Add policy for limiting the session length

chrome/browser/chromeos/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/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/chromeos/login/user_manager.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 log
+// out the current user 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 Logout();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SessionLengthLimiterDelegateImpl);
+};
+
+SessionLengthLimiterDelegateImpl::SessionLengthLimiterDelegateImpl() {
+}
+
+SessionLengthLimiterDelegateImpl::~SessionLengthLimiterDelegateImpl() {
+}
+
+const base::Time SessionLengthLimiterDelegateImpl::GetCurrentTime() const {
+  return base::Time::Now();
+}
+
+void SessionLengthLimiterDelegateImpl::Logout() {
+  browser::AttemptUserExit();
+}
+
+}  // namespace
+
+SessionLengthLimiter::Observer::~Observer() {
+}
+
+SessionLengthLimiter::Delegate::~Delegate() {
+}
+
+SessionLengthLimiter::SessionLengthLimiter(Delegate* delegate,
+                                           PrefService* prefs)
+    : delegate_(delegate ? delegate : new SessionLengthLimiterDelegateImpl) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // Update the session start time in prefs to the current time when going
+  // through a user login. If the browser is restarting after a crash instead,
+  // only update the value if it appears corrupted (value unset, value lying in
+  // the future, zero value).
+  int64 session_start_time = prefs->GetInt64(prefs::kSessionStartTime);
+  int64 now = delegate_->GetCurrentTime().ToInternalValue();
+  if (!UserManager::Get()->HasBrowserRestarted() ||
+      session_start_time <= 0 || session_start_time > now) {
+    prefs->SetInt64(prefs::kSessionStartTime, now);
+    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(prefs);
+  pref_change_registrar_.Add(
+      prefs::kSessionLengthLimit,
+      base::Bind(&SessionLengthLimiter::OnSessionLengthLimitChanged,
+                 base::Unretained(this)));
+  OnSessionLengthLimitChanged();
+}
+
+SessionLengthLimiter::~SessionLengthLimiter() {
+}
+
+void SessionLengthLimiter::Shutdown() {
+  pref_change_registrar_.RemoveAll();
+}
+
+void SessionLengthLimiter::AddObserver(Observer* observer) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  observers_.AddObserver(observer);
+  observer->SessionTimeRemainingChanged(GetRemainingTime().get());
+}
+
+void SessionLengthLimiter::RemoveObserver(Observer* observer) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  observers_.RemoveObserver(observer);
+}
+
+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, calling the observers
+  // one last time to notify them that there is no more limit.
+  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 after calling the observers immediately to notify them that there
+  // now is a limit.
+  session_length_limit_ = base::TimeDelta::FromMilliseconds(
+      std::min(std::max(limit, kSessionLengthLimitMinMs),
+               kSessionLengthLimitMaxMs));
+  StartTimer();
+}
+
+void SessionLengthLimiter::StartTimer() {
+  TimerTick();
+  if (repeating_timer_.IsRunning())
+    return;
+  repeating_timer_.Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kSessionLengthLimitTimerIntervalMs),
+      this,
+      &SessionLengthLimiter::TimerTick);
+}
+
+void SessionLengthLimiter::StopTimer() {
+  if (repeating_timer_.IsRunning())
+    repeating_timer_.Stop();
+  TimerTick();
+}
+
+void SessionLengthLimiter::TimerTick() {
+  scoped_ptr<base::TimeDelta> remaining = GetRemainingTime();
+  FOR_EACH_OBSERVER(Observer, observers_,
+                    SessionTimeRemainingChanged(remaining.get()));
+  // End the session if a limit is set and the remaining time reaches zero.
+  if (remaining && *remaining == base::TimeDelta())
+    delegate_->Logout();
+}
+
+scoped_ptr<base::TimeDelta> SessionLengthLimiter::GetRemainingTime() const {
+  // If no limit is set, return |NULL|.
+  const base::TimeDelta kZeroTimeDelta = base::TimeDelta();
+  if (session_length_limit_ == kZeroTimeDelta)
+    return scoped_ptr<base::TimeDelta>();
+  // If a limit is set, return the remaining time, clamped so that it never
+  // falls below zero.
+  base::TimeDelta remaining = session_length_limit_ -
+      (delegate_->GetCurrentTime() - session_start_time_);
+  if (remaining < kZeroTimeDelta)
+    remaining = kZeroTimeDelta;
+  return scoped_ptr<base::TimeDelta>(new base::TimeDelta(remaining));
+}
+
+}  // namespace chromeos