chrome/browser/prefs/pref_service.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/prefs/pref_service.h"

#include <algorithm>

#include "base/bind.h"
#include "base/command_line.h"
#include "base/file_path.h"
#include "base/file_util.h"
#include "base/logging.h"
#include "base/message_loop.h"
#include "base/metrics/histogram.h"
#include "base/stl_util.h"
#include "base/string_number_conversions.h"
#include "base/string_util.h"
#include "base/value_conversions.h"
#include "build/build_config.h"
#include "chrome/browser/browser_process.h"
#include "chrome/browser/extensions/extension_pref_store.h"
#include "chrome/browser/policy/configuration_policy_pref_store.h"
#include "chrome/browser/prefs/command_line_pref_store.h"
#include "chrome/browser/prefs/default_pref_store.h"
#include "chrome/browser/prefs/overlay_user_pref_store.h"
#include "chrome/browser/prefs/pref_model_associator.h"
#include "chrome/browser/prefs/pref_notifier_impl.h"
#include "chrome/browser/prefs/pref_value_store.h"
#include "chrome/browser/profiles/profile.h"
#include "chrome/browser/ui/prefs/prefs_tab_helper.h"
#include "chrome/browser/ui/profile_error_dialog.h"
#include "chrome/common/json_pref_store.h"
#include "chrome/common/pref_names.h"
#include "content/public/browser/browser_thread.h"
#include "grit/chromium_strings.h"
#include "grit/generated_resources.h"
#include "ui/base/l10n/l10n_util.h"

using content::BrowserThread;

namespace {

// A helper function for RegisterLocalized*Pref that creates a Value* based on
// the string value in the locale dll.  Because we control the values in a
// locale dll, this should always return a Value of the appropriate type.
Value* CreateLocaleDefaultValue(base::Value::Type type, int message_id) {
  std::string resource_string = l10n_util::GetStringUTF8(message_id);
  DCHECK(!resource_string.empty());
  switch (type) {
    case Value::TYPE_BOOLEAN: {
      if ("true" == resource_string)
        return Value::CreateBooleanValue(true);
      if ("false" == resource_string)
        return Value::CreateBooleanValue(false);
      break;
    }

    case Value::TYPE_INTEGER: {
      int val;
      base::StringToInt(resource_string, &val);
      return Value::CreateIntegerValue(val);
    }

    case Value::TYPE_DOUBLE: {
      double val;
      base::StringToDouble(resource_string, &val);
      return Value::CreateDoubleValue(val);
    }

    case Value::TYPE_STRING: {
      return Value::CreateStringValue(resource_string);
    }

    default: {
      NOTREACHED() <<
          "list and dictionary types cannot have default locale values";
    }
  }
  NOTREACHED();
  return Value::CreateNullValue();
}

// Forwards a notification after a PostMessage so that we can wait for the
// MessageLoop to run.
void NotifyReadError(int message_id) {
  ShowProfileErrorDialog(message_id);
}

// Shows notifications which correspond to PersistentPrefStore's reading errors.
class ReadErrorHandler : public PersistentPrefStore::ReadErrorDelegate {
 public:
  virtual void OnError(PersistentPrefStore::PrefReadError error) {
    if (error != PersistentPrefStore::PREF_READ_ERROR_NONE) {
      // Failing to load prefs on startup is a bad thing(TM). See bug 38352 for
      // an example problem that this can cause.
      // Do some diagnosis and try to avoid losing data.
      int message_id = 0;
      if (error <= PersistentPrefStore::PREF_READ_ERROR_JSON_TYPE) {
        message_id = IDS_PREFERENCES_CORRUPT_ERROR;
      } else if (error != PersistentPrefStore::PREF_READ_ERROR_NO_FILE) {
        message_id = IDS_PREFERENCES_UNREADABLE_ERROR;
      }

      if (message_id) {
        BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
            base::Bind(&NotifyReadError, message_id));
      }
      UMA_HISTOGRAM_ENUMERATION("PrefService.ReadError", error,
                                PersistentPrefStore::PREF_READ_ERROR_MAX_ENUM);
    }
  }
};

