gecko-dev/toolkit/components/extensions/ExtensionChild.jsm

/* 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/. */

"use strict";

/* exported ExtensionChild */

this.EXPORTED_SYMBOLS = ["ExtensionChild"];

/*
 * This file handles addon logic that is independent of the chrome process.
 * When addons run out-of-process, this is the main entry point.
 * Its primary function is managing addon globals.
 *
 * Don't put contentscript logic here, use ExtensionContent.jsm instead.
 */

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

Cu.import("resource://gre/modules/Services.jsm");
Cu.import("resource://gre/modules/XPCOMUtils.jsm");

XPCOMUtils.defineLazyModuleGetters(this, {
  ExtensionContent: "resource://gre/modules/ExtensionContent.jsm",
  MessageChannel: "resource://gre/modules/MessageChannel.jsm",
  NativeApp: "resource://gre/modules/NativeMessaging.jsm",
  PromiseUtils: "resource://gre/modules/PromiseUtils.jsm",
});

Cu.import("resource://gre/modules/ExtensionCommon.jsm");
Cu.import("resource://gre/modules/ExtensionUtils.jsm");

const {
  DefaultMap,
  EventEmitter,
  LimitedSet,
  defineLazyGetter,
  getMessageManager,
  getUniqueId,
  withHandlingUserInput,
} = ExtensionUtils;

const {
  EventManager,
  LocalAPIImplementation,
  LocaleData,
  NoCloneSpreadArgs,
  SchemaAPIInterface,
} = ExtensionCommon;

const isContentProcess = Services.appinfo.processType == Services.appinfo.PROCESS_TYPE_CONTENT;

// Copy an API object from |source| into the scope |dest|.
function injectAPI(source, dest) {
  for (let prop in source) {
    // Skip names prefixed with '_'.
    if (prop[0] == "_") {
      continue;
    }

    let desc = Object.getOwnPropertyDescriptor(source, prop);
    if (typeof(desc.value) == "function") {
      Cu.exportFunction(desc.value, dest, {defineAs: prop});
    } else if (typeof(desc.value) == "object") {
      let obj = Cu.createObjectIn(dest, {defineAs: prop});
      injectAPI(desc.value, obj);
    } else {
      Object.defineProperty(dest, prop, desc);
    }
  }
}

/**
 * Abstraction for a Port object in the extension API.
 *
 * @param {BaseContext} context The context that owns this port.
 * @param {nsIMessageSender} senderMM The message manager to send messages to.
 * @param {Array<nsIMessageListenerManager>} receiverMMs Message managers to
 *     listen on.
 * @param {string} name Arbitrary port name as defined by the addon.
 * @param {string} id An ID that uniquely identifies this port's channel.
 * @param {object} sender The `port.sender` property.
 * @param {object} recipient The recipient of messages sent from this port.
 */
class Port {
  constructor(context, senderMM, receiverMMs, name, id, sender, recipient) {
    this.context = context;
    this.senderMM = senderMM;
    this.receiverMMs = receiverMMs;
    this.name = name;
    this.id = id;
    this.sender = sender;
    this.recipient = recipient;
    this.disconnected = false;
    this.disconnectListeners = new Set();
    this.unregisterMessageFuncs = new Set();

    // Common options for onMessage and onDisconnect.
    this.handlerBase = {
      messageFilterStrict: {portId: id},

      filterMessage: (sender, recipient) => {
        return sender.contextId !== this.context.contextId;
      },
    };

    this.disconnectHandler = Object.assign({
      receiveMessage: ({data}) => this.disconnectByOtherEnd(data),
    }, this.handlerBase);

