Reject the descriptions that attempt to change the order of m= sections

webrtc/pc/peerconnectioninterface_unittest.cc

Index: webrtc/pc/peerconnectioninterface_unittest.cc
diff --git a/webrtc/pc/peerconnectioninterface_unittest.cc b/webrtc/pc/peerconnectioninterface_unittest.cc
index 565704e935cc677cf6aebeb5640626fae468ee0d..ccf64d241594c3055f47a6a95f7d7053aba86dd7 100644
--- a/webrtc/pc/peerconnectioninterface_unittest.cc
+++ b/webrtc/pc/peerconnectioninterface_unittest.cc
@@ -8,6 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include <algorithm>
 #include <memory>
 #include <sstream>
 #include <string>
@@ -3831,6 +3832,39 @@ TEST_F(PeerConnectionInterfaceTest, CreateAnswerWithoutRemoteDescription) {
   EXPECT_TRUE(DoCreateAnswer(&answer, nullptr));
 }
 
+// Test that an error is returned if a description is applied that doesn't
+// respect the order of existing media sections.
+TEST_F(PeerConnectionInterfaceTest,
+       MediaSectionOrderEnforcedForSubsequentOffers) {
+  CreatePeerConnection();
+  FakeConstraints constraints;
+  constraints.SetMandatoryReceiveAudio(true);
+  constraints.SetMandatoryReceiveVideo(true);
+  std::unique_ptr<SessionDescriptionInterface> offer;
+  ASSERT_TRUE(DoCreateOffer(&offer, &constraints));
+  EXPECT_TRUE(DoSetRemoteDescription(std::move(offer)));
+
+  std::unique_ptr<SessionDescriptionInterface> answer;
+  ASSERT_TRUE(DoCreateAnswer(&answer, nullptr));
+  EXPECT_TRUE(DoSetLocalDescription(std::move(answer)));
+
+  // A remote offer with different m=line order should be rejected.
+  ASSERT_TRUE(DoCreateOffer(&offer, &constraints));
+  std::reverse(offer->description()->contents().begin(),
+               offer->description()->contents().end());
+  std::reverse(offer->description()->transport_infos().begin(),
+               offer->description()->transport_infos().end());
+  EXPECT_FALSE(DoSetRemoteDescription(std::move(offer)));
+
+  // A subsequent local offer with different m=line order should be rejected.
+  ASSERT_TRUE(DoCreateOffer(&offer, &constraints));
+  std::reverse(offer->description()->contents().begin(),
+               offer->description()->contents().end());
+  std::reverse(offer->description()->transport_infos().begin(),
+               offer->description()->transport_infos().end());
+  EXPECT_FALSE(DoSetLocalDescription(std::move(offer)));
+}
+
 class PeerConnectionMediaConfigTest : public testing::Test {
  protected:
   void SetUp() override {