Implemented update checking functionality

lib/updater.js

Index: lib/updater.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/updater.js
@@ -0,0 +1,92 @@
+/*
+ * This file is part of Adblock Plus <http://adblockplus.org/>,
+ * Copyright (C) 2006-2013 Eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+let {Prefs} = require("prefs");
+let updateUrl = (_appInfo.developmentBuild ? Prefs.update_url_devbuild : Prefs.update_url_release);
+updateUrl = updateUrl.replace(/%NAME%/g, encodeURIComponent(_appInfo.name))
+                     .replace(/%ID%/g, encodeURIComponent(_appInfo.id))
+                     .replace(/%VERSION%/g, encodeURIComponent(_appInfo.version))
+                     .replace(/%APP%/g, encodeURIComponent(_appInfo.platform));
+
+const HOURS_TO_MILLIS = 60 * 60 * 1000;
+const MIN_CHECK_INTERVAL = 18 * HOURS_TO_MILLIS;
+const MAX_CHECK_INTERVAL = 30 * HOURS_TO_MILLIS;
+
+const TYPE_AUTOMATIC = 0;
+const TYPE_MANUAL = 1;
+
+let checkForUpdates = exports.checkForUpdates = function checkForUpdates(forceCheck, callback)
+{
+  let now = Date.now();
+  if (!forceCheck && now < Prefs.next_update_check)
+  {
+    if (Prefs.next_update_check - now > MAX_CHECK_INTERVAL)
+      Prefs.next_update_check = now + MAX_CHECK_INTERVAL;
+
+    window.setTimeout(checkForUpdates, Prefs.next_update_check - now);
+    return;
+  }
+
+  Prefs.next_update_check = now + MIN_CHECK_INTERVAL +
+      Math.random() * (MAX_CHECK_INTERVAL - MIN_CHECK_INTERVAL);
+  if (!forceCheck)
+    window.setTimeout(checkForUpdates, Prefs.next_update_check - now);
+
+  let url = updateUrl.replace(/%TYPE%/g, forceCheck ? TYPE_MANUAL : TYPE_AUTOMATIC);
+  let request = new XMLHttpRequest();
+  request.open("GET", url);
+  request.addEventListener("load", function()
+  {
+    try
+    {
+      let data = JSON.parse(request.responseText);
+      let updateInfo = null;
+      if (_appInfo.name in data)
+        updateInfo = data[_appInfo.name];
+      else if (_appInfo.name + "/" + _appInfo.platform in data)
+        updateInfo = data[_appInfo.name + "/" + _appInfo.platform];
+
+      if (updateInfo && "version" in updateInfo && "url" in updateInfo &&
+          Services.vc.compare(updateInfo.version, _appInfo.version) > 0)
+      {
+        if (updateInfo.url.indexOf("https://") != 0)
+          throw new Error("Invalid update URL, HTTPS is mandatory for updates");
+        _triggerEvent("updateAvailable", updateInfo.url);
+      }
+      if (callback)
+        callback(null);
+    }
+    catch (e)
+    {
+      Cu.reportError(e);
+      if (callback)
+        callback(e);
+    }
+  }, false);
+
+  request.addEventListener("error", function()
+  {
+    let e = new Error("Update check failed (channel status " + request.channel.status + ")");
+    Cu.reportError(e);
+    if (callback)
+      callback(e);
+  }, false);
+
+  request.send(null);
+}
+
+window.setTimeout(checkForUpdates, 0.1 * HOURS_TO_MILLIS);