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/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
* vim: sw=2 ts=2 sts=2 et filetype=javascript
* 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
let global = Cu.getGlobalForObject({});
// Some global imports expose additional symbols; for example,
// `Cu.importGlobalProperties(["MessageChannel"])` imports `MessageChannel`
// and `MessagePort`. This table maps those extra symbols to the main
// import name.
const EXTRA_GLOBAL_NAME_TO_IMPORT_NAME = {
MessagePort: "MessageChannel",
};
/**
* Redefines the given property on the given object with the given
* value. This can be used to redefine getter properties which do not
* implement setters.
*/
function redefine(object, prop, value) {
Object.defineProperty(object, prop, {
configurable: true,
enumerable: true,
value,
writable: true,
});
return value;
}
export var XPCOMUtils = {
/**
* Defines a getter on a specified object that will be created upon first use.
*
* @param aObject
* The object to define the lazy getter on.
* @param aName
* The name of the getter to define on aObject.
* @param aLambda
* A function that returns what the getter should return. This will
* only ever be called once.
*/
defineLazyGetter(aObject, aName, aLambda) {
ChromeUtils.defineLazyGetter(aObject, aName, aLambda);
},
/**
* Defines a getter on a specified object for a script. The script will not
* be loaded until first use.
*
* @param aObject
* The object to define the lazy getter on.
* @param aNames
* The name of the getter to define on aObject for the script.
* This can be a string if the script exports only one symbol,
* or an array of strings if the script can be first accessed
* from several different symbols.
* @param aResource
* The URL used to obtain the script.
*/
defineLazyScriptGetter(aObject, aNames, aResource) {
if (!Array.isArray(aNames)) {
aNames = [aNames];
}
for (let name of aNames) {
Object.defineProperty(aObject, name, {
get() {
XPCOMUtils._scriptloader.loadSubScript(aResource, aObject);
return aObject[name];
},
set(value) {
redefine(aObject, name, value);
},
configurable: true,
enumerable: true,
});
}
},
/**
* Overrides the scriptloader definition for tests to help with globals
* tracking. Should only be used for tests.
*
* @param {object} aObject
* The alternative script loader object to use.
*/
overrideScriptLoaderForTests(aObject) {
Cu.crashIfNotInAutomation();
delete this._scriptloader;
this._scriptloader = aObject;
},
/**
* Defines a getter property on the given object for each of the given
* global names as accepted by Cu.importGlobalProperties. These
* properties are imported into the shared JSM module global, and then
* copied onto the given object, no matter which global the object
* belongs to.
*
* @param {object} aObject
* The object on which to define the properties.
* @param {string[]} aNames
* The list of global properties to define.
*/
defineLazyGlobalGetters(aObject, aNames) {
for (let name of aNames) {
this.defineLazyGetter(aObject, name, () => {
if (!(name in global)) {
let importName = EXTRA_GLOBAL_NAME_TO_IMPORT_NAME[name] || name;
// eslint-disable-next-line mozilla/reject-importGlobalProperties, no-unused-vars
Cu.importGlobalProperties([importName]);
}
return global[name];
});
}
},
/**
* Defines a getter on a specified object for a service. The service will not
* be obtained until first use.
*
* @param aObject
* The object to define the lazy getter on.
* @param aName
* The name of the getter to define on aObject for the service.
* @param aContract
* The contract used to obtain the service.
* @param aInterfaceName
* The name of the interface to query the service to.
*/
defineLazyServiceGetter(aObject, aName, aContract, aInterfaceName) {
this.defineLazyGetter(aObject, aName, () => {
if (aInterfaceName) {
return Cc[aContract].getService(Ci[aInterfaceName]);
}
return Cc[aContract].getService().wrappedJSObject;
});
},
/**
* Defines a lazy service getter on a specified object for each
* property in the given object.
*
* @param aObject
* The object to define the lazy getter on.
