net/quic/core/quic_unacked_packet_map.cc

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/quic/core/quic_unacked_packet_map.h"

#include "base/logging.h"
#include "base/stl_util.h"
#include "net/quic/chromium/quic_utils_chromium.h"
#include "net/quic/core/quic_bug_tracker.h"
#include "net/quic/core/quic_connection_stats.h"
#include "net/quic/core/quic_flags.h"
#include "net/quic/core/quic_utils.h"

using std::max;

namespace net {

QuicUnackedPacketMap::QuicUnackedPacketMap()
    : largest_sent_packet_(0),
      largest_observed_(0),
      least_unacked_(1),
      bytes_in_flight_(0),
      pending_crypto_packet_count_(0) {}

QuicUnackedPacketMap::~QuicUnackedPacketMap() {
  QuicPacketNumber index = least_unacked_;
  for (UnackedPacketMap::iterator it = unacked_packets_.begin();
       it != unacked_packets_.end(); ++it, ++index) {
    QuicUtils::DeleteFrames(&it->retransmittable_frames);
  }
}

void QuicUnackedPacketMap::AddSentPacket(SerializedPacket* packet,
                                         QuicPacketNumber old_packet_number,
                                         TransmissionType transmission_type,
                                         QuicTime sent_time,
                                         bool set_in_flight) {
  QuicPacketNumber packet_number = packet->packet_number;
  QuicPacketLength bytes_sent = packet->encrypted_length;
  QUIC_BUG_IF(largest_sent_packet_ >= packet_number) << packet_number;
  DCHECK_GE(packet_number, least_unacked_ + unacked_packets_.size());
  while (least_unacked_ + unacked_packets_.size() < packet_number) {
    unacked_packets_.push_back(TransmissionInfo());
    unacked_packets_.back().is_unackable = true;
  }

  const bool has_crypto_handshake =
      packet->has_crypto_handshake == IS_HANDSHAKE;
  TransmissionInfo info(packet->encryption_level, packet->packet_number_length,
                        transmission_type, sent_time, bytes_sent,
                        has_crypto_handshake, packet->num_padding_bytes);
  if (old_packet_number > 0) {
    TransferRetransmissionInfo(old_packet_number, packet_number,
                               transmission_type, &info);
  }

  largest_sent_packet_ = packet_number;
  if (set_in_flight) {
    bytes_in_flight_ += bytes_sent;
    info.in_flight = true;
  }
  unacked_packets_.push_back(info);
  // Swap the ack listeners and retransmittable frames to avoid allocations.
  // TODO(ianswett): Could use emplace_back when Chromium can.
  if (old_packet_number == 0) {
    if (has_crypto_handshake) {
      ++pending_crypto_packet_count_;
    }

    packet->retransmittable_frames.swap(
        unacked_packets_.back().retransmittable_frames);
    unacked_packets_.back().ack_listeners.swap(packet->listeners);
  }
}

void QuicUnackedPacketMap::RemoveObsoletePackets() {
  while (!unacked_packets_.empty()) {
    if (!IsPacketUseless(least_unacked_, unacked_packets_.front())) {
      break;
    }

    unacked_packets_.pop_front();
    ++least_unacked_;
  }
}

void QuicUnackedPacketMap::TransferRetransmissionInfo(
    QuicPacketNumber old_packet_number,
    QuicPacketNumber new_packet_number,
    TransmissionType transmission_type,
    TransmissionInfo* info) {
  if (old_packet_number < least_unacked_) {
    // This can happen when a retransmission packet is queued because of write
    // blocked socket, and the original packet gets acked before the
    // retransmission gets sent.
    return;
  }
  if (old_packet_number > largest_sent_packet_) {
    QUIC_BUG << "Old TransmissionInfo never existed for :" << old_packet_number
             << " largest_sent:" << largest_sent_packet_;
    return;
  }
  DCHECK_GE(new_packet_number, least_unacked_ + unacked_packets_.size());
  DCHECK_NE(NOT_RETRANSMISSION, transmission_type);

  TransmissionInfo* transmission_info =
      &unacked_packets_.at(old_packet_number - least_unacked_);
  QuicFrames* frames = &transmission_info->retransmittable_frames;
  for (AckListenerWrapper& wrapper : transmission_info->ack_listeners) {
    wrapper.ack_listener->OnPacketRetransmitted(wrapper.length);
  }

  // Swap the frames and preserve num_padding_bytes and has_crypto_handshake.
  frames->swap(info->retransmittable_frames);
  info->has_crypto_handshake = transmission_info->has_crypto_handshake;
  transmission_info->has_crypto_handshake = false;
  info->num_padding_bytes = transmission_info->num_padding_bytes;

