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