code: func (process *TeleportProcess) createListener(listenerType, address string) (net.Listener, error) {
  	listener, err := net.Listen("tcp", address)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	process.Lock()
  	defer process.Unlock()
  	r := RegisteredListener{Type: listenerType, Address: address, Listener: listener}
  	process.registeredListeners = append(process.registeredListeners, r)
  	return listener, nil
  }
docs: // createListener creates listener and adds to a list of tracked listeners