Some more issues I noticed while testing:

• When you have two tabs open, the session expires, and you log in again in one of the tabs, the other tabs almost immediately sends an outdated null expiry message and thus shows the dialog telling you the session has expired, even though it's still valid. I think once the session is expired, no more messages should be sent
• When the dialog opens, it shows 120 regardless of the actual remaining time for a second
• In some cases I end up with the session-expiry endpoint getting hit with tons of requests per second. This happens because moment.utc(sessionExpiry).subtract('120', 'seconds') - moment.utc() will return NaN when sessionExpiry is null.

But that aside, I think the syncing works really well!

I think the whole logic of the react component can be vastly simplified. I might push something tomorrow...

Thanks for the review @ThiefMaster, sure I welcome simplifying the component, please let me know if it's something i can also do on my end. Thanks.

Now that I'm back from the xmas break I finally found some time to finish the simplified version. Have a look at session_expiry_new.js from my last commit. To test the re-login part, I suggest setting SESSION_LIFETIME = 30 in indico.conf, and for refreshing SESSION_LIFETIME = 1300 works well.

When testing it with two browser tabs it synced nicely, but avoids the huge complexity of having a separate component that's just running the interval, and also the useRefs (refs often make code harder to read/maintain).

Wow it was a total rewrite!!! The component works nicely. I just have a couple of comments about the syncing which I don't know if some were done on purpose or not.

1. The dialog first appears at 1 sec less than the value of SHOW_DIALOG_THRESHOLD
2. The timing of the snooze may not be straightforward to understand for a user. It’s nice when there is still 2 minutes left and you hit on snooze then it shows again after 1 minute. But hitting on snooze when it’s 20 seconds left or 10 seconds left, it would be too often for it to be showing up again and again in half the time.
3. After snoozing on one window and the session is refreshed on another window, the next time the dialog appears on the snoozed window depends on the previous snooze time. For example if my session lasts for 3600s and I hit snooze at just 20 Seconds before expiry and then refresh the session in another window for another 3600s, then the next time the countdown appears on the snoozed browser would be at 20/2=10 instead of at SHOW_DIALOG_THRESHOLD
4. The interval does not stop even after the session has expired. So "ignoring new expiry on expired session" is actually only ignored on the next interval but it syncs up the expired tabs again in the intervals after that

1. I didn't really test for off-by-one since one second doesn't really matter. Anyway should be an easy fix ;)
2. Yes, this could easily be adjusted.
3. Might have missed resetting it (I know I added a reset when you refresh 'locally')
4. Not sure I understand. The interval keeps running but it should ignore any updates from other tabs etc. Or do you mean that the expired one keeps sending out data to other tabs?

The interval keeps running but it should ignore any updates from other tabs etc.

4. Yes exactly this - the interval keeps running but it does not ignore updates from other tabs after a while

1,3,4 are fixed. Any suggestion for a better snooze behavior in point 2? (also see my more verbose msg on matrix)