modules/remote_bitrate_estimator/congestion_control_feedback_tracker.cc

/*
 *  Copyright (c) 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.
 */

#include "modules/remote_bitrate_estimator/congestion_control_feedback_tracker.h"

#include <cstdint>
#include <tuple>
#include <vector>

#include "absl/algorithm/container.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "modules/rtp_rtcp/source/rtcp_packet/congestion_control_feedback.h"
#include "modules/rtp_rtcp/source/rtp_packet_received.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/network/ecn_marking.h"

namespace webrtc {

constexpr int kMaxPacketsPerSsrc = 16384;

void CongestionControlFeedbackTracker::ReceivedPacket(
    const RtpPacketReceived& packet) {
  if (packets_.size() > kMaxPacketsPerSsrc) {
    RTC_LOG(LS_VERBOSE)
        << "Unexpected number of packets without sending reports:"
        << packets_.size();
    return;
  }
  int64_t unwrapped_sequence_number =
      unwrapper_.Unwrap(packet.SequenceNumber());
  if (last_sequence_number_in_feedback_ &&
      unwrapped_sequence_number < *last_sequence_number_in_feedback_ + 1) {
    RTC_LOG(LS_WARNING)
        << "Received packet unorderered between feeedback. SSRC: "
        << packet.Ssrc() << " Seq: " << packet.SequenceNumber()
        << " last feedback: "
        << static_cast<uint16_t>(*last_sequence_number_in_feedback_);
    // TODO: bugs.webrtc.org/374550342 - According to spec, the old packets
    // should be reported again. But at the moment, we dont store history of
    // packet we already reported and thus, they will be reported as lost.
    // Note that this is likely not a problem in webrtc since the packets will
    // also be removed from the send history when they are first reported as
    // received.
    last_sequence_number_in_feedback_ = unwrapped_sequence_number - 1;
  }
  packets_.push_back({.ssrc = packet.Ssrc(),
                      .unwrapped_sequence_number = unwrapped_sequence_number,
                      .arrival_time = packet.arrival_time(),
                      .ecn = packet.ecn()});
}

void CongestionControlFeedbackTracker::AddPacketsToFeedback(
    Timestamp feedback_time,
    std::vector<rtcp::CongestionControlFeedback::PacketInfo>& packet_feedback) {
  if (packets_.empty()) {
    return;
  }
  absl::c_sort(packets_, [](const PacketInfo& a, const PacketInfo& b) {
    return std::tie(a.unwrapped_sequence_number, a.arrival_time) <
           std::tie(b.unwrapped_sequence_number, b.arrival_time);
  });
  if (!last_sequence_number_in_feedback_) {
    last_sequence_number_in_feedback_ =
        packets_.front().unwrapped_sequence_number - 1;
  }

  auto packet_it = packets_.begin();
  uint32_t ssrc = packet_it->ssrc;
  for (int64_t sequence_number = *last_sequence_number_in_feedback_ + 1;
       sequence_number <= packets_.back().unwrapped_sequence_number &&
       sequence_number <=
           *last_sequence_number_in_feedback_ + kMaxPacketsPerSsrc;
       ++sequence_number) {
    RTC_DCHECK(packet_it != packets_.end());
    RTC_DCHECK_EQ(ssrc, packet_it->ssrc);

    rtc::EcnMarking ecn = rtc::EcnMarking::kNotEct;
    TimeDelta arrival_time_offset = TimeDelta::MinusInfinity();

    if (sequence_number == packet_it->unwrapped_sequence_number) {
      arrival_time_offset = feedback_time - packet_it->arrival_time;
      ecn = packet_it->ecn;
      ++packet_it;
      while (packet_it != packets_.end() &&
             packet_it->unwrapped_sequence_number == sequence_number) {
        // According to RFC 8888:
        // If duplicate copies of a particular RTP packet are received, then the
        // arrival time of the first copy to arrive MUST be reported. If any of
        // the copies of the duplicated packet are ECN-CE marked, then an ECN-CE
        // mark MUST be reported for that packet; otherwise, the ECN mark of the
        // first copy to arrive is reported.
        if (packet_it->ecn == rtc::EcnMarking::kCe) {
          ecn = rtc::EcnMarking::kCe;
        }
        RTC_LOG(LS_WARNING) << "Received duplicate packet ssrc:" << ssrc
                            << " seq:" << static_cast<uint16_t>(sequence_number)
                            << " ecn: " << static_cast<int>(ecn);
        ++packet_it;
      }
    }  // else - the packet has not been received yet.
    packet_feedback.push_back(
        {.ssrc = ssrc,
         .sequence_number = static_cast<uint16_t>(sequence_number),
         .arrival_time_offset = arrival_time_offset,
         .ecn = ecn});
  }
  last_sequence_number_in_feedback_ = packets_.back().unwrapped_sequence_number;
  packets_.clear();
}

}  // namespace webrtc