1 files changed, 73 insertions, 0 deletions
diff --git a/toolkit/modules/Battery.jsm b/toolkit/modules/Battery.jsm
new file mode 100644
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+++ b/toolkit/modules/Battery.jsm
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+// -*- Mode: javascript; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// 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";
+
+/** This module wraps around navigator.getBattery (https://developer.mozilla.org/en-US/docs/Web/API/Navigator.getBattery).
+  * and provides a framework for spoofing battery values in test code.
+  * To spoof the battery values, set `Debugging.fake = true` after exporting this with a BackstagePass,
+  * after which you can spoof a property yb setting the relevant property of the BatteryManager object.
+  */
+this.EXPORTED_SYMBOLS = ["GetBattery", "Battery"];
+
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+const Cu = Components.utils;
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
+
+// Load Services, for the BatteryManager API
+XPCOMUtils.defineLazyModuleGetter(this, "Services",
+  "resource://gre/modules/Services.jsm");
+
+// Values for the fake battery. See the documentation of Navigator.battery for the meaning of each field.
+var gFakeBattery = {
+  charging: false,
+  chargingTime: 0,
+  dischargingTime: Infinity,
+  level: 1,
+}
+
+// BackendPass-exported object for toggling spoofing
+this.Debugging = {
+  /**
+   * If `false`, use the DOM Battery implementation.
+   * Set it to `true` if you need to fake battery values
+   * for testing or debugging purposes.
+   */
+  fake: false
+}
+
+this.GetBattery = function () {
+  return new Services.appShell.hiddenDOMWindow.Promise(function (resolve, reject) {
+    // Return fake values if spoofing is enabled, otherwise fetch the real values from the BatteryManager API
+    if (Debugging.fake) {
+      resolve(gFakeBattery);
+      return;
+    }
+    Services.appShell.hiddenDOMWindow.navigator.getBattery().then(resolve, reject);
+  });
+};
+
+this.Battery = {};
+
+for (let k of ["charging", "chargingTime", "dischargingTime", "level"]) {
+  let prop = k;
+  Object.defineProperty(this.Battery, prop, {
+    get: function() {
+      // Return fake value if spoofing is enabled, otherwise fetch the real value from the BatteryManager API
+      if (Debugging.fake) {
+        return gFakeBattery[prop];
+      }
+      return Services.appShell.hiddenDOMWindow.navigator.battery[prop];
+    },
+    set: function(fakeSetting) {
+      if (!Debugging.fake) {
+        throw new Error("Tried to set fake battery value when battery spoofing was disabled");
+      }
+      gFakeBattery[prop] = fakeSetting;
+    }
+  })
+}