339 lines
12 KiB
JavaScript
339 lines
12 KiB
JavaScript
/* @@package_name - v@@version - @@timestamp */
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/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
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/* vim: set sts=2 sw=2 et tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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"use strict";
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if (typeof browser === "undefined") {
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// Wrapping the bulk of this polyfill in a one-time-use function is a minor
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// optimization for Firefox. Since Spidermonkey does not fully parse the
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// contents of a function until the first time it's called, and since it will
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// never actually need to be called, this allows the polyfill to be included
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// in Firefox nearly for free.
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const wrapAPIs = () => {
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const apiMetadata = {/* include("api-metadata.json") */};
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/**
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* A WeakMap subclass which creates and stores a value for any key which does
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* not exist when accessed, but behaves exactly as an ordinary WeakMap
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* otherwise.
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*
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* @param {function} createItem
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* A function which will be called in order to create the value for any
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* key which does not exist, the first time it is accessed. The
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* function receives, as its only argument, the key being created.
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*/
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class DefaultWeakMap extends WeakMap {
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constructor(createItem, items = undefined) {
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super(items);
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this.createItem = createItem;
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}
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get(key) {
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if (!this.has(key)) {
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this.set(key, this.createItem(key));
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}
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return super.get(key);
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}
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}
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/**
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* Returns true if the given object is an object with a `then` method, and can
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* therefore be assumed to behave as a Promise.
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*
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* @param {*} value The value to test.
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* @returns {boolean} True if the value is thenable.
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*/
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const isThenable = value => {
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return value && typeof value === "object" && typeof value.then === "function";
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};
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/**
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* Creates and returns a function which, when called, will resolve or reject
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* the given promise based on how it is called:
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*
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* - If, when called, `chrome.runtime.lastError` contains a non-null object,
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* the promise is rejected with that value.
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* - If the function is called with exactly one argument, the promise is
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* resolved to that value.
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* - Otherwise, the promise is resolved to an array containing all of the
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* function's arguments.
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*
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* @param {object} promise
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* An object containing the resolution and rejection functions of a
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* promise.
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* @param {function} promise.resolve
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* The promise's resolution function.
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* @param {function} promise.rejection
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* The promise's rejection function.
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*
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* @returns {function}
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* The generated callback function.
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*/
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const makeCallback = promise => {
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return (...callbackArgs) => {
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if (chrome.runtime.lastError) {
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promise.reject(chrome.runtime.lastError);
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} else if (callbackArgs.length === 1) {
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promise.resolve(callbackArgs[0]);
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} else {
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promise.resolve(callbackArgs);
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}
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};
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};
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/**
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* Creates a wrapper function for a method with the given name and metadata.
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*
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* @param {string} name
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* The name of the method which is being wrapped.
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* @param {object} metadata
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* Metadata about the method being wrapped.
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* @param {integer} metadata.minArgs
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* The minimum number of arguments which must be passed to the
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* function. If called with fewer than this number of arguments, the
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* wrapper will raise an exception.
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* @param {integer} metadata.maxArgs
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* The maximum number of arguments which may be passed to the
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* function. If called with more than this number of arguments, the
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* wrapper will raise an exception.
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*
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* @returns {function(object, ...*)}
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* The generated wrapper function.
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*/
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const wrapAsyncFunction = (name, metadata) => {
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return function asyncFunctionWrapper(target, ...args) {
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if (args.length < metadata.minArgs) {
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throw new Error(`Expected at least ${metadata.minArgs} arguments for ${name}(), got ${args.length}`);
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}
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if (args.length > metadata.maxArgs) {
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throw new Error(`Expected at most ${metadata.maxArgs} arguments for ${name}(), got ${args.length}`);
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}
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return new Promise((resolve, reject) => {
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target[name](...args, makeCallback({resolve, reject}));
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});
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};
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};
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/**
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* Wraps an existing method of the target object, so that calls to it are
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* intercepted by the given wrapper function. The wrapper function receives,
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* as its first argument, the original `target` object, followed by each of
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* the arguments passed to the orginal method.
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*
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* @param {object} target
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* The original target object that the wrapped method belongs to.
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* @param {function} method
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* The method being wrapped. This is used as the target of the Proxy
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* object which is created to wrap the method.
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* @param {function} wrapper
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* The wrapper function which is called in place of a direct invocation
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* of the wrapped method.
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*
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* @returns {Proxy<function>}
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* A Proxy object for the given method, which invokes the given wrapper
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* method in its place.
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*/
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const wrapMethod = (target, method, wrapper) => {
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return new Proxy(method, {
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apply(targetMethod, thisObj, args) {
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return wrapper.call(thisObj, target, ...args);
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},
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});
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};
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let hasOwnProperty = Function.call.bind(Object.prototype.hasOwnProperty);
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/**
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* Wraps an object in a Proxy which intercepts and wraps certain methods
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* based on the given `wrappers` and `metadata` objects.
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*
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* @param {object} target
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* The target object to wrap.
