Mongodb 错误：发送到客户端后无法设置标头

Question

I am basically creating a user registration form where I check if the submitted passwords match and then check if the user already exists by querying the collection to see if the submitted username or email already exist. If all of the data passed the checks then I create I new user. My issue is that if the username or email already exist then the user is still created. Shouldn't returning a status if a user is found stop the function?

Front end submission:

submitNewUser() {
    axios.post('http://localhost:5000/api/settings/users', {
         name: this.newUser.name,
         username: this.newUser.username,
         email: this.newUser.email,
         password: this.newUser.password,
         confirm_password: this.newUser.confirm_password,
         role: this.newUser.role
    })
    .then(() => {
        this.getUsers();
    })
    .catch(error => {
        console.log(error);
    })
}

The user has to be signed in to create a new user so I user passport check if token contains a valid user

passport authentication check:

const JwtStrategy = require('passport-jwt').Strategy;
const ExtractJwt = require('passport-jwt').ExtractJwt;
const User = require('../models/User');
const key = require('./keys').secret;

const opts = {};
opts.jwtFromRequest = ExtractJwt.fromAuthHeaderAsBearerToken();
opts.secretOrKey = key;

module.exports = passport => {
    passport.use(
        new JwtStrategy(opts, (jwt_payload, done) =>{
            User.findById(jwt_payload._id).then(user => {
                if (user) return done(null, user);
                return done(null, false);
            }).catch(err => {
                console.log(err);
            });
        })
    );
};

End route:

router.post('/users', passport.authenticate('jwt', {
    session: false
}), (req, res) => {
    let companyId = req.user.company_id;

    let {
        name,
        username,
        email,
        password,
        confirm_password,
        role,
    } = req.body;

    //Check that passwords match
    if( password !== confirm_password ) {
        return res.status(400).json({
            msg: "Passwords do not match"
        })
    }

    //Check for unique username 
    User.findOne({ username: username })
        .then(user => {
            console.log('username')
            if(user) {
                return res.status(400).json({
                    msg: "Username is already taken."
                });
            }
        })
        .catch(error => console.log(error));

    //check for unique email
    User.findOne({ email: email })
        .then(user => {
            console.log('email')
            if(user) {
                return res.status(400).json({
                    msg: "Email is already registered. Did you forget your password?"
                });
            }
        })
        .catch(error => console.log(error));

    let newUser = new User({
        name,
        username,
        password,
        email,
        user_role: role,
        company_id: companyId,
    });

    // Hash password
    bcrypt.genSalt(10, (err, salt) => {
        bcrypt.hash(newUser.password, salt, (err, hash) => {
            if(err) throw err;
            newUser.password = hash;
            newUser.save()
                .then(user => {
                    return res.status(201).json({
                        success: true,
                        msg: "User is now registered."
                    });
                })
                .catch(error => console.log(error));
        });
    });
});

This is an error that I get if the user already exists:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:482:11)
    at ServerResponse.header (C:\Users\Reece\OneDrive\Desktop\Fyber Docs\Valentis-Pipeline-MEVN-App\node_modules\express\lib\response.js:771:10)
    at ServerResponse.send (C:\Users\Reece\OneDrive\Desktop\Fyber Docs\Valentis-Pipeline-MEVN-App\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (C:\Users\Reece\OneDrive\Desktop\Fyber Docs\Valentis-Pipeline-MEVN-App\node_modules\express\lib\response.js:267:15)
    at User.findOne.then.user (C:\Users\Reece\OneDrive\Desktop\Fyber Docs\Valentis-Pipeline-MEVN-App\server\routes\api\settings.js:106:40)
    at processTicksAndRejections (internal/process/next_tick.js:81:5)

Answer 1

Due to the async nature, (req, res) => { is returning before any of your calls to mongodb are either succeeding or failing, yet you still use the res object to send a response back to the client.

I don't know exactly how to deal with this in the framework you're using, but the framework appears to populate res 's header with data and send it back to the client before you start to modify the res object.