DataPathResult continuousMemoryBuildScheduleEncrypt()

in quic/api/QuicTransportFunctions.cpp [188:289]

• 90 lines of code
• 13 McCabe index (conditional complexity)

DataPathResult continuousMemoryBuildScheduleEncrypt(
    QuicConnectionStateBase& connection,
    PacketHeader header,
    PacketNumberSpace pnSpace,
    PacketNum packetNum,
    uint64_t cipherOverhead,
    QuicPacketScheduler& scheduler,
    uint64_t writableBytes,
    IOBufQuicBatch& ioBufBatch,
    const Aead& aead,
    const PacketNumberCipher& headerCipher) {
  auto buf = connection.bufAccessor->obtain();
  auto prevSize = buf->length();
  connection.bufAccessor->release(std::move(buf));

  auto rollbackBuf = [&]() {
    auto buf = connection.bufAccessor->obtain();
    buf->trimEnd(buf->length() - prevSize);
    connection.bufAccessor->release(std::move(buf));
  };

  // It's the scheduler's job to invoke encode header
  InplaceQuicPacketBuilder pktBuilder(
      *connection.bufAccessor,
      connection.udpSendPacketLen,
      std::move(header),
      getAckState(connection, pnSpace).largestAckedByPeer.value_or(0));
  pktBuilder.accountForCipherOverhead(cipherOverhead);
  CHECK(scheduler.hasData());
  auto result =
      scheduler.scheduleFramesForPacket(std::move(pktBuilder), writableBytes);
  CHECK(connection.bufAccessor->ownsBuffer());
  auto& packet = result.packet;
  if (!packet || packet->packet.frames.empty()) {
    rollbackBuf();
    ioBufBatch.flush();
    if (connection.loopDetectorCallback) {
      connection.writeDebugState.noWriteReason = NoWriteReason::NO_FRAME;
    }
    return DataPathResult::makeBuildFailure();
  }
  if (!packet->body) {
    // No more space remaining.
    rollbackBuf();
    ioBufBatch.flush();
    if (connection.loopDetectorCallback) {
      connection.writeDebugState.noWriteReason = NoWriteReason::NO_BODY;
    }
    return DataPathResult::makeBuildFailure();
  }
  CHECK(!packet->header->isChained());
  auto headerLen = packet->header->length();
  buf = connection.bufAccessor->obtain();
  CHECK(
      packet->body->data() > buf->data() &&
      packet->body->tail() <= buf->tail());
  CHECK(
      packet->header->data() >= buf->data() &&
      packet->header->tail() < buf->tail());
  // Trim off everything before the current packet, and the header length, so
  // buf's data starts from the body part of buf.
  buf->trimStart(prevSize + headerLen);
  // buf and packetBuf is actually the same.
  auto packetBuf =
      aead.inplaceEncrypt(std::move(buf), packet->header.get(), packetNum);
  CHECK(packetBuf->headroom() == headerLen + prevSize);
  // Include header back.
  packetBuf->prepend(headerLen);

  HeaderForm headerForm = packet->packet.header.getHeaderForm();
  encryptPacketHeader(
      headerForm,
      packetBuf->writableData(),
      headerLen,
      packetBuf->data() + headerLen,
      packetBuf->length() - headerLen,
      headerCipher);
  CHECK(!packetBuf->isChained());
  auto encodedSize = packetBuf->length();
  auto encodedBodySize = encodedSize - headerLen;
  // Include previous packets back.
  packetBuf->prepend(prevSize);
  connection.bufAccessor->release(std::move(packetBuf));
#if !FOLLY_MOBILE
  bool isD6DProbe = pnSpace == PacketNumberSpace::AppData &&
      connection.d6d.lastProbe.hasValue() &&
      connection.d6d.lastProbe->packetNum == packetNum;
  if (!isD6DProbe && encodedSize > connection.udpSendPacketLen) {
    LOG_EVERY_N(ERROR, 5000)
        << "Quic sending pkt larger than limit, encodedSize=" << encodedSize;
  }
#endif
  // TODO: I think we should add an API that doesn't need a buffer.
  bool ret = ioBufBatch.write(nullptr /* no need to pass buf */, encodedSize);
  // update stats and connection
  if (ret) {
    QUIC_STATS(connection.statsCallback, onWrite, encodedSize);
    QUIC_STATS(connection.statsCallback, onPacketSent);
  }
  return DataPathResult::makeWriteResult(
      ret, std::move(result), encodedSize, encodedBodySize);
}