* @param aServices
* An object with a property for each service to be
* imported, where the property name is the name of the
* symbol to define, and the value is a 1 or 2 element array
* containing the contract ID and, optionally, the interface
* name of the service, as passed to defineLazyServiceGetter.
*/
defineLazyServiceGetters(aObject, aServices) {
for (let [name, service] of Object.entries(aServices)) {
// Note: This is hot code, and cross-compartment array wrappers
// are not JIT-friendly to destructuring or spread operators, so
// we need to use indexed access instead.
this.defineLazyServiceGetter(
aObject,
name,
service[0],
service[1] || null
);
}
},
/**
* Defines a getter on a specified object for a module. The module will not
* be imported until first use. The getter allows to execute setup and
* teardown code (e.g. to register/unregister to services) and accepts
* a proxy object which acts on behalf of the module until it is imported.
*
* @param aObject
* The object to define the lazy getter on.
* @param aName
* The name of the getter to define on aObject for the module.
* @param aResource
* The URL used to obtain the module.
* @param aSymbol
* The name of the symbol exported by the module.
* This parameter is optional and defaults to aName.
* @param aPreLambda
* A function that is executed when the proxy is set up.
* This will only ever be called once.
* @param aPostLambda
* A function that is executed when the module has been imported to
* run optional teardown procedures on the proxy object.
* This will only ever be called once.
* @param aProxy
* An object which acts on behalf of the module to be imported until
* the module has been imported.
*/
defineLazyModuleGetter(
aObject,
aName,
aResource,
aSymbol,
aPreLambda,
aPostLambda,
aProxy
) {
if (arguments.length == 3) {
ChromeUtils.defineModuleGetter(aObject, aName, aResource);
return;
}
let proxy = aProxy || {};
if (typeof aPreLambda === "function") {
aPreLambda.apply(proxy);
}
this.defineLazyGetter(aObject, aName, () => {
var temp = {};
try {
temp = ChromeUtils.import(aResource);
if (typeof aPostLambda === "function") {
aPostLambda.apply(proxy);
}
} catch (ex) {
console.error("Failed to load module " + aResource + ".");
throw ex;
}
return temp[aSymbol || aName];
});
},
/**
* Defines a lazy module getter on a specified object for each
* property in the given object.
*
* @param aObject
* The object to define the lazy getter on.
* @param aModules
* An object with a property for each module property to be
* imported, where the property name is the name of the
* imported symbol and the value is the module URI.
*/
defineLazyModuleGetters(aObject, aModules) {
for (let [name, module] of Object.entries(aModules)) {
ChromeUtils.defineModuleGetter(aObject, name, module);
}
},
/**
* Defines a getter on a specified object for preference value. The
* preference is read the first time that the property is accessed,
* and is thereafter kept up-to-date using a preference observer.
*
* @param aObject
* The object to define the lazy getter on.
* @param aName
* The name of the getter property to define on aObject.
* @param aPreference
* The name of the preference to read.
* @param aDefaultPrefValue
* The default value to use, if the preference is not defined.
* This is the default value of the pref, before applying aTransform.
* @param aOnUpdate
* A function to call upon update. Receives as arguments
* `(aPreference, previousValue, newValue)`
* @param aTransform
* An optional function to transform the value. If provided,
* this function receives the new preference value as an argument
* and its return value is used by the getter.
*/
defineLazyPreferenceGetter(
aObject,
aName,
aPreference,
aDefaultPrefValue = null,
aOnUpdate = null,
aTransform = val => val
) {
if (AppConstants.DEBUG && aDefaultPrefValue !== null) {
let prefType = Services.prefs.getPrefType(aPreference);
if (prefType != Ci.nsIPrefBranch.PREF_INVALID) {
// The pref may get defined after the lazy getter is called
// at which point the code here won't know the expected type.
