[Feature request] Allow loading data from browser storage (IndexedDB/other) to avoid re-downloading files

[Semphriss]

I have an application compiled with Emscripten that outputs a .data of 250Mb.

My users are reporting download times varying between 2 and 30+ minutes. Given the size of the data file, most browsers will refuse to cache it.

Given that the application requires persistent storage, my plan is to store the contents of the data file on the client using IndexedDB and feed it to the application, to avoid an unnecessary request.

After some research, I found that although it is possible to change the location of the data file (e. g. for CDN hosting), it is not possible to point the Emscripten-compiled code to a non-remote location, whether it be a Blob object, an IndexedDB entry, or anything else.

Would it be possible to implement such a feature?

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_{The project in question is SuperTux, you can find the development build here}

[kripken]

I don't think that's possible atm. However, once the new filesystem work (#15041) is done, it should be easier to add this, I think.