Move shared files in net/quic/ into net/quic/core/

net/quic/quic_connection.cc

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "net/quic/quic_connection.h"
-
-#include <string.h>
-#include <sys/types.h>
-
-#include <algorithm>
-#include <iterator>
-#include <limits>
-#include <memory>
-#include <set>
-#include <utility>
-
-#include "base/format_macros.h"
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/metrics/histogram_macros.h"
-#include "base/stl_util.h"
-#include "base/strings/string_number_conversions.h"
-#include "base/strings/stringprintf.h"
-#include "net/base/address_family.h"
-#include "net/base/ip_address.h"
-#include "net/base/net_errors.h"
-#include "net/quic/crypto/crypto_protocol.h"
-#include "net/quic/crypto/quic_decrypter.h"
-#include "net/quic/crypto/quic_encrypter.h"
-#include "net/quic/proto/cached_network_parameters.pb.h"
-#include "net/quic/quic_bandwidth.h"
-#include "net/quic/quic_bug_tracker.h"
-#include "net/quic/quic_config.h"
-#include "net/quic/quic_flags.h"
-#include "net/quic/quic_packet_generator.h"
-#include "net/quic/quic_sent_packet_manager.h"
-#include "net/quic/quic_utils.h"
-
-using base::StringPiece;
-using base::StringPrintf;
-using std::list;
-using std::make_pair;
-using std::max;
-using std::min;
-using std::numeric_limits;
-using std::set;
-using std::string;
-using std::vector;
-
-namespace net {
-
-class QuicDecrypter;
-class QuicEncrypter;
-
-namespace {
-
-// The largest gap in packets we'll accept without closing the connection.
-// This will likely have to be tuned.
-const QuicPacketNumber kMaxPacketGap = 5000;
-
-// Maximum number of acks received before sending an ack in response.
-const QuicPacketCount kMaxPacketsReceivedBeforeAckSend = 20;
-
-// Maximum number of retransmittable packets received before sending an ack.
-const QuicPacketCount kDefaultRetransmittablePacketsBeforeAck = 2;
-// Minimum number of packets received before ack decimation is enabled.
-// This intends to avoid the beginning of slow start, when CWNDs may be
-// rapidly increasing.
-const QuicPacketCount kMinReceivedBeforeAckDecimation = 100;
-// Wait for up to 10 retransmittable packets before sending an ack.
-const QuicPacketCount kMaxRetransmittablePacketsBeforeAck = 10;
-// One quarter RTT delay when doing ack decimation.
-const float kAckDecimationDelay = 0.25;
-// One eighth RTT delay when doing ack decimation.
-const float kShortAckDecimationDelay = 0.125;
-
-bool Near(QuicPacketNumber a, QuicPacketNumber b) {
-  QuicPacketNumber delta = (a > b) ? a - b : b - a;
-  return delta <= kMaxPacketGap;
-}
-
-bool IsInitializedIPEndPoint(const IPEndPoint& address) {
-  return net::GetAddressFamily(address.address()) !=
-         net::ADDRESS_FAMILY_UNSPECIFIED;
-}
-
-// An alarm that is scheduled to send an ack if a timeout occurs.
-class AckAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit AckAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override {
-    DCHECK(connection_->ack_frame_updated());
-    QuicConnection::ScopedPacketBundler bundler(connection_,
-                                                QuicConnection::SEND_ACK);
-  }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(AckAlarmDelegate);
-};
-
-// This alarm will be scheduled any time a data-bearing packet is sent out.
-// When the alarm goes off, the connection checks to see if the oldest packets
-// have been acked, and retransmit them if they have not.
-class RetransmissionAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit RetransmissionAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override { connection_->OnRetransmissionTimeout(); }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(RetransmissionAlarmDelegate);
-};
-
-// An alarm that is scheduled when the SentPacketManager requires a delay
-// before sending packets and fires when the packet may be sent.
-class SendAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit SendAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override { connection_->WriteAndBundleAcksIfNotBlocked(); }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(SendAlarmDelegate);
-};
-
-class TimeoutAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit TimeoutAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override { connection_->CheckForTimeout(); }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(TimeoutAlarmDelegate);
-};
-
-class PingAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit PingAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override { connection_->OnPingTimeout(); }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(PingAlarmDelegate);
-};
-
-class MtuDiscoveryAlarmDelegate : public QuicAlarm::Delegate {
- public:
-  explicit MtuDiscoveryAlarmDelegate(QuicConnection* connection)
-      : connection_(connection) {}
-
-  void OnAlarm() override { connection_->DiscoverMtu(); }
-
- private:
-  QuicConnection* connection_;
-
-  DISALLOW_COPY_AND_ASSIGN(MtuDiscoveryAlarmDelegate);
-};
-
-// Listens for acks of MTU discovery packets and raises the maximum packet size
-// of the connection if the probe succeeds.
-class MtuDiscoveryAckListener : public QuicAckListenerInterface {
- public:
-  MtuDiscoveryAckListener(QuicConnection* connection, QuicByteCount probe_size)
-      : connection_(connection), probe_size_(probe_size) {}
-
-  void OnPacketAcked(int /*acked_bytes*/,
-                     QuicTime::Delta /*ack delay time*/) override {
-    // MTU discovery packets are not retransmittable, so it must be acked.
-    MaybeIncreaseMtu();
-  }
-
-  void OnPacketRetransmitted(int /*retransmitted_bytes*/) override {}
-
- protected:
-  // MtuDiscoveryAckListener is ref counted.
-  ~MtuDiscoveryAckListener() override {}
-
- private:
-  void MaybeIncreaseMtu() {
-    if (probe_size_ > connection_->max_packet_length()) {
-      connection_->SetMaxPacketLength(probe_size_);
-    }
-  }
-
-  QuicConnection* connection_;
-  QuicByteCount probe_size_;
-
-  DISALLOW_COPY_AND_ASSIGN(MtuDiscoveryAckListener);
-};
-
-}  // namespace
-
-#define ENDPOINT \
-  (perspective_ == Perspective::IS_SERVER ? "Server: " : "Client: ")
-
-QuicConnection::QuicConnection(QuicConnectionId connection_id,
-                               IPEndPoint address,
-                               QuicConnectionHelperInterface* helper,
-                               QuicAlarmFactory* alarm_factory,
-                               QuicPacketWriter* writer,
-                               bool owns_writer,
-                               Perspective perspective,
-                               const QuicVersionVector& supported_versions)
-    : framer_(supported_versions,
-              helper->GetClock()->ApproximateNow(),
-              perspective),
-      helper_(helper),
-      alarm_factory_(alarm_factory),
-      per_packet_options_(nullptr),
-      writer_(writer),
-      owns_writer_(owns_writer),
-      encryption_level_(ENCRYPTION_NONE),
-      has_forward_secure_encrypter_(false),
-      first_required_forward_secure_packet_(0),
-      clock_(helper->GetClock()),
-      random_generator_(helper->GetRandomGenerator()),
-      connection_id_(connection_id),
-      peer_address_(address),
-      active_peer_migration_type_(NO_CHANGE),
-      highest_packet_sent_before_peer_migration_(0),
-      last_packet_decrypted_(false),
-      last_size_(0),
-      current_packet_data_(nullptr),
-      last_decrypted_packet_level_(ENCRYPTION_NONE),
-      should_last_packet_instigate_acks_(false),
-      largest_seen_packet_with_ack_(0),
-      largest_seen_packet_with_stop_waiting_(0),
-      max_undecryptable_packets_(0),
-      pending_version_negotiation_packet_(false),
-      save_crypto_packets_as_termination_packets_(false),
-      idle_timeout_connection_close_behavior_(
-          ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET),
-      close_connection_after_five_rtos_(false),
-      received_packet_manager_(&stats_),
-      ack_queued_(false),
-      num_retransmittable_packets_received_since_last_ack_sent_(0),
-      last_ack_had_missing_packets_(false),
-      num_packets_received_since_last_ack_sent_(0),
-      stop_waiting_count_(0),
-      ack_mode_(TCP_ACKING),
-      ack_decimation_delay_(kAckDecimationDelay),
-      delay_setting_retransmission_alarm_(false),
-      pending_retransmission_alarm_(false),
-      defer_send_in_response_to_packets_(false),
-      arena_(),
-      ack_alarm_(alarm_factory_->CreateAlarm(arena_.New<AckAlarmDelegate>(this),
-                                             &arena_)),
-      retransmission_alarm_(alarm_factory_->CreateAlarm(
-          arena_.New<RetransmissionAlarmDelegate>(this),
-          &arena_)),
-      send_alarm_(
-          alarm_factory_->CreateAlarm(arena_.New<SendAlarmDelegate>(this),
-                                      &arena_)),
-      resume_writes_alarm_(
-          alarm_factory_->CreateAlarm(arena_.New<SendAlarmDelegate>(this),
-                                      &arena_)),
-      timeout_alarm_(
-          alarm_factory_->CreateAlarm(arena_.New<TimeoutAlarmDelegate>(this),
-                                      &arena_)),
-      ping_alarm_(
-          alarm_factory_->CreateAlarm(arena_.New<PingAlarmDelegate>(this),
-                                      &arena_)),
-      mtu_discovery_alarm_(alarm_factory_->CreateAlarm(
-          arena_.New<MtuDiscoveryAlarmDelegate>(this),
-          &arena_)),
-      visitor_(nullptr),
-      debug_visitor_(nullptr),
-      packet_generator_(connection_id_,
-                        &framer_,
-                        random_generator_,
-                        helper->GetBufferAllocator(),
-                        this),
-      idle_network_timeout_(QuicTime::Delta::Infinite()),
-      handshake_timeout_(QuicTime::Delta::Infinite()),
-      time_of_last_received_packet_(clock_->ApproximateNow()),
-      time_of_last_sent_new_packet_(clock_->ApproximateNow()),
-      last_send_for_timeout_(clock_->ApproximateNow()),
-      packet_number_of_last_sent_packet_(0),
-      sent_packet_manager_(new QuicSentPacketManager(perspective,
-                                                     kDefaultPathId,
-                                                     clock_,
-                                                     &stats_,
-                                                     kCubic,
-                                                     kNack,
-                                                     /*delegate=*/nullptr)),
-      version_negotiation_state_(START_NEGOTIATION),
-      perspective_(perspective),
-      connected_(true),
-      can_truncate_connection_ids_(true),
-      mtu_discovery_target_(0),
-      mtu_probe_count_(0),
-      packets_between_mtu_probes_(kPacketsBetweenMtuProbesBase),
-      next_mtu_probe_at_(kPacketsBetweenMtuProbesBase),
-      largest_received_packet_size_(0),
-      goaway_sent_(false),
-      goaway_received_(false),
-      multipath_enabled_(false) {
-  DVLOG(1) << ENDPOINT
-           << "Created connection with connection_id: " << connection_id;
-  framer_.set_visitor(this);
-  framer_.set_received_entropy_calculator(&received_packet_manager_);
-  last_stop_waiting_frame_.least_unacked = 0;
-  stats_.connection_creation_time = clock_->ApproximateNow();
-  if (FLAGS_quic_enable_multipath) {
-    sent_packet_manager_.reset(new QuicMultipathSentPacketManager(
-        sent_packet_manager_.release(), this));
-  }
-  // TODO(ianswett): Supply the NetworkChangeVisitor as a constructor argument
-  // and make it required non-null, because it's always used.
-  sent_packet_manager_->SetNetworkChangeVisitor(this);
-  // Allow the packet writer to potentially reduce the packet size to a value
-  // even smaller than kDefaultMaxPacketSize.
-  SetMaxPacketLength(perspective_ == Perspective::IS_SERVER
-                         ? kDefaultServerMaxPacketSize
-                         : kDefaultMaxPacketSize);
-  received_packet_manager_.SetVersion(version());
-}
-
-QuicConnection::~QuicConnection() {
-  if (owns_writer_) {
-    delete writer_;
-  }
-  STLDeleteElements(&undecryptable_packets_);
-  ClearQueuedPackets();
-}
-
-void QuicConnection::ClearQueuedPackets() {
-  for (QueuedPacketList::iterator it = queued_packets_.begin();
-       it != queued_packets_.end(); ++it) {
-    // Delete the buffer before calling ClearSerializedPacket, which sets
-    // encrypted_buffer to nullptr.
