Live location sharing - monitor liveness of beacons yet to start (PSF…

…-1081) (#2437)

* monitor liveness of beacons yet to start

* make watch interval a timeout instead

spec/unit/models/beacon.spec.ts

@@ -71,7 +71,7 @@ describe('Beacon', () => {
 
         const advanceDateAndTime = (ms: number) => {
             // bc liveness check uses Date.now we have to advance this mock
-            jest.spyOn(global.Date, 'now').mockReturnValue(now + ms);
+            jest.spyOn(global.Date, 'now').mockReturnValue(Date.now() + ms);
             // then advance time for the interval by the same amount
             jest.advanceTimersByTime(ms);
         };
@@ -224,13 +224,49 @@ describe('Beacon', () => {
                 beacon.monitorLiveness();
 
                 // @ts-ignore
-                expect(beacon.livenessWatchInterval).toBeFalsy();
+                expect(beacon.livenessWatchTimeout).toBeFalsy();
                 advanceDateAndTime(HOUR_MS * 2 + 1);
 
                 // no emit
                 expect(emitSpy).not.toHaveBeenCalled();
             });
 
+            it('checks liveness of beacon at expected start time', () => {
+                // go forward in time to make beacon with timestamp in future
+                jest.spyOn(global.Date, 'now').mockReturnValue(now + HOUR_MS);
+                const futureBeaconEvent = makeBeaconInfoEvent(
+                    userId,
+                    roomId,
+                    {
+                        timeout: HOUR_MS * 3,
+                        isLive: true,
+                    },
+                    '$live123',
+                );
+                // go back to now
+                jest.spyOn(global.Date, 'now').mockReturnValue(now);
+
+                const beacon = new Beacon(futureBeaconEvent);
+                expect(beacon.isLive).toBeFalsy();
+                const emitSpy = jest.spyOn(beacon, 'emit');
+
+                beacon.monitorLiveness();
+
+                // advance to the start timestamp of the beacon
+                advanceDateAndTime(HOUR_MS + 1);
+
+                // beacon is in live period now
+                expect(emitSpy).toHaveBeenCalledTimes(1);
+                expect(emitSpy).toHaveBeenCalledWith(BeaconEvent.LivenessChange, true, beacon);
+
+                // check the expiry monitor is still setup ok
+                // advance to the expiry
+                advanceDateAndTime(HOUR_MS * 3 + 100);
+
+                expect(emitSpy).toHaveBeenCalledTimes(2);
+                expect(emitSpy).toHaveBeenCalledWith(BeaconEvent.LivenessChange, false, beacon);
+            });
+
             it('checks liveness of beacon at expected expiry time', () => {
                 // live beacon was created an hour ago
                 // and has a 3hr duration
@@ -253,12 +289,12 @@ describe('Beacon', () => {
 
                 beacon.monitorLiveness();
                 // @ts-ignore
-                const oldMonitor = beacon.livenessWatchInterval;
+                const oldMonitor = beacon.livenessWatchTimeout;
 
                 beacon.monitorLiveness();
 
                 // @ts-ignore
-                expect(beacon.livenessWatchInterval).not.toEqual(oldMonitor);
+                expect(beacon.livenessWatchTimeout).not.toEqual(oldMonitor);
             });
 
             it('destroy kills liveness monitor and emits', () => {

src/models/beacon.ts

@@ -54,7 +54,7 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
     public readonly roomId: string;
     private _beaconInfo: BeaconInfoState;
     private _isLive: boolean;
-    private livenessWatchInterval: ReturnType<typeof setInterval>;
+    private livenessWatchTimeout: ReturnType<typeof setTimeout>;
     private _latestLocationState: BeaconLocationState | undefined;
 
     constructor(
@@ -109,8 +109,8 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
     }
 
     public destroy(): void {
-        if (this.livenessWatchInterval) {
-            clearInterval(this.livenessWatchInterval);
+        if (this.livenessWatchTimeout) {
+            clearTimeout(this.livenessWatchTimeout);
         }
 
         this._isLive = false;
@@ -122,19 +122,26 @@ export class Beacon extends TypedEventEmitter<Exclude<BeaconEvent, BeaconEvent.N
      * Emits BeaconEvent.LivenessChange when beacon expires
      */
     public monitorLiveness(): void {
-        if (this.livenessWatchInterval) {
-            clearInterval(this.livenessWatchInterval);
+        if (this.livenessWatchTimeout) {
+            clearTimeout(this.livenessWatchTimeout);
         }
 
         this.checkLiveness();
         if (this.isLive) {
             const expiryInMs = (this._beaconInfo?.timestamp + this._beaconInfo?.timeout) - Date.now();
             if (expiryInMs > 1) {
-                this.livenessWatchInterval = setInterval(
+                this.livenessWatchTimeout = setTimeout(
                     () => { this.monitorLiveness(); },
                     expiryInMs,
                 );
             }
+        } else if (this._beaconInfo?.timestamp > Date.now()) {
+            // beacon start timestamp is in the future
+            // check liveness again then
+            this.livenessWatchTimeout = setTimeout(
+                () => { this.monitorLiveness(); },
+                this.beaconInfo?.timestamp - Date.now(),
+            );
         }
     }