1 /* 2 * Copyright (c) 2015 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/nack.h" 12 13 #include <algorithm> 14 15 #include "webrtc/base/checks.h" 16 #include "webrtc/base/logging.h" 17 #include "webrtc/modules/rtp_rtcp/source/byte_io.h" 18 19 using webrtc::RTCPUtility::RtcpCommonHeader; 20 21 namespace webrtc { 22 namespace rtcp { 23 24 // RFC 4585: Feedback format. 25 // 26 // Common packet format: 27 // 28 // 0 1 2 3 29 // 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 30 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 31 // |V=2|P| FMT | PT | length | 32 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 33 // 0 | SSRC of packet sender | 34 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 35 // 4 | SSRC of media source | 36 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 37 // : Feedback Control Information (FCI) : 38 // : : 39 // 40 // Generic NACK (RFC 4585). 41 // 42 // FCI: 43 // 0 1 2 3 44 // 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 45 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 46 // | PID | BLP | 47 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 48 bool Nack::Parse(const RtcpCommonHeader& header, const uint8_t* payload) { 49 RTC_DCHECK(header.packet_type == kPacketType); 50 RTC_DCHECK(header.count_or_format == kFeedbackMessageType); 51 52 if (header.payload_size_bytes < kCommonFeedbackLength + kNackItemLength) { 53 LOG(LS_WARNING) << "Payload length " << header.payload_size_bytes 54 << " is too small for a Nack."; 55 return false; 56 } 57 size_t nack_items = 58 (header.payload_size_bytes - kCommonFeedbackLength) / kNackItemLength; 59 60 ParseCommonFeedback(payload); 61 const uint8_t* next_nack = payload + kCommonFeedbackLength; 62 63 packet_ids_.clear(); 64 packed_.resize(nack_items); 65 for (size_t index = 0; index < nack_items; ++index) { 66 packed_[index].first_pid = ByteReader<uint16_t>::ReadBigEndian(next_nack); 67 packed_[index].bitmask = ByteReader<uint16_t>::ReadBigEndian(next_nack + 2); 68 next_nack += kNackItemLength; 69 } 70 Unpack(); 71 72 return true; 73 } 74 75 bool Nack::Create(uint8_t* packet, 76 size_t* index, 77 size_t max_length, 78 RtcpPacket::PacketReadyCallback* callback) const { 79 RTC_DCHECK(!packed_.empty()); 80 // If nack list can't fit in packet, try to fragment. 81 size_t nack_index = 0; 82 const size_t kCommonFbFmtLength = kHeaderLength + kCommonFeedbackLength; 83 do { 84 size_t bytes_left_in_buffer = max_length - *index; 85 if (bytes_left_in_buffer < kCommonFbFmtLength + kNackItemLength) { 86 if (!OnBufferFull(packet, index, callback)) 87 return false; 88 continue; 89 } 90 size_t num_nack_fields = 91 std::min((bytes_left_in_buffer - kCommonFbFmtLength) / kNackItemLength, 92 packed_.size() - nack_index); 93 94 size_t size_bytes = 95 (num_nack_fields * kNackItemLength) + kCommonFbFmtLength; 96 size_t header_length = ((size_bytes + 3) / 4) - 1; // As 32bit words - 1 97 CreateHeader(kFeedbackMessageType, kPacketType, header_length, packet, 98 index); 99 CreateCommonFeedback(packet + *index); 100 *index += kCommonFeedbackLength; 101 size_t end_index = nack_index + num_nack_fields; 102 for (; nack_index < end_index; ++nack_index) { 103 const auto& item = packed_[nack_index]; 104 ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 0, item.first_pid); 105 ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 2, item.bitmask); 106 *index += kNackItemLength; 107 } 108 RTC_DCHECK_LE(*index, max_length); 109 } while (nack_index < packed_.size()); 110 111 return true; 112 } 113 114 size_t Nack::BlockLength() const { 115 return (packed_.size() * kNackItemLength) + kCommonFeedbackLength + 116 kHeaderLength; 117 } 118 119 void Nack::WithList(const uint16_t* nack_list, size_t length) { 120 RTC_DCHECK(nack_list); 121 RTC_DCHECK(packet_ids_.empty()); 122 RTC_DCHECK(packed_.empty()); 123 packet_ids_.assign(nack_list, nack_list + length); 124 Pack(); 125 } 126 127 void Nack::Pack() { 128 RTC_DCHECK(!packet_ids_.empty()); 129 RTC_DCHECK(packed_.empty()); 130 auto it = packet_ids_.begin(); 131 const auto end = packet_ids_.end(); 132 while (it != end) { 133 PackedNack item; 134 item.first_pid = *it++; 135 // Bitmask specifies losses in any of the 16 packets following the pid. 136 item.bitmask = 0; 137 while (it != end) { 138 uint16_t shift = static_cast<uint16_t>(*it - item.first_pid - 1); 139 if (shift <= 15) { 140 item.bitmask |= (1 << shift); 141 ++it; 142 } else { 143 break; 144 } 145 } 146 packed_.push_back(item); 147 } 148 } 149 150 void Nack::Unpack() { 151 RTC_DCHECK(packet_ids_.empty()); 152 RTC_DCHECK(!packed_.empty()); 153 for (const PackedNack& item : packed_) { 154 packet_ids_.push_back(item.first_pid); 155 uint16_t pid = item.first_pid + 1; 156 for (uint16_t bitmask = item.bitmask; bitmask != 0; bitmask >>= 1, ++pid) 157 if (bitmask & 1) 158 packet_ids_.push_back(pid); 159 } 160 } 161 162 } // namespace rtcp 163 } // namespace webrtc 164
