net/quic/quic_sent_packet_manager.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/quic/quic_sent_packet_manager.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/logging.h"
  10 #include "base/stl_util.h"
  11 #include "net/quic/congestion_control/pacing_sender.h"
  12 #include "net/quic/crypto/crypto_protocol.h"
  13 #include "net/quic/proto/cached_network_parameters.pb.h"
  14 #include "net/quic/quic_ack_notifier_manager.h"
  15 #include "net/quic/quic_connection_stats.h"
  16 #include "net/quic/quic_flags.h"
  17 #include "net/quic/quic_utils_chromium.h"
  18
  19 using std::max;
  20 using std::min;
  21
  22 namespace net {
  23
  24 // The length of the recent min rtt window in seconds. Windowing is disabled for
  25 // values less than or equal to 0.
  26 int32 FLAGS_quic_recent_min_rtt_window_s = 60;
  27
  28 namespace {
  29 static const int64 kDefaultRetransmissionTimeMs = 500;
  30 // TCP RFC calls for 1 second RTO however Linux differs from this default and
  31 // define the minimum RTO to 200ms, we will use the same until we have data to
  32 // support a higher or lower value.
  33 static const int64 kMinRetransmissionTimeMs = 200;
  34 static const int64 kMaxRetransmissionTimeMs = 60000;
  35 // Maximum number of exponential backoffs used for RTO timeouts.
  36 static const size_t kMaxRetransmissions = 10;
  37 // Maximum number of packets retransmitted upon an RTO.
  38 static const size_t kMaxRetransmissionsOnTimeout = 2;
  39
  40 // Ensure the handshake timer isnt't faster than 10ms.
  41 // This limits the tenth retransmitted packet to 10s after the initial CHLO.
  42 static const int64 kMinHandshakeTimeoutMs = 10;
  43
  44 // Sends up to two tail loss probes before firing an RTO,
  45 // per draft RFC draft-dukkipati-tcpm-tcp-loss-probe.
  46 static const size_t kDefaultMaxTailLossProbes = 2;
  47 static const int64 kMinTailLossProbeTimeoutMs = 10;
  48
  49 // Number of unpaced packets to send after quiescence.
  50 static const size_t kInitialUnpacedBurst = 10;
  51
  52 bool HasCryptoHandshake(const TransmissionInfo& transmission_info) {
  53   if (transmission_info.retransmittable_frames == nullptr) {
  54     return false;
  55   }
  56   return transmission_info.retransmittable_frames->HasCryptoHandshake() ==
  57       IS_HANDSHAKE;
  58 }
  59
  60 }  // namespace
  61
  62 #define ENDPOINT \
  63   (perspective_ == Perspective::IS_SERVER ? "Server: " : "Client: ")
  64
  65 QuicSentPacketManager::QuicSentPacketManager(
  66     Perspective perspective,
  67     const QuicClock* clock,
  68     QuicConnectionStats* stats,
  69     CongestionControlType congestion_control_type,
  70     LossDetectionType loss_type,
  71     bool is_secure)
  72     : unacked_packets_(&ack_notifier_manager_),
  73       perspective_(perspective),
  74       clock_(clock),
  75       stats_(stats),
  76       debug_delegate_(nullptr),
  77       network_change_visitor_(nullptr),
  78       initial_congestion_window_(is_secure ? kInitialCongestionWindowSecure
  79                                            : kInitialCongestionWindowInsecure),
  80       send_algorithm_(
  81           SendAlgorithmInterface::Create(clock,
  82                                          &rtt_stats_,
  83                                          congestion_control_type,
  84                                          stats,
  85                                          initial_congestion_window_)),
  86       loss_algorithm_(LossDetectionInterface::Create(loss_type)),
  87       n_connection_simulation_(false),
  88       receive_buffer_bytes_(kDefaultSocketReceiveBuffer),
  89       least_packet_awaited_by_peer_(1),
  90       first_rto_transmission_(0),
  91       consecutive_rto_count_(0),
  92       consecutive_tlp_count_(0),
  93       consecutive_crypto_retransmission_count_(0),
  94       pending_timer_transmission_count_(0),
  95       max_tail_loss_probes_(kDefaultMaxTailLossProbes),
  96       enable_half_rtt_tail_loss_probe_(false),
  97       using_pacing_(false),
  98       use_new_rto_(false),
  99       handshake_confirmed_(false) {}
 100
 101 QuicSentPacketManager::~QuicSentPacketManager() {
 102 }
 103
 104 void QuicSentPacketManager::SetFromConfig(const QuicConfig& config) {
 105   if (config.HasReceivedInitialRoundTripTimeUs() &&
 106       config.ReceivedInitialRoundTripTimeUs() > 0) {
 107     rtt_stats_.set_initial_rtt_us(
 108         max(kMinInitialRoundTripTimeUs,
 109             min(kMaxInitialRoundTripTimeUs,
 110                 config.ReceivedInitialRoundTripTimeUs())));
 111   } else if (config.HasInitialRoundTripTimeUsToSend() &&
 112              config.GetInitialRoundTripTimeUsToSend() > 0) {
 113     rtt_stats_.set_initial_rtt_us(
 114         max(kMinInitialRoundTripTimeUs,
 115             min(kMaxInitialRoundTripTimeUs,
 116                 config.GetInitialRoundTripTimeUsToSend())));
 117   }
 118   // Initial RTT may have changed.
 119   if (network_change_visitor_ != nullptr) {
 120     network_change_visitor_->OnRttChange();
 121   }
 122   // TODO(ianswett): BBR is currently a server only feature.