    MessageChannel.addListener(this.receiverMMs, "Extension:Port:Disconnect", this.disconnectHandler);

    this.context.callOnClose(this);
  }

  api() {
    let portObj = Cu.createObjectIn(this.context.cloneScope);

    let portError = null;
    let publicAPI = {
      name: this.name,

      disconnect: () => {
        this.disconnect();
      },

      postMessage: json => {
        this.postMessage(json);
      },

      onDisconnect: new EventManager(this.context, "Port.onDisconnect", fire => {
        return this.registerOnDisconnect(holder => {
          let error = holder.deserialize(this.context.cloneScope);
          portError = error && this.context.normalizeError(error);
          fire.asyncWithoutClone(portObj);
        });
      }).api(),

      onMessage: new EventManager(this.context, "Port.onMessage", fire => {
        return this.registerOnMessage(holder => {
          let msg = holder.deserialize(this.context.cloneScope);
          fire.asyncWithoutClone(msg, portObj);
        });
      }).api(),

      get error() {
        return portError;
      },
    };

    if (this.sender) {
      publicAPI.sender = this.sender;
    }

    injectAPI(publicAPI, portObj);
    return portObj;
  }

  postMessage(json) {
    if (this.disconnected) {
      throw new this.context.cloneScope.Error("Attempt to postMessage on disconnected port");
    }

    this._sendMessage("Extension:Port:PostMessage", json);
  }

  /**
   * Register a callback that is called when the port is disconnected by the
   * *other* end. The callback is automatically unregistered when the port or
   * context is closed.
   *
   * @param {function} callback Called when the other end disconnects the port.
   *     If the disconnect is caused by an error, the first parameter is an
   *     object with a "message" string property that describes the cause.
   * @returns {function} Function to unregister the listener.
   */
  registerOnDisconnect(callback) {
    let listener = error => {
      if (this.context.active && !this.disconnected) {
        callback(error);
      }
    };
    this.disconnectListeners.add(listener);
    return () => {
      this.disconnectListeners.delete(listener);
    };
  }

  /**
   * Register a callback that is called when a message is received. The callback
   * is automatically unregistered when the port or context is closed.
   *
   * @param {function} callback Called when a message is received.
   * @returns {function} Function to unregister the listener.
   */
  registerOnMessage(callback) {
    let handler = Object.assign({
      receiveMessage: ({data}) => {
        if (this.context.active && !this.disconnected) {
          callback(data);
        }
      },
    }, this.handlerBase);

    let unregister = () => {
      this.unregisterMessageFuncs.delete(unregister);
      MessageChannel.removeListener(this.receiverMMs, "Extension:Port:PostMessage", handler);
    };
    MessageChannel.addListener(this.receiverMMs, "Extension:Port:PostMessage", handler);
    this.unregisterMessageFuncs.add(unregister);
    return unregister;
  }

  _sendMessage(message, data) {
    let options = {
      recipient: Object.assign({}, this.recipient, {portId: this.id}),
      responseType: MessageChannel.RESPONSE_NONE,
    };

    let holder = new StructuredCloneHolder(data);

    return this.context.sendMessage(this.senderMM, message, holder, options);
  }

  handleDisconnection() {
    MessageChannel.removeListener(this.receiverMMs, "Extension:Port:Disconnect", this.disconnectHandler);
    for (let unregister of this.unregisterMessageFuncs) {
      unregister();
    }
    this.context.forgetOnClose(this);
    this.disconnected = true;
  }

  /**
   * Disconnect the port from the other end (which may not even exist).
   *
   * @param {Error|{message: string}} [error] The reason for disconnecting,
   *     if it is an abnormal disconnect.
   */
  disconnectByOtherEnd(error = null) {
    if (this.disconnected) {
      return;
    }

    for (let listener of this.disconnectListeners) {
      listener(error);
    }

    this.handleDisconnection();
  }

  /**
   * Disconnect the port from this end.
   *
   * @param {Error|{message: string}} [error] The reason for disconnecting,
   *     if it is an abnormal disconnect.
   */
  disconnect(error = null) {
    if (this.disconnected) {
      // disconnect() may be called without side effects even after the port is
      // closed - https://developer.chrome.com/extensions/runtime#type-Port
      return;
    }
    this.handleDisconnection();
    if (error) {
      error = {message: this.context.normalizeError(error).message};
    }
    this._sendMessage("Extension:Port:Disconnect", error);
  }