-    delete[] it->encrypted_buffer;
-    QuicUtils::ClearSerializedPacket(&(*it));
-  }
-  queued_packets_.clear();
-}
-
-void QuicConnection::SetFromConfig(const QuicConfig& config) {
-  if (config.negotiated()) {
-    // Handshake complete, set handshake timeout to Infinite.
-    SetNetworkTimeouts(QuicTime::Delta::Infinite(),
-                       config.IdleConnectionStateLifetime());
-    if (config.SilentClose()) {
-      idle_timeout_connection_close_behavior_ =
-          ConnectionCloseBehavior::SILENT_CLOSE;
-    }
-    if (FLAGS_quic_enable_multipath && config.MultipathEnabled()) {
-      multipath_enabled_ = true;
-    }
-  } else {
-    SetNetworkTimeouts(config.max_time_before_crypto_handshake(),
-                       config.max_idle_time_before_crypto_handshake());
-  }
-
-  sent_packet_manager_->SetFromConfig(config);
-  if (config.HasReceivedBytesForConnectionId() &&
-      can_truncate_connection_ids_) {
-    packet_generator_.SetConnectionIdLength(
-        config.ReceivedBytesForConnectionId());
-  }
-  max_undecryptable_packets_ = config.max_undecryptable_packets();
-
-  if (config.HasClientSentConnectionOption(kMTUH, perspective_)) {
-    SetMtuDiscoveryTarget(kMtuDiscoveryTargetPacketSizeHigh);
-  }
-  if (config.HasClientSentConnectionOption(kMTUL, perspective_)) {
-    SetMtuDiscoveryTarget(kMtuDiscoveryTargetPacketSizeLow);
-  }
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnSetFromConfig(config);
-  }
-  if (config.HasClientSentConnectionOption(kACKD, perspective_)) {
-    ack_mode_ = ACK_DECIMATION;
-  }
-  if (config.HasClientSentConnectionOption(kAKD2, perspective_)) {
-    ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
-  }
-  if (config.HasClientSentConnectionOption(kAKD3, perspective_)) {
-    ack_mode_ = ACK_DECIMATION;
-    ack_decimation_delay_ = kShortAckDecimationDelay;
-  }
-  if (config.HasClientSentConnectionOption(kAKD4, perspective_)) {
-    ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
-    ack_decimation_delay_ = kShortAckDecimationDelay;
-  }
-  if (config.HasClientSentConnectionOption(k5RTO, perspective_)) {
-    close_connection_after_five_rtos_ = true;
-  }
-}
-
-void QuicConnection::OnSendConnectionState(
-    const CachedNetworkParameters& cached_network_params) {
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnSendConnectionState(cached_network_params);
-  }
-}
-
-void QuicConnection::OnReceiveConnectionState(
-    const CachedNetworkParameters& cached_network_params) {
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnReceiveConnectionState(cached_network_params);
-  }
-}
-
-void QuicConnection::ResumeConnectionState(
-    const CachedNetworkParameters& cached_network_params,
-    bool max_bandwidth_resumption) {
-  sent_packet_manager_->ResumeConnectionState(cached_network_params,
-                                              max_bandwidth_resumption);
-}
-
-void QuicConnection::SetMaxPacingRate(QuicBandwidth max_pacing_rate) {
-  sent_packet_manager_->SetMaxPacingRate(max_pacing_rate);
-}
-
-void QuicConnection::SetNumOpenStreams(size_t num_streams) {
-  sent_packet_manager_->SetNumOpenStreams(num_streams);
-}
-
-bool QuicConnection::SelectMutualVersion(
-    const QuicVersionVector& available_versions) {
-  // Try to find the highest mutual version by iterating over supported
-  // versions, starting with the highest, and breaking out of the loop once we
-  // find a matching version in the provided available_versions vector.
-  const QuicVersionVector& supported_versions = framer_.supported_versions();
-  for (size_t i = 0; i < supported_versions.size(); ++i) {
-    const QuicVersion& version = supported_versions[i];
-    if (ContainsValue(available_versions, version)) {
-      framer_.set_version(version);
-      return true;
-    }
-  }
-
-  return false;
-}
-
-void QuicConnection::OnError(QuicFramer* framer) {
-  // Packets that we can not or have not decrypted are dropped.
-  // TODO(rch): add stats to measure this.
-  if (!connected_ || last_packet_decrypted_ == false) {
-    return;
-  }
-  CloseConnection(framer->error(), framer->detailed_error(),
-                  ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-}
-
-void QuicConnection::OnPacket() {
-  last_packet_decrypted_ = false;
-}
-
-void QuicConnection::OnPublicResetPacket(const QuicPublicResetPacket& packet) {
-  // Check that any public reset packet with a different connection ID that was
-  // routed to this QuicConnection has been redirected before control reaches
-  // here.  (Check for a bug regression.)
-  DCHECK_EQ(connection_id_, packet.public_header.connection_id);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPublicResetPacket(packet);
-  }
-  const string error_details = "Received public reset.";
-  DVLOG(1) << ENDPOINT << error_details;
-  TearDownLocalConnectionState(QUIC_PUBLIC_RESET, error_details,
-                               ConnectionCloseSource::FROM_PEER);
-}
-
-bool QuicConnection::OnProtocolVersionMismatch(QuicVersion received_version) {
-  DVLOG(1) << ENDPOINT << "Received packet with mismatched version "
-           << received_version;
-  // TODO(satyamshekhar): Implement no server state in this mode.
-  if (perspective_ == Perspective::IS_CLIENT) {
-    const string error_details = "Protocol version mismatch.";
-    QUIC_BUG << ENDPOINT << error_details;
-    TearDownLocalConnectionState(QUIC_INTERNAL_ERROR, error_details,
-                                 ConnectionCloseSource::FROM_SELF);
-    return false;
-  }
-  DCHECK_NE(version(), received_version);
-
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnProtocolVersionMismatch(received_version);
-  }
-
-  switch (version_negotiation_state_) {
-    case START_NEGOTIATION:
-      if (!framer_.IsSupportedVersion(received_version)) {
-        SendVersionNegotiationPacket();
-        version_negotiation_state_ = NEGOTIATION_IN_PROGRESS;
-        return false;
-      }
-      break;
-
-    case NEGOTIATION_IN_PROGRESS:
-      if (!framer_.IsSupportedVersion(received_version)) {
-        SendVersionNegotiationPacket();
-        return false;
-      }
-      break;
-
-    case NEGOTIATED_VERSION:
-      // Might be old packets that were sent by the client before the version
-      // was negotiated. Drop these.
-      return false;
-
-    default:
-      DCHECK(false);
-  }
-
-  version_negotiation_state_ = NEGOTIATED_VERSION;
-  received_packet_manager_.SetVersion(received_version);
-  visitor_->OnSuccessfulVersionNegotiation(received_version);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnSuccessfulVersionNegotiation(received_version);
-  }
-  DVLOG(1) << ENDPOINT << "version negotiated " << received_version;
-
-  // Store the new version.
-  framer_.set_version(received_version);
-
-  // TODO(satyamshekhar): Store the packet number of this packet and close the
-  // connection if we ever received a packet with incorrect version and whose
-  // packet number is greater.
-  return true;
-}
-
-// Handles version negotiation for client connection.
-void QuicConnection::OnVersionNegotiationPacket(
-    const QuicVersionNegotiationPacket& packet) {
-  // Check that any public reset packet with a different connection ID that was
-  // routed to this QuicConnection has been redirected before control reaches
-  // here.  (Check for a bug regression.)
-  DCHECK_EQ(connection_id_, packet.connection_id);
-  if (perspective_ == Perspective::IS_SERVER) {
-    const string error_details = "Server receieved version negotiation packet.";
-    QUIC_BUG << error_details;
-    TearDownLocalConnectionState(QUIC_INTERNAL_ERROR, error_details,
-                                 ConnectionCloseSource::FROM_SELF);
-    return;
-  }
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnVersionNegotiationPacket(packet);
-  }
-
-  if (version_negotiation_state_ != START_NEGOTIATION) {
-    // Possibly a duplicate version negotiation packet.
-    return;
-  }
-
-  if (ContainsValue(packet.versions, version())) {
-    const string error_details =
-        "Server already supports client's version and should have accepted the "
-        "connection.";
-    DLOG(WARNING) << error_details;
-    TearDownLocalConnectionState(QUIC_INVALID_VERSION_NEGOTIATION_PACKET,
-                                 error_details,
-                                 ConnectionCloseSource::FROM_SELF);
-    return;
-  }
-
-  if (!SelectMutualVersion(packet.versions)) {
-    CloseConnection(QUIC_INVALID_VERSION, "No common version found.",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return;
-  }
-
-  DVLOG(1) << ENDPOINT
-           << "Negotiated version: " << QuicVersionToString(version());
-  received_packet_manager_.SetVersion(version());
-  server_supported_versions_ = packet.versions;
-  version_negotiation_state_ = NEGOTIATION_IN_PROGRESS;
-  RetransmitUnackedPackets(ALL_UNACKED_RETRANSMISSION);
-}
-
-bool QuicConnection::OnUnauthenticatedPublicHeader(
-    const QuicPacketPublicHeader& header) {
-  if (header.connection_id == connection_id_) {
-    return true;
-  }
-
-  ++stats_.packets_dropped;
-  DVLOG(1) << ENDPOINT << "Ignoring packet from unexpected ConnectionId: "
-           << header.connection_id << " instead of " << connection_id_;
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnIncorrectConnectionId(header.connection_id);
-  }
-  // If this is a server, the dispatcher routes each packet to the
-  // QuicConnection responsible for the packet's connection ID.  So if control
-  // arrives here and this is a server, the dispatcher must be malfunctioning.
-  DCHECK_NE(Perspective::IS_SERVER, perspective_);
-  return false;
-}
-
-bool QuicConnection::OnUnauthenticatedHeader(const QuicPacketHeader& header) {
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnUnauthenticatedHeader(header);
-  }
-
-  // Check that any public reset packet with a different connection ID that was
-  // routed to this QuicConnection has been redirected before control reaches
-  // here.
-  DCHECK_EQ(connection_id_, header.public_header.connection_id);
-
-  // Multipath is not enabled, but a packet with multipath flag on is received.
-  if (!multipath_enabled_ && header.public_header.multipath_flag) {
-    const string error_details =
-        "Received a packet with multipath flag but multipath is not enabled.";
-    QUIC_BUG << error_details;
-    CloseConnection(QUIC_BAD_MULTIPATH_FLAG, error_details,
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-  if (!packet_generator_.IsPendingPacketEmpty()) {
-    // Incoming packets may change a queued ACK frame.
-    const string error_details =
-        "Pending frames must be serialized before incoming packets are "
-        "processed.";
-    QUIC_BUG << error_details;
-    CloseConnection(QUIC_INTERNAL_ERROR, error_details,
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-
-  // If this packet has already been seen, or the sender has told us that it
-  // will not be retransmitted, then stop processing the packet.
-  if (!received_packet_manager_.IsAwaitingPacket(header.packet_number)) {
-    DVLOG(1) << ENDPOINT << "Packet " << header.packet_number
-             << " no longer being waited for.  Discarding.";
-    if (debug_visitor_ != nullptr) {
-      debug_visitor_->OnDuplicatePacket(header.packet_number);
-    }
-    ++stats_.packets_dropped;
-    return false;
-  }
-
-  return true;
-}
-
-void QuicConnection::OnDecryptedPacket(EncryptionLevel level) {
-  last_decrypted_packet_level_ = level;
-  last_packet_decrypted_ = true;
-
-  // If this packet was foward-secure encrypted and the forward-secure encrypter
-  // is not being used, start using it.
-  if (encryption_level_ != ENCRYPTION_FORWARD_SECURE &&
-      has_forward_secure_encrypter_ && level == ENCRYPTION_FORWARD_SECURE) {
-    SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
-  }
-
-  // Once the server receives a forward secure packet, the handshake is
-  // confirmed.
-  if (FLAGS_quic_no_shlo_listener && level == ENCRYPTION_FORWARD_SECURE &&
-      perspective_ == Perspective::IS_SERVER) {
-    sent_packet_manager_->SetHandshakeConfirmed();
-  }
-}
-
-bool QuicConnection::OnPacketHeader(const QuicPacketHeader& header) {
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPacketHeader(header);
-  }
-
-  // Will be decremented below if we fall through to return true.