 123   if (FLAGS_quic_allow_bbr &&
 124       config.HasReceivedConnectionOptions() &&
 125       ContainsQuicTag(config.ReceivedConnectionOptions(), kTBBR)) {
 126     if (FLAGS_quic_recent_min_rtt_window_s > 0) {
 127       rtt_stats_.set_recent_min_rtt_window(
 128           QuicTime::Delta::FromSeconds(FLAGS_quic_recent_min_rtt_window_s));
 129     }
 130     send_algorithm_.reset(SendAlgorithmInterface::Create(
 131         clock_, &rtt_stats_, kBBR, stats_, initial_congestion_window_));
 132   }
 133   if (config.HasReceivedConnectionOptions() &&
 134       ContainsQuicTag(config.ReceivedConnectionOptions(), kRENO)) {
 135     if (ContainsQuicTag(config.ReceivedConnectionOptions(), kBYTE)) {
 136       send_algorithm_.reset(SendAlgorithmInterface::Create(
 137           clock_, &rtt_stats_, kRenoBytes, stats_, initial_congestion_window_));
 138     } else {
 139       send_algorithm_.reset(SendAlgorithmInterface::Create(
 140           clock_, &rtt_stats_, kReno, stats_, initial_congestion_window_));
 141     }
 142   } else if (config.HasReceivedConnectionOptions() &&
 143              ContainsQuicTag(config.ReceivedConnectionOptions(), kBYTE)) {
 144     send_algorithm_.reset(SendAlgorithmInterface::Create(
 145         clock_, &rtt_stats_, kCubicBytes, stats_, initial_congestion_window_));
 146   }
 147   EnablePacing();
 148
 149   if (config.HasClientSentConnectionOption(k1CON, perspective_)) {
 150     send_algorithm_->SetNumEmulatedConnections(1);
 151   }
 152   if (config.HasClientSentConnectionOption(kNCON, perspective_)) {
 153     n_connection_simulation_ = true;
 154   }
 155   if (config.HasClientSentConnectionOption(kNTLP, perspective_)) {
 156     max_tail_loss_probes_ = 0;
 157   }
 158   if (config.HasClientSentConnectionOption(kTLPR, perspective_)) {
 159     enable_half_rtt_tail_loss_probe_ = true;
 160   }
 161   if (config.HasClientSentConnectionOption(kNRTO, perspective_)) {
 162     use_new_rto_ = true;
 163   }
 164   if (config.HasReceivedConnectionOptions() &&
 165       ContainsQuicTag(config.ReceivedConnectionOptions(), kTIME)) {
 166     loss_algorithm_.reset(LossDetectionInterface::Create(kTime));
 167   }
 168   if (config.HasReceivedSocketReceiveBuffer()) {
 169     receive_buffer_bytes_ =
 170         max(kMinSocketReceiveBuffer,
 171             static_cast<QuicByteCount>(config.ReceivedSocketReceiveBuffer()));
 172     QuicByteCount max_cwnd_bytes = static_cast<QuicByteCount>(
 173         receive_buffer_bytes_ * kConservativeReceiveBufferFraction);
 174     if (FLAGS_quic_limit_max_cwnd) {
 175       max_cwnd_bytes =
 176           min(max_cwnd_bytes, kMaxCongestionWindow * kDefaultTCPMSS);
 177     }
 178     send_algorithm_->SetMaxCongestionWindow(max_cwnd_bytes);
 179   }
 180   send_algorithm_->SetFromConfig(config, perspective_);
 181
 182   if (network_change_visitor_ != nullptr) {
 183     network_change_visitor_->OnCongestionWindowChange();
 184   }
 185 }
 186
 187 void QuicSentPacketManager::ResumeConnectionState(
 188     const CachedNetworkParameters& cached_network_params,
 189     bool max_bandwidth_resumption) {
 190   if (cached_network_params.has_min_rtt_ms()) {
 191     uint32 initial_rtt_us =
 192         kNumMicrosPerMilli * cached_network_params.min_rtt_ms();
 193     rtt_stats_.set_initial_rtt_us(
 194         max(kMinInitialRoundTripTimeUs,
 195             min(kMaxInitialRoundTripTimeUs, initial_rtt_us)));
 196   }
 197   send_algorithm_->ResumeConnectionState(cached_network_params,
 198                                          max_bandwidth_resumption);
 199 }
 200
 201 void QuicSentPacketManager::SetNumOpenStreams(size_t num_streams) {
 202   if (n_connection_simulation_) {
 203     // Ensure the number of connections is between 1 and 5.
 204     send_algorithm_->SetNumEmulatedConnections(
 205         min<size_t>(5, max<size_t>(1, num_streams)));
 206   }
 207 }
 208
 209 void QuicSentPacketManager::OnIncomingAck(const QuicAckFrame& ack_frame,
 210                                           QuicTime ack_receive_time) {
 211   QuicByteCount bytes_in_flight = unacked_packets_.bytes_in_flight();
 212
 213   UpdatePacketInformationReceivedByPeer(ack_frame);
 214   bool rtt_updated = MaybeUpdateRTT(ack_frame, ack_receive_time);
 215   DCHECK_GE(ack_frame.largest_observed, unacked_packets_.largest_observed());
 216   unacked_packets_.IncreaseLargestObserved(ack_frame.largest_observed);
 217
 218   HandleAckForSentPackets(ack_frame);
 219   InvokeLossDetection(ack_receive_time);
 220   // Ignore losses in RTO mode.
 221   if (consecutive_rto_count_ > 0 && !use_new_rto_) {
 222     packets_lost_.clear();
 223   }
 224   MaybeInvokeCongestionEvent(rtt_updated, bytes_in_flight);
 225   unacked_packets_.RemoveObsoletePackets();
 226
 227   sustained_bandwidth_recorder_.RecordEstimate(
 228       send_algorithm_->InRecovery(),
 229       send_algorithm_->InSlowStart(),
 230       send_algorithm_->BandwidthEstimate(),
 231       ack_receive_time,
 232       clock_->WallNow(),
 233       rtt_stats_.smoothed_rtt());
 234
 235   // If we have received a truncated ack, then we need to clear out some
 236   // previous transmissions to allow the peer to actually ACK new packets.
