net/http: add built-in mime type for *.mjs #30547

dkumor · Mar 3, 2019

What version of Go are you using (`go version`)?

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (`go env`)?

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/daniel/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/daniel/.go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build067538039=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Given a folder with the following files:

index.html:

<html>
<body>
<script type="module" src="test.mjs"></script>
</body>
</html>

and test.mjs (see: https://developers.google.com/web/fundamentals/primers/modules)

console.log("hi!");

My code serves the above with http.FileServer, and I navigate to / in my browser, opening index.html

What did you expect to see?

I expected hi to be printed in the javascript console

What did you see instead?

The following error in chrome:

Failed to load module script: The server responded with a non-JavaScript MIME type of "text/plain". Strict MIME type checking is enforced for module scripts per HTML spec.

This is because .mjs is not a recognized mimetype. This can easily be worked around by manually adding .mjs to the mime database:

mime.AddExtensionType(".mjs", "application/javascript")

Or, technically, one can just use .js - but .mjs seems to be commonly used.

However, since es modules are a standard, and will become more common in the future, it would be nice to have the mimetype built in.

bradfitz · Mar 5, 2019

Is there an official spec that's proposing standardizing that mime type for that extension? (something more formal that the page you linked)

dkumor · Mar 5, 2019

That's a good question.

Mime

There is currently a draft starting to take shape towards a special mimetype for mjs, but is a work in progress:
https://datatracker.ietf.org/doc/draft-ietf-dispatch-javascript-mjs/
The existing RFC 4329, specifies only application/javascript as a valid mimetype for javascript
https://tools.ietf.org/html/rfc4329 This is corroborated by the IANA website, which uses application/javascript as the only mimetype for javascript.
https://www.iana.org/assignments/media-types/media-types.xhtml
Node' proposes it to be a "web-compatible javascript mime" https://github.com/nodejs/node-eps/blob/master/002-es-modules.md#321-mime-of-mjs-files
There are people arguing for application/javascript+module, but that is, once again, not formal: tc39/ecma262#322

mjs Extension

I did not find anything "official", other than common usage:

Python merged in application/javascript for mjs extension https://bugs.python.org/issue31715
Node only allows .mjs for es modules: https://nodejs.org/api/esm.html https://github.com/nodejs/node-eps/blob/master/002-es-modules.md
VSCode treats mjs as javascript https://github.com/Microsoft/vscode/blob/4e4e6f9b44dd9e6a53d1f08565c52b8ea9f61a5e/extensions/javascript/package.json#L33

andybons · May 6, 2019

With #31327 landed perhaps this should go in, too.

bradfitz · May 6, 2019

Sure. Send a change. Makes sense to also do it in Go 1.13 to match #31327.

andybons · May 6, 2019

Looks like it was already done in https://golang.org/cl/169502

Closing :)

dkumor · May 6, 2019

It looks like the mime type added was text/javascript in mime/type.go line 72, which was obsoleted, and replaced with application/javascript in RFC 4329.

It is my understanding the mimetype should therefore be application/javascript.
This is corroborated by the IANA website, which uses application/javascript as the only mimetype for javascript (https://www.iana.org/assignments/media-types/media-types.xhtml).

Nevertheless, it is great to hear that the mimetype was added!

bradfitz · May 6, 2019

@dkumor, I sent a fix. Thanks.

gopherbot · May 6, 2019

Change https://golang.org/cl/175459 mentions this issue: mime: update .mjs MIME type to application/json instead of text/json


      mime: update .mjs MIME type from text/ to application/javascript

.mjs should be the same MIME type as .js, and RFC 4329 says that
text/javascript is obsolete, even back in 2006:

    https://tools.ietf.org/html/rfc4329#section-7.1

I didn't notice this when I recently reviewed CL 169502.

Also, re-sort it.

Updates #30547

Change-Id: I8ed8ddaf06c8a08b010423ebd071f39ef3a325e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/175459
Reviewed-by: Andrew Bonventre <andybons@golang.org>
Run-TryBot: Andrew Bonventre <andybons@golang.org>

bradfitz changed the title ~~es modules mjs extension in http.FileServer~~ net/http: add built-in mime type for *.mjs Mar 5, 2019

bradfitz added the NeedsDecision label Mar 5, 2019

bradfitz added this to the Go1.13 milestone May 6, 2019

bradfitz added help wanted NeedsFix labels May 6, 2019

gopherbot removed the NeedsDecision label May 6, 2019

andybons closed this May 6, 2019

gopherbot pushed a commit that referenced this issue May 13, 2019

golang/go

net/http: add built-in mime type for *.mjs #30547

net/http: add built-in mime type for *.mjs #30547

dkumor commented Mar 3, 2019

bradfitz changed the title es modules mjs extension in http.FileServer net/http: add built-in mime type for *.mjs Mar 5, 2019

bradfitz added the NeedsDecision label Mar 5, 2019

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edited

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gopherbot commented May 6, 2019

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net/http: add built-in mime type for *.mjs #30547

Comments

dkumor commented Mar 3, 2019

What version of Go are you using (go version)?

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

What did you do?

What did you expect to see?

What did you see instead?

bradfitz changed the title es modules mjs extension in http.FileServer net/http: add built-in mime type for *.mjs Mar 5, 2019

bradfitz added the NeedsDecision label Mar 5, 2019

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bradfitz commented Mar 5, 2019

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dkumor commented Mar 5, 2019 • edited

Mime

mjs Extension

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andybons commented May 6, 2019

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bradfitz commented May 6, 2019

bradfitz added this to the Go1.13 milestone May 6, 2019

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dkumor commented May 6, 2019 • edited

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gopherbot commented May 6, 2019

What version of Go are you using (`go version`)?

What operating system and processor architecture are you using (`go env`)?

dkumor commented Mar 5, 2019 •

edited

dkumor commented May 6, 2019 •

edited