Content-Length invalid for unicode text

[to-miz]

When generating a http request string, the content-length seems to be calculated using the number of codepoints instead of bytes.
This was generated using insomnia, which uses httpsnippet:

POST /api/v1/test HTTP/1.1
Content-Type: text/plain
User-Agent: insomnia/2023.5.8
Host: localhost:5003
Content-Length: 3

äöü

This is what insomnia actually sends when executing the request (visualized using nc -l localhost 5003)

$ nc -l localhost 5003
POST /api/v1/test HTTP/1.1
Host: localhost:5003
Content-Type: text/plain
User-Agent: insomnia/2023.5.8
Accept: */*
Content-Length: 6

äöü

[erunion]

This is happening because the length is calculated with an ascii encoding instead of utf8.

https://github.com/Kong/httpsnippet/blob/master/src/targets/http/http1.1/client.ts#L72