 237   if (ack_frame.is_truncated && !FLAGS_quic_disable_truncated_ack_handling) {
 238     unacked_packets_.ClearAllPreviousRetransmissions();
 239   }
 240
 241   // Anytime we are making forward progress and have a new RTT estimate, reset
 242   // the backoff counters.
 243   if (rtt_updated) {
 244     if (consecutive_rto_count_ > 0) {
 245       // If the ack acknowledges data sent prior to the RTO,
 246       // the RTO was spurious.
 247       if (ack_frame.largest_observed < first_rto_transmission_) {
 248         // Replace SRTT with latest_rtt and increase the variance to prevent
 249         // a spurious RTO from happening again.
 250         rtt_stats_.ExpireSmoothedMetrics();
 251       } else {
 252         if (!use_new_rto_) {
 253           send_algorithm_->OnRetransmissionTimeout(true);
 254         }
 255       }
 256     }
 257     // Reset all retransmit counters any time a new packet is acked.
 258     consecutive_rto_count_ = 0;
 259     consecutive_tlp_count_ = 0;
 260     consecutive_crypto_retransmission_count_ = 0;
 261   }
 262
 263   if (debug_delegate_ != nullptr) {
 264     debug_delegate_->OnIncomingAck(ack_frame, ack_receive_time,
 265                                    unacked_packets_.largest_observed(),
 266                                    rtt_updated, GetLeastUnacked());
 267   }
 268 }
 269
 270 void QuicSentPacketManager::UpdatePacketInformationReceivedByPeer(
 271     const QuicAckFrame& ack_frame) {
 272   if (ack_frame.missing_packets.Empty()) {
 273     least_packet_awaited_by_peer_ = ack_frame.largest_observed + 1;
 274   } else {
 275     least_packet_awaited_by_peer_ = ack_frame.missing_packets.Min();
 276   }
 277 }
 278
 279 void QuicSentPacketManager::MaybeInvokeCongestionEvent(
 280     bool rtt_updated, QuicByteCount bytes_in_flight) {
 281   if (!rtt_updated && packets_acked_.empty() && packets_lost_.empty()) {
 282     return;
 283   }
 284   send_algorithm_->OnCongestionEvent(rtt_updated, bytes_in_flight,
 285                                      packets_acked_, packets_lost_);
 286   packets_acked_.clear();
 287   packets_lost_.clear();
 288   if (network_change_visitor_ != nullptr) {
 289     network_change_visitor_->OnCongestionWindowChange();
 290   }
 291 }
 292
 293 void QuicSentPacketManager::HandleAckForSentPackets(
 294     const QuicAckFrame& ack_frame) {
 295   // Go through the packets we have not received an ack for and see if this
 296   // incoming_ack shows they've been seen by the peer.
 297   QuicTime::Delta delta_largest_observed =
 298       ack_frame.delta_time_largest_observed;
 299   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 300   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 301        it != unacked_packets_.end(); ++it, ++packet_number) {
 302     if (packet_number > ack_frame.largest_observed) {
 303       // These packets are still in flight.
 304       break;
 305     }
 306
 307     if (ack_frame.missing_packets.Contains(packet_number)) {
 308       // Don't continue to increase the nack count for packets not in flight.
 309       if (!it->in_flight) {
 310         continue;
 311       }
 312       // Consider it multiple nacks when there is a gap between the missing
 313       // packet and the largest observed, since the purpose of a nack
 314       // threshold is to tolerate re-ordering.  This handles both StretchAcks
 315       // and Forward Acks.
 316       // The nack count only increases when the largest observed increases.
 317       QuicPacketCount min_nacks = ack_frame.largest_observed - packet_number;
 318       // Truncated acks can nack the largest observed, so use a min of 1.
 319       if (min_nacks == 0) {
 320         min_nacks = 1;
 321       }
 322       unacked_packets_.NackPacket(packet_number, min_nacks);
 323       continue;
 324     }
 325     // Packet was acked, so remove it from our unacked packet list.
 326     DVLOG(1) << ENDPOINT << "Got an ack for packet " << packet_number;
 327     // If data is associated with the most recent transmission of this
 328     // packet, then inform the caller.
 329     if (it->in_flight) {
 330       packets_acked_.push_back(std::make_pair(packet_number, *it));
 331     }
 332     MarkPacketHandled(packet_number, *it, delta_largest_observed);
 333   }
 334
 335   // Discard any retransmittable frames associated with revived packets.
 336   for (PacketNumberSet::const_iterator revived_it =
 337            ack_frame.revived_packets.begin();
 338        revived_it != ack_frame.revived_packets.end(); ++revived_it) {
 339     MarkPacketRevived(*revived_it, delta_largest_observed);
 340   }
 341 }
 342
 343 bool QuicSentPacketManager::HasRetransmittableFrames(
 344     QuicPacketNumber packet_number) const {
 345   return unacked_packets_.HasRetransmittableFrames(packet_number);
 346 }
 347
 348 void QuicSentPacketManager::RetransmitUnackedPackets(
 349     TransmissionType retransmission_type) {
 350   DCHECK(retransmission_type == ALL_UNACKED_RETRANSMISSION ||
 351          retransmission_type == ALL_INITIAL_RETRANSMISSION);
 352   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 353   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 354        it != unacked_packets_.end(); ++it, ++packet_number) {
 355     const RetransmittableFrames* frames = it->retransmittable_frames;
 356     if (frames != nullptr &&
 357         (retransmission_type == ALL_UNACKED_RETRANSMISSION ||
 358          frames->encryption_level() == ENCRYPTION_INITIAL)) {
 359       MarkForRetransmission(packet_number, retransmission_type);
 360     } else if (it->is_fec_packet) {
 361       // Remove FEC packets from the packet map, since we can't retransmit them.
