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

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dkumor opened this Issue Mar 3, 2019 · 2 comments

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

@bradfitz bradfitz added the NeedsDecision label Mar 5, 2019

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bradfitz commented 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)
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dkumor commented Mar 5, 2019 •
edited

That's a good question.

Mime

mjs Extension

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