-  ++stats_.packets_dropped;
-
-  if (!ProcessValidatedPacket(header)) {
-    return false;
-  }
-
-  // Only migrate connection to a new peer address if a change is not underway.
-  PeerAddressChangeType peer_migration_type =
-      QuicUtils::DetermineAddressChangeType(peer_address_,
-                                            last_packet_source_address_);
-  // Do not migrate connection if the changed address packet is a reordered
-  // packet.
-  if (active_peer_migration_type_ == NO_CHANGE &&
-      peer_migration_type != NO_CHANGE &&
-      (!FLAGS_quic_do_not_migrate_on_old_packet ||
-       header.packet_number > received_packet_manager_.GetLargestObserved())) {
-    StartPeerMigration(header.path_id, peer_migration_type);
-  }
-
-  --stats_.packets_dropped;
-  DVLOG(1) << ENDPOINT << "Received packet header: " << header;
-  last_header_ = header;
-  DCHECK(connected_);
-  return true;
-}
-
-bool QuicConnection::OnStreamFrame(const QuicStreamFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnStreamFrame(frame);
-  }
-  if (frame.stream_id != kCryptoStreamId &&
-      last_decrypted_packet_level_ == ENCRYPTION_NONE) {
-    if (MaybeConsiderAsMemoryCorruption(frame)) {
-      CloseConnection(QUIC_MAYBE_CORRUPTED_MEMORY,
-                      "Received crypto frame on non crypto stream.",
-                      ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-      return false;
-    }
-
-    QUIC_BUG << ENDPOINT
-             << "Received an unencrypted data frame: closing connection"
-             << " packet_number:" << last_header_.packet_number
-             << " stream_id:" << frame.stream_id
-             << " received_packets:" << received_packet_manager_.ack_frame();
-    CloseConnection(QUIC_UNENCRYPTED_STREAM_DATA,
-                    "Unencrypted stream data seen.",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-  visitor_->OnStreamFrame(frame);
-  visitor_->PostProcessAfterData();
-  stats_.stream_bytes_received += frame.data_length;
-  should_last_packet_instigate_acks_ = true;
-  return connected_;
-}
-
-bool QuicConnection::OnAckFrame(const QuicAckFrame& incoming_ack) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnAckFrame(incoming_ack);
-  }
-  DVLOG(1) << ENDPOINT << "OnAckFrame: " << incoming_ack;
-
-  if (last_header_.packet_number <= largest_seen_packet_with_ack_) {
-    DVLOG(1) << ENDPOINT << "Received an old ack frame: ignoring";
-    return true;
-  }
-
-  const char* error = ValidateAckFrame(incoming_ack);
-  if (error != nullptr) {
-    CloseConnection(QUIC_INVALID_ACK_DATA, error,
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-
-  if (send_alarm_->IsSet()) {
-    send_alarm_->Cancel();
-  }
-  ProcessAckFrame(incoming_ack);
-  if (incoming_ack.is_truncated) {
-    should_last_packet_instigate_acks_ = true;
-  }
-  // If the incoming ack's packets set expresses missing packets: peer is still
-  // waiting for a packet lower than a packet that we are no longer planning to
-  // send.
-  // If the incoming ack's packets set expresses received packets: peer is still
-  // acking packets which we never care about.
-  // Send an ack to raise the high water mark.
-  if (!incoming_ack.packets.Empty() &&
-      GetLeastUnacked(incoming_ack.path_id) > incoming_ack.packets.Min()) {
-    ++stop_waiting_count_;
-  } else {
-    stop_waiting_count_ = 0;
-  }
-
-  return connected_;
-}
-
-void QuicConnection::ProcessAckFrame(const QuicAckFrame& incoming_ack) {
-  largest_seen_packet_with_ack_ = last_header_.packet_number;
-  sent_packet_manager_->OnIncomingAck(incoming_ack,
-                                      time_of_last_received_packet_);
-  if (version() <= QUIC_VERSION_33) {
-    sent_entropy_manager_.ClearEntropyBefore(
-        sent_packet_manager_->GetLeastPacketAwaitedByPeer(
-            incoming_ack.path_id) -
-        1);
-  }
-  // Always reset the retransmission alarm when an ack comes in, since we now
-  // have a better estimate of the current rtt than when it was set.
-  SetRetransmissionAlarm();
-}
-
-void QuicConnection::ProcessStopWaitingFrame(
-    const QuicStopWaitingFrame& stop_waiting) {
-  largest_seen_packet_with_stop_waiting_ = last_header_.packet_number;
-  received_packet_manager_.UpdatePacketInformationSentByPeer(stop_waiting);
-}
-
-bool QuicConnection::OnStopWaitingFrame(const QuicStopWaitingFrame& frame) {
-  DCHECK(connected_);
-
-  if (last_header_.packet_number <= largest_seen_packet_with_stop_waiting_) {
-    DVLOG(1) << ENDPOINT << "Received an old stop waiting frame: ignoring";
-    return true;
-  }
-
-  const char* error = ValidateStopWaitingFrame(frame);
-  if (error != nullptr) {
-    CloseConnection(QUIC_INVALID_STOP_WAITING_DATA, error,
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnStopWaitingFrame(frame);
-  }
-
-  last_stop_waiting_frame_ = frame;
-  return connected_;
-}
-
-bool QuicConnection::OnPaddingFrame(const QuicPaddingFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPaddingFrame(frame);
-  }
-  return true;
-}
-
-bool QuicConnection::OnPingFrame(const QuicPingFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPingFrame(frame);
-  }
-  should_last_packet_instigate_acks_ = true;
-  return true;
-}
-
-const char* QuicConnection::ValidateAckFrame(const QuicAckFrame& incoming_ack) {
-  if (incoming_ack.largest_observed > packet_generator_.packet_number()) {
-    DLOG(WARNING) << ENDPOINT << "Peer's observed unsent packet:"
-                  << incoming_ack.largest_observed << " vs "
-                  << packet_generator_.packet_number();
-    // We got an error for data we have not sent.  Error out.
-    return "Largest observed too high.";
-  }
-
-  if (incoming_ack.largest_observed <
-      sent_packet_manager_->GetLargestObserved(incoming_ack.path_id)) {
-    VLOG(1) << ENDPOINT << "Peer's largest_observed packet decreased:"
-            << incoming_ack.largest_observed << " vs "
-            << sent_packet_manager_->GetLargestObserved(incoming_ack.path_id)
-            << " packet_number:" << last_header_.packet_number
-            << " largest seen with ack:" << largest_seen_packet_with_ack_
-            << " connection_id: " << connection_id_;
-    // A new ack has a diminished largest_observed value.  Error out.
-    // If this was an old packet, we wouldn't even have checked.
-    return "Largest observed too low.";
-  }
-
-  if (version() <= QUIC_VERSION_33) {
-    if (!incoming_ack.packets.Empty() &&
-        incoming_ack.packets.Max() > incoming_ack.largest_observed) {
-      LOG(WARNING) << ENDPOINT
-                   << "Peer sent missing packet: " << incoming_ack.packets.Max()
-                   << " which is greater than largest observed: "
-                   << incoming_ack.largest_observed;
-      return "Missing packet higher than largest observed.";
-    }
-
-    if (!incoming_ack.packets.Empty() &&
-        incoming_ack.packets.Min() <
-            sent_packet_manager_->GetLeastPacketAwaitedByPeer(
-                incoming_ack.path_id)) {
-      LOG(WARNING) << ENDPOINT
-                   << "Peer sent missing packet: " << incoming_ack.packets.Min()
-                   << " which is smaller than least_packet_awaited_by_peer_: "
-                   << sent_packet_manager_->GetLeastPacketAwaitedByPeer(
-                          incoming_ack.path_id);
-      return "Missing packet smaller than least awaited.";
-    }
-    if (!sent_entropy_manager_.IsValidEntropy(incoming_ack.largest_observed,
-                                              incoming_ack.packets,
-                                              incoming_ack.entropy_hash)) {
-      DLOG(WARNING) << ENDPOINT << "Peer sent invalid entropy."
-                    << " largest_observed:" << incoming_ack.largest_observed
-                    << " last_received:" << last_header_.packet_number;
-      return "Invalid entropy.";
-    }
-  } else {
-    if (!incoming_ack.packets.Empty() &&
-        incoming_ack.packets.Max() != incoming_ack.largest_observed) {
-      QUIC_BUG << ENDPOINT
-               << "Peer last received packet: " << incoming_ack.packets.Max()
-               << " which is not equal to largest observed: "
-               << incoming_ack.largest_observed;
-      return "Last received packet not equal to largest observed.";
-    }
-  }
-
-  return nullptr;
-}
-
-const char* QuicConnection::ValidateStopWaitingFrame(
-    const QuicStopWaitingFrame& stop_waiting) {
-  if (stop_waiting.least_unacked <
-      received_packet_manager_.peer_least_packet_awaiting_ack()) {
-    DLOG(ERROR) << ENDPOINT << "Peer's sent low least_unacked: "
-                << stop_waiting.least_unacked << " vs "
-                << received_packet_manager_.peer_least_packet_awaiting_ack();
-    // We never process old ack frames, so this number should only increase.
-    return "Least unacked too small.";
-  }
-
-  if (stop_waiting.least_unacked > last_header_.packet_number) {
-    DLOG(ERROR) << ENDPOINT
-                << "Peer sent least_unacked:" << stop_waiting.least_unacked
-                << " greater than the enclosing packet number:"
-                << last_header_.packet_number;
-    return "Least unacked too large.";
-  }
-
-  return nullptr;
-}
-
-bool QuicConnection::OnRstStreamFrame(const QuicRstStreamFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnRstStreamFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT
-           << "RST_STREAM_FRAME received for stream: " << frame.stream_id
-           << " with error: "
-           << QuicUtils::StreamErrorToString(frame.error_code);
-  visitor_->OnRstStream(frame);
-  visitor_->PostProcessAfterData();
-  should_last_packet_instigate_acks_ = true;
-  return connected_;
-}
-
-bool QuicConnection::OnConnectionCloseFrame(
-    const QuicConnectionCloseFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnConnectionCloseFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT
-           << "Received ConnectionClose for connection: " << connection_id()
-           << ", with error: " << QuicUtils::ErrorToString(frame.error_code)
-           << " (" << frame.error_details << ")";
-  TearDownLocalConnectionState(frame.error_code, frame.error_details,
-                               ConnectionCloseSource::FROM_PEER);
-  return connected_;
-}
-
-bool QuicConnection::OnGoAwayFrame(const QuicGoAwayFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnGoAwayFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT << "GOAWAY_FRAME received with last good stream: "
-           << frame.last_good_stream_id
-           << " and error: " << QuicUtils::ErrorToString(frame.error_code)
-           << " and reason: " << frame.reason_phrase;
-
-  goaway_received_ = true;
-  visitor_->OnGoAway(frame);
-  visitor_->PostProcessAfterData();
-  should_last_packet_instigate_acks_ = true;
-  return connected_;
-}
-
-bool QuicConnection::OnWindowUpdateFrame(const QuicWindowUpdateFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnWindowUpdateFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT
-           << "WINDOW_UPDATE_FRAME received for stream: " << frame.stream_id
-           << " with byte offset: " << frame.byte_offset;
-  visitor_->OnWindowUpdateFrame(frame);
-  visitor_->PostProcessAfterData();
-  should_last_packet_instigate_acks_ = true;
-  return connected_;
-}
-
-bool QuicConnection::OnBlockedFrame(const QuicBlockedFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnBlockedFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT
-           << "BLOCKED_FRAME received for stream: " << frame.stream_id;
-  visitor_->OnBlockedFrame(frame);
-  visitor_->PostProcessAfterData();
-  should_last_packet_instigate_acks_ = true;
-  return connected_;
-}
-
-bool QuicConnection::OnPathCloseFrame(const QuicPathCloseFrame& frame) {
-  DCHECK(connected_);
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPathCloseFrame(frame);
-  }
-  DVLOG(1) << ENDPOINT
-           << "PATH_CLOSE_FRAME received for path: " << frame.path_id;
-  OnPathClosed(frame.path_id);
-  return connected_;
-}
-
-void QuicConnection::OnPacketComplete() {
-  // Don't do anything if this packet closed the connection.