  close() {
    this.disconnect();
  }
}

class NativePort extends Port {
  postMessage(data) {
    data = NativeApp.encodeMessage(this.context, data);

    return super.postMessage(data);
  }
}

/**
 * Each extension context gets its own Messenger object. It handles the
 * basics of sendMessage, onMessage, connect and onConnect.
 *
 * @param {BaseContext} context The context to which this Messenger is tied.
 * @param {Array<nsIMessageListenerManager>} messageManagers
 *     The message managers used to receive messages (e.g. onMessage/onConnect
 *     requests).
 * @param {object} sender Describes this sender to the recipient. This object
 *     is extended further by BaseContext's sendMessage method and appears as
 *     the `sender` object to `onConnect` and `onMessage`.
 *     Do not set the `extensionId`, `contextId` or `tab` properties. The former
 *     two are added by BaseContext's sendMessage, while `sender.tab` is set by
 *     the ProxyMessenger in the main process.
 * @param {object} filter A recipient filter to apply to incoming messages from
 *     the broker. Messages are only handled by this Messenger if all key-value
 *     pairs match the `recipient` as specified by the sender of the message.
 *     In other words, this filter defines the required fields of `recipient`.
 * @param {object} [optionalFilter] An additional filter to apply to incoming
 *     messages. Unlike `filter`, the keys from `optionalFilter` are allowed to
 *     be omitted from `recipient`. Only keys that are present in both
 *     `optionalFilter` and `recipient` are applied to filter incoming messages.
 */
class Messenger {
  constructor(context, messageManagers, sender, filter, optionalFilter) {
    this.context = context;
    this.messageManagers = messageManagers;
    this.sender = sender;
    this.filter = filter;
    this.optionalFilter = optionalFilter;
  }

  _sendMessage(messageManager, message, data, recipient) {
    let options = {
      recipient,
      sender: this.sender,
      responseType: MessageChannel.RESPONSE_FIRST,
    };

    return this.context.sendMessage(messageManager, message, data, options);
  }

  sendMessage(messageManager, msg, recipient, responseCallback) {
    let holder = new StructuredCloneHolder(msg);

    let promise = this._sendMessage(messageManager, "Extension:Message", holder, recipient)
      .catch(error => {
        if (error.result == MessageChannel.RESULT_NO_HANDLER) {
          return Promise.reject({message: "Could not establish connection. Receiving end does not exist."});
        } else if (error.result != MessageChannel.RESULT_NO_RESPONSE) {
          return Promise.reject({message: error.message});
        }
      });

    return this.context.wrapPromise(promise, responseCallback);
  }

  sendNativeMessage(messageManager, msg, recipient, responseCallback) {
    msg = NativeApp.encodeMessage(this.context, msg);
    return this.sendMessage(messageManager, msg, recipient, responseCallback);
  }

  _onMessage(name, filter) {
    return new EventManager(this.context, name, fire => {
      let listener = {
        messageFilterPermissive: this.optionalFilter,
        messageFilterStrict: this.filter,

        filterMessage: (sender, recipient) => {
          // Ignore the message if it was sent by this Messenger.
          return (sender.contextId !== this.context.contextId &&
                  filter(sender, recipient));
        },

        receiveMessage: ({target, data: holder, sender, recipient}) => {
          if (!this.context.active) {
            return;
          }

          let sendResponse;
          let response = undefined;
          let promise = new Promise(resolve => {
            sendResponse = value => {
              resolve(value);
              response = promise;
            };
          });

          let message = holder.deserialize(this.context.cloneScope);
          sender = Cu.cloneInto(sender, this.context.cloneScope);
          sendResponse = Cu.exportFunction(sendResponse, this.context.cloneScope);

          // Note: We intentionally do not use runSafe here so that any
          // errors are propagated to the message sender.
          let result = fire.raw(message, sender, sendResponse);
          if (result instanceof this.context.cloneScope.Promise) {
            return result;
          } else if (result === true) {
            return promise;
          }
          return response;
        },
      };

