Can't set headers after they are sent NodeJS Express

Question

Im new to NodeJS and when i try to login with an email and password I get the following error: (Part of it)

Error: Can't set headers after they are sent. at validateHeader (_http_outgoing.js:491:11) at ServerResponse.setHeader (_http_outgoing.js:498:3) at ServerResponse.header (C:\Users\asuss\Desktop\server\node_modules\express\lib\response.js:771:10) at ServerResponse.location (C:\Users\asuss\Desktop\server\node_modules\express\lib\response.js:888:15) at ServerResponse.redirect (C:\Users\asuss\Desktop\server\node_modules\express\lib\response.js:926:18) at app.post (C:\Users\asuss\Desktop\server\app.js:114:9) at Layer.handle [as handle_request] (C:\Users\asuss\Desktop\server\node_modules\express\lib\router\layer.js:95:5) at next (C:\Users\asuss\Desktop\server\node_modules\express\lib\router\route.js:137:13)
at redirectHome (C:\Users\asuss\Desktop\server\app.js:42:9) at Layer.handle [as handle_request] (C:\Users\asuss\Desktop\server\node_modules\express\lib\router\layer.js:95:5) Error: Can't set headers after they are sent. at validateHeader (_http_outgoing.js:491:11) at ServerResponse.setHeader (_http_outgoing.js:498:3) at ServerResponse.header (C:\Users\asuss\Desktop\server\node_modules\express\lib\response.js:771:10) at ServerResponse.location (C:\Users\asuss\Desktop\server\node_modules\express\lib\response.js:888:15)

const express = require('express')
const session = require('express-session')
const bodyParser = require('body-parser')

const users = [
    {id: 1, name: 'Alex', email:'[email protected]', password:"123"},
    {id: 2, name: 'Max', email:'[email protected]', password:"123"},
    {id: 3, name: 'Tiffany', email:'[email protected]', password:"123"}
]

const app = express()

app.use(bodyParser.urlencoded({
    extended: true
}))

app.use(session({
    name: 'sid',
    resave: false,
    saveUninitialized: false,
    secret: "nikivekartal",
    cookie: {
        maxAge: 1000*60*60*2,
        sameSite: true,
    }
}))

const redirectLogin = (req, res, next) => {
    if(!req.session.userId){
        res.redirect('/login')
    }
    else {
        next()
    }
}

const redirectHome = (req, res, next) => {
    if(req.session.userId){
        res.redirect('/home')
    }
    else {
        next()
    }
}

app.get('/', (req, res) => {
    const {userId} = req.session;
    console.log("Session", req.session.userId)
    res.send(`
    <h1>Welcome!</h1>
    ${userId ? `  
    <a href='/home'>Home</a>
    <form method='post' action='/logout'>
        <button>Logout</button>
    </form>
    ` : `
    <a href='/login'>Login</a>
    <a href='/register'>Register</a>
    `}`)
})

app.get('/home', redirectLogin, (req, res) => {
    res.send(`
    <h1>Home</h1>
    <a href='/'>Main</a>
    <ul>
        <li>Apple</li>
        <li>Cherry</li>
    </ul>
    `)
})

// redirectHome mddleware ini eğer user authenticate olmuşsa login'e gitmesin
// home'a gitsin diye koyuyoruz
app.get('/login', redirectHome, (req, res) => {
    res.send(`
    <h1>Login</h1>
    <form method='post' action='/login'>
        <input type='email' name='email' placeholder='Email' required/>
        <input type='password' name='password' placeholder='Password' required/>
        <input type='submit' />
    </form>
    <a href='/register'>Register</a>
    `)
})

app.get('/register', redirectHome, (req, res) => {
    res.send(`

    <h1>Register</h1>
    <form method='post' action='/register'>
        <input name='name' placeholder='Name' required />
        <input type='email' name='email' placeholder='Email' required/>
        <input type='password' name='password' placeholder='Password' required/>
        <input type='submit' />
    </form>
    `)
})

app.post('/login', redirectHome, (req, res) => {
    const {email, password} = req.body

    if(email && password){
        const user = users.find(
            user => user.email === email && user.password === password
        )

        if(user){
            req.session.userId = user.id
            res.redirect('/home')
        }
    }

    res.redirect('/login')
})

app.post('/register', redirectHome, (req, res) => {

})

app.post('/logout', redirectLogin, (req, res) => {

})

app.listen(process.env.PORT || 3000, () => {
    console.log("Server is running");
})

What should I do and why? Thank you for your consideration.

I had this error when i was trying to do a res.render(), while having already done one. I mean, for one user request on a route, i would do two responses. Two different res.renders(), one in the beginning and one after a labor intensive work finishes. The HTTP protocol is 1 response per 1 request. — user1584421

jfriend00 jfriend00 · Accepted Answer · 2019-09-28T17:44:16

Your /login route can call res.redirect() twice. Add a return after one of them to change this:

app.post('/login', redirectHome, (req, res) => {
    const {email, password} = req.body

    if(email && password){
        const user = users.find(
            user => user.email === email && user.password === password
        )

        if(user){
            req.session.userId = user.id
            res.redirect('/home')
        }
    }

    res.redirect('/login')
});

to this:

app.post('/login', redirectHome, (req, res) => {
    const {email, password} = req.body

    if(email && password){
        const user = users.find(
            user => user.email === email && user.password === password
        )

        if(user){
            req.session.userId = user.id
            res.redirect('/home')
            return;                   // <== add this return
        }
    }

    res.redirect('/login')
});

Can't set headers after they are sent NodeJS Express

1 Answers