-  if (!connected_) {
-    ClearLastFrames();
-    return;
-  }
-
-  DVLOG(1) << ENDPOINT << "Got packet " << last_header_.packet_number << " for "
-           << last_header_.public_header.connection_id;
-
-  // An ack will be sent if a missing retransmittable packet was received;
-  const bool was_missing =
-      should_last_packet_instigate_acks_ &&
-      received_packet_manager_.IsMissing(last_header_.packet_number);
-
-  // Record received to populate ack info correctly before processing stream
-  // frames, since the processing may result in a response packet with a bundled
-  // ack.
-  received_packet_manager_.RecordPacketReceived(last_size_, last_header_,
-                                                time_of_last_received_packet_);
-
-  // Process stop waiting frames here, instead of inline, because the packet
-  // needs to be considered 'received' before the entropy can be updated.
-  if (last_stop_waiting_frame_.least_unacked > 0) {
-    ProcessStopWaitingFrame(last_stop_waiting_frame_);
-    if (!connected_) {
-      return;
-    }
-  }
-
-  MaybeQueueAck(was_missing);
-
-  ClearLastFrames();
-  MaybeCloseIfTooManyOutstandingPackets();
-}
-
-void QuicConnection::MaybeQueueAck(bool was_missing) {
-  ++num_packets_received_since_last_ack_sent_;
-  // Always send an ack every 20 packets in order to allow the peer to discard
-  // information from the SentPacketManager and provide an RTT measurement.
-  if (num_packets_received_since_last_ack_sent_ >=
-      kMaxPacketsReceivedBeforeAckSend) {
-    ack_queued_ = true;
-  }
-
-  // Determine whether the newly received packet was missing before recording
-  // the received packet.
-  // Ack decimation with reordering relies on the timer to send an ack, but if
-  // missing packets we reported in the previous ack, send an ack immediately.
-  if (was_missing && (ack_mode_ != ACK_DECIMATION_WITH_REORDERING ||
-                      last_ack_had_missing_packets_)) {
-    ack_queued_ = true;
-  }
-
-  if (should_last_packet_instigate_acks_ && !ack_queued_) {
-    ++num_retransmittable_packets_received_since_last_ack_sent_;
-    if (ack_mode_ != TCP_ACKING &&
-        last_header_.packet_number > kMinReceivedBeforeAckDecimation) {
-      // Ack up to 10 packets at once.
-      if (num_retransmittable_packets_received_since_last_ack_sent_ >=
-          kMaxRetransmittablePacketsBeforeAck) {
-        ack_queued_ = true;
-      } else if (!ack_alarm_->IsSet()) {
-        // Wait the minimum of a quarter min_rtt and the delayed ack time.
-        QuicTime::Delta ack_delay = std::min(
-            DelayedAckTime(), sent_packet_manager_->GetRttStats()->min_rtt() *
-                                  ack_decimation_delay_);
-        ack_alarm_->Set(clock_->ApproximateNow() + ack_delay);
-      }
-    } else {
-      // Ack with a timer or every 2 packets by default.
-      if (num_retransmittable_packets_received_since_last_ack_sent_ >=
-          kDefaultRetransmittablePacketsBeforeAck) {
-        ack_queued_ = true;
-      } else if (!ack_alarm_->IsSet()) {
-        ack_alarm_->Set(clock_->ApproximateNow() + DelayedAckTime());
-      }
-    }
-
-    // If there are new missing packets to report, send an ack immediately.
-    if (received_packet_manager_.HasNewMissingPackets()) {
-      if (ack_mode_ == ACK_DECIMATION_WITH_REORDERING) {
-        // Wait the minimum of an eighth min_rtt and the existing ack time.
-        QuicTime ack_time =
-            clock_->ApproximateNow() +
-            0.125 * sent_packet_manager_->GetRttStats()->min_rtt();
-        if (!ack_alarm_->IsSet() || ack_alarm_->deadline() > ack_time) {
-          ack_alarm_->Update(ack_time, QuicTime::Delta::Zero());
-        }
-      } else {
-        ack_queued_ = true;
-      }
-    }
-  }
-
-  if (ack_queued_) {
-    ack_alarm_->Cancel();
-  }
-}
-
-void QuicConnection::ClearLastFrames() {
-  should_last_packet_instigate_acks_ = false;
-  last_stop_waiting_frame_.least_unacked = 0;
-}
-
-void QuicConnection::MaybeCloseIfTooManyOutstandingPackets() {
-  if (version() > QUIC_VERSION_33) {
-    return;
-  }
-  // This occurs if we don't discard old packets we've sent fast enough.
-  // It's possible largest observed is less than least unacked.
-  if (sent_packet_manager_->GetLargestObserved(last_header_.path_id) >
-      (sent_packet_manager_->GetLeastUnacked(last_header_.path_id) +
-       kMaxTrackedPackets)) {
-    CloseConnection(
-        QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS,
-        StringPrintf("More than %" PRIu64 " outstanding.", kMaxTrackedPackets),
-        ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-  }
-  // This occurs if there are received packet gaps and the peer does not raise
-  // the least unacked fast enough.
-  if (received_packet_manager_.NumTrackedPackets() > kMaxTrackedPackets) {
-    CloseConnection(
-        QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS,
-        StringPrintf("More than %" PRIu64 " outstanding.", kMaxTrackedPackets),
-        ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-  }
-}
-
-const QuicFrame QuicConnection::GetUpdatedAckFrame() {
-  return received_packet_manager_.GetUpdatedAckFrame(clock_->ApproximateNow());
-}
-
-void QuicConnection::PopulateStopWaitingFrame(
-    QuicStopWaitingFrame* stop_waiting) {
-  stop_waiting->least_unacked = GetLeastUnacked(stop_waiting->path_id);
-  if (version() <= QUIC_VERSION_33) {
-    stop_waiting->entropy_hash = sent_entropy_manager_.GetCumulativeEntropy(
-        stop_waiting->least_unacked - 1);
-  }
-}
-
-QuicPacketNumber QuicConnection::GetLeastUnacked(QuicPathId path_id) const {
-  return sent_packet_manager_->GetLeastUnacked(path_id);
-}
-
-void QuicConnection::MaybeSendInResponseToPacket() {
-  if (!connected_) {
-    return;
-  }
-  // Now that we have received an ack, we might be able to send packets which
-  // are queued locally, or drain streams which are blocked.
-  if (defer_send_in_response_to_packets_) {
-    send_alarm_->Update(clock_->ApproximateNow(), QuicTime::Delta::Zero());
-  } else {
-    WriteAndBundleAcksIfNotBlocked();
-  }
-}
-
-void QuicConnection::SendVersionNegotiationPacket() {
-  // TODO(alyssar): implement zero server state negotiation.
-  pending_version_negotiation_packet_ = true;
-  if (writer_->IsWriteBlocked()) {
-    visitor_->OnWriteBlocked();
-    return;
-  }
-  DVLOG(1) << ENDPOINT << "Sending version negotiation packet: {"
-           << QuicVersionVectorToString(framer_.supported_versions()) << "}";
-  std::unique_ptr<QuicEncryptedPacket> version_packet(
-      packet_generator_.SerializeVersionNegotiationPacket(
-          framer_.supported_versions()));
-  WriteResult result = writer_->WritePacket(
-      version_packet->data(), version_packet->length(),
-      self_address().address(), peer_address(), per_packet_options_);
-
-  if (result.status == WRITE_STATUS_ERROR) {
-    OnWriteError(result.error_code);
-    return;
-  }
-  if (result.status == WRITE_STATUS_BLOCKED) {
-    visitor_->OnWriteBlocked();
-    if (writer_->IsWriteBlockedDataBuffered()) {
-      pending_version_negotiation_packet_ = false;
-    }
-    return;
-  }
-
-  pending_version_negotiation_packet_ = false;
-}
-
-QuicConsumedData QuicConnection::SendStreamData(
-    QuicStreamId id,
-    QuicIOVector iov,
-    QuicStreamOffset offset,
-    bool fin,
-    QuicAckListenerInterface* listener) {
-  if (!fin && iov.total_length == 0) {
-    QUIC_BUG << "Attempt to send empty stream frame";
-    return QuicConsumedData(0, false);
-  }
-
-  // Opportunistically bundle an ack with every outgoing packet.
-  // Particularly, we want to bundle with handshake packets since we don't know
-  // which decrypter will be used on an ack packet following a handshake
-  // packet (a handshake packet from client to server could result in a REJ or a
-  // SHLO from the server, leading to two different decrypters at the server.)
-  ScopedRetransmissionScheduler alarm_delayer(this);
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  // The optimized path may be used for data only packets which fit into a
-  // standard buffer and don't need padding.
-  if (id != kCryptoStreamId && !packet_generator_.HasQueuedFrames() &&
-      iov.total_length > kMaxPacketSize) {
-    // Use the fast path to send full data packets.
-    return packet_generator_.ConsumeDataFastPath(id, iov, offset, fin,
-                                                 listener);
-  }
-  return packet_generator_.ConsumeData(id, iov, offset, fin, listener);
-}
-
-void QuicConnection::SendRstStream(QuicStreamId id,
-                                   QuicRstStreamErrorCode error,
-                                   QuicStreamOffset bytes_written) {
-  // Opportunistically bundle an ack with this outgoing packet.
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  packet_generator_.AddControlFrame(QuicFrame(new QuicRstStreamFrame(
-      id, AdjustErrorForVersion(error, version()), bytes_written)));
-
-  if (error == QUIC_STREAM_NO_ERROR) {
-    // All data for streams which are reset with QUIC_STREAM_NO_ERROR must
-    // be received by the peer.
-    return;
-  }
-
-  sent_packet_manager_->CancelRetransmissionsForStream(id);
-  // Remove all queued packets which only contain data for the reset stream.
-  QueuedPacketList::iterator packet_iterator = queued_packets_.begin();
-  while (packet_iterator != queued_packets_.end()) {
-    QuicFrames* retransmittable_frames =
-        &packet_iterator->retransmittable_frames;
-    if (retransmittable_frames->empty()) {
-      ++packet_iterator;
-      continue;
-    }
-    QuicUtils::RemoveFramesForStream(retransmittable_frames, id);
-    if (!retransmittable_frames->empty()) {
-      ++packet_iterator;
-      continue;
-    }
-    delete[] packet_iterator->encrypted_buffer;
-    QuicUtils::ClearSerializedPacket(&(*packet_iterator));
-    packet_iterator = queued_packets_.erase(packet_iterator);
-  }
-}
-
-void QuicConnection::SendWindowUpdate(QuicStreamId id,
-                                      QuicStreamOffset byte_offset) {
-  // Opportunistically bundle an ack with this outgoing packet.
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  packet_generator_.AddControlFrame(
-      QuicFrame(new QuicWindowUpdateFrame(id, byte_offset)));
-}
-
-void QuicConnection::SendBlocked(QuicStreamId id) {
-  // Opportunistically bundle an ack with this outgoing packet.
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  packet_generator_.AddControlFrame(QuicFrame(new QuicBlockedFrame(id)));
-}
-
-void QuicConnection::SendPathClose(QuicPathId path_id) {
-  // Opportunistically bundle an ack with this outgoing packet.
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  packet_generator_.AddControlFrame(QuicFrame(new QuicPathCloseFrame(path_id)));
-  OnPathClosed(path_id);
-}
-
-const QuicConnectionStats& QuicConnection::GetStats() {
-  const RttStats* rtt_stats = sent_packet_manager_->GetRttStats();
-
-  // Update rtt and estimated bandwidth.
-  QuicTime::Delta min_rtt = rtt_stats->min_rtt();
-  if (min_rtt.IsZero()) {
-    // If min RTT has not been set, use initial RTT instead.
-    min_rtt = QuicTime::Delta::FromMicroseconds(rtt_stats->initial_rtt_us());
-  }
-  stats_.min_rtt_us = min_rtt.ToMicroseconds();
-
-  QuicTime::Delta srtt = rtt_stats->smoothed_rtt();
-  if (srtt.IsZero()) {
-    // If SRTT has not been set, use initial RTT instead.
