code: func (r *Resolver) Lookup(instance, service, domain string, entries chan<- *ServiceEntry) error {
  	params := defaultParams(service)
  	params.Instance = instance
  	if domain != "" {
  		params.Domain = domain
  	}
  	params.Entries = entries
  
  	go r.c.mainloop(params)
  
  	err := r.c.query(params)
  	if err != nil {
  		r.Exit <- true
  		return err
  	}
  
  	return nil
  }
docs: // Look up a specific service by its name and type in a given domain