shell: Look at the wall clock to measure session idle time

Counting timer ticks works only when the ticks come on time. Usually
they do, but browsers might decide to not run our JavaScript for
whatever reason, especially if the tab is actually idle or minimized
or otherwise hidden.

By looking at the wall clock time, the session gets logged out
immediately once the timer ticks start coming again (and it has indeed
been idle long enough).

See https://issues.redhat.com/browse/COCKPIT-1418

Author: mvollmer

pkg/shell/idle.tsx

@@ -27,13 +27,15 @@ export class IdleTimeoutState extends EventEmitter<IdleTimeoutStateEvents> {
 
     #final_countdown_timer: number = -1;
     #session_timeout: number = 0;
-    #current_idle_time: number = 0;
+    #idle_start_time: number;
 
     final_countdown: null | number = null;
 
     constructor() {
         super();
 
+        this.#idle_start_time = Date.now();
+
         cockpit.dbus(null, { bus: "internal" }).call("/config", "cockpit.Config", "GetUInt",
                                                      ["Session", "IdleTimeout", 0, 240, 0], {})
                 .then(result => {
@@ -54,27 +56,24 @@ export class IdleTimeoutState extends EventEmitter<IdleTimeoutStateEvents> {
     }
 
     #idleTick = () => {
-        this.#current_idle_time += 5000;
-        if (this.final_countdown === null &&
-            this.#current_idle_time >= this.#session_timeout - this.#final_countdown_secs * 1000) {
+        const idle_time = Date.now() - this.#idle_start_time;
+        if (this.final_countdown === null && idle_time >= this.#session_timeout - this.#final_countdown_secs * 1000) {
             // It's the final countdown...
-            this.final_countdown = this.#final_countdown_secs;
             this.#final_countdown_timer = window.setInterval(this.#finalCountdownTick, 1000);
-            this.#update();
+            this.#finalCountdownTick();
         }
     };
 
     #finalCountdownTick = () => {
-        cockpit.assert(this.final_countdown !== null);
-        this.final_countdown -= 1;
+        this.final_countdown = Math.floor((this.#idle_start_time + this.#session_timeout - Date.now()) / 1000);
         if (this.final_countdown <= 0)
             cockpit.logout(true, _("You have been logged out due to inactivity."));
         this.#update();
     };
 
     #resetTimer = () => {
         if (this.final_countdown === null)
-            this.#current_idle_time = 0;
+            this.#idle_start_time = Date.now();
     };
 
     setupIdleResetEventListeners(win: Window) {
@@ -92,8 +91,8 @@ export class IdleTimeoutState extends EventEmitter<IdleTimeoutStateEvents> {
     }
 
     cancel_final_countdown() {
-        this.#current_idle_time = 0;
         this.final_countdown = null;
+        this.#resetTimer();
         window.clearInterval(this.#final_countdown_timer);
         this.#update();
     }