js/xpconnect/loader/XPCOMUtils.jsm
author Michal Novotny <michal.novotny@gmail.com>
Fri, 04 Jan 2013 00:27:04 +0100
changeset 123097 cddc8be15e62676b51f29001b2281779b01255cc
parent 116587 5ce71981e005a52d4cb0b831ad3db9284f2fb356
permissions -rw-r--r--
Bug 725993 - Remove usage of STORE_ON_DISK_AS_FILE flag in media cache, r=roc

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 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
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Utilities for JavaScript components loaded by the JS component
 * loader.
 *
 * Import into a JS component using
 * 'Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");'
 *
 * Exposing a JS 'class' as a component using these utility methods consists
 * of several steps:
 * 0. Import XPCOMUtils, as described above.
 * 1. Declare the 'class' (or multiple classes) implementing the component(s):
 *  function MyComponent() {
 *    // constructor
 *  }
 *  MyComponent.prototype = {
 *    // properties required for XPCOM registration:
 *    classID:          Components.ID("{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}"),
 *
 *    // [optional] custom factory (an object implementing nsIFactory). If not
 *    // provided, the default factory is used, which returns
 *    // |(new MyComponent()).QueryInterface(iid)| in its createInstance().
 *    _xpcom_factory: { ... },
 *
 *    // QueryInterface implementation, e.g. using the generateQI helper
 *    QueryInterface: XPCOMUtils.generateQI(
 *      [Components.interfaces.nsIObserver,
 *       Components.interfaces.nsIMyInterface,
 *       "nsIFoo",
 *       "nsIBar" ]),
 *
 *    // [optional] classInfo implementation, e.g. using the generateCI helper.
 *    // Will be automatically returned from QueryInterface if that was
 *    // generated with the generateQI helper.
 *    classInfo: XPCOMUtils.generateCI(
 *      {classID: Components.ID("{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}"),
 *       contractID: "@example.com/xxx;1",
 *       classDescription: "unique text description",
 *       interfaces: [Components.interfaces.nsIObserver,
 *                    Components.interfaces.nsIMyInterface,
 *                    "nsIFoo",
 *                    "nsIBar"],
 *       flags: Ci.nsIClassInfo.SINGLETON}),
 *
 *    // The following properties were used prior to Mozilla 2, but are no
 *    // longer supported. They may still be included for compatibility with
 *    // prior versions of XPCOMUtils. In Mozilla 2, this information is
 *    // included in the .manifest file which registers this JS component.
 *    classDescription: "unique text description",
 *    contractID:       "@example.com/xxx;1",
 *
 *    // [optional] an array of categories to register this component in.
 *    _xpcom_categories: [{
 *      // Each object in the array specifies the parameters to pass to
 *      // nsICategoryManager.addCategoryEntry(). 'true' is passed for
 *      // both aPersist and aReplace params.
 *      category: "some-category",
 *      // optional, defaults to the object's classDescription
 *      entry: "entry name",
 *      // optional, defaults to the object's contractID (unless
 *      // 'service' is specified)
 *      value: "...",
 *      // optional, defaults to false. When set to true, and only if 'value'
 *      // is not specified, the concatenation of the string "service," and the
 *      // object's contractID is passed as aValue parameter of addCategoryEntry.
 *      service: true,
 *      // optional, it can be an array of applications' IDs in the form:
 *      // [ "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}", ... ]
 *      // If defined the component will be registered in this category only for
 *      // the provided applications.
 *      apps: [...]
 *    }],
 *
 *    // ...component implementation...
 *  };
 *
 * 2. Create an array of component constructors (like the one
 * created in step 1):
 *  var components = [MyComponent];
 *
 * 3. Define the NSGetFactory entry point:
 *  this.NSGetFactory = XPCOMUtils.generateNSGetFactory(components);
 */


this.EXPORTED_SYMBOLS = [ "XPCOMUtils" ];

const Cc = Components.classes;
const Ci = Components.interfaces;
const Cr = Components.results;
const Cu = Components.utils;

this.XPCOMUtils = {
  /**
   * Generate a QueryInterface implementation. The returned function must be
   * assigned to the 'QueryInterface' property of a JS object. When invoked on
   * that object, it checks if the given iid is listed in the |interfaces|
   * param, and if it is, returns |this| (the object it was called on).
   * If the JS object has a classInfo property it'll be returned for the
   * nsIClassInfo IID, generateCI can be used to generate the classInfo
   * property.
   */
  generateQI: function XPCU_generateQI(interfaces) {
    /* Note that Ci[Ci.x] == Ci.x for all x */
    return makeQI([Ci[i].name for each (i in interfaces) if (Ci[i])]);
  },

  /**
   * Generate a ClassInfo implementation for a component. The returned object
   * must be assigned to the 'classInfo' property of a JS object. The first and
   * only argument should be an object that contains a number of optional
   * properties: "interfaces", "contractID", "classDescription", "classID" and
   * "flags". The values of the properties will be returned as the values of the
   * various properties of the nsIClassInfo implementation.
   */
  generateCI: function XPCU_generateCI(classInfo)
  {
    if (QueryInterface in classInfo)
      throw Error("In generateCI, don't use a component for generating classInfo");
    /* Note that Ci[Ci.x] == Ci.x for all x */
    var _interfaces = [Ci[i] for each (i in classInfo.interfaces) if (Ci[i])];
    return {
      getInterfaces: function XPCU_getInterfaces(countRef) {
        countRef.value = _interfaces.length;
        return _interfaces;
      },
      getHelperForLanguage: function XPCU_getHelperForLanguage(language) null,
      contractID: classInfo.contractID,
      classDescription: classInfo.classDescription,
      classID: classInfo.classID,
      implementationLanguage: Ci.nsIProgrammingLanguage.JAVASCRIPT,
      flags: classInfo.flags,
      QueryInterface: this.generateQI([Ci.nsIClassInfo])
    };
  },

