Bug 1885936 - Part 3: Implement data collection for gamepads. r=tschuster

Differential Revision: https://phabricator.services.mozilla.com/D207981

toolkit/actors/UserCharacteristicsChild.sys.mjs

@@ -40,13 +40,45 @@ export class UserCharacteristicsChild extends JSWindowActorChild {
   // that requires loading time.
   async collectUserCharacteristicsDataWithDelay() {
     lazy.console.debug("Calling collectUserCharacteristicsDataWithDelay()");
+
+    await this.populateGamepadsInfo();
+  }
+
+  async populateGamepadsInfo() {
+    lazy.console.debug("Calling populateGamepadsInfo()");
+    let gamepads = await this.contentWindow.navigator.requestAllGamepads();
+
+    lazy.console.debug(`Found ${gamepads.length} gamepads`);
+
+    let gamepadsInfo = [];
+
+    for (const gamepad of gamepads) {
+      // We use an array to represent a gamepad device because it uses less size
+      // then an object when convert to a JSON string. So, we can fit the string
+      // into a Glean string which has a 100 size limitation.
+      let data = [];
+      data.push(gamepad.id);
+      data.push(gamepad?.hand ?? "");
+      data.push(gamepad.buttons.length);
+      data.push(gamepad.axes?.length ?? 0);
+      data.push(gamepad.hapticActuators?.length ?? 0);
+      data.push(gamepad.lightIndicators?.length ?? 0);
+      data.push(gamepad.touchEvents?.length ?? 0);
+
+      gamepadsInfo.push(JSON.stringify(data));
+    }
+
+    lazy.console.debug(`Reporting gamepad: ${gamepadsInfo}`);
+    this.userDataDetails.output.gamepads = gamepadsInfo;
   }
 
   async handleEvent(event) {
     lazy.console.debug("Got ", event.type);
     switch (event.type) {
       case "UserCharacteristicsDataDone":
-        this.userDataDetails = event.detail;
+        // Clone the data so we can modify it. Otherwise, we cannot change it
+        // because it's behind Xray wrapper.
+        this.userDataDetails = structuredClone(event.detail);
 
         await this.collectUserCharacteristicsData();
 

toolkit/components/resistfingerprinting/UserCharacteristicsPageService.sys.mjs

@@ -181,6 +181,10 @@ export class UserCharacteristicsPageService {
         lazy.console.debug("Populating Glean metrics...");
         Glean.characteristics.timezone.set(data.output.foo);
 
+        for (let gamepad of data.output.gamepads) {
+          Glean.characteristics.gamepads.add(gamepad);
+        }
+
         lazy.console.debug("Unregistering actor");
         Services.obs.notifyObservers(
           null,

toolkit/components/resistfingerprinting/content/usercharacteristics.js

@@ -25,6 +25,17 @@ function debug(...args) {
 debug("Debug Line");
 debug("Another debug line, with", { an: "object" });
 
+// A hacky way to ensure all GamePad related services are running by the time we
+// want to know about GamePads. This will attach a listener for this window to
+// the GamePadManager, creating it if it doesn't exist. When GamePadManager is
+// created (either now or earlier) it will also create a GamePadEventChannel
+// between the GamePadManager and the parent process. When that's created, the
+// Parent will create a GamePadPlatformService if it's not already created, and
+// when that Service gets created it kicks off a background thread to monitor
+// for gamepads attached to the machine. We need to give that background thread
+// time to run so all the data is there when we request it.
+navigator.getGamepads();
+
 // The first time we put a real value in here, please update browser_usercharacteristics.js
 let output = {
   foo: "Hello World",

toolkit/components/resistfingerprinting/metrics.yaml

@@ -534,6 +534,33 @@ characteristics:
     data_sensitivity:
       - technical
 
+  gamepads:
+    type: string_list
+    description: >
+      The information of the gamepads inserted on the user device. Each string
+      represents one gamepad. We use a JSON array to describe a gamepad, every
+      value represents one property of the gamepad. Following are the details:
+        index 0: The ID of the game pad
+        index 1: Which hand for the gamepad.
+        index 2: Number of buttons
+        index 3: Number of axes
+        index 4: Number of haptics
+        index 5: Number of lights
+        index 6: Number of touches
+    lifetime: application
+    send_in_pings:
+      - user-characteristics
+    notification_emails:
+      - tom@mozilla.com
+      - tihuang@mozilla.com
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1885936
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1885936#c2
+    expires: never
+    data_sensitivity:
+      - technical
+
   prefs_intl_accept_languages:
     type: string
     description: >