Support change detection and reloading in ConfigDirPolicyProvider.

BUG=52418
TEST=unit tests

Review URL: http://codereview.chromium.org/3124025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@56832 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 414 insertions, 21 deletions

diff --git a/chrome/browser/policy/config_dir_policy_provider.cc b/chrome/browser/policy/config_dir_policy_provider.cc
index 59509fc..8c64efa 100644
--- a/chrome/browser/policy/config_dir_policy_provider.cc
+++ b/chrome/browser/policy/config_dir_policy_provider.cc
@@ -8,22 +8,109 @@
 
 #include "base/file_util.h"
 #include "base/logging.h"
-#include "base/scoped_ptr.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/common/json_value_serializer.h"
 
-ConfigDirPolicyProvider::ConfigDirPolicyProvider(const FilePath& config_dir)
-    : config_dir_(config_dir) {
+namespace {
+
+// Amount of time we wait for the files in the policy directory to settle before
+// trying to load it. This alleviates the problem of reading partially written
+// files and allows to batch quasi-simultaneous changes.
+const int kSettleIntervalSeconds = 5;
+
+// The time interval for rechecking policy. This is our fallback in case the
+// directory watch fails or doesn't report a change.
+const int kReloadIntervalMinutes = 15;
+
+}  // namespace
+
+// PolicyDirLoader implementation:
+
+PolicyDirLoader::PolicyDirLoader(
+    base::WeakPtr<ConfigDirPolicyProvider> provider,
+    const FilePath& config_dir,
+    int settle_interval_seconds,
+    int reload_interval_minutes)
+    : provider_(provider),
+      origin_loop_(MessageLoop::current()),
+      config_dir_(config_dir),
+      reload_task_(NULL),
+      settle_interval_seconds_(settle_interval_seconds),
+      reload_interval_minutes_(reload_interval_minutes) {
+  // Force an initial load, so GetPolicy() works.
+  policy_.reset(Load());
+  DCHECK(policy_.get());
 }
 
-bool ConfigDirPolicyProvider::Provide(ConfigurationPolicyStore* store) {
-  scoped_ptr<DictionaryValue> policy(ReadPolicies());
-  DecodePolicyValueTree(policy.get(), store);
-  return true;
+void PolicyDirLoader::Stop() {
+  if (!ChromeThread::CurrentlyOn(ChromeThread::FILE)) {
+    ChromeThread::PostTask(ChromeThread::FILE, FROM_HERE,
+                           NewRunnableMethod(this, &PolicyDirLoader::Stop));
+    return;
+  }
+
+  if (reload_task_) {
+    reload_task_->Cancel();
+    reload_task_ = NULL;
+  }
 }
 
-DictionaryValue* ConfigDirPolicyProvider::ReadPolicies() {
+void PolicyDirLoader::Reload() {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::FILE));
+
+  // Check the directory time in order to see whether a reload is required.
+  base::Time now = base::Time::Now();
+  base::TimeDelta delay;
+  if (!IsSafeToReloadPolicy(now, &delay)) {
+    ScheduleReloadTask(delay);
+    return;
+  }
+
+  // Load the policy definitions.
+  scoped_ptr<DictionaryValue> new_policy(Load());
+
+  // Check again in case the directory has changed while reading it.
+  if (!IsSafeToReloadPolicy(now, &delay)) {
+    ScheduleReloadTask(delay);
+    return;
+  }
+
+  // Replace policy definition.
+  bool changed = false;
+  {
+    AutoLock lock(lock_);
+    changed = !policy_->Equals(new_policy.get());
+    policy_.reset(new_policy.release());
+  }
+
+  // There's a change, report it!
+  if (changed) {
+    LOG(INFO) << "Policy reload from " << config_dir_.value() << " succeeded.";
+    origin_loop_->PostTask(FROM_HERE,
+        NewRunnableMethod(this, &PolicyDirLoader::NotifyPolicyChanged));
+  }
+
+  // As a safeguard in case the file watcher fails, schedule a reload task
+  // that'll make us recheck after a reasonable interval.
+  ScheduleReloadTask(base::TimeDelta::FromMinutes(reload_interval_minutes_));
+}
+
+DictionaryValue* PolicyDirLoader::GetPolicy() {
+  AutoLock lock(lock_);
+  return static_cast<DictionaryValue*>(policy_->DeepCopy());
+}
+
+void PolicyDirLoader::OnFilePathChanged(const FilePath& path) {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::FILE));
+  Reload();
+}
+
+void PolicyDirLoader::OnError() {
+  LOG(ERROR) << "FileWatcher on " << config_dir_.value() << " failed.";
+}
+
+DictionaryValue* PolicyDirLoader::Load() {
   // Enumerate the files and sort them lexicographically.
   std::set<FilePath> files;
   file_util::FileEnumerator file_enumerator(config_dir_, false,
@@ -56,6 +143,105 @@ DictionaryValue* ConfigDirPolicyProvider::ReadPolicies() {
   return policy;
 }
 
