var app = require('express')();
var server = app.listen(process.env.PORT || 3000);
var io = require('socket.io')(server);
// next line is the money
app.set('socketio', io);
exports.foo = function(req,res){
// now use socket.io in your routes file
var io = req.app.get('socketio');
io.emit('hi!');
}