gecko-dev/devtools/server/actors/webbrowser.js

/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
/* 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";

var { Ci } = require("chrome");
var Services = require("Services");
var promise = require("promise");
const defer = require("devtools/shared/defer");
var { DebuggerServer } = require("devtools/server/main");
var DevToolsUtils = require("devtools/shared/DevToolsUtils");

loader.lazyRequireGetter(this, "RootActor", "devtools/server/actors/root", true);
loader.lazyRequireGetter(this, "BrowserAddonActor", "devtools/server/actors/addon", true);
loader.lazyRequireGetter(this, "WebExtensionParentActor", "devtools/server/actors/webextension-parent", true);
loader.lazyRequireGetter(this, "WorkerActorList", "devtools/server/actors/worker-list", true);
loader.lazyRequireGetter(this, "ServiceWorkerRegistrationActorList", "devtools/server/actors/worker-list", true);
loader.lazyRequireGetter(this, "ProcessActorList", "devtools/server/actors/process", true);
loader.lazyImporter(this, "AddonManager", "resource://gre/modules/AddonManager.jsm");

/**
 * Browser-specific actors.
 */

/**
 * Yield all windows of type |windowType|, from the oldest window to the
 * youngest, using nsIWindowMediator::getEnumerator. We're usually
 * interested in "navigator:browser" windows.
 */
function* allAppShellDOMWindows(windowType) {
  let e = Services.wm.getEnumerator(windowType);
  while (e.hasMoreElements()) {
    yield e.getNext();
  }
}

exports.allAppShellDOMWindows = allAppShellDOMWindows;

/**
 * Retrieve the window type of the top-level window |window|.
 */
function appShellDOMWindowType(window) {
  /* This is what nsIWindowMediator's enumerator checks. */
  return window.document.documentElement.getAttribute("windowtype");
}

/**
 * Send Debugger:Shutdown events to all "navigator:browser" windows.
 */
function sendShutdownEvent() {
  for (let win of allAppShellDOMWindows(DebuggerServer.chromeWindowType)) {
    let evt = win.document.createEvent("Event");
    evt.initEvent("Debugger:Shutdown", true, false);
    win.document.documentElement.dispatchEvent(evt);
  }
}

exports.sendShutdownEvent = sendShutdownEvent;

/**
 * Construct a root actor appropriate for use in a server running in a
 * browser. The returned root actor:
 * - respects the factories registered with DebuggerServer.addGlobalActor,
 * - uses a BrowserTabList to supply tab actors,
 * - sends all navigator:browser window documents a Debugger:Shutdown event
 *   when it exits.
 *
 * * @param connection DebuggerServerConnection
 *          The conection to the client.
 */
function createRootActor(connection) {
  return new RootActor(connection, {
    tabList: new BrowserTabList(connection),
    addonList: new BrowserAddonList(connection),
    workerList: new WorkerActorList(connection, {}),
    serviceWorkerRegistrationList:
      new ServiceWorkerRegistrationActorList(connection),
    processList: new ProcessActorList(),
    globalActorFactories: DebuggerServer.globalActorFactories,
    onShutdown: sendShutdownEvent
  });
}