+bool PolicyDirLoader::IsSafeToReloadPolicy(const base::Time& now,
+                                           base::TimeDelta* delay) {
+  DCHECK(delay);
+  file_util::FileInfo dir_info;
+
+  // Reading an empty directory or a file is always safe.
+  if (!file_util::GetFileInfo(config_dir_, &dir_info) ||
+      !dir_info.is_directory) {
+    return true;
+  }
+
+  // Check for too recent changes.
+  base::TimeDelta settleInterval(
+      base::TimeDelta::FromSeconds(settle_interval_seconds_));
+  base::TimeDelta age = now - dir_info.last_modified;
+  if (age < settleInterval) {
+    *delay = settleInterval - age;
+    return false;
+  }
+
+  return true;
+}
+
+void PolicyDirLoader::ScheduleReloadTask(const base::TimeDelta& delay) {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::FILE));
+
+  if (reload_task_)
+    reload_task_->Cancel();
+
+  reload_task_ = NewRunnableMethod(this, &PolicyDirLoader::ReloadFromTask);
+  ChromeThread::PostDelayedTask(ChromeThread::FILE, FROM_HERE, reload_task_,
+                                delay.InMilliseconds());
+}
+
+void PolicyDirLoader::NotifyPolicyChanged() {
+  DCHECK_EQ(origin_loop_, MessageLoop::current());
+  if (provider_)
+    provider_->NotifyStoreOfPolicyChange();
+}
+
+void PolicyDirLoader::ReloadFromTask() {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::FILE));
+
+  // Drop the reference to the reload task, since the task might be the only
+  // referer that keeps us alive, so we should not Cancel() it.
+  reload_task_ = NULL;
+
+  Reload();
+}
+
+// PolicyDirWatcher implementation:
+
+void PolicyDirWatcher::Init(PolicyDirLoader* loader) {
+  // Initialization can happen early when the file thread is not yet available.
+  // So post a task to ourselves on th UI thread which will run after threading
+  // is up and schedule watch initialization on the file thread.
+  ChromeThread::PostTask(ChromeThread::UI, FROM_HERE,
+      NewRunnableMethod(this,
+                        &PolicyDirWatcher::InitWatcher,
+                        scoped_refptr<PolicyDirLoader>(loader)));
+}
+
+void PolicyDirWatcher::InitWatcher(
+    const scoped_refptr<PolicyDirLoader>& loader) {
+  if (!ChromeThread::CurrentlyOn(ChromeThread::FILE)) {
+    ChromeThread::PostTask(ChromeThread::FILE, FROM_HERE,
+        NewRunnableMethod(this, &PolicyDirWatcher::InitWatcher, loader));
+    return;
+  }
+
+  if (!Watch(loader->config_dir(), loader.get()))
+    loader->OnError();
+
+  // There might have been changes to the directory in the time between
+  // construction of the loader and initialization of the watcher. Call reload
+  // to detect if that is the case.
+  loader->Reload();
+}
+
+// ConfigDirPolicyProvider implementation:
+
+ConfigDirPolicyProvider::ConfigDirPolicyProvider(const FilePath& config_dir) {
+  loader_ = new PolicyDirLoader(AsWeakPtr(), config_dir, kSettleIntervalSeconds,
+                                kReloadIntervalMinutes);
+  watcher_ = new PolicyDirWatcher;
+  watcher_->Init(loader_.get());
+}
+
+ConfigDirPolicyProvider::~ConfigDirPolicyProvider() {
+  loader_->Stop();
+}
+
+bool ConfigDirPolicyProvider::Provide(ConfigurationPolicyStore* store) {
+  scoped_ptr<DictionaryValue> policy(loader_->GetPolicy());
+  DCHECK(policy.get());
+  DecodePolicyValueTree(policy.get(), store);
+  return true;
+}
+
 void ConfigDirPolicyProvider::DecodePolicyValueTree(
     DictionaryValue* policies,
     ConfigurationPolicyStore* store) {
@@ -71,4 +257,3 @@ void ConfigDirPolicyProvider::DecodePolicyValueTree(
   // TODO(mnissler): Handle preference overrides once |ConfigurationPolicyStore|
   // supports it.
 }
-
diff --git a/chrome/browser/policy/config_dir_policy_provider.h b/chrome/browser/policy/config_dir_policy_provider.h
index 9412ff2..d299423 100644
--- a/chrome/browser/policy/config_dir_policy_provider.h
+++ b/chrome/browser/policy/config_dir_policy_provider.h
@@ -8,9 +8,111 @@
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
+#include "base/lock.h"
+#include "base/ref_counted.h"
+#include "base/scoped_ptr.h"
+#include "base/weak_ptr.h"
+#include "chrome/browser/file_path_watcher.h"
 #include "chrome/browser/policy/configuration_policy_provider.h"
 
