void QuicServerWorker::handleNetworkData()

in quic/server/QuicServerWorker.cpp [330:455]
114 lines of code
16 McCabe index (conditional complexity)

void QuicServerWorker::handleNetworkData(
    const folly::SocketAddress& client,
    Buf data,
    const TimePoint& packetReceiveTime,
    bool isForwardedData) noexcept {
  try {
    if (shutdown_) {
      VLOG(4) << "Packet received after shutdown, dropping";
      QUIC_STATS(
          statsCallback_, onPacketDropped, PacketDropReason::SERVER_SHUTDOWN);
      return;
    }

    if (isBlockListedSrcPort_(client.getPort())) {
      VLOG(4) << "Dropping packet with blocklisted src port: "
              << client.getPort();
      QUIC_STATS(
          statsCallback_, onPacketDropped, PacketDropReason::INVALID_SRC_PORT);
      return;
    }

    if (!callback_) {
      VLOG(0) << "Worker callback is null.  Dropping packet.";
      QUIC_STATS(
          statsCallback_,
          onPacketDropped,
          PacketDropReason::WORKER_NOT_INITIALIZED);
      return;
    }
    folly::io::Cursor cursor(data.get());
    if (!cursor.canAdvance(sizeof(uint8_t))) {
      VLOG(4) << "Dropping packet too small";
      QUIC_STATS(
          statsCallback_, onPacketDropped, PacketDropReason::INVALID_PACKET);
      return;
    }
    uint8_t initialByte = cursor.readBE<uint8_t>();
    HeaderForm headerForm = getHeaderForm(initialByte);

    if (headerForm == HeaderForm::Short) {
      folly::Expected<ShortHeaderInvariant, TransportErrorCode>
          parsedShortHeader = parseShortHeaderInvariants(initialByte, cursor);
      if (!parsedShortHeader) {
        if (!tryHandlingAsHealthCheck(client, *data)) {
          QUIC_STATS(
              statsCallback_, onPacketDropped, PacketDropReason::PARSE_ERROR);
          VLOG(6) << "Failed to parse short header";
        }
        return;
      }
      RoutingData routingData(
          headerForm,
          false, /* isInitial */
          false, /* is0Rtt */
          false, /* isUsingClientConnId */
          std::move(parsedShortHeader->destinationConnId),
          folly::none);
      return forwardNetworkData(
          client,
          std::move(routingData),
          NetworkData(std::move(data), packetReceiveTime),
          folly::none, /* quicVersion */
          isForwardedData);
    }

    folly::Expected<ParsedLongHeaderInvariant, TransportErrorCode>
        parsedLongHeader = parseLongHeaderInvariant(initialByte, cursor);
    if (!parsedLongHeader) {
      if (!tryHandlingAsHealthCheck(client, *data)) {
        QUIC_STATS(
            statsCallback_, onPacketDropped, PacketDropReason::PARSE_ERROR);
        VLOG(6) << "Failed to parse long header";
      }
      return;
    }

    // TODO: check version before looking at type
    LongHeader::Types longHeaderType = parseLongHeaderType(initialByte);
    bool isInitial = longHeaderType == LongHeader::Types::Initial;
    bool is0Rtt = longHeaderType == LongHeader::Types::ZeroRtt;
    bool isUsingClientConnId = isInitial || is0Rtt;

    if (isInitial) {
      // This stats gets updated even if the client initial will be dropped.
      QUIC_STATS(
          statsCallback_,
          onClientInitialReceived,
          parsedLongHeader->invariant.version);
    }

    if (maybeSendVersionNegotiationPacketOrDrop(
            client,
            isInitial,
            parsedLongHeader->invariant,
            data->computeChainDataLength())) {
      return;
    }

    if (!isUsingClientConnId &&
        parsedLongHeader->invariant.dstConnId.size() <
            kMinSelfConnectionIdV1Size) {
      // drop packet if connId is present but is not valid.
      VLOG(3) << "Dropping packet due to invalid connectionId";
      QUIC_STATS(
          statsCallback_, onPacketDropped, PacketDropReason::INVALID_PACKET);
      return;
    }
    RoutingData routingData(
        headerForm,
        isInitial,
        is0Rtt,
        isUsingClientConnId,
        std::move(parsedLongHeader->invariant.dstConnId),
        std::move(parsedLongHeader->invariant.srcConnId));
    return forwardNetworkData(
        client,
        std::move(routingData),
        NetworkData(std::move(data), packetReceiveTime),
        parsedLongHeader->invariant.version,
        isForwardedData);
  } catch (const std::exception& ex) {
    // Drop the packet.
    QUIC_STATS(statsCallback_, onPacketDropped, PacketDropReason::PARSE_ERROR);
    VLOG(6) << "Failed to parse packet header " << ex.what();
  }
}