text: // 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 CHROME_BROWSER_NET_DNS_PROBE_SERVICE_H_
  #define CHROME_BROWSER_NET_DNS_PROBE_SERVICE_H_
  
  #include <vector>
  
  #include "base/basictypes.h"
  #include "base/bind.h"
  #include "base/memory/scoped_ptr.h"
  #include "base/time/time.h"
  #include "chrome/browser/net/dns_probe_runner.h"
  #include "chrome/common/net/net_error_info.h"
  #include "net/base/network_change_notifier.h"
  
  namespace net {
  class DnsClient;
  struct DnsConfig;
  }
  
  namespace chrome_browser_net {
  
  // Probes the system and public DNS servers to determine the (probable) cause
  // of a recent DNS-related page load error.  Coalesces multiple probe requests
  // (perhaps from multiple tabs) and caches the results.
  //
  // Uses a single DNS attempt per config, and doesn't randomize source ports.
  class DnsProbeService : public net::NetworkChangeNotifier::DNSObserver {
   public:
    typedef base::Callback<void(chrome_common_net::DnsProbeStatus result)>
        ProbeCallback;
  
    DnsProbeService();
    virtual ~DnsProbeService();
  
    virtual void ProbeDns(const ProbeCallback& callback);
  
    // NetworkChangeNotifier::DNSObserver implementation:
    virtual void OnDNSChanged() OVERRIDE;
  
    void SetSystemClientForTesting(scoped_ptr<net::DnsClient> system_client);
    void SetPublicClientForTesting(scoped_ptr<net::DnsClient> public_client);
    void ClearCachedResultForTesting();
  
   private:
    enum State {
      STATE_NO_RESULT,
      STATE_PROBE_RUNNING,
      STATE_RESULT_CACHED,
    };
  
    void SetSystemClientToCurrentConfig();
    void SetPublicClientToGooglePublicDns();
  
    // Starts a probe (runs system and public probes).
    void StartProbes();
    void OnProbeComplete();
    // Calls all |pending_callbacks_| with the |cached_result_|.
    void CallCallbacks();
    // Clears a cached probe result.
    void ClearCachedResult();
  
    bool CachedResultIsExpired() const;
  
    State state_;
    std::vector<ProbeCallback> pending_callbacks_;
    base::Time probe_start_time_;
    chrome_common_net::DnsProbeStatus cached_result_;
  
    // DnsProbeRunners for the system DNS configuration and a public DNS server.
    DnsProbeRunner system_runner_;
    DnsProbeRunner public_runner_;
  
    DISALLOW_COPY_AND_ASSIGN(DnsProbeService);
  };
  
  }  // namespace chrome_browser_net
  
  #endif  // CHROME_BROWSER_NET_DNS_PROBE_SERVICE_H_
  