code: func (n *discovery) AddMapping(protocol string, extPort, intPort int,
  	name string, lifetime time.Duration) error {
  	if err := n.wait(); err != nil {
  		return err
  	}
  	return n.found.AddMapping(protocol, extPort, intPort, name, lifetime)
  }
docs: // AddMapping maps an external port to a local port for a specific
  // service.