From 0d9574332f5efcd09c973c59659b70ca90a6a801 Mon Sep 17 00:00:00 2001
From: Libor Polčák <ipolcak@fit.vutbr.cz>
Date: Aug 25 2021 14:03:20 +0000
Subject: Wrap timestamps of Gamepad instances to limit precision


Note that the code is not tested as MDN claims that there is no support
in browsers.

---

diff --git a/common/levels.js b/common/levels.js
index 563aae1..980cd20 100644
--- a/common/levels.js
+++ b/common/levels.js
@@ -92,6 +92,8 @@ var wrapping_groups = {
 				"window.Date",
 				// DOM
 				"Event.prototype.timeStamp",
+				// GP
+				"Gamepad.prototype.timestamp",
 			],
 		},
 		{
diff --git a/common/wrappingS-GP.js b/common/wrappingS-GP.js
index 8e98aec..97b9fb2 100644
--- a/common/wrappingS-GP.js
+++ b/common/wrappingS-GP.js
@@ -48,9 +48,31 @@
  * mitigate the event to fire and consequently, it is possible that an
  * adversary can learn that a gamepad was (dis)connected but there was no
  * change in the result of the navigator.getGamepads() API.
+ *
+ * The gamepad representing object carries a timestamp of the last change of
+ * the gamepad. As we allow wrapping of several ways to obtain timestamps,
+ * we need to provide the same precision for the Gamepad object.
  */
 
 (function() {
+	var remember_past_ts_values = `var precision = args[0];
+				var doNoise = args[1];
+				var pastValues = {};
+				${rounding_function}
+				${noise_function}
+				var mitigationF = rounding_function;
+				if (doNoise === true){
+					mitigationF = function(value, precision) {
+						let params = [value, precision];
+						if (params in pastValues) {
+							return pastValues[params];
+						}
+						let result = noise_function(...params);
+						pastValues[params] = result;
+						return result;
+					}
+				}
+			`;
 	var wrappers = [
 		{
 			parent_object: "navigator",
@@ -61,6 +83,37 @@
 					return new window.Array();
 				`,
 		},
+		{
+			/**
+			 * \see https://developer.mozilla.org/en-US/docs/Web/API/Gamepad/timestamp
+			 * \note that at the time of the writing of the prototype, the timestamp
+			 * property was not supported by any browser.
+			 */
+			parent_object: "Gamepad.prototype",
+			parent_object_property: "timestamp",
+			wrapped_objects: [],
+			helping_code: remember_past_ts_values + `let origGet = Object.getOwnPropertyDescriptor(Event.prototype, "timeStamp").get`,
+			post_wrapping_code: [
+				{
+					code_type: "object_properties",
+					parent_object: "Gamepad.prototype",
+					parent_object_property: "timestamp",
+					wrapped_objects: [],
+					/**  \brief replaces Gamepad.timestamp getter to create
+					 * a timestamp with the desired precision.
+					 */
+					wrapped_properties: [
+						{
+							property_name: "get",
+							property_value: `
+								function() {
+									return mitigationF(origGet.call(this), precision);
+								}`,
+						},
+					],
+				}
+			],
+		},
 	]
 	add_wrappers(wrappers);
 })()