/**
 * A live list of BrowserTabActors representing the current browser tabs,
 * to be provided to the root actor to answer 'listTabs' requests.
 *
 * This object also takes care of listening for TabClose events and
 * onCloseWindow notifications, and exiting the BrowserTabActors concerned.
 *
 * (See the documentation for RootActor for the definition of the "live
 * list" interface.)
 *
 * @param connection DebuggerServerConnection
 *     The connection in which this list's tab actors may participate.
 *
 * Some notes:
 *
 * This constructor is specific to the desktop browser environment; it
 * maintains the tab list by tracking XUL windows and their XUL documents'
 * "tabbrowser", "tab", and "browser" elements. What's entailed in maintaining
 * an accurate list of open tabs in this context?
 *
 * - Opening and closing XUL windows:
 *
 * An nsIWindowMediatorListener is notified when new XUL windows (i.e., desktop
 * windows) are opened and closed. It is not notified of individual content
 * browser tabs coming and going within such a XUL window. That seems
 * reasonable enough; it's concerned with XUL windows, not tab elements in the
 * window's XUL document.
 *
 * However, even if we attach TabOpen and TabClose event listeners to each XUL
 * window as soon as it is created:
 *
 * - we do not receive a TabOpen event for the initial empty tab of a new XUL
 *   window; and
 *
 * - we do not receive TabClose events for the tabs of a XUL window that has
 *   been closed.
 *
 * This means that TabOpen and TabClose events alone are not sufficient to
 * maintain an accurate list of live tabs and mark tab actors as closed
 * promptly. Our nsIWindowMediatorListener onCloseWindow handler must find and
 * exit all actors for tabs that were in the closing window.
 *
 * Since this is a bit hairy, we don't make each individual attached tab actor
 * responsible for noticing when it has been closed; we watch for that, and
 * promise to call each actor's 'exit' method when it's closed, regardless of
 * how we learn the news.
 *
 * - nsIWindowMediator locks
 *
 * nsIWindowMediator holds a lock protecting its list of top-level windows
 * while it calls nsIWindowMediatorListener methods. nsIWindowMediator's
 * GetEnumerator method also tries to acquire that lock. Thus, enumerating
 * windows from within a listener method deadlocks (bug 873589). Rah. One
 * can sometimes work around this by leaving the enumeration for a later
 * tick.
 *
 * - Dragging tabs between windows:
 *
 * When a tab is dragged from one desktop window to another, we receive a
 * TabOpen event for the new tab, and a TabClose event for the old tab; tab XUL
 * elements do not really move from one document to the other (although their
 * linked browser's content window objects do).
 *
 * However, while we could thus assume that each tab stays with the XUL window
 * it belonged to when it was created, I'm not sure this is behavior one should
 * rely upon. When a XUL window is closed, we take the less efficient, more
 * conservative approach of simply searching the entire table for actors that
 * belong to the closing XUL window, rather than trying to somehow track which
 * XUL window each tab belongs to.
 *
 * - Title changes:
 *
 * For tabs living in the child process, we listen for DOMTitleChange message
 * via the top-level window's message manager. Doing this also allows listening
 * for title changes on Fennec.
 * But as these messages aren't sent for tabs loaded in the parent process,
 * we also listen for TabAttrModified event, which is fired only on Firefox
 * desktop.
 */
function BrowserTabList(connection) {
  this._connection = connection;

  /*
   * The XUL document of a tabbed browser window has "tab" elements, whose
   * 'linkedBrowser' JavaScript properties are "browser" elements; those
   * browsers' 'contentWindow' properties are wrappers on the tabs' content
   * window objects.
   *
   * This map's keys are "browser" XUL elements; it maps each browser element
   * to the tab actor we've created for its content window, if we've created
   * one. This map serves several roles:
   *
   * - During iteration, we use it to find actors we've created previously.
   *
   * - On a TabClose event, we use it to find the tab's actor and exit it.
   *
   * - When the onCloseWindow handler is called, we iterate over it to find all
   *   tabs belonging to the closing XUL window, and exit them.
   *
   * - When it's empty, and the onListChanged hook is null, we know we can
   *   stop listening for events and notifications.
   *
   * We listen for TabClose events and onCloseWindow notifications in order to
   * send onListChanged notifications, but also to tell actors when their
   * referent has gone away and remove entries for dead browsers from this map.
   * If that code is working properly, neither this map nor the actors in it
   * should ever hold dead tabs alive.
   */
  this._actorByBrowser = new Map();

  /* The current onListChanged handler, or null. */
  this._onListChanged = null;

  /*
   * True if we've been iterated over since we last called our onListChanged
   * hook.
   */
  this._mustNotify = false;

  /* True if we're testing, and should throw if consistency checks fail. */
  this._testing = false;
}

BrowserTabList.prototype.constructor = BrowserTabList;

/**
 * Get the selected browser for the given navigator:browser window.
 * @private
 * @param window nsIChromeWindow
 *        The navigator:browser window for which you want the selected browser.
 * @return nsIDOMElement|null
 *         The currently selected xul:browser element, if any. Note that the
 *         browser window might not be loaded yet - the function will return
 *         |null| in such cases.
 */
BrowserTabList.prototype._getSelectedBrowser = function (window) {
  return window.gBrowser ? window.gBrowser.selectedBrowser : null;
};