}  // namespace

PrefServiceBase* PrefServiceBase::ForProfile(Profile* profile) {
  return profile->GetPrefs();
}

// static
PrefService* PrefService::CreatePrefService(
    const FilePath& pref_filename,
    policy::PolicyService* policy_service,
    PrefStore* extension_prefs,
    bool async) {
  using policy::ConfigurationPolicyPrefStore;

#if defined(OS_LINUX)
  // We'd like to see what fraction of our users have the preferences
  // stored on a network file system, as we've had no end of troubles
  // with NFS/AFS.
  // TODO(evanm): remove this once we've collected state.
  file_util::FileSystemType fstype;
  if (file_util::GetFileSystemType(pref_filename.DirName(), &fstype)) {
    UMA_HISTOGRAM_ENUMERATION("PrefService.FileSystemType",
                              static_cast<int>(fstype),
                              file_util::FILE_SYSTEM_TYPE_COUNT);
  }
#endif

#if defined(ENABLE_CONFIGURATION_POLICY)
  ConfigurationPolicyPrefStore* managed =
      ConfigurationPolicyPrefStore::CreateMandatoryPolicyPrefStore(
          policy_service);
  ConfigurationPolicyPrefStore* recommended =
      ConfigurationPolicyPrefStore::CreateRecommendedPolicyPrefStore(
          policy_service);
#else
  ConfigurationPolicyPrefStore* managed = NULL;
  ConfigurationPolicyPrefStore* recommended = NULL;
#endif  // ENABLE_CONFIGURATION_POLICY

  CommandLinePrefStore* command_line =
      new CommandLinePrefStore(CommandLine::ForCurrentProcess());
  JsonPrefStore* user = new JsonPrefStore(
      pref_filename,
      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE));
  DefaultPrefStore* default_pref_store = new DefaultPrefStore();

  PrefNotifierImpl* pref_notifier = new PrefNotifierImpl();
  PrefModelAssociator* pref_sync_associator = new PrefModelAssociator();

  return new PrefService(
      pref_notifier,
      new PrefValueStore(
          managed,
          extension_prefs,
          command_line,
          user,
          recommended,
          default_pref_store,
          pref_sync_associator,
          pref_notifier),
      user,
      default_pref_store,
      pref_sync_associator,
      async);
}

PrefService* PrefService::CreateIncognitoPrefService(
    PrefStore* incognito_extension_prefs) {
  pref_service_forked_ = true;
  PrefNotifierImpl* pref_notifier = new PrefNotifierImpl();
  OverlayUserPrefStore* incognito_pref_store =
      new OverlayUserPrefStore(user_pref_store_.get());
  PrefsTabHelper::InitIncognitoUserPrefStore(incognito_pref_store);
  return new PrefService(
      pref_notifier,
      pref_value_store_->CloneAndSpecialize(
          NULL,  // managed
          incognito_extension_prefs,
          NULL,  // command_line_prefs
          incognito_pref_store,
          NULL,  // recommended
          default_store_.get(),
          NULL,  // pref_sync_associator
          pref_notifier),
      incognito_pref_store,
      default_store_.get(),
      NULL,
      false);
}

PrefService::PrefService(PrefNotifierImpl* pref_notifier,
                         PrefValueStore* pref_value_store,
                         PersistentPrefStore* user_prefs,
                         DefaultPrefStore* default_store,
                         PrefModelAssociator* pref_sync_associator,
                         bool async)
    : pref_notifier_(pref_notifier),
      pref_value_store_(pref_value_store),
      user_pref_store_(user_prefs),
      default_store_(default_store),
      pref_sync_associator_(pref_sync_associator),
      pref_service_forked_(false) {
  pref_notifier_->SetPrefService(this);
  if (pref_sync_associator_.get())
    pref_sync_associator_->SetPrefService(this);
  InitFromStorage(async);
}

PrefService::~PrefService() {
  DCHECK(CalledOnValidThread());
  STLDeleteContainerPointers(prefs_.begin(), prefs_.end());
  prefs_.clear();