  // Transfer the AckListeners if any are present.
  info->ack_listeners.swap(transmission_info->ack_listeners);
  QUIC_BUG_IF(frames == nullptr)
      << "Attempt to retransmit packet with no "
      << "retransmittable frames: " << old_packet_number;

  // Don't link old transmissions to new ones when version or
  // encryption changes.
  if (transmission_type == ALL_INITIAL_RETRANSMISSION ||
      transmission_type == ALL_UNACKED_RETRANSMISSION) {
    transmission_info->is_unackable = true;
  } else {
    transmission_info->retransmission = new_packet_number;
  }
  // Proactively remove obsolete packets so the least unacked can be raised.
  RemoveObsoletePackets();
}

bool QuicUnackedPacketMap::HasRetransmittableFrames(
    QuicPacketNumber packet_number) const {
  DCHECK_GE(packet_number, least_unacked_);
  DCHECK_LT(packet_number, least_unacked_ + unacked_packets_.size());
  return !unacked_packets_[packet_number - least_unacked_]
              .retransmittable_frames.empty();
}

void QuicUnackedPacketMap::RemoveRetransmittability(TransmissionInfo* info) {
  while (info->retransmission != 0) {
    const QuicPacketNumber retransmission = info->retransmission;
    info->retransmission = 0;
    info = &unacked_packets_[retransmission - least_unacked_];
  }
  MaybeRemoveRetransmittableFrames(info);
}

void QuicUnackedPacketMap::RemoveRetransmittability(
    QuicPacketNumber packet_number) {
  DCHECK_GE(packet_number, least_unacked_);
  DCHECK_LT(packet_number, least_unacked_ + unacked_packets_.size());
  TransmissionInfo* info = &unacked_packets_[packet_number - least_unacked_];
  RemoveRetransmittability(info);
}

void QuicUnackedPacketMap::MaybeRemoveRetransmittableFrames(
    TransmissionInfo* transmission_info) {
  if (transmission_info->has_crypto_handshake) {
    DCHECK(!transmission_info->retransmittable_frames.empty());
    DCHECK_LT(0u, pending_crypto_packet_count_);
    --pending_crypto_packet_count_;
    transmission_info->has_crypto_handshake = false;
  }
  QuicUtils::DeleteFrames(&transmission_info->retransmittable_frames);
}

void QuicUnackedPacketMap::IncreaseLargestObserved(
    QuicPacketNumber largest_observed) {
  DCHECK_LE(largest_observed_, largest_observed);
  largest_observed_ = largest_observed;
}

bool QuicUnackedPacketMap::IsPacketUsefulForMeasuringRtt(
    QuicPacketNumber packet_number,
    const TransmissionInfo& info) const {
  // Packet can be used for RTT measurement if it may yet be acked as the
  // largest observed packet by the receiver.
  return !info.is_unackable && packet_number > largest_observed_;
}

bool QuicUnackedPacketMap::IsPacketUsefulForCongestionControl(
    const TransmissionInfo& info) const {
  // Packet contributes to congestion control if it is considered inflight.
  return info.in_flight;
}

bool QuicUnackedPacketMap::IsPacketUsefulForRetransmittableData(
    const TransmissionInfo& info) const {
  // Packet may have retransmittable frames, or the data may have been
  // retransmitted with a new packet number.
  return !info.retransmittable_frames.empty() ||
         // Allow for an extra 1 RTT before stopping to track old packets.
         info.retransmission > largest_observed_;
}

bool QuicUnackedPacketMap::IsPacketUseless(QuicPacketNumber packet_number,
                                           const TransmissionInfo& info) const {
  return !IsPacketUsefulForMeasuringRtt(packet_number, info) &&
         !IsPacketUsefulForCongestionControl(info) &&
         !IsPacketUsefulForRetransmittableData(info);
}

bool QuicUnackedPacketMap::IsUnacked(QuicPacketNumber packet_number) const {
  if (packet_number < least_unacked_ ||
      packet_number >= least_unacked_ + unacked_packets_.size()) {
    return false;
  }
  return !IsPacketUseless(packet_number,
                          unacked_packets_[packet_number - least_unacked_]);
}

void QuicUnackedPacketMap::NotifyAndClearListeners(
    std::list<AckListenerWrapper>* ack_listeners,
    QuicTime::Delta ack_delay_time) {
  for (const AckListenerWrapper& wrapper : *ack_listeners) {
    wrapper.ack_listener->OnPacketAcked(wrapper.length, ack_delay_time);
  }
  ack_listeners->clear();
}

void QuicUnackedPacketMap::NotifyAndClearListeners(
    QuicPacketNumber packet_number,
    QuicTime::Delta ack_delay_time) {
  DCHECK_GE(packet_number, least_unacked_);
  DCHECK_LT(packet_number, least_unacked_ + unacked_packets_.size());
  TransmissionInfo* info = &unacked_packets_[packet_number - least_unacked_];
  NotifyAndClearListeners(&info->ack_listeners, ack_delay_time);
}

