modules/rtp_rtcp/source/rtp_packet.cc - src/webrtc - Git at Google

 /*
  *  Copyright (c) 2016 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 "webrtc/modules/rtp_rtcp/source/rtp_packet.h"

 #include <cstring>
 #include <utility>

 #include "webrtc/common_types.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_header_extension_map.h"
 #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/random.h"
 #include "webrtc/rtc_base/safe_conversions.h"

 namespace webrtc {
 namespace {
 constexpr size_t kFixedHeaderSize = 12;
 constexpr uint8_t kRtpVersion = 2;
 constexpr uint16_t kOneByteExtensionId = 0xBEDE;
 constexpr size_t kOneByteHeaderSize = 1;
 constexpr size_t kDefaultPacketSize = 1500;
 }  // namespace

 constexpr int RtpPacket::kMaxExtensionHeaders;
 constexpr int RtpPacket::kMinExtensionId;
 constexpr int RtpPacket::kMaxExtensionId;

 //  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|X|  CC   |M|     PT      |       sequence number         |
 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 // |                           timestamp                           |
 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 // |           synchronization source (SSRC) identifier            |
 // +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
 // |            Contributing source (CSRC) identifiers             |
 // |                             ....                              |
 // +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
 // |One-byte eXtensions id = 0xbede|       length in 32bits        |
 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 // |                          Extensions                           |
 // |                             ....                              |
 // +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
 // |                           Payload                             |
 // |             ....              :  padding...                   |
 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 // |               padding         | Padding size  |
 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 RtpPacket::RtpPacket() : RtpPacket(nullptr, kDefaultPacketSize) {}

 RtpPacket::RtpPacket(const ExtensionManager* extensions)
     : RtpPacket(extensions, kDefaultPacketSize) {}

 RtpPacket::RtpPacket(const RtpPacket&) = default;

 RtpPacket::RtpPacket(const ExtensionManager* extensions, size_t capacity)
     : buffer_(capacity) {
   RTC_DCHECK_GE(capacity, kFixedHeaderSize);
   Clear();
   if (extensions) {
     IdentifyExtensions(*extensions);
   } else {
     for (size_t i = 0; i < kMaxExtensionHeaders; ++i)
       extension_entries_[i].type = ExtensionManager::kInvalidType;
   }
 }

 RtpPacket::~RtpPacket() {}

 void RtpPacket::IdentifyExtensions(const ExtensionManager& extensions) {
   for (int i = 0; i < kMaxExtensionHeaders; ++i)
     extension_entries_[i].type = extensions.GetType(i + 1);
 }

 bool RtpPacket::Parse(const uint8_t* buffer, size_t buffer_size) {
   if (!ParseBuffer(buffer, buffer_size)) {
     Clear();
     return false;
   }
   buffer_.SetData(buffer, buffer_size);
   RTC_DCHECK_EQ(size(), buffer_size);
   return true;
 }

 bool RtpPacket::Parse(rtc::ArrayView<const uint8_t> packet) {
   return Parse(packet.data(), packet.size());
 }

 bool RtpPacket::Parse(rtc::CopyOnWriteBuffer buffer) {
   if (!ParseBuffer(buffer.cdata(), buffer.size())) {
     Clear();
     return false;
   }
   size_t buffer_size = buffer.size();
   buffer_ = std::move(buffer);
   RTC_DCHECK_EQ(size(), buffer_size);
   return true;
 }

 bool RtpPacket::Marker() const {
   RTC_DCHECK_EQ(marker_, (data()[1] & 0x80) != 0);
   return marker_;
 }

 uint8_t RtpPacket::PayloadType() const {
   RTC_DCHECK_EQ(payload_type_, data()[1] & 0x7f);
   return payload_type_;
 }

 uint16_t RtpPacket::SequenceNumber() const {
   RTC_DCHECK_EQ(sequence_number_,
                 ByteReader<uint16_t>::ReadBigEndian(data() + 2));
   return sequence_number_;
 }

 uint32_t RtpPacket::Timestamp() const {
   RTC_DCHECK_EQ(timestamp_, ByteReader<uint32_t>::ReadBigEndian(data() + 4));
   return timestamp_;
 }

 uint32_t RtpPacket::Ssrc() const {
   RTC_DCHECK_EQ(ssrc_, ByteReader<uint32_t>::ReadBigEndian(data() + 8));
   return ssrc_;
 }

 std::vector<uint32_t> RtpPacket::Csrcs() const {
   size_t num_csrc = data()[0] & 0x0F;
   RTC_DCHECK_GE(capacity(), kFixedHeaderSize + num_csrc * 4);
   std::vector<uint32_t> csrcs(num_csrc);
   for (size_t i = 0; i < num_csrc; ++i) {
     csrcs[i] =
         ByteReader<uint32_t>::ReadBigEndian(&data()[kFixedHeaderSize + i * 4]);
   }
   return csrcs;
 }

