Cannot set headers after they are sent to the client error nodejs error

When I am trying to post login data in Postman I get an error Cannot set headers after they are sent to the client.

const router = require('express').Router();
const User = require('../models/user');
const Crypto = require('crypto-js');
const { response } = require('express');
const secretKey = process.env.SECRET_KEY;
//  Create a registration

router.post('/rejestracja', async (req, res)=>{
    const nowyUser = new User({
        email: req.body.email,
        password: Crypto.AES.encrypt(req.body.password, process.env.SEC_KEY).toString(),
        firstName: req.body.firstName,
        surname: req.body.surname,
        username: req.body.username,
    });
    try{
        const newedUser = await nowyUser.save();
        res.status(201).json(newedUser);
    }
    catch(err){res.status(500).json(err)};
})
 
// Create a login

router.post('/login', async (req, res) => {
    try{
        const user = await User.findOne({email: req.body.email});
        !user && res.status(401).json("i/lub hasło jest nieprawidłowy");
        

        const securedPass = Crypto.AES.decrypt( user.password, process.env.SECRET_KEY);
        const password = securedPass.toString(Crypto.enc.Utf8);
        
        password !== req.body.password && res.status(401).json("Email i/lub hasło jest nieprawidłowy");
        
        response.status(200).json(user);
        console.log("dziala");
    } 
    catch(err) {
        res.status(500).json({message: err.message});
    }
    
});


module.exports = router

Error Scr

I’ve tried to put process.env.SEC_KEY in this file but it doesn’t work

Answer

It seems that you’re trying to send response twice:

password !== req.body.password && res.status(401).json("Email i/lub hasło jest nieprawidłowy");
    
response.status(200).json(user);

Also you’re using response imported form the express. I’m not sure why you need it, but you probably should use the existing res instead.

All in all, I believe that the solution you’re looking for is this:

if (password !== req.body.password) {
  res.status(401).json("Email i/lub hasło jest nieprawidłowy");
} else {
  res.status(200).json(user);
}

Good luck 🙂