      MessageChannel.addListener(this.messageManagers, "Extension:Message", listener);
      return () => {
        MessageChannel.removeListener(this.messageManagers, "Extension:Message", listener);
      };
    }).api();
  }

  onMessage(name) {
    return this._onMessage(name, sender => sender.id === this.sender.id);
  }

  onMessageExternal(name) {
    return this._onMessage(name, sender => sender.id !== this.sender.id);
  }

  _connect(messageManager, port, recipient) {
    let msg = {
      name: port.name,
      portId: port.id,
    };

    this._sendMessage(messageManager, "Extension:Connect", msg, recipient).catch(error => {
      if (error.result === MessageChannel.RESULT_NO_HANDLER) {
        error = {message: "Could not establish connection. Receiving end does not exist."};
      } else if (error.result === MessageChannel.RESULT_DISCONNECTED) {
        error = null;
      }
      port.disconnectByOtherEnd(new StructuredCloneHolder(error));
    });

    return port.api();
  }

  connect(messageManager, name, recipient) {
    let portId = getUniqueId();

    let port = new Port(this.context, messageManager, this.messageManagers, name, portId, null, recipient);

    return this._connect(messageManager, port, recipient);
  }

  connectNative(messageManager, name, recipient) {
    let portId = getUniqueId();

    let port = new NativePort(this.context, messageManager, this.messageManagers, name, portId, null, recipient);

    return this._connect(messageManager, port, recipient);
  }

  _onConnect(name, filter) {
    return new EventManager(this.context, name, fire => {
      let listener = {
        messageFilterPermissive: this.optionalFilter,
        messageFilterStrict: this.filter,

        filterMessage: (sender, recipient) => {
          // Ignore the port if it was created by this Messenger.
          return (sender.contextId !== this.context.contextId &&
                  filter(sender, recipient));
        },

        receiveMessage: ({target, data: message, sender}) => {
          let {name, portId} = message;
          let mm = getMessageManager(target);
          let recipient = Object.assign({}, sender);
          if (recipient.tab) {
            recipient.tabId = recipient.tab.id;
            delete recipient.tab;
          }
          let port = new Port(this.context, mm, this.messageManagers, name, portId, sender, recipient);
          fire.asyncWithoutClone(port.api());
          return true;
        },
      };

      MessageChannel.addListener(this.messageManagers, "Extension:Connect", listener);
      return () => {
        MessageChannel.removeListener(this.messageManagers, "Extension:Connect", listener);
      };
    }).api();
  }

  onConnect(name) {
    return this._onConnect(name, sender => sender.id === this.sender.id);
  }

  onConnectExternal(name) {
    return this._onConnect(name, sender => sender.id !== this.sender.id);
  }
}

// For test use only.
var ExtensionManager = {
  extensions: new Map(),
};

// Represents a browser extension in the content process.
class BrowserExtensionContent extends EventEmitter {
  constructor(data) {
    super();

    this.data = data;
    this.id = data.id;
    this.uuid = data.uuid;
    this.instanceId = data.instanceId;

    this.MESSAGE_EMIT_EVENT = `Extension:EmitEvent:${this.instanceId}`;
    Services.cpmm.addMessageListener(this.MESSAGE_EMIT_EVENT, this);

    defineLazyGetter(this, "scripts", () => {
      return data.contentScripts.map(scriptData => new ExtensionContent.Script(this, scriptData));
    });

    this.webAccessibleResources = data.webAccessibleResources.map(res => new MatchGlob(res));
    this.whiteListedHosts = new MatchPatternSet(data.whiteListedHosts, {ignorePath: true});
    this.permissions = data.permissions;
    this.optionalPermissions = data.optionalPermissions;
    this.principal = data.principal;

    this.localeData = new LocaleData(data.localeData);

    this.manifest = data.manifest;
    this.baseURI = Services.io.newURI(data.baseURL);

    // Only used in addon processes.
    this.views = new Set();

    // Only used for devtools views.
    this.devtoolsViews = new Set();