 size_t RtpPacket::headers_size() const {
   return payload_offset_;
 }

 size_t RtpPacket::payload_size() const {
   return payload_size_;
 }

 size_t RtpPacket::padding_size() const {
   return padding_size_;
 }

 rtc::ArrayView<const uint8_t> RtpPacket::payload() const {
   return rtc::MakeArrayView(data() + payload_offset_, payload_size_);
 }

 rtc::CopyOnWriteBuffer RtpPacket::Buffer() const {
   return buffer_;
 }

 size_t RtpPacket::capacity() const {
   return buffer_.capacity();
 }

 size_t RtpPacket::size() const {
   size_t ret = payload_offset_ + payload_size_ + padding_size_;
   RTC_DCHECK_EQ(buffer_.size(), ret);
   return ret;
 }

 const uint8_t* RtpPacket::data() const {
   return buffer_.cdata();
 }

 size_t RtpPacket::FreeCapacity() const {
   return capacity() - size();
 }

 size_t RtpPacket::MaxPayloadSize() const {
   return capacity() - payload_offset_;
 }

 void RtpPacket::CopyHeaderFrom(const RtpPacket& packet) {
   RTC_DCHECK_GE(capacity(), packet.headers_size());

   marker_ = packet.marker_;
   payload_type_ = packet.payload_type_;
   sequence_number_ = packet.sequence_number_;
   timestamp_ = packet.timestamp_;
   ssrc_ = packet.ssrc_;
   payload_offset_ = packet.payload_offset_;
   for (size_t i = 0; i < kMaxExtensionHeaders; ++i) {
     extension_entries_[i] = packet.extension_entries_[i];
   }
   extensions_size_ = packet.extensions_size_;
   buffer_.SetData(packet.data(), packet.headers_size());
   // Reset payload and padding.
   payload_size_ = 0;
   padding_size_ = 0;
 }

 void RtpPacket::SetMarker(bool marker_bit) {
   marker_ = marker_bit;
   if (marker_) {
     WriteAt(1, data()[1] | 0x80);
   } else {
     WriteAt(1, data()[1] & 0x7F);
   }
 }

 void RtpPacket::SetPayloadType(uint8_t payload_type) {
   RTC_DCHECK_LE(payload_type, 0x7Fu);
   payload_type_ = payload_type;
   WriteAt(1, (data()[1] & 0x80) | payload_type);
 }

 void RtpPacket::SetSequenceNumber(uint16_t seq_no) {
   sequence_number_ = seq_no;
   ByteWriter<uint16_t>::WriteBigEndian(WriteAt(2), seq_no);
 }

 void RtpPacket::SetTimestamp(uint32_t timestamp) {
   timestamp_ = timestamp;
   ByteWriter<uint32_t>::WriteBigEndian(WriteAt(4), timestamp);
 }

 void RtpPacket::SetSsrc(uint32_t ssrc) {
   ssrc_ = ssrc;
   ByteWriter<uint32_t>::WriteBigEndian(WriteAt(8), ssrc);
 }

 void RtpPacket::SetCsrcs(const std::vector<uint32_t>& csrcs) {
   RTC_DCHECK_EQ(extensions_size_, 0);
   RTC_DCHECK_EQ(payload_size_, 0);
   RTC_DCHECK_EQ(padding_size_, 0);
   RTC_DCHECK_LE(csrcs.size(), 0x0fu);
   RTC_DCHECK_LE(kFixedHeaderSize + 4 * csrcs.size(), capacity());
   payload_offset_ = kFixedHeaderSize + 4 * csrcs.size();
   WriteAt(0, (data()[0] & 0xF0) | rtc::dchecked_cast<uint8_t>(csrcs.size()));
   size_t offset = kFixedHeaderSize;
   for (uint32_t csrc : csrcs) {
     ByteWriter<uint32_t>::WriteBigEndian(WriteAt(offset), csrc);
     offset += 4;
   }
   buffer_.SetSize(payload_offset_);
 }

 bool RtpPacket::HasRawExtension(int id) const {
   if (id == ExtensionManager::kInvalidId)
     return false;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   return extension_entries_[id - 1].offset != 0;
 }

 rtc::ArrayView<const uint8_t> RtpPacket::GetRawExtension(int id) const {
   if (id == ExtensionManager::kInvalidId)
     return nullptr;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   const ExtensionInfo& extension = extension_entries_[id - 1];
   if (extension.offset == 0)
     return nullptr;
   return rtc::MakeArrayView(data() + extension.offset, extension.length);
 }

 bool RtpPacket::SetRawExtension(int id, rtc::ArrayView<const uint8_t> data) {
   auto buffer = AllocateRawExtension(id, data.size());
   if (buffer.empty())
     return false;
   RTC_DCHECK_EQ(buffer.size(), data.size());
   memcpy(buffer.data(), data.data(), data.size());
   return true;
 }

 rtc::ArrayView<uint8_t> RtpPacket::AllocateRawExtension(int id, size_t length) {
   if (id == ExtensionManager::kInvalidId)
     return nullptr;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   RTC_DCHECK_GE(length, 1);
   RTC_DCHECK_LE(length, 16);

   ExtensionInfo* extension_entry = &extension_entries_[id - 1];
   if (extension_entry->offset != 0) {
     // Extension already reserved. Check if same length is used.
     if (extension_entry->length == length)
       return rtc::MakeArrayView(WriteAt(extension_entry->offset), length);