+class ConfigDirPolicyProvider;
 class DictionaryValue;
+class MessageLoop;
+
+// FilePathWatcher delegate implementation that handles change notifications for
+// the configuration directory. It keeps the authorative version of the
+// currently effective policy dictionary and updates it as appropriate.
+class PolicyDirLoader : public FilePathWatcher::Delegate {
+ public:
+  // Create a new loader that'll load its data from |config_dir|.
+  PolicyDirLoader(base::WeakPtr<ConfigDirPolicyProvider> provider,
+                  const FilePath& config_dir,
+                  int settle_interval_second,
+                  int reload_interval_minutes);
+
+  // Stops any pending reload tasks.
+  void Stop();
+
+  // Reloads the policies and sends out a notification, if appropriate. Must be
+  // called on the file thread.
+  void Reload();
+
+  // Get the current dictionary value object. Ownership of the returned value is
+  // transferred to the caller.
+  DictionaryValue* GetPolicy();
+
+  const FilePath& config_dir() { return config_dir_; }
+
+  // FilePathWatcher::Delegate implementation:
+  void OnFilePathChanged(const FilePath& path);
+  void OnError();
+
+ private:
+  // Load the policy information. Ownership of the return value is transferred
+  // to the caller.
+  DictionaryValue* Load();
+
+  // Check the directory modification time to see whether reading the
+  // configuration directory is safe. If not, returns false and the delay until
+  // it is considered safe to reload in |delay|.
+  bool IsSafeToReloadPolicy(const base::Time& now, base::TimeDelta* delay);
+
+  // Post a reload task. Must be called on the file thread.
+  void ScheduleReloadTask(const base::TimeDelta& delay);
+
+  // Notifies the policy provider to send out a policy changed notification.
+  // Must be called on |origin_loop_|.
+  void NotifyPolicyChanged();
+
+  // Invoked from the reload task on the file thread.
+  void ReloadFromTask();
+
+  // The provider this loader is associated with. Access only on the thread that
+  // called the constructor. See |origin_loop_| below.
+  base::WeakPtr<ConfigDirPolicyProvider> provider_;
+
+  // The message loop on which this object was constructed and |provider_|
+  // received on. Recorded so we can call back into the non thread safe provider
+  // to fire the notification.
+  MessageLoop* origin_loop_;
+
+  // The directory in which we look for configuration files.
+  const FilePath config_dir_;
+
+  // Protects |policy_|.
+  Lock lock_;
+
+  // The current policy definition.
+  scoped_ptr<DictionaryValue> policy_;
+
+  // The reload task. Access only on the file thread. Holds a reference to the
+  // currently posted task, so we can cancel and repost it if necessary.
+  CancelableTask* reload_task_;
+
+  // Settle and reload intervals.
+  const int settle_interval_seconds_;
+  const int reload_interval_minutes_;
+
+  DISALLOW_COPY_AND_ASSIGN(PolicyDirLoader);
+};
+
+// Wraps a FilePathWatcher for the configuration directory and takes care of
+// initializing the watcher object on the file thread.
+class PolicyDirWatcher : public FilePathWatcher,
+                         public base::RefCountedThreadSafe<PolicyDirWatcher> {
+ public:
+  PolicyDirWatcher() {}
+
+  // Run initialization. This is in a separate method since we need to post a
+  // task (which cannot be done from the constructor).
+  void Init(PolicyDirLoader* loader);
+
+ private:
+  // Actually sets up the watch with the FilePathWatcher code.
+  void InitWatcher(const scoped_refptr<PolicyDirLoader>& loader);
+
+  DISALLOW_COPY_AND_ASSIGN(PolicyDirWatcher);
+};
 
