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/quic_ack_notifier_manager.h"
  14 #include "net/quic/quic_connection_stats.h"
  15 #include "net/quic/quic_flags.h"
  16 #include "net/quic/quic_utils_chromium.h"
  17
  18 using std::max;
  19 using std::min;
  20
  21 namespace net {
  22
  23 // The length of the recent min rtt window in seconds. Windowing is disabled for
  24 // values less than or equal to 0.
  25 int32 FLAGS_quic_recent_min_rtt_window_s = 60;
  26
  27 namespace {
  28 static const int64 kDefaultRetransmissionTimeMs = 500;
  29 // TCP RFC calls for 1 second RTO however Linux differs from this default and
  30 // define the minimum RTO to 200ms, we will use the same until we have data to
  31 // support a higher or lower value.
  32 static const int64 kMinRetransmissionTimeMs = 200;
  33 static const int64 kMaxRetransmissionTimeMs = 60000;
  34 // Maximum number of exponential backoffs used for RTO timeouts.
  35 static const size_t kMaxRetransmissions = 10;
  36 // Maximum number of packets retransmitted upon an RTO.
  37 static const size_t kMaxRetransmissionsOnTimeout = 2;
  38
  39 // Ensure the handshake timer isnt't faster than 10ms.
  40 // This limits the tenth retransmitted packet to 10s after the initial CHLO.
  41 static const int64 kMinHandshakeTimeoutMs = 10;
  42
  43 // Sends up to two tail loss probes before firing an RTO,
  44 // per draft RFC draft-dukkipati-tcpm-tcp-loss-probe.
  45 static const size_t kDefaultMaxTailLossProbes = 2;
  46 static const int64 kMinTailLossProbeTimeoutMs = 10;
  47
  48 // Number of samples before we force a new recent min rtt to be captured.
  49 static const size_t kNumMinRttSamplesAfterQuiescence = 2;
  50
  51 // Number of unpaced packets to send after quiescence.
  52 static const size_t kInitialUnpacedBurst = 10;
  53
  54 // Fraction of the receive buffer that can be used for encrypted bytes.
  55 // Allows a 5% overhead for IP and UDP framing, as well as ack only packets.
  56 static const float kUsableRecieveBufferFraction = 0.95f;
  57
  58 bool HasCryptoHandshake(const TransmissionInfo& transmission_info) {
  59   if (transmission_info.retransmittable_frames == nullptr) {
  60     return false;
  61   }
  62   return transmission_info.retransmittable_frames->HasCryptoHandshake() ==
  63       IS_HANDSHAKE;
  64 }
  65
  66 }  // namespace
  67
  68 #define ENDPOINT (is_server_ ? "Server: " : " Client: ")
  69
  70 QuicSentPacketManager::QuicSentPacketManager(
  71     bool is_server,
  72     const QuicClock* clock,
  73     QuicConnectionStats* stats,
  74     CongestionControlType congestion_control_type,
  75     LossDetectionType loss_type,
  76     bool is_secure)
  77     : unacked_packets_(),
  78       is_server_(is_server),
  79       clock_(clock),
  80       stats_(stats),
  81       debug_delegate_(nullptr),
  82       network_change_visitor_(nullptr),
  83       initial_congestion_window_(is_secure ? kInitialCongestionWindowSecure
  84                                            : kInitialCongestionWindowInsecure),
  85       send_algorithm_(
  86           SendAlgorithmInterface::Create(clock,
  87                                          &rtt_stats_,
  88                                          congestion_control_type,
  89                                          stats,
  90                                          initial_congestion_window_)),
  91       loss_algorithm_(LossDetectionInterface::Create(loss_type)),
  92       n_connection_simulation_(false),
  93       receive_buffer_bytes_(kDefaultSocketReceiveBuffer),
  94       least_packet_awaited_by_peer_(1),
  95       first_rto_transmission_(0),
  96       consecutive_rto_count_(0),
  97       consecutive_tlp_count_(0),
  98       consecutive_crypto_retransmission_count_(0),
  99       pending_timer_transmission_count_(0),
 100       max_tail_loss_probes_(kDefaultMaxTailLossProbes),
 101       using_pacing_(false),
 102       use_new_rto_(false),
 103       handshake_confirmed_(false) {
 104 }
 105
 106 QuicSentPacketManager::~QuicSentPacketManager() {
 107 }
 108
 109 void QuicSentPacketManager::SetFromConfig(const QuicConfig& config) {
 110   if (config.HasReceivedInitialRoundTripTimeUs() &&
 111       config.ReceivedInitialRoundTripTimeUs() > 0) {
 112     rtt_stats_.set_initial_rtt_us(
 113         max(kMinInitialRoundTripTimeUs,
 114             min(kMaxInitialRoundTripTimeUs,
 115                 config.ReceivedInitialRoundTripTimeUs())));
 116   } else if (config.HasInitialRoundTripTimeUsToSend() &&
 117              config.GetInitialRoundTripTimeUsToSend() > 0) {
 118     rtt_stats_.set_initial_rtt_us(
 119         max(kMinInitialRoundTripTimeUs,
 120             min(kMaxInitialRoundTripTimeUs,
 121                 config.GetInitialRoundTripTimeUsToSend())));
 122   }
 123   // Initial RTT may have changed.
 124   if (network_change_visitor_ != nullptr) {
 125     network_change_visitor_->OnRttChange();
 126   }
 127   // TODO(ianswett): BBR is currently a server only feature.