     LOG(LS_ERROR) << "Length mismatch for extension id " << id << " type "
                   << static_cast<int>(extension_entry->type) << ": expected "
                   << static_cast<int>(extension_entry->length) << ". received "
                   << length;
     return nullptr;
   }
   if (payload_size_ > 0) {
     LOG(LS_ERROR) << "Can't add new extension id " << id
                   << " after payload was set.";
     return nullptr;
   }
   if (padding_size_ > 0) {
     LOG(LS_ERROR) << "Can't add new extension id " << id
                   << " after padding was set.";
     return nullptr;
   }

   size_t num_csrc = data()[0] & 0x0F;
   size_t extensions_offset = kFixedHeaderSize + (num_csrc * 4) + 4;
   size_t new_extensions_size = extensions_size_ + kOneByteHeaderSize + length;
   if (extensions_offset + new_extensions_size > capacity()) {
     LOG(LS_ERROR)
         << "Extension cannot be registered: Not enough space left in buffer.";
     return nullptr;
   }

   // All checks passed, write down the extension headers.
   if (extensions_size_ == 0) {
     RTC_DCHECK_EQ(payload_offset_, kFixedHeaderSize + (num_csrc * 4));
     WriteAt(0, data()[0] | 0x10);  // Set extension bit.
     // Profile specific ID always set to OneByteExtensionHeader.
     ByteWriter<uint16_t>::WriteBigEndian(WriteAt(extensions_offset - 4),
                                          kOneByteExtensionId);
   }

   uint8_t one_byte_header = rtc::dchecked_cast<uint8_t>(id) << 4;
   one_byte_header |= rtc::dchecked_cast<uint8_t>(length - 1);
   WriteAt(extensions_offset + extensions_size_, one_byte_header);

   extension_entry->offset = rtc::dchecked_cast<uint16_t>(
       extensions_offset + extensions_size_ + kOneByteHeaderSize);
   extension_entry->length = rtc::dchecked_cast<uint8_t>(length);
   extensions_size_ = rtc::dchecked_cast<uint16_t>(new_extensions_size);

   // Update header length field.
   uint16_t extensions_words = (extensions_size_ + 3) / 4;  // Wrap up to 32bit.
   ByteWriter<uint16_t>::WriteBigEndian(WriteAt(extensions_offset - 2),
                                        extensions_words);
   // Fill extension padding place with zeroes.
   size_t extension_padding_size = 4 * extensions_words - extensions_size_;
   memset(WriteAt(extensions_offset + extensions_size_), 0,
          extension_padding_size);
   payload_offset_ = extensions_offset + 4 * extensions_words;
   buffer_.SetSize(payload_offset_);
   return rtc::MakeArrayView(WriteAt(extension_entry->offset), length);
 }

 uint8_t* RtpPacket::AllocatePayload(size_t size_bytes) {
   // Reset payload size to 0. If CopyOnWrite buffer_ was shared, this will cause
   // reallocation and memcpy. Keeping just header reduces memcpy size.
   SetPayloadSize(0);
   return SetPayloadSize(size_bytes);
 }

 uint8_t* RtpPacket::SetPayloadSize(size_t size_bytes) {
   RTC_DCHECK_EQ(padding_size_, 0);
   if (payload_offset_ + size_bytes > capacity()) {
     LOG(LS_WARNING) << "Cannot set payload, not enough space in buffer.";
     return nullptr;
   }
   payload_size_ = size_bytes;
   buffer_.SetSize(payload_offset_ + payload_size_);
   return WriteAt(payload_offset_);
 }

 bool RtpPacket::SetPadding(uint8_t size_bytes, Random* random) {
   RTC_DCHECK(random);
   if (payload_offset_ + payload_size_ + size_bytes > capacity()) {
     LOG(LS_WARNING) << "Cannot set padding size " << size_bytes << ", only "
                     << (capacity() - payload_offset_ - payload_size_)
                     << " bytes left in buffer.";
     return false;
   }
   padding_size_ = size_bytes;
   buffer_.SetSize(payload_offset_ + payload_size_ + padding_size_);
   if (padding_size_ > 0) {
     size_t padding_offset = payload_offset_ + payload_size_;
     size_t padding_end = padding_offset + padding_size_;
     for (size_t offset = padding_offset; offset < padding_end - 1; ++offset) {
       WriteAt(offset, random->Rand<uint8_t>());
     }
     WriteAt(padding_end - 1, padding_size_);
     WriteAt(0, data()[0] | 0x20);  // Set padding bit.
   } else {
     WriteAt(0, data()[0] & ~0x20);  // Clear padding bit.
   }
   return true;
 }

 void RtpPacket::Clear() {
   marker_ = false;
   payload_type_ = 0;
   sequence_number_ = 0;
   timestamp_ = 0;
   ssrc_ = 0;
   payload_offset_ = kFixedHeaderSize;
   payload_size_ = 0;
   padding_size_ = 0;
   extensions_size_ = 0;
   for (ExtensionInfo& location : extension_entries_) {
     location.offset = 0;
     location.length = 0;
   }