/**
 * Produces an iterable (in this case a generator) to enumerate all available
 * browser tabs.
 */
BrowserTabList.prototype._getBrowsers = function* () {
  // Iterate over all navigator:browser XUL windows.
  for (let win of allAppShellDOMWindows(DebuggerServer.chromeWindowType)) {
    // For each tab in this XUL window, ensure that we have an actor for
    // it, reusing existing actors where possible. We actually iterate
    // over 'browser' XUL elements, and BrowserTabActor uses
    // browser.contentWindow as the debuggee global.
    for (let browser of this._getChildren(win)) {
      yield browser;
    }
  }
};

BrowserTabList.prototype._getChildren = function (window) {
  if (!window.gBrowser) {
    return [];
  }
  let { gBrowser } = window;
  if (!gBrowser.browsers) {
    return [];
  }
  return gBrowser.browsers.filter(browser => {
    // Filter tabs that are closing. listTabs calls made right after TabClose
    // events still list tabs in process of being closed.
    let tab = gBrowser.getTabForBrowser(browser);
    return !tab.closing;
  });
};

BrowserTabList.prototype.getList = function () {
  let topXULWindow = Services.wm.getMostRecentWindow(
    DebuggerServer.chromeWindowType);
  let selectedBrowser = null;
  if (topXULWindow) {
    selectedBrowser = this._getSelectedBrowser(topXULWindow);
  }

  // As a sanity check, make sure all the actors presently in our map get
  // picked up when we iterate over all windows' tabs.
  let initialMapSize = this._actorByBrowser.size;
  this._foundCount = 0;

  // To avoid mysterious behavior if tabs are closed or opened mid-iteration,
  // we update the map first, and then make a second pass over it to yield
  // the actors. Thus, the sequence yielded is always a snapshot of the
  // actors that were live when we began the iteration.

  let actorPromises = [];

  for (let browser of this._getBrowsers()) {
    let selected = browser === selectedBrowser;
    actorPromises.push(
      this._getActorForBrowser(browser)
          .then(actor => {
            // Set the 'selected' properties on all actors correctly.
            actor.selected = selected;
            return actor;
          }, e => {
            if (e.error === "tabDestroyed") {
              // Return null if a tab was destroyed while retrieving the tab list.
              return null;
            }

            // Forward unexpected errors.
            throw e;
          })
    );
  }

  if (this._testing && initialMapSize !== this._foundCount) {
    throw new Error("_actorByBrowser map contained actors for dead tabs");
  }

  this._mustNotify = true;
  this._checkListening();

  return promise.all(actorPromises).then(values => {
    // Filter out null values if we received a tabDestroyed error.
    return values.filter(value => value != null);
  });
};

BrowserTabList.prototype._getActorForBrowser = function (browser) {
  // Do we have an existing actor for this browser? If not, create one.
  let actor = this._actorByBrowser.get(browser);
  if (actor) {
    this._foundCount++;
    return actor.update();
  }

  actor = new BrowserTabActor(this._connection, browser);
  this._actorByBrowser.set(browser, actor);
  this._checkListening();
  return actor.connect();
};

BrowserTabList.prototype.getTab = function ({ outerWindowID, tabId }) {
  if (typeof outerWindowID == "number") {
    // First look for in-process frames with this ID
    let window = Services.wm.getOuterWindowWithId(outerWindowID);
    // Safety check to prevent debugging top level window via getTab
    if (window instanceof Ci.nsIDOMChromeWindow) {
      return promise.reject({
        error: "forbidden",
        message: "Window with outerWindowID '" + outerWindowID + "' is chrome"
      });
    }
    if (window) {
      let iframe = window.QueryInterface(Ci.nsIInterfaceRequestor)
                         .getInterface(Ci.nsIDOMWindowUtils)
                         .containerElement;
      if (iframe) {
        return this._getActorForBrowser(iframe);
      }
    }
    // Then also look on registered <xul:browsers> when using outerWindowID for
    // OOP tabs
    for (let browser of this._getBrowsers()) {
      if (browser.outerWindowID == outerWindowID) {
        return this._getActorForBrowser(browser);
      }
    }
    return promise.reject({
      error: "noTab",
      message: "Unable to find tab with outerWindowID '" + outerWindowID + "'"
    });
  } else if (typeof tabId == "number") {
    // Tabs OOP
    for (let browser of this._getBrowsers()) {
      if (browser.frameLoader &&
          browser.frameLoader.tabParent &&
          browser.frameLoader.tabParent.tabId === tabId) {
        return this._getActorForBrowser(browser);
      }
    }
    return promise.reject({
      error: "noTab",
      message: "Unable to find tab with tabId '" + tabId + "'"
    });
  }

