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- // 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"
- #include "build/build_config.h"
- #if BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_APPLE) && !BUILDFLAG(IS_OPENBSD) && \
- !BUILDFLAG(IS_ANDROID) && !BUILDFLAG(IS_FUCHSIA)
- #include <resolv.h>
- #include "base/lazy_instance.h"
- #include "base/notreached.h"
- #include "base/synchronization/lock.h"
- #include "base/task/current_thread.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(crbug.com/971411): Convert to SystemDnsConfigChangeNotifier because this
- // really only cares about system DNS config changes, not Chrome effective
- // config changes.
- class DnsReloader : public NetworkChangeNotifier::DNSObserver {
- public:
- DnsReloader(const DnsReloader&) = delete;
- DnsReloader& operator=(const DnsReloader&) = delete;
- // NetworkChangeNotifier::DNSObserver:
- void OnDNSChanged() override {
- base::AutoLock lock(lock_);
- resolver_generation_++;
- }
- 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_;
- res_ninit(&_res);
- tls_reload_state_.Set(std::move(new_reload_state));
- } 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.
- res_nclose(&_res);
- res_ninit(&_res);
- }
- }
- private:
- 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_;
- };
- base::LazyInstance<DnsReloader>::Leaky
- g_dns_reloader = LAZY_INSTANCE_INITIALIZER;
- } // namespace
- void EnsureDnsReloaderInit() {
- g_dns_reloader.Pointer();
- }
- void DnsReloaderMaybeReload() {
- // This routine can be called by any of the DNS worker threads.
- DnsReloader* dns_reloader = g_dns_reloader.Pointer();
- dns_reloader->MaybeReload();
- }
- } // namespace net
- #endif // BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_APPLE) && !BUILDFLAG(IS_OPENBSD)
- // && !BUILDFLAG(IS_ANDROID)
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