blob: 1c014a6501990b42c44a162a0995d439428a5843 [file] [log] [blame]
// 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/dns/dns_reloader.h"
#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) && \
!defined(OS_ANDROID) && !defined(OS_FUCHSIA)
#include <resolv.h>
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/message_loop/message_loop_current.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_local.h"
#include "net/base/network_change_notifier.h"
namespace net {
namespace {
// On Linux/BSD, changes to /etc/resolv.conf can go unnoticed thus resulting
// in DNS queries failing either because nameservers are unknown on startup
// or because nameserver info has changed as a result of e.g. connecting to
// a new network. Some distributions patch glibc to stat /etc/resolv.conf
// to try to automatically detect such changes but these patches are not
// universal and even patched systems such as Jaunty appear to need calls
// to res_ninit to reload the nameserver information in different threads.
// To fix this, on systems with FilePathWatcher support, we use
// NetworkChangeNotifier::DNSObserver to monitor /etc/resolv.conf to
// enable us to respond to DNS changes and reload the resolver state.
// OpenBSD does not have thread-safe res_ninit/res_nclose so we can't do
// the same trick there and most *BSD's don't yet have support for
// FilePathWatcher (but perhaps the new kqueue mac code just needs to be
// ported to *BSD to support that).
// Android does not have /etc/resolv.conf. The system takes care of nameserver
// changes, so none of this is needed.
// TODO( Convert to SystemDnsConfigChangeNotifier because this
// really only cares about system DNS config changes, not Chrome effective
// config changes.
class DnsReloader : public NetworkChangeNotifier::DNSObserver {
// NetworkChangeNotifier::DNSObserver:
void OnDNSChanged() override {
base::AutoLock lock(lock_);
void MaybeReload() {
ReloadState* reload_state = tls_reload_state_.Get();
base::AutoLock lock(lock_);
if (!reload_state) {
auto new_reload_state = std::make_unique<ReloadState>();
new_reload_state->resolver_generation = resolver_generation_;
} else if (reload_state->resolver_generation != resolver_generation_) {
reload_state->resolver_generation = resolver_generation_;
// It is safe to call res_nclose here since we know res_ninit will have
// been called above.
struct ReloadState {
~ReloadState() { res_nclose(&_res); }
int resolver_generation;
DnsReloader() { NetworkChangeNotifier::AddDNSObserver(this); }
~DnsReloader() override {
NOTREACHED(); // LeakyLazyInstance is not destructed.
base::Lock lock_; // Protects resolver_generation_.
int resolver_generation_ = 0;
friend struct base::LazyInstanceTraitsBase<DnsReloader>;
// We use thread local storage to identify which ReloadState to interact with.
base::ThreadLocalOwnedPointer<ReloadState> tls_reload_state_;
} // namespace
void EnsureDnsReloaderInit() {
void DnsReloaderMaybeReload() {
// This routine can be called by any of the DNS worker threads.
DnsReloader* dns_reloader = g_dns_reloader.Pointer();
} // namespace net
#endif // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) &&
// !defined(OS_ANDROID)