Add generation of CCFB in offer (RFC8888 support)

Bug: webrtc:42225697
Change-Id: I288a808c4aae852212b09fdf9551e20fe3066e39
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/367205
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43341}

pc/BUILD.gn

@@ -2213,6 +2213,7 @@ if (rtc_include_tests && !build_with_chromium) {
   rtc_test("peerconnection_unittests") {
     testonly = true
     sources = [
+      "congestion_control_integrationtest.cc",
       "data_channel_integrationtest.cc",
       "data_channel_unittest.cc",
       "dtmf_sender_unittest.cc",

pc/DEPS

@@ -14,6 +14,7 @@ include_rules = [
   "+net/dcsctp",
   "+p2p",
   "+system_wrappers",
+  "+absl/strings/str_cat.h",
 ]
 
 specific_include_rules = {

pc/congestion_control_integrationtest.cc

@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2024 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.
+ */
+
+// This file contains tests that verify that congestion control options
+// are correctly negotiated in the SDP offer/answer.
+
+#include <string>
+
+#include "absl/strings/str_cat.h"
+#include "api/peer_connection_interface.h"
+#include "pc/test/integration_test_helpers.h"
+#include "test/field_trial.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+
+using testing::HasSubstr;
+
+class PeerConnectionCongestionControlTest
+    : public PeerConnectionIntegrationBaseTest {
+ public:
+  PeerConnectionCongestionControlTest()
+      : PeerConnectionIntegrationBaseTest(SdpSemantics::kUnifiedPlan) {}
+};
+
+TEST_F(PeerConnectionCongestionControlTest, OfferContainsCcfbIfEnabled) {
+  test::ScopedFieldTrials trials(
+      "WebRTC-RFC8888CongestionControlFeedback/Enabled/");
+  ASSERT_TRUE(CreatePeerConnectionWrappers());
+  caller()->AddAudioVideoTracks();
+  auto offer = caller()->CreateOfferAndWait();
+  std::string offer_str = absl::StrCat(*offer);
+  EXPECT_THAT(offer_str, HasSubstr("a=rtcp-fb:* ack ccfb\r\n"));
+}
+
+}  // namespace webrtc

pc/media_session.cc

@@ -1974,7 +1974,10 @@ RTCError MediaSessionDescriptionFactory::AddRtpContentForOffer(
   } else {
     content_description = std::make_unique<VideoContentDescription>();
   }
-
+  // RFC 8888 support.
+  content_description->set_rtcp_fb_ack_ccfb(
+      transport_desc_factory_->trials().IsEnabled(
+          "WebRTC-RFC8888CongestionControlFeedback"));
   auto error = CreateMediaContentOffer(
       media_description_options, session_options, codecs_to_include,
       header_extensions, ssrc_generator(), current_streams,

pc/session_description.h

@@ -114,6 +114,13 @@ class MediaContentDescription {
     remote_estimate_ = remote_estimate;
   }
 
+  // Support of RFC 8888 feedback messages.
+  // This is a transport-wide property, but is signalled in SDP
+  // at the m-line level; its mux category is IDENTICAL-PER-PT,
+  // and only wildcard is allowed. RFC 8888 section 6.
+  bool rtcp_fb_ack_ccfb() const { return rtcp_fb_ack_ccfb_; }
+  void set_rtcp_fb_ack_ccfb(bool enable) { rtcp_fb_ack_ccfb_ = enable; }
+
   int bandwidth() const { return bandwidth_; }
   void set_bandwidth(int bandwidth) { bandwidth_ = bandwidth; }
   std::string bandwidth_type() const { return bandwidth_type_; }
@@ -257,6 +264,7 @@ class MediaContentDescription {
   bool rtcp_mux_ = false;
   bool rtcp_reduced_size_ = false;
   bool remote_estimate_ = false;
+  bool rtcp_fb_ack_ccfb_ = false;
   int bandwidth_ = kAutoBandwidth;
   std::string bandwidth_type_ = kApplicationSpecificBandwidth;
 

pc/webrtc_sdp.cc

@@ -1947,6 +1947,14 @@ void BuildRtpmap(const MediaContentDescription* media_desc,
       AddAttributeLine(kCodecParamPTime, ptime, message);
     }
   }
+  if (media_desc->rtcp_fb_ack_ccfb()) {
+    // RFC 8888 section 6
+    rtc::StringBuilder os;
+    InitAttrLine(kAttributeRtcpFb, &os);
+    os << kSdpDelimiterColon;
+    os << "* ack ccfb";
+    AddLine(os.str(), message);
+  }
 }
 
 void BuildCandidate(const std::vector<Candidate>& candidates,