Line data Source code
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 : #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/common_header.h"
19 :
20 : namespace webrtc {
21 : namespace rtcp {
22 : constexpr uint8_t Nack::kFeedbackMessageType;
23 : constexpr size_t Nack::kNackItemLength;
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 0 : Nack::Nack() {}
49 0 : Nack::~Nack() {}
50 :
51 0 : bool Nack::Parse(const CommonHeader& packet) {
52 0 : RTC_DCHECK_EQ(packet.type(), kPacketType);
53 0 : RTC_DCHECK_EQ(packet.fmt(), kFeedbackMessageType);
54 :
55 0 : if (packet.payload_size_bytes() < kCommonFeedbackLength + kNackItemLength) {
56 0 : LOG(LS_WARNING) << "Payload length " << packet.payload_size_bytes()
57 0 : << " is too small for a Nack.";
58 0 : return false;
59 : }
60 : size_t nack_items =
61 0 : (packet.payload_size_bytes() - kCommonFeedbackLength) / kNackItemLength;
62 :
63 0 : ParseCommonFeedback(packet.payload());
64 0 : const uint8_t* next_nack = packet.payload() + kCommonFeedbackLength;
65 :
66 0 : packet_ids_.clear();
67 0 : packed_.resize(nack_items);
68 0 : for (size_t index = 0; index < nack_items; ++index) {
69 0 : packed_[index].first_pid = ByteReader<uint16_t>::ReadBigEndian(next_nack);
70 0 : packed_[index].bitmask = ByteReader<uint16_t>::ReadBigEndian(next_nack + 2);
71 0 : next_nack += kNackItemLength;
72 : }
73 0 : Unpack();
74 :
75 0 : return true;
76 : }
77 :
78 0 : bool Nack::Create(uint8_t* packet,
79 : size_t* index,
80 : size_t max_length,
81 : RtcpPacket::PacketReadyCallback* callback) const {
82 0 : RTC_DCHECK(!packed_.empty());
83 : // If nack list can't fit in packet, try to fragment.
84 0 : constexpr size_t kNackHeaderLength = kHeaderLength + kCommonFeedbackLength;
85 0 : for (size_t nack_index = 0; nack_index < packed_.size();) {
86 0 : size_t bytes_left_in_buffer = max_length - *index;
87 0 : if (bytes_left_in_buffer < kNackHeaderLength + kNackItemLength) {
88 0 : if (!OnBufferFull(packet, index, callback))
89 0 : return false;
90 0 : continue;
91 : }
92 : size_t num_nack_fields =
93 0 : std::min((bytes_left_in_buffer - kNackHeaderLength) / kNackItemLength,
94 0 : packed_.size() - nack_index);
95 :
96 : size_t payload_size_bytes =
97 0 : kCommonFeedbackLength + (num_nack_fields * kNackItemLength);
98 : size_t payload_size_32bits =
99 0 : rtc::CheckedDivExact<size_t>(payload_size_bytes, 4);
100 : CreateHeader(kFeedbackMessageType, kPacketType, payload_size_32bits, packet,
101 0 : index);
102 :
103 0 : CreateCommonFeedback(packet + *index);
104 0 : *index += kCommonFeedbackLength;
105 :
106 0 : size_t nack_end_index = nack_index + num_nack_fields;
107 0 : for (; nack_index < nack_end_index; ++nack_index) {
108 0 : const PackedNack& item = packed_[nack_index];
109 0 : ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 0, item.first_pid);
110 0 : ByteWriter<uint16_t>::WriteBigEndian(packet + *index + 2, item.bitmask);
111 0 : *index += kNackItemLength;
112 : }
113 0 : RTC_DCHECK_LE(*index, max_length);
114 : }
115 :
116 0 : return true;
117 : }
118 :
119 0 : size_t Nack::BlockLength() const {
120 : return kHeaderLength + kCommonFeedbackLength +
121 0 : packed_.size() * kNackItemLength;
122 : }
123 :
124 0 : void Nack::SetPacketIds(const uint16_t* nack_list, size_t length) {
125 0 : RTC_DCHECK(nack_list);
126 0 : RTC_DCHECK(packet_ids_.empty());
127 0 : RTC_DCHECK(packed_.empty());
128 0 : packet_ids_.assign(nack_list, nack_list + length);
129 0 : Pack();
130 0 : }
131 :
132 0 : void Nack::Pack() {
133 0 : RTC_DCHECK(!packet_ids_.empty());
134 0 : RTC_DCHECK(packed_.empty());
135 0 : auto it = packet_ids_.begin();
136 0 : const auto end = packet_ids_.end();
137 0 : while (it != end) {
138 : PackedNack item;
139 0 : item.first_pid = *it++;
140 : // Bitmask specifies losses in any of the 16 packets following the pid.
141 0 : item.bitmask = 0;
142 0 : while (it != end) {
143 0 : uint16_t shift = static_cast<uint16_t>(*it - item.first_pid - 1);
144 0 : if (shift <= 15) {
145 0 : item.bitmask |= (1 << shift);
146 0 : ++it;
147 : } else {
148 0 : break;
149 : }
150 : }
151 0 : packed_.push_back(item);
152 : }
153 0 : }
154 :
155 0 : void Nack::Unpack() {
156 0 : RTC_DCHECK(packet_ids_.empty());
157 0 : RTC_DCHECK(!packed_.empty());
158 0 : for (const PackedNack& item : packed_) {
159 0 : packet_ids_.push_back(item.first_pid);
160 0 : uint16_t pid = item.first_pid + 1;
161 0 : for (uint16_t bitmask = item.bitmask; bitmask != 0; bitmask >>= 1, ++pid) {
162 0 : if (bitmask & 1)
163 0 : packet_ids_.push_back(pid);
164 : }
165 : }
166 0 : }
167 :
168 : } // namespace rtcp
169 : } // namespace webrtc
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