code: func WriteJSON(w http.ResponseWriter, obj interface{}) error {
  	writeContentType(w, jsonContentType)
  	jsonBytes, err := json.Marshal(obj)
  	if err != nil {
  		return err
  	}
  	_, err = w.Write(jsonBytes)
  	return err
  }
docs: // WriteJSON marshals the given interface object and writes it with custom ContentType.