[net/dns] Isolate DnsConfigWatcher from DnsConfigService.

net/dns/dns_config_service.h

 // 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.
 
 #ifndef NET_DNS_DNS_CONFIG_SERVICE_H_
 #define NET_DNS_DNS_CONFIG_SERVICE_H_
 #pragma once
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time.h"
 #include "base/timer.h"
 // Needed on shared build with MSVS2010 to avoid multiple definitions of
 // std::vector<IPEndPoint>.
 #include "net/base/address_list.h"
 #include "net/base/ip_endpoint.h"  // win requires size of IPEndPoint
+#include "net/base/network_change_notifier.h"
 #include "net/base/net_export.h"
 #include "net/dns/dns_hosts.h"
 
 namespace base {
 class Value;
 }
 
 namespace net {
 
 // DnsConfig stores configuration of the system resolver.
@@ skipping 36 matching lines @@
   base::TimeDelta timeout;
   // Maximum number of attempts, see res_state.retry.
   int attempts;
   // Round robin entries in |nameservers| for subsequent requests.
   bool rotate;
   // Enable EDNS0 extensions.
   bool edns0;
 };
 
 
-// Service for watching when the system DNS settings have changed.
-// Depending on the platform, watches files in /etc/ or Windows registry.
+// Service for reading system DNS settings, on demand or when signalled by
+// NetworkChangeNotifier.
 class NET_EXPORT_PRIVATE DnsConfigService
-  : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+    : NON_EXPORTED_BASE(public base::NonThreadSafe),
+      public NetworkChangeNotifier::DNSObserver {
  public:
-  // Callback interface for the client, called on the same thread as Watch().
+  // Callback interface for the client, called on the same thread as Read() and
+  // Watch().
   typedef base::Callback<void(const DnsConfig& config)> CallbackType;
 
   // Creates the platform-specific DnsConfigService.
   static scoped_ptr<DnsConfigService> CreateSystemService();
 
   DnsConfigService();
   virtual ~DnsConfigService();
 
-  // Immediately starts watching system configuration for changes and attempts
-  // to read the configuration. For some platform implementations, the current
-  // thread must have an IO loop (for base::files::FilePathWatcher).
-  virtual void Watch(const CallbackType& callback) = 0;
+  // Attempts to read the configuration. Will run |callback| when succeeded.
+  // Can be called at most once.
+  void Read(const CallbackType& callback);
+
+  // Registers for notifications at NetworkChangeNotifier. Will attempt to read
+  // config after watch is started by NetworkChangeNotifier. Will run |callback|
+  // iff config changes from last call or should be withdrawn.
+  // Can be called at most once.
+  virtual void Watch(const CallbackType& callback);
 
  protected:
   friend class DnsHostsReader;
 
   // Called when the current config (except hosts) has changed.
   void InvalidateConfig();
   // Called when the current hosts have changed.
   void InvalidateHosts();
 
   // Called with new config. |config|.hosts is ignored.
   void OnConfigRead(const DnsConfig& config);
   // Called with new hosts. Rest of the config is assumed unchanged.
   void OnHostsRead(const DnsHosts& hosts);
 
-  void set_callback(const CallbackType& callback) {
-    callback_ = callback;
-  }
+  // NetworkChangeNotifier::DNSObserver:
+  // Must be defined by implementations.
+  virtual void OnDNSChanged(unsigned detail) OVERRIDE = 0;
 
  private:
   void StartTimer();
   // Called when the timer expires.
   void OnTimeout();
   // Called when the config becomes complete.
   void OnCompleteConfig();
 
   CallbackType callback_;
 
   DnsConfig dns_config_;
 
-  // True after On*Read, before Invalidate*. Tell if the config is complete.
+  // True after On*Read, before Invalidate*. Tells if the config is complete.
   bool have_config_;
   bool have_hosts_;
   // True if receiver needs to be updated when the config becomes complete.
   bool need_update_;
 
   // Started in Invalidate*, cleared in On*Read.
   base::OneShotTimer<DnsConfigService> timer_;
 
- private:
   DISALLOW_COPY_AND_ASSIGN(DnsConfigService);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_CONFIG_SERVICE_H_