Protect all uses of JSON.parse against exceptions.

remoting/webapp/client_screen.js

 // Copyright (c) 2012 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
  * Functions related to the 'client screen' for Chromoting.
  */
 
 'use strict';
@@ skipping 357 matching lines @@
  * Parse the response from the server to a request to resolve a support id.
  *
  * @param {XMLHttpRequest} xhr The XMLHttpRequest object.
  * @return {void} Nothing.
  */
 function parseServerResponse_(xhr) {
   remoting.supportHostsXhr_ = null;
   console.log('parseServerResponse: xhr = ' + xhr);
   if (xhr.status == 200) {
     var host = /** @type {{data: {jabberId: string, publicKey: string}}} */
-        JSON.parse(xhr.responseText);
-    if (host.data && host.data.jabberId && host.data.publicKey) {
+        jsonParseSafe(xhr.responseText);
+    if (host && host.data && host.data.jabberId && host.data.publicKey) {
       remoting.hostJid = host.data.jabberId;
       remoting.hostPublicKey = host.data.publicKey;
       var split = remoting.hostJid.split('/');
       document.getElementById('connected-to').innerText = split[0];
       startSession_();
       return;
+    } else {
+      console.error('Invalid "support-hosts" response from server.');
     }
   }
   var errorMsg = remoting.Error.GENERIC;
   if (xhr.status == 404) {
     errorMsg = remoting.Error.INVALID_ACCESS_CODE;
   } else if (xhr.status == 0) {
     errorMsg = remoting.Error.NO_RESPONSE;
   } else if (xhr.status == 503) {
     errorMsg = remoting.Error.SERVICE_UNAVAILABLE;
   } else {
@@ skipping 140 matching lines @@
             pin, 'spake2_hmac,spake2_plain', remoting.hostId,
             /** @type {string} */ (remoting.oauth2.getCachedEmail()),
             remoting.ClientSession.Mode.ME2ME, onClientStateChange_);
     remoting.clientSession.createPluginAndConnect(
         document.getElementById('session-mode'),
         token);
   } else {
     showConnectError_(remoting.Error.AUTHENTICATION_FAILED);
   }
 }