   memset(WriteAt(0), 0, kFixedHeaderSize);
   buffer_.SetSize(kFixedHeaderSize);
   WriteAt(0, kRtpVersion << 6);
 }

 bool RtpPacket::ParseBuffer(const uint8_t* buffer, size_t size) {
   if (size < kFixedHeaderSize) {
     return false;
   }
   const uint8_t version = buffer[0] >> 6;
   if (version != kRtpVersion) {
     return false;
   }
   const bool has_padding = (buffer[0] & 0x20) != 0;
   const bool has_extension = (buffer[0] & 0x10) != 0;
   const uint8_t number_of_crcs = buffer[0] & 0x0f;
   marker_ = (buffer[1] & 0x80) != 0;
   payload_type_ = buffer[1] & 0x7f;

   sequence_number_ = ByteReader<uint16_t>::ReadBigEndian(&buffer[2]);
   timestamp_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[4]);
   ssrc_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[8]);
   if (size < kFixedHeaderSize + number_of_crcs * 4) {
     return false;
   }
   payload_offset_ = kFixedHeaderSize + number_of_crcs * 4;

   if (has_padding) {
     padding_size_ = buffer[size - 1];
     if (padding_size_ == 0) {
       LOG(LS_WARNING) << "Padding was set, but padding size is zero";
       return false;
     }
   } else {
     padding_size_ = 0;
   }

   extensions_size_ = 0;
   for (ExtensionInfo& location : extension_entries_) {
     location.offset = 0;
     location.length = 0;
   }
   if (has_extension) {
     /* RTP header extension, RFC 3550.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      defined by profile       |           length              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        header extension                       |
     |                             ....                              |
     */
     size_t extension_offset = payload_offset_ + 4;
     if (extension_offset > size) {
       return false;
     }
     uint16_t profile =
         ByteReader<uint16_t>::ReadBigEndian(&buffer[payload_offset_]);
     size_t extensions_capacity =
         ByteReader<uint16_t>::ReadBigEndian(&buffer[payload_offset_ + 2]);
     extensions_capacity *= 4;
     if (extension_offset + extensions_capacity > size) {
       return false;
     }
     if (profile != kOneByteExtensionId) {
       LOG(LS_WARNING) << "Unsupported rtp extension " << profile;
     } else {
       constexpr uint8_t kPaddingId = 0;
       constexpr uint8_t kReservedId = 15;
       while (extensions_size_ + kOneByteHeaderSize < extensions_capacity) {
         int id = buffer[extension_offset + extensions_size_] >> 4;
         if (id == kReservedId) {
           break;
         } else if (id == kPaddingId) {
           extensions_size_++;
           continue;
         }
         uint8_t length =
             1 + (buffer[extension_offset + extensions_size_] & 0xf);
         if (extensions_size_ + kOneByteHeaderSize + length >
             extensions_capacity) {
           LOG(LS_WARNING) << "Oversized rtp header extension.";
           break;
         }

         size_t idx = id - 1;
         if (extension_entries_[idx].length != 0) {
           LOG(LS_VERBOSE) << "Duplicate rtp header extension id " << id
                           << ". Overwriting.";
         }

         extensions_size_ += kOneByteHeaderSize;
         extension_entries_[idx].offset =
             rtc::dchecked_cast<uint16_t>(extension_offset + extensions_size_);
         extension_entries_[idx].length = rtc::dchecked_cast<uint16_t>(length);
         extensions_size_ += length;
       }
     }
     payload_offset_ = extension_offset + extensions_capacity;
   }

   if (payload_offset_ + padding_size_ > size) {
     return false;
   }
   payload_size_ = size - payload_offset_ - padding_size_;
   return true;
 }

 rtc::ArrayView<const uint8_t> RtpPacket::FindExtension(
     ExtensionType type) const {
   for (const ExtensionInfo& extension : extension_entries_) {
     if (extension.type == type) {
       if (extension.length == 0) {
         // Extension is registered but not set.
         return nullptr;
       }
       return rtc::MakeArrayView(data() + extension.offset, extension.length);
     }
   }
   return nullptr;
 }

 rtc::ArrayView<uint8_t> RtpPacket::AllocateExtension(ExtensionType type,
                                                      size_t length) {
   for (int i = 0; i < kMaxExtensionHeaders; ++i) {
     if (extension_entries_[i].type == type) {
       int extension_id = i + 1;
       return AllocateRawExtension(extension_id, length);
     }
   }
   // Extension not registered.
   return nullptr;
 }

 uint8_t* RtpPacket::WriteAt(size_t offset) {
   return buffer_.data() + offset;
 }

 void RtpPacket::WriteAt(size_t offset, uint8_t byte) {
   buffer_.data()[offset] = byte;
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2016 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 "webrtc/modules/rtp_rtcp/source/rtp_packet.h"

