code: private void endWithMessage(ServerHttpExchange http, String data) {
        endedWithMessage.set(true);
        boolean jsonp = "true".equals(params.get("cettia-transport-jsonp"));
        if (jsonp) {
          try {
            data = params.get("cettia-transport-callback") + "(" + mapper.writeValueAsString(data) + ");";
          } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
          }
        }
        http.setHeader("content-type", (jsonp ? "text/javascript" : "text/plain") + "; charset=utf-8").end(data);
      }
docs: Regard it as http.endWithMessage