void QuicTransportBase::writeSocketData()

in quic/api/QuicTransportBase.cpp [2987:3095]
88 lines of code
22 McCabe index (conditional complexity)

void QuicTransportBase::writeSocketData() {
  if (socket_) {
    ++(conn_->writeCount); // incremented on each write (or write attempt)

    // record current number of sent packets to detect delta
    const auto beforeTotalBytesSent = conn_->lossState.totalBytesSent;
    const auto beforeTotalPacketsSent = conn_->lossState.totalPacketsSent;
    const auto beforeTotalAckElicitingPacketsSent =
        conn_->lossState.totalAckElicitingPacketsSent;
    const auto beforeNumOutstandingPackets =
        conn_->outstandings.numOutstanding();

    // if we're starting to write from app limited, notify observers
    if (conn_->waitingForAppData && conn_->congestionController) {
      notifyStartWritingFromAppRateLimited();
      conn_->waitingForAppData = false;
    }
    writeData();
    if (closeState_ != CloseState::CLOSED) {
      if (conn_->pendingEvents.closeTransport == true) {
        throw QuicTransportException(
            "Max packet number reached",
            TransportErrorCode::PROTOCOL_VIOLATION);
      }
      setLossDetectionAlarm(*conn_, *this);

      // check for change in number of packets
      const auto afterTotalBytesSent = conn_->lossState.totalBytesSent;
      const auto afterTotalPacketsSent = conn_->lossState.totalPacketsSent;
      const auto afterTotalAckElicitingPacketsSent =
          conn_->lossState.totalAckElicitingPacketsSent;
      const auto afterNumOutstandingPackets =
          conn_->outstandings.numOutstanding();
      CHECK_LE(beforeTotalPacketsSent, afterTotalPacketsSent);
      CHECK_LE(
          beforeTotalAckElicitingPacketsSent,
          afterTotalAckElicitingPacketsSent);
      CHECK_LE(beforeNumOutstandingPackets, afterNumOutstandingPackets);
      CHECK_EQ(
          afterNumOutstandingPackets - beforeNumOutstandingPackets,
          afterTotalAckElicitingPacketsSent -
              beforeTotalAckElicitingPacketsSent);
      const bool newPackets = (afterTotalPacketsSent > beforeTotalPacketsSent);
      const bool newOutstandingPackets =
          (afterTotalAckElicitingPacketsSent >
           beforeTotalAckElicitingPacketsSent);

      // if packets sent, notify observers
      if (newPackets) {
        notifyPacketsWritten(
            afterTotalPacketsSent - beforeTotalPacketsSent
            /* numPacketsWritten */,
            afterTotalAckElicitingPacketsSent -
                beforeTotalAckElicitingPacketsSent
            /* numAckElicitingPacketsWritten */,
            afterTotalBytesSent - beforeTotalBytesSent /* numBytesWritten */);
      }
      if (conn_->loopDetectorCallback && newOutstandingPackets) {
        conn_->writeDebugState.currentEmptyLoopCount = 0;
      } else if (
          conn_->writeDebugState.needsWriteLoopDetect &&
          conn_->loopDetectorCallback) {
        // TODO: Currently we will to get some stats first. Then we may filter
        // out some errors here. For example, socket fail to write might be a
        // legit case to filter out.
        conn_->loopDetectorCallback->onSuspiciousWriteLoops(
            ++conn_->writeDebugState.currentEmptyLoopCount,
            conn_->writeDebugState.writeDataReason,
            conn_->writeDebugState.noWriteReason,
            conn_->writeDebugState.schedulerName);
      }
      // If we sent a new packet and the new packet was either the first
      // packet after quiescence or after receiving a new packet.
      if (newOutstandingPackets &&
          (beforeNumOutstandingPackets == 0 ||
           conn_->receivedNewPacketBeforeWrite)) {
        // Reset the idle timer because we sent some data.
        setIdleTimer();
        conn_->receivedNewPacketBeforeWrite = false;
      }
      // Check if we are app-limited after finish this round of sending
      auto currentSendBufLen = conn_->flowControlState.sumCurStreamBufferLen;
      auto lossBufferEmpty = !conn_->streamManager->hasLoss() &&
          conn_->cryptoState->initialStream.lossBuffer.empty() &&
          conn_->cryptoState->handshakeStream.lossBuffer.empty() &&
          conn_->cryptoState->oneRttStream.lossBuffer.empty();
      if (conn_->congestionController &&
          currentSendBufLen < conn_->udpSendPacketLen && lossBufferEmpty &&
          conn_->congestionController->getWritableBytes()) {
        conn_->congestionController->setAppLimited();
        // notify via connection call and any observer callbacks
        if (transportReadyNotified_) {
          connCallback_->onAppRateLimited();
        }
        notifyAppRateLimited();
        conn_->waitingForAppData = true;
      }
    }
  }
  // Writing data could write out an ack which could cause us to cancel
  // the ack timer. But we need to call scheduleAckTimeout() for it to take
  // effect.
  scheduleAckTimeout();
  schedulePathValidationTimeout();
  // Writing data could write out a d6d probe, for which we need to schedule a
  // probe timeout
  scheduleD6DProbeTimeout();
  updateWriteLooper(false);
}