code: func interfaceByIP(ip string) (string, int, error) {
  	ifaces, err := netInterfaces()
  	if err != nil {
  		return "", 0, err
  	}
  
  	for _, iface := range ifaces {
  		ifaceIP, mask, err := ipByInterface(iface.Name)
  		if err == nil && ip == ifaceIP {
  			return iface.Name, mask, nil
  		}
  	}
  
  	return "", 0, fmt.Errorf("no matching interface found for IP %s", ip)
  }
docs: // interfaceByIP returns the local network interface name that is using the
  // specified IP address. Returns an error if no matching interface is found.