AsciiJSON is incorrect w.r.t RFC4627

[rickb777]

render/json.go defines AsciiJSON and some internal names jsonContentType, jsonpContentType, jsonAsciiContentType. This shows a misunderstanding of RFC4627 section 3: "JSON text SHALL be encoded in Unicode".

From the RFC, it follows

• the content type application/json implies that the content is UTF-8 or UTF-16 or UTF-32 - the RFC describes how the decoder detects the correct UTF from the first bytes.
• it is not helpful to use the term ASCII, even if the JSON content happens to be an ASCII-subset of UTF-8

AsciiJSON doesn't do what its name suggests. It should be deprecated (and later removed)

Because Go strings are UTF-8 by default, it is equally correct to use the content-type with charset (application/json;charset=utf-8) and without charset (application/json). The longer form takes a few more bytes but eliminates the (tiny) chance of there being a faulty decoder at the other end and it getting it wrong.

But if someone wants to force the encoding to be some other UTF (e.g. UTF-16 for Asian content), there isn't a way to do that in Gin and maybe that's what is needed. For Asian content, the advantage would be that the UTF-16 encoding would take fewer bytes (a bit less than two-thirds) than UTF-8 encoding for the same content.

So perhaps replace AsciiJSON with JSON_UTF16LE and JSON_UTF16BE. The render methods would need to ensure that the written content is correctly transcoded into the chosen UTF-16 encoding.