  let topXULWindow = Services.wm.getMostRecentWindow(
    DebuggerServer.chromeWindowType);
  if (topXULWindow) {
    let selectedBrowser = this._getSelectedBrowser(topXULWindow);
    return this._getActorForBrowser(selectedBrowser);
  }
  return promise.reject({
    error: "noTab",
    message: "Unable to find any selected browser"
  });
};

Object.defineProperty(BrowserTabList.prototype, "onListChanged", {
  enumerable: true,
  configurable: true,
  get() {
    return this._onListChanged;
  },
  set(v) {
    if (v !== null && typeof v !== "function") {
      throw new Error(
        "onListChanged property may only be set to 'null' or a function");
    }
    this._onListChanged = v;
    this._checkListening();
  }
});

/**
 * The set of tabs has changed somehow. Call our onListChanged handler, if
 * one is set, and if we haven't already called it since the last iteration.
 */
BrowserTabList.prototype._notifyListChanged = function () {
  if (!this._onListChanged) {
    return;
  }
  if (this._mustNotify) {
    this._onListChanged();
    this._mustNotify = false;
  }
};

/**
 * Exit |actor|, belonging to |browser|, and notify the onListChanged
 * handle if needed.
 */
BrowserTabList.prototype._handleActorClose = function (actor, browser) {
  if (this._testing) {
    if (this._actorByBrowser.get(browser) !== actor) {
      throw new Error("BrowserTabActor not stored in map under given browser");
    }
    if (actor.browser !== browser) {
      throw new Error("actor's browser and map key don't match");
    }
  }

  this._actorByBrowser.delete(browser);
  actor.exit();

  this._notifyListChanged();
  this._checkListening();
};

/**
 * Make sure we are listening or not listening for activity elsewhere in
 * the browser, as appropriate. Other than setting up newly created XUL
 * windows, all listener / observer management should happen here.
 */
BrowserTabList.prototype._checkListening = function () {
  /*
   * If we have an onListChanged handler that we haven't sent an announcement
   * to since the last iteration, we need to watch for tab creation as well as
   * change of the currently selected tab and tab title changes of tabs in
   * parent process via TabAttrModified (tabs oop uses DOMTitleChanges).
   *
   * Oddly, we don't need to watch for 'close' events here. If our actor list
   * is empty, then either it was empty the last time we iterated, and no
   * close events are possible, or it was not empty the last time we
   * iterated, but all the actors have since been closed, and we must have
   * sent a notification already when they closed.
   */
  this._listenForEventsIf(this._onListChanged && this._mustNotify,
                          "_listeningForTabOpen",
                          ["TabOpen", "TabSelect", "TabAttrModified"]);

  /* If we have live actors, we need to be ready to mark them dead. */
  this._listenForEventsIf(this._actorByBrowser.size > 0,
                          "_listeningForTabClose",
                          ["TabClose", "TabRemotenessChange"]);

  /*
   * We must listen to the window mediator in either case, since that's the
   * only way to find out about tabs that come and go when top-level windows
   * are opened and closed.
   */
  this._listenToMediatorIf((this._onListChanged && this._mustNotify) ||
                           (this._actorByBrowser.size > 0));

  /*
   * We also listen for title changed from the child process.
   * This allows listening for title changes from Fennec and OOP tabs in Fx.
   */
  this._listenForMessagesIf(this._onListChanged && this._mustNotify,
                            "_listeningForTitleChange",
                            ["DOMTitleChanged"]);
};

