当我尝试从 MongoDB 到 postman 获取发布数据时，出现无法设置 header 错误

Question

const router = require("express").Router();
const user = require("../models/user");
const cryptoJs = require("crypto-js");
const dotenv = require("dotenv").config();

router.post("/register", async (req, res) => {
    const newUser = new user({
        username: req.body.username,
        password: cryptoJs.AES.encrypt(req.body.password, process.env.pass),
    });

    try {
        const savedUser = await newUser.save();
        res.status(201).json(savedUser);
    } catch (error) {
        res.status(500).json(error);
    }
});

router.post("/login", async (req, res) => {
    try {
        const oneUser = await user.findOne({ username: req.body.username });
        if (!oneUser) {
            res.status(401).json("Wrong credentials");
        }

        const hp = cryptoJs.AES.decrypt(oneUser.password, process.env.pass);
        const password = hp.toString(cryptoJs.enc.Utf8);

        if (password !== req.body.password) {
            res.status(401).json("Wrong credentials");
        }

        res.status(200).json(oneUser);
    } catch (error) {
        res.sendStatus(500).json(error);
    }
});

module.exports = router;

//so, there is the code. everything works fine up to the /login section, when I input the right username and password, it gets me the matching user from the database, but when I input the wrong username and the right password immediately after. it says "wrong credentials which is also fine, But when I input the wrong password after all the previous inputs, it brings this error " Cannot set headers after they are sent to the client enter code here "

Answer 1

The set header error when will display that you send/return two "res" so use you have to use if-else not if

Answer 2

So the problem is that you send a response to the client, while you already sent a response to the client. When the password is different, you send "Wrong Credentials", but the script will also try to send the oneUser Mongo Object.

To get rid of that, either use an if.. else.. like @Evan proposed, either return the response so you're sure that the script stop there.

The "if/else" solution

if (password !== req.body.password) {
     res.status(401).json("Wrong credentials");
}
else {
     res.status(200).json(oneUser); // will be sent if the condition before is not completed
}

The "return" solution

if (password !== req.body.password) {
     return res.status(401).json("Wrong credentials"); // if the password is different, this will stop the script here
}

res.status(200).json(oneUser);

Answer 3

its better you improve youre block condition like

if (condition){
// do something 
}
else {
//do something else
}

OR you can return youre response. it means that when you want to send response return something and exit from the function. this solution in your code is

router.post("/register", async (req, res) => {
    const newUser = new user({
        username: req.body.username,
        password: cryptoJs.AES.encrypt(req.body.password, process.env.pass),
    });

    try {
        const savedUser = await newUser.save();
       return res.status(201).json(savedUser);
    } catch (error) {
       return res.status(500).json(error);
    }
});

router.post("/login", async (req, res) => {
    try {
        const oneUser = await user.findOne({ username: req.body.username });
        if (!oneUser) {
       return res.status(401).json("Wrong credentials");
        }

        const hp = cryptoJs.AES.decrypt(oneUser.password, process.env.pass);
        const password = hp.toString(cryptoJs.enc.Utf8);

        if (password !== req.body.password) {
           return res.status(401).json("Wrong credentials");
        }

        return res.status(200).json(oneUser);
    } catch (error) {
        return res.sendStatus(500).json(error);
    }
});