chromium/third_party/webrtc/modules/rtp_rtcp/source/rtcp_packet/congestion_control_feedback.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/rtp_rtcp/source/rtcp_packet/congestion_control_feedback.h"

#include <cstddef>
#include <cstdint>
#include <utility>
#include <vector>

#include "api/array_view.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "modules/rtp_rtcp/source/byte_io.h"
#include "rtc_base/network/ecn_marking.h"

namespace webrtc {
namespace rtcp {

/*
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |V=2|P| FMT=11  |   PT = 205    |          length               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 SSRC of RTCP packet sender                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   SSRC of 1st RTP Stream                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          begin_seq            |          num_reports          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |R|ECN|  Arrival time offset    | ...                           .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                               .
     .                                                               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   SSRC of nth RTP Stream                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          begin_seq            |          num_reports          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |R|ECN|  Arrival time offset    | ...                           |
     .                                                               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Report Timestamp (32 bits)                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/

namespace {

constexpr size_t kSenderSsrcLength = …;
constexpr size_t kHeaderPerMediaSssrcLength = …;
constexpr size_t kTimestampLength = …;

// RFC-3168, Section 5
constexpr uint16_t kEcnEct1 = …;
constexpr uint16_t kEcnEct0 = …;
constexpr uint16_t kEcnCe = …;

// Arrival time offset (ATO, 13 bits):
// The arrival time of the RTP packet at the receiver, as an offset before the
// time represented by the Report Timestamp (RTS) field of this RTCP congestion
// control feedback report. The ATO field is in units of 1/1024 seconds (this
// unit is chosen to give exact offsets from the RTS field) so, for example, an
// ATO value of 512 indicates that the corresponding RTP packet arrived exactly
// half a second before the time instant represented by the RTS field. If the
// measured value is greater than 8189/1024 seconds (the value that would be
// coded as 0x1FFD), the value 0x1FFE MUST be reported to indicate an over-range
// measurement. If the measurement is unavailable or if the arrival time of the
// RTP packet is after the time represented by the RTS field, then an ATO value
// of 0x1FFF MUST be reported for the packet.
uint16_t To13bitAto(TimeDelta arrival_time_offset) { … }

TimeDelta AtoToTimeDelta(uint16_t receive_info) { … }

uint16_t To2BitEcn(rtc::EcnMarking ecn_marking) { … }

rtc::EcnMarking ToEcnMarking(uint16_t receive_info) { … }

}  // namespace

CongestionControlFeedback ::CongestionControlFeedback(
    std::vector<PacketInfo> packets,
    uint32_t compact_ntp_timestamp)
    : … { … }

bool CongestionControlFeedback::Create(uint8_t* buffer,
                                       size_t* position,
                                       size_t max_length,
                                       PacketReadyCallback callback) const { … }

size_t CongestionControlFeedback::BlockLength() const { … }

bool CongestionControlFeedback::Parse(const rtcp::CommonHeader& packet) { … }
}  // namespace rtcp
}  // namespace webrtc