Allow ProxyConfigService to report "no configuration set"

net/proxy/proxy_config_service.h

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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_PROXY_PROXY_CONFIG_SERVICE_H_
 #define NET_PROXY_PROXY_CONFIG_SERVICE_H_
 #pragma once
 
 namespace net {
 
 class ProxyConfig;
 
 // Service for watching when the proxy settings have changed.
 class ProxyConfigService {
  public:
+  // Indicates whether proxy configuration is valid, and if not, why.
+  enum ConfigAvailability {
+    // Configuration is pending, observers will be notified later.
+    CONFIG_PENDING,
+    // Configuration is present and valid.
+    CONFIG_VALID,
+    // No configuration is set.
+    CONFIG_UNSET
+  };
+
   // Observer for being notified when the proxy settings have changed.
   class Observer {
    public:
     virtual ~Observer() {}
-    virtual void OnProxyConfigChanged(const ProxyConfig& config) = 0;
+    // Notification callback that should be invoked by ProxyConfigService
+    // implementors whenever the configuration changes. |availability| indicates
+    // the new availability status and can be CONFIG_UNSET or CONFIG_VALID (in
+    // which case |config| contains the configuration). Implementors must not
+    // pass CONFIG_PENDING.
+    virtual void OnProxyConfigChanged(const ProxyConfig& config,
+                                      ConfigAvailability availability) = 0;
   };
 
   virtual ~ProxyConfigService() {}
 
   // Adds/Removes an observer that will be called whenever the proxy
   // configuration has changed.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
-  // Gets the most recent value of the proxy configuration. Returns false if
-  // it is not available yet. In the case where we returned false, it is
-  // guaranteed that subscribed observers will be notified of a change at
+  // Gets the most recent availability status. If a configuration is present,
+  // the proxy configuration is written to |config| and CONFIG_VALID is
+  // returned. Returns CONFIG_PENDING if it is not available yet. In this case,
+  // it is guaranteed that subscribed observers will be notified of a change at
   // some point in the future once the configuration is available.
   // Note that to avoid re-entrancy problems, implementations should not
   // dispatch any change notifications from within this function.
-  virtual bool GetLatestProxyConfig(ProxyConfig* config) = 0;
+  virtual ConfigAvailability GetLatestProxyConfig(ProxyConfig* config) = 0;
 
   // ProxyService will call this periodically during periods of activity.
   // It can be used as a signal for polling-based implementations.
   //
   // Note that this is purely used as an optimization -- polling
   // implementations could simply set a global timer that goes off every
   // X seconds at which point they check for changes. However that has
   // the disadvantage of doing continuous work even during idle periods.
   virtual void OnLazyPoll() {}
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_CONFIG_SERVICE_H_