How to use socket.io in app route

I develop my first project with nodejs. I use express 3 as framework and socket.io for the client server communication. At the moment I’m trying to create a register form. It works quite well, but I’m not sure how to use socket.io and express together correctly.

I check if the email and the password are valid, if they are not, I would like to push a json object the client.

I use this app route:

app.post('/user', function (req, res) {
    var user = new User(req.body.user), 
        errors;

    function userSaveFailed() {
        res.render('index');
    }

    errors = user.validation(req.body.user.confirm);
    user.save(errors, function (err) {
        if (err) {
            // Here I would like to send the Object to the client.
            io.sockets.on('connection', function (socket) {
                socket.emit('registration', {
                    errors : errors
                });
            });
            return userSaveFailed();
        }
        res.render('user/new.jade');
    });
});

Well, the client gets the json object, but if another client connects to '/' he also gets the object. I guess I use the socket.io wrong. What’s the common way to use a .emit() in an app route? Is it necessary to use a global authorization for socket.io and express for this test?