-    srtt = QuicTime::Delta::FromMicroseconds(rtt_stats->initial_rtt_us());
-  }
-  stats_.srtt_us = srtt.ToMicroseconds();
-
-  stats_.estimated_bandwidth = sent_packet_manager_->BandwidthEstimate();
-  stats_.max_packet_size = packet_generator_.GetCurrentMaxPacketLength();
-  stats_.max_received_packet_size = largest_received_packet_size_;
-  return stats_;
-}
-
-void QuicConnection::ProcessUdpPacket(const IPEndPoint& self_address,
-                                      const IPEndPoint& peer_address,
-                                      const QuicReceivedPacket& packet) {
-  if (!connected_) {
-    return;
-  }
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnPacketReceived(self_address, peer_address, packet);
-  }
-  last_size_ = packet.length();
-  current_packet_data_ = packet.data();
-
-  last_packet_destination_address_ = self_address;
-  last_packet_source_address_ = peer_address;
-  if (!IsInitializedIPEndPoint(self_address_)) {
-    self_address_ = last_packet_destination_address_;
-  }
-  if (!IsInitializedIPEndPoint(peer_address_)) {
-    peer_address_ = last_packet_source_address_;
-  }
-
-  stats_.bytes_received += packet.length();
-  ++stats_.packets_received;
-
-  time_of_last_received_packet_ = packet.receipt_time();
-  DVLOG(1) << ENDPOINT << "time of last received packet: "
-           << time_of_last_received_packet_.ToDebuggingValue();
-
-  ScopedRetransmissionScheduler alarm_delayer(this);
-  if (!framer_.ProcessPacket(packet)) {
-    // If we are unable to decrypt this packet, it might be
-    // because the CHLO or SHLO packet was lost.
-    if (framer_.error() == QUIC_DECRYPTION_FAILURE) {
-      if (encryption_level_ != ENCRYPTION_FORWARD_SECURE &&
-          undecryptable_packets_.size() < max_undecryptable_packets_) {
-        QueueUndecryptablePacket(packet);
-      } else if (debug_visitor_ != nullptr) {
-        debug_visitor_->OnUndecryptablePacket();
-      }
-    }
-    DVLOG(1) << ENDPOINT << "Unable to process packet.  Last packet processed: "
-             << last_header_.packet_number;
-    current_packet_data_ = nullptr;
-    return;
-  }
-
-  ++stats_.packets_processed;
-  if (active_peer_migration_type_ != NO_CHANGE &&
-      sent_packet_manager_->GetLargestObserved(last_header_.path_id) >
-          highest_packet_sent_before_peer_migration_) {
-    OnPeerMigrationValidated(last_header_.path_id);
-  }
-  MaybeProcessUndecryptablePackets();
-  MaybeSendInResponseToPacket();
-  SetPingAlarm();
-  current_packet_data_ = nullptr;
-}
-
-void QuicConnection::OnCanWrite() {
-  DCHECK(!writer_->IsWriteBlocked());
-
-  WriteQueuedPackets();
-  WritePendingRetransmissions();
-
-  // Sending queued packets may have caused the socket to become write blocked,
-  // or the congestion manager to prohibit sending.  If we've sent everything
-  // we had queued and we're still not blocked, let the visitor know it can
-  // write more.
-  if (!CanWrite(HAS_RETRANSMITTABLE_DATA)) {
-    return;
-  }
-
-  {
-    ScopedPacketBundler bundler(this, SEND_ACK_IF_QUEUED);
-    visitor_->OnCanWrite();
-    visitor_->PostProcessAfterData();
-  }
-
-  // After the visitor writes, it may have caused the socket to become write
-  // blocked or the congestion manager to prohibit sending, so check again.
-  if (visitor_->WillingAndAbleToWrite() && !resume_writes_alarm_->IsSet() &&
-      CanWrite(HAS_RETRANSMITTABLE_DATA)) {
-    // We're not write blocked, but some stream didn't write out all of its
-    // bytes. Register for 'immediate' resumption so we'll keep writing after
-    // other connections and events have had a chance to use the thread.
-    resume_writes_alarm_->Set(clock_->ApproximateNow());
-  }
-}
-
-void QuicConnection::WriteIfNotBlocked() {
-  if (!writer_->IsWriteBlocked()) {
-    OnCanWrite();
-  }
-}
-
-void QuicConnection::WriteAndBundleAcksIfNotBlocked() {
-  if (!writer_->IsWriteBlocked()) {
-    ScopedPacketBundler bundler(this, SEND_ACK_IF_QUEUED);
-    OnCanWrite();
-  }
-}
-
-bool QuicConnection::ProcessValidatedPacket(const QuicPacketHeader& header) {
-  if (header.fec_flag) {
-    // Drop any FEC packet.
-    return false;
-  }
-
-  if (perspective_ == Perspective::IS_SERVER &&
-      IsInitializedIPEndPoint(self_address_) &&
-      IsInitializedIPEndPoint(last_packet_destination_address_) &&
-      (!(self_address_ == last_packet_destination_address_))) {
-    CloseConnection(QUIC_ERROR_MIGRATING_ADDRESS,
-                    "Self address migration is not supported at the server.",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-
-  if (!Near(header.packet_number, last_header_.packet_number)) {
-    DVLOG(1) << ENDPOINT << "Packet " << header.packet_number
-             << " out of bounds.  Discarding";
-    CloseConnection(QUIC_INVALID_PACKET_HEADER, "packet number out of bounds.",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return false;
-  }
-
-  if (version_negotiation_state_ != NEGOTIATED_VERSION) {
-    if (perspective_ == Perspective::IS_SERVER) {
-      if (!header.public_header.version_flag) {
-        // Packets should have the version flag till version negotiation is
-        // done.
-        string error_details =
-            StringPrintf("%s Packet %" PRIu64
-                         " without version flag before version negotiated.",
-                         ENDPOINT, header.packet_number);
-        DLOG(WARNING) << error_details;
-        CloseConnection(QUIC_INVALID_VERSION, error_details,
-                        ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-        return false;
-      } else {
-        DCHECK_EQ(1u, header.public_header.versions.size());
-        DCHECK_EQ(header.public_header.versions[0], version());
-        version_negotiation_state_ = NEGOTIATED_VERSION;
-        received_packet_manager_.SetVersion(version());
-        visitor_->OnSuccessfulVersionNegotiation(version());
-        if (debug_visitor_ != nullptr) {
-          debug_visitor_->OnSuccessfulVersionNegotiation(version());
-        }
-      }
-    } else {
-      DCHECK(!header.public_header.version_flag);
-      // If the client gets a packet without the version flag from the server
-      // it should stop sending version since the version negotiation is done.
-      packet_generator_.StopSendingVersion();
-      version_negotiation_state_ = NEGOTIATED_VERSION;
-      received_packet_manager_.SetVersion(version());
-      visitor_->OnSuccessfulVersionNegotiation(version());
-      if (debug_visitor_ != nullptr) {
-        debug_visitor_->OnSuccessfulVersionNegotiation(version());
-      }
-    }
-  }
-
-  DCHECK_EQ(NEGOTIATED_VERSION, version_negotiation_state_);
-
-  if (last_size_ > largest_received_packet_size_) {
-    largest_received_packet_size_ = last_size_;
-  }
-
-  if (perspective_ == Perspective::IS_SERVER &&
-      encryption_level_ == ENCRYPTION_NONE &&
-      last_size_ > packet_generator_.GetCurrentMaxPacketLength()) {
-    SetMaxPacketLength(last_size_);
-  }
-  return true;
-}
-
-void QuicConnection::WriteQueuedPackets() {
-  DCHECK(!writer_->IsWriteBlocked());
-
-  if (pending_version_negotiation_packet_) {
-    SendVersionNegotiationPacket();
-  }
-
-  QueuedPacketList::iterator packet_iterator = queued_packets_.begin();
-  while (packet_iterator != queued_packets_.end() &&
-         WritePacket(&(*packet_iterator))) {
-    delete[] packet_iterator->encrypted_buffer;
-    QuicUtils::ClearSerializedPacket(&(*packet_iterator));
-    packet_iterator = queued_packets_.erase(packet_iterator);
-  }
-}
-
-void QuicConnection::WritePendingRetransmissions() {
-  // Keep writing as long as there's a pending retransmission which can be
-  // written.
-  while (sent_packet_manager_->HasPendingRetransmissions()) {
-    const PendingRetransmission pending =
-        sent_packet_manager_->NextPendingRetransmission();
-    if (!CanWrite(HAS_RETRANSMITTABLE_DATA)) {
-      break;
-    }
-
-    // Re-packetize the frames with a new packet number for retransmission.
-    // Retransmitted packets use the same packet number length as the
-    // original.
-    // Flush the packet generator before making a new packet.
-    // TODO(ianswett): Implement ReserializeAllFrames as a separate path that
-    // does not require the creator to be flushed.
-    packet_generator_.FlushAllQueuedFrames();
-    char buffer[kMaxPacketSize];
-    packet_generator_.ReserializeAllFrames(pending, buffer, kMaxPacketSize);
-  }
-}
-
-void QuicConnection::RetransmitUnackedPackets(
-    TransmissionType retransmission_type) {
-  sent_packet_manager_->RetransmitUnackedPackets(retransmission_type);
-
-  WriteIfNotBlocked();
-}
-
-void QuicConnection::NeuterUnencryptedPackets() {
-  sent_packet_manager_->NeuterUnencryptedPackets();
-  // This may have changed the retransmission timer, so re-arm it.
-  SetRetransmissionAlarm();
-}
-
-bool QuicConnection::ShouldGeneratePacket(
-    HasRetransmittableData retransmittable,
-    IsHandshake handshake) {
-  // We should serialize handshake packets immediately to ensure that they
-  // end up sent at the right encryption level.
-  if (handshake == IS_HANDSHAKE) {
-    return true;
-  }
-
-  return CanWrite(retransmittable);
-}
-
-bool QuicConnection::CanWrite(HasRetransmittableData retransmittable) {
-  if (!connected_) {
-    return false;
-  }
-
-  if (writer_->IsWriteBlocked()) {
-    visitor_->OnWriteBlocked();
-    return false;
-  }
-
-  // Allow acks to be sent immediately.
-  // TODO(ianswett): Remove retransmittable from
-  // SendAlgorithmInterface::TimeUntilSend.
-  if (retransmittable == NO_RETRANSMITTABLE_DATA) {
-    return true;
-  }
-  // If the send alarm is set, wait for it to fire.
-  if (send_alarm_->IsSet()) {
-    return false;
-  }
-
-  // TODO(fayang): If delay is not infinite, the next packet will be created and
-  // sent on path_id.
-  QuicPathId path_id = kInvalidPathId;
-  QuicTime now = clock_->Now();
-  QuicTime::Delta delay =
-      sent_packet_manager_->TimeUntilSend(now, retransmittable, &path_id);
-  if (delay.IsInfinite()) {
-    DCHECK_EQ(kInvalidPathId, path_id);
-    send_alarm_->Cancel();
-    return false;
-  }
-
-  DCHECK_NE(kInvalidPathId, path_id);
-  // If the scheduler requires a delay, then we can not send this packet now.
-  if (!delay.IsZero()) {
-    send_alarm_->Update(now + delay, QuicTime::Delta::FromMilliseconds(1));
-    DVLOG(1) << ENDPOINT << "Delaying sending " << delay.ToMilliseconds()
-             << "ms";
-    return false;
-  }
-  return true;
-}
-
-bool QuicConnection::WritePacket(SerializedPacket* packet) {
-  if (packet->packet_number <
-      sent_packet_manager_->GetLargestSentPacket(packet->path_id)) {
-    QUIC_BUG << "Attempt to write packet:" << packet->packet_number << " after:"
-             << sent_packet_manager_->GetLargestSentPacket(packet->path_id);
-    CloseConnection(QUIC_INTERNAL_ERROR, "Packet written out of order.",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return true;
-  }
-  if (ShouldDiscardPacket(*packet)) {
-    ++stats_.packets_discarded;
-    return true;
-  }
-  // Termination packets are encrypted and saved, so don't exit early.
-  const bool is_termination_packet = IsTerminationPacket(*packet);
-  if (writer_->IsWriteBlocked() && !is_termination_packet) {
-    return false;
-  }
-
-  QuicPacketNumber packet_number = packet->packet_number;
-  DCHECK_LE(packet_number_of_last_sent_packet_, packet_number);
-  packet_number_of_last_sent_packet_ = packet_number;
-
-  QuicPacketLength encrypted_length = packet->encrypted_length;
-  // Termination packets are eventually owned by TimeWaitListManager.
-  // Others are deleted at the end of this call.
