Fixing issue with default stream upon setting 2nd remote description.

talk/app/webrtc/peerconnection.cc

Index: talk/app/webrtc/peerconnection.cc
diff --git a/talk/app/webrtc/peerconnection.cc b/talk/app/webrtc/peerconnection.cc
index caa892d00b9b04802c15908b04f97bd4ddf3cfb1..6fbafc718efb3f3ae1da9d29c105cc96dd66d586 100644
--- a/talk/app/webrtc/peerconnection.cc
+++ b/talk/app/webrtc/peerconnection.cc
@@ -1087,6 +1087,26 @@ void PeerConnection::SetRemoteDescription(
   }
 
   const cricket::SessionDescription* remote_desc = desc->description();
+  const cricket::ContentInfo* audio_content = GetFirstAudioContent(remote_desc);
+  const cricket::ContentInfo* video_content = GetFirstVideoContent(remote_desc);

[pthatcher1, 2015/12/03 20:07:39]

I think you can use 

const cricket::AudioContentDescription* audio =
GetFirstAudioContentDescriptionr(remote_desc);

To save a few casts and lines.

[Taylor Brandstetter, 2015/12/04 22:04:54]

I still need the ContentInfo pointers to tell if they're rejected later. But I
can do something similar.

+
+  remote_peer_msid_supported_ |= remote_desc->msid_supported();
+  // Just in case the peer supports MSID, but doesn't indicate so with
+  // "a=msid-semantic"...
+  if (audio_content &&
+      !static_cast<const cricket::AudioContentDescription*>(
+           audio_content->description)
+           ->streams()
+           .empty()) {
+    remote_peer_msid_supported_ = true;
+  }
+  if (video_content &&
+      !static_cast<const cricket::VideoContentDescription*>(
+           video_content->description)
+           ->streams()
+           .empty()) {
+    remote_peer_msid_supported_ = true;
+  }

[pthatcher1, 2015/12/03 20:07:40]

I think it could be:

auto audio = GetFirstAudioContentDescription(remote_desc);
auto video = GetVideoAudioContentDescriptionr(remote_desc);
if (remote_desc->msid_supported() ||
    (audio && !audio->streams.empty() ||
    (video && !video->streams.empty()) {
  remote_peer_supports_msid_ = true;
}

[Taylor Brandstetter, 2015/12/04 22:04:54]

Done.

 
   // We wait to signal new streams until we finish processing the description,
   // since only at that point will new streams have all their tracks.
@@ -1094,7 +1114,6 @@ void PeerConnection::SetRemoteDescription(
 
   // Find all audio rtp streams and create corresponding remote AudioTracks
   // and MediaStreams.
-  const cricket::ContentInfo* audio_content = GetFirstAudioContent(remote_desc);
   if (audio_content) {
     if (audio_content->rejected) {
       RemoveTracks(cricket::MEDIA_TYPE_AUDIO);
@@ -1102,17 +1121,17 @@ void PeerConnection::SetRemoteDescription(
       const cricket::AudioContentDescription* desc =
           static_cast<const cricket::AudioContentDescription*>(
               audio_content->description);

[pthatcher1, 2015/12/03 20:07:40]

This line (or 3) could go away if you use the function I mentioned before.

[Taylor Brandstetter, 2015/12/04 22:04:54]

Done.

-      UpdateRemoteStreamsList(GetActiveStreams(desc), desc->type(),
-                              new_streams);
-      remote_info_.default_audio_track_needed =
-          !remote_desc->msid_supported() && desc->streams().empty() &&
+      bool default_audio_track_needed =
+          !remote_peer_msid_supported_ && desc->streams().empty() &&
           MediaContentDirectionHasSend(desc->direction());
+      UpdateRemoteStreamsList(GetActiveStreams(desc),
+                              default_audio_track_needed, desc->type(),
+                              new_streams);
     }
   }
 
   // Find all video rtp streams and create corresponding remote VideoTracks
   // and MediaStreams.
-  const cricket::ContentInfo* video_content = GetFirstVideoContent(remote_desc);
   if (video_content) {
     if (video_content->rejected) {
       RemoveTracks(cricket::MEDIA_TYPE_VIDEO);
@@ -1120,11 +1139,12 @@ void PeerConnection::SetRemoteDescription(
       const cricket::VideoContentDescription* desc =
           static_cast<const cricket::VideoContentDescription*>(
               video_content->description);
-      UpdateRemoteStreamsList(GetActiveStreams(desc), desc->type(),
-                              new_streams);
-      remote_info_.default_video_track_needed =
-          !remote_desc->msid_supported() && desc->streams().empty() &&
+      bool default_video_track_needed =
+          !remote_peer_msid_supported_ && desc->streams().empty() &&
           MediaContentDirectionHasSend(desc->direction());
+      UpdateRemoteStreamsList(GetActiveStreams(desc),
+                              default_video_track_needed, desc->type(),
+                              new_streams);
     }
   }
 
@@ -1147,15 +1167,7 @@ void PeerConnection::SetRemoteDescription(
     observer_->OnAddStream(new_stream);
   }
 
-  // Find removed MediaStreams.
-  if (remote_info_.IsDefaultMediaStreamNeeded() &&
-      remote_streams_->find(kDefaultStreamLabel) != nullptr) {
-    // The default media stream already exists. No need to do anything.
-  } else {
-    UpdateEndedRemoteMediaStreams();
-    remote_info_.msid_supported |= remote_streams_->count() > 0;
-  }
-  MaybeCreateDefaultStream();
+  UpdateEndedRemoteMediaStreams();
 
