1package dnsutil
2
3import (
4	"net"
5	"strings"
6)
7
8// ExtractAddressFromReverse turns a standard PTR reverse record name
9// into an IP address. This works for ipv4 or ipv6.
10//
11// 54.119.58.176.in-addr.arpa. becomes 176.58.119.54. If the conversion
12// fails the empty string is returned.
13func ExtractAddressFromReverse(reverseName string) string {
14	search := ""
15
16	f := reverse
17
18	switch {
19	case strings.HasSuffix(reverseName, IP4arpa):
20		search = strings.TrimSuffix(reverseName, IP4arpa)
21	case strings.HasSuffix(reverseName, IP6arpa):
22		search = strings.TrimSuffix(reverseName, IP6arpa)
23		f = reverse6
24	default:
25		return ""
26	}
27
28	// Reverse the segments and then combine them.
29	return f(strings.Split(search, "."))
30}
31
32// IsReverse returns 0 is name is not in a reverse zone. Anything > 0 indicates
33// name is in a reverse zone. The returned integer will be 1 for in-addr.arpa. (IPv4)
34// and 2 for ip6.arpa. (IPv6).
35func IsReverse(name string) int {
36	if strings.HasSuffix(name, IP4arpa) {
37		return 1
38	}
39	if strings.HasSuffix(name, IP6arpa) {
40		return 2
41	}
42	return 0
43}
44
45func reverse(slice []string) string {
46	for i := 0; i < len(slice)/2; i++ {
47		j := len(slice) - i - 1
48		slice[i], slice[j] = slice[j], slice[i]
49	}
50	ip := net.ParseIP(strings.Join(slice, ".")).To4()
51	if ip == nil {
52		return ""
53	}
54	return ip.String()
55}
56
57// reverse6 reverse the segments and combine them according to RFC3596:
58// b.a.9.8.7.6.5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2
59// is reversed to 2001:db8::567:89ab
60func reverse6(slice []string) string {
61	for i := 0; i < len(slice)/2; i++ {
62		j := len(slice) - i - 1
63		slice[i], slice[j] = slice[j], slice[i]
64	}
65	slice6 := []string{}
66	for i := 0; i < len(slice)/4; i++ {
67		slice6 = append(slice6, strings.Join(slice[i*4:i*4+4], ""))
68	}
69	ip := net.ParseIP(strings.Join(slice6, ":")).To16()
70	if ip == nil {
71		return ""
72	}
73	return ip.String()
74}
75
76const (
77	// IP4arpa is the reverse tree suffix for v4 IP addresses.
78	IP4arpa = ".in-addr.arpa."
79	// IP6arpa is the reverse tree suffix for v6 IP addresses.
80	IP6arpa = ".ip6.arpa."
81)
82