Yeah, looks like we're inconsistent here. Content-Dispositions are different, but we've supported them in ParseMediaType forever (my fault, I guess), despite them not being media types technically. So I guess we could be looser in FormatMediaType for symmetry.

Too late for Go 1.5.

If you wouldn't mind @rasky, could you provide me with some failing test samples or just values that should be accepted yet are failing? Thanks.

@odeke-em

fmt.Println(mime.ParseMediaType(`attachment; filename="????.png"; filename*=UTF-8''%E6%95%B0%E6%8D%AE%E7%BB%9F%E8%AE%A1.png`))
fmt.Println(mime.FormatMediaType("attachment", map[string]string{"filename": "数据统计.png"}))
fmt.Println(mime.FormatMediaType("attachment", map[string]string{"filename": "test.png"}))

Seems to be working with current Go (go1.11).

@andrius4669, does it? https://play.golang.org/p/ndwGaJDMBO4

I see:

attachment map[filename:数据统计.png] <nil>

attachment; filename=test.png

@zensh, do you expect the middle case to work? I guess it should encode it with UTF-8 the same way as the first line parses?

@bradfitz sorry, I didn't meant samples specified by zensh.
Initial issue about FormatMediaType and ParseMediaType not being symmetric about both allowing disposition has been fixed apparently, it now allows that.
It currently cannot encode non-ASCII unicode chatacters because it doesn't implement encoding specified in RFC 2231 section 4, and instead intentionally fail if it detects such input.
#28849 was somewhat related to this (and I was told to fill separate feature request about RFC2231 encoding).
I guess this issue could be used for discussion about that encoding, if you think this is right.

Sorta working on this now.

Change https://golang.org/cl/154760 mentions this issue: mime: encode CTL and non-US-ASCII characters in FormatMediaType

#29328

@andrius4669 👍