network_time_tracker: add temporary time protocol.

components/network_time/network_time_tracker.h

 // Copyright 2014 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 COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
 #define COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
 
 #include <memory>
 
+#include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/clock.h"
 #include "base/time/time.h"
+#include "base/timer/timer.h"
+#include "net/url_request/url_fetcher_delegate.h"
+#include "net/url_request/url_request_context_getter.h"
 
 class PrefRegistrySimple;
 class PrefService;
 
 namespace base {
 class TickClock;
-}
+}  // namespace base
+
+namespace client_update_protocol {
+class Ecdsa;
+}  // namespace client_udpate_protocol
+
+namespace net {
+class URLFetcher;
+class URLRequestContextGetter;
+}  // namespace net
 
 namespace network_time {
 
 // Clock resolution is platform dependent.
 #if defined(OS_WIN)
 const int64_t kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
 #else
 const int64_t kTicksResolutionMs = 1;  // Assume 1ms for non-windows platforms.
 #endif
 
 // A class that receives network time updates and can provide the network time
 // for a corresponding local time. This class is not thread safe.
-class NetworkTimeTracker {
+class NetworkTimeTracker : public net::URLFetcherDelegate {
  public:
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
+  // Constructor.  Arguments may be stubbed out for tests.  |getter|, if not
+  // null, will cause automatic queries to a time server.  Otherwise, time is
+  // available only if |UpdateNetworkTime| is called.
   NetworkTimeTracker(std::unique_ptr<base::Clock> clock,
                      std::unique_ptr<base::TickClock> tick_clock,
-                     PrefService* pref_service);
-  ~NetworkTimeTracker();
+                     PrefService* pref_service,
+                     scoped_refptr<net::URLRequestContextGetter>& getter);

[mmenke, 2016/04/28 15:17:09]

Bug:  Passing by non-const ref is not allowed.

There was some discussion of best form on chromium-dev.  I believe the decision
was passing refptrs directly, and using std::move when you're going to hold on
to a reference is the best option?

[mab, 2016/04/29 19:42:07]

I think this is moot.  Looking more closely, I see that the pattern here is that
a URLRequestContextGetter is an explicitly reference-counted object, & that the
pattern seems to be that system_request_context() returns a raw pointer.

In short, what seems to be done elsewhere is a plain-pointer argument with
scoped_refptr interally.  SG?

[Ryan Sleevi, 2016/04/29 21:16:29]

If you're going to take a reference, the recommendation is to pass as
scoped_refptr<> getter and std::move(). This is both consistent with the
semantics of how we pass std::unique_ptr<>, while also consistent with how
std::shared_ptr<> works (where you can't take a reference from a naked pointer,
due to external refcounting, versus Chromium's internal ref counting)

Now that we have std::move(), pass as the object you'll store.

[mab, 2016/04/29 21:35:36]

Fair enough, done.

+  ~NetworkTimeTracker() override;
 
   // Sets |network_time| to an estimate of the true time.  Returns true if time
   // is available, and false otherwise.  If |uncertainty| is non-NULL, it will
   // be set to an estimate of the error range.
   //
   // Network time may be available on startup if deserialized from a pref.
   // Failing that, a call to |UpdateNetworkTime| is required to make time
   // available to callers of |GetNetworkTime|.  Subsequently, network time may
   // become unavailable if |NetworkTimeTracker| has reason to believe it is no
   // longer accurate.  Consumers should even be prepared to handle the case
   // where calls to |GetNetworkTime| never once succeeds.
   bool GetNetworkTime(base::Time* network_time,
                       base::TimeDelta* uncertainty) const;
 
   // Calculates corresponding time ticks according to the given parameters.
   // The provided |network_time| is precise at the given |resolution| and
   // represent the time between now and up to |latency| + (now - |post_time|)
   // ago.
   void UpdateNetworkTime(base::Time network_time,
                          base::TimeDelta resolution,
                          base::TimeDelta latency,
                          base::TimeTicks post_time);
 
  private:
+  friend class NetworkTimeTrackerTest;
+  FRIEND_TEST_ALL_PREFIXES(NetworkTimeTrackerTest, UpdateFromNetwork);
+  FRIEND_TEST_ALL_PREFIXES(NetworkTimeTrackerTest, NoNetworkQueryWhileSynced);
+  FRIEND_TEST_ALL_PREFIXES(NetworkTimeTrackerTest,
+                           UpdateFromNetworkBadSignature);
+
+  // If synchronization has been lost, sends a query to the secure time service.
+  // Upon response, execution resumes in |OnURLFetchComplete|.
+  void QueryTimeService();
+
+  // net::URLFetcherDelegate:
+  // Called to process responses from the secure time service.
+  void OnURLFetchComplete(const net::URLFetcher* source) override;
+
+  // State variables for internally-managed secure time service queries.
+  base::RepeatingTimer query_timer_;
+  scoped_refptr<net::URLRequestContextGetter> getter_;
+  std::unique_ptr<net::URLFetcher> time_fetcher_;
+  base::TimeTicks fetch_started_;
+  std::unique_ptr<client_update_protocol::Ecdsa> query_signer_;
+
   // The |Clock| and |TickClock| are used to sanity-check one another, allowing
   // the NetworkTimeTracker to notice e.g. suspend/resume events and clock
   // resets.
   std::unique_ptr<base::Clock> clock_;
   std::unique_ptr<base::TickClock> tick_clock_;
 
   PrefService* pref_service_;
 
   // Network time based on last call to UpdateNetworkTime().
   mutable base::Time network_time_at_last_measurement_;
@@ skipping 13 matching lines @@
   base::ThreadChecker thread_checker_;
 
   bool received_network_time_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
 };
 
 }  // namespace network_time
 
 #endif  // COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_