code: func IsProxyableHostname(ctx context.Context, resolv Resolver, hostname string) error {
  	resp, err := resolv.LookupIPAddr(ctx, hostname)
  	if err != nil {
  		return err
  	}
  
  	if len(resp) == 0 {
  		return ErrNoAddresses
  	}
  
  	for _, host := range resp {
  		if err := isProxyableIP(host.IP); err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // IsProxyableHostname checks if the IP addresses for a given hostname are permitted to be proxied