void QuicServerTransport::writeData()

in quic/server/QuicServerTransport.cpp [181:349]
157 lines of code
34 McCabe index (conditional complexity)

void QuicServerTransport::writeData() {
  if (!conn_->clientConnectionId || !conn_->serverConnectionId) {
    return;
  }
  auto version = conn_->version.value_or(*(conn_->originalVersion));
  const ConnectionId& srcConnId = *conn_->serverConnectionId;
  const ConnectionId& destConnId = *conn_->clientConnectionId;
  if (closeState_ == CloseState::CLOSED) {
    if (conn_->peerConnectionError &&
        hasReceivedPacketsAtLastCloseSent(*conn_)) {
      // The peer sent us an error, we are in draining state now.
      return;
    }
    if (hasReceivedPacketsAtLastCloseSent(*conn_) &&
        hasNotReceivedNewPacketsSinceLastCloseSent(*conn_)) {
      // We did not receive any new packets, do not sent a new close frame.
      return;
    }
    updateLargestReceivedPacketsAtLastCloseSent(*conn_);
    if (conn_->oneRttWriteCipher) {
      CHECK(conn_->oneRttWriteHeaderCipher);
      writeShortClose(
          *socket_,
          *conn_,
          destConnId,
          conn_->localConnectionError,
          *conn_->oneRttWriteCipher,
          *conn_->oneRttWriteHeaderCipher);
    }
    if (conn_->handshakeWriteCipher) {
      CHECK(conn_->handshakeWriteHeaderCipher);
      writeLongClose(
          *socket_,
          *conn_,
          srcConnId,
          destConnId,
          LongHeader::Types::Handshake,
          conn_->localConnectionError,
          *conn_->handshakeWriteCipher,
          *conn_->handshakeWriteHeaderCipher,
          version);
    }
    if (conn_->initialWriteCipher) {
      CHECK(conn_->initialHeaderCipher);
      writeLongClose(
          *socket_,
          *conn_,
          srcConnId,
          destConnId,
          LongHeader::Types::Initial,
          conn_->localConnectionError,
          *conn_->initialWriteCipher,
          *conn_->initialHeaderCipher,
          version);
    }
    return;
  }
  uint64_t packetLimit =
      (isConnectionPaced(*conn_)
           ? conn_->pacer->updateAndGetWriteBatchSize(Clock::now())
           : conn_->transportSettings.writeConnectionDataPacketsLimit);
  // At the end of this function, clear out any probe packets credit we didn't
  // use.
  SCOPE_EXIT {
    conn_->pendingEvents.numProbePackets = {};
  };
  if (conn_->initialWriteCipher) {
    auto& initialCryptoStream =
        *getCryptoStream(*conn_->cryptoState, EncryptionLevel::Initial);
    CryptoStreamScheduler initialScheduler(*conn_, initialCryptoStream);
    auto& numProbePackets =
        conn_->pendingEvents.numProbePackets[PacketNumberSpace::Initial];
    if ((numProbePackets && initialCryptoStream.retransmissionBuffer.size() &&
         conn_->outstandings.packetCount[PacketNumberSpace::Initial]) ||
        initialScheduler.hasData() ||
        (conn_->ackStates.initialAckState.needsToSendAckImmediately &&
         hasAcksToSchedule(conn_->ackStates.initialAckState))) {
      CHECK(conn_->initialWriteCipher);
      CHECK(conn_->initialHeaderCipher);

      auto res = writeCryptoAndAckDataToSocket(
          *socket_,
          *conn_,
          srcConnId /* src */,
          destConnId /* dst */,
          LongHeader::Types::Initial,
          *conn_->initialWriteCipher,
          *conn_->initialHeaderCipher,
          version,
          packetLimit);

      packetLimit -= res.packetsWritten;
      serverConn_->numHandshakeBytesSent += res.bytesWritten;
    }
    if (!packetLimit && !conn_->pendingEvents.anyProbePackets()) {
      return;
    }
  }
  if (conn_->handshakeWriteCipher) {
    auto& handshakeCryptoStream =
        *getCryptoStream(*conn_->cryptoState, EncryptionLevel::Handshake);
    CryptoStreamScheduler handshakeScheduler(*conn_, handshakeCryptoStream);
    auto& numProbePackets =
        conn_->pendingEvents.numProbePackets[PacketNumberSpace::Handshake];
    if ((conn_->outstandings.packetCount[PacketNumberSpace::Handshake] &&
         handshakeCryptoStream.retransmissionBuffer.size() &&
         numProbePackets) ||
        handshakeScheduler.hasData() ||
        (conn_->ackStates.handshakeAckState.needsToSendAckImmediately &&
         hasAcksToSchedule(conn_->ackStates.handshakeAckState))) {
      CHECK(conn_->handshakeWriteCipher);
      CHECK(conn_->handshakeWriteHeaderCipher);
      auto res = writeCryptoAndAckDataToSocket(
          *socket_,
          *conn_,
          srcConnId /* src */,
          destConnId /* dst */,
          LongHeader::Types::Handshake,
          *conn_->handshakeWriteCipher,
          *conn_->handshakeWriteHeaderCipher,
          version,
          packetLimit);

      packetLimit -= res.packetsWritten;
      serverConn_->numHandshakeBytesSent += res.bytesWritten;
    }
    if (!packetLimit && !conn_->pendingEvents.anyProbePackets()) {
      return;
    }
  }
  if (conn_->oneRttWriteCipher) {
    CHECK(conn_->oneRttWriteHeaderCipher);
    // TODO(yangchi): I don't know which one to prioritize. I can see arguments
    // both ways. I'm going with writing regular packets first since they
    // contain ack and flow control update and other important info.
    auto writeLoopBeginTime = Clock::now();
    packetLimit -= writeQuicDataToSocket(
                       *socket_,
                       *conn_,
                       srcConnId /* src */,
                       destConnId /* dst */,
                       *conn_->oneRttWriteCipher,
                       *conn_->oneRttWriteHeaderCipher,
                       version,
                       packetLimit,
                       writeLoopBeginTime)
                       .packetsWritten;
    if (packetLimit) {
      packetLimit -= writePacketizationRequest(
          *serverConn_,
          destConnId,
          packetLimit,
          *conn_->oneRttWriteCipher,
          writeLoopBeginTime);
    }

    // D6D probes should be paced
    if (packetLimit && conn_->pendingEvents.d6d.sendProbePacket) {
      writeD6DProbeToSocket(
          *socket_,
          *conn_,
          srcConnId,
          destConnId,
          *conn_->oneRttWriteCipher,
          *conn_->oneRttWriteHeaderCipher,
          version);
    }
  }
}