App crashes, after the verification of jwt token-CodePudding

Firstly, I added the token in post request, then it successfully gives the response message "Email verified".

But after, the user's jwt token is verified, then suddenly app crashes and throws the error:

node:internal/process/promises:246
          triggerUncaughtException(err, true /* fromPromise */);
          ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at new NodeError (node:internal/errors:363:5)
    at ServerResponse.setHeader (node:_http_outgoing:574:11)
    at ServerResponse.header (E:\WEB_DEV\frontend2\backend\node_modules\express\lib\response.js:771:10)
    at ServerResponse.send (E:\WEB_DEV\frontend2\backend\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (E:\WEB_DEV\frontend2\backend\node_modules\express\lib\response.js:267:15)
    at E:\WEB_DEV\frontend2\backend\middleware\authMiddleware.js:28:37
    at processTicksAndRejections (node:internal/process/task_queues:96:5) {
  code: 'ERR_HTTP_HEADERS_SENT'
}
[nodemon] app crashed - waiting for file changes before starting...

Here is the token verification code:

const jwt = require('jsonwebtoken');
const client = require('../configs/database');

exports.verifyToken = (req, res) => {
    const token = req.headers.authorization;
    jwt.verify(token, process.env.SECRET_KEY, (err, decoded) => {
        if (err) {
            res.status(500).json({
                error: "Server error found"
            })
        }
        console.log(decoded.email);
        const userEmail = decoded.email;
        client.query(`SELECT * FROM login WHERE email = '${userEmail}'`)
            .then((data) => {
                // console.log(data);
                if (data.rows.length == 0) {
                    res.status(404).send("Token not verified");
                }
                else {
                    req.email = userEmail;
                    res.status(200).send("Email verified");
                    next();   //problem occurs here**
                }
            })
            .catch((err) => {
                if (err) {
                    res.status(500).json({
                        message: "Database error occurred",
                        error: err,
                    })
                }

            })
    })
}

Cause of crash of app, "Middleware working" isn't displayed.

const express = require('express')
const router = express.Router();
const { verifyToken } = require('../middleware/authMiddleware');
// const { addProducts } = require('../controllers/products');


router.post("/add", verifyToken, (req, res) => {
    res.send("Middleware working");
})

CodePudding user response：

You should not use next() after sending a response.

So the solution here would be to use next() when the token is verified. So your req, res goes on to the /add route.

If the token is not valid you send a response like you do now.

So just remove res.status(200).send("Email verified");