	#include <cstring>
	#include <utility>

	#include "webrtc/common_types.h"
	#include "webrtc/modules/rtp_rtcp/include/rtp_header_extension_map.h"
	#include "webrtc/modules/rtp_rtcp/source/byte_io.h"
	#include "webrtc/rtc_base/checks.h"
	#include "webrtc/rtc_base/logging.h"
	#include "webrtc/rtc_base/random.h"
	#include "webrtc/rtc_base/safe_conversions.h"

	namespace webrtc {
	namespace {
	constexpr size_t kFixedHeaderSize = 12;
	constexpr uint8_t kRtpVersion = 2;
	constexpr uint16_t kOneByteExtensionId = 0xBEDE;
	constexpr size_t kOneByteHeaderSize = 1;
	constexpr size_t kDefaultPacketSize = 1500;
	} // namespace

	constexpr int RtpPacket::kMaxExtensionHeaders;
	constexpr int RtpPacket::kMinExtensionId;
	constexpr int RtpPacket::kMaxExtensionId;

	// 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\|X\| CC \|M\| PT \| sequence number \|
	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// \| timestamp \|
	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// \| synchronization source (SSRC) identifier \|
	// +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
	// \| Contributing source (CSRC) identifiers \|
	// \| .... \|
	// +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
	// \|One-byte eXtensions id = 0xbede\| length in 32bits \|
	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// \| Extensions \|
	// \| .... \|
	// +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
	// \| Payload \|
	// \| .... : padding... \|
	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// \| padding \| Padding size \|
	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	RtpPacket::RtpPacket() : RtpPacket(nullptr, kDefaultPacketSize) {}

	RtpPacket::RtpPacket(const ExtensionManager* extensions)
	: RtpPacket(extensions, kDefaultPacketSize) {}

	RtpPacket::RtpPacket(const RtpPacket&) = default;

	RtpPacket::RtpPacket(const ExtensionManager* extensions, size_t capacity)
	: buffer_(capacity) {
	RTC_DCHECK_GE(capacity, kFixedHeaderSize);
	Clear();
	if (extensions) {
	IdentifyExtensions(*extensions);
	} else {
	for (size_t i = 0; i < kMaxExtensionHeaders; ++i)
	extension_entries_[i].type = ExtensionManager::kInvalidType;
	}
	}

	RtpPacket::~RtpPacket() {}

	void RtpPacket::IdentifyExtensions(const ExtensionManager& extensions) {
	for (int i = 0; i < kMaxExtensionHeaders; ++i)
	extension_entries_[i].type = extensions.GetType(i + 1);
	}

	bool RtpPacket::Parse(const uint8_t* buffer, size_t buffer_size) {
	if (!ParseBuffer(buffer, buffer_size)) {
	Clear();
	return false;
	}
	buffer_.SetData(buffer, buffer_size);
	RTC_DCHECK_EQ(size(), buffer_size);
	return true;
	}

	bool RtpPacket::Parse(rtc::ArrayView<const uint8_t> packet) {
	return Parse(packet.data(), packet.size());
	}

	bool RtpPacket::Parse(rtc::CopyOnWriteBuffer buffer) {
	if (!ParseBuffer(buffer.cdata(), buffer.size())) {
	Clear();
	return false;
	}
	size_t buffer_size = buffer.size();
	buffer_ = std::move(buffer);
	RTC_DCHECK_EQ(size(), buffer_size);
	return true;
	}

	bool RtpPacket::Marker() const {
	RTC_DCHECK_EQ(marker_, (data()[1] & 0x80) != 0);
	return marker_;
	}

	uint8_t RtpPacket::PayloadType() const {
	RTC_DCHECK_EQ(payload_type_, data()[1] & 0x7f);
	return payload_type_;
	}

	uint16_t RtpPacket::SequenceNumber() const {
	RTC_DCHECK_EQ(sequence_number_,
	ByteReader<uint16_t>::ReadBigEndian(data() + 2));
	return sequence_number_;
	}

	uint32_t RtpPacket::Timestamp() const {
	RTC_DCHECK_EQ(timestamp_, ByteReader<uint32_t>::ReadBigEndian(data() + 4));
	return timestamp_;
	}

	uint32_t RtpPacket::Ssrc() const {
	RTC_DCHECK_EQ(ssrc_, ByteReader<uint32_t>::ReadBigEndian(data() + 8));
	return ssrc_;
	}

	std::vector<uint32_t> RtpPacket::Csrcs() const {
	size_t num_csrc = data()[0] & 0x0F;
	RTC_DCHECK_GE(capacity(), kFixedHeaderSize + num_csrc * 4);
	std::vector<uint32_t> csrcs(num_csrc);
	for (size_t i = 0; i < num_csrc; ++i) {
	csrcs[i] =
	ByteReader<uint32_t>::ReadBigEndian(&data()[kFixedHeaderSize + i * 4]);
	}
	return csrcs;
	}

	size_t RtpPacket::headers_size() const {
	return payload_offset_;
	}

	size_t RtpPacket::payload_size() const {
	return payload_size_;
	}

	size_t RtpPacket::padding_size() const {
	return padding_size_;
	}

	rtc::ArrayView<const uint8_t> RtpPacket::payload() const {
	return rtc::MakeArrayView(data() + payload_offset_, payload_size_);
	}

