Firefox streaming compilation needs Content-Type header set

[Brion Vibber]

I noticed on Firefox 58 I'm getting warnings like this in the console, with code built on 1.37.28:

    wasm streaming compile failed: TypeError: Response has unsupported MIME type

    falling back to ArrayBuffer instantiation

and the .wasm file shows up twice in the network list in dev tools. The file is shown as cached on the second load, and in subsequent page views, but I don't know if that'll hold for larger .wasm executables than my relatively small codecs.

Fix is to reconfigure the web server to serve .wasm files as application/wasm instead of defaulting to something like application/octet-stream.

In Apache, this would be:

    AddType application/wasm .wasm

and while one is in there; to also enable transparent gzip:

    AddOutputFilterByType DEFLATE application/wasm

This decreases the network transfer size nicely as a bonus. :)

-- brion

[Alon Zakai]

Thanks! Very important stuff. I added a section to the wiki,

https://github.com/kripken/emscripten/wiki/WebAssembly#web-server-setup

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[Brian Gavin]

Thanks for the info Brion.

Do you know it effects other web browser?

Brian Gavin

[Derek Schuff]

Yes, the requirement on mime type is part of the spec. See https://webassembly.github.io/spec/web-api/index.html#streaming-modules

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