 128   if (FLAGS_quic_allow_bbr &&
 129       config.HasReceivedConnectionOptions() &&
 130       ContainsQuicTag(config.ReceivedConnectionOptions(), kTBBR)) {
 131     if (FLAGS_quic_recent_min_rtt_window_s > 0) {
 132       rtt_stats_.set_recent_min_rtt_window(
 133           QuicTime::Delta::FromSeconds(FLAGS_quic_recent_min_rtt_window_s));
 134     }
 135     send_algorithm_.reset(SendAlgorithmInterface::Create(
 136         clock_, &rtt_stats_, kBBR, stats_, initial_congestion_window_));
 137   }
 138   if (config.HasReceivedConnectionOptions() &&
 139       ContainsQuicTag(config.ReceivedConnectionOptions(), kRENO)) {
 140     send_algorithm_.reset(SendAlgorithmInterface::Create(
 141         clock_, &rtt_stats_, kReno, stats_, initial_congestion_window_));
 142   }
 143   if (HasClientSentConnectionOption(config, kPACE) ||
 144       FLAGS_quic_enable_pacing ||
 145       (FLAGS_quic_allow_bbr && HasClientSentConnectionOption(config, kTBBR))) {
 146     EnablePacing();
 147   }
 148   if (HasClientSentConnectionOption(config, k1CON)) {
 149     send_algorithm_->SetNumEmulatedConnections(1);
 150   }
 151   if (HasClientSentConnectionOption(config, kNCON)) {
 152     n_connection_simulation_ = true;
 153   }
 154   if (HasClientSentConnectionOption(config, kNTLP)) {
 155     max_tail_loss_probes_ = 0;
 156   }
 157   if (HasClientSentConnectionOption(config, kNRTO)) {
 158     use_new_rto_ = true;
 159   }
 160   if (config.HasReceivedConnectionOptions() &&
 161       ContainsQuicTag(config.ReceivedConnectionOptions(), kTIME)) {
 162     loss_algorithm_.reset(LossDetectionInterface::Create(kTime));
 163   }
 164   if (config.HasReceivedSocketReceiveBuffer()) {
 165     receive_buffer_bytes_ =
 166         max(kMinSocketReceiveBuffer,
 167             static_cast<QuicByteCount>(config.ReceivedSocketReceiveBuffer()));
 168   }
 169   send_algorithm_->SetFromConfig(config, is_server_, using_pacing_);
 170
 171   if (network_change_visitor_ != nullptr) {
 172     network_change_visitor_->OnCongestionWindowChange();
 173   }
 174 }
 175
 176 bool QuicSentPacketManager::ResumeConnectionState(
 177     const CachedNetworkParameters& cached_network_params) {
 178   if (cached_network_params.has_min_rtt_ms()) {
 179     uint32 initial_rtt_us =
 180         kNumMicrosPerMilli * cached_network_params.min_rtt_ms();
 181     rtt_stats_.set_initial_rtt_us(
 182         max(kMinInitialRoundTripTimeUs,
 183             min(kMaxInitialRoundTripTimeUs, initial_rtt_us)));
 184   }
 185   return send_algorithm_->ResumeConnectionState(cached_network_params);
 186 }
 187
 188 void QuicSentPacketManager::SetNumOpenStreams(size_t num_streams) {
 189   if (n_connection_simulation_) {
 190     // Ensure the number of connections is between 1 and 5.
 191     send_algorithm_->SetNumEmulatedConnections(
 192         min<size_t>(5, max<size_t>(1, num_streams)));
 193   }
 194 }
 195
 196 bool QuicSentPacketManager::HasClientSentConnectionOption(
 197     const QuicConfig& config, QuicTag tag) const {
 198   if (is_server_) {
 199     if (config.HasReceivedConnectionOptions() &&
 200         ContainsQuicTag(config.ReceivedConnectionOptions(), tag)) {
 201       return true;
 202     }
 203   } else if (config.HasSendConnectionOptions() &&
 204              ContainsQuicTag(config.SendConnectionOptions(), tag)) {
 205     return true;
 206   }
 207   return false;
 208 }
 209
 210 void QuicSentPacketManager::OnIncomingAck(const QuicAckFrame& ack_frame,
 211                                           QuicTime ack_receive_time) {
 212   QuicByteCount bytes_in_flight = unacked_packets_.bytes_in_flight();
 213
 214   UpdatePacketInformationReceivedByPeer(ack_frame);
 215   bool rtt_updated = MaybeUpdateRTT(ack_frame, ack_receive_time);
 216   DCHECK_GE(ack_frame.largest_observed, unacked_packets_.largest_observed());
 217   unacked_packets_.IncreaseLargestObserved(ack_frame.largest_observed);
 218
 219   HandleAckForSentPackets(ack_frame);
 220   InvokeLossDetection(ack_receive_time);
 221   // Ignore losses in RTO mode.
 222   if (consecutive_rto_count_ > 0 && !use_new_rto_) {
 223     packets_lost_.clear();
 224   }
 225   MaybeInvokeCongestionEvent(rtt_updated, bytes_in_flight);
 226   unacked_packets_.RemoveObsoletePackets();
 227
 228   sustained_bandwidth_recorder_.RecordEstimate(
 229       send_algorithm_->InRecovery(),
 230       send_algorithm_->InSlowStart(),
 231       send_algorithm_->BandwidthEstimate(),
 232       ack_receive_time,
 233       clock_->WallNow(),
 234       rtt_stats_.smoothed_rtt());
 235
 236   // If we have received a truncated ack, then we need to clear out some
 237   // previous transmissions to allow the peer to actually ACK new packets.
 238   if (ack_frame.is_truncated) {
 239     unacked_packets_.ClearAllPreviousRetransmissions();
 240   }
 241
 242   // Anytime we are making forward progress and have a new RTT estimate, reset
 243   // the backoff counters.