   SetSessionDescriptionMsg* msg = new SetSessionDescriptionMsg(observer);
   signaling_thread()->Post(this, MSG_SET_SESSIONDESCRIPTION_SUCCESS, msg);
@@ -1492,25 +1504,30 @@ bool PeerConnection::GetOptionsForAnswer(
 
 void PeerConnection::RemoveTracks(cricket::MediaType media_type) {
   UpdateLocalTracks(std::vector<cricket::StreamParams>(), media_type);
-  UpdateRemoteStreamsList(std::vector<cricket::StreamParams>(), media_type,
-                          nullptr);
+  UpdateRemoteStreamsList(std::vector<cricket::StreamParams>(), false,
+                          media_type, nullptr);
 }
 
 void PeerConnection::UpdateRemoteStreamsList(
     const cricket::StreamParamsVec& streams,
+    bool default_track_needed,
     cricket::MediaType media_type,
     StreamCollection* new_streams) {
   TrackInfos* current_tracks = GetRemoteTracks(media_type);
 
   // Find removed tracks. I.e., tracks where the track id or ssrc don't match
-  // the
-  // new StreamParam.
+  // the new StreamParam.
   auto track_it = current_tracks->begin();
   while (track_it != current_tracks->end()) {
     const TrackInfo& info = *track_it;
     const cricket::StreamParams* params =
         cricket::GetStreamBySsrc(streams, info.ssrc);
     if (!params || params->id != info.track_id) {
+      // If this is a default track, and we still need it, don't remove it.
+      if (info.stream_label == kDefaultStreamLabel && default_track_needed) {
+        ++track_it;
+        continue;
+      }
       OnRemoteTrackRemoved(info.stream_label, info.track_id, media_type);
       track_it = current_tracks->erase(track_it);
     } else {
@@ -1542,6 +1559,27 @@ void PeerConnection::UpdateRemoteStreamsList(
       OnRemoteTrackSeen(stream_label, track_id, ssrc, media_type);
     }
   }
+
+  // Add default track if necessary.
+  if (default_track_needed) {
+    rtc::scoped_refptr<MediaStreamInterface> stream =
+        remote_streams_->find(kDefaultStreamLabel);

[pthatcher1, 2015/12/03 20:07:40]

A better name for that variable might be "default_stream"

[Taylor Brandstetter, 2015/12/04 22:04:54]

Done.

+    if (!stream) {
+      // Create the new default MediaStream.
+      stream = remote_stream_factory_->CreateMediaStream(kDefaultStreamLabel);
+      remote_streams_->AddStream(stream);
+      new_streams->AddStream(stream);
+    }
+    std::string track_id = (media_type == cricket::MEDIA_TYPE_AUDIO)
+                               ? kDefaultAudioTrackLabel
+                               : kDefaultVideoTrackLabel;

[pthatcher1, 2015/12/03 20:07:40]

And that default_track_id

[Taylor Brandstetter, 2015/12/04 22:04:54]

Done.

+    const TrackInfo* track_info =
+        FindTrackInfo(*current_tracks, kDefaultStreamLabel, track_id);

[pthatcher1, 2015/12/03 20:07:40]

And that default_track

[Taylor Brandstetter, 2015/12/04 22:04:54]

Done.

+    if (!track_info) {
+      current_tracks->push_back(TrackInfo(kDefaultStreamLabel, track_id, 0));
+      OnRemoteTrackSeen(kDefaultStreamLabel, track_id, 0, media_type);
+    }
+  }
 }
 
 void PeerConnection::OnRemoteTrackSeen(const std::string& stream_label,
@@ -1604,41 +1642,6 @@ void PeerConnection::UpdateEndedRemoteMediaStreams() {
   }
 }
 
-void PeerConnection::MaybeCreateDefaultStream() {
-  if (!remote_info_.IsDefaultMediaStreamNeeded()) {
-    return;
-  }
-
-  bool default_created = false;
-
-  rtc::scoped_refptr<MediaStreamInterface> default_remote_stream =
-      remote_streams_->find(kDefaultStreamLabel);
-  if (default_remote_stream == nullptr) {
-    default_created = true;
-    default_remote_stream =
-        remote_stream_factory_->CreateMediaStream(kDefaultStreamLabel);
-    remote_streams_->AddStream(default_remote_stream);
-  }
-  if (remote_info_.default_audio_track_needed &&
-      default_remote_stream->GetAudioTracks().size() == 0) {
-    remote_audio_tracks_.push_back(
-        TrackInfo(kDefaultStreamLabel, kDefaultAudioTrackLabel, 0));
-    OnRemoteTrackSeen(kDefaultStreamLabel, kDefaultAudioTrackLabel, 0,
-                      cricket::MEDIA_TYPE_AUDIO);
-  }
-  if (remote_info_.default_video_track_needed &&
-      default_remote_stream->GetVideoTracks().size() == 0) {
-    remote_video_tracks_.push_back(
-        TrackInfo(kDefaultStreamLabel, kDefaultVideoTrackLabel, 0));
-    OnRemoteTrackSeen(kDefaultStreamLabel, kDefaultVideoTrackLabel, 0,
-                      cricket::MEDIA_TYPE_VIDEO);
-  }
-  if (default_created) {
-    stats_->AddStream(default_remote_stream);
-    observer_->OnAddStream(default_remote_stream);
-  }
-}
-
 void PeerConnection::EndRemoteTracks(cricket::MediaType media_type) {
   TrackInfos* current_tracks = GetRemoteTracks(media_type);
   for (TrackInfos::iterator track_it = current_tracks->begin();