Support change detection and reloading in ConfigDirPolicyProvider.

chrome/browser/policy/config_dir_policy_provider.cc

Index: chrome/browser/policy/config_dir_policy_provider.cc
diff --git a/chrome/browser/policy/config_dir_policy_provider.cc b/chrome/browser/policy/config_dir_policy_provider.cc
index 59509fce336884480fc703b757bc27d9e91907ac..8c64efaa14eb781cf7191f28fb161fb8cc5b362d 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.
 }
-