1 files changed, 125 insertions, 0 deletions
diff --git a/components/network_time/network_time_tracker.cc b/components/network_time/network_time_tracker.cc
new file mode 100644
index 0000000..76ee415
--- /dev/null
+++ b/components/network_time/network_time_tracker.cc
@@ -0,0 +1,125 @@
+// 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.
+
+#include "components/network_time/network_time_tracker.h"
+
+#include "base/basictypes.h"
+#include "base/i18n/time_formatting.h"
+#include "base/logging.h"
+#include "base/prefs/pref_registry_simple.h"
+#include "base/prefs/pref_service.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/time/tick_clock.h"
+#include "components/network_time/network_time_pref_names.h"
+
+namespace network_time {
+
+namespace {
+
+// Clock resolution is platform dependent.
+#if defined(OS_WIN)
+const int64 kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
+#else
+const int64 kTicksResolutionMs = 1;  // Assume 1ms for non-windows platforms.
+#endif
+
+// Number of time measurements performed in a given network time calculation.
+const int kNumTimeMeasurements = 5;
+
+}  // namespace
+
+// static
+void NetworkTimeTracker::RegisterPrefs(PrefRegistrySimple* registry) {
+  registry->RegisterDictionaryPref(prefs::kNetworkTimeMapping,
+                                   new base::DictionaryValue());
+}
+
+NetworkTimeTracker::NetworkTimeTracker(scoped_ptr<base::TickClock> tick_clock,
+                                       PrefService* pref_service)
+    : tick_clock_(tick_clock.Pass()),
+      pref_service_(pref_service),
+      received_network_time_(false) {
+  const base::DictionaryValue* time_mapping =
+      pref_service_->GetDictionary(prefs::kNetworkTimeMapping);
+  double local_time_js = 0;
+  double network_time_js = 0;
+  if (time_mapping->GetDouble("local", &local_time_js) &&
+      time_mapping->GetDouble("network", &network_time_js)) {
+    base::Time local_time_saved = base::Time::FromJsTime(local_time_js);
+    base::Time local_time_now = base::Time::Now();
+    if (local_time_saved > local_time_now ||
+        local_time_now - local_time_saved > base::TimeDelta::FromDays(7)) {
+      // Drop saved mapping if clock skew has changed or the data is too old.
+      pref_service_->ClearPref(prefs::kNetworkTimeMapping);
+    } else {
+      network_time_ = base::Time::FromJsTime(network_time_js) +
+          (local_time_now - local_time_saved);
+      network_time_ticks_ = base::TimeTicks::Now();
+    }
+  }
+}
+
+NetworkTimeTracker::~NetworkTimeTracker() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+void NetworkTimeTracker::UpdateNetworkTime(base::Time network_time,
+                                           base::TimeDelta resolution,
+                                           base::TimeDelta latency,
+                                           base::TimeTicks post_time) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "Network time updating to "
+           << base::UTF16ToUTF8(
+                  base::TimeFormatFriendlyDateAndTime(network_time));
+  // Update network time on every request to limit dependency on ticks lag.
+  // TODO(mad): Find a heuristic to avoid augmenting the
+  // network_time_uncertainty_ too much by a particularly long latency.
+  // Maybe only update when the the new time either improves in accuracy or
+  // drifts too far from |network_time_|.
+  network_time_ = network_time;
+
+  // Calculate the delay since the network time was received.
+  base::TimeTicks now = tick_clock_->NowTicks();
+  base::TimeDelta task_delay = now - post_time;
+  // Estimate that the time was set midway through the latency time.
+  network_time_ticks_ = now - task_delay - latency / 2;
+
+  // Can't assume a better time than the resolution of the given time
+  // and 5 ticks measurements are involved, each with their own uncertainty.
+  // 1 & 2 are the ones used to compute the latency, 3 is the Now() from when
+  // this task was posted, 4 is the Now() above and 5 will be the Now() used in
+  // GetNetworkTime().
+  network_time_uncertainty_ =
+      resolution + latency + kNumTimeMeasurements *
+      base::TimeDelta::FromMilliseconds(kTicksResolutionMs);
+
+  received_network_time_ = true;
+
+  base::Time network_time_now;
+  if (GetNetworkTime(base::TimeTicks::Now(), &network_time_now, NULL)) {
+    // Update time mapping if tracker received time update from server, i.e.
+    // mapping is accurate.
+    base::Time local_now = base::Time::Now();
+    base::DictionaryValue time_mapping;
+    time_mapping.SetDouble("local", local_now.ToJsTime());
+    time_mapping.SetDouble("network", network_time_now.ToJsTime());
+    pref_service_->Set(prefs::kNetworkTimeMapping, time_mapping);
+  }
+}
+
+bool NetworkTimeTracker::GetNetworkTime(base::TimeTicks time_ticks,
+                                        base::Time* network_time,
+                                        base::TimeDelta* uncertainty) const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(network_time);
+  if (network_time_.is_null())
+    return false;
+  DCHECK(!network_time_ticks_.is_null());
+  *network_time = network_time_ + (time_ticks - network_time_ticks_);
+  if (uncertainty)
+    *uncertainty = network_time_uncertainty_;
+  return true;
+}
+
+}  // namespace network_time