WebAssembly doesn't work on Firefox/Chrome due to missing MIME type

[DesWurstes@…]

WebAssembly's MIME type is application/wasm. If not set; Firefox, Chrome and Vivaldi won't be able to run the WASM.

Here's the Chrome error message:

util.js:1632 wasm streaming compile failed: TypeError: Failed to execute 'compile' on 'WebAssembly': Incorrect response MIME type. Expected 'application/wasm'.

Could you please add application/wasm wasm to nginx/conf/mime.types?

[Maxim Dounin]

Thanks for your suggestion. Note that if you want to add additional types or serve some files with specific custom types, you can do so using the types directive, see ​the documentation for examples.

Some related facts as found during a quick investigation, just for the record:

• The application/wasm MIME type is not something ​officially registered, though there is a ​provisional registration.
• The the WebAssembly specification isn't yet complete, though there is a ​public draft.
• The MIME type isn't present neither in ​Apache mime.types, nor in ​Python.
• It looks like it was (or going to be) added to IIS, see ​comments here.
• It was added to ​mime-db as used by Github Pages.

Note that we generally only add most popular types to the mime.types as shipped with nginx. It is not currently clear if application/wasm is one of such types, so leaving this open for now. If you are reading this and also want (or don't want) application/wasm to be added, please comment.

[dbrgn@…]

If you are reading this and also want (or don't want) application/wasm to be added, please comment.

I signed up here to say: Yes, I'd also like to see this type added! :)

The the WebAssembly specification isn't yet complete, though there is a ​public draft.

It's true that the spec isn't complete, but in the meantime the WebAssembly MVP (​https://webassembly.org/docs/mvp/) has shipped across all major browsers (at least Firefox, Chrome, Edge, Safari).

Oh, and it seems that the mime type has been ​added to cpython as well.

[ccouzens@…]

If you are reading this and also want (or don't want) application/wasm to be added, please comment.

Yes please, I would like to see this added. I have a ​patch, although it isn't exactly a complicated change.

The WebAssembly specification isn't yet complete, though there is a ​public draft.

It's now a "Proposed Recommendation", which is the final step to becoming a W3C recommendation (although they stress until it's a recommendation it's still a draft).

I think on balance it's reasonable for nginx to hold off until it's a W3C recommendation. I imagine it's easier for the nginx project to add it once it has become a recommendation, than to remove it should it fail.

[ccouzens@…]

The WebAssembly? specification isn't yet complete, though there is a ​public draft.

It's now a W3C recommendation. I think this happened today.
And it says that it should be served with the mime type application/wasm

​https://www.w3.org/TR/wasm-web-api-1/#streaming-modules

[https://stackoverflow.com/users/4228964/florent]

Please add this mime type.
I forgot multiple times to add it to the config file and it's a pain in a multi-host configuration where you can only declare it in a single file.
Without this mime/type, all libraries based on emscripten will fail streaming compilation and instead revert to ArrayBuffer.
Streaming compilation can save almost all wasm compilation time.
​https://developers.google.com/web/updates/2018/04/loading-wasm

[Laurence 'GreenReaper' Parry]

This is a common enough issue for users of Flash emulator Ruffle (which is getting a lot of attention right now) that it ​has adding the MIME type as the first thing to do after downloading and extracting files for web deployment.

(I initially tried just adding the script, since WASM had been a thing for a while and I didn't think it'd be an issue; then went back to see that advice after finding an error message in Firefox's JS console about it and tried fixing it in several places, getting more and more confused, only to realize the type had been cached along with the rest of the response.)

​It trips up other people in unrelated software as well

[Maxim Dounin]

See also #2168.

[Maxim Dounin <mdounin@…>]

In 7834:b3f4d83d6fd0/nginx:

MIME: added application/wasm type (ticket #1606).

[Maxim Dounin]

Committed. Thanks for prodding this.