 362       unacked_packets_.RemoveFromInFlight(packet_number);
 363     }
 364   }
 365 }
 366
 367 void QuicSentPacketManager::NeuterUnencryptedPackets() {
 368   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 369   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 370        it != unacked_packets_.end(); ++it, ++packet_number) {
 371     const RetransmittableFrames* frames = it->retransmittable_frames;
 372     if (frames != nullptr && frames->encryption_level() == ENCRYPTION_NONE) {
 373       // Once you're forward secure, no unencrypted packets will be sent, crypto
 374       // or otherwise. Unencrypted packets are neutered and abandoned, to ensure
 375       // they are not retransmitted or considered lost from a congestion control
 376       // perspective.
 377       pending_retransmissions_.erase(packet_number);
 378       unacked_packets_.RemoveFromInFlight(packet_number);
 379       unacked_packets_.RemoveRetransmittability(packet_number);
 380     }
 381   }
 382 }
 383
 384 void QuicSentPacketManager::MarkForRetransmission(
 385     QuicPacketNumber packet_number,
 386     TransmissionType transmission_type) {
 387   const TransmissionInfo& transmission_info =
 388       unacked_packets_.GetTransmissionInfo(packet_number);
 389   LOG_IF(DFATAL, transmission_info.retransmittable_frames == nullptr);
 390   // Both TLP and the new RTO leave the packets in flight and let the loss
 391   // detection decide if packets are lost.
 392   if (transmission_type != TLP_RETRANSMISSION &&
 393       transmission_type != RTO_RETRANSMISSION) {
 394     unacked_packets_.RemoveFromInFlight(packet_number);
 395   }
 396   // TODO(ianswett): Currently the RTO can fire while there are pending NACK
 397   // retransmissions for the same data, which is not ideal.
 398   if (ContainsKey(pending_retransmissions_, packet_number)) {
 399     return;
 400   }
 401
 402   pending_retransmissions_[packet_number] = transmission_type;
 403 }
 404
 405 void QuicSentPacketManager::RecordSpuriousRetransmissions(
 406     const PacketNumberList& all_transmissions,
 407     QuicPacketNumber acked_packet_number) {
 408   for (PacketNumberList::const_reverse_iterator it = all_transmissions.rbegin();
 409        it != all_transmissions.rend() && *it > acked_packet_number; ++it) {
 410     // ianswett: Prevents crash in b/20552846.
 411     if (*it < unacked_packets_.GetLeastUnacked() ||
 412         *it > unacked_packets_.largest_sent_packet()) {
 413       LOG(DFATAL) << "Retransmission out of range:" << *it
 414                   << " least unacked:" << unacked_packets_.GetLeastUnacked()
 415                   << " largest sent:" << unacked_packets_.largest_sent_packet();
 416       return;
 417     }
 418     const TransmissionInfo& retransmit_info =
 419         unacked_packets_.GetTransmissionInfo(*it);
 420
 421     stats_->bytes_spuriously_retransmitted += retransmit_info.bytes_sent;
 422     ++stats_->packets_spuriously_retransmitted;
 423     if (debug_delegate_ != nullptr) {
 424       debug_delegate_->OnSpuriousPacketRetransmission(
 425           retransmit_info.transmission_type, retransmit_info.bytes_sent);
 426     }
 427   }
 428 }
 429
 430 bool QuicSentPacketManager::HasPendingRetransmissions() const {
 431   return !pending_retransmissions_.empty();
 432 }
 433
 434 QuicSentPacketManager::PendingRetransmission
 435     QuicSentPacketManager::NextPendingRetransmission() {
 436   LOG_IF(DFATAL, pending_retransmissions_.empty())
 437       << "Unexpected call to PendingRetransmissions() with empty pending "
 438       << "retransmission list. Corrupted memory usage imminent.";
 439   QuicPacketNumber packet_number = pending_retransmissions_.begin()->first;
 440   TransmissionType transmission_type = pending_retransmissions_.begin()->second;
 441   if (unacked_packets_.HasPendingCryptoPackets()) {
 442     // Ensure crypto packets are retransmitted before other packets.
 443     for (const auto& pair : pending_retransmissions_) {
 444       if (HasCryptoHandshake(
 445               unacked_packets_.GetTransmissionInfo(pair.first))) {
 446         packet_number = pair.first;
 447         transmission_type = pair.second;
 448         break;
 449       }
 450     }
 451   }
 452   DCHECK(unacked_packets_.IsUnacked(packet_number)) << packet_number;
 453   const TransmissionInfo& transmission_info =
 454       unacked_packets_.GetTransmissionInfo(packet_number);
 455   DCHECK(transmission_info.retransmittable_frames);
 456
 457   return PendingRetransmission(packet_number, transmission_type,
 458                                *transmission_info.retransmittable_frames,
 459                                transmission_info.packet_number_length);
 460 }
 461
 462 void QuicSentPacketManager::MarkPacketRevived(
 463     QuicPacketNumber packet_number,
 464     QuicTime::Delta delta_largest_observed) {
 465   if (!unacked_packets_.IsUnacked(packet_number)) {
 466     return;
 467   }
 468
 469   const TransmissionInfo& transmission_info =
 470       unacked_packets_.GetTransmissionInfo(packet_number);
 471   QuicPacketNumber newest_transmission =
 472       transmission_info.all_transmissions == nullptr
 473           ? packet_number
 474           : *transmission_info.all_transmissions->rbegin();
 475   // This packet has been revived at the receiver. If we were going to
 476   // retransmit it, do not retransmit it anymore.
