Wrong headers definition in withDecoder

[valeriobelli]

Is your feature request related to a problem? Please describe.
Inside the withDecoder combinator is used the withHeaders to inject automatically the headers:

• Accept: application/json
• Content-Type: application/json

The ratio is clear and it's to indicate to a backend service the needs of a JSON-like response body to be decoded. Actually, this need is indicated using the Accept request header, as described by https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept.

Therefore, the Content-Type: application/json that is injected automatically ends to be useless since a request can be sent also with other types of data that should/could be defined by the end-user. Moreover, it can also be a source of bugs if it's put at the end of a functional pipeline, as in the following example:

pipe(
  request,
  withHeaders({ 
    'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8'
  }),
  withDecoder(codec),
)

Describe the solution you'd like

The solution I thought is pretty simple: removing the Content-Type from the withHeaders combinator used inside withDecoder combinator moving the responsibility of setting the media type with Content-Type to the end-user.

[StefanoMagrassi]

@DrugoLeb thank you for your hint.

I changed the tag of the issue into "bug" because, as you pointed out, the Content-Type header on request side can be other than application/json and a different value provided by the user could be wrongly overriden