  // Reset pointers so accesses after destruction reliably crash.
  pref_value_store_.reset();
  user_pref_store_ = NULL;
  default_store_ = NULL;
  pref_sync_associator_.reset();
  pref_notifier_.reset();
}

void PrefService::InitFromStorage(bool async) {
  if (!async) {
    ReadErrorHandler error_handler;
    error_handler.OnError(user_pref_store_->ReadPrefs());
  } else {
    // Guarantee that initialization happens after this function returned.
    MessageLoop::current()->PostTask(
        FROM_HERE,
        base::Bind(&PersistentPrefStore::ReadPrefsAsync,
                   user_pref_store_.get(),
                   new ReadErrorHandler()));
  }
}

bool PrefService::ReloadPersistentPrefs() {
  return user_pref_store_->ReadPrefs() ==
             PersistentPrefStore::PREF_READ_ERROR_NONE;
}

void PrefService::CommitPendingWrite() {
  DCHECK(CalledOnValidThread());
  user_pref_store_->CommitPendingWrite();
}

namespace {

// If there's no g_browser_process or no local state, return true (for testing).
bool IsLocalStatePrefService(PrefService* prefs) {
  return (!g_browser_process ||
          !g_browser_process->local_state() ||
          g_browser_process->local_state() == prefs);
}

// If there's no g_browser_process, return true (for testing).
bool IsProfilePrefService(PrefService* prefs) {
  // TODO(zea): uncomment this once all preferences are only ever registered
  // with either the local_state's pref service or the profile's pref service.
  // return (!g_browser_process || g_browser_process->local_state() != prefs);
  return true;
}

}  // namespace


// Local State prefs.
void PrefService::RegisterBooleanPref(const char* path,
                                      bool default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     Value::CreateBooleanValue(default_value),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterIntegerPref(const char* path, int default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     Value::CreateIntegerValue(default_value),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterDoublePref(const char* path, double default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     Value::CreateDoubleValue(default_value),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterStringPref(const char* path,
                                     const std::string& default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     Value::CreateStringValue(default_value),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterFilePathPref(const char* path,
                                       const FilePath& default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     Value::CreateStringValue(default_value.value()),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterListPref(const char* path) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     new ListValue(),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterListPref(const char* path, ListValue* default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     default_value,
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterDictionaryPref(const char* path) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     new DictionaryValue(),
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterDictionaryPref(const char* path,
                                         DictionaryValue* default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(path,
                     default_value,
                     UNSYNCABLE_PREF);
}

void PrefService::RegisterLocalizedBooleanPref(const char* path,
                                               int locale_default_message_id) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_BOOLEAN, locale_default_message_id),
      UNSYNCABLE_PREF);
}

void PrefService::RegisterLocalizedIntegerPref(const char* path,
                                               int locale_default_message_id) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_INTEGER, locale_default_message_id),
      UNSYNCABLE_PREF);
}

void PrefService::RegisterLocalizedDoublePref(const char* path,
                                              int locale_default_message_id) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_DOUBLE, locale_default_message_id),
      UNSYNCABLE_PREF);
}

void PrefService::RegisterLocalizedStringPref(const char* path,
                                              int locale_default_message_id) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_STRING, locale_default_message_id),
      UNSYNCABLE_PREF);
}

void PrefService::RegisterInt64Pref(const char* path, int64 default_value) {
  // If this fails, the pref service in use is a profile pref service, so the
  // sync status must be provided (see profile pref registration calls below).
  DCHECK(IsLocalStatePrefService(this));
  RegisterPreference(
      path,
      Value::CreateStringValue(base::Int64ToString(default_value)),
      UNSYNCABLE_PREF);
}

