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// 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 "quic/core/quic_received_packet_manager.h"
#include <algorithm>
#include <limits>
#include <utility>
#include "quic/core/congestion_control/rtt_stats.h"
#include "quic/core/crypto/crypto_protocol.h"
#include "quic/core/quic_connection_stats.h"
#include "quic/platform/api/quic_bug_tracker.h"
#include "quic/platform/api/quic_flags.h"
#include "quic/platform/api/quic_logging.h"
namespace quic {
namespace {
// The maximum number of packets to ack immediately after a missing packet for
// fast retransmission to kick in at the sender. This limit is created to
// reduce the number of acks sent that have no benefit for fast retransmission.
// Set to the number of nacks needed for fast retransmit plus one for protection
// against an ack loss
const size_t kMaxPacketsAfterNewMissing = 4;
// One eighth RTT delay when doing ack decimation.
const float kShortAckDecimationDelay = 0.125;
} // namespace
QuicReceivedPacketManager::QuicReceivedPacketManager()
: QuicReceivedPacketManager(nullptr) {}
QuicReceivedPacketManager::QuicReceivedPacketManager(QuicConnectionStats* stats)
: ack_frame_updated_(false),
max_ack_ranges_(0),
time_largest_observed_(QuicTime::Zero()),
save_timestamps_(false),
stats_(stats),
num_retransmittable_packets_received_since_last_ack_sent_(0),
min_received_before_ack_decimation_(kMinReceivedBeforeAckDecimation),
ack_frequency_(kDefaultRetransmittablePacketsBeforeAck),
ack_decimation_delay_(kAckDecimationDelay),
unlimited_ack_decimation_(false),
one_immediate_ack_(false),
ignore_order_(false),
local_max_ack_delay_(
QuicTime::Delta::FromMilliseconds(kDefaultDelayedAckTimeMs)),
ack_timeout_(QuicTime::Zero()),
time_of_previous_received_packet_(QuicTime::Zero()),
was_last_packet_missing_(false),
last_ack_frequency_frame_sequence_number_(-1) {}
QuicReceivedPacketManager::~QuicReceivedPacketManager() {}
void QuicReceivedPacketManager::SetFromConfig(const QuicConfig& config,
Perspective perspective) {
if (config.HasClientSentConnectionOption(kAKD3, perspective)) {
ack_decimation_delay_ = kShortAckDecimationDelay;
}
if (config.HasClientSentConnectionOption(kAKDU, perspective)) {
unlimited_ack_decimation_ = true;
}
if (config.HasClientSentConnectionOption(k1ACK, perspective)) {
one_immediate_ack_ = true;
}
}
void QuicReceivedPacketManager::RecordPacketReceived(
const QuicPacketHeader& header,
QuicTime receipt_time) {
const QuicPacketNumber packet_number = header.packet_number;
QUICHE_DCHECK(IsAwaitingPacket(packet_number))
<< " packet_number:" << packet_number;
was_last_packet_missing_ = IsMissing(packet_number);
if (!ack_frame_updated_) {
ack_frame_.received_packet_times.clear();
}
ack_frame_updated_ = true;
if (LargestAcked(ack_frame_).IsInitialized() &&
LargestAcked(ack_frame_) > packet_number) {
// Record how out of order stats.
++stats_->packets_reordered;
stats_->max_sequence_reordering =
std::max(stats_->max_sequence_reordering,
LargestAcked(ack_frame_) - packet_number);
int64_t reordering_time_us =
(receipt_time - time_largest_observed_).ToMicroseconds();
stats_->max_time_reordering_us =
std::max(stats_->max_time_reordering_us, reordering_time_us);
}
if (!LargestAcked(ack_frame_).IsInitialized() ||
packet_number > LargestAcked(ack_frame_)) {
ack_frame_.largest_acked = packet_number;
time_largest_observed_ = receipt_time;
}
ack_frame_.packets.Add(packet_number);
if (save_timestamps_) {
// The timestamp format only handles packets in time order.
