DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659
/* -*- 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
 * 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: ChromeUtils.generateQI(
 *      [Components.interfaces.nsIObserver,
 *       Components.interfaces.nsIMyInterface,
 *       "nsIFoo",
 *       "nsIBar" ]),
 *
 *    // 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",
 *
 *    // ...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);
 */


var EXPORTED_SYMBOLS = [ "XPCOMUtils" ];

let global = Cu.getGlobalForObject({});

const nsIFactoryQI = ChromeUtils.generateQI([Ci.nsIFactory]);

// 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 = {
  Headers: "fetch",
  MessagePort: "MessageChannel",
  Request: "fetch",
  Response: "fetch",
};

/**
 * 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;
}

var XPCOMUtils = {
  /**
   * Generate a NSGetFactory function given an array of components.
   */
  generateNSGetFactory: function XPCU_generateNSGetFactory(componentsArray) {
    let classes = {};
    for (let i = 0; i < componentsArray.length; i++) {
        let component = componentsArray[i];
        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)
  {
    let redefining = false;
    Object.defineProperty(aObject, aName, {
      get: function () {
        if (!redefining) {
          // Make sure we don't get into an infinite recursion loop if
          // the getter lambda does something shady.
          redefining = true;
          return redefine(aObject, aName, aLambda.apply(aObject));
        }
      },
      configurable: true,
      enumerable: true
    });
  },

  /**
   * 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: function XPCU_defineLazyScriptGetter(aObject, aNames,
                                                               aResource)
  {
    if (!Array.isArray(aNames)) {
      aNames = [aNames];
    }
    for (let name of aNames) {
      Object.defineProperty(aObject, name, {
        get: function() {
          Services.scriptloader.loadSubScript(aResource, aObject);
          return aObject[name];
        },
        set(value) {
          redefine(aObject, name, value);
        },
        configurable: true,
        enumerable: true
      });
    }
  },

  /**
   * 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;
          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: function XPCU_defineLazyServiceGetter(aObject, aName,
                                                                 aContract,
                                                                 aInterfaceName)
  {
    this.defineLazyGetter(aObject, aName, function XPCU_serviceLambda() {
      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: function XPCU_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: function XPCU_defineLazyModuleGetter(
                                   aObject, aName, aResource, aSymbol,
                                   aPreLambda, aPostLambda, aProxy)
  {
    if (arguments.length == 3) {
      return ChromeUtils.defineModuleGetter(aObject, aName, aResource);
    }

    let proxy = aProxy || {};

    if (typeof(aPreLambda) === "function") {
      aPreLambda.apply(proxy);
    }

    this.defineLazyGetter(aObject, aName, function XPCU_moduleLambda() {
      var temp = {};
      try {
        ChromeUtils.import(aResource, temp);

        if (typeof(aPostLambda) === "function") {
          aPostLambda.apply(proxy);
        }
      } catch (ex) {
        Cu.reportError("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: function XPCU_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 aDefaultValue
   *        The default value to use, if the preference is not defined.
   * @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: function XPCU_defineLazyPreferenceGetter(
                                   aObject, aName, aPreference,
                                   aDefaultValue = null,
                                   aOnUpdate = null,
                                   aTransform = val => val)
  {
    // 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 = aDefaultValue;
            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();
    });
  },

  /**
   * 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);
        },
        QueryInterface: nsIFactoryQI
      }
    }
    return factory;
  },

  /**
   * 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);
      },
      QueryInterface: nsIFactoryQI
    };
  },

  /**
   * Defines a non-writable property on an object.
   */
  defineConstant: function XPCOMUtils__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: function XPCOMUtils__defineLazyProxy(aObject, aName, aInitFuncOrResource,
                                                        aStubProperties, aUntrapCallback) {
    let initFunc = aInitFuncOrResource;

    if (typeof(aInitFuncOrResource) == "string") {
      initFunc = function () {
        let tmp = {};
        ChromeUtils.import(aInitFuncOrResource, tmp);
        return tmp[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;
  },
};

/**
 * 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([Ci.nsIObserver, Ci.nsISupportsWeakReference]);

ChromeUtils.defineModuleGetter(this, "Services",
                               "resource://gre/modules/Services.jsm");