcheson wrote:
>
> If a remote peer does not trickle in any resolvable candidates (for
> example, their stun binding fails), then there is no ice connectivity, and
> therefore, no actual media flows.
>
> However, if webrtcbin returns resolvable candidates, the browser will
> attempt to perform stun bindings against these candidates. When that
> happens, libnice's NiceAgent will emit the
> "initial-binding-request-received" signal, and it will also discover the
> remote side as a peer reflexive candidate, and emit the
> "new-remote-candidate-full" signal. In the case of a peer reflexive
> candidate, ice connectivity could be established if this candidate were
> added back to the ice agent's list of remote candidates.
>
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> --
>
> Olivier Crête olivier.crete at collabora.com
>
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