    /* eslint-disable mozilla/balanced-listeners */
    this.on("add-permissions", (ignoreEvent, permissions) => {
      if (permissions.permissions.length > 0) {
        for (let perm of permissions.permissions) {
          this.permissions.add(perm);
        }
      }

      if (permissions.origins.length > 0) {
        let patterns = this.whiteListedHosts.patterns.map(host => host.pattern);

        this.whiteListedHosts = new MatchPatternSet([...patterns, ...permissions.origins],
                                                    {ignorePath: true});
      }

      if (this.policy) {
        this.policy.permissions = Array.from(this.permissions);
        this.policy.allowedOrigins = this.whiteListedHosts;
      }
    });

    this.on("remove-permissions", (ignoreEvent, permissions) => {
      if (permissions.permissions.length > 0) {
        for (let perm of permissions.permissions) {
          this.permissions.delete(perm);
        }
      }

      if (permissions.origins.length > 0) {
        let origins = permissions.origins.map(
          origin => new MatchPattern(origin, {ignorePath: true}).pattern);

        this.whiteListedHosts = new MatchPatternSet(
          this.whiteListedHosts.patterns
              .filter(host => !origins.includes(host.pattern)));
      }

      if (this.policy) {
        this.policy.permissions = Array.from(this.permissions);
        this.policy.allowedOrigins = this.whiteListedHosts;
      }
    });
    /* eslint-enable mozilla/balanced-listeners */

    ExtensionManager.extensions.set(this.id, this);
  }

  shutdown() {
    ExtensionManager.extensions.delete(this.id);
    ExtensionContent.shutdownExtension(this);
    Services.cpmm.removeMessageListener(this.MESSAGE_EMIT_EVENT, this);
    if (isContentProcess) {
      MessageChannel.abortResponses({extensionId: this.id});
    }
  }

  getContext(window) {
    return ExtensionContent.getContext(this, window);
  }

  emit(event, ...args) {
    Services.cpmm.sendAsyncMessage(this.MESSAGE_EMIT_EVENT, {event, args});

    super.emit(event, ...args);
  }

  receiveMessage({name, data}) {
    if (name === this.MESSAGE_EMIT_EVENT) {
      super.emit(data.event, ...data.args);
    }
  }

  localizeMessage(...args) {
    return this.localeData.localizeMessage(...args);
  }

  localize(...args) {
    return this.localeData.localize(...args);
  }

  hasPermission(perm) {
    let match = /^manifest:(.*)/.exec(perm);
    if (match) {
      return this.manifest[match[1]] != null;
    }
    return this.permissions.has(perm);
  }
}

/**
 * An object that runs an remote implementation of an API.
 */
class ProxyAPIImplementation extends SchemaAPIInterface {
  /**
   * @param {string} namespace The full path to the namespace that contains the
   *     `name` member. This may contain dots, e.g. "storage.local".
   * @param {string} name The name of the method or property.
   * @param {ChildAPIManager} childApiManager The owner of this implementation.
   */
  constructor(namespace, name, childApiManager) {
    super();
    this.path = `${namespace}.${name}`;
    this.childApiManager = childApiManager;
  }

  revoke() {
    let map = this.childApiManager.listeners.get(this.path);
    for (let listener of map.keys()) {
      this.removeListener(listener);
    }

    this.path = null;
    this.childApiManager = null;
  }

  callFunctionNoReturn(args) {
    this.childApiManager.callParentFunctionNoReturn(this.path, args);
  }

  callAsyncFunction(args, callback, requireUserInput) {
    if (requireUserInput) {
      let context = this.childApiManager.context;
      let winUtils = context.contentWindow.getInterface(Ci.nsIDOMWindowUtils);
      if (!winUtils.isHandlingUserInput) {
        let err = new context.cloneScope.Error(`${this.path} may only be called from a user input handler`);
        return context.wrapPromise(Promise.reject(err), callback);
      }
    }
    return this.childApiManager.callParentAsyncFunction(this.path, args, callback);
  }

  addListener(listener, args) {
    let map = this.childApiManager.listeners.get(this.path);

    if (map.listeners.has(listener)) {
      // TODO: Called with different args?
      return;
    }

