code: func (h *Hosts) Lookup(host string) (ip net.IP) {
  	if h == nil || host == "" {
  		return
  	}
  
  	h.mux.RLock()
  	defer h.mux.RUnlock()
  
  	for _, h := range h.hosts {
  		if h.Hostname == host {
  			ip = h.IP
  			break
  		}
  		for _, alias := range h.Aliases {
  			if alias == host {
  				ip = h.IP
  				break
  			}
  		}
  	}
  	if ip != nil && Debug {
  		log.Logf("[hosts] hit: %s %s", host, ip.String())
  	}
  	return
  }
docs: // Lookup searches the IP address corresponds to the given host from the host table.