Gatsbill Gatsbill - 5 months ago 21
JSON Question

res.json Can't set headers after they are sent

I'm learning node Js and i'm trying to do a simple subscribe/log_in app.
I'm having issue with res.json not working as intended.

Got this error when i'm trying to subscribe : Can't set headers after they are sent

This is my server side script :

var express = require('express');
var swig = require('swig');
var ent = require('ent');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var session = require('express-session');

var app = express();

// Environnement
app.set('port', process.env.PORT || 3000);
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use("/public", express.static(__dirname + "/public"));
app.engine('html', swig.renderFile);
app.set('view engine', 'html');
app.set('views', __dirname + '/views');
app.set('view cache', false);
swig.setDefaults({ cache: false });
app.use(session({
secret: 'poussixthetruefighteroftheparadise',
saveUninitialized: true,
resave: true
}));

//MongoDB
var db = mongoose.connect('mongodb://127.0.0.1:27017/maBase');
var userSchema = new mongoose.Schema({
login: String,
mail: String,
password: String
});
var user = db.model('user', userSchema)

// variables globales
var state;




// Page Principale
app.get('/', function(req,res){

if (req.session.user) {
res.render('accueil.html',{});
} else {
res.redirect('/connection');
}

});

// Page connection
app.route('/connection')
.get(function(req, res) {

res.render('index.html',{});

if (req.session.state) {
res.json({state: req.session.state});
}

})
.post(function(req, res) {

user.find({login: req.body.login, password: req.body.password}).limit(1).exec(function (err, users) {

if (err) { console.log(err) };

if (!users.length) {

console.log('connection pas ok');

res.json({state: '5'});

}
else {

console.log('connection ok');
res.redirect('/');

}

});

});


// Ajouter Utilisateur
app.post('/connection/ajouter', function(req,res){

var login = req.body.login;
var mail = req.body.mail;

user.find({$or: [{login: login}, {mail: mail}]}).limit(1).exec(function (err, users) {

if (err) { console.log(err) };

if (!users.length) {

console.log('login et mail ok');

if (req.body.password == req.body.password2) {

if (req.body.password.length > 6) {

var values = new user({
login: ent.encode(req.body.login),
mail: ent.encode(req.body.mail),
password: ent.encode(req.body.password)
});

values.save(function(err, values) {

if (err) return console.error(err);

console.log('utilisateur enregistré');

req.session.state = '6';
res.redirect('/connection');

});

} else {

console.log('Mot de passe trop court');

req.session.state = '3';
res.redirect('/connection');

}


} else {

console.log('mot de passe différent');

req.session.state = '4';
res.redirect('/connection');

}

}

else {

console.log('login ou mail déja utilisé');

if (users[0].mail == mail) {

console.log('mail déja utilisé');
req.session.state = '2';
res.redirect('/connection');

} else {

console.log('login déja utilisé');
req.session.state = '1';
res.redirect('/connection');

}

console.log(users);

}

});

});




app.listen(app.get('port'), function(){
console.log('Express server listening on port ' + app.get('port'));
});


And my client side script :

<html>
<head>
<title>test</title>
<link rel="stylesheet" href="public/css/reset.css">
<link rel="stylesheet" href="public/css/connection.css">
</head>
<body>

<div id="content">

<a href="http://localhost:3000"><img src="public/images/icone.jpg" alt="gatsbill"></a>

<div id="wrap">

<div id="espacehaut"></div>
<div class="click" id="con" style="display: block;">Se connecter</div>
<div class="click" id="sub" style="display: none;">S'inscrire</div>

<div id="connection" style="display: none;">
<div id="message1" class="message" style="display: none;"></div>
<form action="/connection/" method="post" id="form_connection">
<input type="text" name="login" id="login" placeholder="Login" value="" required="" autofocus="">
<input type="password" name="password" id="password" placeholder="Password" required="">
<input type="submit" name="submit" value="Connect">
</form>
</div>

<div id="subscribe" style="">
<p id="p">Pour vous inscrire,<br> Veuillez remplir les champs ci-dessous</p>
<div id="message2" class="message" style="display: none;"></div>
<form action="/connection/ajouter/" method="post" id="form_inscription">
<input type="text" name="login" placeholder="Login" value="" required="" autofocus="">
<input type="email" name="mail" placeholder="Email" value="" required="">
<input type="password" name="password" placeholder="Password" required="">
<input type="password" name="password2" placeholder="Password" required="">
<input type="submit" name="submit" value="Create account">
</form>
</div>

<div id="espacebas"></div>

</div>
</div>

<!-- Script -->
<script src="http://code.jquery.com/jquery-1.10.1.min.js"></script>
<script type="text/javascript" src="public/js/connection.js"></script>
<script>

$.getJSON( "http://localhost:3000/connection", function(data){
if( data.state ) {
state = parseInt(data.state);
switch (state) {
case 1:
formulaire();
$("#message2").text("login déja utilisé");
break;

case 2:
formulaire();
$("#message2").text("mail déja utilisé");
break;

case 3:
formulaire();
$("#message2").text("Mot de passe trop court");
break;

case 4:
formulaire();
$("#message2").text("mot de passe différent");
break;

case 5:
connect();
$("#message1").text("connection pas ok");
break;

case 6:
connect();
$("#message1").text("vous pouvez maintenant vous connecter");
break;

}
}
});

</script>

</body>
</html>


When i'm trying to subscribe with two different password this is what I have :

A white page with only this :

{"state":"4"}

And of course this error in node Js console: Can't set headers after they are sent

Answer

Welcome to nodejs/express!

This is where you are getting your "Can't set headers after they are sent" error in the console:

// Page connection
app.route('/connection')
    .get(function(req, res) {

        res.render('index.html',{});

        if (req.session.state) {
            res.json({state: req.session.state});
        }

    })

In this configuration, res.render and res.json will both call res.end() which is basically like trying to send a response twice to the client.

You should place a return statement before res.render or set {state: req.session.state} as the second param to your res.render() call and then use a swig template to display that data.

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