code: function attachToHttpServer(httpServer, onConnectionCallback) {
    // socket.io 
    var socketIoOptions = extend({}, {
      path: config.socketPath
    });
    var sockets = io.listen(httpServer, socketIoOptions);
    debug("Attaching to http.Server");
    return attachToSocketIo(sockets, onConnectionCallback);
  
  }
docs: Listen for socket.io events on httpServer.
  
  @param {http.Server} httpServer. The server to attach socket.io to.
  @param {Function} onConnectionCallback. Called when a socket client connects.
  - @param {Error} err. Null if nothing bad happened.
  - @param {EventEmitter} client. Event client.