[net] Add DNS-related signals and NetLog to NetworkChangeNotifier.

net/base/network_change_notifier_mac.cc

Index: net/base/network_change_notifier_mac.cc
diff --git a/net/base/network_change_notifier_mac.cc b/net/base/network_change_notifier_mac.cc
index ca314a199f9f6343b105a034bde290f5c55d3e72..702cc2e6c372f3b1b8f9cdf766c425e426856c4b 100644
--- a/net/base/network_change_notifier_mac.cc
+++ b/net/base/network_change_notifier_mac.cc
@@ -5,6 +5,13 @@
 #include "net/base/network_change_notifier_mac.h"
 
 #include <netinet/in.h>
+#include <resolv.h>
+
+#include "base/threading/thread.h"
+
+#ifndef _PATH_RESCONF  // Normally defined in <resolv.h>
+#define _PATH_RESCONF "/etc/resolv.conf"
+#endif
 
 namespace net {
 
@@ -14,6 +21,62 @@ static bool CalculateReachability(SCNetworkConnectionFlags flags) {
   return reachable && !connection_required;
 }
 
+class NetworkChangeNotifierMac::DNSWatcher : public base::Thread {
+ public:
+  DNSWatcher() : watching_dns_(false) {}
+
+  virtual void Init() OVERRIDE {
+    base::AutoLock lock(watching_dns_lock_);
+    watching_dns_ = true;
+    if (!resolv_watcher_.Watch(
+          FilePath(FILE_PATH_LITERAL(_PATH_RESCONF)),
+          base::Bind(&DNSWatcher::OnDNSFileChanged,
+                     base::Unretained(this),
+                     static_cast<unsigned>(CHANGE_DNS_SETTINGS)))) {
+      LOG(ERROR) << "Failed to setup watch for /etc/resolv.conf";
+      watching_dns_ = false;
+    }
+    if (!hosts_watcher_.Watch(
+            FilePath(FILE_PATH_LITERAL("/etc/hosts")),
+            base::Bind(&DNSWatcher::OnDNSFileChanged,
+                       base::Unretained(this),
+                       static_cast<unsigned>(CHANGE_DNS_HOSTS)))) {
+      LOG(ERROR) << "Failed to setup watch for /etc/hosts";
+      watching_dns_ = false;
+    }
+  }
+
+  virtual void CleanUp() OVERRIDE {
+    base::AutoLock lock(watching_dns_lock_);
+    watching_dns_ = false;
+    resolv_watcher_.Cancel();
+    hosts_watcher_.Cancel();
+  }
+
+  bool IsWatching() const {
+    base::AutoLock lock(watching_dns_lock_);
+    return watching_dns_;
+  }
+
+ private:
+  // Called from FilePathWatcherCallback.
+  void OnDNSFileChanged(unsigned detail, bool watch_success) {
+    if (!watch_success) {
+      LOG(ERROR) << "DNS watch failed.";
+      base::AutoLock lock(watching_dns_lock_);
+      watching_dns_ = false;
+    }
+    // Always notify observers so that they can check IsWatchingDNS().
+    NetworkChangeNotifier::NotifyObserversOfDNSChange(detail);
+  }
+
+  FilePathWatcherCallback resolv_watcher_;
+  FilePathWatcherCallback hosts_watcher_;
+
+  bool watching_dns_;
+  mutable base::Lock watching_dns_lock_;
+};
+
 NetworkChangeNotifierMac::NetworkChangeNotifierMac()
     : online_state_(UNINITIALIZED),
       initial_state_cv_(&online_state_lock_),
@@ -21,6 +84,10 @@ NetworkChangeNotifierMac::NetworkChangeNotifierMac()
   // Must be initialized after the rest of this object, as it may call back into
   // SetInitialState().
   config_watcher_.reset(new NetworkConfigWatcherMac(&forwarder_));
+
+  dns_watcher_.reset(new DNSWatcher());
+  dns_watcher_->StartWithOptions(
+      base::Thread::Options(MessageLoop::TYPE_IO, 0));
 }
 
 NetworkChangeNotifierMac::~NetworkChangeNotifierMac() {
@@ -46,6 +113,10 @@ bool NetworkChangeNotifierMac::IsCurrentlyOffline() const {
   return online_state_ == OFFLINE;
 }
 
+bool NetworkChangeNotifierMac::IsCurrentlyWatchingDNS() const {
+  return dns_watcher_->IsWatching();
+}
+
 void NetworkChangeNotifierMac::SetInitialState() {
   // Called on notifier thread.