Error: can't set header after they are sent - node.js

Question

I have two schemas, one for user and one for friendship system (follow system)
module.exports = mongoose.model('User', {
email: {
type: String,
unique: true,
lowercase: true
},
password:String,
profile: {
fullname: String,
gender: String,
role: {type: String, default: 'Autorizado'},
country: String },
});
and this for friend system
module.exports = mongoose.model('Friendship', {
follower: String,
followed: String
});
I'm using passport to auth my users... the problem is that I want lo load the user information and the friend information related to the user globally using res.locals I make this happen using 2 functions in login post route....
router.post('/login', userController.postLogin,friendController.getFollow);
this is my postlogin function
exports.postLogin = function(req, res, next) {
passport.authenticate('local', function(err, user, info) {
if (err) return next(err);
if (!user) {
req.flash('errors', { msg: info.message });
return res.redirect('/login');
}
req.logIn(user, function(err) {
if (err) return next(err);
req.flash('success', { msg: 'Success! You are logged in.' });
res.redirect('/');
});
})
(req, res, next);
};
When I try to execute this code everything goes fine but when I log in I get the header error please how can I solved this or other way to get the user and follow information and use it in every view?.
EDIT 3: only works in the next two views
Single User page
<%= info.profile.fullname %>
<br>
<%= info.email %>
<br>
<%= info.profile.country %>
<br>
<%= user.follow %>
<br>
<% if(user && (user._id != info.id)){ %>
<br>
<form action="/follow/<%= info._id %>" method="post">
<button type="submit">Follow</button></form>
<%}%>
<br>
atras
List of Registered User
<%if (user) {%>
<h1>Hola <%= user.profile.fullname %> </h1>
<%}%>
<br>
<% users.forEach(function (user) {%>
<p><%= user.profile.fullname %></p>
<%});%>
Home
This is my index and in this view the user.follow doesn't work
<%if (!user) {%>
sign up
<br>
login
<%} else { %>
<h1>Hola <%= user.profile.fullname %> Eres lo Maximo</h1>
perfil
<br>
Logout
<br>
<%}%>
<br>
Lista de Usuarios
EDIT 4: new deserializeUser config.
passport.deserializeUser(function(id, done) {
User.findById(id, function(err, user) {
FF.find({ follower:id }, function(err, follow) {
user.follow = follow;
});
done(err, user);
});
});
EDIT 5: This is my route code
router.get('/', function(req, res) {
res.render('index');
});
router.get('/login', userController.getLogin);
router.post('/login', userController.postLogin);
router.get('/logout', userController.logout);
router.get('/signup', userController.getSignup);
router.post('/signup', userController.postSignup);
router.get('/profile', passportConf.isAuthenticated, userController.getAccount);
router.post('/profile', passportConf.isAuthenticated, userController.postUpdateProfile);

Answer 1

You had friendController.getFollow which would've worked only for the request of '/login' page, so the follow object wouldn't have been persistently available on other routes. To fix that you had to put all that code inside the passport.deserializeUser function.
Inside the passport.deserializeUser function you could only call done once so you had to put the logic to find follow inside the callback of User.find so that you could attach follow to user.
This allowed you to remove the friendController.getFollow from your '/login' route which I think was the cause of your error.