/*
 * Add or remove event listeners for all XUL windows.
 *
 * @param shouldListen boolean
 *    True if we should add event handlers; false if we should remove them.
 * @param guard string
 *    The name of a guard property of 'this', indicating whether we're
 *    already listening for those events.
 * @param eventNames array of strings
 *    An array of event names.
 */
BrowserTabList.prototype._listenForEventsIf =
  function (shouldListen, guard, eventNames) {
    if (!shouldListen !== !this[guard]) {
      let op = shouldListen ? "addEventListener" : "removeEventListener";
      for (let win of allAppShellDOMWindows(DebuggerServer.chromeWindowType)) {
        for (let name of eventNames) {
          win[op](name, this, false);
        }
      }
      this[guard] = shouldListen;
    }
  };

/*
 * Add or remove message listeners for all XUL windows.
 *
 * @param aShouldListen boolean
 *    True if we should add message listeners; false if we should remove them.
 * @param aGuard string
 *    The name of a guard property of 'this', indicating whether we're
 *    already listening for those messages.
 * @param aMessageNames array of strings
 *    An array of message names.
 */
BrowserTabList.prototype._listenForMessagesIf =
  function (shouldListen, guard, messageNames) {
    if (!shouldListen !== !this[guard]) {
      let op = shouldListen ? "addMessageListener" : "removeMessageListener";
      for (let win of allAppShellDOMWindows(DebuggerServer.chromeWindowType)) {
        for (let name of messageNames) {
          win.messageManager[op](name, this);
        }
      }
      this[guard] = shouldListen;
    }
  };

/**
 * Implement nsIMessageListener.
 */
BrowserTabList.prototype.receiveMessage = DevToolsUtils.makeInfallible(
  function (message) {
    let browser = message.target;
    switch (message.name) {
      case "DOMTitleChanged": {
        let actor = this._actorByBrowser.get(browser);
        if (actor) {
          this._notifyListChanged();
          this._checkListening();
        }
        break;
      }
    }
  });

/**
 * Implement nsIDOMEventListener.
 */
BrowserTabList.prototype.handleEvent =
DevToolsUtils.makeInfallible(function (event) {
  let browser = event.target.linkedBrowser;
  switch (event.type) {
    case "TabOpen":
    case "TabSelect": {
      /* Don't create a new actor; iterate will take care of that. Just notify. */
      this._notifyListChanged();
      this._checkListening();
      break;
    }
    case "TabClose": {
      let actor = this._actorByBrowser.get(browser);
      if (actor) {
        this._handleActorClose(actor, browser);
      }
      break;
    }
    case "TabRemotenessChange": {
      // We have to remove the cached actor as we have to create a new instance.
      let actor = this._actorByBrowser.get(browser);
      if (actor) {
        this._actorByBrowser.delete(browser);
        // Don't create a new actor; iterate will take care of that. Just notify.
        this._notifyListChanged();
        this._checkListening();
      }
      break;
    }
    case "TabAttrModified": {
      // Remote <browser> title changes are handled via DOMTitleChange message
      // TabAttrModified is only here for browsers in parent process which
      // don't send this message.
      if (browser.isRemoteBrowser) {
        break;
      }
      let actor = this._actorByBrowser.get(browser);
      if (actor) {
        // TabAttrModified is fired in various cases, here only care about title
        // changes
        if (event.detail.changed.includes("label")) {
          this._notifyListChanged();
          this._checkListening();
        }
      }
      break;
    }
  }
}, "BrowserTabList.prototype.handleEvent");

/*
 * If |shouldListen| is true, ensure we've registered a listener with the
 * window mediator. Otherwise, ensure we haven't registered a listener.
 */
BrowserTabList.prototype._listenToMediatorIf = function (shouldListen) {
  if (!shouldListen !== !this._listeningToMediator) {
    let op = shouldListen ? "addListener" : "removeListener";
    Services.wm[op](this);
    this._listeningToMediator = shouldListen;
  }
};

/**
 * nsIWindowMediatorListener implementation.
 *
 * See _onTabClosed for explanation of why we needn't actually tweak any
 * actors or tables here.
 *
 * An nsIWindowMediatorListener's methods get passed all sorts of windows; we
 * only care about the tab containers. Those have 'getBrowser' methods.
 */
BrowserTabList.prototype.onWindowTitleChange = () => { };

BrowserTabList.prototype.onOpenWindow =
DevToolsUtils.makeInfallible(function (window) {
  let handleLoad = DevToolsUtils.makeInfallible(() => {
    /* We don't want any further load events from this window. */
    window.removeEventListener("load", handleLoad);

    if (appShellDOMWindowType(window) !== DebuggerServer.chromeWindowType) {
      return;
    }