 477   pending_retransmissions_.erase(newest_transmission);
 478
 479   // The AckNotifierManager needs to be notified for revived packets,
 480   // since it indicates the packet arrived from the appliction's perspective.
 481   ack_notifier_manager_.OnPacketAcked(newest_transmission,
 482                                       delta_largest_observed);
 483
 484   unacked_packets_.RemoveRetransmittability(packet_number);
 485 }
 486
 487 void QuicSentPacketManager::MarkPacketHandled(
 488     QuicPacketNumber packet_number,
 489     const TransmissionInfo& info,
 490     QuicTime::Delta delta_largest_observed) {
 491   QuicPacketNumber newest_transmission =
 492       info.all_transmissions == nullptr ? packet_number
 493                                         : *info.all_transmissions->rbegin();
 494   // Remove the most recent packet, if it is pending retransmission.
 495   pending_retransmissions_.erase(newest_transmission);
 496
 497   // The AckNotifierManager needs to be notified about the most recent
 498   // transmission, since that's the one only one it tracks.
 499   ack_notifier_manager_.OnPacketAcked(newest_transmission,
 500                                       delta_largest_observed);
 501   if (newest_transmission != packet_number) {
 502     RecordSpuriousRetransmissions(*info.all_transmissions, packet_number);
 503     // Remove the most recent packet from flight if it's a crypto handshake
 504     // packet, since they won't be acked now that one has been processed.
 505     // Other crypto handshake packets won't be in flight, only the newest
 506     // transmission of a crypto packet is in flight at once.
 507     // TODO(ianswett): Instead of handling all crypto packets special,
 508     // only handle nullptr encrypted packets in a special way.
 509     if (HasCryptoHandshake(
 510         unacked_packets_.GetTransmissionInfo(newest_transmission))) {
 511       unacked_packets_.RemoveFromInFlight(newest_transmission);
 512     }
 513   }
 514
 515   unacked_packets_.RemoveFromInFlight(packet_number);
 516   unacked_packets_.RemoveRetransmittability(packet_number);
 517 }
 518
 519 bool QuicSentPacketManager::IsUnacked(QuicPacketNumber packet_number) const {
 520   return unacked_packets_.IsUnacked(packet_number);
 521 }
 522
 523 bool QuicSentPacketManager::HasUnackedPackets() const {
 524   return unacked_packets_.HasUnackedPackets();
 525 }
 526
 527 QuicPacketNumber QuicSentPacketManager::GetLeastUnacked() const {
 528   return unacked_packets_.GetLeastUnacked();
 529 }
 530
 531 bool QuicSentPacketManager::OnPacketSent(
 532     SerializedPacket* serialized_packet,
 533     QuicPacketNumber original_packet_number,
 534     QuicTime sent_time,
 535     QuicByteCount bytes,
 536     TransmissionType transmission_type,
 537     HasRetransmittableData has_retransmittable_data) {
 538   QuicPacketNumber packet_number = serialized_packet->packet_number;
 539   DCHECK_LT(0u, packet_number);
 540   DCHECK(!unacked_packets_.IsUnacked(packet_number));
 541   LOG_IF(DFATAL, bytes == 0) << "Cannot send empty packets.";
 542
 543   if (original_packet_number != 0) {
 544     PendingRetransmissionMap::iterator it =
 545         pending_retransmissions_.find(original_packet_number);
 546     if (it != pending_retransmissions_.end()) {
 547       pending_retransmissions_.erase(it);
 548     } else {
 549       DLOG(DFATAL) << "Expected packet number to be in "
 550                    << "pending_retransmissions_.  packet_number: "
 551                    << original_packet_number;
 552     }
 553     // Inform the ack notifier of retransmissions so it can calculate the
 554     // retransmit rate.
 555     ack_notifier_manager_.OnPacketRetransmitted(original_packet_number,
 556                                                 packet_number, bytes);
 557   }
 558
 559   if (pending_timer_transmission_count_ > 0) {
 560     --pending_timer_transmission_count_;
 561   }
 562
 563   // Only track packets as in flight that the send algorithm wants us to track.
 564   // Since FEC packets should also be counted towards the congestion window,
 565   // consider them as retransmittable for the purposes of congestion control.
 566   HasRetransmittableData has_congestion_controlled_data =
 567       serialized_packet->is_fec_packet ? HAS_RETRANSMITTABLE_DATA
 568                                        : has_retransmittable_data;
 569   const bool in_flight = send_algorithm_->OnPacketSent(
 570       sent_time, unacked_packets_.bytes_in_flight(), packet_number, bytes,
 571       has_congestion_controlled_data);
 572
 573   unacked_packets_.AddSentPacket(*serialized_packet, original_packet_number,
 574                                  transmission_type, sent_time, bytes,
 575                                  in_flight);
 576
 577   // Take ownership of the retransmittable frames before exiting.
 578   serialized_packet->retransmittable_frames = nullptr;
 579   // Reset the retransmission timer anytime a pending packet is sent.
 580   return in_flight;
 581 }
 582
 583 void QuicSentPacketManager::OnRetransmissionTimeout() {
 584   DCHECK(unacked_packets_.HasInFlightPackets());
 585   DCHECK_EQ(0u, pending_timer_transmission_count_);
 586   // Handshake retransmission, timer based loss detection, TLP, and RTO are
 587   // implemented with a single alarm. The handshake alarm is set when the
 588   // handshake has not completed, the loss alarm is set when the loss detection
 589   // algorithm says to, and the TLP and  RTO alarms are set after that.
 590   // The TLP alarm is always set to run for under an RTO.