 // A policy provider implementation backed by a set of files in a given
 // directory. The files should contain JSON-formatted policy settings. They are
@@ -18,24 +120,26 @@ class DictionaryValue;
 // ConfigurationPolicyProvider interface. The files are consulted in
 // lexicographic file name order, so the last value read takes precedence in
 // case of preference key collisions.
-class ConfigDirPolicyProvider : public ConfigurationPolicyProvider {
+class ConfigDirPolicyProvider
+    : public ConfigurationPolicyProvider,
+      public base::SupportsWeakPtr<ConfigDirPolicyProvider> {
  public:
   explicit ConfigDirPolicyProvider(const FilePath& config_dir);
-  virtual ~ConfigDirPolicyProvider() { }
+  virtual ~ConfigDirPolicyProvider();
 
   // ConfigurationPolicyProvider implementation.
   virtual bool Provide(ConfigurationPolicyStore* store);
 
  private:
-  // Read and merge the files from the configuration directory.
-  DictionaryValue* ReadPolicies();
-
   // Decodes the value tree and writes the configuration to the given |store|.
   void DecodePolicyValueTree(DictionaryValue* policies,
                              ConfigurationPolicyStore* store);
 
-  // The directory in which we look for configuration files.
-  const FilePath config_dir_;
+  // Watches for changes to the configuration directory.
+  scoped_refptr<PolicyDirWatcher> watcher_;
+
+  // The loader object we use internally.
+  scoped_refptr<PolicyDirLoader> loader_;
 
   DISALLOW_COPY_AND_ASSIGN(ConfigDirPolicyProvider);
 };
diff --git a/chrome/browser/policy/config_dir_policy_provider_unittest.cc b/chrome/browser/policy/config_dir_policy_provider_unittest.cc
index 9e3d25b..c7a2e94 100644
--- a/chrome/browser/policy/config_dir_policy_provider_unittest.cc
+++ b/chrome/browser/policy/config_dir_policy_provider_unittest.cc
@@ -9,9 +9,24 @@
 #include "chrome/browser/policy/mock_configuration_policy_store.h"
 #include "chrome/common/json_value_serializer.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "testing/gmock/include/gmock/gmock.h"
 
-class ConfigDirPolicyProviderTest : public testing::Test {
+using testing::Mock;
+
+namespace {
+
+// Shorter reload intervals for testing PolicyDirWatcher.
+const int kSettleIntervalSecondsForTesting = 0;
+const int kReloadIntervalMinutesForTesting = 1;
+
+}  // namespace
+
+class ConfigDirPolicyProviderTestBase : public testing::Test {
  protected:
+  ConfigDirPolicyProviderTestBase()
+      : ui_thread_(ChromeThread::UI, &loop_),
+        file_thread_(ChromeThread::FILE, &loop_) {}
+
   virtual void SetUp() {
     // Determine the directory to use for testing.
     ASSERT_TRUE(PathService::Get(base::DIR_TEMP, &test_dir_));
@@ -22,12 +37,10 @@ class ConfigDirPolicyProviderTest : public testing::Test {
     file_util::Delete(test_dir_, true);
     file_util::CreateDirectory(test_dir_);
     ASSERT_TRUE(file_util::DirectoryExists(test_dir_));
-
-    // Create a fresh policy store mock.
-    policy_store_.reset(new MockConfigurationPolicyStore());
   }
 
   virtual void TearDown() {
+    loop_.RunAllPending();
     // Clean up test directory.
     ASSERT_TRUE(file_util::Delete(test_dir_, true));
     ASSERT_FALSE(file_util::PathExists(test_dir_));
@@ -40,10 +53,101 @@ class ConfigDirPolicyProviderTest : public testing::Test {
     JSONStringValueSerializer serializer(&data);
     serializer.Serialize(dict);
     FilePath file_path(test_dir_.AppendASCII(file_name));
-    file_util::WriteFile(file_path, data.c_str(), data.size());
+    ASSERT_TRUE(file_util::WriteFile(file_path, data.c_str(), data.size()));
   }
 