 244   if (rtt_updated) {
 245     if (consecutive_rto_count_ > 0) {
 246       // If the ack acknowledges data sent prior to the RTO,
 247       // the RTO was spurious.
 248       if (ack_frame.largest_observed < first_rto_transmission_) {
 249         // Replace SRTT with latest_rtt and increase the variance to prevent
 250         // a spurious RTO from happening again.
 251         rtt_stats_.ExpireSmoothedMetrics();
 252       } else {
 253         if (!use_new_rto_) {
 254           send_algorithm_->OnRetransmissionTimeout(true);
 255         }
 256       }
 257     }
 258     // Reset all retransmit counters any time a new packet is acked.
 259     consecutive_rto_count_ = 0;
 260     consecutive_tlp_count_ = 0;
 261     consecutive_crypto_retransmission_count_ = 0;
 262   }
 263
 264   if (debug_delegate_ != nullptr) {
 265     debug_delegate_->OnIncomingAck(ack_frame, ack_receive_time,
 266                                    unacked_packets_.largest_observed(),
 267                                    rtt_updated, GetLeastUnacked());
 268   }
 269 }
 270
 271 void QuicSentPacketManager::UpdatePacketInformationReceivedByPeer(
 272     const QuicAckFrame& ack_frame) {
 273   if (ack_frame.missing_packets.empty()) {
 274     least_packet_awaited_by_peer_ = ack_frame.largest_observed + 1;
 275   } else {
 276     least_packet_awaited_by_peer_ = *(ack_frame.missing_packets.begin());
 277   }
 278 }
 279
 280 void QuicSentPacketManager::MaybeInvokeCongestionEvent(
 281     bool rtt_updated, QuicByteCount bytes_in_flight) {
 282   if (!rtt_updated && packets_acked_.empty() && packets_lost_.empty()) {
 283     return;
 284   }
 285   send_algorithm_->OnCongestionEvent(rtt_updated, bytes_in_flight,
 286                                      packets_acked_, packets_lost_);
 287   packets_acked_.clear();
 288   packets_lost_.clear();
 289   if (network_change_visitor_ != nullptr) {
 290     network_change_visitor_->OnCongestionWindowChange();
 291   }
 292 }
 293
 294 void QuicSentPacketManager::HandleAckForSentPackets(
 295     const QuicAckFrame& ack_frame) {
 296   // Go through the packets we have not received an ack for and see if this
 297   // incoming_ack shows they've been seen by the peer.
 298   QuicTime::Delta delta_largest_observed =
 299       ack_frame.delta_time_largest_observed;
 300   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 301   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 302        it != unacked_packets_.end(); ++it, ++sequence_number) {
 303     if (sequence_number > ack_frame.largest_observed) {
 304       // These packets are still in flight.
 305       break;
 306     }
 307
 308     if (ContainsKey(ack_frame.missing_packets, sequence_number)) {
 309       // Don't continue to increase the nack count for packets not in flight.
 310       if (!it->in_flight) {
 311         continue;
 312       }
 313       // Consider it multiple nacks when there is a gap between the missing
 314       // packet and the largest observed, since the purpose of a nack
 315       // threshold is to tolerate re-ordering.  This handles both StretchAcks
 316       // and Forward Acks.
 317       // The nack count only increases when the largest observed increases.
 318       QuicPacketCount min_nacks = ack_frame.largest_observed - sequence_number;
 319       // Truncated acks can nack the largest observed, so use a min of 1.
 320       if (min_nacks == 0) {
 321         min_nacks = 1;
 322       }
 323       unacked_packets_.NackPacket(sequence_number, min_nacks);
 324       continue;
 325     }
 326     // Packet was acked, so remove it from our unacked packet list.
 327     DVLOG(1) << ENDPOINT << "Got an ack for packet " << sequence_number;
 328     // If data is associated with the most recent transmission of this
 329     // packet, then inform the caller.
 330     if (it->in_flight) {
 331       packets_acked_.push_back(std::make_pair(sequence_number, *it));
 332     }
 333     MarkPacketHandled(sequence_number, *it, delta_largest_observed);
 334   }
 335
 336   // Discard any retransmittable frames associated with revived packets.
 337   for (SequenceNumberSet::const_iterator revived_it =
 338            ack_frame.revived_packets.begin();
 339        revived_it != ack_frame.revived_packets.end(); ++revived_it) {
 340     MarkPacketRevived(*revived_it, delta_largest_observed);
 341   }
 342 }
 343
 344 bool QuicSentPacketManager::HasRetransmittableFrames(
 345     QuicPacketSequenceNumber sequence_number) const {
 346   return unacked_packets_.HasRetransmittableFrames(sequence_number);
 347 }
 348
 349 void QuicSentPacketManager::RetransmitUnackedPackets(
 350     TransmissionType retransmission_type) {
 351   DCHECK(retransmission_type == ALL_UNACKED_RETRANSMISSION ||
 352          retransmission_type == ALL_INITIAL_RETRANSMISSION);
 353   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 354   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 355        it != unacked_packets_.end(); ++it, ++sequence_number) {
 356     const RetransmittableFrames* frames = it->retransmittable_frames;
 357     if (frames != nullptr &&
 358         (retransmission_type == ALL_UNACKED_RETRANSMISSION ||
 359          frames->encryption_level() == ENCRYPTION_INITIAL)) {
 360       MarkForRetransmission(sequence_number, retransmission_type);
 361     } else if (it->is_fec_packet) {
 362       // Remove FEC packets from the packet map, since we can't retransmit them.
