sdp: reject spec simulcast answers without the rid extension

which is mandatory to implement per
  https://datatracker.ietf.org/doc/html/rfc8853#section-5.5

BUG=chromium:1422258

Change-Id: I3639b15453aaa074fbe9f26b722f5997b439224a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/306661
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40208}

api/rtp_transceiver_interface.h

@@ -41,7 +41,6 @@ struct RTC_EXPORT RtpTransceiverInit final {
   // The added RtpTransceiver will be added to these streams.
   std::vector<std::string> stream_ids;
 
-  // TODO(bugs.webrtc.org/7600): Not implemented.
   std::vector<RtpEncodingParameters> send_encodings;
 };
 

pc/peer_connection_simulcast_unittest.cc

@@ -538,9 +538,9 @@ TEST_F(PeerConnectionSimulcastTests,
   ValidateTransceiverParameters(transceiver, expected_layers);
 }
 
-// Tests that simulcast is disabled if the RID extension is not negotiated
-// regardless of if the RIDs and simulcast attribute were negotiated properly.
-TEST_F(PeerConnectionSimulcastTests, NegotiationDoesNotHaveRidExtension) {
+// Tests that a simulcast answer is rejected if the RID extension is not
+// negotiated.
+TEST_F(PeerConnectionSimulcastTests, NegotiationDoesNotHaveRidExtensionFails) {
   auto local = CreatePeerConnectionWrapper();
   auto remote = CreatePeerConnectionWrapper();
   auto layers = CreateLayers({"1", "2", "3"}, true);
@@ -570,8 +570,7 @@ TEST_F(PeerConnectionSimulcastTests, NegotiationDoesNotHaveRidExtension) {
                                .receive_layers()
                                .GetAllLayers()
                                .size());
-  EXPECT_TRUE(local->SetRemoteDescription(std::move(answer), &err)) << err;
-  ValidateTransceiverParameters(transceiver, expected_layers);
+  EXPECT_FALSE(local->SetRemoteDescription(std::move(answer), &err)) << err;
 }
 
 TEST_F(PeerConnectionSimulcastTests, SimulcastAudioRejected) {

pc/sdp_offer_answer.cc

@@ -538,6 +538,30 @@ RTCError ValidateBundledRtpHeaderExtensions(
   return RTCError::OK();
 }
 
+RTCError ValidateRtpHeaderExtensionsForSpecSimulcast(
+    const cricket::SessionDescription& description) {
+  for (const ContentInfo& content : description.contents()) {
+    if (content.type != MediaProtocolType::kRtp) {
+      continue;
+    }
+    const auto media_description = content.media_description();
+    if (!media_description->HasSimulcast()) {
+      continue;
+    }
+    auto extensions = media_description->rtp_header_extensions();
+    auto it = absl::c_find_if(extensions, [](const RtpExtension& ext) {
+      return ext.uri == RtpExtension::kRidUri;
+    });
+    if (it == extensions.end()) {
+      return RTCError(RTCErrorType::INVALID_PARAMETER,
+                      "The media section with MID='" + content.mid() +
+                          "' negotiates simulcast but does not negotiate "
+                          "the RID RTP header extension.");
+    }
+  }
+  return RTCError::OK();
+}
+
 bool IsValidOfferToReceiveMedia(int value) {
   typedef PeerConnectionInterface::RTCOfferAnswerOptions Options;
   return (value >= Options::kUndefined) &&
@@ -3602,6 +3626,12 @@ RTCError SdpOfferAnswerHandler::ValidateSessionDescription(
             "which is not supported with Unified Plan.");
       }
     }
+    // Validate spec-simulcast which only works if the remote end negotiated the
+    // mid and rid header extension.
+    error = ValidateRtpHeaderExtensionsForSpecSimulcast(*sdesc->description());
+    if (!error.ok()) {
+      return error;
+    }
   }
 
   return RTCError::OK();

pc/sdp_offer_answer_unittest.cc

@@ -548,4 +548,55 @@ TEST_F(SdpOfferAnswerTest, RejectedDataChannelsDoGetReofferedWhenActive) {
 
 #endif  // WEBRTC_HAVE_SCTP
 
+TEST_F(SdpOfferAnswerTest, SimulcastAnswerWithNoRidsIsRejected) {
+  auto pc = CreatePeerConnection();
+
+  RtpTransceiverInit init;
+  RtpEncodingParameters rid1;
+  rid1.rid = "1";
+  init.send_encodings.push_back(rid1);
+  RtpEncodingParameters rid2;
+  rid2.rid = "2";
+  init.send_encodings.push_back(rid2);
+
+  auto transceiver = pc->AddTransceiver(cricket::MEDIA_TYPE_VIDEO, init);
+  EXPECT_TRUE(pc->CreateOfferAndSetAsLocal());
+  auto mid = pc->pc()->local_description()->description()->contents()[0].mid();
+
+  // A SDP answer with simulcast but without mid/rid extensions.
+  std::string sdp =
+      "v=0\r\n"
+      "o=- 4131505339648218884 3 IN IP4 **-----**\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "a=ice-ufrag:zGWFZ+fVXDeN6UoI/136\r\n"
+      "a=ice-pwd:9AUNgUqRNI5LSIrC1qFD2iTR\r\n"
+      "a=fingerprint:sha-256 "
+      "AD:52:52:E0:B1:37:34:21:0E:15:8E:B7:56:56:7B:B4:39:0E:6D:1C:F5:84:A7:EE:"
+      "B5:27:3E:30:B1:7D:69:42\r\n"
+      "a=setup:passive\r\n"
+      "m=video 9 UDP/TLS/RTP/SAVPF 96\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtcp:9 IN IP4 0.0.0.0\r\n"
+      "a=mid:" +
+      mid +
+      "\r\n"
+      "a=recvonly\r\n"
+      "a=rtcp-mux\r\n"
+      "a=rtcp-rsize\r\n"
+      "a=rtpmap:96 VP8/90000\r\n"
+      "a=rid:1 recv\r\n"
+      "a=rid:2 recv\r\n"
+      "a=simulcast:recv 1;2\r\n";
+  std::string extensions =
+      "a=extmap:9 urn:ietf:params:rtp-hdrext:sdes:mid\r\n"
+      "a=extmap:10 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id\r\n";
+  auto answer = CreateSessionDescription(SdpType::kAnswer, sdp);
+  EXPECT_FALSE(pc->SetRemoteDescription(std::move(answer)));
+
+  auto answer_with_extensions =
+      CreateSessionDescription(SdpType::kAnswer, sdp + extensions);
+  EXPECT_TRUE(pc->SetRemoteDescription(std::move(answer_with_extensions)));
+}
+
 }  // namespace webrtc