// Profile prefs (must use the sync_status variable).
void PrefService::RegisterBooleanPref(const char* path,
                                      bool default_value,
                                      PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path,
                     Value::CreateBooleanValue(default_value),
                     sync_status);
}

void PrefService::RegisterIntegerPref(const char* path,
                                      int default_value,
                                      PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path,
                     Value::CreateIntegerValue(default_value),
                     sync_status);
}

void PrefService::RegisterDoublePref(const char* path,
                                     double default_value,
                                     PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path,
                     Value::CreateDoubleValue(default_value),
                     sync_status);
}

void PrefService::RegisterStringPref(const char* path,
                                     const std::string& default_value,
                                     PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path,
                     Value::CreateStringValue(default_value),
                     sync_status);
}

void PrefService::RegisterFilePathPref(const char* path,
                                       const FilePath& default_value,
                                       PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path,
                     Value::CreateStringValue(default_value.value()),
                     sync_status);
}

void PrefService::RegisterListPref(const char* path,
                                   PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path, new ListValue(), sync_status);
}

void PrefService::RegisterListPref(const char* path,
                                   ListValue* default_value,
                                   PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path, default_value, sync_status);
}

void PrefService::RegisterDictionaryPref(const char* path,
                                         PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path, new DictionaryValue(), sync_status);
}

void PrefService::RegisterDictionaryPref(const char* path,
                                         DictionaryValue* default_value,
                                         PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(path, default_value, sync_status);
}

void PrefService::RegisterLocalizedBooleanPref(const char* path,
                                               int locale_default_message_id,
                                               PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_BOOLEAN, locale_default_message_id),
      sync_status);
}

void PrefService::RegisterLocalizedIntegerPref(const char* path,
                                               int locale_default_message_id,
                                               PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_INTEGER, locale_default_message_id),
      sync_status);
}

void PrefService::RegisterLocalizedDoublePref(const char* path,
                                              int locale_default_message_id,
                                              PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_DOUBLE, locale_default_message_id),
      sync_status);
}

void PrefService::RegisterLocalizedStringPref(const char* path,
                                              int locale_default_message_id,
                                              PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      CreateLocaleDefaultValue(Value::TYPE_STRING, locale_default_message_id),
      sync_status);
}

void PrefService::RegisterInt64Pref(const char* path,
                                    int64 default_value,
                                    PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      Value::CreateStringValue(base::Int64ToString(default_value)),
      sync_status);
}

void PrefService::RegisterUint64Pref(const char* path,
                                     uint64 default_value,
                                     PrefSyncStatus sync_status) {
  DCHECK(IsProfilePrefService(this));
  RegisterPreference(
      path,
      Value::CreateStringValue(base::Uint64ToString(default_value)),
      sync_status);
}

bool PrefService::GetBoolean(const char* path) const {
  DCHECK(CalledOnValidThread());

  bool result = false;

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return result;
  }
  bool rv = pref->GetValue()->GetAsBoolean(&result);
  DCHECK(rv);
  return result;
}

int PrefService::GetInteger(const char* path) const {
  DCHECK(CalledOnValidThread());

  int result = 0;

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return result;
  }
  bool rv = pref->GetValue()->GetAsInteger(&result);
  DCHECK(rv);
  return result;
}

double PrefService::GetDouble(const char* path) const {
  DCHECK(CalledOnValidThread());

  double result = 0.0;

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return result;
  }
  bool rv = pref->GetValue()->GetAsDouble(&result);
  DCHECK(rv);
  return result;
}

std::string PrefService::GetString(const char* path) const {
  DCHECK(CalledOnValidThread());

  std::string result;

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return result;
  }
  bool rv = pref->GetValue()->GetAsString(&result);
  DCHECK(rv);
  return result;
}

FilePath PrefService::GetFilePath(const char* path) const {
  DCHECK(CalledOnValidThread());

  FilePath result;

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return FilePath(result);
  }
  bool rv = base::GetValueAsFilePath(*pref->GetValue(), &result);
  DCHECK(rv);
  return result;
}

bool PrefService::HasPrefPath(const char* path) const {
  const Preference* pref = FindPreference(path);
  return pref && !pref->IsDefaultValue();
}

