addIceCandidate: prefer ice candidate sdpMid over sdpMLineIndex

as described in JSEP
  https://tools.ietf.org/html/rfc8829#section-3.5.2.1
 If the MID field is present in a received IceCandidate, it
 MUST be used for identification; otherwise, the "m=" section
 index is used instead.

BUG=webrtc:12479

Change-Id: I688a5e59024fe8cc6a170c216c6f14536084cfb9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208100
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/master@{#33357}

pc/peer_connection_ice_unittest.cc

@@ -1452,4 +1452,24 @@ TEST_P(PeerConnectionIceTest, CloseDoesNotTransitionGatheringStateToComplete) {
             pc->pc()->ice_gathering_state());
 }
 
+TEST_P(PeerConnectionIceTest, PrefersMidOverMLineIndex) {
+  const SocketAddress kCalleeAddress("1.1.1.1", 1111);
+
+  auto caller = CreatePeerConnectionWithAudioVideo();
+  auto callee = CreatePeerConnectionWithAudioVideo();
+
+  ASSERT_TRUE(callee->SetRemoteDescription(caller->CreateOfferAndSetAsLocal()));
+  ASSERT_TRUE(
+      caller->SetRemoteDescription(callee->CreateAnswerAndSetAsLocal()));
+
+  // |candidate.transport_name()| is empty.
+  cricket::Candidate candidate = CreateLocalUdpCandidate(kCalleeAddress);
+  auto* audio_content = cricket::GetFirstAudioContent(
+      caller->pc()->local_description()->description());
+  std::unique_ptr<IceCandidateInterface> ice_candidate =
+      CreateIceCandidate(audio_content->name, 65535, candidate);
+  EXPECT_TRUE(caller->pc()->AddIceCandidate(ice_candidate.get()));
+  EXPECT_TRUE(caller->pc()->RemoveIceCandidates({candidate}));
+}
+
 }  // namespace webrtc

pc/sdp_offer_answer.cc

@@ -4532,20 +4532,7 @@ bool SdpOfferAnswerHandler::ReadyToUseRemoteCandidate(
 RTCErrorOr<const cricket::ContentInfo*> SdpOfferAnswerHandler::FindContentInfo(
     const SessionDescriptionInterface* description,
     const IceCandidateInterface* candidate) {
-  if (candidate->sdp_mline_index() >= 0) {
+  if (!candidate->sdp_mid().empty()) {
-    size_t mediacontent_index =
-        static_cast<size_t>(candidate->sdp_mline_index());
-    size_t content_size = description->description()->contents().size();
-    if (mediacontent_index < content_size) {
-      return &description->description()->contents()[mediacontent_index];
-    } else {
-      return RTCError(RTCErrorType::INVALID_RANGE,
-                      "Media line index (" +
-                          rtc::ToString(candidate->sdp_mline_index()) +
-                          ") out of range (number of mlines: " +
-                          rtc::ToString(content_size) + ").");
-    }
-  } else if (!candidate->sdp_mid().empty()) {
     auto& contents = description->description()->contents();
     auto it = absl::c_find_if(
         contents, [candidate](const cricket::ContentInfo& content_info) {
@@ -4559,6 +4546,19 @@ RTCErrorOr<const cricket::ContentInfo*> SdpOfferAnswerHandler::FindContentInfo(
     } else {
       return &*it;
     }
+  } else if (candidate->sdp_mline_index() >= 0) {
+    size_t mediacontent_index =
+        static_cast<size_t>(candidate->sdp_mline_index());
+    size_t content_size = description->description()->contents().size();
+    if (mediacontent_index < content_size) {
+      return &description->description()->contents()[mediacontent_index];
+    } else {
+      return RTCError(RTCErrorType::INVALID_RANGE,
+                      "Media line index (" +
+                          rtc::ToString(candidate->sdp_mline_index()) +
+                          ") out of range (number of mlines: " +
+                          rtc::ToString(content_size) + ").");
+    }
   }
 
   return RTCError(RTCErrorType::INVALID_PARAMETER,

test/pc/e2e/sdp/sdp_changer.cc

@@ -524,9 +524,11 @@ SignalingInterceptor::PatchOffererIceCandidates(
         context_.simulcast_infos_by_mid.find(candidate->sdp_mid());
     if (simulcast_info_it != context_.simulcast_infos_by_mid.end()) {
       // This is candidate for simulcast section, so it should be transformed
-      // into candidates for replicated sections
+      // into candidates for replicated sections. The sdpMLineIndex is set to
-      out.push_back(CreateIceCandidate(simulcast_info_it->second->rids[0], 0,
+      // -1 and ignored if the rid is present.
-                                       candidate->candidate()));
+      for (auto rid : simulcast_info_it->second->rids) {
+        out.push_back(CreateIceCandidate(rid, -1, candidate->candidate()));
+      }
     } else {
       out.push_back(CreateIceCandidate(candidate->sdp_mid(),
                                        candidate->sdp_mline_index(),
@@ -550,6 +552,9 @@ SignalingInterceptor::PatchAnswererIceCandidates(
       // section.
       out.push_back(CreateIceCandidate(simulcast_info_it->second->mid, 0,
                                        candidate->candidate()));
+    } else if (context_.simulcast_infos_by_rid.size()) {
+      // When using simulcast and bundle, put everything on the first m-line.
+      out.push_back(CreateIceCandidate("", 0, candidate->candidate()));
     } else {
       out.push_back(CreateIceCandidate(candidate->sdp_mid(),
                                        candidate->sdp_mline_index(),