   FilePath test_dir_;
+  MessageLoop loop_;
+  ChromeThread ui_thread_;
+  ChromeThread file_thread_;
+};
+
+// A mock provider that allows us to capture to reload notifications.
+class MockConfigDirPolicyProvider : public ConfigDirPolicyProvider {
+ public:
+  explicit MockConfigDirPolicyProvider(const FilePath& config_dir_)
+      : ConfigDirPolicyProvider(config_dir_) {}
+
+  MOCK_METHOD0(NotifyStoreOfPolicyChange, void());
+};
+
+class PolicyDirLoaderTest : public ConfigDirPolicyProviderTestBase {
+ protected:
+  PolicyDirLoaderTest() {}
+
+  virtual void SetUp() {
+    ConfigDirPolicyProviderTestBase::SetUp();
+    provider_.reset(new MockConfigDirPolicyProvider(test_dir_));
+  }
+
+  virtual void TearDown() {
+    provider_.reset(NULL);
+    ConfigDirPolicyProviderTestBase::TearDown();
+  }
+
+  scoped_ptr<MockConfigDirPolicyProvider> provider_;
+};
+
+TEST_F(PolicyDirLoaderTest, BasicLoad) {
+  DictionaryValue test_dict;
+  test_dict.SetString("HomepageLocation", "http://www.google.com");
+  WriteConfigFile(test_dict, "config_file");
+
+  scoped_refptr<PolicyDirLoader> loader_(
+      new PolicyDirLoader(provider_->AsWeakPtr(), test_dir_,
+                          kSettleIntervalSecondsForTesting,
+                          kReloadIntervalMinutesForTesting));
+  scoped_ptr<DictionaryValue> policy(loader_->GetPolicy());
+  EXPECT_TRUE(policy.get());
+  EXPECT_EQ(1U, policy->size());
+
+  std::string str_value;
+  EXPECT_TRUE(policy->GetString("HomepageLocation", &str_value));
+  EXPECT_EQ("http://www.google.com", str_value);
+
+  loader_->Stop();
+}
+
+TEST_F(PolicyDirLoaderTest, TestRefresh) {
+  scoped_refptr<PolicyDirLoader> loader_(
+      new PolicyDirLoader(provider_->AsWeakPtr(), test_dir_,
+                          kSettleIntervalSecondsForTesting,
+                          kReloadIntervalMinutesForTesting));
+  scoped_ptr<DictionaryValue> policy(loader_->GetPolicy());
+  EXPECT_TRUE(policy.get());
+  EXPECT_EQ(0U, policy->size());
+
+  DictionaryValue test_dict;
+  test_dict.SetString("HomepageLocation", "http://www.google.com");
+  WriteConfigFile(test_dict, "config_file");
+
+  EXPECT_CALL(*provider_, NotifyStoreOfPolicyChange()).Times(1);
+  loader_->OnFilePathChanged(test_dir_.AppendASCII("config_file"));
+
+  // Run the loop. The refresh should be handled immediately since the settle
+  // interval has been disabled.
+  loop_.RunAllPending();
+  Mock::VerifyAndClearExpectations(provider_.get());
+
+  policy.reset(loader_->GetPolicy());
+  EXPECT_TRUE(policy.get());
+  EXPECT_EQ(1U, policy->size());
+
+  std::string str_value;
+  EXPECT_TRUE(policy->GetString("HomepageLocation", &str_value));
+  EXPECT_EQ("http://www.google.com", str_value);
+
+  loader_->Stop();
+}
+
+class ConfigDirPolicyProviderTest : public ConfigDirPolicyProviderTestBase {
+ protected:
+  virtual void SetUp() {
+    ConfigDirPolicyProviderTestBase::SetUp();
+    // Create a fresh policy store mock.
+    policy_store_.reset(new MockConfigurationPolicyStore());
+  }
+
   scoped_ptr<MockConfigurationPolicyStore> policy_store_;
 };