DictionaryValue* PrefService::GetPreferenceValues() const {
  DCHECK(CalledOnValidThread());
  DictionaryValue* out = new DictionaryValue;
  DefaultPrefStore::const_iterator i = default_store_->begin();
  for (; i != default_store_->end(); ++i) {
    const Preference* pref = FindPreference(i->first.c_str());
    DCHECK(pref);
    const Value* value = pref->GetValue();
    DCHECK(value);
    out->Set(i->first, value->DeepCopy());
  }
  return out;
}

const PrefService::Preference* PrefService::FindPreference(
    const char* pref_name) const {
  DCHECK(CalledOnValidThread());
  Preference p(this, pref_name, Value::TYPE_NULL);
  PreferenceSet::const_iterator it = prefs_.find(&p);
  if (it != prefs_.end())
    return *it;
  const base::Value::Type type = default_store_->GetType(pref_name);
  if (type == Value::TYPE_NULL)
    return NULL;
  Preference* new_pref = new Preference(this, pref_name, type);
  prefs_.insert(new_pref);
  return new_pref;
}

bool PrefService::ReadOnly() const {
  return user_pref_store_->ReadOnly();
}

PrefService::PrefInitializationStatus PrefService::GetInitializationStatus()
    const {
  if (!user_pref_store_->IsInitializationComplete())
    return INITIALIZATION_STATUS_WAITING;

  switch (user_pref_store_->GetReadError()) {
    case PersistentPrefStore::PREF_READ_ERROR_NONE:
      return INITIALIZATION_STATUS_SUCCESS;
    case PersistentPrefStore::PREF_READ_ERROR_NO_FILE:
      return INITIALIZATION_STATUS_CREATED_NEW_PROFILE;
    default:
      return INITIALIZATION_STATUS_ERROR;
  }
}

bool PrefService::IsManagedPreference(const char* pref_name) const {
  const Preference* pref = FindPreference(pref_name);
  return pref && pref->IsManaged();
}

bool PrefService::IsUserModifiablePreference(const char* pref_name) const {
  const Preference* pref = FindPreference(pref_name);
  return pref && pref->IsUserModifiable();
}

const DictionaryValue* PrefService::GetDictionary(const char* path) const {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return NULL;
  }
  const Value* value = pref->GetValue();
  if (value->GetType() != Value::TYPE_DICTIONARY) {
    NOTREACHED();
    return NULL;
  }
  return static_cast<const DictionaryValue*>(value);
}

const base::Value* PrefService::GetUserPrefValue(const char* path) const {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to get an unregistered pref: " << path;
    return NULL;
  }

  // Look for an existing preference in the user store. If it doesn't
  // exist, return NULL.
  base::Value* value = NULL;
  if (user_pref_store_->GetMutableValue(path, &value) != PrefStore::READ_OK)
    return NULL;

  if (!value->IsType(pref->GetType())) {
    NOTREACHED() << "Pref value type doesn't match registered type.";
    return NULL;
  }

  return value;
}

const base::Value* PrefService::GetDefaultPrefValue(const char* path) const {
  DCHECK(CalledOnValidThread());
  // Lookup the preference in the default store.
  const base::Value* value = NULL;
  if (default_store_->GetValue(path, &value) != PrefStore::READ_OK) {
    NOTREACHED() << "Default value missing for pref: " << path;
    return NULL;
  }
  return value;
}

const ListValue* PrefService::GetList(const char* path) const {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return NULL;
  }
  const Value* value = pref->GetValue();
  if (value->GetType() != Value::TYPE_LIST) {
    NOTREACHED();
    return NULL;
  }
  return static_cast<const ListValue*>(value);
}

void PrefService::AddPrefObserver(const char* path,
                                  content::NotificationObserver* obs) {
  pref_notifier_->AddPrefObserver(path, obs);
}

void PrefService::RemovePrefObserver(const char* path,
                                     content::NotificationObserver* obs) {
  pref_notifier_->RemovePrefObserver(path, obs);
}

void PrefService::RegisterPreference(const char* path,
                                     Value* default_value,
                                     PrefSyncStatus sync_status) {
  DCHECK(CalledOnValidThread());

  // The main code path takes ownership, but most don't. We'll be safe.
  scoped_ptr<Value> scoped_value(default_value);

  if (FindPreference(path)) {
    NOTREACHED() << "Tried to register duplicate pref " << path;
    return;
  }

  base::Value::Type orig_type = default_value->GetType();
  DCHECK(orig_type != Value::TYPE_NULL && orig_type != Value::TYPE_BINARY) <<
         "invalid preference type: " << orig_type;