 363       unacked_packets_.RemoveFromInFlight(sequence_number);
 364     }
 365   }
 366 }
 367
 368 void QuicSentPacketManager::NeuterUnencryptedPackets() {
 369   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 370   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 371        it != unacked_packets_.end(); ++it, ++sequence_number) {
 372     const RetransmittableFrames* frames = it->retransmittable_frames;
 373     if (frames != nullptr && frames->encryption_level() == ENCRYPTION_NONE) {
 374       // Once you're forward secure, no unencrypted packets will be sent, crypto
 375       // or otherwise. Unencrypted packets are neutered and abandoned, to ensure
 376       // they are not retransmitted or considered lost from a congestion control
 377       // perspective.
 378       pending_retransmissions_.erase(sequence_number);
 379       unacked_packets_.RemoveFromInFlight(sequence_number);
 380       unacked_packets_.RemoveRetransmittability(sequence_number);
 381     }
 382   }
 383 }
 384
 385 void QuicSentPacketManager::MarkForRetransmission(
 386     QuicPacketSequenceNumber sequence_number,
 387     TransmissionType transmission_type) {
 388   const TransmissionInfo& transmission_info =
 389       unacked_packets_.GetTransmissionInfo(sequence_number);
 390   LOG_IF(DFATAL, transmission_info.retransmittable_frames == nullptr);
 391   // Both TLP and the new RTO leave the packets in flight and let the loss
 392   // detection decide if packets are lost.
 393   if (transmission_type != TLP_RETRANSMISSION &&
 394       transmission_type != RTO_RETRANSMISSION) {
 395     unacked_packets_.RemoveFromInFlight(sequence_number);
 396   }
 397   // TODO(ianswett): Currently the RTO can fire while there are pending NACK
 398   // retransmissions for the same data, which is not ideal.
 399   if (ContainsKey(pending_retransmissions_, sequence_number)) {
 400     return;
 401   }
 402
 403   pending_retransmissions_[sequence_number] = transmission_type;
 404 }
 405
 406 void QuicSentPacketManager::RecordSpuriousRetransmissions(
 407     const SequenceNumberList& all_transmissions,
 408     QuicPacketSequenceNumber acked_sequence_number) {
 409   for (SequenceNumberList::const_reverse_iterator it =
 410            all_transmissions.rbegin();
 411        it != all_transmissions.rend() && *it > acked_sequence_number; ++it) {
 412     const TransmissionInfo& retransmit_info =
 413         unacked_packets_.GetTransmissionInfo(*it);
 414
 415     stats_->bytes_spuriously_retransmitted += retransmit_info.bytes_sent;
 416     ++stats_->packets_spuriously_retransmitted;
 417     if (debug_delegate_ != nullptr) {
 418       debug_delegate_->OnSpuriousPacketRetransmission(
 419           retransmit_info.transmission_type, retransmit_info.bytes_sent);
 420     }
 421   }
 422 }
 423
 424 bool QuicSentPacketManager::HasPendingRetransmissions() const {
 425   return !pending_retransmissions_.empty();
 426 }
 427
 428 QuicSentPacketManager::PendingRetransmission
 429     QuicSentPacketManager::NextPendingRetransmission() {
 430   LOG_IF(DFATAL, pending_retransmissions_.empty())
 431       << "Unexpected call to PendingRetransmissions() with empty pending "
 432       << "retransmission list. Corrupted memory usage imminent.";
 433   QuicPacketSequenceNumber sequence_number =
 434       pending_retransmissions_.begin()->first;
 435   TransmissionType transmission_type = pending_retransmissions_.begin()->second;
 436   if (unacked_packets_.HasPendingCryptoPackets()) {
 437     // Ensure crypto packets are retransmitted before other packets.
 438     for (const auto& pair : pending_retransmissions_) {
 439       if (HasCryptoHandshake(
 440               unacked_packets_.GetTransmissionInfo(pair.first))) {
 441         sequence_number = pair.first;
 442         transmission_type = pair.second;
 443         break;
 444       }
 445     }
 446   }
 447   DCHECK(unacked_packets_.IsUnacked(sequence_number)) << sequence_number;
 448   const TransmissionInfo& transmission_info =
 449       unacked_packets_.GetTransmissionInfo(sequence_number);
 450   DCHECK(transmission_info.retransmittable_frames);
 451
 452   return PendingRetransmission(sequence_number,
 453                                transmission_type,
 454                                *transmission_info.retransmittable_frames,
 455                                transmission_info.sequence_number_length);
 456 }
 457
 458 void QuicSentPacketManager::MarkPacketRevived(
 459     QuicPacketSequenceNumber sequence_number,
 460     QuicTime::Delta delta_largest_observed) {
 461   if (!unacked_packets_.IsUnacked(sequence_number)) {
 462     return;
 463   }
 464
 465   const TransmissionInfo& transmission_info =
 466       unacked_packets_.GetTransmissionInfo(sequence_number);
 467   QuicPacketSequenceNumber newest_transmission =
 468       transmission_info.all_transmissions == nullptr
 469           ? sequence_number
 470           : *transmission_info.all_transmissions->rbegin();
 471   // This packet has been revived at the receiver. If we were going to
 472   // retransmit it, do not retransmit it anymore.
 473   pending_retransmissions_.erase(newest_transmission);
 474
 475   // The AckNotifierManager needs to be notified for revived packets,
 476   // since it indicates the packet arrived from the appliction's perspective.
 477   ack_notifier_manager_.OnPacketAcked(newest_transmission,
 478                                       delta_largest_observed);
 479
 480   unacked_packets_.RemoveRetransmittability(sequence_number);
 481 }
 482
 483 void QuicSentPacketManager::MarkPacketHandled(
 484     QuicPacketSequenceNumber sequence_number,
 485     const TransmissionInfo& info,
 486     QuicTime::Delta delta_largest_observed) {
 487   QuicPacketSequenceNumber newest_transmission =
 488       info.all_transmissions == nullptr ?