 591   switch (GetRetransmissionMode()) {
 592     case HANDSHAKE_MODE:
 593       ++stats_->crypto_retransmit_count;
 594       RetransmitCryptoPackets();
 595       return;
 596     case LOSS_MODE: {
 597       ++stats_->loss_timeout_count;
 598       QuicByteCount bytes_in_flight = unacked_packets_.bytes_in_flight();
 599       InvokeLossDetection(clock_->Now());
 600       MaybeInvokeCongestionEvent(false, bytes_in_flight);
 601       return;
 602     }
 603     case TLP_MODE:
 604       // If no tail loss probe can be sent, because there are no retransmittable
 605       // packets, execute a conventional RTO to abandon old packets.
 606       ++stats_->tlp_count;
 607       ++consecutive_tlp_count_;
 608       pending_timer_transmission_count_ = 1;
 609       // TLPs prefer sending new data instead of retransmitting data, so
 610       // give the connection a chance to write before completing the TLP.
 611       return;
 612     case RTO_MODE:
 613       ++stats_->rto_count;
 614       RetransmitRtoPackets();
 615       return;
 616   }
 617 }
 618
 619 void QuicSentPacketManager::RetransmitCryptoPackets() {
 620   DCHECK_EQ(HANDSHAKE_MODE, GetRetransmissionMode());
 621   ++consecutive_crypto_retransmission_count_;
 622   bool packet_retransmitted = false;
 623   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 624   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 625        it != unacked_packets_.end(); ++it, ++packet_number) {
 626     // Only retransmit frames which are in flight, and therefore have been sent.
 627     if (!it->in_flight || it->retransmittable_frames == nullptr ||
 628         it->retransmittable_frames->HasCryptoHandshake() != IS_HANDSHAKE) {
 629       continue;
 630     }
 631     packet_retransmitted = true;
 632     MarkForRetransmission(packet_number, HANDSHAKE_RETRANSMISSION);
 633     ++pending_timer_transmission_count_;
 634   }
 635   DCHECK(packet_retransmitted) << "No crypto packets found to retransmit.";
 636 }
 637
 638 bool QuicSentPacketManager::MaybeRetransmitTailLossProbe() {
 639   if (pending_timer_transmission_count_ == 0) {
 640     return false;
 641   }
 642   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 643   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 644        it != unacked_packets_.end(); ++it, ++packet_number) {
 645     // Only retransmit frames which are in flight, and therefore have been sent.
 646     if (!it->in_flight || it->retransmittable_frames == nullptr) {
 647       continue;
 648     }
 649     if (!handshake_confirmed_) {
 650       DCHECK_NE(IS_HANDSHAKE, it->retransmittable_frames->HasCryptoHandshake());
 651     }
 652     MarkForRetransmission(packet_number, TLP_RETRANSMISSION);
 653     return true;
 654   }
 655   DLOG(ERROR)
 656       << "No retransmittable packets, so RetransmitOldestPacket failed.";
 657   return false;
 658 }
 659
 660 void QuicSentPacketManager::RetransmitRtoPackets() {
 661   LOG_IF(DFATAL, pending_timer_transmission_count_ > 0)
 662       << "Retransmissions already queued:" << pending_timer_transmission_count_;
 663   // Mark two packets for retransmission.
 664   QuicPacketNumber packet_number = unacked_packets_.GetLeastUnacked();
 665   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 666        it != unacked_packets_.end(); ++it, ++packet_number) {
 667     if (it->retransmittable_frames != nullptr &&
 668         pending_timer_transmission_count_ < kMaxRetransmissionsOnTimeout) {
 669       MarkForRetransmission(packet_number, RTO_RETRANSMISSION);
 670       ++pending_timer_transmission_count_;
 671     }
 672     // Abandon non-retransmittable data that's in flight to ensure it doesn't
 673     // fill up the congestion window.
 674     if (it->retransmittable_frames == nullptr && it->in_flight &&
 675         it->all_transmissions == nullptr) {
 676       unacked_packets_.RemoveFromInFlight(packet_number);
 677     }
 678   }
 679   if (pending_timer_transmission_count_ > 0) {
 680     if (consecutive_rto_count_ == 0) {
 681       first_rto_transmission_ = unacked_packets_.largest_sent_packet() + 1;
 682     }
 683     ++consecutive_rto_count_;
 684   }
 685 }
 686
 687 QuicSentPacketManager::RetransmissionTimeoutMode
 688     QuicSentPacketManager::GetRetransmissionMode() const {
 689   DCHECK(unacked_packets_.HasInFlightPackets());
 690   if (!handshake_confirmed_ && unacked_packets_.HasPendingCryptoPackets()) {
 691     return HANDSHAKE_MODE;
 692   }
 693   if (loss_algorithm_->GetLossTimeout() != QuicTime::Zero()) {
 694     return LOSS_MODE;
 695   }
 696   if (consecutive_tlp_count_ < max_tail_loss_probes_) {
 697     if (unacked_packets_.HasUnackedRetransmittableFrames()) {
 698       return TLP_MODE;
 699     }
 700   }
 701   return RTO_MODE;
 702 }
 703
 704 void QuicSentPacketManager::InvokeLossDetection(QuicTime time) {
 705   PacketNumberSet lost_packets = loss_algorithm_->DetectLostPackets(
 706       unacked_packets_, time, unacked_packets_.largest_observed(), rtt_stats_);
 707   for (PacketNumberSet::const_iterator it = lost_packets.begin();
 708        it != lost_packets.end(); ++it) {
 709     QuicPacketNumber packet_number = *it;
 710     const TransmissionInfo& transmission_info =
 711         unacked_packets_.GetTransmissionInfo(packet_number);
 712     // TODO(ianswett): If it's expected the FEC packet may repair the loss, it
 713     // should be recorded as a loss to the send algorithm, but not retransmitted
 714     // until it's known whether the FEC packet arrived.