  // For ListValue and DictionaryValue with non empty default, empty value
  // for |path| needs to be persisted in |user_pref_store_|. So that
  // non empty default is not used when user sets an empty ListValue or
  // DictionaryValue.
  bool needs_empty_value = false;
  if (orig_type == base::Value::TYPE_LIST) {
    const base::ListValue* list = NULL;
    if (default_value->GetAsList(&list) && !list->empty())
      needs_empty_value = true;
  } else if (orig_type == base::Value::TYPE_DICTIONARY) {
    const base::DictionaryValue* dict = NULL;
    if (default_value->GetAsDictionary(&dict) && !dict->empty())
      needs_empty_value = true;
  }
  if (needs_empty_value)
    user_pref_store_->MarkNeedsEmptyValue(path);

  // Hand off ownership.
  default_store_->SetDefaultValue(path, scoped_value.release());

  // Register with sync if necessary.
  if (sync_status == SYNCABLE_PREF && pref_sync_associator_.get())
    pref_sync_associator_->RegisterPref(path);
}

void PrefService::UnregisterPreference(const char* path) {
  DCHECK(CalledOnValidThread());

  Preference p(this, path, Value::TYPE_NULL);
  PreferenceSet::iterator it = prefs_.find(&p);
  if (it == prefs_.end()) {
    NOTREACHED() << "Trying to unregister an unregistered pref: " << path;
    return;
  }

  delete *it;
  prefs_.erase(it);
  default_store_->RemoveDefaultValue(path);
  if (pref_sync_associator_.get() &&
      pref_sync_associator_->IsPrefRegistered(path)) {
    pref_sync_associator_->UnregisterPref(path);
  }
}

void PrefService::ClearPref(const char* path) {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to clear an unregistered pref: " << path;
    return;
  }
  user_pref_store_->RemoveValue(path);
}

void PrefService::Set(const char* path, const Value& value) {
  SetUserPrefValue(path, value.DeepCopy());
}

void PrefService::SetBoolean(const char* path, bool value) {
  SetUserPrefValue(path, Value::CreateBooleanValue(value));
}

void PrefService::SetInteger(const char* path, int value) {
  SetUserPrefValue(path, Value::CreateIntegerValue(value));
}

void PrefService::SetDouble(const char* path, double value) {
  SetUserPrefValue(path, Value::CreateDoubleValue(value));
}

void PrefService::SetString(const char* path, const std::string& value) {
  SetUserPrefValue(path, Value::CreateStringValue(value));
}

void PrefService::SetFilePath(const char* path, const FilePath& value) {
  SetUserPrefValue(path, base::CreateFilePathValue(value));
}

void PrefService::SetInt64(const char* path, int64 value) {
  SetUserPrefValue(path, Value::CreateStringValue(base::Int64ToString(value)));
}

int64 PrefService::GetInt64(const char* path) const {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return 0;
  }
  std::string result("0");
  bool rv = pref->GetValue()->GetAsString(&result);
  DCHECK(rv);

  int64 val;
  base::StringToInt64(result, &val);
  return val;
}

void PrefService::SetUint64(const char* path, uint64 value) {
  SetUserPrefValue(path, Value::CreateStringValue(base::Uint64ToString(value)));
}

uint64 PrefService::GetUint64(const char* path) const {
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to read an unregistered pref: " << path;
    return 0;
  }
  std::string result("0");
  bool rv = pref->GetValue()->GetAsString(&result);
  DCHECK(rv);

  uint64 val;
  base::StringToUint64(result, &val);
  return val;
}

Value* PrefService::GetMutableUserPref(const char* path,
                                       base::Value::Type type) {
  CHECK(type == Value::TYPE_DICTIONARY || type == Value::TYPE_LIST);
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to get an unregistered pref: " << path;
    return NULL;
  }
  if (pref->GetType() != type) {
    NOTREACHED() << "Wrong type for GetMutableValue: " << path;
    return NULL;
  }

