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// Copyright 2020 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/dns/resolve_context.h"
#include <utility>
#include "base/logging.h"
#include "base/time/time.h"
#include "net/base/network_change_notifier.h"
#include "net/dns/dns_session.h"
#include "net/dns/host_cache.h"
namespace net {
ResolveContext::ResolveContext(URLRequestContext* url_request_context,
bool enable_caching)
: url_request_context_(url_request_context),
host_cache_(enable_caching ? HostCache::CreateDefaultCache() : nullptr) {}
ResolveContext::~ResolveContext() = default;
base::Optional<size_t> ResolveContext::DohServerIndexToUse(
size_t starting_doh_server_index,
DnsConfig::SecureDnsMode secure_dns_mode,
const DnsSession* session) {
if (!IsCurrentSession(session))
return base::nullopt;
CHECK_LT(starting_doh_server_index, doh_server_availability_.size());
size_t index = starting_doh_server_index;
base::TimeTicks oldest_server_failure;
base::Optional<size_t> oldest_available_server_failure_index;
do {
CHECK_LT(index, doh_server_availability_.size());
// For a server to be considered "available", the server must have a
// successful probe status if we are in AUTOMATIC mode.
if (secure_dns_mode == DnsConfig::SecureDnsMode::SECURE ||
doh_server_availability_[index]) {
// If number of failures on this server doesn't exceed |config_.attempts|,
// return its index. |config_.attempts| will generally be more restrictive
// than |kAutomaticModeFailureLimit|, although this is not guaranteed.
if (current_session_->GetLastDohFailureCount(index) <
session->config().attempts) {
return index;
// Track oldest failed available server.
base::TimeTicks cur_server_failure =
if (!oldest_available_server_failure_index ||
cur_server_failure < oldest_server_failure) {
oldest_server_failure = cur_server_failure;
oldest_available_server_failure_index = index;
index = (index + 1) % session->config().dns_over_https_servers.size();
} while (index != starting_doh_server_index);
// If we are here it means that there are either no available DoH servers or
// that all available DoH servers have at least |config_.attempts| consecutive
// failures. In the latter case, we'll return the available DoH server that
// failed least recently. In the former case we return nullopt.
return oldest_available_server_failure_index;
size_t ResolveContext::NumAvailableDohServers(const DnsSession* session) const {
if (!IsCurrentSession(session))
return 0;
size_t count = 0;
for (const auto& probe_result : doh_server_availability_) {
if (probe_result)
return count;
bool ResolveContext::GetDohServerAvailability(size_t doh_server_index,
const DnsSession* session) const {
if (!IsCurrentSession(session))
return false;
CHECK_LT(doh_server_index, doh_server_availability_.size());
return doh_server_availability_[doh_server_index];
void ResolveContext::SetProbeSuccess(size_t doh_server_index,
bool success,
const DnsSession* session) {
if (!IsCurrentSession(session))
bool doh_available_before = NumAvailableDohServers(session) > 0;
CHECK_LT(doh_server_index, doh_server_availability_.size());
doh_server_availability_[doh_server_index] = success;
// TODO( Consider figuring out some way to only for the
// first context enabling DoH or the last context disabling DoH.
if (doh_available_before != NumAvailableDohServers(session) > 0)
void ResolveContext::InvalidateCaches(DnsSession* new_session) {
if (host_cache_)
// DNS config is constant for any given session, so if the current session is
// unchanged, any per-session data is safe to keep, even if it's dependent on
// a specific config.
if (new_session && new_session == current_session_.get())
if (new_session) {
current_session_ = new_session->GetWeakPtr();
new_session->config().dns_over_https_servers.size(), false);
} else {
bool ResolveContext::IsCurrentSession(const DnsSession* session) const {
if (session == current_session_.get()) {
return true;
return false;
} // namespace net