	rtc::CopyOnWriteBuffer RtpPacket::Buffer() const {
	return buffer_;
	}

	size_t RtpPacket::capacity() const {
	return buffer_.capacity();
	}

	size_t RtpPacket::size() const {
	size_t ret = payload_offset_ + payload_size_ + padding_size_;
	RTC_DCHECK_EQ(buffer_.size(), ret);
	return ret;
	}

	const uint8_t* RtpPacket::data() const {
	return buffer_.cdata();
	}

	size_t RtpPacket::FreeCapacity() const {
	return capacity() - size();
	}

	size_t RtpPacket::MaxPayloadSize() const {
	return capacity() - payload_offset_;
	}

	void RtpPacket::CopyHeaderFrom(const RtpPacket& packet) {
	RTC_DCHECK_GE(capacity(), packet.headers_size());

	marker_ = packet.marker_;
	payload_type_ = packet.payload_type_;
	sequence_number_ = packet.sequence_number_;
	timestamp_ = packet.timestamp_;
	ssrc_ = packet.ssrc_;
	payload_offset_ = packet.payload_offset_;
	for (size_t i = 0; i < kMaxExtensionHeaders; ++i) {
	extension_entries_[i] = packet.extension_entries_[i];
	}
	extensions_size_ = packet.extensions_size_;
	buffer_.SetData(packet.data(), packet.headers_size());
	// Reset payload and padding.
	payload_size_ = 0;
	padding_size_ = 0;
	}

	void RtpPacket::SetMarker(bool marker_bit) {
	marker_ = marker_bit;
	if (marker_) {
	WriteAt(1, data()[1] \| 0x80);
	} else {
	WriteAt(1, data()[1] & 0x7F);
	}
	}

	void RtpPacket::SetPayloadType(uint8_t payload_type) {
	RTC_DCHECK_LE(payload_type, 0x7Fu);
	payload_type_ = payload_type;
	WriteAt(1, (data()[1] & 0x80) \| payload_type);
	}

	void RtpPacket::SetSequenceNumber(uint16_t seq_no) {
	sequence_number_ = seq_no;
	ByteWriter<uint16_t>::WriteBigEndian(WriteAt(2), seq_no);
	}

	void RtpPacket::SetTimestamp(uint32_t timestamp) {
	timestamp_ = timestamp;
	ByteWriter<uint32_t>::WriteBigEndian(WriteAt(4), timestamp);
	}

	void RtpPacket::SetSsrc(uint32_t ssrc) {
	ssrc_ = ssrc;
	ByteWriter<uint32_t>::WriteBigEndian(WriteAt(8), ssrc);
	}

	void RtpPacket::SetCsrcs(const std::vector<uint32_t>& csrcs) {
	RTC_DCHECK_EQ(extensions_size_, 0);
	RTC_DCHECK_EQ(payload_size_, 0);
	RTC_DCHECK_EQ(padding_size_, 0);
	RTC_DCHECK_LE(csrcs.size(), 0x0fu);
	RTC_DCHECK_LE(kFixedHeaderSize + 4 * csrcs.size(), capacity());
	payload_offset_ = kFixedHeaderSize + 4 * csrcs.size();
	WriteAt(0, (data()[0] & 0xF0) \| rtc::dchecked_cast<uint8_t>(csrcs.size()));
	size_t offset = kFixedHeaderSize;
	for (uint32_t csrc : csrcs) {
	ByteWriter<uint32_t>::WriteBigEndian(WriteAt(offset), csrc);
	offset += 4;
	}
	buffer_.SetSize(payload_offset_);
	}

	bool RtpPacket::HasRawExtension(int id) const {
	if (id == ExtensionManager::kInvalidId)
	return false;
	RTC_DCHECK_GE(id, kMinExtensionId);
	RTC_DCHECK_LE(id, kMaxExtensionId);
	return extension_entries_[id - 1].offset != 0;
	}

	rtc::ArrayView<const uint8_t> RtpPacket::GetRawExtension(int id) const {
	if (id == ExtensionManager::kInvalidId)
	return nullptr;
	RTC_DCHECK_GE(id, kMinExtensionId);
	RTC_DCHECK_LE(id, kMaxExtensionId);
	const ExtensionInfo& extension = extension_entries_[id - 1];
	if (extension.offset == 0)
	return nullptr;
	return rtc::MakeArrayView(data() + extension.offset, extension.length);
	}

	bool RtpPacket::SetRawExtension(int id, rtc::ArrayView<const uint8_t> data) {
	auto buffer = AllocateRawExtension(id, data.size());
	if (buffer.empty())
	return false;
	RTC_DCHECK_EQ(buffer.size(), data.size());
	memcpy(buffer.data(), data.data(), data.size());
	return true;
	}

	rtc::ArrayView<uint8_t> RtpPacket::AllocateRawExtension(int id, size_t length) {
	if (id == ExtensionManager::kInvalidId)
	return nullptr;
	RTC_DCHECK_GE(id, kMinExtensionId);
	RTC_DCHECK_LE(id, kMaxExtensionId);
	RTC_DCHECK_GE(length, 1);
	RTC_DCHECK_LE(length, 16);