 489           sequence_number : *info.all_transmissions->rbegin();
 490   // Remove the most recent packet, if it is pending retransmission.
 491   pending_retransmissions_.erase(newest_transmission);
 492
 493   // The AckNotifierManager needs to be notified about the most recent
 494   // transmission, since that's the one only one it tracks.
 495   ack_notifier_manager_.OnPacketAcked(newest_transmission,
 496                                       delta_largest_observed);
 497   if (newest_transmission != sequence_number) {
 498     RecordSpuriousRetransmissions(*info.all_transmissions, sequence_number);
 499     // Remove the most recent packet from flight if it's a crypto handshake
 500     // packet, since they won't be acked now that one has been processed.
 501     // Other crypto handshake packets won't be in flight, only the newest
 502     // transmission of a crypto packet is in flight at once.
 503     // TODO(ianswett): Instead of handling all crypto packets special,
 504     // only handle nullptr encrypted packets in a special way.
 505     if (HasCryptoHandshake(
 506         unacked_packets_.GetTransmissionInfo(newest_transmission))) {
 507       unacked_packets_.RemoveFromInFlight(newest_transmission);
 508     }
 509   }
 510
 511   unacked_packets_.RemoveFromInFlight(sequence_number);
 512   unacked_packets_.RemoveRetransmittability(sequence_number);
 513 }
 514
 515 bool QuicSentPacketManager::IsUnacked(
 516     QuicPacketSequenceNumber sequence_number) const {
 517   return unacked_packets_.IsUnacked(sequence_number);
 518 }
 519
 520 bool QuicSentPacketManager::HasUnackedPackets() const {
 521   return unacked_packets_.HasUnackedPackets();
 522 }
 523
 524 QuicPacketSequenceNumber
 525 QuicSentPacketManager::GetLeastUnacked() const {
 526   return unacked_packets_.GetLeastUnacked();
 527 }
 528
 529 bool QuicSentPacketManager::OnPacketSent(
 530     SerializedPacket* serialized_packet,
 531     QuicPacketSequenceNumber original_sequence_number,
 532     QuicTime sent_time,
 533     QuicByteCount bytes,
 534     TransmissionType transmission_type,
 535     HasRetransmittableData has_retransmittable_data) {
 536   QuicPacketSequenceNumber sequence_number = serialized_packet->sequence_number;
 537   DCHECK_LT(0u, sequence_number);
 538   DCHECK(!unacked_packets_.IsUnacked(sequence_number));
 539   LOG_IF(DFATAL, bytes == 0) << "Cannot send empty packets.";
 540
 541   if (original_sequence_number != 0) {
 542     PendingRetransmissionMap::iterator it =
 543         pending_retransmissions_.find(original_sequence_number);
 544     if (it != pending_retransmissions_.end()) {
 545       pending_retransmissions_.erase(it);
 546     } else {
 547       DLOG(DFATAL) << "Expected sequence number to be in "
 548                    << "pending_retransmissions_.  sequence_number: "
 549                    << original_sequence_number;
 550     }
 551     // Inform the ack notifier of retransmissions so it can calculate the
 552     // retransmit rate.
 553     ack_notifier_manager_.OnPacketRetransmitted(original_sequence_number,
 554                                                 sequence_number, bytes);
 555   }
 556
 557   if (pending_timer_transmission_count_ > 0) {
 558     --pending_timer_transmission_count_;
 559   }
 560
 561   if (unacked_packets_.bytes_in_flight() == 0) {
 562     // TODO(ianswett): Consider being less aggressive to force a new
 563     // recent_min_rtt, likely by not discarding a relatively new sample.
 564     DVLOG(1) << "Sampling a new recent min rtt within 2 samples. currently:"
 565              << rtt_stats_.recent_min_rtt().ToMilliseconds() << "ms";
 566     rtt_stats_.SampleNewRecentMinRtt(kNumMinRttSamplesAfterQuiescence);
 567   }
 568
 569   // Only track packets as in flight that the send algorithm wants us to track.
 570   // Since FEC packets should also be counted towards the congestion window,
 571   // consider them as retransmittable for the purposes of congestion control.
 572   HasRetransmittableData has_congestion_controlled_data =
 573       serialized_packet->is_fec_packet ? HAS_RETRANSMITTABLE_DATA
 574                                        : has_retransmittable_data;
 575   const bool in_flight =
 576       send_algorithm_->OnPacketSent(sent_time,
 577                                     unacked_packets_.bytes_in_flight(),
 578                                     sequence_number,
 579                                     bytes,
 580                                     has_congestion_controlled_data);
 581
 582   unacked_packets_.AddSentPacket(*serialized_packet,
 583                                  original_sequence_number,
 584                                  transmission_type,
 585                                  sent_time,
 586                                  bytes,
 587                                  in_flight);
 588
 589   // Take ownership of the retransmittable frames before exiting.
 590   serialized_packet->retransmittable_frames = nullptr;
 591   // Reset the retransmission timer anytime a pending packet is sent.
 592   return in_flight;
 593 }
 594
 595 void QuicSentPacketManager::OnRetransmissionTimeout() {
 596   DCHECK(unacked_packets_.HasInFlightPackets());
 597   DCHECK_EQ(0u, pending_timer_transmission_count_);
 598   // Handshake retransmission, timer based loss detection, TLP, and RTO are
 599   // implemented with a single alarm. The handshake alarm is set when the
 600   // handshake has not completed, the loss alarm is set when the loss detection
 601   // algorithm says to, and the TLP and  RTO alarms are set after that.
