RFC8843 : Accept offer with a=group:BUNDLE line even if it has conflicting ice-ufrag values

[Odinvt]

Your environment.

• Pion Version: v3.2.14
• PBX: Asterisk v18 (WebRTC mode)

What did you do?

Pion receives an SDP as offer which is then provided to SetRemoteDescription :

v=0
o=- 852496663 852496663 IN IP4 ...........
s=Asterisk
c=IN IP4 ................
t=0 0
a=group:BUNDLE audio-0 video-1 video-2
m=audio 11514 UDP/TLS/RTP/SAVPF 107 101
a=connection:new
a=setup:actpass
a=fingerprint:SHA-256 3E:E0:8A:06:36:56:73:9E:72:08:61:5D:13:38:C0:42:9A:25:3E:34:E7:03:7F:6E:F5:9F:B9:2C:7D:C7:02:C5
a=ice-ufrag:6992ba23181e294c0bd380af7ac57964
a=ice-pwd:7d1090fb4b82e27374cf42b8363b631d
a=candidate:H9387b5c9 1 UDP 2130706431 .............. 11514 typ host
a=candidate:Hd30485b5 1 UDP 2130706431 .............. 11514 typ host
a=rtpmap:107 opus/48000/2
a=fmtp:107 useinbandfec=1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=maxptime:20
a=sendrecv
a=rtcp-mux
a=ssrc:2081773396 cname:43c36c43-de21-4f8b-8ab7-4580bac88350
a=mid:audio-0
m=video 16464 UDP/TLS/RTP/SAVPF 100
a=connection:new
a=setup:actpass
a=fingerprint:SHA-256 43:DC:6D:4D:8B:7E:FE:47:3C:F3:18:6B:B7:D8:B0:0A:1F:20:55:18:60:AF:2F:46:E9:1F:A6:FE:F5:E0:22:4B
a=ice-ufrag:287c549566e5ca694b2aaf053d484b35
a=ice-pwd:548946fd5d6c7cb068bbcfb656593bb8
a=candidate:H9387b5c9 1 UDP 2130706431 ................... 16464 typ host
a=candidate:Hd30485b5 1 UDP 2130706431 ................... 16464 typ host
a=rtpmap:100 VP8/90000
a=sendrecv
a=rtcp-mux
a=ssrc:181453472 cname:efb36874-07c8-46aa-93cf-82f2237ae446
a=mid:video-1
m=video 16690 UDP/TLS/RTP/SAVPF 100
a=connection:new
a=setup:actpass
a=fingerprint:SHA-256 6D:37:49:4E:43:C8:D0:1F:49:50:17:36:F6:1B:2D:62:2F:CC:6F:51:B3:8F:D3:28:AF:02:37:0D:08:EA:83:53
a=ice-ufrag:194467e75266fb7d26b5d08f2521c42c
a=ice-pwd:037f3c931c992e497733cb7401d07efe
a=candidate:H9387b5c9 1 UDP 2130706431 ......................... 16690 typ host
a=candidate:Hd30485b5 1 UDP 2130706431 ......................... 16690 typ host
a=rtpmap:100 VP8/90000
a=recvonly
a=rtcp-mux
a=ssrc:27453603 cname:69161142-12b4-4468-b0d2-51c7229292e2
a=mid:video-2

What did you expect?

I expect Pion to follow the RFC8843 and accept that offer even if it has conflicting ice-ufrag values because it has the
a=group:BUNDLE line. Then choose which stream's transport it wants to use (typically the first one but the RFC allows to choose any one). And respond with an answer with bundling enabled for the chosen transport.

What happened?

Error : SetRemoteDescription called with multiple conflicting ice-ufrag values

[Odinvt]

For anyone interested in a workaround for this for the moment :

If you're sure the originator of the offer supports Bundling and an attribute a=group:BUNDLE is included in the offer, you just need to hack the SDP using pion/sdp package for Pion to accept it. Mainly :

1/ Copy the same values of ice-ufrag, ice-pwd and fingerprint from the first media description to all the others
2/ Set each media description's port to the port of the first media description (MediaDescriptions[i].MediaName.Port = MediaDescriptions[0].MediaName.Port)
3/ Replace all media description's candidates with the candidate list from the first media description
4/ Generate the answer

if you need proper ice-lite functionality in the answer, setting it to true in the Settings Engine is not enough. You need to also hack the resulting answer to :
1/ Include your IP in Origin and all the ConnectionInformation lines.
2/ Wait for the host candidate you're interested in from Pion.
3/ Plug that same candidate in all the Media Descriptions
4/ Take that candidate's port and Set each media description's port to that port (mediaDesc.MediaName.Port = sdp.RangedPort{Value: int(candidate.Port)})

And you're set ! Your peer connection should be connected and ice connectivity should be properly established as mine did.