	ExtensionInfo* extension_entry = &extension_entries_[id - 1];
	if (extension_entry->offset != 0) {
	// Extension already reserved. Check if same length is used.
	if (extension_entry->length == length)
	return rtc::MakeArrayView(WriteAt(extension_entry->offset), length);

	LOG(LS_ERROR) << "Length mismatch for extension id " << id << " type "
	<< static_cast<int>(extension_entry->type) << ": expected "
	<< static_cast<int>(extension_entry->length) << ". received "
	<< length;
	return nullptr;
	}
	if (payload_size_ > 0) {
	LOG(LS_ERROR) << "Can't add new extension id " << id
	<< " after payload was set.";
	return nullptr;
	}
	if (padding_size_ > 0) {
	LOG(LS_ERROR) << "Can't add new extension id " << id
	<< " after padding was set.";
	return nullptr;
	}

	size_t num_csrc = data()[0] & 0x0F;
	size_t extensions_offset = kFixedHeaderSize + (num_csrc * 4) + 4;
	size_t new_extensions_size = extensions_size_ + kOneByteHeaderSize + length;
	if (extensions_offset + new_extensions_size > capacity()) {
	LOG(LS_ERROR)
	<< "Extension cannot be registered: Not enough space left in buffer.";
	return nullptr;
	}

	// All checks passed, write down the extension headers.
	if (extensions_size_ == 0) {
	RTC_DCHECK_EQ(payload_offset_, kFixedHeaderSize + (num_csrc * 4));
	WriteAt(0, data()[0] \| 0x10); // Set extension bit.
	// Profile specific ID always set to OneByteExtensionHeader.
	ByteWriter<uint16_t>::WriteBigEndian(WriteAt(extensions_offset - 4),
	kOneByteExtensionId);
	}

	uint8_t one_byte_header = rtc::dchecked_cast<uint8_t>(id) << 4;
	one_byte_header \|= rtc::dchecked_cast<uint8_t>(length - 1);
	WriteAt(extensions_offset + extensions_size_, one_byte_header);

	extension_entry->offset = rtc::dchecked_cast<uint16_t>(
	extensions_offset + extensions_size_ + kOneByteHeaderSize);
	extension_entry->length = rtc::dchecked_cast<uint8_t>(length);
	extensions_size_ = rtc::dchecked_cast<uint16_t>(new_extensions_size);

	// Update header length field.
	uint16_t extensions_words = (extensions_size_ + 3) / 4; // Wrap up to 32bit.
	ByteWriter<uint16_t>::WriteBigEndian(WriteAt(extensions_offset - 2),
	extensions_words);
	// Fill extension padding place with zeroes.
	size_t extension_padding_size = 4 * extensions_words - extensions_size_;
	memset(WriteAt(extensions_offset + extensions_size_), 0,
	extension_padding_size);
	payload_offset_ = extensions_offset + 4 * extensions_words;
	buffer_.SetSize(payload_offset_);
	return rtc::MakeArrayView(WriteAt(extension_entry->offset), length);
	}

	uint8_t* RtpPacket::AllocatePayload(size_t size_bytes) {
	// Reset payload size to 0. If CopyOnWrite buffer_ was shared, this will cause
	// reallocation and memcpy. Keeping just header reduces memcpy size.
	SetPayloadSize(0);
	return SetPayloadSize(size_bytes);
	}

	uint8_t* RtpPacket::SetPayloadSize(size_t size_bytes) {
	RTC_DCHECK_EQ(padding_size_, 0);
	if (payload_offset_ + size_bytes > capacity()) {
	LOG(LS_WARNING) << "Cannot set payload, not enough space in buffer.";
	return nullptr;
	}
	payload_size_ = size_bytes;
	buffer_.SetSize(payload_offset_ + payload_size_);
	return WriteAt(payload_offset_);
	}

	bool RtpPacket::SetPadding(uint8_t size_bytes, Random* random) {
	RTC_DCHECK(random);
	if (payload_offset_ + payload_size_ + size_bytes > capacity()) {
	LOG(LS_WARNING) << "Cannot set padding size " << size_bytes << ", only "
	<< (capacity() - payload_offset_ - payload_size_)
	<< " bytes left in buffer.";
	return false;
	}
	padding_size_ = size_bytes;
	buffer_.SetSize(payload_offset_ + payload_size_ + padding_size_);
	if (padding_size_ > 0) {
	size_t padding_offset = payload_offset_ + payload_size_;
	size_t padding_end = padding_offset + padding_size_;
	for (size_t offset = padding_offset; offset < padding_end - 1; ++offset) {
	WriteAt(offset, random->Rand<uint8_t>());
	}
	WriteAt(padding_end - 1, padding_size_);
	WriteAt(0, data()[0] \| 0x20); // Set padding bit.
	} else {
	WriteAt(0, data()[0] & ~0x20); // Clear padding bit.
	}
	return true;
	}

