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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode:nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef mozilla_intl_LocaleService_h__
#define mozilla_intl_LocaleService_h__
#include "nsIObserver.h"
#include "nsString.h"
#include "nsTArray.h"
#include "nsWeakReference.h"
#include "MozLocaleBindings.h"
#include "mozilla/intl/ICU4CGlue.h"
#include "mozILocaleService.h"
namespace mozilla {
namespace intl {
* LocaleService is a manager of language negotiation in Gecko.
* It's intended to be the core place for collecting available and
* requested languages and negotiating them to produce a fallback
* chain of locales for the application.
* Client / Server
* LocaleService may operate in one of two modes:
* server
* in the server mode, LocaleService is collecting and negotiating
* languages. It also subscribes to relevant observers.
* There should be at most one server per application instance.
* client
* in the client mode, LocaleService is not responsible for collecting
* or reacting to any system changes. It still distributes information
* about locales, but internally, it gets information from the server
* instance instead of collecting it on its own. This prevents any data
* desynchronization and minimizes the cost of running the service.
* In both modes, all get* methods should work the same way and all
* static methods are available.
* In the server mode, other components may inform LocaleService about their
* status either via calls to set* methods or via observer events.
* In the client mode, only the process communication should provide data
* to the LocaleService.
* At the moment desktop apps use the parent process in the server mode, and
* content processes in the client mode.
* Locale / Language
* The terms `Locale ID` and `Language ID` are used slightly differently
* by different organizations. Mozilla uses the term `Language ID` to describe
* a string that contains information about the language itself, script,
* region and variant. For example "en-Latn-US-mac" is a correct Language ID.
* Locale ID contains a Language ID plus a number of extension tags that
* contain information that go beyond language inforamation such as
* preferred currency, date/time formatting etc.
* An example of a Locale ID is `en-Latn-US-x-hc-h12-ca-gregory`
* At the moment we do not support full extension tag system, but we
* try to be specific when naming APIs, so the service is for locales,
* but we negotiate between languages etc.
class LocaleService final : public mozILocaleService,
public nsIObserver,
public nsSupportsWeakReference {
* List of available language negotiation strategies.
* See the mozILocaleService.idl for detailed description of the
* strategies.
static const int32_t kLangNegStrategyFiltering = 0;
static const int32_t kLangNegStrategyMatching = 1;
static const int32_t kLangNegStrategyLookup = 2;
explicit LocaleService(bool aIsServer);
* Create (if necessary) and return a raw pointer to the singleton instance.
* Use this accessor in C++ code that just wants to call a method on the
* instance, but does not need to hold a reference, as in
* nsAutoCString str;
* LocaleService::GetInstance()->GetAppLocaleAsLangTag(str);
static LocaleService* GetInstance();
* Return an addRef'd pointer to the singleton instance. This is used by the
* XPCOM constructor that exists to support usage from JS.
static already_AddRefed<LocaleService> GetInstanceAddRefed() {
return RefPtr<LocaleService>(GetInstance()).forget();
* Canonicalize a Unicode Language Identifier string.
* The operation is:
* * Normalizing casing (`eN-Us-Windows` -> `en-US-windows`)
* * Switching `_` to `-` (`en_US` -> `en-US`)
* * Rejecting invalid identifiers (`e21-X` sets aLocale to `und` and
* returns false)
* * Normalizing Mozilla's `ja-JP-mac` to `ja-JP-macos`
* * Cutting off POSIX dot postfix (`en-US.utf8` -> `en-US`)
* This operation should be used on any external input before
* it gets used in internal operations.
static bool CanonicalizeLanguageId(nsACString& aLocale) {
return ffi::unic_langid_canonicalize(&aLocale);
* This method should only be called in the client mode.
* It replaces all the language negotiation and is supposed to be called
* in order to bring the client LocaleService in sync with the server
* LocaleService.
* Currently, it's called by the IPC code.
void AssignAppLocales(const nsTArray<nsCString>& aAppLocales);
void AssignRequestedLocales(const nsTArray<nsCString>& aRequestedLocales);
* Those two functions allow to trigger cache invalidation on one of the
* three cached values.
* In most cases, the functions will be called by the observer in
* LocaleService itself, but in a couple special cases, we have the
* other component call this manually instead of sending a global event.
* If the result differs from the previous list, it will additionally
* trigger a corresponding event
* This code should be called only in the server mode..
void RequestedLocalesChanged();
void LocalesChanged();
* This function keeps the pref setting updated.
void WebExposedLocalesChanged();
* Returns whether the locale is RTL.
static bool IsLocaleRTL(const nsACString& aLocale);
* Returns whether the current app locale is RTL.
* This method respects this override:
* - `intl.l10n.pseudo`
bool IsAppLocaleRTL();
static bool LanguagesMatch(const nsACString& aRequested,
const nsACString& aAvailable);
bool IsServer();
* Create a component from intl/components with the current app's locale. This
* is a convenience method for efficient string management with the app
* locale.
template <typename T, typename... Args>
static Result<UniquePtr<T>, ICUError> TryCreateComponent(Args... args) {
// 32 is somewhat arbitrary for the length, but it should fit common
// locales, but locales such as the following will be heap allocated:
// "de-u-ca-gregory-fw-mon-hc-h23-co-phonebk-ka-noignore-kb-false-kc-
// false-kf-false-kh-false-kk-false-kn-false-kr-space-ks-level1-kv-space-cf-
// standard-cu-eur-ms-metric-nu-latn-lb-strict-lw-normal-ss-none-tz-atvie-em-
// default-rg-atzzzz-sd-atat1-va-posix"
nsAutoCStringN<32> appLocale;
return T::TryCreate(appLocale.get(), args...);
* Create a component from intl/components with a given locale, but fallback
* to the app locale if it doesn't work.
template <typename T, typename... Args>
static Result<UniquePtr<T>, ICUError> TryCreateComponentWithLocale(
const char* aLocale, Args... args) {
auto result = T::TryCreate(aLocale, args...);
if (result.isOk()) {
return result;
return TryCreateComponent<T>(args...);
void NegotiateAppLocales(nsTArray<nsCString>& aRetVal);
void InitPackagedLocales();
void RemoveObservers();
virtual ~LocaleService() = default;
nsAutoCStringN<16> mDefaultLocale;
nsTArray<nsCString> mAppLocales;
nsTArray<nsCString> mRequestedLocales;
nsTArray<nsCString> mAvailableLocales;
nsTArray<nsCString> mPackagedLocales;
nsTArray<nsCString> mWebExposedLocales;
const bool mIsServer;
static StaticRefPtr<LocaleService> sInstance;
} // namespace intl
} // namespace mozilla
#endif /* mozilla_intl_LocaleService_h__ */