 602   // The TLP alarm is always set to run for under an RTO.
 603   switch (GetRetransmissionMode()) {
 604     case HANDSHAKE_MODE:
 605       ++stats_->crypto_retransmit_count;
 606       RetransmitCryptoPackets();
 607       return;
 608     case LOSS_MODE: {
 609       ++stats_->loss_timeout_count;
 610       QuicByteCount bytes_in_flight = unacked_packets_.bytes_in_flight();
 611       InvokeLossDetection(clock_->Now());
 612       MaybeInvokeCongestionEvent(false, bytes_in_flight);
 613       return;
 614     }
 615     case TLP_MODE:
 616       // If no tail loss probe can be sent, because there are no retransmittable
 617       // packets, execute a conventional RTO to abandon old packets.
 618       ++stats_->tlp_count;
 619       ++consecutive_tlp_count_;
 620       pending_timer_transmission_count_ = 1;
 621       // TLPs prefer sending new data instead of retransmitting data, so
 622       // give the connection a chance to write before completing the TLP.
 623       return;
 624     case RTO_MODE:
 625       ++stats_->rto_count;
 626       RetransmitRtoPackets();
 627       return;
 628   }
 629 }
 630
 631 void QuicSentPacketManager::RetransmitCryptoPackets() {
 632   DCHECK_EQ(HANDSHAKE_MODE, GetRetransmissionMode());
 633   ++consecutive_crypto_retransmission_count_;
 634   bool packet_retransmitted = false;
 635   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 636   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 637        it != unacked_packets_.end(); ++it, ++sequence_number) {
 638     // Only retransmit frames which are in flight, and therefore have been sent.
 639     if (!it->in_flight || it->retransmittable_frames == nullptr ||
 640         it->retransmittable_frames->HasCryptoHandshake() != IS_HANDSHAKE) {
 641       continue;
 642     }
 643     packet_retransmitted = true;
 644     MarkForRetransmission(sequence_number, HANDSHAKE_RETRANSMISSION);
 645     ++pending_timer_transmission_count_;
 646   }
 647   DCHECK(packet_retransmitted) << "No crypto packets found to retransmit.";
 648 }
 649
 650 bool QuicSentPacketManager::MaybeRetransmitTailLossProbe() {
 651   if (pending_timer_transmission_count_ == 0) {
 652     return false;
 653   }
 654   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 655   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 656        it != unacked_packets_.end(); ++it, ++sequence_number) {
 657     // Only retransmit frames which are in flight, and therefore have been sent.
 658     if (!it->in_flight || it->retransmittable_frames == nullptr) {
 659       continue;
 660     }
 661     if (!handshake_confirmed_) {
 662       DCHECK_NE(IS_HANDSHAKE, it->retransmittable_frames->HasCryptoHandshake());
 663     }
 664     MarkForRetransmission(sequence_number, TLP_RETRANSMISSION);
 665     return true;
 666   }
 667   DLOG(FATAL)
 668     << "No retransmittable packets, so RetransmitOldestPacket failed.";
 669   return false;
 670 }
 671
 672 void QuicSentPacketManager::RetransmitRtoPackets() {
 673   LOG_IF(DFATAL, pending_timer_transmission_count_ > 0)
 674       << "Retransmissions already queued:" << pending_timer_transmission_count_;
 675   // Mark two packets for retransmission.
 676   QuicPacketSequenceNumber sequence_number = unacked_packets_.GetLeastUnacked();
 677   for (QuicUnackedPacketMap::const_iterator it = unacked_packets_.begin();
 678        it != unacked_packets_.end(); ++it, ++sequence_number) {
 679     if (it->retransmittable_frames != nullptr &&
 680         pending_timer_transmission_count_ < kMaxRetransmissionsOnTimeout) {
 681       MarkForRetransmission(sequence_number, RTO_RETRANSMISSION);
 682       ++pending_timer_transmission_count_;
 683     }
 684     // Abandon non-retransmittable data that's in flight to ensure it doesn't
 685     // fill up the congestion window.
 686     if (it->retransmittable_frames == nullptr && it->in_flight &&
 687         it->all_transmissions == nullptr) {
 688       unacked_packets_.RemoveFromInFlight(sequence_number);
 689     }
 690   }
 691   if (pending_timer_transmission_count_ > 0) {
 692     if (consecutive_rto_count_ == 0) {
 693       first_rto_transmission_ = unacked_packets_.largest_sent_packet() + 1;
 694     }
 695     ++consecutive_rto_count_;
 696   }
 697 }
 698
 699 QuicSentPacketManager::RetransmissionTimeoutMode
 700     QuicSentPacketManager::GetRetransmissionMode() const {
 701   DCHECK(unacked_packets_.HasInFlightPackets());
 702   if (!handshake_confirmed_ && unacked_packets_.HasPendingCryptoPackets()) {
 703     return HANDSHAKE_MODE;
 704   }
 705   if (loss_algorithm_->GetLossTimeout() != QuicTime::Zero()) {
 706     return LOSS_MODE;
 707   }
 708   if (consecutive_tlp_count_ < max_tail_loss_probes_) {
 709     if (unacked_packets_.HasUnackedRetransmittableFrames()) {
 710       return TLP_MODE;
 711     }
 712   }
 713   return RTO_MODE;
 714 }
 715
 716 void QuicSentPacketManager::InvokeLossDetection(QuicTime time) {
 717   SequenceNumberSet lost_packets =
 718       loss_algorithm_->DetectLostPackets(unacked_packets_,
 719                                          time,
 720                                          unacked_packets_.largest_observed(),
 721                                          rtt_stats_);
 722   for (SequenceNumberSet::const_iterator it = lost_packets.begin();
 723        it != lost_packets.end(); ++it) {
 724     QuicPacketSequenceNumber sequence_number = *it;
 725     const TransmissionInfo& transmission_info =
 726         unacked_packets_.GetTransmissionInfo(sequence_number);
 727     // TODO(ianswett): If it's expected the FEC packet may repair the loss, it
 728     // should be recorded as a loss to the send algorithm, but not retransmitted
 729     // until it's known whether the FEC packet arrived.