void QuicUnackedPacketMap::RemoveFromInFlight(TransmissionInfo* info) {
  if (info->in_flight) {
    QUIC_BUG_IF(bytes_in_flight_ < info->bytes_sent);
    bytes_in_flight_ -= info->bytes_sent;
    info->in_flight = false;
  }
}

void QuicUnackedPacketMap::RemoveFromInFlight(QuicPacketNumber packet_number) {
  DCHECK_GE(packet_number, least_unacked_);
  DCHECK_LT(packet_number, least_unacked_ + unacked_packets_.size());
  TransmissionInfo* info = &unacked_packets_[packet_number - least_unacked_];
  RemoveFromInFlight(info);
}

void QuicUnackedPacketMap::RestoreToInFlight(QuicPacketNumber packet_number) {
  DCHECK_GE(packet_number, least_unacked_);
  DCHECK_LT(packet_number, least_unacked_ + unacked_packets_.size());
  TransmissionInfo* info = &unacked_packets_[packet_number - least_unacked_];
  DCHECK(!info->is_unackable);
  bytes_in_flight_ += info->bytes_sent;
  info->in_flight = true;
}

void QuicUnackedPacketMap::CancelRetransmissionsForStream(
    QuicStreamId stream_id) {
  QuicPacketNumber packet_number = least_unacked_;
  for (UnackedPacketMap::iterator it = unacked_packets_.begin();
       it != unacked_packets_.end(); ++it, ++packet_number) {
    QuicFrames* frames = &it->retransmittable_frames;
    if (frames->empty()) {
      continue;
    }
    QuicUtils::RemoveFramesForStream(frames, stream_id);
    if (frames->empty()) {
      RemoveRetransmittability(packet_number);
    }
  }
}

bool QuicUnackedPacketMap::HasUnackedPackets() const {
  return !unacked_packets_.empty();
}

bool QuicUnackedPacketMap::HasInFlightPackets() const {
  return bytes_in_flight_ > 0;
}

const TransmissionInfo& QuicUnackedPacketMap::GetTransmissionInfo(
    QuicPacketNumber packet_number) const {
  return unacked_packets_[packet_number - least_unacked_];
}

TransmissionInfo* QuicUnackedPacketMap::GetMutableTransmissionInfo(
    QuicPacketNumber packet_number) {
  return &unacked_packets_[packet_number - least_unacked_];
}

QuicTime QuicUnackedPacketMap::GetLastPacketSentTime() const {
  UnackedPacketMap::const_reverse_iterator it = unacked_packets_.rbegin();
  while (it != unacked_packets_.rend()) {
    if (it->in_flight) {
      QUIC_BUG_IF(it->sent_time == QuicTime::Zero())
          << "Sent time can never be zero for a packet in flight.";
      return it->sent_time;
    }
    ++it;
  }
  QUIC_BUG << "GetLastPacketSentTime requires in flight packets.";
  return QuicTime::Zero();
}

size_t QuicUnackedPacketMap::GetNumUnackedPacketsDebugOnly() const {
  size_t unacked_packet_count = 0;
  QuicPacketNumber packet_number = least_unacked_;
  for (UnackedPacketMap::const_iterator it = unacked_packets_.begin();
       it != unacked_packets_.end(); ++it, ++packet_number) {
    if (!IsPacketUseless(packet_number, *it)) {
      ++unacked_packet_count;
    }
  }
  return unacked_packet_count;
}

bool QuicUnackedPacketMap::HasMultipleInFlightPackets() const {
  if (bytes_in_flight_ > kDefaultTCPMSS) {
    return true;
  }
  size_t num_in_flight = 0;
  for (UnackedPacketMap::const_reverse_iterator it = unacked_packets_.rbegin();
       it != unacked_packets_.rend(); ++it) {
    if (it->in_flight) {
      ++num_in_flight;
    }
    if (num_in_flight > 1) {
      return true;
    }
  }
  return false;
}

bool QuicUnackedPacketMap::HasPendingCryptoPackets() const {
  return pending_crypto_packet_count_ > 0;
}

bool QuicUnackedPacketMap::HasUnackedRetransmittableFrames() const {
  for (UnackedPacketMap::const_reverse_iterator it = unacked_packets_.rbegin();
       it != unacked_packets_.rend(); ++it) {
    if (it->in_flight && !it->retransmittable_frames.empty()) {
      return true;
    }
  }
  return false;
}

QuicPacketNumber QuicUnackedPacketMap::GetLeastUnacked() const {
  return least_unacked_;
}

}  // namespace net