-  if (is_termination_packet) {
-    if (termination_packets_.get() == nullptr) {
-      termination_packets_.reset(
-          new std::vector<std::unique_ptr<QuicEncryptedPacket>>);
-    }
-    // Copy the buffer so it's owned in the future.
-    char* buffer_copy = QuicUtils::CopyBuffer(*packet);
-    termination_packets_->push_back(std::unique_ptr<QuicEncryptedPacket>(
-        new QuicEncryptedPacket(buffer_copy, encrypted_length, true)));
-    // This assures we won't try to write *forced* packets when blocked.
-    // Return true to stop processing.
-    if (writer_->IsWriteBlocked()) {
-      visitor_->OnWriteBlocked();
-      return true;
-    }
-  }
-
-  DCHECK_LE(encrypted_length, kMaxPacketSize);
-  DCHECK_LE(encrypted_length, packet_generator_.GetCurrentMaxPacketLength());
-  DVLOG(1) << ENDPOINT << "Sending packet " << packet_number << " : "
-           << (IsRetransmittable(*packet) == HAS_RETRANSMITTABLE_DATA
-                   ? "data bearing "
-                   : " ack only ")
-           << ", encryption level: "
-           << QuicUtils::EncryptionLevelToString(packet->encryption_level)
-           << ", encrypted length:" << encrypted_length;
-  DVLOG(2) << ENDPOINT << "packet(" << packet_number << "): " << std::endl
-           << QuicUtils::HexDump(
-                  StringPiece(packet->encrypted_buffer, encrypted_length));
-
-  // Measure the RTT from before the write begins to avoid underestimating the
-  // min_rtt_, especially in cases where the thread blocks or gets swapped out
-  // during the WritePacket below.
-  QuicTime packet_send_time = clock_->Now();
-  WriteResult result = writer_->WritePacket(
-      packet->encrypted_buffer, encrypted_length, self_address().address(),
-      peer_address(), per_packet_options_);
-  if (result.error_code == ERR_IO_PENDING) {
-    DCHECK_EQ(WRITE_STATUS_BLOCKED, result.status);
-  }
-
-  if (result.status == WRITE_STATUS_BLOCKED) {
-    visitor_->OnWriteBlocked();
-    // If the socket buffers the the data, then the packet should not
-    // be queued and sent again, which would result in an unnecessary
-    // duplicate packet being sent.  The helper must call OnCanWrite
-    // when the write completes, and OnWriteError if an error occurs.
-    if (!writer_->IsWriteBlockedDataBuffered()) {
-      return false;
-    }
-  }
-  if (result.status != WRITE_STATUS_ERROR && debug_visitor_ != nullptr) {
-    // Pass the write result to the visitor.
-    debug_visitor_->OnPacketSent(*packet, packet->original_path_id,
-                                 packet->original_packet_number,
-                                 packet->transmission_type, packet_send_time);
-  }
-  if (packet->transmission_type == NOT_RETRANSMISSION) {
-    time_of_last_sent_new_packet_ = packet_send_time;
-    if (IsRetransmittable(*packet) == HAS_RETRANSMITTABLE_DATA &&
-        last_send_for_timeout_ <= time_of_last_received_packet_) {
-      last_send_for_timeout_ = packet_send_time;
-    }
-  }
-  SetPingAlarm();
-  MaybeSetMtuAlarm();
-  DVLOG(1) << ENDPOINT << "time we began writing last sent packet: "
-           << packet_send_time.ToDebuggingValue();
-
-  if (!FLAGS_quic_simple_packet_number_length) {
-    // TODO(ianswett): Change the packet number length and other packet creator
-    // options by a more explicit API than setting a struct value directly,
-    // perhaps via the NetworkChangeVisitor.
-    packet_generator_.UpdateSequenceNumberLength(
-        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
-        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
-  }
-
-  bool reset_retransmission_alarm = sent_packet_manager_->OnPacketSent(
-      packet, packet->original_path_id, packet->original_packet_number,
-      packet_send_time, packet->transmission_type, IsRetransmittable(*packet));
-
-  if (reset_retransmission_alarm || !retransmission_alarm_->IsSet()) {
-    SetRetransmissionAlarm();
-  }
-
-  if (FLAGS_quic_simple_packet_number_length) {
-    // The packet number length must be updated after OnPacketSent, because it
-    // may change the packet number length in packet.
-    packet_generator_.UpdateSequenceNumberLength(
-        sent_packet_manager_->GetLeastPacketAwaitedByPeer(packet->path_id),
-        sent_packet_manager_->EstimateMaxPacketsInFlight(max_packet_length()));
-  }
-
-  stats_.bytes_sent += result.bytes_written;
-  ++stats_.packets_sent;
-  if (packet->transmission_type != NOT_RETRANSMISSION) {
-    stats_.bytes_retransmitted += result.bytes_written;
-    ++stats_.packets_retransmitted;
-  }
-
-  if (result.status == WRITE_STATUS_ERROR) {
-    OnWriteError(result.error_code);
-    DLOG(ERROR) << ENDPOINT << "failed writing " << encrypted_length
-                << " bytes "
-                << " from host " << (self_address().address().empty()
-                                         ? " empty address "
-                                         : self_address().ToStringWithoutPort())
-                << " to address " << peer_address().ToString();
-    return false;
-  }
-
-  return true;
-}
-
-bool QuicConnection::ShouldDiscardPacket(const SerializedPacket& packet) {
-  if (!connected_) {
-    DVLOG(1) << ENDPOINT << "Not sending packet as connection is disconnected.";
-    return true;
-  }
-
-  QuicPacketNumber packet_number = packet.packet_number;
-  if (encryption_level_ == ENCRYPTION_FORWARD_SECURE &&
-      packet.encryption_level == ENCRYPTION_NONE) {
-    // Drop packets that are NULL encrypted since the peer won't accept them
-    // anymore.
-    DVLOG(1) << ENDPOINT << "Dropping NULL encrypted packet: " << packet_number
-             << " since the connection is forward secure.";
-    return true;
-  }
-
-  return false;
-}
-
-void QuicConnection::OnWriteError(int error_code) {
-  const string error_details = "Write failed with error: " +
-                               base::IntToString(error_code) + " (" +
-                               ErrorToString(error_code) + ")";
-  DVLOG(1) << ENDPOINT << error_details;
-  // We can't send an error as the socket is presumably borked.
-  TearDownLocalConnectionState(QUIC_PACKET_WRITE_ERROR, error_details,
-                               ConnectionCloseSource::FROM_SELF);
-}
-
-void QuicConnection::OnSerializedPacket(SerializedPacket* serialized_packet) {
-  DCHECK_NE(kInvalidPathId, serialized_packet->path_id);
-  if (serialized_packet->encrypted_buffer == nullptr) {
-    // We failed to serialize the packet, so close the connection.
-    // TearDownLocalConnectionState does not send close packet, so no infinite
-    // loop here.
-    // TODO(ianswett): This is actually an internal error, not an
-    // encryption failure.
-    TearDownLocalConnectionState(
-        QUIC_ENCRYPTION_FAILURE,
-        "Serialized packet does not have an encrypted buffer.",
-        ConnectionCloseSource::FROM_SELF);
-    return;
-  }
-  SendOrQueuePacket(serialized_packet);
-}
-
-void QuicConnection::OnUnrecoverableError(QuicErrorCode error,
-                                          const string& error_details,
-                                          ConnectionCloseSource source) {
-  // The packet creator or generator encountered an unrecoverable error: tear
-  // down local connection state immediately.
-  TearDownLocalConnectionState(error, error_details, source);
-}
-
-void QuicConnection::OnCongestionChange() {
-  visitor_->OnCongestionWindowChange(clock_->ApproximateNow());
-
-  // Uses the connection's smoothed RTT. If zero, uses initial_rtt.
-  QuicTime::Delta rtt = sent_packet_manager_->GetRttStats()->smoothed_rtt();
-  if (rtt.IsZero()) {
-    rtt = QuicTime::Delta::FromMicroseconds(
-        sent_packet_manager_->GetRttStats()->initial_rtt_us());
-  }
-
-  if (debug_visitor_)
-    debug_visitor_->OnRttChanged(rtt);
-}
-
-void QuicConnection::OnPathDegrading() {
-  visitor_->OnPathDegrading();
-}
-
-void QuicConnection::OnPathMtuIncreased(QuicPacketLength packet_size) {
-  DCHECK(FLAGS_quic_no_mtu_discovery_ack_listener);
-  if (packet_size > max_packet_length()) {
-    SetMaxPacketLength(packet_size);
-  }
-}
-
-void QuicConnection::OnHandshakeComplete() {
-  sent_packet_manager_->SetHandshakeConfirmed();
-  // The client should immediately ack the SHLO to confirm the handshake is
-  // complete with the server.
-  if (perspective_ == Perspective::IS_CLIENT && !ack_queued_ &&
-      ack_frame_updated()) {
-    ack_alarm_->Update(clock_->ApproximateNow(), QuicTime::Delta::Zero());
-  }
-}
-
-void QuicConnection::SendOrQueuePacket(SerializedPacket* packet) {
-  // The caller of this function is responsible for checking CanWrite().
-  if (packet->encrypted_buffer == nullptr) {
-    QUIC_BUG << "packet.encrypted_buffer == nullptr in to SendOrQueuePacket";
-    return;
-  }
-  if (version() <= QUIC_VERSION_33) {
-    sent_entropy_manager_.RecordPacketEntropyHash(packet->packet_number,
-                                                  packet->entropy_hash);
-  }
-  // If there are already queued packets, queue this one immediately to ensure
-  // it's written in sequence number order.
-  if (!queued_packets_.empty() || !WritePacket(packet)) {
-    // Take ownership of the underlying encrypted packet.
-    packet->encrypted_buffer = QuicUtils::CopyBuffer(*packet);
-    queued_packets_.push_back(*packet);
-    packet->retransmittable_frames.clear();
-  }
-
-  QuicUtils::ClearSerializedPacket(packet);
-  // If a forward-secure encrypter is available but is not being used and the
-  // next packet number is the first packet which requires
-  // forward security, start using the forward-secure encrypter.
-  if (encryption_level_ != ENCRYPTION_FORWARD_SECURE &&
-      has_forward_secure_encrypter_ &&
-      packet->packet_number >= first_required_forward_secure_packet_ - 1) {
-    SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
-  }
-}
-
-void QuicConnection::OnPingTimeout() {
-  if (!retransmission_alarm_->IsSet()) {
-    SendPing();
-  }
-}
-
-void QuicConnection::SendPing() {
-  ScopedPacketBundler bundler(this, SEND_ACK_IF_QUEUED);
-  packet_generator_.AddControlFrame(QuicFrame(QuicPingFrame()));
-  // Send PING frame immediately, without checking for congestion window bounds.
-  packet_generator_.FlushAllQueuedFrames();
-}
-
-void QuicConnection::SendAck() {
-  ack_alarm_->Cancel();
-  ack_queued_ = false;
-  stop_waiting_count_ = 0;
-  num_retransmittable_packets_received_since_last_ack_sent_ = 0;
-  last_ack_had_missing_packets_ = received_packet_manager_.HasMissingPackets();
-  num_packets_received_since_last_ack_sent_ = 0;
-
-  packet_generator_.SetShouldSendAck(true);
-}
-
-void QuicConnection::OnRetransmissionTimeout() {
-  DCHECK(sent_packet_manager_->HasUnackedPackets());
-
-  if (close_connection_after_five_rtos_ &&
-      sent_packet_manager_->GetConsecutiveRtoCount() >= 4) {
-    // Close on the 5th consecutive RTO, so after 4 previous RTOs have occurred.
-    CloseConnection(QUIC_TOO_MANY_RTOS, "5 consecutive retransmission timeouts",
-                    ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-    return;
-  }
-
-  sent_packet_manager_->OnRetransmissionTimeout();
-  WriteIfNotBlocked();
-
-  // A write failure can result in the connection being closed, don't attempt to
-  // write further packets, or to set alarms.
-  if (!connected_) {
-    return;
-  }
-
-  // In the TLP case, the SentPacketManager gives the connection the opportunity
-  // to send new data before retransmitting.
-  if (sent_packet_manager_->MaybeRetransmitTailLossProbe()) {
-    // Send the pending retransmission now that it's been queued.
-    WriteIfNotBlocked();
-  }
-
-  // Ensure the retransmission alarm is always set if there are unacked packets
-  // and nothing waiting to be sent.
