[Webkit-unassigned] [Bug 252664] REGRESSION: Previewing projects broken in Construct 3 web app with Safari TP 163

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=252664

--- Comment #9 from Ashley Gullen <ashley at scirra.com> ---
I spent a while debugging this and I think what happens is this. It's part of a feature to serve local data from URLs using the SW.

1. On startup the main window posts to the SW a map of blobs to serve locally (URL string keys -> blob values)
2. The SW receives this map, and stores it by the client ID it came from.
3. Later fetch events in the SW look up the client ID of the fetch event. If it finds a map of blobs to serve for the client ID, then it looks for that URL in the map. If the lookup succeeds it responds to the fetch with that blob, else the request goes out to network.

What I believe is happening is that when running in a Web Worker, the client IDs for fetch events from the worker are different to those from the main window. Therefore the SW does not find the map of blobs to serve, and falls back to going to network (which returns 404).

In Chrome the client IDs for fetch events from the Web Worker is the same as those for the main window, and therefore the lookup succeeds and content is served from the map.

So this seems to be a compat difference between Chrome and Safari over whether fetch events from the main window and a web worker are the same or not. It seems in both cases, clients.matchAll() in the SW returns only the main window and not any web workers; this seems to suggest to me that Safari TP is incorrect here? I'm not sure what the spec says though.

NOTE: this issue is still marked resolved duplicate of an unrelated issue. Please reopen it as there is evidence of a compat issue/breaking change in Safari that is yet to be resolved.

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