UnhandledPromiseRejectionWarning: 错误 [ERR_HTTP_HEADERS_SENT] - setInterval & Axios.post 错误处理

Question

I've tried to handle this warning via Googling. However, as I couldn't solve this warning, I'm asking this question.

The following warning is what I'm facing now:

(node:39452) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:485:11)
    at ServerResponse.header 
...
    at ServerResponse.send 
...
    at ServerResponse.json 
...
    at ServerResponse.send 
...
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async Timeout.priceAlarm [as _onTimeout] 
(node:39452) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)

When "priceAlarm" is called, it is okay. However, when "intervalPriceAlarm = setInterval(priceAlarm, 3000, res, chatId);"is done, it shows the warning at axios.post... catch(error) part.

Does anyone have good idea to handle it?

Thank you.

function priceAlarm(res, chatId) {
                axios
                  .get(url)
                  .then((response) => {
                    currentBtcBitfinexUsd = getPrice(
                      response.data.tickers,
                      "BTC",
                      "USD",
                      "bitfinex"
                    );

                    axios
                      .post( `${telegramBotUrl}${apiToken}/sendMessage`, {
                        chat_id: chatId,
                        text:
                          "\nBitfinex- BTC(USD):" +
                          currentBtcBitfinexUsd,
                      })
                      .then((response) => {
                        res.status(200).send(response);
                      })
                      .catch((error) => {
                        res.send(error); //****this part shows an error!*****
                      });

                  })
                  .catch((error) => {
                    console.log(error);
                  });
} 

function intervalAlarm(res,chatId){
  if (alarmFlag == 1 && intervalPriceAlarm == null) {
    intervalPriceAlarm = setInterval(priceAlarm, 3000, res, chatId);
    console.log(intervalPriceAlarm); //need to remove it
  }else{
    console.log("doing nothing");
  }
}

app.post("/", (req,res) =>{ 
     const chatId = req.body.message.chat.id;
     const sentMessage = req.body.message.text;

     if (sentMessage.match(/price/gi)) {
       priceAlarm(res, chatId); //No problem at all
     } else if (sentMessage.match(/start/gi)) {
       alarmFlag=1;       
       res.status(200).send({});
     } else if(sentMessage.match(/stop/gi)){
       alarmFlag=0;
       res.status(200).send({});
     } else {
       res.status(200).send({});
     }
    intervalAlarm(res,chatId);  // here setInterval part.
});

Answer 1

This is a server-side error due to the fact that the server can't re-write HTTP headers of a response it already sent to the client. Consequently, you can't res.send() twice the same res , but you do it in your code

// here the first time
priceAlarm(res, chatId); //No problem at all

// here the second time
intervalAlarm(res,chatId);  // here setInterval part.

You'll have to rewrite your code, because that's a base behavior of HTTP that the server can't send data to the client after sending a response already. So that's not an express problem, that's an HTTP limitation. If you want your server to be able to "push" data to your client, you'll have to use websockets instead.