proposal: mime: expand on what is covered by builtinTypes

[AidanWelch]

Proposal Details

Right now,

mime/type.go includes what seems to be a somewhat arbitrary list of built-in types:

var builtinTypesLower = map[string]string{
	".avif": "image/avif",
	".css":  "text/css; charset=utf-8",
	".gif":  "image/gif",
	".htm":  "text/html; charset=utf-8",
	".html": "text/html; charset=utf-8",
	".jpeg": "image/jpeg",
	".jpg":  "image/jpeg",
	".js":   "text/javascript; charset=utf-8",
	".json": "application/json",
	".mjs":  "text/javascript; charset=utf-8",
	".pdf":  "application/pdf",
	".png":  "image/png",
	".svg":  "image/svg+xml",
	".wasm": "application/wasm",
	".webp": "image/webp",
	".xml":  "text/xml; charset=utf-8",
}

I think some guidance on what should be included in this would be good, rather than a consumer of the package not realizing there are arbitrary gaps. In the meantime I will submit a PR that will incorporate all MDN defined "Common Types" (which also I have to admit is arbitrary, but at least covers more common usecases.)

[seankhliao]

what's included is based on WHATWG mime sniffing
https://mimesniff.spec.whatwg.org/
this gives us a clear spec to adhere to, rather than an arbitrary list.

[AidanWelch]

@seankhliao Wow, thanks for the quick response, but I'm confused as to where that actually specifies specifically just the mime types specified in builtinTypes. From my understanding that would be more relevant for net/http's DetectContentType that is actually sniffing. But, for mime's ExtensionsByType and TypeByExtension don't we have the assumption that the file extension/type is truthful and we're trying to determine the most likely type from that- whereas sniffing wouldn't even care about the given type or extension? (And so sniffing would give most(all?) plaintext types for example the same extension/type)

[gopherbot]

Change https://go.dev/cl/614376 mentions this issue: mime: extend "builtinTypes" to include a more complete list of common types

[gabyhelp]

Related Issues and Documentation

• mime: extend "builtinTypes" to include a more complete list of common types #69533

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