Can't send headers after they are sent - node.js

Question

I am new to nodejs. I have been trying to create a simple login and register system using mongodb and express. I have created the entire app but with one error:
var express = require('express')
, passport = require('passport')
, util = require('util')
, LocalStrategy = require('passport-local').Strategy;
var bodyParser = require('body-parser');
var cookieParser = require('cookie-parser');
var session = require('express-session');
//var flash = require('connect-flash');
var monk = require('monk');
var db = monk('localhost:27017/loginsystem');
var collection = db.get('messagescollection');
function findById(id, fn) {
var collection = db.get('messagescollection');
collection.findOne({ _id: id }).on('success', function (doc) {
fn(null, doc);
});
}
function findByUsername(username, fn) {
collection.findOne({ username: username }).on('success', function(doc) {
return fn(null, doc);
});
return fn(null, null);
}
var app = express();
app.use(bodyParser.json()); // for parsing application/json
app.use(bodyParser.urlencoded({ extended: true })); // for parsing application/x-www-form-urlencoded
app.use(function(req,res,next){
req.db = db;
next();
});
app.use(cookieParser());
app.use(session({
secret: 'keyboard cat'
hours
}));
app.use(passport.initialize());
app.use(passport.session());
passport.serializeUser(function(user, done) {
console.log("user",user);
done(null, user._id);
});
passport.deserializeUser(function(id, done) {
console.log(id,"id");
findById(id, function (err, user) {
done(err, user);
});
});
passport.use(new LocalStrategy(
function(username, password, done) {
findByUsername(username, function(err, user) {
if (err) { return done(err); }
if (!user) { return done(null, false, { message: 'Unknown user ' + username }); }
if (user.password != password) { return done(null, false, { message: 'Invalid password' }); }
return done(null, user);
})
}
));
app.use(express.static(__dirname + '/public'));
app.get('/account', ensureAuthenticated, function(req, res){
res.send(req.user);
});
app.get('/login', function(req, res){
res.redirect("/login.html") //redirect back to homepage
});
app.get('/register', function(req, res) {
res.redirect("/register.html") //redirect back to homepage
})
app.post('/login', passport.authenticate('local', { failureRedirect: '/login'}), function(req, res) {
console.log("success",req.user);
res.redirect('/account');
});
app.post('/register', function(req, res) {
console.log(req.body);
// Submit to the DB
collection.insert({
"username" : req.body.username,
"email" : req.body.email,
"password" : req.body.password
}, function (err, doc) {
if (err) {
// If it failed, return error
res.send("There was a problem adding the information to the database.");
}
else {
//res.redirect('/account');
}
});
});
app.get('/logout', function(req, res){
req.logout();
res.redirect('/');
});
app.listen(9000);
function ensureAuthenticated(req, res, next) {
console.log("req.user",req.user,req.session);
if (req.isAuthenticated()) { return next(); }
res.redirect('/login');
}
When I register, the user is added to the database. And it is redirected to /login but when I login then I get this error:
Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:335:11)
at ServerResponse.header (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/express/lib/response.js:700:10)
at ServerResponse.res.location (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/express/lib/response.js:814:8)
at ServerResponse.redirect (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/express/lib/response.js:853:8)
at /home/mareebsiddiqui/SummerOfCode/loginsystem/app.js:130:7
at Layer.handle [as handle_request] (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/express/lib/router/layer.js:82:5)
at next (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/express/lib/router/route.js:110:13)
at complete (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/passport/lib/middleware/authenticate.js:243:13)
at /home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/passport/lib/middleware/authenticate.js:250:15
at pass (/home/mareebsiddiqui/SummerOfCode/loginsystem/node_modules/passport/lib/authenticator.js:427:14)
How could I resolve this issue? Thanks.
EDIT: I know that there are many questions with the same title but there problems are different. This error is caused by many different situations and my situation is different from others. I have a problem of redirects whereas other questions have problems of ending a response.

Answer 1

You should use return response.<method>. For example, return response.redirect().
Also, response.end() might be helpful.