Generate key_worker.js

Instead of calling importScripts, which is prone to relative path
issues, generate the worker script with everything it needs included.

Gruntfile.js

@@ -60,6 +60,16 @@ module.exports = function(grunt) {
         ],
         dest: 'js/libtextsecure.js',
       },
+      key_worker: {
+        options: {
+          banner: 'var window = this;\n',
+        },
+        src: [
+          'js/libtextsecure.js',
+          'libtextsecure/key_worker.js'
+        ],
+        dest: 'js/key_worker.js'
+      },
       libtextsecuretest: {
         src: [
           'components/mocha/mocha.js',
@@ -152,6 +162,10 @@ module.exports = function(grunt) {
         files: ['./libtextsecure/*.js', './libtextsecure/storage/*.js'],
         tasks: ['concat:libtextsecure']
       },
+      key_worker: {
+        files: ['<%= concat.key_worker.src %>'],
+        tasks: ['concat:key_worker']
+      },
       dist: {
         files: ['<%= dist.src %>'],
         tasks: ['copy']

libtextsecure/key_worker.js

@@ -0,0 +1,75 @@
+/* vim: ts=4:sw=4
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+'use strict';
+
+/*
+*  Load this script in a Web Worker to generate new prekeys without
+*  tying up the main thread.
+*  https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
+*
+*  Because workers don't have access to the window or localStorage, we
+*  create our own version that proxies back to the caller for actual
+*  storage.
+*
+*  Example usage:
+*
+    var myWorker = new Worker('/js/key_worker.js');
+    myWorker.onmessage = function(e) {
+        switch(e.data.method) {
+            case 'set':
+                localStorage.setItem(e.data.key, e.data.value);
+                break;
+            case 'remove':
+                localStorage.removeItem(e.data.key);
+                break;
+            case 'done':
+                console.log(e.data.keys);
+        }
+    };
+*/
+var store = {};
+window.textsecure.storage.impl = {
+    /*****************************
+    *** Override Storage Routines ***
+    *****************************/
+    put: function(key, value) {
+        if (value === undefined)
+            throw new Error("Tried to store undefined");
+        store[key] = value;
+        postMessage({method: 'set', key: key, value: value});
+    },
+
+    get: function(key, defaultValue) {
+        if (key in store) {
+            return store[key];
+        } else {
+            return defaultValue;
+        }
+    },
+
+    remove: function(key) {
+        delete store[key];
+        postMessage({method: 'remove', key: key});
+    },
+};
+onmessage = function(e) {
+    store = e.data;
+    textsecure.protocol_wrapper.generateKeys().then(function(keys) {
+        postMessage({method: 'done', keys: keys});
+        close();
+    });
+}