    let id = getUniqueId();

    map.ids.set(id, listener);
    map.listeners.set(listener, id);

    this.childApiManager.messageManager.sendAsyncMessage("API:AddListener", {
      childId: this.childApiManager.id,
      listenerId: id,
      path: this.path,
      args,
    });
  }

  removeListener(listener) {
    let map = this.childApiManager.listeners.get(this.path);

    if (!map.listeners.has(listener)) {
      return;
    }

    let id = map.listeners.get(listener);
    map.listeners.delete(listener);
    map.ids.delete(id);
    map.removedIds.add(id);

    this.childApiManager.messageManager.sendAsyncMessage("API:RemoveListener", {
      childId: this.childApiManager.id,
      listenerId: id,
      path: this.path,
    });
  }

  hasListener(listener) {
    let map = this.childApiManager.listeners.get(this.path);
    return map.listeners.has(listener);
  }
}

// We create one instance of this class for every extension context that
// needs to use remote APIs. It uses the message manager to communicate
// with the ParentAPIManager singleton in ExtensionParent.jsm. It
// handles asynchronous function calls as well as event listeners.
class ChildAPIManager {
  constructor(context, messageManager, localAPICan, contextData) {
    this.context = context;
    this.messageManager = messageManager;
    this.url = contextData.url;

    // The root namespace of all locally implemented APIs. If an extension calls
    // an API that does not exist in this object, then the implementation is
    // delegated to the ParentAPIManager.
    this.localApis = localAPICan.root;
    this.apiCan = localAPICan;

    this.id = `${context.extension.id}.${context.contextId}`;

    MessageChannel.addListener(messageManager, "API:RunListener", this);
    messageManager.addMessageListener("API:CallResult", this);

    this.messageFilterStrict = {childId: this.id};

    this.listeners = new DefaultMap(() => ({
      ids: new Map(),
      listeners: new Map(),
      removedIds: new LimitedSet(10),
    }));

    // Map[callId -> Deferred]
    this.callPromises = new Map();

    let params = {
      childId: this.id,
      extensionId: context.extension.id,
      principal: context.principal,
    };
    Object.assign(params, contextData);

    this.messageManager.sendAsyncMessage("API:CreateProxyContext", params);

    this.permissionsChangedCallbacks = new Set();
    this.updatePermissions = null;
    if (this.context.extension.optionalPermissions.length > 0) {
      this.updatePermissions = () => {
        for (let callback of this.permissionsChangedCallbacks) {
          try {
            callback();
          } catch (err) {
            Cu.reportError(err);
          }
        }
      };
      this.context.extension.on("add-permissions", this.updatePermissions);
      this.context.extension.on("remove-permissions", this.updatePermissions);
    }
  }

  receiveMessage({name, messageName, data}) {
    if (data.childId != this.id) {
      return;
    }

    switch (name || messageName) {
      case "API:RunListener":
        let map = this.listeners.get(data.path);
        let listener = map.ids.get(data.listenerId);

        if (listener) {
          let args = data.args.deserialize(this.context.cloneScope);
          let fire = () => this.context.runSafeWithoutClone(listener, ...args);
          return (data.handlingUserInput) ?
                 withHandlingUserInput(this.context.contentWindow, fire) : fire();
        }
        if (!map.removedIds.has(data.listenerId)) {
          Services.console.logStringMessage(
            `Unknown listener at childId=${data.childId} path=${data.path} listenerId=${data.listenerId}\n`);
        }
        break;

      case "API:CallResult":
        let deferred = this.callPromises.get(data.callId);
        if ("error" in data) {
          deferred.reject(data.error);
        } else {
          let result = data.result.deserialize(this.context.cloneScope);

          deferred.resolve(new NoCloneSpreadArgs(result));
        }
        this.callPromises.delete(data.callId);
        break;
    }
  }

  /**
   * Call a function in the parent process and ignores its return value.
   *
   * @param {string} path The full name of the method, e.g. "tabs.create".
   * @param {Array} args The parameters for the function.
   */
  callParentFunctionNoReturn(path, args) {
    this.messageManager.sendAsyncMessage("API:Call", {
      childId: this.id,
      path,
      args,
    });
  }

