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package dnsutil
import (
"net"
"strings"
)
// ExtractAddressFromReverse turns a standard PTR reverse record name
// into an IP address. This works for ipv4 or ipv6.
//
// 54.119.58.176.in-addr.arpa. becomes 176.58.119.54. If the conversion
// failes the empty string is returned.
func ExtractAddressFromReverse(reverseName string) string {
search := ""
f := reverse
switch {
case strings.HasSuffix(reverseName, v4arpaSuffix):
search = strings.TrimSuffix(reverseName, v4arpaSuffix)
case strings.HasSuffix(reverseName, v6arpaSuffix):
search = strings.TrimSuffix(reverseName, v6arpaSuffix)
f = reverse6
default:
return ""
}
// Reverse the segments and then combine them.
return f(strings.Split(search, "."))
}
func reverse(slice []string) string {
for i := 0; i < len(slice)/2; i++ {
j := len(slice) - i - 1
slice[i], slice[j] = slice[j], slice[i]
}
ip := net.ParseIP(strings.Join(slice, ".")).To4()
if ip == nil {
return ""
}
return ip.String()
}
// reverse6 reverse the segments and combine them according to RFC3596:
// 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
// is reversed to 2001:db8::567:89ab
func reverse6(slice []string) string {
for i := 0; i < len(slice)/2; i++ {
j := len(slice) - i - 1
slice[i], slice[j] = slice[j], slice[i]
}
slice6 := []string{}
for i := 0; i < len(slice)/4; i++ {
slice6 = append(slice6, strings.Join(slice[i*4:i*4+4], ""))
}
ip := net.ParseIP(strings.Join(slice6, ":")).To16()
if ip == nil {
return ""
}
return ip.String()
}
const (
// v4arpaSuffix is the reverse tree suffix for v4 IP addresses.
v4arpaSuffix = ".in-addr.arpa."
// v6arpaSuffix is the reverse tree suffix for v6 IP addresses.
v6arpaSuffix = ".ip6.arpa."
)
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