net/dcsctp/packet/chunk/iforward_tsn_chunk.cc

/*
 *  Copyright (c) 2021 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 "net/dcsctp/packet/chunk/iforward_tsn_chunk.h"

#include <stddef.h>
#include <stdint.h>

#include <optional>
#include <string>
#include <utility>
#include <vector>

#include "api/array_view.h"
#include "net/dcsctp/packet/bounded_byte_reader.h"
#include "net/dcsctp/packet/bounded_byte_writer.h"
#include "net/dcsctp/packet/chunk/forward_tsn_common.h"
#include "net/dcsctp/packet/tlv_trait.h"
#include "rtc_base/strings/string_builder.h"

namespace dcsctp {

// https://tools.ietf.org/html/rfc8260#section-2.3.1

//   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
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |   Type = 194  | Flags = 0x00  |      Length = Variable        |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |                       New Cumulative TSN                      |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |       Stream Identifier       |          Reserved           |U|
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |                       Message Identifier                      |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  \                                                               \
//  /                                                               /
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |       Stream Identifier       |          Reserved           |U|
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//  |                       Message Identifier                      |
//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
constexpr int IForwardTsnChunk::kType;

std::optional<IForwardTsnChunk> IForwardTsnChunk::Parse(
    rtc::ArrayView<const uint8_t> data) {
  std::optional<BoundedByteReader<kHeaderSize>> reader = ParseTLV(data);
  if (!reader.has_value()) {
    return std::nullopt;
  }

  TSN new_cumulative_tsn(reader->Load32<4>());

  size_t streams_skipped =
      reader->variable_data_size() / kSkippedStreamBufferSize;
  std::vector<SkippedStream> skipped_streams;
  skipped_streams.reserve(streams_skipped);
  size_t offset = 0;
  for (size_t i = 0; i < streams_skipped; ++i) {
    BoundedByteReader<kSkippedStreamBufferSize> sub_reader =
        reader->sub_reader<kSkippedStreamBufferSize>(offset);

    StreamID stream_id(sub_reader.Load16<0>());
    IsUnordered unordered(sub_reader.Load8<3>() & 0x01);
    MID mid(sub_reader.Load32<4>());
    skipped_streams.emplace_back(unordered, stream_id, mid);
    offset += kSkippedStreamBufferSize;
  }
  RTC_DCHECK(offset == reader->variable_data_size());
  return IForwardTsnChunk(new_cumulative_tsn, std::move(skipped_streams));
}

void IForwardTsnChunk::SerializeTo(std::vector<uint8_t>& out) const {
  rtc::ArrayView<const SkippedStream> skipped = skipped_streams();
  size_t variable_size = skipped.size() * kSkippedStreamBufferSize;
  BoundedByteWriter<kHeaderSize> writer = AllocateTLV(out, variable_size);

  writer.Store32<4>(*new_cumulative_tsn());
  size_t offset = 0;
  for (size_t i = 0; i < skipped.size(); ++i) {
    BoundedByteWriter<kSkippedStreamBufferSize> sub_writer =
        writer.sub_writer<kSkippedStreamBufferSize>(offset);

    sub_writer.Store16<0>(*skipped[i].stream_id);
    sub_writer.Store8<3>(skipped[i].unordered ? 1 : 0);
    sub_writer.Store32<4>(*skipped[i].mid);
    offset += kSkippedStreamBufferSize;
  }
  RTC_DCHECK(offset == variable_size);
}

std::string IForwardTsnChunk::ToString() const {
  rtc::StringBuilder sb;
  sb << "I-FORWARD-TSN, new_cumulative_tsn=" << *new_cumulative_tsn();
  return sb.Release();
}

}  // namespace dcsctp