tor-browser

nack.cc (6045B)

---

/*
*  Copyright (c) 2015 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/nack.h"

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

#include "modules/rtp_rtcp/source/byte_io.h"
#include "modules/rtp_rtcp/source/rtcp_packet/common_header.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"

namespace webrtc {
namespace rtcp {
// RFC 4585: Feedback format.
//
// Common packet format:
//
//    0                   1                   2                   3
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |V=2|P|   FMT   |       PT      |          length               |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 0 |                  SSRC of packet sender                        |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 4 |                  SSRC of media source                         |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   :            Feedback Control Information (FCI)                 :
//   :                                                               :
//
// Generic NACK (RFC 4585).
//
// FCI:
//    0                   1                   2                   3
//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//   |            PID                |             BLP               |
//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Nack::Nack() = default;
Nack::Nack(const Nack& rhs) = default;
Nack::~Nack() = default;

bool Nack::Parse(const CommonHeader& packet) {
 RTC_DCHECK_EQ(packet.type(), kPacketType);
 RTC_DCHECK_EQ(packet.fmt(), kFeedbackMessageType);

 if (packet.payload_size_bytes() < kCommonFeedbackLength + kNackItemLength) {
   RTC_LOG(LS_WARNING) << "Payload length " << packet.payload_size_bytes()
                       << " is too small for a Nack.";
   return false;
 }
 size_t nack_items =
     (packet.payload_size_bytes() - kCommonFeedbackLength) / kNackItemLength;

 ParseCommonFeedback(packet.payload());
 const uint8_t* next_nack = packet.payload() + kCommonFeedbackLength;

 packet_ids_.clear();
 packed_.resize(nack_items);
 for (size_t index = 0; index < nack_items; ++index) {
   packed_[index].first_pid = ByteReader<uint16_t>::ReadBigEndian(next_nack);
   packed_[index].bitmask = ByteReader<uint16_t>::ReadBigEndian(next_nack + 2);
   next_nack += kNackItemLength;
 }
 Unpack();

 return true;
}

size_t Nack::BlockLength() const {
 return kHeaderLength + kCommonFeedbackLength +
        packed_.size() * kNackItemLength;
}

bool Nack::Create(uint8_t* packet,
                 size_t* index,
                 size_t max_length,
                 PacketReadyCallback callback) const {
 RTC_DCHECK(!packed_.empty());
 // If nack list can't fit in packet, try to fragment.
 constexpr size_t kNackHeaderLength = kHeaderLength + kCommonFeedbackLength;
 for (size_t nack_index = 0; nack_index < packed_.size();) {
   size_t bytes_left_in_buffer = max_length - *index;
   if (bytes_left_in_buffer < kNackHeaderLength + kNackItemLength) {
     if (!OnBufferFull(packet, index, callback))
       return false;
     continue;
   }
   size_t num_nack_fields =
       std::min((bytes_left_in_buffer - kNackHeaderLength) / kNackItemLength,
                packed_.size() - nack_index);

   size_t payload_size_bytes =
       kCommonFeedbackLength + (num_nack_fields * kNackItemLength);
   size_t payload_size_32bits = CheckedDivExact<size_t>(payload_size_bytes, 4);
   CreateHeader(kFeedbackMessageType, kPacketType, payload_size_32bits, packet,
                index);

   CreateCommonFeedback(packet + *index);
   *index += kCommonFeedbackLength;

   size_t nack_end_index = nack_index + num_nack_fields;
   for (; nack_index < nack_end_index; ++nack_index) {
     const PackedNack& item = packed_[nack_index];
     ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 0, item.first_pid);
     ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 2, item.bitmask);
     *index += kNackItemLength;
   }
   RTC_DCHECK_LE(*index, max_length);
 }

 return true;
}

void Nack::SetPacketIds(const uint16_t* nack_list, size_t length) {
 RTC_DCHECK(nack_list);
 SetPacketIds(std::vector<uint16_t>(nack_list, nack_list + length));
}

void Nack::SetPacketIds(std::vector<uint16_t> nack_list) {
 RTC_DCHECK(packet_ids_.empty());
 RTC_DCHECK(packed_.empty());
 packet_ids_ = std::move(nack_list);
 Pack();
}

void Nack::Pack() {
 RTC_DCHECK(!packet_ids_.empty());
 RTC_DCHECK(packed_.empty());
 auto it = packet_ids_.begin();
 const auto end = packet_ids_.end();
 while (it != end) {
   PackedNack item;
   item.first_pid = *it++;
   // Bitmask specifies losses in any of the 16 packets following the pid.
   item.bitmask = 0;
   while (it != end) {
     uint16_t shift = static_cast<uint16_t>(*it - item.first_pid - 1);
     if (shift <= 15) {
       item.bitmask |= (1 << shift);
       ++it;
     } else {
       break;
     }
   }
   packed_.push_back(item);
 }
}

void Nack::Unpack() {
 RTC_DCHECK(packet_ids_.empty());
 RTC_DCHECK(!packed_.empty());
 for (const PackedNack& item : packed_) {
   packet_ids_.push_back(item.first_pid);
   uint16_t pid = item.first_pid + 1;
   for (uint16_t bitmask = item.bitmask; bitmask != 0; bitmask >>= 1, ++pid) {
     if (bitmask & 1)
       packet_ids_.push_back(pid);
   }
 }
}

}  // namespace rtcp
}  // namespace webrtc