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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
      6 #define COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
      7 
      8 #include "base/memory/scoped_ptr.h"
      9 #include "base/threading/thread_checker.h"
     10 #include "base/time/time.h"
     11 
     12 class PrefRegistrySimple;
     13 class PrefService;
     14 
     15 namespace base {
     16 class TickClock;
     17 }
     18 
     19 namespace network_time {
     20 
     21 // A class that receives network time updates and can provide the network time
     22 // for a corresponding local time. This class is not thread safe.
     23 class NetworkTimeTracker {
     24  public:
     25   static void RegisterPrefs(PrefRegistrySimple* registry);
     26 
     27   NetworkTimeTracker(scoped_ptr<base::TickClock> tick_clock,
     28                      PrefService* pref_service);
     29   ~NetworkTimeTracker();
     30 
     31   // Returns the network time corresponding to |time_ticks| if network time
     32   // is available. Returns false if no network time is available yet. Can also
     33   // return the error range if |uncertainty| isn't NULL.
     34   bool GetNetworkTime(base::TimeTicks time_ticks,
     35                       base::Time* network_time,
     36                       base::TimeDelta* uncertainty) const;
     37 
     38   // Calculates corresponding time ticks according to the given parameters.
     39   // The provided |network_time| is precise at the given |resolution| and
     40   // represent the time between now and up to |latency| + (now - |post_time|)
     41   // ago.
     42   void UpdateNetworkTime(base::Time network_time,
     43                          base::TimeDelta resolution,
     44                          base::TimeDelta latency,
     45                          base::TimeTicks post_time);
     46 
     47   bool received_network_time() const {
     48     return received_network_time_;
     49   }
     50 
     51  private:
     52   // For querying current time ticks.
     53   scoped_ptr<base::TickClock> tick_clock_;
     54 
     55   PrefService* pref_service_;
     56 
     57   // Network time based on last call to UpdateNetworkTime().
     58   base::Time network_time_;
     59 
     60   // The estimated local time from |tick_clock| that corresponds with
     61   // |network_time|. Assumes the actual network time measurement was performed
     62   // midway through the latency time, and does not account for suspect/resume
     63   // events since the network time was measured.
     64   // See UpdateNetworkTime(..) implementation for details.
     65   base::TimeTicks network_time_ticks_;
     66 
     67   // Uncertainty of |network_time_| based on added inaccuracies/resolution.
     68   // See UpdateNetworkTime(..) implementation for details.
     69   base::TimeDelta network_time_uncertainty_;
     70 
     71   base::ThreadChecker thread_checker_;
     72 
     73   bool received_network_time_;
     74 
     75   DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
     76 };
     77 
     78 }  // namespace network_time
     79 
     80 #endif  // COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
     81