From e1b685a50a578f18aa9b023506e87a86dbeecf11 Mon Sep 17 00:00:00 2001
From: Florent Castelli <orphis@webrtc.org>
Date: Fri, 30 Apr 2021 19:11:37 +0200
Subject: [PATCH] simulcast: Limit audio transceivers to single stream

We don't support audio simulcast, so we should reject the layers
early during an addTransceiver() call.

Bug: webrtc:12719
Change-Id: Ieeb92c66de741e9b11943e0173a6f2e052926f13
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/216685
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33886}
---
 pc/peer_connection.cc                    |  6 ++++--
 pc/peer_connection_simulcast_unittest.cc | 24 ++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index 0323636f02..e2b3b61058 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -997,9 +997,11 @@ PeerConnection::AddTransceiver(
   parameters.encodings = init.send_encodings;
 
   // Encodings are dropped from the tail if too many are provided.
-  if (parameters.encodings.size() > kMaxSimulcastStreams) {
+  size_t max_simulcast_streams =
+      media_type == cricket::MEDIA_TYPE_VIDEO ? kMaxSimulcastStreams : 1u;
+  if (parameters.encodings.size() > max_simulcast_streams) {
     parameters.encodings.erase(
-        parameters.encodings.begin() + kMaxSimulcastStreams,
+        parameters.encodings.begin() + max_simulcast_streams,
         parameters.encodings.end());
   }
 
diff --git a/pc/peer_connection_simulcast_unittest.cc b/pc/peer_connection_simulcast_unittest.cc
index 8822a980f7..31385754b7 100644
--- a/pc/peer_connection_simulcast_unittest.cc
+++ b/pc/peer_connection_simulcast_unittest.cc
@@ -157,9 +157,10 @@ class PeerConnectionSimulcastTests : public ::testing::Test {
 
   rtc::scoped_refptr<RtpTransceiverInterface> AddTransceiver(
       PeerConnectionWrapper* pc,
-      const std::vector<SimulcastLayer>& layers) {
+      const std::vector<SimulcastLayer>& layers,
+      cricket::MediaType media_type = cricket::MEDIA_TYPE_VIDEO) {
     auto init = CreateTransceiverInit(layers);
-    return pc->AddTransceiver(cricket::MEDIA_TYPE_VIDEO, init);
+    return pc->AddTransceiver(media_type, init);
   }
 
   SimulcastDescription RemoveSimulcast(SessionDescriptionInterface* sd) {
@@ -556,6 +557,25 @@ TEST_F(PeerConnectionSimulcastTests, NegotiationDoesNotHaveRidExtension) {
   ValidateTransceiverParameters(transceiver, expected_layers);
 }
 
+TEST_F(PeerConnectionSimulcastTests, SimulcastAudioRejected) {
+  auto local = CreatePeerConnectionWrapper();
+  auto remote = CreatePeerConnectionWrapper();
+  auto layers = CreateLayers({"1", "2", "3", "4"}, true);
+  auto transceiver =
+      AddTransceiver(local.get(), layers, cricket::MEDIA_TYPE_AUDIO);
+  // Should only have the first layer.
+  auto parameters = transceiver->sender()->GetParameters();
+  EXPECT_EQ(1u, parameters.encodings.size());
+  EXPECT_THAT(parameters.encodings,
+              ElementsAre(Field("rid", &RtpEncodingParameters::rid, Eq(""))));
+  ExchangeOfferAnswer(local.get(), remote.get(), {});
+  // Still have a single layer after negotiation
+  parameters = transceiver->sender()->GetParameters();
+  EXPECT_EQ(1u, parameters.encodings.size());
+  EXPECT_THAT(parameters.encodings,
+              ElementsAre(Field("rid", &RtpEncodingParameters::rid, Eq(""))));
+}
+
 #if RTC_METRICS_ENABLED
 //
 // Checks the logged metrics when simulcast is not used.