Implement recieving NACK in RtcpTranceiver

Bug: webrtc:8239
Change-Id: I41d6c3252bbffeab66ded7ed294f82134351541a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/254800
Reviewed-by: Emil Lundmark <lndmrk@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36254}

modules/rtp_rtcp/source/rtcp_transceiver_config.h

@@ -97,6 +97,9 @@ class RtpStreamRtcpHandler {
     int last_clock_rate_ = 90'000;
   };
   virtual RtpStats SentStats() = 0;
+
+  virtual void OnNack(uint32_t sender_ssrc,
+                      rtc::ArrayView<const uint16_t> sequence_numbers) {}
 };
 
 struct RtcpTransceiverConfig {

modules/rtp_rtcp/source/rtcp_transceiver_impl.cc

@@ -351,10 +351,34 @@ void RtcpTransceiverImpl::HandlePayloadSpecificFeedback(
 void RtcpTransceiverImpl::HandleRtpFeedback(
     const rtcp::CommonHeader& rtcp_packet_header,
     Timestamp now) {
-  // Transport feedback is the only message handled right now.
+  switch (rtcp_packet_header.fmt()) {
-  if (rtcp_packet_header.fmt() !=
+    case rtcp::Nack::kFeedbackMessageType:
-          rtcp::TransportFeedback::kFeedbackMessageType ||
+      HandleNack(rtcp_packet_header);
-      config_.network_link_observer == nullptr) {
+      break;
+    case rtcp::TransportFeedback::kFeedbackMessageType:
+      HandleTransportFeedback(rtcp_packet_header, now);
+      break;
+  }
+}
+
+void RtcpTransceiverImpl::HandleNack(
+    const rtcp::CommonHeader& rtcp_packet_header) {
+  rtcp::Nack nack;
+  if (local_senders_.empty() || !nack.Parse(rtcp_packet_header)) {
+    return;
+  }
+  auto it = local_senders_by_ssrc_.find(nack.media_ssrc());
+  if (it != local_senders_by_ssrc_.end()) {
+    it->second->handler->OnNack(nack.sender_ssrc(), nack.packet_ids());
+  }
+}
+
+void RtcpTransceiverImpl::HandleTransportFeedback(
+    const rtcp::CommonHeader& rtcp_packet_header,
+    Timestamp now) {
+  RTC_DCHECK_EQ(rtcp_packet_header.fmt(),
+                rtcp::TransportFeedback::kFeedbackMessageType);
+  if (config_.network_link_observer == nullptr) {
     return;
   }
   rtcp::TransportFeedback feedback;

modules/rtp_rtcp/source/rtcp_transceiver_impl.h

@@ -105,6 +105,9 @@ class RtcpTransceiverImpl {
       Timestamp now);
   void HandleRtpFeedback(const rtcp::CommonHeader& rtcp_packet_header,
                          Timestamp now);
+  void HandleNack(const rtcp::CommonHeader& rtcp_packet_header);
+  void HandleTransportFeedback(const rtcp::CommonHeader& rtcp_packet_header,
+                               Timestamp now);
   void HandleExtendedReports(const rtcp::CommonHeader& rtcp_packet_header,
                              Timestamp now);
   // Extended Reports blocks handlers.

modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc

@@ -40,6 +40,7 @@ namespace {
 
 using ::testing::_;
 using ::testing::ElementsAre;
+using ::testing::ElementsAreArray;
 using ::testing::Ge;
 using ::testing::NiceMock;
 using ::testing::Return;
@@ -82,6 +83,10 @@ class MockRtpStreamRtcpHandler : public RtpStreamRtcpHandler {
   }
 
   MOCK_METHOD(RtpStats, SentStats, (), (override));
+  MOCK_METHOD(void,
+              OnNack,
+              (uint32_t, rtc::ArrayView<const uint16_t>),
+              (override));
 
  private:
   int num_calls_ = 0;
@@ -1044,6 +1049,30 @@ TEST(RtcpTransceiverImplTest, SendsNack) {
   EXPECT_EQ(rtcp_parser.nack()->packet_ids(), kMissingSequenceNumbers);
 }
 
+TEST(RtcpTransceiverImplTest, ReceivesNack) {
+  static constexpr uint32_t kRemoteSsrc = 4321;
+  static constexpr uint32_t kMediaSsrc1 = 1234;
+  static constexpr uint32_t kMediaSsrc2 = 1235;
+  std::vector<uint16_t> kMissingSequenceNumbers = {34, 37, 38};
+  RtcpTransceiverConfig config = DefaultTestConfig();
+  RtcpTransceiverImpl rtcp_transceiver(config);
+
+  MockRtpStreamRtcpHandler local_stream1;
+  MockRtpStreamRtcpHandler local_stream2;
+  EXPECT_CALL(local_stream1,
+              OnNack(kRemoteSsrc, ElementsAreArray(kMissingSequenceNumbers)));
+  EXPECT_CALL(local_stream2, OnNack).Times(0);
+
+  EXPECT_TRUE(rtcp_transceiver.AddMediaSender(kMediaSsrc1, &local_stream1));
+  EXPECT_TRUE(rtcp_transceiver.AddMediaSender(kMediaSsrc2, &local_stream2));
+
+  rtcp::Nack nack;
+  nack.SetSenderSsrc(kRemoteSsrc);
+  nack.SetMediaSsrc(kMediaSsrc1);
+  nack.SetPacketIds(kMissingSequenceNumbers);
+  rtcp_transceiver.ReceivePacket(nack.Build(), config.clock->CurrentTime());
+}
+
 TEST(RtcpTransceiverImplTest, RequestKeyFrameWithPictureLossIndication) {
   const uint32_t kSenderSsrc = 1234;
   const uint32_t kRemoteSsrc = 4321;