let prefTypeForDefaultValue = {
boolean: Ci.nsIPrefBranch.PREF_BOOL,
number: Ci.nsIPrefBranch.PREF_INT,
string: Ci.nsIPrefBranch.PREF_STRING,
}[typeof aDefaultPrefValue];
if (prefTypeForDefaultValue != prefType) {
throw new Error(
`Default value does not match preference type (Got ${prefTypeForDefaultValue}, expected ${prefType}) for ${aPreference}`
);
}
}
}
// Note: We need to keep a reference to this observer alive as long
// as aObject is alive. This means that all of our getters need to
// explicitly close over the variable that holds the object, and we
// cannot define a value in place of a getter after we read the
// preference.
let observer = {
QueryInterface: XPCU_lazyPreferenceObserverQI,
value: undefined,
observe(subject, topic, data) {
if (data == aPreference) {
if (aOnUpdate) {
let previous = this.value;
// Fetch and cache value.
this.value = undefined;
let latest = lazyGetter();
aOnUpdate(data, previous, latest);
} else {
// Empty cache, next call to the getter will cause refetch.
this.value = undefined;
}
}
},
};
let defineGetter = get => {
Object.defineProperty(aObject, aName, {
configurable: true,
enumerable: true,
get,
});
};
function lazyGetter() {
if (observer.value === undefined) {
let prefValue;
switch (Services.prefs.getPrefType(aPreference)) {
case Ci.nsIPrefBranch.PREF_STRING:
prefValue = Services.prefs.getStringPref(aPreference);
break;
case Ci.nsIPrefBranch.PREF_INT:
prefValue = Services.prefs.getIntPref(aPreference);
break;
case Ci.nsIPrefBranch.PREF_BOOL:
prefValue = Services.prefs.getBoolPref(aPreference);
break;
case Ci.nsIPrefBranch.PREF_INVALID:
prefValue = aDefaultPrefValue;
break;
default:
// This should never happen.
throw new Error(
`Error getting pref ${aPreference}; its value's type is ` +
`${Services.prefs.getPrefType(aPreference)}, which I don't ` +
`know how to handle.`
);
}
observer.value = aTransform(prefValue);
}
return observer.value;
}
defineGetter(() => {
Services.prefs.addObserver(aPreference, observer, true);
defineGetter(lazyGetter);
return lazyGetter();
});
},
/**
* Defines a non-writable property on an object.
*/
defineConstant(aObj, aName, aValue) {
Object.defineProperty(aObj, aName, {
value: aValue,
enumerable: true,
writable: false,
});
},
/**
* Defines a proxy which acts as a lazy object getter that can be passed
* around as a reference, and will only be evaluated when something in
* that object gets accessed.
*
* The evaluation can be triggered by a function call, by getting or
* setting a property, calling this as a constructor, or enumerating
* the properties of this object (e.g. during an iteration).
*
* Please note that, even after evaluated, the object given to you
* remains being the proxy object (which forwards everything to the
* real object). This is important to correctly use these objects
* in pairs of add+remove listeners, for example.
* If your use case requires access to the direct object, you can
* get it through the untrap callback.
*
* @param aObject
* The object to define the lazy getter on.
*
* You can pass null to aObject if you just want to get this
* proxy through the return value.
*
* @param aName
* The name of the getter to define on aObject.
*
* @param aInitFuncOrResource
* A function or a module that defines what this object actually
* should be when it gets evaluated. This will only ever be called once.
*
* Short-hand: If you pass a string to this parameter, it will be treated
* as the URI of a module to be imported, and aName will be used as
* the symbol to retrieve from the module.
*
* @param aStubProperties
* In this parameter, you can provide an object which contains
* properties from the original object that, when accessed, will still
* prevent the entire object from being evaluated.
*
* These can be copies or simplified versions of the original properties.
*
* One example is to provide an alternative QueryInterface implementation
* to avoid the entire object from being evaluated when it's added as an
* observer (as addObserver calls object.QueryInterface(Ci.nsIObserver)).