  /**
   * Calls a function in the parent process and returns its result
   * asynchronously.
   *
   * @param {string} path The full name of the method, e.g. "tabs.create".
   * @param {Array} args The parameters for the function.
   * @param {function(*)} [callback] The callback to be called when the function
   *     completes.
   * @param {object} [options] Extra options.
   * @param {boolean} [options.noClone = false] If true, do not clone
   *     the arguments into an extension sandbox before calling the API
   *     method.
   * @returns {Promise|undefined} Must be void if `callback` is set, and a
   *     promise otherwise. The promise is resolved when the function completes.
   */
  callParentAsyncFunction(path, args, callback, options = {}) {
    let callId = getUniqueId();
    let deferred = PromiseUtils.defer();
    this.callPromises.set(callId, deferred);

    this.messageManager.sendAsyncMessage("API:Call", {
      childId: this.id,
      callId,
      path,
      args,
      noClone: options.noClone || false,
    });

    return this.context.wrapPromise(deferred.promise, callback);
  }

  /**
   * Create a proxy for an event in the parent process. The returned event
   * object shares its internal state with other instances. For instance, if
   * `removeListener` is used on a listener that was added on another object
   * through `addListener`, then the event is unregistered.
   *
   * @param {string} path The full name of the event, e.g. "tabs.onCreated".
   * @returns {object} An object with the addListener, removeListener and
   *   hasListener methods. See SchemaAPIInterface for documentation.
   */
  getParentEvent(path) {
    path = path.split(".");

    let name = path.pop();
    let namespace = path.join(".");

    let impl = new ProxyAPIImplementation(namespace, name, this);
    return {
      addListener: (listener, ...args) => impl.addListener(listener, args),
      removeListener: (listener) => impl.removeListener(listener),
      hasListener: (listener) => impl.hasListener(listener),
    };
  }

  close() {
    this.messageManager.sendAsyncMessage("API:CloseProxyContext", {childId: this.id});
    if (this.updatePermissions) {
      this.context.extension.off("add-permissions", this.updatePermissions);
      this.context.extension.off("remove-permissions", this.updatePermissions);
    }
  }

  get cloneScope() {
    return this.context.cloneScope;
  }

  get principal() {
    return this.context.principal;
  }

  shouldInject(namespace, name, allowedContexts) {
    // Do not generate content script APIs, unless explicitly allowed.
    if (this.context.envType === "content_child" &&
        !allowedContexts.includes("content")) {
      return false;
    }
    if (allowedContexts.includes("addon_parent_only")) {
      return false;
    }

    // Do not generate devtools APIs, unless explicitly allowed.
    if (this.context.envType === "devtools_child" &&
        !allowedContexts.includes("devtools")) {
      return false;
    }

    // Do not generate devtools APIs, unless explicitly allowed.
    if (this.context.envType !== "devtools_child" &&
        allowedContexts.includes("devtools_only")) {
      return false;
    }

    return true;
  }

  getImplementation(namespace, name) {
    this.apiCan.findAPIPath(`${namespace}.${name}`);
    let obj = this.apiCan.findAPIPath(namespace);

    if (obj && name in obj) {
      return new LocalAPIImplementation(obj, name, this.context);
    }

    return this.getFallbackImplementation(namespace, name);
  }

  getFallbackImplementation(namespace, name) {
    // No local API found, defer implementation to the parent.
    return new ProxyAPIImplementation(namespace, name, this);
  }

  hasPermission(permission) {
    return this.context.extension.hasPermission(permission);
  }

  isPermissionRevokable(permission) {
    return this.context.extension.optionalPermissions.includes(permission);
  }

  setPermissionsChangedCallback(callback) {
    this.permissionsChangedCallbacks.add(callback);
  }
}

var ExtensionChild = {
  BrowserExtensionContent,
  ChildAPIManager,
  Messenger,
  Port,
};