	void RtpPacket::Clear() {
	marker_ = false;
	payload_type_ = 0;
	sequence_number_ = 0;
	timestamp_ = 0;
	ssrc_ = 0;
	payload_offset_ = kFixedHeaderSize;
	payload_size_ = 0;
	padding_size_ = 0;
	extensions_size_ = 0;
	for (ExtensionInfo& location : extension_entries_) {
	location.offset = 0;
	location.length = 0;
	}

	memset(WriteAt(0), 0, kFixedHeaderSize);
	buffer_.SetSize(kFixedHeaderSize);
	WriteAt(0, kRtpVersion << 6);
	}

	bool RtpPacket::ParseBuffer(const uint8_t* buffer, size_t size) {
	if (size < kFixedHeaderSize) {
	return false;
	}
	const uint8_t version = buffer[0] >> 6;
	if (version != kRtpVersion) {
	return false;
	}
	const bool has_padding = (buffer[0] & 0x20) != 0;
	const bool has_extension = (buffer[0] & 0x10) != 0;
	const uint8_t number_of_crcs = buffer[0] & 0x0f;
	marker_ = (buffer[1] & 0x80) != 0;
	payload_type_ = buffer[1] & 0x7f;

	sequence_number_ = ByteReader<uint16_t>::ReadBigEndian(&buffer[2]);
	timestamp_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[4]);
	ssrc_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[8]);
	if (size < kFixedHeaderSize + number_of_crcs * 4) {
	return false;
	}
	payload_offset_ = kFixedHeaderSize + number_of_crcs * 4;

	if (has_padding) {
	padding_size_ = buffer[size - 1];
	if (padding_size_ == 0) {
	LOG(LS_WARNING) << "Padding was set, but padding size is zero";
	return false;
	}
	} else {
	padding_size_ = 0;
	}

	extensions_size_ = 0;
	for (ExtensionInfo& location : extension_entries_) {
	location.offset = 0;
	location.length = 0;
	}
	if (has_extension) {
	/* RTP header extension, RFC 3550.
	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
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| defined by profile \| length \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| header extension \|
	\| .... \|
	*/
	size_t extension_offset = payload_offset_ + 4;
	if (extension_offset > size) {
	return false;
	}
	uint16_t profile =
	ByteReader<uint16_t>::ReadBigEndian(&buffer[payload_offset_]);
	size_t extensions_capacity =
	ByteReader<uint16_t>::ReadBigEndian(&buffer[payload_offset_ + 2]);
	extensions_capacity *= 4;
	if (extension_offset + extensions_capacity > size) {
	return false;
	}
	if (profile != kOneByteExtensionId) {
	LOG(LS_WARNING) << "Unsupported rtp extension " << profile;
	} else {
	constexpr uint8_t kPaddingId = 0;
	constexpr uint8_t kReservedId = 15;
	while (extensions_size_ + kOneByteHeaderSize < extensions_capacity) {
	int id = buffer[extension_offset + extensions_size_] >> 4;
	if (id == kReservedId) {
	break;
	} else if (id == kPaddingId) {
	extensions_size_++;
	continue;
	}
	uint8_t length =
	1 + (buffer[extension_offset + extensions_size_] & 0xf);
	if (extensions_size_ + kOneByteHeaderSize + length >
	extensions_capacity) {
	LOG(LS_WARNING) << "Oversized rtp header extension.";
	break;
	}

	size_t idx = id - 1;
	if (extension_entries_[idx].length != 0) {
	LOG(LS_VERBOSE) << "Duplicate rtp header extension id " << id
	<< ". Overwriting.";
	}

	extensions_size_ += kOneByteHeaderSize;
	extension_entries_[idx].offset =
	rtc::dchecked_cast<uint16_t>(extension_offset + extensions_size_);
	extension_entries_[idx].length = rtc::dchecked_cast<uint16_t>(length);
	extensions_size_ += length;
	}
	}
	payload_offset_ = extension_offset + extensions_capacity;
	}

	if (payload_offset_ + padding_size_ > size) {
	return false;
	}
	payload_size_ = size - payload_offset_ - padding_size_;
	return true;
	}

	rtc::ArrayView<const uint8_t> RtpPacket::FindExtension(
	ExtensionType type) const {
	for (const ExtensionInfo& extension : extension_entries_) {
	if (extension.type == type) {
	if (extension.length == 0) {
	// Extension is registered but not set.
	return nullptr;
	}
	return rtc::MakeArrayView(data() + extension.offset, extension.length);
	}
	}
	return nullptr;
	}

	rtc::ArrayView<uint8_t> RtpPacket::AllocateExtension(ExtensionType type,
	size_t length) {
	for (int i = 0; i < kMaxExtensionHeaders; ++i) {
	if (extension_entries_[i].type == type) {
	int extension_id = i + 1;
	return AllocateRawExtension(extension_id, length);
	}
	}
	// Extension not registered.
	return nullptr;
	}

	uint8_t* RtpPacket::WriteAt(size_t offset) {
	return buffer_.data() + offset;
	}

	void RtpPacket::WriteAt(size_t offset, uint8_t byte) {
	buffer_.data()[offset] = byte;
	}

	} // namespace webrtc