if (!ack_frame_.received_packet_times.empty() &&
ack_frame_.received_packet_times.back().second > receipt_time) {
QUIC_LOG(WARNING)
<< "Receive time went backwards from: "
<< ack_frame_.received_packet_times.back().second.ToDebuggingValue()
<< " to " << receipt_time.ToDebuggingValue();
} else {
ack_frame_.received_packet_times.push_back(
std::make_pair(packet_number, receipt_time));
}
}
if (least_received_packet_number_.IsInitialized()) {
least_received_packet_number_ =
std::min(least_received_packet_number_, packet_number);
} else {
least_received_packet_number_ = packet_number;
}
}
bool QuicReceivedPacketManager::IsMissing(QuicPacketNumber packet_number) {
return LargestAcked(ack_frame_).IsInitialized() &&
packet_number < LargestAcked(ack_frame_) &&
!ack_frame_.packets.Contains(packet_number);
}
bool QuicReceivedPacketManager::IsAwaitingPacket(
QuicPacketNumber packet_number) const {
return quic::IsAwaitingPacket(ack_frame_, packet_number,
peer_least_packet_awaiting_ack_);
}
const QuicFrame QuicReceivedPacketManager::GetUpdatedAckFrame(
QuicTime approximate_now) {
if (time_largest_observed_ == QuicTime::Zero()) {
// We have received no packets.
ack_frame_.ack_delay_time = QuicTime::Delta::Infinite();
} else {
// Ensure the delta is zero if approximate now is "in the past".
ack_frame_.ack_delay_time = approximate_now < time_largest_observed_
? QuicTime::Delta::Zero()
: approximate_now - time_largest_observed_;
}
while (max_ack_ranges_ > 0 &&
ack_frame_.packets.NumIntervals() > max_ack_ranges_) {
ack_frame_.packets.RemoveSmallestInterval();
}
// Clear all packet times if any are too far from largest observed.
// It's expected this is extremely rare.
for (auto it = ack_frame_.received_packet_times.begin();
it != ack_frame_.received_packet_times.end();) {
if (LargestAcked(ack_frame_) - it->first >=
std::numeric_limits<uint8_t>::max()) {
it = ack_frame_.received_packet_times.erase(it);
} else {
++it;
}
}
#if QUIC_FRAME_DEBUG
QuicFrame frame = QuicFrame(&ack_frame_);
frame.delete_forbidden = true;
return frame;
#else // QUIC_FRAME_DEBUG
return QuicFrame(&ack_frame_);
#endif // QUIC_FRAME_DEBUG
}
void QuicReceivedPacketManager::DontWaitForPacketsBefore(
QuicPacketNumber least_unacked) {
if (!least_unacked.IsInitialized()) {
return;
}
// ValidateAck() should fail if peer_least_packet_awaiting_ack shrinks.
QUICHE_DCHECK(!peer_least_packet_awaiting_ack_.IsInitialized() ||
peer_least_packet_awaiting_ack_ <= least_unacked);
if (!peer_least_packet_awaiting_ack_.IsInitialized() ||
least_unacked > peer_least_packet_awaiting_ack_) {
peer_least_packet_awaiting_ack_ = least_unacked;
bool packets_updated = ack_frame_.packets.RemoveUpTo(least_unacked);
if (packets_updated) {
// Ack frame gets updated because packets set is updated because of stop
// waiting frame.
ack_frame_updated_ = true;
}
}
QUICHE_DCHECK(ack_frame_.packets.Empty() ||
!peer_least_packet_awaiting_ack_.IsInitialized() ||
ack_frame_.packets.Min() >= peer_least_packet_awaiting_ack_);
}
QuicTime::Delta QuicReceivedPacketManager::GetMaxAckDelay(
QuicPacketNumber last_received_packet_number,
const RttStats& rtt_stats) const {
if (AckFrequencyFrameReceived() ||
last_received_packet_number < PeerFirstSendingPacketNumber() +
min_received_before_ack_decimation_) {
return local_max_ack_delay_;
}
// Wait for the minimum of the ack decimation delay or the delayed ack time
// before sending an ack.
