fix: extract rtp capabilities crash

[AlexanderPanaev]

Fixes #192.

Hit this on Android, libmediasoupclient 3.5.0 + libwebrtc M140. Reproduces when the only m=audio section in the SDP is rejected and a video produce runs. We only got there by alternating the mic and camera buttons quickly.

The offer at that moment, the live video section and the rejected audio one:

  m=video 55603 UDP/TLS/RTP/SAVPF 96 97 98 ...                                                                                                                                       
  a=mid:0                                                                                                                                                                            
  a=sendonly                                                                                                                                                                         
  a=extmap:1 ... a=extmap:14                       <- 13 extmap lines                                                                                                                
  a=rtpmap:96 VP8/90000                                                                                                                                                              
                                                                                                                                                                                     
  m=audio 0 UDP/TLS/RTP/SAVPF 111 63 9 0 8 13 110 126                                                                                                                                
  a=mid:44                                                                                                                                                                           
  a=inactive                                                                                                                                                                         
  a=rtpmap:111 opus/48000/2                                                                                                                                                          
  a=rtcp-fb:111 transport-cc                                                                                                                                                         
  a=fmtp:111 minptime=10;useinbandfec=1            <- no extmap at all    

Utils.cpp:136 then reads a key that is not there, on a const json&:

for (const auto& ext : m["ext"])

The call is a video produce, but it dies on the audio section - the mic was off, so the only m=audio in the SDP was the rejected one.

[DEBUG] Handler::Send() | [kind:video, track->id():ARDAMSv0]
[TRACE] PeerConnection::CreateOffer()
[TRACE] Sdp::Utils::extractRtpCapabilities()
[ERROR] transport_jni::JNI_SendTransport_Produce() | [json.exception.type_error.305] cannot use operator[] with a string argument with number

[ibc]

This is not the proper fix. Port could be != 0 and still there could be no a=ext lines and it would crash the same way. All the fields must be checked before iterating them. It's a global bug in that code.

[AlexanderPanaev]

Got it, thanks. I applied an approach similar to the fix @richmonkey, who reported #192, made in his fork (richmonkey@a9578ad), but only guarding the arrays before iterating, as mediasoup-client does for fmtp, rtcpFb and ext
(commonUtils.ts).

All four arrays (rtp, fmtp, rtcpFb, ext) are checked. rtp and fmtp are always set by the parser (parser.cpp), but I kept the check for consistency.

[jmillan]

@AlexanderPanaev can you please run npm run lint to fix the lint issues?

[AlexanderPanaev]

@AlexanderPanaev can you please run npm run lint to fix the lint issues?

local npm run lint is fine, ci failed because it cannon install clang-format.

[jmillan]

Yes. Fixed. Can you please merge the latest v3?

[AlexanderPanaev]

Yes. Fixed. Can you please merge the latest v3?

Done.

[jmillan]

Thanks @AlexanderPanaev 👍