the request body couldn't be sent correctly if content set to 'application/json; charset=utf-8'

[lopaz]

the following code doesn't work:
wretch().content('application/json; charset=utf-8').url('http://...').post(json)

it seems that charset=utf-8 is not allowed:

wretch/src/wretcher.ts

Lines 199 to 206 in 2631890

	typeof body === "object" && (
	!headers ||
	Object.entries(headers).every(([k, v]) =>
	k.toLowerCase() !== CONTENT_TYPE_HEADER.toLowerCase() ||
	v === JSON_MIME
	)
	) ? this.json(body) :
	this.body(body)

wretch/src/wretcher.ts

Lines 12 to 13 in 2631890

	const JSON_MIME = "application/json"
	const CONTENT_TYPE_HEADER = "Content-Type"

not sure if this is a bug, since json is the default content-type and utf-8 is the default chareset for json, which means content('application/json; charset=utf-8') is totally redundant.

[elbywan]

Hi @lopaz, thanks for reporting the issue!

not sure if this is a bug, since json is the default content-type and utf-8 is the default chareset for json, which means content('application/json; charset=utf-8') is totally redundant.

I think this is a bug, wretch should never override a Content-Type header having a custom charset. I'll push a fix to prevent this behaviour!

With that said, in theory according to RFC-4627 for the application/json content type the encoding is determined by the first four bytes of the payload:

JSON text SHALL be encoded in Unicode.  The default encoding is UTF-8.

Since the first two characters of a JSON text will always be ASCII
characters [RFC0020], it is possible to determine whether an octet
stream is UTF-8, UTF-16 (BE or LE), or UTF-32 (BE or LE) by looking
at the pattern of nulls in the first four octets.

I also noticed that browsers often override the content-type value regardless of the fetch options. So in practice, in that context omitting the charset should not matter since browsers add the value themselves.

[elbywan]

I just released version 1.7.3 with the fix 📦. Feel free to reopen if I missed something 😉.

[lopaz]

@elbywan Good job. I didn't realize the charset-overwritten issue.

There's still another one, using wretch().content('application/json; charset=utf-8').url('http://...').post({foo: 'bar'}), the request payload would be [object Object] instead of {foo: 'bar'}, which made the request failed.

[elbywan]

@lopaz Good catch! I pushed a commit (af48887) that should solve the problem.

[lopaz]

Confirmed, fixed in 1.7.4 👍