    // Listen for future tab activity.
    if (this._listeningForTabOpen) {
      window.addEventListener("TabOpen", this);
      window.addEventListener("TabSelect", this);
      window.addEventListener("TabAttrModified", this);
    }
    if (this._listeningForTabClose) {
      window.addEventListener("TabClose", this);
      window.addEventListener("TabRemotenessChange", this);
    }
    if (this._listeningForTitleChange) {
      window.messageManager.addMessageListener("DOMTitleChanged", this);
    }

    // As explained above, we will not receive a TabOpen event for this
    // document's initial tab, so we must notify our client of the new tab
    // this will have.
    this._notifyListChanged();
  });

  /*
   * You can hardly do anything at all with a XUL window at this point; it
   * doesn't even have its document yet. Wait until its document has
   * loaded, and then see what we've got. This also avoids
   * nsIWindowMediator enumeration from within listeners (bug 873589).
   */
  window = window.QueryInterface(Ci.nsIInterfaceRequestor)
                 .getInterface(Ci.nsIDOMWindow);

  window.addEventListener("load", handleLoad);
}, "BrowserTabList.prototype.onOpenWindow");

BrowserTabList.prototype.onCloseWindow =
DevToolsUtils.makeInfallible(function (window) {
  window = window.QueryInterface(Ci.nsIInterfaceRequestor)
                   .getInterface(Ci.nsIDOMWindow);

  if (appShellDOMWindowType(window) !== DebuggerServer.chromeWindowType) {
    return;
  }

  /*
   * nsIWindowMediator deadlocks if you call its GetEnumerator method from
   * a nsIWindowMediatorListener's onCloseWindow hook (bug 873589), so
   * handle the close in a different tick.
   */
  Services.tm.dispatchToMainThread(DevToolsUtils.makeInfallible(() => {
    /*
     * Scan the entire map for actors representing tabs that were in this
     * top-level window, and exit them.
     */
    for (let [browser, actor] of this._actorByBrowser) {
      /* The browser document of a closed window has no default view. */
      if (!browser.ownerGlobal) {
        this._handleActorClose(actor, browser);
      }
    }
  }, "BrowserTabList.prototype.onCloseWindow's delayed body"));
}, "BrowserTabList.prototype.onCloseWindow");

exports.BrowserTabList = BrowserTabList;

/**
 * Creates a tab actor for handling requests to a single browser frame.
 * Both <xul:browser> and <iframe mozbrowser> are supported.
 * This actor is a shim that connects to a ContentActor in a remote browser process.
 * All RDP packets get forwarded using the message manager.
 *
 * @param connection The main RDP connection.
 * @param browser <xul:browser> or <iframe mozbrowser> element to connect to.
 */
function BrowserTabActor(connection, browser) {
  this._conn = connection;
  this._browser = browser;
  this._form = null;
  this.exited = false;
}

BrowserTabActor.prototype = {
  connect() {
    let onDestroy = () => {
      if (this._deferredUpdate) {
        // Reject the update promise if the tab was destroyed while requesting an update
        this._deferredUpdate.reject({
          error: "tabDestroyed",
          message: "Tab destroyed while performing a BrowserTabActor update"
        });
      }
      this.exit();
    };
    let connect = DebuggerServer.connectToChild(this._conn, this._browser, onDestroy);
    return connect.then(form => {
      this._form = form;
      return this;
    });
  },

  get _tabbrowser() {
    if (this._browser && typeof this._browser.getTabBrowser == "function") {
      return this._browser.getTabBrowser();
    }
    return null;
  },

  get _mm() {
    // Get messageManager from XUL browser (which might be a specialized tunnel for RDM)
    // or else fallback to asking the frameLoader itself.
    return this._browser.messageManager ||
           this._browser.frameLoader.messageManager;
  },

  update() {
    // If the child happens to be crashed/close/detach, it won't have _form set,
    // so only request form update if some code is still listening on the other
    // side.
    if (!this.exited) {
      this._deferredUpdate = defer();
      let onFormUpdate = msg => {
        // There may be more than just one childtab.js up and running
        if (this._form.actor != msg.json.actor) {
          return;
        }
        this._mm.removeMessageListener("debug:form", onFormUpdate);
        this._form = msg.json;
        this._deferredUpdate.resolve(this);
      };
      this._mm.addMessageListener("debug:form", onFormUpdate);
      this._mm.sendAsyncMessage("debug:form");
      return this._deferredUpdate.promise;
    }

