[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

@@ -1254,7 +1254,14 @@ PeerConnection::AddTrackUnifiedPlan(
              : 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 @@ PeerConnection::AddTransceiver(
 
   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 @@ PeerConnection::CreateAndAddTransceiver(
     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);

pc/peerconnection_rtp_unittest.cc

@@ -1253,6 +1253,67 @@ TEST_F(PeerConnectionRtpTestUnifiedPlan, AddRemoveAddTrackOffersWorksVideo) {
   EXPECT_EQ(sender1, sender2);
 }
 
+// Test that CreateOffer succeeds if two tracks with the same label are added.
+TEST_F(PeerConnectionRtpTestUnifiedPlan, CreateOfferSameTrackLabel) {
+  auto caller = CreatePeerConnection();
+
+  auto audio_sender = caller->AddAudioTrack("track", {});
+  auto video_sender = caller->AddVideoTrack("track", {});
+
+  EXPECT_TRUE(caller->CreateOffer());
+
+  EXPECT_EQ(audio_sender->track()->id(), video_sender->track()->id());
+  EXPECT_NE(audio_sender->id(), video_sender->id());
+}
+
+// Test that CreateAnswer succeeds if two tracks with the same label are added.
+TEST_F(PeerConnectionRtpTestUnifiedPlan, CreateAnswerSameTrackLabel) {
+  auto caller = CreatePeerConnection();
+  auto callee = CreatePeerConnection();
+
+  RtpTransceiverInit recvonly;
+  recvonly.direction = RtpTransceiverDirection::kRecvOnly;
+  caller->AddTransceiver(cricket::MEDIA_TYPE_AUDIO, recvonly);
+  caller->AddTransceiver(cricket::MEDIA_TYPE_VIDEO, recvonly);
+
+  ASSERT_TRUE(callee->SetRemoteDescription(caller->CreateOffer()));
+
+  auto audio_sender = callee->AddAudioTrack("track", {});
+  auto video_sender = callee->AddVideoTrack("track", {});
+
+  EXPECT_TRUE(callee->CreateAnswer());
+
+  EXPECT_EQ(audio_sender->track()->id(), video_sender->track()->id());
+  EXPECT_NE(audio_sender->id(), video_sender->id());
+}
+
+// Test that calling AddTrack, RemoveTrack and AddTrack again creates a second
+// m= section with a random sender id (different from the first, now rejected,
+// m= section).
+TEST_F(PeerConnectionRtpTestUnifiedPlan,
+       AddRemoveAddTrackGeneratesNewSenderId) {
+  auto caller = CreatePeerConnection();
+  auto callee = CreatePeerConnection();
+
+  auto track = caller->CreateVideoTrack("video");
+  auto sender1 = caller->AddTrack(track);
+  ASSERT_TRUE(caller->ExchangeOfferAnswerWith(callee.get()));
+
+  caller->pc()->RemoveTrack(sender1);
+  ASSERT_TRUE(caller->ExchangeOfferAnswerWith(callee.get()));
+
+  auto sender2 = caller->AddTrack(track);
+
+  EXPECT_NE(sender1, sender2);
+  EXPECT_NE(sender1->id(), sender2->id());
+  std::string sender2_id = sender2->id();
+
+  ASSERT_TRUE(caller->ExchangeOfferAnswerWith(callee.get()));
+
+  // The sender's ID should not change after negotiation.
+  EXPECT_EQ(sender2_id, sender2->id());
+}
+
 // Test that OnRenegotiationNeeded is fired if SetDirection is called on an
 // active RtpTransceiver with a new direction.
 TEST_F(PeerConnectionRtpTestUnifiedPlan,

pc/peerconnectioninterface_unittest.cc

@@ -1762,7 +1762,7 @@ TEST_P(PeerConnectionInterfaceTest, IceCandidates) {
 
 // Test that CreateOffer and CreateAnswer will fail if the track labels are
 // not unique.
-TEST_P(PeerConnectionInterfaceTest, CreateOfferAnswerWithInvalidStream) {
+TEST_F(PeerConnectionInterfaceTestPlanB, CreateOfferAnswerWithInvalidStream) {
   CreatePeerConnectionWithoutDtls();
   // Create a regular offer for the CreateAnswer test later.
   std::unique_ptr<SessionDescriptionInterface> offer;