How to configure F# JSON type provider to use UTF-8 for POST requests?

I need to encode as UTF-8 HTTP payloads sent using F# JSON type provider JsonValue.Request method.

The Request allows specifying HTTP headers but JSON type provider takes care of setting Content-Type header as "application/json" without specifying "charset" qualifier. If I try to set content type myself I end up with duplicate header value (causing an error indeed). And with only "application/json" the following code selects defauls encoding:

let getEncoding contentType =
    let charset = charsetRegex.Match(contentType)
    if charset.Success then
        Encoding.GetEncoding charset.Groups.[1].Value
    else
        HttpEncodings.PostDefaultEncoding

PostDefaultEncoding is is ISO-8859-1 which is not suitable in our scenario.

Any idea how PostDefaultEncoding can be overridden for JsonValue.Request payload?

I think the JsonValue.Request method is just a convenient helper that covers the most common scenarios, but does not necessarily give you all the power you need for making arbitrary requests. (That said, UTF-8 sounds like a more reasonable default.)

The most general F# Data function is Http.Request, which lets you upload data in any way:

let buffer = System.Text.Encoding.UTF8.GetBytes "👍👍👍"
Http.RequestString
  ( "https://httpbin.org/post", 
    httpMethod="POST", 
    body=HttpRequestBody.BinaryUpload buffer )

So, if you replace "👍👍👍" with yourJsonValue.ToString(), this should send the request with UTF-8 encoded body.