Fix the JS error "EventSource is not defined" caused by PaleMoon

[wxiaoguang]

Background

Some browsers (like Pale Moon, Firefox<53) don't support EventSource in SharedWorkerGlobalScope. It's a bug https://stackoverflow.com/questions/25234493/server-sent-events-in-firefox-shared-web-workers .

Gitea's eventsource.sharedworker.js needs EventSource when doing "new Source(url)".

Before 1.17, even if JS error occurs, there is no prompt to end users, the code just didn't work.

Since 1.17, the UI will show JS errors, so if a users is using a such browser, they will see a JS error prompt. Thanks to our global JS error handler, we catch this problem now.

Solution

The simple solution is to check whether there is a EventSource class in global (the self, aka SharedWorkerGlobalScope). If no EventSource class, just post a message back to the caller, in case the caller would like to use a fallback method to do its work.

Although it's feasible to make the worker's caller to handle the 'no-event-source' message to use a fallback method, I think it's out of the scope of this PR, because in such case, the real-time polling just never worked before, it's not worth to do the fix for the browser's bugs.

Now, the callers fall back to periodic poller if there is no EventSource

ps: there seems to be a backend bug, the worker can not get the "stop" event for stopwatch or the "1->0" change for notification when using EventSource, while other functions (stopwatch start event by EventSource/PeriodicPoller, stopwatch stop event by PeriodicPoller, notification by EventSource/PeriodicPoller) are all tested on my side.

Close #20572

[zeripath]

This PR does not do fallback to the poller function.

[wxiaoguang]

This PR does not do fallback to the poller function.

Yup, described in the comment already

Although it's feasible to make the worker's caller to handle the 'no-event-source' message to use a fallback method, I think it's out of the scope of this PR, because in such case, the real-time polling just never worked before, it's not worth to do the fix for the browser's bugs.

If there is one more people like to add the fallback back, I can do it.

[wxiaoguang]

@zeripath the poller is back

[silverwind]

LGTM after above suggestions.

[lunny]

Maybe it's valuable to backport to v1.17 when possible.

[wxiaoguang]

I would like to wait for feedbacks from users (#20572 (comment)) first.

[wxiaoguang]

The main branch has been confirmed by #20572 (comment)

The backport for 1.17 is in #20663

[wolfbeast]

I just upgraded to 1.17.1 and this error doesn't seem to be fixed on Pale Moon.

JavaScript error: ReferenceError: EventSource is not defined (https://repo.palemoon.org/assets/js/eventsource.sharedworker.js @ 1:0). Open browser console to see more details.

22:23:58.501 worker error error { target: SharedWorker, isTrusted: true, message: "ReferenceError: EventSource is not defined", filename: "https://repo.palemoon.org/assets/js/eventsource.sharedworker.js", lineno: 1, colno: 85, srcElement: SharedWorker, eventPhase: 0, bubbles: false, cancelable: true, defaultPrevented: false } 1 index.js:37:15854
	Gg/< https://repo.palemoon.org/assets/js/index.js:37:15854

[wxiaoguang]

Cache problem (I have read other comments, just put a comment for it here)

[silverwind]

Cache issue will be solved with #20813.

[wolfbeast]

Cache issue will be solved with #20813.

Awesome! It bit me because even a hard refresh didn't actually get me where I wanted to. Only a full browser cache purge did the trick (may even need a browser restart, depending on configuration!)