 730     ++stats_->packets_lost;
 731     packets_lost_.push_back(std::make_pair(sequence_number, transmission_info));
 732     DVLOG(1) << ENDPOINT << "Lost packet " << sequence_number;
 733
 734     if (transmission_info.retransmittable_frames != nullptr) {
 735       MarkForRetransmission(sequence_number, LOSS_RETRANSMISSION);
 736     } else {
 737       // Since we will not retransmit this, we need to remove it from
 738       // unacked_packets_.   This is either the current transmission of
 739       // a packet whose previous transmission has been acked, a packet that has
 740       // been TLP retransmitted, or an FEC packet.
 741       unacked_packets_.RemoveFromInFlight(sequence_number);
 742     }
 743   }
 744 }
 745
 746 bool QuicSentPacketManager::MaybeUpdateRTT(
 747     const QuicAckFrame& ack_frame,
 748     const QuicTime& ack_receive_time) {
 749   // We rely on delta_time_largest_observed to compute an RTT estimate, so we
 750   // only update rtt when the largest observed gets acked.
 751   // NOTE: If ack is a truncated ack, then the largest observed is in fact
 752   // unacked, and may cause an RTT sample to be taken.
 753   if (!unacked_packets_.IsUnacked(ack_frame.largest_observed)) {
 754     return false;
 755   }
 756   // We calculate the RTT based on the highest ACKed sequence number, the lower
 757   // sequence numbers will include the ACK aggregation delay.
 758   const TransmissionInfo& transmission_info =
 759       unacked_packets_.GetTransmissionInfo(ack_frame.largest_observed);
 760   // Ensure the packet has a valid sent time.
 761   if (transmission_info.sent_time == QuicTime::Zero()) {
 762     LOG(DFATAL) << "Acked packet has zero sent time, largest_observed:"
 763                 << ack_frame.largest_observed;
 764     return false;
 765   }
 766
 767   QuicTime::Delta send_delta =
 768       ack_receive_time.Subtract(transmission_info.sent_time);
 769   rtt_stats_.UpdateRtt(
 770       send_delta, ack_frame.delta_time_largest_observed, ack_receive_time);
 771
 772   if (network_change_visitor_ != nullptr) {
 773     network_change_visitor_->OnRttChange();
 774   }
 775
 776   return true;
 777 }
 778
 779 QuicTime::Delta QuicSentPacketManager::TimeUntilSend(
 780     QuicTime now,
 781     HasRetransmittableData retransmittable) {
 782   // The TLP logic is entirely contained within QuicSentPacketManager, so the
 783   // send algorithm does not need to be consulted.
 784   if (pending_timer_transmission_count_ > 0) {
 785     return QuicTime::Delta::Zero();
 786   }
 787   if (unacked_packets_.bytes_in_flight() >=
 788       kUsableRecieveBufferFraction * receive_buffer_bytes_) {
 789     return QuicTime::Delta::Infinite();
 790   }
 791   return send_algorithm_->TimeUntilSend(
 792       now, unacked_packets_.bytes_in_flight(), retransmittable);
 793 }
 794
 795 // Uses a 25ms delayed ack timer. Also helps with better signaling
 796 // in low-bandwidth (< ~384 kbps), where an ack is sent per packet.
 797 // Ensures that the Delayed Ack timer is always set to a value lesser
 798 // than the retransmission timer's minimum value (MinRTO). We want the
 799 // delayed ack to get back to the QUIC peer before the sender's
 800 // retransmission timer triggers.  Since we do not know the
 801 // reverse-path one-way delay, we assume equal delays for forward and
 802 // reverse paths, and ensure that the timer is set to less than half
 803 // of the MinRTO.
 804 // There may be a value in making this delay adaptive with the help of
 805 // the sender and a signaling mechanism -- if the sender uses a
 806 // different MinRTO, we may get spurious retransmissions. May not have
 807 // any benefits, but if the delayed ack becomes a significant source
 808 // of (likely, tail) latency, then consider such a mechanism.
 809 const QuicTime::Delta QuicSentPacketManager::DelayedAckTime() const {
 810   return QuicTime::Delta::FromMilliseconds(min(kMaxDelayedAckTimeMs,
 811                                                kMinRetransmissionTimeMs / 2));
 812 }
 813
 814 const QuicTime QuicSentPacketManager::GetRetransmissionTime() const {
 815   // Don't set the timer if there are no packets in flight or we've already
 816   // queued a tlp transmission and it hasn't been sent yet.
 817   if (!unacked_packets_.HasInFlightPackets() ||
 818       pending_timer_transmission_count_ > 0) {
 819     return QuicTime::Zero();
 820   }
 821   switch (GetRetransmissionMode()) {
 822     case HANDSHAKE_MODE:
 823       return clock_->ApproximateNow().Add(GetCryptoRetransmissionDelay());
 824     case LOSS_MODE:
 825       return loss_algorithm_->GetLossTimeout();
 826     case TLP_MODE: {
 827       // TODO(ianswett): When CWND is available, it would be preferable to
 828       // set the timer based on the earliest retransmittable packet.
