Hangouts remote desktop part IV - Host installer

remoting/webapp/host_installer.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview
+ *
+ * HostInstaller allows the caller to download the host binary and monitor the
+ * install progress of the host by pinging the host periodically via native
+ * messaging.
+ *
+ * To download the host and wait for install:
+ *   var hostInstaller = new remoting.HostInstaller();
+ *   hostInstaller.downloadAndWaitForInstall().then(function() {
+ *      // Install has completed.
+ *   }, function(){
+ *      // Download has failed.
+ *   })
+ *
+ * To stop listening to the install progress:
+ *   hostInstaller.cancel();
+ */
+
+'use strict';
+
+/** @suppress {duplicate} */
+var remoting = remoting || {};
+
+/**
+ * @constructor
+ */
+remoting.HostInstaller = function() {
+  /**
+   * @type {Promise}
+   * @private
+   */
+  this.downloadAndWaitForInstallPromise_ = null;
+
+  /**
+   * @type {number|null}

[Jamie, 2014/08/13 02:50:39]

I think this is equivalent to ?number

[kelvinp, 2014/08/14 00:09:34]

Done.

+   * @private
+   */
+  this.checkInstallIntervalId_ = null;
+};
+
+/**
+ * @return {Promise}  The promise will resolve to a boolean value indicating
+ *     whether the host is installed or not.
+ */
+remoting.HostInstaller.prototype.isInstalled = function() {
+  // Always do a fresh check as we don't get notified when the host is
+  // uninstalled.
+
+  /** @param {function(*=):void} resolve */
+  return new Promise(function(resolve) {

[Jamie, 2014/08/13 02:50:39]

Why resolve(bool) instead of resolve/reject? I think the latter would make for
clearer code because you wouldn't need as many conditionals later on.

[kelvinp, 2014/08/14 00:09:34]

I think as a pattern, reject should be used for handling exception instead of
passing return value.  

+    // TODO(kelvinp): Use different native messaging ports for the Me2me host
+    // vs It2MeHost.
+    /** @type {chrome.runtime.Port} */
+    var port =
+        chrome.runtime.connectNative('com.google.chrome.remote_assistance');
+
+    function onMessage() {
+      port.onDisconnect.removeListener(onDisconnected);
+      port.onMessage.removeListener(onMessage);
+      port.disconnect();
+      resolve(true);
+    }
+
+    function onDisconnected() {
+      port.onDisconnect.removeListener(onDisconnected);
+      port.onMessage.removeListener(onMessage);
+      resolve(false);
+    }
+
+    port.onDisconnect.addListener(onDisconnected);
+    port.onMessage.addListener(onMessage);
+    port.postMessage({type: 'hello'});
+  });
+};
+
+/**
+ * @throws {Error}  Throws when the there is not matching host binary for the

[Jamie, 2014/08/13 02:50:39]

s/when/if/
s/the//
s/not/no/

[kelvinp, 2014/08/14 00:09:34]

Done.

+ *     current platform.

[Jamie, 2014/08/13 02:50:39]

@private

[kelvinp, 2014/08/14 00:09:33]

Done.

+ */
+remoting.HostInstaller.prototype.download_ = function() {
+  /** @type {Object.<string,string>} */
+  var hostDownloadUrls = {
+    'Win32' : 'http://dl.google.com/dl/edgedl/chrome-remote-desktop/' +
+        'chromeremotedesktophost.msi',
+    'MacIntel' : 'https://dl.google.com/chrome-remote-desktop/' +
+        'chromeremotedesktop.dmg',
+    'Linux x86_64' : 'https://dl.google.com/linux/direct/' +
+        'chrome-remote-desktop_current_amd64.deb',
+    'Linux i386' : 'https://dl.google.com/linux/direct/' +
+        'chrome-remote-desktop_current_i386.deb'
+  };
+
+  var hostPackageUrl = hostDownloadUrls[navigator.platform];
+  if (hostPackageUrl === undefined) {
+    throw new Error(remoting.Error.CANCELLED);
+  }
+
+  // Start downloading the package.
+  if (remoting.isAppsV2) {
+    // TODO(jamiewalch): Use chrome.downloads when it is available to
+    // apps v2 (http://crbug.com/174046)
+    window.open(hostPackageUrl);
+  } else {
+    window.location = hostPackageUrl;
+  }
+};
+
+/** @return {Promise} */
+remoting.HostInstaller.prototype.downloadAndWaitForInstall = function() {
+  /** @type {remoting.HostInstaller} */
+  var that = this;
+  /**
+   * @type {number}
+   * @const
+   */
+  var CHECK_INSTALL_INTERVAL_IN_MILLISECONDS = 1000;
+
+  /** @param {boolean} installed */
+  return this.isInstalled().then(function(installed){
+    if (installed) {
+      return Promise.resolve(true);
+    }
+
+    if (that.downloadAndWaitForInstallPromise_ !== null) {

[Jamie, 2014/08/13 02:50:38]

Why is it important to save this promise rather than returning a new one each
time? I can't quite get my head round what it means to call then() on a promise
more than once; what will happen?

[kelvinp, 2014/08/14 00:09:33]

The downloadAndWaitForInstallPromise_ is quite expensive (due to the underlying
setInterval call), so I want to make sure there is only one active setInterval
timer at any given moment.

Calling myPromise.then(onResolve) is like hooking an one off event.  The promise
engine will simply invoke |onResolve| when the |myPromise| fulfills.

  promise.then(function() {console.log('hello1')})
  promise.then(function() {console.log('hello2')})
when the promise fulfills
hello1
hello2

+      that.downloadAndWaitForInstallPromise_ = new Promise(
+        /** @param {Function} resolve */
+        function(resolve){
+          that.download_();
+          that.checkInstallIntervalId_ = window.setInterval(function() {
+            /** @param {boolean} installed */
+            that.isInstalled().then(function(installed) {
+              if (installed) {
+                that.cancel();
+                resolve();
+              }
+            });
+          }, CHECK_INSTALL_INTERVAL_IN_MILLISECONDS);
+      });
+    }
+    return that.downloadAndWaitForInstallPromise_;
+  });
+};
+
+/**
+ * Stops waiting for the host to be installed.
+ * For example
+ *   var promise = hostInstaller.downloadAndWaitForInstall();
+ *   hostInstaller.cancel(); // This will prevent |promise| from fulfilling.
+ */
+remoting.HostInstaller.prototype.cancel = function() {
+  if (this.checkInstallIntervalId_ !== null) {
+    window.clearInterval(this.checkInstallIntervalId_);
+    this.checkInstallIntervalId_ = null;
+  }
+  this.downloadAndWaitForInstallPromise_ = null;
+};