  /**
   * Generate a NSGetFactory function given an array of components.
   */
  generateNSGetFactory: function XPCU_generateNSGetFactory(componentsArray) {
    let classes = {};
    for each (let component in componentsArray) {
        if (!(component.prototype.classID instanceof Components.ID))
          throw Error("In generateNSGetFactory, classID missing or incorrect for component " + component);

        classes[component.prototype.classID] = this._getFactory(component);
    }
    return function NSGetFactory(cid) {
      let cidstring = cid.toString();
      if (cidstring in classes)
        return classes[cidstring];
      throw Cr.NS_ERROR_FACTORY_NOT_REGISTERED;
    }
  },

  /**
   * 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: function XPCU_defineLazyGetter(aObject, aName, aLambda)
  {
    Object.defineProperty(aObject, aName, {
      get: function () {
        delete aObject[aName];
        return aObject[aName] = aLambda.apply(aObject);
      },
      configurable: true,
      enumerable: true
    });
  },

  /**
   * 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: function XPCU_defineLazyServiceGetter(aObject, aName,
                                                                 aContract,
                                                                 aInterfaceName)
  {
    this.defineLazyGetter(aObject, aName, function XPCU_serviceLambda() {
      return Cc[aContract].getService(Ci[aInterfaceName]);
    });
  },

  /**
   * Defines a getter on a specified object for a module.  The module will not
   * be imported 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 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.
   */
  defineLazyModuleGetter: function XPCU_defineLazyModuleGetter(aObject, aName,
                                                               aResource,
                                                               aSymbol)
  {
    this.defineLazyGetter(aObject, aName, function XPCU_moduleLambda() {
      var temp = {};
      Cu.import(aResource, temp);
      return temp[aSymbol || aName];
    });
  },

  /**
   * Convenience access to category manager
   */
  get categoryManager() {
    return Components.classes["@mozilla.org/categorymanager;1"]
           .getService(Ci.nsICategoryManager);
  },

  /**
   * Helper which iterates over a nsISimpleEnumerator.
   * @param e The nsISimpleEnumerator to iterate over.
   * @param i The expected interface for each element.
   */
  IterSimpleEnumerator: function XPCU_IterSimpleEnumerator(e, i)
  {
    while (e.hasMoreElements())
      yield e.getNext().QueryInterface(i);
  },

  /**
   * Helper which iterates over a string enumerator.
   * @param e The string enumerator (nsIUTF8StringEnumerator or
   *          nsIStringEnumerator) over which to iterate.
   */
  IterStringEnumerator: function XPCU_IterStringEnumerator(e)
  {
    while (e.hasMore())
      yield e.getNext();
  },

  /**
   * Returns an nsIFactory for |component|.
   */
  _getFactory: function XPCOMUtils__getFactory(component) {
    var factory = component.prototype._xpcom_factory;
    if (!factory) {
      factory = {
        createInstance: function(outer, iid) {
          if (outer)
            throw Cr.NS_ERROR_NO_AGGREGATION;
          return (new component()).QueryInterface(iid);
        }
      }
    }
    return factory;
  },

  /**
   * Allows you to fake a relative import. Expects the global object from the
   * module that's calling us, and the relative filename that we wish to import.
   */
  importRelative: function XPCOMUtils__importRelative(that, path) {
    if (!("__URI__" in that))
      throw Error("importRelative may only be used from a JSM, and its first argument "+
                  "must be that JSM's global object (hint: use this)");
    let uri = that.__URI__;
    let i = uri.lastIndexOf("/");
    Components.utils.import(uri.substring(0, i+1) + path, that);
  },

  /**
   * generates a singleton nsIFactory implementation that can be used as
   * the _xpcom_factory of the component.
   * @param aServiceConstructor
   *        Constructor function of the component.
   */
  generateSingletonFactory:
  function XPCOMUtils_generateSingletonFactory(aServiceConstructor) {
    return {
      _instance: null,
      createInstance: function XPCU_SF_createInstance(aOuter, aIID) {
        if (aOuter !== null) {
          throw Cr.NS_ERROR_NO_AGGREGATION;
        }
        if (this._instance === null) {
          this._instance = new aServiceConstructor();
        }
        return this._instance.QueryInterface(aIID);
      },
      lockFactory: function XPCU_SF_lockFactory(aDoLock) {
        throw Cr.NS_ERROR_NOT_IMPLEMENTED;
      },
      QueryInterface: XPCOMUtils.generateQI([Ci.nsIFactory])
    };
  },
};

/**
 * Helper for XPCOMUtils.generateQI to avoid leaks - see bug 381651#c1
 */
function makeQI(interfaceNames) {
  return function XPCOMUtils_QueryInterface(iid) {
    if (iid.equals(Ci.nsISupports))
      return this;
    if (iid.equals(Ci.nsIClassInfo) && "classInfo" in this)
      return this.classInfo;
    for each(let interfaceName in interfaceNames) {
      if (Ci[interfaceName].equals(iid))
        return this;
    }

    throw Cr.NS_ERROR_NO_INTERFACE;
  };
}