 829       // Base the updated timer on the send time of the last packet.
 830       const QuicTime sent_time = unacked_packets_.GetLastPacketSentTime();
 831       const QuicTime tlp_time = sent_time.Add(GetTailLossProbeDelay());
 832       // Ensure the TLP timer never gets set to a time in the past.
 833       return QuicTime::Max(clock_->ApproximateNow(), tlp_time);
 834     }
 835     case RTO_MODE: {
 836       // The RTO is based on the first outstanding packet.
 837       const QuicTime sent_time = unacked_packets_.GetLastPacketSentTime();
 838       QuicTime rto_time = sent_time.Add(GetRetransmissionDelay());
 839       // Wait for TLP packets to be acked before an RTO fires.
 840       QuicTime tlp_time =
 841           unacked_packets_.GetLastPacketSentTime().Add(GetTailLossProbeDelay());
 842       return QuicTime::Max(tlp_time, rto_time);
 843     }
 844   }
 845   DCHECK(false);
 846   return QuicTime::Zero();
 847 }
 848
 849 const QuicTime::Delta QuicSentPacketManager::GetCryptoRetransmissionDelay()
 850     const {
 851   // This is equivalent to the TailLossProbeDelay, but slightly more aggressive
 852   // because crypto handshake messages don't incur a delayed ack time.
 853   QuicTime::Delta srtt = rtt_stats_.smoothed_rtt();
 854   if (srtt.IsZero()) {
 855     srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us());
 856   }
 857   int64 delay_ms = max(kMinHandshakeTimeoutMs,
 858                        static_cast<int64>(1.5 * srtt.ToMilliseconds()));
 859   return QuicTime::Delta::FromMilliseconds(
 860       delay_ms << consecutive_crypto_retransmission_count_);
 861 }
 862
 863 const QuicTime::Delta QuicSentPacketManager::GetTailLossProbeDelay() const {
 864   QuicTime::Delta srtt = rtt_stats_.smoothed_rtt();
 865   if (srtt.IsZero()) {
 866     srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_.initial_rtt_us());
 867   }
 868   if (!unacked_packets_.HasMultipleInFlightPackets()) {
 869     return QuicTime::Delta::Max(
 870         srtt.Multiply(2), srtt.Multiply(1.5).Add(
 871             QuicTime::Delta::FromMilliseconds(kMinRetransmissionTimeMs / 2)));
 872   }
 873   return QuicTime::Delta::FromMilliseconds(
 874       max(kMinTailLossProbeTimeoutMs,
 875           static_cast<int64>(2 * srtt.ToMilliseconds())));
 876 }
 877
 878 const QuicTime::Delta QuicSentPacketManager::GetRetransmissionDelay() const {
 879   QuicTime::Delta retransmission_delay = send_algorithm_->RetransmissionDelay();
 880   // TODO(rch): This code should move to |send_algorithm_|.
 881   if (retransmission_delay.IsZero()) {
 882     // We are in the initial state, use default timeout values.
 883     retransmission_delay =
 884         QuicTime::Delta::FromMilliseconds(kDefaultRetransmissionTimeMs);
 885   } else if (retransmission_delay.ToMilliseconds() < kMinRetransmissionTimeMs) {
 886     retransmission_delay =
 887         QuicTime::Delta::FromMilliseconds(kMinRetransmissionTimeMs);
 888   }
 889
 890   // Calculate exponential back off.
 891   retransmission_delay = retransmission_delay.Multiply(
 892       1 << min<size_t>(consecutive_rto_count_, kMaxRetransmissions));
 893
 894   if (retransmission_delay.ToMilliseconds() > kMaxRetransmissionTimeMs) {
 895     return QuicTime::Delta::FromMilliseconds(kMaxRetransmissionTimeMs);
 896   }
 897   return retransmission_delay;
 898 }
 899
 900 const RttStats* QuicSentPacketManager::GetRttStats() const {
 901   return &rtt_stats_;
 902 }
 903
 904 QuicBandwidth QuicSentPacketManager::BandwidthEstimate() const {
 905   // TODO(ianswett): Remove BandwidthEstimate from SendAlgorithmInterface
 906   // and implement the logic here.
 907   return send_algorithm_->BandwidthEstimate();
 908 }
 909
 910 bool QuicSentPacketManager::HasReliableBandwidthEstimate() const {
 911   return send_algorithm_->HasReliableBandwidthEstimate();
 912 }
 913
 914 const QuicSustainedBandwidthRecorder&
 915 QuicSentPacketManager::SustainedBandwidthRecorder() const {
 916   return sustained_bandwidth_recorder_;
 917 }
 918
 919 QuicPacketCount QuicSentPacketManager::EstimateMaxPacketsInFlight(
 920     QuicByteCount max_packet_length) const {
 921   return send_algorithm_->GetCongestionWindow() / max_packet_length;
 922 }
 923
 924 QuicPacketCount QuicSentPacketManager::GetCongestionWindowInTcpMss() const {
 925   return send_algorithm_->GetCongestionWindow() / kDefaultTCPMSS;
 926 }
 927
 928 QuicPacketCount QuicSentPacketManager::GetSlowStartThresholdInTcpMss() const {
 929   return send_algorithm_->GetSlowStartThreshold() / kDefaultTCPMSS;
 930 }
 931
 932 void QuicSentPacketManager::OnSerializedPacket(
 933     const SerializedPacket& serialized_packet) {
 934   ack_notifier_manager_.OnSerializedPacket(serialized_packet);
 935 }
 936
 937 void QuicSentPacketManager::EnablePacing() {
 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