Header should not be set before the message is written #1175

This is a function generated for a strict echo server:

func (response GetUsers200JSONResponse) VisitGetUsersResponse(w http.ResponseWriter) error {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(200)

	return json.NewEncoder(w).Encode(response)
}

The problem is that the response object here can still fail validation (in my case, if I set "abc" in the email field, I get an error from the JSON marshalling function) and thus return an error - but the header is already set (and sent) to 200, so the respnse will have a status code of 200 - no matter what middlewares/error handlers are used (request also gets r.Commited = true on WriteHeader).

I think the proper way of implementing this function would be something like

func (response GetUsers200JSONResponse) aVisitGetUsersResponse(w http.ResponseWriter) error {
   err := json.NewEncoder(w).Encode(response)
   if err != nil {
   	return err    
   }

   w.Header().Set("Content-Type", "application/json")
   w.WriteHeader(200)
   return nil
}