mime: TypeByExtension returns incorrect value for .webm extension

[jkbcz]

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

$ go version
go version go1.26.0 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
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/jakubc/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/jakubc/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2514599944=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/jakubc/repos/bcc-code/bcc-chat/api/go.mod'
GOMODCACHE='/home/jakubc/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/jakubc/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/jakubc/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.26.0.linux-amd64'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/jakubc/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/jakubc/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.26.0.linux-amd64/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'
GOROOT/bin/go version: go version go1.26.0 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.26.0
uname -sr: Linux 6.19.2-2-cachyos
LSB Version:	n/a
Distributor ID:	cachyos
Description:	CachyOS
Release:	rolling
Codename:	n/a
/usr/lib/libc.so.6: GNU C Library (GNU libc) stable release version 2.43.

What did you do?

Checking mime type by extension for .webm extension
mime.TypeByExtension(".webm")

What did you expect to see?

video/webm

What did you see instead?

audio/webm
According to https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/MIME_types/Common_types .webm extension should resolve to video/webm

I would be happy to contribute a fix for this

[seankhliao]

Seems like it's valid for both audio/webm and video/webm, but video should take priority
https://go-review.googlesource.com/c/go/+/614376
https://chromium.googlesource.com/chromium/src.git/+/refs/heads/main/net/base/mime_util.cc#169
https://github.com/mozilla-firefox/firefox/blob/main/uriloader/exthandler/nsExternalHelperAppService.cpp#L485

feel free to send a cl

[gabyhelp]

Related Issues

• mime: incorrect definition of extension by mime type audio/webm #22318 (closed)
• mime: TypeByExtension is case sensitive #8350 (closed)
• mime: Add mime type for avif image file format #44602 (closed)
• net/http: add video/mpeg to DetectContentType #50376 (closed)
• mime: wrong extensions list for content type "image/jpeg" when using built-in types #36524 (closed)
• mime: ExtensionsByType is non-deterministic for image/jpeg #39283 (closed)
• mime: glob pattern is not expanded #52609
• mime: mime.ExtensionsByType returns an unexpected extension ",v" for "text/plain" #52065 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/747340 mentions this issue: mime: assign video/webm type to .webm extension