-  // This happens if the loss algorithm invokes a timer based loss, but the
-  // packet doesn't need to be retransmitted.
-  if (!HasQueuedData() && !retransmission_alarm_->IsSet()) {
-    SetRetransmissionAlarm();
-  }
-}
-
-void QuicConnection::SetEncrypter(EncryptionLevel level,
-                                  QuicEncrypter* encrypter) {
-  packet_generator_.SetEncrypter(level, encrypter);
-  if (level == ENCRYPTION_FORWARD_SECURE) {
-    has_forward_secure_encrypter_ = true;
-    first_required_forward_secure_packet_ =
-        packet_number_of_last_sent_packet_ +
-        // 3 times the current congestion window (in slow start) should cover
-        // about two full round trips worth of packets, which should be
-        // sufficient.
-        3 *
-            sent_packet_manager_->EstimateMaxPacketsInFlight(
-                max_packet_length());
-  }
-}
-
-void QuicConnection::SetDiversificationNonce(const DiversificationNonce nonce) {
-  DCHECK_EQ(Perspective::IS_SERVER, perspective_);
-  packet_generator_.SetDiversificationNonce(nonce);
-}
-
-void QuicConnection::SetDefaultEncryptionLevel(EncryptionLevel level) {
-  encryption_level_ = level;
-  packet_generator_.set_encryption_level(level);
-}
-
-void QuicConnection::SetDecrypter(EncryptionLevel level,
-                                  QuicDecrypter* decrypter) {
-  framer_.SetDecrypter(level, decrypter);
-}
-
-void QuicConnection::SetAlternativeDecrypter(EncryptionLevel level,
-                                             QuicDecrypter* decrypter,
-                                             bool latch_once_used) {
-  framer_.SetAlternativeDecrypter(level, decrypter, latch_once_used);
-}
-
-const QuicDecrypter* QuicConnection::decrypter() const {
-  return framer_.decrypter();
-}
-
-const QuicDecrypter* QuicConnection::alternative_decrypter() const {
-  return framer_.alternative_decrypter();
-}
-
-void QuicConnection::QueueUndecryptablePacket(
-    const QuicEncryptedPacket& packet) {
-  DVLOG(1) << ENDPOINT << "Queueing undecryptable packet.";
-  undecryptable_packets_.push_back(packet.Clone());
-}
-
-void QuicConnection::MaybeProcessUndecryptablePackets() {
-  if (undecryptable_packets_.empty() || encryption_level_ == ENCRYPTION_NONE) {
-    return;
-  }
-
-  while (connected_ && !undecryptable_packets_.empty()) {
-    DVLOG(1) << ENDPOINT << "Attempting to process undecryptable packet";
-    QuicEncryptedPacket* packet = undecryptable_packets_.front();
-    if (!framer_.ProcessPacket(*packet) &&
-        framer_.error() == QUIC_DECRYPTION_FAILURE) {
-      DVLOG(1) << ENDPOINT << "Unable to process undecryptable packet...";
-      break;
-    }
-    DVLOG(1) << ENDPOINT << "Processed undecryptable packet!";
-    ++stats_.packets_processed;
-    delete packet;
-    undecryptable_packets_.pop_front();
-  }
-
-  // Once forward secure encryption is in use, there will be no
-  // new keys installed and hence any undecryptable packets will
-  // never be able to be decrypted.
-  if (encryption_level_ == ENCRYPTION_FORWARD_SECURE) {
-    if (debug_visitor_ != nullptr) {
-      // TODO(rtenneti): perhaps more efficient to pass the number of
-      // undecryptable packets as the argument to OnUndecryptablePacket so that
-      // we just need to call OnUndecryptablePacket once?
-      for (size_t i = 0; i < undecryptable_packets_.size(); ++i) {
-        debug_visitor_->OnUndecryptablePacket();
-      }
-    }
-    STLDeleteElements(&undecryptable_packets_);
-  }
-}
-
-void QuicConnection::CloseConnection(
-    QuicErrorCode error,
-    const string& error_details,
-    ConnectionCloseBehavior connection_close_behavior) {
-  DCHECK(!error_details.empty());
-  if (!connected_) {
-    DVLOG(1) << "Connection is already closed.";
-    return;
-  }
-
-  DVLOG(1) << ENDPOINT << "Closing connection: " << connection_id()
-           << ", with error: " << QuicUtils::ErrorToString(error) << " ("
-           << error << "), and details:  " << error_details;
-
-  if (connection_close_behavior ==
-      ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET) {
-    SendConnectionClosePacket(error, error_details);
-  }
-
-  TearDownLocalConnectionState(error, error_details,
-                               ConnectionCloseSource::FROM_SELF);
-}
-
-void QuicConnection::SendConnectionClosePacket(QuicErrorCode error,
-                                               const string& details) {
-  DVLOG(1) << ENDPOINT << "Sending connection close packet.";
-  ClearQueuedPackets();
-  ScopedPacketBundler ack_bundler(this, SEND_ACK);
-  QuicConnectionCloseFrame* frame = new QuicConnectionCloseFrame();
-  frame->error_code = error;
-  frame->error_details = details;
-  packet_generator_.AddControlFrame(QuicFrame(frame));
-  packet_generator_.FlushAllQueuedFrames();
-}
-
-void QuicConnection::TearDownLocalConnectionState(
-    QuicErrorCode error,
-    const string& error_details,
-    ConnectionCloseSource source) {
-  if (!connected_) {
-    DVLOG(1) << "Connection is already closed.";
-    return;
-  }
-  connected_ = false;
-  DCHECK(visitor_ != nullptr);
-  // TODO(rtenneti): crbug.com/546668. A temporary fix. Added a check for null
-  // |visitor_| to fix crash bug. Delete |visitor_| check and histogram after
-  // fix is merged.
-  if (visitor_ != nullptr) {
-    visitor_->OnConnectionClosed(error, error_details, source);
-  } else {
-    UMA_HISTOGRAM_BOOLEAN("Net.QuicCloseConnection.NullVisitor", true);
-  }
-  if (debug_visitor_ != nullptr) {
-    debug_visitor_->OnConnectionClosed(error, error_details, source);
-  }
-  // Cancel the alarms so they don't trigger any action now that the
-  // connection is closed.
-  CancelAllAlarms();
-}
-
-void QuicConnection::CancelAllAlarms() {
-  ack_alarm_->Cancel();
-  ping_alarm_->Cancel();
-  resume_writes_alarm_->Cancel();
-  retransmission_alarm_->Cancel();
-  send_alarm_->Cancel();
-  timeout_alarm_->Cancel();
-  mtu_discovery_alarm_->Cancel();
-}
-
-void QuicConnection::SendGoAway(QuicErrorCode error,
-                                QuicStreamId last_good_stream_id,
-                                const string& reason) {
-  if (goaway_sent_) {
-    return;
-  }
-  goaway_sent_ = true;
-
-  DVLOG(1) << ENDPOINT << "Going away with error "
-           << QuicUtils::ErrorToString(error) << " (" << error << ")";
-
-  // Opportunistically bundle an ack with this outgoing packet.
-  ScopedPacketBundler ack_bundler(this, SEND_ACK_IF_PENDING);
-  packet_generator_.AddControlFrame(
-      QuicFrame(new QuicGoAwayFrame(error, last_good_stream_id, reason)));
-}
-
-QuicByteCount QuicConnection::max_packet_length() const {
-  return packet_generator_.GetCurrentMaxPacketLength();
-}
-
-void QuicConnection::SetMaxPacketLength(QuicByteCount length) {
-  return packet_generator_.SetMaxPacketLength(LimitMaxPacketSize(length));
-}
-
-bool QuicConnection::HasQueuedData() const {
-  return pending_version_negotiation_packet_ || !queued_packets_.empty() ||
-         packet_generator_.HasQueuedFrames();
-}
-
-void QuicConnection::EnableSavingCryptoPackets() {
-  save_crypto_packets_as_termination_packets_ = true;
-}
-
-bool QuicConnection::CanWriteStreamData() {
-  // Don't write stream data if there are negotiation or queued data packets
-  // to send. Otherwise, continue and bundle as many frames as possible.
-  if (pending_version_negotiation_packet_ || !queued_packets_.empty()) {
-    return false;
-  }
-
-  IsHandshake pending_handshake =
-      visitor_->HasPendingHandshake() ? IS_HANDSHAKE : NOT_HANDSHAKE;
-  // Sending queued packets may have caused the socket to become write blocked,
-  // or the congestion manager to prohibit sending.  If we've sent everything
-  // we had queued and we're still not blocked, let the visitor know it can
-  // write more.
-  return ShouldGeneratePacket(HAS_RETRANSMITTABLE_DATA, pending_handshake);
-}
-
-void QuicConnection::SetNetworkTimeouts(QuicTime::Delta handshake_timeout,
-                                        QuicTime::Delta idle_timeout) {
-  QUIC_BUG_IF(idle_timeout > handshake_timeout)
-      << "idle_timeout:" << idle_timeout.ToMilliseconds()
-      << " handshake_timeout:" << handshake_timeout.ToMilliseconds();
-  // Adjust the idle timeout on client and server to prevent clients from
-  // sending requests to servers which have already closed the connection.
-  if (perspective_ == Perspective::IS_SERVER) {
-    idle_timeout = idle_timeout + QuicTime::Delta::FromSeconds(3);
-  } else if (idle_timeout > QuicTime::Delta::FromSeconds(1)) {
-    idle_timeout = idle_timeout - QuicTime::Delta::FromSeconds(1);
-  }
-  handshake_timeout_ = handshake_timeout;
-  idle_network_timeout_ = idle_timeout;
-
-  SetTimeoutAlarm();
-}
-
-void QuicConnection::CheckForTimeout() {
-  QuicTime now = clock_->ApproximateNow();
-  QuicTime time_of_last_packet =
-      max(time_of_last_received_packet_, last_send_for_timeout_);
-
-  // |delta| can be < 0 as |now| is approximate time but |time_of_last_packet|
-  // is accurate time. However, this should not change the behavior of
-  // timeout handling.
-  QuicTime::Delta idle_duration = now - time_of_last_packet;
-  DVLOG(1) << ENDPOINT << "last packet "
-           << time_of_last_packet.ToDebuggingValue()
-           << " now:" << now.ToDebuggingValue()
-           << " idle_duration:" << idle_duration.ToMicroseconds()
-           << " idle_network_timeout: "
-           << idle_network_timeout_.ToMicroseconds();
-  if (idle_duration >= idle_network_timeout_) {
-    const string error_details = "No recent network activity.";
-    DVLOG(1) << ENDPOINT << error_details;
-    CloseConnection(QUIC_NETWORK_IDLE_TIMEOUT, error_details,
-                    idle_timeout_connection_close_behavior_);
-    return;
-  }
-
-  if (!handshake_timeout_.IsInfinite()) {
-    QuicTime::Delta connected_duration = now - stats_.connection_creation_time;
-    DVLOG(1) << ENDPOINT
-             << "connection time: " << connected_duration.ToMicroseconds()
-             << " handshake timeout: " << handshake_timeout_.ToMicroseconds();
-    if (connected_duration >= handshake_timeout_) {
-      const string error_details = "Handshake timeout expired.";
-      DVLOG(1) << ENDPOINT << error_details;
-      CloseConnection(QUIC_HANDSHAKE_TIMEOUT, error_details,
-                      ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
-      return;
-    }
-  }
-
-  SetTimeoutAlarm();
-}
-
-void QuicConnection::SetTimeoutAlarm() {
-  QuicTime time_of_last_packet =
-      max(time_of_last_received_packet_, time_of_last_sent_new_packet_);
-
-  QuicTime deadline = time_of_last_packet + idle_network_timeout_;
-  if (!handshake_timeout_.IsInfinite()) {
-    deadline =
-        min(deadline, stats_.connection_creation_time + handshake_timeout_);
-  }
-
-  timeout_alarm_->Update(deadline, QuicTime::Delta::Zero());
-}
-
-void QuicConnection::SetPingAlarm() {
-  if (perspective_ == Perspective::IS_SERVER) {
-    // Only clients send pings.
-    return;
-  }
-  if (!visitor_->HasOpenDynamicStreams()) {
-    ping_alarm_->Cancel();
-    // Don't send a ping unless there are open streams.
