net/quic/quic_received_packet_manager.cc

// Copyright 2013 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/quic_received_packet_manager.h"

#include "base/logging.h"
#include "net/base/linked_hash_map.h"

using std::make_pair;
using std::max;
using std::min;

namespace net {

QuicReceivedPacketManager::QuicReceivedPacketManager()
    : packets_entropy_hash_(0),
      largest_sequence_number_(0),
      peer_largest_observed_packet_(0),
      least_packet_awaited_by_peer_(1),
      peer_least_packet_awaiting_ack_(0),
      time_largest_observed_(QuicTime::Zero()) {
  received_info_.largest_observed = 0;
  received_info_.entropy_hash = 0;
}

QuicReceivedPacketManager::~QuicReceivedPacketManager() {}

void QuicReceivedPacketManager::RecordPacketReceived(
    const QuicPacketHeader& header, QuicTime receipt_time) {
  QuicPacketSequenceNumber sequence_number = header.packet_sequence_number;
  DCHECK(IsAwaitingPacket(sequence_number));

  InsertMissingPacketsBetween(
      &received_info_,
      max(received_info_.largest_observed + 1, peer_least_packet_awaiting_ack_),
      header.packet_sequence_number);

  if (received_info_.largest_observed > header.packet_sequence_number) {
    // We've gotten one of the out of order packets - remove it from our
    // "missing packets" list.
    DVLOG(1) << "Removing " << sequence_number << " from missing list";
    received_info_.missing_packets.erase(sequence_number);
  }
  if (header.packet_sequence_number > received_info_.largest_observed) {
    received_info_.largest_observed = header.packet_sequence_number;
    time_largest_observed_ = receipt_time;
  }
  RecordPacketEntropyHash(sequence_number, header.entropy_hash);
}

bool QuicReceivedPacketManager::IsAwaitingPacket(
    QuicPacketSequenceNumber sequence_number) {
  return ::net::IsAwaitingPacket(received_info_, sequence_number);
}

void QuicReceivedPacketManager::UpdateReceivedPacketInfo(
    ReceivedPacketInfo* received_info, QuicTime approximate_now) {
  *received_info = received_info_;
  received_info->entropy_hash = EntropyHash(received_info_.largest_observed);
  if (time_largest_observed_ == QuicTime::Zero()) {
    // We have not received any new higher sequence numbers since we sent our
    // last ACK.
    received_info->delta_time_largest_observed = QuicTime::Delta::Infinite();
  } else {
    received_info->delta_time_largest_observed =
        approximate_now.Subtract(time_largest_observed_);

    time_largest_observed_ = QuicTime::Zero();
  }
}

void QuicReceivedPacketManager::RecordPacketEntropyHash(
    QuicPacketSequenceNumber sequence_number,
    QuicPacketEntropyHash entropy_hash) {
  if (sequence_number < largest_sequence_number_) {
    DLOG(INFO) << "Ignoring received packet entropy for sequence_number:"
               << sequence_number << " less than largest_peer_sequence_number:"
               << largest_sequence_number_;
    return;
  }
  packets_entropy_.insert(make_pair(sequence_number, entropy_hash));
  packets_entropy_hash_ ^= entropy_hash;
  DVLOG(2) << "setting cumulative received entropy hash to: "
           << static_cast<int>(packets_entropy_hash_)
           << " updated with sequence number " << sequence_number
           << " entropy hash: " << static_cast<int>(entropy_hash);
}

QuicPacketEntropyHash QuicReceivedPacketManager::EntropyHash(
    QuicPacketSequenceNumber sequence_number) const {
  DCHECK_LE(sequence_number, received_info_.largest_observed);
  DCHECK_GE(sequence_number, largest_sequence_number_);
  if (sequence_number == received_info_.largest_observed) {
    return packets_entropy_hash_;
  }

  ReceivedEntropyMap::const_iterator it =
      packets_entropy_.upper_bound(sequence_number);
  // When this map is empty we should only query entropy for
  // received_info_.largest_observed, since no other entropy can be correctly
  // calculated, because we're not storing the entropy for any prior packets.
  // TODO(rtenneti): add support for LOG_IF_EVERY_N_SEC to chromium.
  // LOG_IF_EVERY_N_SEC(DFATAL, it == packets_entropy_.end(), 10)
  LOG_IF(DFATAL, it == packets_entropy_.end())
      << "EntropyHash may be unknown. largest_received: "
      << received_info_.largest_observed
      << " sequence_number: " << sequence_number;