QuicTime::Delta ack_delay = std::min(
local_max_ack_delay_, rtt_stats.min_rtt() * ack_decimation_delay_);
if (GetQuicReloadableFlag(quic_ack_delay_alarm_granularity)) {
QUIC_RELOADABLE_FLAG_COUNT(quic_ack_delay_alarm_granularity);
ack_delay = std::max(ack_delay, kAlarmGranularity);
}
return ack_delay;
}
void QuicReceivedPacketManager::MaybeUpdateAckFrequency(
QuicPacketNumber last_received_packet_number) {
if (AckFrequencyFrameReceived()) {
// Skip Ack Decimation below after receiving an AckFrequencyFrame from the
// other end point.
return;
}
if (last_received_packet_number <
PeerFirstSendingPacketNumber() + min_received_before_ack_decimation_) {
return;
}
ack_frequency_ = unlimited_ack_decimation_
? std::numeric_limits<size_t>::max()
: kMaxRetransmittablePacketsBeforeAck;
}
void QuicReceivedPacketManager::MaybeUpdateAckTimeout(
bool should_last_packet_instigate_acks,
QuicPacketNumber last_received_packet_number,
QuicTime now,
const RttStats* rtt_stats) {
if (!ack_frame_updated_) {
// ACK frame has not been updated, nothing to do.
return;
}
if (!ignore_order_ && was_last_packet_missing_ &&
last_sent_largest_acked_.IsInitialized() &&
last_received_packet_number < last_sent_largest_acked_) {
// Only ack immediately if an ACK frame was sent with a larger largest acked
// than the newly received packet number.
ack_timeout_ = now;
return;
}
if (!should_last_packet_instigate_acks) {
return;
}
++num_retransmittable_packets_received_since_last_ack_sent_;
MaybeUpdateAckFrequency(last_received_packet_number);
if (num_retransmittable_packets_received_since_last_ack_sent_ >=
ack_frequency_) {
ack_timeout_ = now;
return;
}
if (!ignore_order_ && HasNewMissingPackets()) {
ack_timeout_ = now;
return;
}
QuicTime updated_ack_time =
now + GetMaxAckDelay(last_received_packet_number, *rtt_stats);
if (!ack_timeout_.IsInitialized() || ack_timeout_ > updated_ack_time) {
ack_timeout_ = updated_ack_time;
}
}
void QuicReceivedPacketManager::ResetAckStates() {
ack_frame_updated_ = false;
ack_timeout_ = QuicTime::Zero();
num_retransmittable_packets_received_since_last_ack_sent_ = 0;
last_sent_largest_acked_ = LargestAcked(ack_frame_);
}
bool QuicReceivedPacketManager::HasMissingPackets() const {
if (ack_frame_.packets.Empty()) {
return false;
}
if (ack_frame_.packets.NumIntervals() > 1) {
return true;
}
return peer_least_packet_awaiting_ack_.IsInitialized() &&
ack_frame_.packets.Min() > peer_least_packet_awaiting_ack_;
}
bool QuicReceivedPacketManager::HasNewMissingPackets() const {
if (one_immediate_ack_) {
return HasMissingPackets() && ack_frame_.packets.LastIntervalLength() == 1;
}
return HasMissingPackets() &&
ack_frame_.packets.LastIntervalLength() <= kMaxPacketsAfterNewMissing;
}
bool QuicReceivedPacketManager::ack_frame_updated() const {
return ack_frame_updated_;
}
QuicPacketNumber QuicReceivedPacketManager::GetLargestObserved() const {
return LargestAcked(ack_frame_);
}
QuicPacketNumber QuicReceivedPacketManager::PeerFirstSendingPacketNumber()
const {
if (!least_received_packet_number_.IsInitialized()) {
QUIC_BUG << "No packets have been received yet";
return QuicPacketNumber(1);
}
return least_received_packet_number_;
}
bool QuicReceivedPacketManager::IsAckFrameEmpty() const {
return ack_frame_.packets.Empty();
}
void QuicReceivedPacketManager::OnAckFrequencyFrame(
const QuicAckFrequencyFrame& frame) {
int64_t new_sequence_number = frame.sequence_number;
if (new_sequence_number <= last_ack_frequency_frame_sequence_number_) {
// Ignore old ACK_FREQUENCY frames.
return;
}
last_ack_frequency_frame_sequence_number_ = new_sequence_number;
ack_frequency_ = frame.packet_tolerance;
local_max_ack_delay_ = frame.max_ack_delay;
ignore_order_ = frame.ignore_order;
}
} // namespace quic