Return false if PeerConnection::GetStats() is called on invalid tracks

webrtc/api/peerconnection.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 868 matching lines @@
                               MediaStreamTrackInterface* track,
                               StatsOutputLevel level) {
   TRACE_EVENT0("webrtc", "PeerConnection::GetStats");
   RTC_DCHECK(signaling_thread()->IsCurrent());
   if (!VERIFY(observer != NULL)) {
     LOG(LS_ERROR) << "GetStats - observer is NULL.";
     return false;
   }
 
   stats_->UpdateStats(level);
+  if (!stats_->IsValidTrack(track)) {

[Taylor Brandstetter, 2016/11/03 22:47:01]

May be worth logging a warning here.

Also, you could add a comment explaining "The StatsCollector is used to tell if
a track is valid because it may remember tracks that the PeerConnection
previously removed." I didn't realize this at first.

Oh, and one more thing; a null track *should not* be an error. That should just
equate to "no track selector specified, gather all stats". So you could change
the condition to:

"if (track && !stats_->IsValidTrack(track))"

[Zhi Huang, 2016/11/03 23:17:27]

I realized that the nullptr is not an error. The nullptr condition was inside
the IsValidTrack() before. I'll move it here.

Done.

+    return false;
+  }
   signaling_thread()->Post(RTC_FROM_HERE, this, MSG_GETSTATS,
                            new GetStatsMsg(observer, track));
   return true;
 }
 
 void PeerConnection::GetStats(RTCStatsCollectorCallback* callback) {
   RTC_DCHECK(stats_collector_);
   stats_collector_->GetStatsReport(callback);
 }
 
@@ skipping 1442 matching lines @@
 
 bool PeerConnection::StartRtcEventLog_w(rtc::PlatformFile file,
                                         int64_t max_size_bytes) {
   return event_log_->StartLogging(file, max_size_bytes);
 }
 
 void PeerConnection::StopRtcEventLog_w() {
   event_log_->StopLogging();
 }
 }  // namespace webrtc