*
* Once the object has been evaluated, the properties from the real
* object will be used instead of the ones provided here.
*
* @param aUntrapCallback
* A function that gets called once when the object has just been evaluated.
* You can use this to do some work (e.g. setting properties) that you need
* to do on this object but that can wait until it gets evaluated.
*
* Another use case for this is to use during code development to log when
* this object gets evaluated, to make sure you're not accidentally triggering
* it earlier than expected.
*/
defineLazyProxy(
aObject,
aName,
aInitFuncOrResource,
aStubProperties,
aUntrapCallback
) {
let initFunc = aInitFuncOrResource;
if (typeof aInitFuncOrResource == "string") {
initFunc = () => ChromeUtils.import(aInitFuncOrResource)[aName];
}
let handler = new LazyProxyHandler(
aName,
initFunc,
aStubProperties,
aUntrapCallback
);
/*
* We cannot simply create a lazy getter for the underlying
* object and pass it as the target of the proxy, because
* just passing it in `new Proxy` means it would get
* evaluated. Becase of this, a full handler needs to be
* implemented (the LazyProxyHandler).
*
* So, an empty object is used as the target, and the handler
* replaces it on every call with the real object.
*/
let proxy = new Proxy({}, handler);
if (aObject) {
Object.defineProperty(aObject, aName, {
value: proxy,
enumerable: true,
writable: true,
});
}
return proxy;
},
};
XPCOMUtils.defineLazyGetter(XPCOMUtils, "_scriptloader", () => {
return Services.scriptloader;
});
/**
* LazyProxyHandler
* This class implements the handler used
* in the proxy from defineLazyProxy.
*
* This handler forwards all calls to an underlying object,
* stored as `this.realObject`, which is obtained as the returned
* value from aInitFunc, which will be called on the first time
* time that it needs to be used (with an exception in the get() trap
* for the properties provided in the `aStubProperties` parameter).
*/
class LazyProxyHandler {
constructor(aName, aInitFunc, aStubProperties, aUntrapCallback) {
this.pending = true;
this.name = aName;
this.initFuncOrResource = aInitFunc;
this.stubProperties = aStubProperties;
this.untrapCallback = aUntrapCallback;
}
getObject() {
if (this.pending) {
this.realObject = this.initFuncOrResource.call(null);
if (this.untrapCallback) {
this.untrapCallback.call(null, this.realObject);
this.untrapCallback = null;
}
this.pending = false;
this.stubProperties = null;
}
return this.realObject;
}
getPrototypeOf(target) {
return Reflect.getPrototypeOf(this.getObject());
}
setPrototypeOf(target, prototype) {
return Reflect.setPrototypeOf(this.getObject(), prototype);
}
isExtensible(target) {
return Reflect.isExtensible(this.getObject());
}
preventExtensions(target) {
return Reflect.preventExtensions(this.getObject());
}
getOwnPropertyDescriptor(target, prop) {
return Reflect.getOwnPropertyDescriptor(this.getObject(), prop);
}
defineProperty(target, prop, descriptor) {
return Reflect.defineProperty(this.getObject(), prop, descriptor);
}
has(target, prop) {
return Reflect.has(this.getObject(), prop);
}
get(target, prop, receiver) {
if (
this.pending &&
this.stubProperties &&
Object.prototype.hasOwnProperty.call(this.stubProperties, prop)
) {
return this.stubProperties[prop];
}
return Reflect.get(this.getObject(), prop, receiver);
}
set(target, prop, value, receiver) {
return Reflect.set(this.getObject(), prop, value, receiver);
}
deleteProperty(target, prop) {
return Reflect.deleteProperty(this.getObject(), prop);
}
ownKeys(target) {
return Reflect.ownKeys(this.getObject());
}
}
var XPCU_lazyPreferenceObserverQI = ChromeUtils.generateQI([
"nsIObserver",
"nsISupportsWeakReference",
]);