Improve ssrc-group validation

disallowing more than one ssrc-group with the same semantic
and primary ssrc.

BUG=chromium:1477075

Change-Id: I4bce0555cd49834725d9b97693d26c971bc5d5c2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/318822
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40694}

media/engine/webrtc_video_engine.cc

@@ -305,6 +305,23 @@ static bool ValidateStreamParams(const StreamParams& sp) {
     return false;
   }
 
+  // Validate that a primary SSRC can only have one ssrc-group per semantics.
+  std::map<uint32_t, std::set<std::string>> primary_ssrc_to_semantics;
+  for (const auto& group : sp.ssrc_groups) {
+    auto result = primary_ssrc_to_semantics.try_emplace(
+        group.ssrcs[0], std::set<std::string>({group.semantics}));
+    if (!result.second) {
+      // A duplicate SSRC was found, check for duplicate semantics.
+      auto semantics_it = result.first->second.insert(group.semantics);
+      if (!semantics_it.second) {
+        RTC_LOG(LS_ERROR) << "Duplicate ssrc-group '" << group.semantics
+                          << " for primary SSRC " << group.ssrcs[0] << " "
+                          << sp.ToString();
+        return false;
+      }
+    }
+  }
+
   std::vector<uint32_t> primary_ssrcs;
   sp.GetPrimarySsrcs(&primary_ssrcs);
   for (const auto& semantic :

pc/sdp_offer_answer_unittest.cc

@@ -890,4 +890,44 @@ TEST_F(SdpOfferAnswerTest,
   EXPECT_FALSE(pc->SetLocalDescription(std::move(modified_offer)));
 }
 
+TEST_F(SdpOfferAnswerTest, AllowOnlyOneSsrcGroupPerSemanticAndPrimarySsrc) {
+  auto pc = CreatePeerConnection();
+
+  pc->AddAudioTrack("audio_track", {});
+  pc->AddVideoTrack("video_track", {});
+  auto offer = pc->CreateOffer();
+  auto& offer_contents = offer->description()->contents();
+  ASSERT_EQ(offer_contents.size(), 2u);
+  uint32_t audio_ssrc = offer_contents[0].media_description()->first_ssrc();
+  ASSERT_EQ(offer_contents[1].media_description()->streams().size(), 1u);
+  auto& video_stream = offer->description()
+                           ->contents()[1]
+                           .media_description()
+                           ->mutable_streams()[0];
+  ASSERT_EQ(video_stream.ssrcs.size(), 2u);
+  ASSERT_EQ(video_stream.ssrc_groups.size(), 1u);
+  video_stream.ssrcs.push_back(audio_ssrc);
+  video_stream.ssrc_groups.push_back(
+      {cricket::kFidSsrcGroupSemantics, {video_stream.ssrcs[0], audio_ssrc}});
+  std::string sdp;
+  offer->ToString(&sdp);
+
+  // Trim the last two lines which contain ssrc-specific attributes
+  // that we change/munge above. Guarded with expectation about what
+  // should be removed in case the SDP generation changes.
+  size_t end = sdp.rfind("\r\n");
+  end = sdp.rfind("\r\n", end - 2);
+  end = sdp.rfind("\r\n", end - 2);
+  EXPECT_EQ(sdp.substr(end + 2), "a=ssrc:" + rtc::ToString(audio_ssrc) +
+                                     " cname:" + video_stream.cname +
+                                     "\r\n"
+                                     "a=ssrc:" +
+                                     rtc::ToString(audio_ssrc) +
+                                     " msid:- video_track\r\n");
+
+  auto modified_offer =
+      CreateSessionDescription(SdpType::kOffer, sdp.substr(0, end + 2));
+  EXPECT_FALSE(pc->SetLocalDescription(std::move(modified_offer)));
+}
+
 }  // namespace webrtc