 715     ++stats_->packets_lost;
 716     packets_lost_.push_back(std::make_pair(packet_number, transmission_info));
 717     DVLOG(1) << ENDPOINT << "Lost packet " << packet_number;
 718
 719     if (transmission_info.retransmittable_frames != nullptr) {
 720       MarkForRetransmission(packet_number, LOSS_RETRANSMISSION);
 721     } else {
 722       // Since we will not retransmit this, we need to remove it from
 723       // unacked_packets_.   This is either the current transmission of
 724       // a packet whose previous transmission has been acked, a packet that has
 725       // been TLP retransmitted, or an FEC packet.
 726       unacked_packets_.RemoveFromInFlight(packet_number);
 727     }
 728   }
 729 }
 730
 731 bool QuicSentPacketManager::MaybeUpdateRTT(
 732     const QuicAckFrame& ack_frame,
 733     const QuicTime& ack_receive_time) {
 734   // We rely on delta_time_largest_observed to compute an RTT estimate, so we
 735   // only update rtt when the largest observed gets acked.
 736   // NOTE: If ack is a truncated ack, then the largest observed is in fact
 737   // unacked, and may cause an RTT sample to be taken.
 738   if (!unacked_packets_.IsUnacked(ack_frame.largest_observed)) {
 739     return false;
 740   }
 741   // We calculate the RTT based on the highest ACKed packet number, the lower
 742   // packet numbers will include the ACK aggregation delay.
 743   const TransmissionInfo& transmission_info =
 744       unacked_packets_.GetTransmissionInfo(ack_frame.largest_observed);
 745   // Ensure the packet has a valid sent time.
 746   if (transmission_info.sent_time == QuicTime::Zero()) {
 747     LOG(DFATAL) << "Acked packet has zero sent time, largest_observed:"
 748                 << ack_frame.largest_observed;
 749     return false;
 750   }
 751
 752   QuicTime::Delta send_delta =
 753       ack_receive_time.Subtract(transmission_info.sent_time);
 754   rtt_stats_.UpdateRtt(
 755       send_delta, ack_frame.delta_time_largest_observed, ack_receive_time);
 756
 757   if (network_change_visitor_ != nullptr) {
 758     network_change_visitor_->OnRttChange();
 759   }
 760
 761   return true;
 762 }
 763
 764 QuicTime::Delta QuicSentPacketManager::TimeUntilSend(
 765     QuicTime now,
 766     HasRetransmittableData retransmittable) {
 767   // The TLP logic is entirely contained within QuicSentPacketManager, so the
 768   // send algorithm does not need to be consulted.
 769   if (pending_timer_transmission_count_ > 0) {
 770     return QuicTime::Delta::Zero();
 771   }
 772   return send_algorithm_->TimeUntilSend(
 773       now, unacked_packets_.bytes_in_flight(), retransmittable);
 774 }
 775
 776 // Uses a 25ms delayed ack timer. Also helps with better signaling
 777 // in low-bandwidth (< ~384 kbps), where an ack is sent per packet.
 778 // Ensures that the Delayed Ack timer is always set to a value lesser
 779 // than the retransmission timer's minimum value (MinRTO). We want the
 780 // delayed ack to get back to the QUIC peer before the sender's
 781 // retransmission timer triggers.  Since we do not know the
 782 // reverse-path one-way delay, we assume equal delays for forward and
 783 // reverse paths, and ensure that the timer is set to less than half
 784 // of the MinRTO.
 785 // There may be a value in making this delay adaptive with the help of
 786 // the sender and a signaling mechanism -- if the sender uses a
 787 // different MinRTO, we may get spurious retransmissions. May not have
 788 // any benefits, but if the delayed ack becomes a significant source
 789 // of (likely, tail) latency, then consider such a mechanism.
 790 const QuicTime::Delta QuicSentPacketManager::DelayedAckTime() const {
 791   return QuicTime::Delta::FromMilliseconds(min(kMaxDelayedAckTimeMs,
 792                                                kMinRetransmissionTimeMs / 2));
 793 }
 794
 795 const QuicTime QuicSentPacketManager::GetRetransmissionTime() const {
 796   // Don't set the timer if there are no packets in flight or we've already
 797   // queued a tlp transmission and it hasn't been sent yet.
 798   if (!unacked_packets_.HasInFlightPackets() ||
 799       pending_timer_transmission_count_ > 0) {
 800     return QuicTime::Zero();
 801   }
 802   switch (GetRetransmissionMode()) {
 803     case HANDSHAKE_MODE:
 804       return clock_->ApproximateNow().Add(GetCryptoRetransmissionDelay());
 805     case LOSS_MODE:
 806       return loss_algorithm_->GetLossTimeout();
 807     case TLP_MODE: {
 808       // TODO(ianswett): When CWND is available, it would be preferable to
 809       // set the timer based on the earliest retransmittable packet.
 810       // Base the updated timer on the send time of the last packet.
 811       const QuicTime sent_time = unacked_packets_.GetLastPacketSentTime();
 812       const QuicTime tlp_time = sent_time.Add(GetTailLossProbeDelay());
 813       // Ensure the TLP timer never gets set to a time in the past.
 814       return QuicTime::Max(clock_->ApproximateNow(), tlp_time);
 815     }
 816     case RTO_MODE: {
 817       // The RTO is based on the first outstanding packet.
 818       const QuicTime sent_time = unacked_packets_.GetLastPacketSentTime();
 819       QuicTime rto_time = sent_time.Add(GetRetransmissionDelay());
 820       // Wait for TLP packets to be acked before an RTO fires.
 821       QuicTime tlp_time =
 822           unacked_packets_.GetLastPacketSentTime().Add(GetTailLossProbeDelay());
 823       return QuicTime::Max(tlp_time, rto_time);
 824     }
 825   }
 826   DCHECK(false);
 827   return QuicTime::Zero();
 828 }
 829
 830 const QuicTime::Delta QuicSentPacketManager::GetCryptoRetransmissionDelay()
 831     const {
 832   // This is equivalent to the TailLossProbeDelay, but slightly more aggressive
 833   // because crypto handshake messages don't incur a delayed ack time.