    return this.connect();
  },

  /**
   * If we don't have a title from the content side because it's a zombie tab, try to find
   * it on the chrome side.
   */
  get title() {
    // On Fennec, we can check the session store data for zombie tabs
    if (this._browser && this._browser.__SS_restore) {
      let sessionStore = this._browser.__SS_data;
      // Get the last selected entry
      let entry = sessionStore.entries[sessionStore.index - 1];
      return entry.title;
    }
    // If contentTitle is empty (e.g. on a not-yet-restored tab), but there is a
    // tabbrowser (i.e. desktop Firefox, but not Fennec), we can use the label
    // as the title.
    if (this._tabbrowser) {
      let tab = this._tabbrowser.getTabForBrowser(this._browser);
      if (tab) {
        return tab.label;
      }
    }
    return "";
  },

  /**
   * If we don't have a url from the content side because it's a zombie tab, try to find
   * it on the chrome side.
   */
  get url() {
    // On Fennec, we can check the session store data for zombie tabs
    if (this._browser && this._browser.__SS_restore) {
      let sessionStore = this._browser.__SS_data;
      // Get the last selected entry
      let entry = sessionStore.entries[sessionStore.index - 1];
      return entry.url;
    }
    return null;
  },

  form() {
    let form = Object.assign({}, this._form);
    // In some cases, the title and url fields might be empty.  Zombie tabs (not yet
    // restored) are a good example.  In such cases, try to look up values for these
    // fields using other data in the parent process.
    if (!form.title) {
      form.title = this.title;
    }
    if (!form.url) {
      form.url = this.url;
    }
    return form;
  },

  exit() {
    this._browser = null;
    this._form = null;
    this.exited = true;
  },
};

exports.BrowserTabActor = BrowserTabActor;

function BrowserAddonList(connection) {
  this._connection = connection;
  this._actorByAddonId = new Map();
  this._onListChanged = null;
}

BrowserAddonList.prototype.getList = function () {
  let deferred = defer();
  AddonManager.getAllAddons((addons) => {
    for (let addon of addons) {
      let actor = this._actorByAddonId.get(addon.id);
      if (!actor) {
        if (addon.isWebExtension) {
          actor = new WebExtensionParentActor(this._connection, addon);
        } else {
          actor = new BrowserAddonActor(this._connection, addon);
        }

        this._actorByAddonId.set(addon.id, actor);
      }
    }

    deferred.resolve([...this._actorByAddonId].map(([_, actor]) => actor));
  });

  return deferred.promise;
};

Object.defineProperty(BrowserAddonList.prototype, "onListChanged", {
  enumerable: true,
  configurable: true,
  get() {
    return this._onListChanged;
  },
  set(v) {
    if (v !== null && typeof v != "function") {
      throw new Error(
        "onListChanged property may only be set to 'null' or a function");
    }
    this._onListChanged = v;
    this._adjustListener();
  }
});

BrowserAddonList.prototype.onInstalled = function (addon) {
  this._notifyListChanged();
  this._adjustListener();
};

BrowserAddonList.prototype.onUninstalled = function (addon) {
  this._actorByAddonId.delete(addon.id);
  this._notifyListChanged();
  this._adjustListener();
};

BrowserAddonList.prototype._notifyListChanged = function () {
  if (this._onListChanged) {
    this._onListChanged();
  }
};

BrowserAddonList.prototype._adjustListener = function () {
  if (this._onListChanged) {
    // As long as the callback exists, we need to listen for changes
    // so we can notify about add-on changes.
    AddonManager.addAddonListener(this);
  } else if (this._actorByAddonId.size === 0) {
    // When the callback does not exist, we only need to keep listening
    // if the actor cache will need adjusting when add-ons change.
    AddonManager.removeAddonListener(this);
  }
};

exports.BrowserAddonList = BrowserAddonList;

exports.register = function (handle) {
  handle.setRootActor(createRootActor);
};

exports.unregister = function (handle) {
  handle.setRootActor(null);
};