  // Look for an existing preference in the user store. If it doesn't
  // exist or isn't the correct type, create a new user preference.
  Value* value = NULL;
  if (user_pref_store_->GetMutableValue(path, &value) != PrefStore::READ_OK ||
      !value->IsType(type)) {
    if (type == Value::TYPE_DICTIONARY) {
      value = new DictionaryValue;
    } else if (type == Value::TYPE_LIST) {
      value = new ListValue;
    } else {
      NOTREACHED();
    }
    user_pref_store_->SetValueSilently(path, value);
  }
  return value;
}

void PrefService::ReportUserPrefChanged(const std::string& key) {
  user_pref_store_->ReportValueChanged(key);
}

void PrefService::SetUserPrefValue(const char* path, Value* new_value) {
  scoped_ptr<Value> owned_value(new_value);
  DCHECK(CalledOnValidThread());

  const Preference* pref = FindPreference(path);
  if (!pref) {
    NOTREACHED() << "Trying to write an unregistered pref: " << path;
    return;
  }
  if (pref->GetType() != new_value->GetType()) {
    NOTREACHED() << "Trying to set pref " << path
                 << " of type " << pref->GetType()
                 << " to value of type " << new_value->GetType();
    return;
  }

  user_pref_store_->SetValue(path, owned_value.release());
}

syncer::SyncableService* PrefService::GetSyncableService() {
  return pref_sync_associator_.get();
}

void PrefService::UpdateCommandLinePrefStore(CommandLine* command_line) {
  // If |pref_service_forked_| is true, then this PrefService and the forked
  // copies will be out of sync.
  DCHECK(!pref_service_forked_);
  pref_value_store_->UpdateCommandLinePrefStore(
      new CommandLinePrefStore(command_line));
}

///////////////////////////////////////////////////////////////////////////////
// PrefService::Preference

PrefService::Preference::Preference(const PrefService* service,
                                    const char* name,
                                    base::Value::Type type)
      : name_(name),
        type_(type),
        pref_service_(service) {
  DCHECK(name);
  DCHECK(service);
}

const std::string PrefService::Preference::name() const {
  return name_;
}

base::Value::Type PrefService::Preference::GetType() const {
  return type_;
}

const Value* PrefService::Preference::GetValue() const {
  DCHECK(pref_service_->FindPreference(name_.c_str())) <<
      "Must register pref before getting its value";

  const Value* found_value = NULL;
  if (pref_value_store()->GetValue(name_, type_, &found_value)) {
    DCHECK(found_value->IsType(type_));
    return found_value;
  }

  // Every registered preference has at least a default value.
  NOTREACHED() << "no valid value found for registered pref " << name_;
  return NULL;
}

const Value* PrefService::Preference::GetRecommendedValue() const {
  DCHECK(pref_service_->FindPreference(name_.c_str())) <<
      "Must register pref before getting its value";

  const Value* found_value = NULL;
  if (pref_value_store()->GetRecommendedValue(name_, type_, &found_value)) {
    DCHECK(found_value->IsType(type_));
    return found_value;
  }

  // The pref has no recommended value.
  return NULL;
}

bool PrefService::Preference::IsManaged() const {
  return pref_value_store()->PrefValueInManagedStore(name_.c_str());
}

bool PrefService::Preference::IsRecommended() const {
  return pref_value_store()->PrefValueFromRecommendedStore(name_.c_str());
}

bool PrefService::Preference::HasExtensionSetting() const {
  return pref_value_store()->PrefValueInExtensionStore(name_.c_str());
}

bool PrefService::Preference::HasUserSetting() const {
  return pref_value_store()->PrefValueInUserStore(name_.c_str());
}

bool PrefService::Preference::IsExtensionControlled() const {
  return pref_value_store()->PrefValueFromExtensionStore(name_.c_str());
}

bool PrefService::Preference::IsUserControlled() const {
  return pref_value_store()->PrefValueFromUserStore(name_.c_str());
}

bool PrefService::Preference::IsDefaultValue() const {
  return pref_value_store()->PrefValueFromDefaultStore(name_.c_str());
}

bool PrefService::Preference::IsUserModifiable() const {
  return pref_value_store()->PrefValueUserModifiable(name_.c_str());
}

bool PrefService::Preference::IsExtensionModifiable() const {
  return pref_value_store()->PrefValueExtensionModifiable(name_.c_str());
}