Can I return an error(by application/json) in DecodeRequestFunc?

[Chise1]

like:

func decodePostProfileRequest(_ context.Context, r *http.Request) (request interface{}, err error) {
	var req postProfileRequest
	if e := json.NewDecoder(r.Body).Decode(&req.Profile); e != nil {
		return nil, e
	}
	return req, nil
}

I want to write some info to *http.request.Response. But I failed.
Can I only return info by err?

[Chise1]

I know it.