quiche/quic/core/quic_ping_manager.cc

// Copyright (c) 2022 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 "quiche/quic/core/quic_ping_manager.h"

#include "quiche/quic/platform/api/quic_flags.h"

namespace quic {

namespace {

// Maximum shift used to calculate retransmittable on wire timeout. For 200ms
// initial retransmittable on wire delay, this would get a maximum of 200ms * (1
// << 10) = 204.8s
const int kMaxRetransmittableOnWireDelayShift = 10;

class AlarmDelegate : public QuicAlarm::DelegateWithContext {
 public:
  explicit AlarmDelegate(QuicPingManager* manager,
                         QuicConnectionContext* context)
      : QuicAlarm::DelegateWithContext(context), manager_(manager) {}
  AlarmDelegate(const AlarmDelegate&) = delete;
  AlarmDelegate& operator=(const AlarmDelegate&) = delete;

  void OnAlarm() override { manager_->OnAlarm(); }

 private:
  QuicPingManager* manager_;
};

}  // namespace

QuicPingManager::QuicPingManager(Perspective perspective, Delegate* delegate,
                                 QuicConnectionArena* arena,
                                 QuicAlarmFactory* alarm_factory,
                                 QuicConnectionContext* context)
    : perspective_(perspective),
      delegate_(delegate),
      alarm_(alarm_factory->CreateAlarm(
          arena->New<AlarmDelegate>(this, context), arena)) {}

void QuicPingManager::SetAlarm(QuicTime now, bool should_keep_alive,
                               bool has_in_flight_packets) {
  UpdateDeadlines(now, should_keep_alive, has_in_flight_packets);
  const QuicTime earliest_deadline = GetEarliestDeadline();
  if (!earliest_deadline.IsInitialized()) {
    alarm_->Cancel();
    return;
  }
  if (earliest_deadline == keep_alive_deadline_) {
    // Use 1s granularity for keep-alive time.
    alarm_->Update(earliest_deadline, QuicTime::Delta::FromSeconds(1));
    return;
  }
  alarm_->Update(earliest_deadline, kAlarmGranularity);
}

void QuicPingManager::OnAlarm() {
  const QuicTime earliest_deadline = GetEarliestDeadline();
  if (!earliest_deadline.IsInitialized()) {
    QUIC_BUG(quic_ping_manager_alarm_fires_unexpectedly)
        << "QuicPingManager alarm fires unexpectedly.";
    return;
  }
  // Please note, alarm does not get re-armed here, and we are relying on caller
  // to SetAlarm later.
  if (earliest_deadline == retransmittable_on_wire_deadline_) {
    retransmittable_on_wire_deadline_ = QuicTime::Zero();
    if (GetQuicFlag(quic_max_aggressive_retransmittable_on_wire_ping_count) !=
        0) {
      ++consecutive_retransmittable_on_wire_count_;
    }
    ++retransmittable_on_wire_count_;
    delegate_->OnRetransmittableOnWireTimeout();
    return;
  }
  if (earliest_deadline == keep_alive_deadline_) {
    keep_alive_deadline_ = QuicTime::Zero();
    delegate_->OnKeepAliveTimeout();
  }
}

void QuicPingManager::Stop() {
  alarm_->PermanentCancel();
  retransmittable_on_wire_deadline_ = QuicTime::Zero();
  keep_alive_deadline_ = QuicTime::Zero();
}

void QuicPingManager::UpdateDeadlines(QuicTime now, bool should_keep_alive,
                                      bool has_in_flight_packets) {
  // Reset keep-alive deadline given it will be set later (with left edge
  // |now|).
  keep_alive_deadline_ = QuicTime::Zero();
  if (perspective_ == Perspective::IS_SERVER &&
      initial_retransmittable_on_wire_timeout_.IsInfinite()) {
    // The PING alarm exists to support two features:
    // 1) clients send PINGs every 15s to prevent NAT timeouts,
    // 2) both clients and servers can send retransmittable on the wire PINGs
    // (ROWP) while ShouldKeepConnectionAlive is true and there is no packets in
    // flight.
    QUICHE_DCHECK(!retransmittable_on_wire_deadline_.IsInitialized());
    return;
  }
  if (!should_keep_alive) {
    // Don't send a ping unless the application (ie: HTTP/3) says to, usually
    // because it is expecting a response from the peer.
    retransmittable_on_wire_deadline_ = QuicTime::Zero();
    return;
  }
  if (perspective_ == Perspective::IS_CLIENT) {
    // Clients send 15s PINGs to avoid NATs from timing out.
    keep_alive_deadline_ = now + keep_alive_timeout_;
  }
  if (initial_retransmittable_on_wire_timeout_.IsInfinite() ||
      has_in_flight_packets ||
      retransmittable_on_wire_count_ >
          GetQuicFlag(quic_max_retransmittable_on_wire_ping_count)) {
    // No need to set retransmittable-on-wire timeout.
    retransmittable_on_wire_deadline_ = QuicTime::Zero();
    return;
  }

  QUICHE_DCHECK_LT(initial_retransmittable_on_wire_timeout_,
                   keep_alive_timeout_);
  QuicTime::Delta retransmittable_on_wire_timeout =
      initial_retransmittable_on_wire_timeout_;
  const int max_aggressive_retransmittable_on_wire_count =
      GetQuicFlag(quic_max_aggressive_retransmittable_on_wire_ping_count);
  QUICHE_DCHECK_LE(0, max_aggressive_retransmittable_on_wire_count);
  if (consecutive_retransmittable_on_wire_count_ >
      max_aggressive_retransmittable_on_wire_count) {
    // Exponentially back off the timeout if the number of consecutive
    // retransmittable on wire pings has exceeds the allowance.
    int shift = std::min(consecutive_retransmittable_on_wire_count_ -
                             max_aggressive_retransmittable_on_wire_count,
                         kMaxRetransmittableOnWireDelayShift);
    retransmittable_on_wire_timeout =
        initial_retransmittable_on_wire_timeout_ * (1 << shift);
  }
  if (retransmittable_on_wire_deadline_.IsInitialized() &&
      retransmittable_on_wire_deadline_ <
          now + retransmittable_on_wire_timeout) {
    // Alarm is set to an earlier time. Do not postpone it.
    return;
  }
  retransmittable_on_wire_deadline_ = now + retransmittable_on_wire_timeout;
}

QuicTime QuicPingManager::GetEarliestDeadline() const {
  QuicTime earliest_deadline = QuicTime::Zero();
  for (QuicTime t : {retransmittable_on_wire_deadline_, keep_alive_deadline_}) {
    if (!t.IsInitialized()) {
      continue;
    }
    if (!earliest_deadline.IsInitialized() || t < earliest_deadline) {
      earliest_deadline = t;
    }
  }
  return earliest_deadline;
}

}  // namespace quic