commit 07563732f66cddc77213e84c70a1a38f3e8961a5
author Steve Anton <steveanton@webrtc.org> Tue Jun 26 18:13:50 2018
committer Commit Bot <commit-bot@chromium.org> Tue Jun 26 19:06:17 2018
tree 96e202e336b8edfa9ec65fd6e4fccdaf06538d09
parent 1bc97160787380fed1560397416d50c3609025b1

[Unified Plan] Avoid offering two senders with the same ID

This can happen with the following sequence of API calls:
1) AddTrack(track) + offer/answer
2) RemoveTrack(track's sender) + offer/answer
3) AddTrack(same track)

Since the first transceiver had already been used to send, it will
not get re-used by the second call to AddTrack. Another RtpSender
will be created with its ID = the track ID. But the code hits a
DCHECK when CreateOffer is later called since both m= sections will
offer the same track ID component of the MSID.

The fix implemented here is to randomly generate a sender ID if
there is already an RtpSender with the track's ID.

Bug: webrtc:8734
Change-Id: Ic2dda23d66e364e77ff7505e1c37e53105a17dae
Reviewed-on: https://webrtc-review.googlesource.com/84249
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23748}

pc/peerconnection.cc

diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index db18ca3..d953833 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -1254,7 +1254,14 @@
              : cricket::MEDIA_TYPE_VIDEO);
     RTC_LOG(LS_INFO) << "Adding " << cricket::MediaTypeToString(media_type)
                      << " transceiver in response to a call to AddTrack.";
-    auto sender = CreateSender(media_type, track->id(), track, stream_ids);
+    std::string sender_id = track->id();
+    // Avoid creating a sender with an existing ID by generating a random ID.
+    // This can happen if this is the second time AddTrack has created a sender
+    // for this track.
+    if (FindSenderById(sender_id)) {
+      sender_id = rtc::CreateRandomUuid();
+    }
+    auto sender = CreateSender(media_type, sender_id, track, stream_ids);
     auto receiver = CreateReceiver(media_type, rtc::CreateRandomUuid());
     transceiver = CreateAndAddTransceiver(sender, receiver);
     transceiver->internal()->set_created_by_addtrack(true);
@@ -1399,9 +1406,12 @@
 
   RTC_LOG(LS_INFO) << "Adding " << cricket::MediaTypeToString(media_type)
                    << " transceiver in response to a call to AddTransceiver.";
-  auto sender =
-      CreateSender(media_type, (track ? track->id() : rtc::CreateRandomUuid()),
-                   track, init.stream_ids);
+  // Set the sender ID equal to the track ID if the track is specified unless
+  // that sender ID is already in use.
+  std::string sender_id =
+      (track && !FindSenderById(track->id()) ? track->id()
+                                             : rtc::CreateRandomUuid());
+  auto sender = CreateSender(media_type, sender_id, track, init.stream_ids);
   auto receiver = CreateReceiver(media_type, rtc::CreateRandomUuid());
   auto transceiver = CreateAndAddTransceiver(sender, receiver);
   transceiver->internal()->set_direction(init.direction);
@@ -1466,6 +1476,11 @@
     rtc::scoped_refptr<RtpSenderProxyWithInternal<RtpSenderInternal>> sender,
     rtc::scoped_refptr<RtpReceiverProxyWithInternal<RtpReceiverInternal>>
         receiver) {
+  // Ensure that the new sender does not have an ID that is already in use by
+  // another sender.
+  // Allow receiver IDs to conflict since those come from remote SDP (which
+  // could be invalid, but should not cause a crash).
+  RTC_DCHECK(!FindSenderById(sender->id()));
   auto transceiver = RtpTransceiverProxyWithInternal<RtpTransceiver>::Create(
       signaling_thread(), new RtpTransceiver(sender, receiver));
   transceivers_.push_back(transceiver);