  // TODO(satyamshekhar): Make this O(1).
  QuicPacketEntropyHash hash = packets_entropy_hash_;
  for (; it != packets_entropy_.end(); ++it) {
    hash ^= it->second;
  }
  return hash;
}

void QuicReceivedPacketManager::RecalculateEntropyHash(
    QuicPacketSequenceNumber peer_least_unacked,
    QuicPacketEntropyHash entropy_hash) {
  DCHECK_LE(peer_least_unacked, received_info_.largest_observed);
  if (peer_least_unacked < largest_sequence_number_) {
    DLOG(INFO) << "Ignoring received peer_least_unacked:" << peer_least_unacked
               << " less than largest_peer_sequence_number:"
               << largest_sequence_number_;
    return;
  }
  largest_sequence_number_ = peer_least_unacked;
  packets_entropy_hash_ = entropy_hash;
  ReceivedEntropyMap::iterator it =
      packets_entropy_.lower_bound(peer_least_unacked);
  // TODO(satyamshekhar): Make this O(1).
  for (; it != packets_entropy_.end(); ++it) {
    packets_entropy_hash_ ^= it->second;
  }
  // Discard entropies before least unacked.
  packets_entropy_.erase(
      packets_entropy_.begin(),
      packets_entropy_.lower_bound(
          min(peer_least_unacked, received_info_.largest_observed)));
}

void QuicReceivedPacketManager::UpdatePacketInformationReceivedByPeer(
    const QuicAckFrame& incoming_ack) {
  // ValidateAck should fail if largest_observed ever shrinks.
  DCHECK_LE(peer_largest_observed_packet_,
            incoming_ack.received_info.largest_observed);
  peer_largest_observed_packet_ = incoming_ack.received_info.largest_observed;

  if (incoming_ack.received_info.missing_packets.empty()) {
    least_packet_awaited_by_peer_ = peer_largest_observed_packet_ + 1;
  } else {
    least_packet_awaited_by_peer_ =
        *(incoming_ack.received_info.missing_packets.begin());
  }
}

bool QuicReceivedPacketManager::DontWaitForPacketsBefore(
    QuicPacketSequenceNumber least_unacked) {
  size_t missing_packets_count = received_info_.missing_packets.size();
  received_info_.missing_packets.erase(
      received_info_.missing_packets.begin(),
      received_info_.missing_packets.lower_bound(least_unacked));
  return missing_packets_count != received_info_.missing_packets.size();
}

void QuicReceivedPacketManager::UpdatePacketInformationSentByPeer(
    const QuicAckFrame& incoming_ack) {
  // ValidateAck() should fail if peer_least_packet_awaiting_ack_ shrinks.
  DCHECK_LE(peer_least_packet_awaiting_ack_,
            incoming_ack.sent_info.least_unacked);
  if (incoming_ack.sent_info.least_unacked > peer_least_packet_awaiting_ack_) {
    bool missed_packets =
        DontWaitForPacketsBefore(incoming_ack.sent_info.least_unacked);
    if (missed_packets || incoming_ack.sent_info.least_unacked >
            received_info_.largest_observed + 1) {
      DVLOG(1) << "Updating entropy hashed since we missed packets";
      // There were some missing packets that we won't ever get now. Recalculate
      // the received entropy hash.
      RecalculateEntropyHash(incoming_ack.sent_info.least_unacked,
                             incoming_ack.sent_info.entropy_hash);
    }
    peer_least_packet_awaiting_ack_ = incoming_ack.sent_info.least_unacked;
  }
  DCHECK(received_info_.missing_packets.empty() ||
         *received_info_.missing_packets.begin() >=
             peer_least_packet_awaiting_ack_);
}

size_t QuicReceivedPacketManager::GetNumMissingPackets() {
  return received_info_.missing_packets.size();
}

}  // namespace net