-    return;
-  }
-  QuicTime::Delta ping_timeout = QuicTime::Delta::FromSeconds(kPingTimeoutSecs);
-  ping_alarm_->Update(clock_->ApproximateNow() + ping_timeout,
-                      QuicTime::Delta::FromSeconds(1));
-}
-
-void QuicConnection::SetRetransmissionAlarm() {
-  if (delay_setting_retransmission_alarm_) {
-    pending_retransmission_alarm_ = true;
-    return;
-  }
-  QuicTime retransmission_time = sent_packet_manager_->GetRetransmissionTime();
-  retransmission_alarm_->Update(retransmission_time,
-                                QuicTime::Delta::FromMilliseconds(1));
-}
-
-void QuicConnection::MaybeSetMtuAlarm() {
-  // Do not set the alarm if the target size is less than the current size.
-  // This covers the case when |mtu_discovery_target_| is at its default value,
-  // zero.
-  if (mtu_discovery_target_ <= max_packet_length()) {
-    return;
-  }
-
-  if (mtu_probe_count_ >= kMtuDiscoveryAttempts) {
-    return;
-  }
-
-  if (mtu_discovery_alarm_->IsSet()) {
-    return;
-  }
-
-  if (packet_number_of_last_sent_packet_ >= next_mtu_probe_at_) {
-    // Use an alarm to send the MTU probe to ensure that no ScopedPacketBundlers
-    // are active.
-    mtu_discovery_alarm_->Set(clock_->ApproximateNow());
-  }
-}
-
-QuicConnection::ScopedPacketBundler::ScopedPacketBundler(
-    QuicConnection* connection,
-    AckBundling ack_mode)
-    : connection_(connection),
-      already_in_batch_mode_(connection != nullptr &&
-                             connection->packet_generator_.InBatchMode()) {
-  if (connection_ == nullptr) {
-    return;
-  }
-  // Move generator into batch mode. If caller wants us to include an ack,
-  // check the delayed-ack timer to see if there's ack info to be sent.
-  if (!already_in_batch_mode_) {
-    DVLOG(2) << "Entering Batch Mode.";
-    connection_->packet_generator_.StartBatchOperations();
-  }
-  if (ShouldSendAck(ack_mode)) {
-    DVLOG(1) << "Bundling ack with outgoing packet.";
-    DCHECK(ack_mode == SEND_ACK || connection_->ack_frame_updated() ||
-           connection_->stop_waiting_count_ > 1);
-    connection_->SendAck();
-  }
-}
-
-bool QuicConnection::ScopedPacketBundler::ShouldSendAck(
-    AckBundling ack_mode) const {
-  switch (ack_mode) {
-    case SEND_ACK:
-      return true;
-    case SEND_ACK_IF_QUEUED:
-      return connection_->ack_queued();
-    case SEND_ACK_IF_PENDING:
-      return connection_->ack_alarm_->IsSet() ||
-             connection_->stop_waiting_count_ > 1;
-    default:
-      QUIC_BUG << "Unsupported ack_mode.";
-      return true;
-  }
-}
-
-QuicConnection::ScopedPacketBundler::~ScopedPacketBundler() {
-  if (connection_ == nullptr) {
-    return;
-  }
-  // If we changed the generator's batch state, restore original batch state.
-  if (!already_in_batch_mode_) {
-    DVLOG(2) << "Leaving Batch Mode.";
-    connection_->packet_generator_.FinishBatchOperations();
-  }
-  DCHECK_EQ(already_in_batch_mode_,
-            connection_->packet_generator_.InBatchMode());
-}
-
-QuicConnection::ScopedRetransmissionScheduler::ScopedRetransmissionScheduler(
-    QuicConnection* connection)
-    : connection_(connection),
-      already_delayed_(connection_->delay_setting_retransmission_alarm_) {
-  connection_->delay_setting_retransmission_alarm_ = true;
-}
-
-QuicConnection::ScopedRetransmissionScheduler::
-    ~ScopedRetransmissionScheduler() {
-  if (already_delayed_) {
-    return;
-  }
-  connection_->delay_setting_retransmission_alarm_ = false;
-  if (connection_->pending_retransmission_alarm_) {
-    connection_->SetRetransmissionAlarm();
-    connection_->pending_retransmission_alarm_ = false;
-  }
-}
-
-HasRetransmittableData QuicConnection::IsRetransmittable(
-    const SerializedPacket& packet) {
-  // Retransmitted packets retransmittable frames are owned by the unacked
-  // packet map, but are not present in the serialized packet.
-  if (packet.transmission_type != NOT_RETRANSMISSION ||
-      !packet.retransmittable_frames.empty()) {
-    return HAS_RETRANSMITTABLE_DATA;
-  } else {
-    return NO_RETRANSMITTABLE_DATA;
-  }
-}
-
-bool QuicConnection::IsTerminationPacket(const SerializedPacket& packet) {
-  if (packet.retransmittable_frames.empty()) {
-    return false;
-  }
-  for (const QuicFrame& frame : packet.retransmittable_frames) {
-    if (frame.type == CONNECTION_CLOSE_FRAME) {
-      return true;
-    }
-    if (save_crypto_packets_as_termination_packets_ &&
-        frame.type == STREAM_FRAME &&
-        frame.stream_frame->stream_id == kCryptoStreamId) {
-      return true;
-    }
-  }
-  return false;
-}
-
-void QuicConnection::SetMtuDiscoveryTarget(QuicByteCount target) {
-  mtu_discovery_target_ = LimitMaxPacketSize(target);
-}
-
-QuicByteCount QuicConnection::LimitMaxPacketSize(
-    QuicByteCount suggested_max_packet_size) {
-  if (peer_address_.address().empty()) {
-    QUIC_BUG << "Attempted to use a connection without a valid peer address";
-    return suggested_max_packet_size;
-  }
-
-  const QuicByteCount writer_limit = writer_->GetMaxPacketSize(peer_address());
-
-  QuicByteCount max_packet_size = suggested_max_packet_size;
-  if (max_packet_size > writer_limit) {
-    max_packet_size = writer_limit;
-  }
-  if (max_packet_size > kMaxPacketSize) {
-    max_packet_size = kMaxPacketSize;
-  }
-  return max_packet_size;
-}
-
-void QuicConnection::SendMtuDiscoveryPacket(QuicByteCount target_mtu) {
-  // Currently, this limit is ensured by the caller.
-  DCHECK_EQ(target_mtu, LimitMaxPacketSize(target_mtu));
-
-  // Create a listener for the new probe.  The ownership of the listener is
-  // transferred to the AckNotifierManager.  The notifier will get destroyed
-  // before the connection (because it's stored in one of the connection's
-  // subfields), hence |this| pointer is guaranteed to stay valid at all times.
-  scoped_refptr<MtuDiscoveryAckListener> last_mtu_discovery_ack_listener(
-      new MtuDiscoveryAckListener(this, target_mtu));
-
-  // Send the probe.
-  packet_generator_.GenerateMtuDiscoveryPacket(
-      target_mtu, FLAGS_quic_no_mtu_discovery_ack_listener
-                      ? nullptr
-                      : last_mtu_discovery_ack_listener.get());
-}
-
-void QuicConnection::DiscoverMtu() {
-  DCHECK(!mtu_discovery_alarm_->IsSet());
-
-  // Check if the MTU has been already increased.
-  if (mtu_discovery_target_ <= max_packet_length()) {
-    return;
-  }
-
-  // Calculate the packet number of the next probe *before* sending the current
-  // one.  Otherwise, when SendMtuDiscoveryPacket() is called,
-  // MaybeSetMtuAlarm() will not realize that the probe has been just sent, and
-  // will reschedule this probe again.
-  packets_between_mtu_probes_ *= 2;
-  next_mtu_probe_at_ =
-      packet_number_of_last_sent_packet_ + packets_between_mtu_probes_ + 1;
-  ++mtu_probe_count_;
-
-  DVLOG(2) << "Sending a path MTU discovery packet #" << mtu_probe_count_;
-  SendMtuDiscoveryPacket(mtu_discovery_target_);
-
-  DCHECK(!mtu_discovery_alarm_->IsSet());
-}
-
-void QuicConnection::OnPeerMigrationValidated(QuicPathId path_id) {
-  if (active_peer_migration_type_ == NO_CHANGE) {
-    QUIC_BUG << "No migration underway.";
-    return;
-  }
-  highest_packet_sent_before_peer_migration_ = 0;
-  active_peer_migration_type_ = NO_CHANGE;
-}
-
-// TODO(jri): Modify method to start migration whenever a new IP address is seen
-// from a packet with sequence number > the one that triggered the previous
-// migration. This should happen even if a migration is underway, since the
-// most recent migration is the one that we should pay attention to.
-void QuicConnection::StartPeerMigration(
-    QuicPathId path_id,
-    PeerAddressChangeType peer_migration_type) {
-  // TODO(fayang): Currently, all peer address change type are allowed. Need to
-  // add a method ShouldAllowPeerAddressChange(PeerAddressChangeType type) to
-  // determine whether |type| is allowed.
-  if (active_peer_migration_type_ != NO_CHANGE ||
-      peer_migration_type == NO_CHANGE) {
-    QUIC_BUG << "Migration underway or no new migration started.";
-    return;
-  }
-  DVLOG(1) << ENDPOINT << "Peer's ip:port changed from "
-           << peer_address_.ToString() << " to "
-           << last_packet_source_address_.ToString()
-           << ", migrating connection.";
-
-  highest_packet_sent_before_peer_migration_ =
-      packet_number_of_last_sent_packet_;
-  peer_address_ = last_packet_source_address_;
-  active_peer_migration_type_ = peer_migration_type;
-
-  // TODO(jri): Move these calls to OnPeerMigrationValidated. Rename
-  // OnConnectionMigration methods to OnPeerMigration.
-  visitor_->OnConnectionMigration(peer_migration_type);
-  sent_packet_manager_->OnConnectionMigration(path_id, peer_migration_type);
-}
-
-void QuicConnection::OnPathClosed(QuicPathId path_id) {
-  // Stop receiving packets on this path.
-  framer_.OnPathClosed(path_id);
-}
-
-bool QuicConnection::ack_frame_updated() const {
-  return received_packet_manager_.ack_frame_updated();
-}
-
-StringPiece QuicConnection::GetCurrentPacket() {
-  if (current_packet_data_ == nullptr) {
-    return StringPiece();
-  }
-  return StringPiece(current_packet_data_, last_size_);
-}
-
-bool QuicConnection::MaybeConsiderAsMemoryCorruption(
-    const QuicStreamFrame& frame) {
-  if (frame.stream_id == kCryptoStreamId ||
-      last_decrypted_packet_level_ != ENCRYPTION_NONE) {
-    return false;
-  }
-
-  if (perspective_ == Perspective::IS_SERVER &&
-      frame.data_length >= sizeof(kCHLO) &&
-      strncmp(frame.data_buffer, reinterpret_cast<const char*>(&kCHLO),
-              sizeof(kCHLO)) == 0) {
-    return true;
-  }
-
-  if (perspective_ == Perspective::IS_CLIENT &&
-      frame.data_length >= sizeof(kREJ) &&
-      strncmp(frame.data_buffer, reinterpret_cast<const char*>(&kREJ),
-              sizeof(kREJ)) == 0) {
-    return true;
-  }
-
-  return false;
-}
-
-// Uses a 25ms delayed ack timer. Also helps with better signaling
-// in low-bandwidth (< ~384 kbps), where an ack is sent per packet.
-// Ensures that the Delayed Ack timer is always set to a value lesser
-// than the retransmission timer's minimum value (MinRTO). We want the
-// delayed ack to get back to the QUIC peer before the sender's
-// retransmission timer triggers.  Since we do not know the
-// reverse-path one-way delay, we assume equal delays for forward and
-// reverse paths, and ensure that the timer is set to less than half
-// of the MinRTO.
-// There may be a value in making this delay adaptive with the help of
-// the sender and a signaling mechanism -- if the sender uses a
-// different MinRTO, we may get spurious retransmissions. May not have
-// any benefits, but if the delayed ack becomes a significant source
-// of (likely, tail) latency, then consider such a mechanism.
-const QuicTime::Delta QuicConnection::DelayedAckTime() {
-  return QuicTime::Delta::FromMilliseconds(
-      min(kMaxDelayedAckTimeMs, kMinRetransmissionTimeMs / 2));
-}
-
-}  // namespace net