 834   QuicTime::Delta srtt = rtt_stats_.smoothed_rtt();
 835   if (srtt.IsZero()) {
 836     srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us());
 837   }
 838   int64 delay_ms = max(kMinHandshakeTimeoutMs,
 839                        static_cast<int64>(1.5 * srtt.ToMilliseconds()));
 840   return QuicTime::Delta::FromMilliseconds(
 841       delay_ms << consecutive_crypto_retransmission_count_);
 842 }
 843
 844 const QuicTime::Delta QuicSentPacketManager::GetTailLossProbeDelay() const {
 845   QuicTime::Delta srtt = rtt_stats_.smoothed_rtt();
 846   if (srtt.IsZero()) {
 847     srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us());
 848   }
 849   if (enable_half_rtt_tail_loss_probe_ && consecutive_tlp_count_ == 0u) {
 850     return QuicTime::Delta::FromMilliseconds(
 851         max(kMinTailLossProbeTimeoutMs,
 852             static_cast<int64>(0.5 * srtt.ToMilliseconds())));
 853   }
 854   if (!unacked_packets_.HasMultipleInFlightPackets()) {
 855     return QuicTime::Delta::Max(
 856         srtt.Multiply(2), srtt.Multiply(1.5).Add(
 857             QuicTime::Delta::FromMilliseconds(kMinRetransmissionTimeMs / 2)));
 858   }
 859   return QuicTime::Delta::FromMilliseconds(
 860       max(kMinTailLossProbeTimeoutMs,
 861           static_cast<int64>(2 * srtt.ToMilliseconds())));
 862 }
 863
 864 const QuicTime::Delta QuicSentPacketManager::GetRetransmissionDelay() const {
 865   QuicTime::Delta retransmission_delay = send_algorithm_->RetransmissionDelay();
 866   if (retransmission_delay.IsZero()) {
 867     // We are in the initial state, use default timeout values.
 868     retransmission_delay =
 869         QuicTime::Delta::FromMilliseconds(kDefaultRetransmissionTimeMs);
 870   } else if (retransmission_delay.ToMilliseconds() < kMinRetransmissionTimeMs) {
 871     retransmission_delay =
 872         QuicTime::Delta::FromMilliseconds(kMinRetransmissionTimeMs);
 873   }
 874
 875   // Calculate exponential back off.
 876   retransmission_delay = retransmission_delay.Multiply(
 877       1 << min<size_t>(consecutive_rto_count_, kMaxRetransmissions));
 878
 879   if (retransmission_delay.ToMilliseconds() > kMaxRetransmissionTimeMs) {
 880     return QuicTime::Delta::FromMilliseconds(kMaxRetransmissionTimeMs);
 881   }
 882   return retransmission_delay;
 883 }
 884
 885 const RttStats* QuicSentPacketManager::GetRttStats() const {
 886   return &rtt_stats_;
 887 }
 888
 889 QuicBandwidth QuicSentPacketManager::BandwidthEstimate() const {
 890   // TODO(ianswett): Remove BandwidthEstimate from SendAlgorithmInterface
 891   // and implement the logic here.
 892   return send_algorithm_->BandwidthEstimate();
 893 }
 894
 895 const QuicSustainedBandwidthRecorder&
 896 QuicSentPacketManager::SustainedBandwidthRecorder() const {
 897   return sustained_bandwidth_recorder_;
 898 }
 899
 900 QuicPacketCount QuicSentPacketManager::EstimateMaxPacketsInFlight(
 901     QuicByteCount max_packet_length) const {
 902   return send_algorithm_->GetCongestionWindow() / max_packet_length;
 903 }
 904
 905 QuicPacketCount QuicSentPacketManager::GetCongestionWindowInTcpMss() const {
 906   return send_algorithm_->GetCongestionWindow() / kDefaultTCPMSS;
 907 }
 908
 909 QuicByteCount QuicSentPacketManager::GetCongestionWindowInBytes() const {
 910   return send_algorithm_->GetCongestionWindow();
 911 }
 912
 913 QuicPacketCount QuicSentPacketManager::GetSlowStartThresholdInTcpMss() const {
 914   return send_algorithm_->GetSlowStartThreshold() / kDefaultTCPMSS;
 915 }
 916
 917 void QuicSentPacketManager::OnSerializedPacket(
 918     const SerializedPacket& serialized_packet) {
 919   ack_notifier_manager_.OnSerializedPacket(serialized_packet);
 920 }
 921
 922 void QuicSentPacketManager::CancelRetransmissionsForStream(
 923     QuicStreamId stream_id) {
 924   unacked_packets_.CancelRetransmissionsForStream(stream_id);
 925   PendingRetransmissionMap::iterator it = pending_retransmissions_.begin();
 926   while (it != pending_retransmissions_.end()) {
 927     if (HasRetransmittableFrames(it->first)) {
 928       ++it;
 929       continue;
 930     }
 931     it = pending_retransmissions_.erase(it);
 932   }
 933 }
 934
 935 void QuicSentPacketManager::EnablePacing() {
 936   // TODO(ianswett): Replace with a method which wraps the send algorithm in a
 937   // pacer every time a new algorithm is set.
 938   if (using_pacing_) {
 939     return;
 940   }
 941
 942   // Set up a pacing sender with a 1 millisecond alarm granularity, the same as
 943   // the default granularity of the Linux kernel's FQ qdisc.
 944   using_pacing_ = true;
 945   send_algorithm_.reset(
 946       new PacingSender(send_algorithm_.release(),
 947                        QuicTime::Delta::FromMilliseconds(1),
 948                        kInitialUnpacedBurst));
 949 }
 950
 951 }  // namespace net