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 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parse(const RtcpCommonHeader & header,const uint8_t * payload)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
Create(uint8_t * packet,size_t * index,size_t max_length,RtcpPacket::PacketReadyCallback * callback) const75 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
BlockLength() const114 size_t Nack::BlockLength() const {
115 return (packed_.size() * kNackItemLength) + kCommonFeedbackLength +
116 kHeaderLength;
117 }
118
WithList(const uint16_t * nack_list,size_t length)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
Pack()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
Unpack()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