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*
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* @param {object} [wrappers = {}]
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* An object tree containing wrapper functions for special cases. Any
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* function present in this object tree is called in place of the
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* method in the same location in the `target` object tree. These
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* wrapper methods are invoked as described in {@see wrapMethod}.
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*
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* @param {object} [metadata = {}]
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* An object tree containing metadata used to automatically generate
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* Promise-based wrapper functions for asynchronous. Any function in
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* the `target` object tree which has a corresponding metadata object
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* in the same location in the `metadata` tree is replaced with an
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* automatically-generated wrapper function, as described in
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* {@see wrapAsyncFunction}
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*
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* @returns {Proxy<object>}
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*/
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const wrapObject = (target, wrappers = {}, metadata = {}) => {
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let cache = Object.create(null);
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let handlers = {
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has(target, prop) {
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return prop in target || prop in cache;
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},
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get(target, prop, receiver) {
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if (prop in cache) {
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return cache[prop];
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}
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if (!(prop in target)) {
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return undefined;
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}
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let value = target[prop];
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if (typeof value === "function") {
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// This is a method on the underlying object. Check if we need to do
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// any wrapping.
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if (typeof wrappers[prop] === "function") {
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// We have a special-case wrapper for this method.
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value = wrapMethod(target, target[prop], wrappers[prop]);
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} else if (hasOwnProperty(metadata, prop)) {
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// This is an async method that we have metadata for. Create a
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// Promise wrapper for it.
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let wrapper = wrapAsyncFunction(prop, metadata[prop]);
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value = wrapMethod(target, target[prop], wrapper);
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} else {
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// This is a method that we don't know or care about. Return the
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// original method, bound to the underlying object.
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value = value.bind(target);
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}
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} else if (typeof value === "object" && value !== null &&
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(hasOwnProperty(wrappers, prop) ||
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hasOwnProperty(metadata, prop))) {
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// This is an object that we need to do some wrapping for the children
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// of. Create a sub-object wrapper for it with the appropriate child
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// metadata.
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value = wrapObject(value, wrappers[prop], metadata[prop]);
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} else {
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// We don't need to do any wrapping for this property,
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// so just forward all access to the underlying object.
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Object.defineProperty(cache, prop, {
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configurable: true,
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enumerable: true,
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get() {
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return target[prop];
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},
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set(value) {
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target[prop] = value;
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},
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});
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return value;
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}
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cache[prop] = value;
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return value;
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},
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set(target, prop, value, receiver) {
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if (prop in cache) {
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cache[prop] = value;
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} else {
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target[prop] = value;
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}
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return true;
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},
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defineProperty(target, prop, desc) {
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return Reflect.defineProperty(cache, prop, desc);
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},
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deleteProperty(target, prop) {
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return Reflect.deleteProperty(cache, prop);
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},
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};
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return new Proxy(target, handlers);
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};
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/**
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* Creates a set of wrapper functions for an event object, which handles
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* wrapping of listener functions that those messages are passed.
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*
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* A single wrapper is created for each listener function, and stored in a
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* map. Subsequent calls to `addListener`, `hasListener`, or `removeListener`
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* retrieve the original wrapper, so that attempts to remove a
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* previously-added listener work as expected.
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*
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* @param {DefaultWeakMap<function, function>} wrapperMap
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* A DefaultWeakMap object which will create the appropriate wrapper
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* for a given listener function when one does not exist, and retrieve
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* an existing one when it does.
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*
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* @returns {object}
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*/
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const wrapEvent = wrapperMap => ({
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addListener(target, listener, ...args) {
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target.addListener(wrapperMap.get(listener), ...args);
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},
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hasListener(target, listener) {
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return target.hasListener(wrapperMap.get(listener));
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},
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removeListener(target, listener) {
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target.removeListener(wrapperMap.get(listener));
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},
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});
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const onMessageWrappers = new DefaultWeakMap(listener => {
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if (typeof listener !== "function") {
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return listener;
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}
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/**
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* Wraps a message listener function so that it may send responses based on
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* its return value, rather than by returning a sentinel value and calling a
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* callback. If the listener function returns a Promise, the response is
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* sent when the promise either resolves or rejects.
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*
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* @param {*} message
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* The message sent by the other end of the channel.
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* @param {object} sender
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* Details about the sender of the message.
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* @param {function(*)} sendResponse
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* A callback which, when called with an arbitrary argument, sends
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* that value as a response.
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* @returns {boolean}
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* True if the wrapped listener returned a Promise, which will later
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* yield a response. False otherwise.
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*/
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return function onMessage(message, sender, sendResponse) {
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let result = listener(message, sender);
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if (isThenable(result)) {
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result.then(sendResponse, error => {
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console.error(error);
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sendResponse(error);
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});
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return true;
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} else if (result !== undefined) {
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sendResponse(result);
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}
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};
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});
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const staticWrappers = {
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runtime: {
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onMessage: wrapEvent(onMessageWrappers),
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},
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};
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return wrapObject(chrome, staticWrappers, apiMetadata);
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};
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this.browser = wrapAPIs();
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}
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