kubernetes dnsclient 代码
文件路径：/third_party/forked/golang/net/dnsclient.go
/ Copyright 2009 The Go Authors. All rights reserved.
/ Use of this source code is governed by a BSD-style
/ license that can be found in the LICENSE file.
/ This package is copied from Go library net.
/ https://golang.org/src/net/dnsclient.go
/ The original private function reverseaddr
/ is exported as public function.
package net
import "net"
/ Reverseaddr returns the in-addr.arpa. or ip6.arpa. hostname of the IP
/ address addr suitable for rDNS (PTR) record lookup or an error if it fails
/ to parse the IP address.
func Reverseaddr(addr string) (arpa string, err error) {
ip := net.ParseIP(addr)
if ip == nil {
return "", &net.DNSError{Err: "unrecognized address", Name: addr}
}
if ip.To4() != nil {
return uitoa(uint(ip[15])) + "." + uitoa(uint(ip[14])) + "." + uitoa(uint(ip[13])) + "." + uitoa(uint(ip[12])) + ".in-addr.arpa.", nil
}
/ Must be IPv6
buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))
/ Add it, in reverse, to the buffer
for i := len(ip) - 1; i >= 0; i-- {
v := ip[i]
buf = append(buf, hexDigit[v&0xF],
'.',
hexDigit[v>>4],
'.')
}
/ Append "ip6.arpa." and return (buf already has the final .)
buf = append(buf, "ip6.arpa."...)
return string(buf), nil
}
/ Convert unsigned integer to decimal string.
func uitoa(val uint) string {
if val == 0 { / avoid string allocation
return "0"
}
var buf [20]byte / big enough for 64bit value base 10
i := len(buf) - 1
for val >= 10 {
q := val / 10
buf[i] = byte('0' + val - q*10)
i--
val = q
}
/ val < 10
buf[i] = byte('0' + val)
return string(buf[i:])
}
const hexDigit = "0123456789abcdef"