Add policy for limiting the session length

chrome/browser/chromeos/power/session_length_limiter.cc

+// 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.
+
+#include "chrome/browser/chromeos/power/session_length_limiter.h"
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/prefs/public/pref_service_base.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/common/pref_names.h"
+
+namespace chromeos {
+
+namespace {
+
+// The minimum session time limit that can be set.
+const int kSessionLengthLimitMinMs = 30 * 1000; // 30 seconds.
+
+// The maximum session time limit that can be set.
+const int kSessionLengthLimitMaxMs = 24 * 60 * 60 * 1000; // 24 hours.
+
+// The interval at which to fire periodic callbacks and check whether the
+// session time limit has been reached.
+const int kSessionLengthLimitTimerIntervalMs = 1000;
+
+// A default delegate implementation that returns the current time and does end
+// the current user's session when requested. This can be replaced with a mock
+// in tests.
+class SessionLengthLimiterDelegateImpl : public SessionLengthLimiter::Delegate {
+ public:
+  SessionLengthLimiterDelegateImpl();
+  virtual ~SessionLengthLimiterDelegateImpl();
+
+  virtual const base::Time GetCurrentTime() const;
+  virtual void StopSession();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SessionLengthLimiterDelegateImpl);
+};
+
+SessionLengthLimiterDelegateImpl::SessionLengthLimiterDelegateImpl() {
+}
+
+SessionLengthLimiterDelegateImpl::~SessionLengthLimiterDelegateImpl() {
+}
+
+const base::Time SessionLengthLimiterDelegateImpl::GetCurrentTime() const {
+  return base::Time::Now();
+}
+
+void SessionLengthLimiterDelegateImpl::StopSession() {
+  browser::AttemptUserExit();
+}
+
+}  // namespace
+
+SessionLengthLimiter::Delegate::~Delegate() {
+}
+
+// static
+void SessionLengthLimiter::RegisterPrefs(PrefService* local_state) {
+  local_state->RegisterInt64Pref(prefs::kSessionStartTime,
+                                 0,
+                                 PrefService::UNSYNCABLE_PREF);
+  local_state->RegisterIntegerPref(prefs::kSessionLengthLimit,
+                                   0,
+                                   PrefService::UNSYNCABLE_PREF);
+}
+
+SessionLengthLimiter::SessionLengthLimiter(Delegate* delegate,
+                                           bool browser_restarted)
+    : delegate_(delegate ? delegate : new SessionLengthLimiterDelegateImpl) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // If this is a user login, set the session start time in local state to the
+  // current time. If this a browser restart after a crash, set the session
+  // start time only if its current value appears corrupted (value unset, value
+  // lying in the future, zero value).
+  PrefService* local_state = g_browser_process->local_state();
+  int64 session_start_time = local_state->GetInt64(prefs::kSessionStartTime);
+  int64 now = delegate_->GetCurrentTime().ToInternalValue();
+  if (!browser_restarted ||
+      session_start_time <= 0 || session_start_time > now) {
+    local_state->SetInt64(prefs::kSessionStartTime, now);
+    // Ensure that the session start time is persisted to local state.
+    local_state->CommitPendingWrite();
+    session_start_time = now;
+  }
+  session_start_time_ = base::Time::FromInternalValue(session_start_time);
+
+  // Listen for changes to the session length limit.
+  pref_change_registrar_.Init(local_state);
+  pref_change_registrar_.Add(
+      prefs::kSessionLengthLimit,
+      base::Bind(&SessionLengthLimiter::OnSessionLengthLimitChanged,
+                 base::Unretained(this)));
+  OnSessionLengthLimitChanged();
+}
+
+void SessionLengthLimiter::OnSessionLengthLimitChanged() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  int limit;
+  const PrefServiceBase::Preference* session_length_limit_pref =
+      pref_change_registrar_.prefs()->
+          FindPreference(prefs::kSessionLengthLimit);
+  // If no session length limit is set, stop the timer.
+  if (session_length_limit_pref->IsDefaultValue() ||
+      !session_length_limit_pref->GetValue()->GetAsInteger(&limit)) {
+    session_length_limit_ = base::TimeDelta();
+    StopTimer();
+    return;
+  }
+
+  // If a session length limit is set, clamp it to the valid range and start
+  // the timer.
+  session_length_limit_ = base::TimeDelta::FromMilliseconds(
+      std::min(std::max(limit, kSessionLengthLimitMinMs),
+               kSessionLengthLimitMaxMs));
+  StartTimer();
+}
+
+void SessionLengthLimiter::StartTimer() {
+  if (repeating_timer_ && repeating_timer_->IsRunning())
+    return;
+  if (!repeating_timer_)
+    repeating_timer_.reset(new base::RepeatingTimer<SessionLengthLimiter>);
+  repeating_timer_->Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kSessionLengthLimitTimerIntervalMs),
+      this,
+      &SessionLengthLimiter::UpdateRemainingTime);
+}
+
+void SessionLengthLimiter::StopTimer() {
+  if (!repeating_timer_)
+    return;
+  repeating_timer_.reset();
+  UpdateRemainingTime();
+}
+
+void SessionLengthLimiter::UpdateRemainingTime() {
+  const base::TimeDelta kZeroTimeDelta = base::TimeDelta();
+  // If no session length limit is set, return.
+  if (session_length_limit_ == kZeroTimeDelta)
+    return;
+
+  // Calculate the remaining session time, clamping so that it never falls below
+  // zero.
+  base::TimeDelta remaining = session_length_limit_ -
+      (delegate_->GetCurrentTime() - session_start_time_);
+  if (remaining < kZeroTimeDelta)
+    remaining = kZeroTimeDelta;
+
+  // End the session if the remaining time reaches zero.
+  if (remaining == base::TimeDelta())
+    delegate_->StopSession();
+}
+
+}  // namespace chromeos