// external services have no instances
	if service.External() {
		return ""
	}
	ipa, ise := netip.ParseAddr(service.DefaultAddress)
	if ise != nil {
		return ""
	}
	ip := ipa.As4()
	ip[2] = byte(1)
	ip[3] = byte(version)
	return netip.AddrFrom4(ip).String()

		return "", fmt.Errorf("netaddr.ParseIP(%q): invalid IP address", orig)
	}
	if strings.Contains(s[i+1:], ".") {
		ip, err := parseIPv4Slow(s[i+1:])
		if err != nil {
			return "", err
		}
		a4 := ip.As4()
		s = fmt.Sprintf("%s:%02x%02x:%02x%02x", s[:i], a4[0], a4[1], a4[2], a4[3])
	}

	// Find and expand a ::, if any.
	fs := strings.Split(s, "::")
	switch len(fs) {
	case 1:
		// No ::, nothing to do.

		if ipa, _ := netip.ParseAddr(host); ipa.IsValid() {
			// Use the 4-byte representation of the IP address when possible.
			ip := ipa.AsSlice()
			if ipa.Is4In6() {
				eip := ipa.As4()
				ip = eip[:]
			}
			ids = append(ids, Identity{Type: TypeIP, Value: ip})
		} else if strings.HasPrefix(host, spiffe.URIPrefix) {
			ids = append(ids, Identity{Type: TypeURI, Value: []byte(host)})
		} else {

	addr := ap.Addr()
	if !addr.Is4() {
		return syscall.SockaddrInet4{}, &AddrError{Err: "non-IPv4 address", Addr: addr.String()}
	}
	sa := syscall.SockaddrInet4{
		Addr: addr.As4(),
		Port: int(ap.Port()),
	}
	return sa, nil
}

func addrPortToSockaddrInet6(ap netip.AddrPort) (syscall.SockaddrInet6, error) {
	// ipToSockaddrInet6 has special handling here for zero length slices.