Reject the descriptions that attempt to change the order of m= section in current local description.

webrtc/pc/peerconnectioninterface_unittest.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 1223 matching lines @@
     const cricket::AudioContentDescription* audio_content_desc =
         static_cast<const cricket::AudioContentDescription*>(description);
     RTC_DCHECK(audio_content_desc);
     for (size_t i = 0; i < audio_content_desc->codecs().size(); ++i) {
       if (audio_content_desc->codecs()[i].name == "CN")
         return true;
     }
     return false;
   }
 
+  void ReorderMediaSections(SessionDescriptionInterface* session_description) {

[Taylor Brandstetter, 2017/09/14 00:41:47]

nit: This could be simplified by using std::reverse. It then would be such a
small amount of code it could go in the test itself:

std::reverse(offer->description()->contents().begin(),
             offer->description()->contents().end());
std::reverse(offer->description()->transport_infos().begin(),
             offer->description()->transport_infos().end());

+    if (!session_description) {
+      return;
+    }
+    auto desc = session_description->description();
+    RTC_DCHECK(desc);
+    RTC_DCHECK(desc->contents().size() == desc->transport_infos().size());
+    // Reorder the ContentInfo.
+    if (desc->contents().empty()) {
+      return;
+    }
+    size_t num_msections = desc->contents().size();
+    auto first_content_info = desc->contents()[0];
+    for (size_t i = 1; i < num_msections; ++i) {
+      desc->contents()[i - 1] = desc->contents()[i];
+    }
+    desc->contents()[num_msections - 1] = first_content_info;
+
+    // Reorder the TransportInfo.
+    if (desc->transport_infos().empty()) {
+      return;
+    }
+    auto first_transport_info = desc->transport_infos()[0];
+    for (size_t i = 1; i < num_msections; ++i) {
+      desc->transport_infos()[i - 1] = desc->transport_infos()[i];
+    }
+    desc->transport_infos()[num_msections - 1] = first_transport_info;
+  }
+
   std::unique_ptr<rtc::VirtualSocketServer> vss_;
   rtc::AutoSocketServerThread main_;
   rtc::scoped_refptr<FakeAudioCaptureModule> fake_audio_capture_module_;
   cricket::FakePortAllocator* port_allocator_ = nullptr;
   FakeRTCCertificateGenerator* fake_certificate_generator_ = nullptr;
   rtc::scoped_refptr<webrtc::PeerConnectionFactoryInterface> pc_factory_;
   rtc::scoped_refptr<PeerConnectionFactoryForTest> pc_factory_for_test_;
   rtc::scoped_refptr<PeerConnectionInterface> pc_;
   MockPeerConnectionObserver observer_;
   rtc::scoped_refptr<StreamCollection> reference_collection_;
@@ skipping 2557 matching lines @@
   CreatePeerConnection();
   // Creating answer fails because the remote description is unset.
   std::unique_ptr<SessionDescriptionInterface> answer;
   EXPECT_FALSE(DoCreateAnswer(&answer, nullptr));
 
   // Createing answer succeeds when the remote description is set.
   CreateOfferAsRemoteDescription();
   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(offer.release()));
+
+  std::unique_ptr<SessionDescriptionInterface> answer;
+  ASSERT_TRUE(DoCreateAnswer(&answer, nullptr));
+  EXPECT_TRUE(DoSetLocalDescription(answer.release()));
+
+  // An remote offer with different m=line order would be rejected.

[Taylor Brandstetter, 2017/09/14 00:41:47]

nit: "A" instead of "An", and "should" instead of "would"

+  ASSERT_TRUE(DoCreateOffer(&offer, &constraints));
+  ReorderMediaSections(offer.get());
+  EXPECT_FALSE(DoSetRemoteDescription(offer.release()));
+
+  // A subsequent local offer with different m=line order would be rejected.
+  ASSERT_TRUE(DoCreateOffer(&offer, &constraints));
+  ReorderMediaSections(offer.get());
+  EXPECT_FALSE(DoSetLocalDescription(offer.release()));
+}
+
 class PeerConnectionMediaConfigTest : public testing::Test {
  protected:
   void SetUp() override {
     pcf_ = PeerConnectionFactoryForTest::CreatePeerConnectionFactoryForTest();
     pcf_->Initialize();
   }
   const cricket::MediaConfig TestCreatePeerConnection(
       const PeerConnectionInterface::RTCConfiguration& config,
       const MediaConstraintsInterface* constraints) {
     rtc::scoped_refptr<PeerConnectionInterface> pc(pcf_->CreatePeerConnection(
@@ skipping 100 matching lines @@
   EXPECT_NE(a, f);
 
   PeerConnectionInterface::RTCConfiguration g;
   g.disable_ipv6 = true;
   EXPECT_NE(a, g);
 
   PeerConnectionInterface::RTCConfiguration h(
       PeerConnectionInterface::RTCConfigurationType::kAggressive);
   EXPECT_NE(a, h);
 }