71 lines
1.3 KiB
Go
71 lines
1.3 KiB
Go
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package util
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import (
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"net"
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"strings"
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)
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// convert character to hex number
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func charToHex(n byte) int8 {
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if n >= '0' && n <= '9' {
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return int8(n) - '0'
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} else if (n|0x20) >= 'a' && (n|0x20) <= 'f' {
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return (int8(n) | 0x20) - 'a' + 10
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}
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return -1
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}
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// parse IPv6 reverse address
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func ipParseArpa6(s string) net.IP {
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if len(s) != 63 {
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return nil
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}
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ip6 := make(net.IP, 16)
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for i := 0; i != 64; i += 4 {
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// parse "0.1."
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n := charToHex(s[i])
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n2 := charToHex(s[i+2])
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if s[i+1] != '.' || (i != 60 && s[i+3] != '.') ||
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n < 0 || n2 < 0 {
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return nil
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}
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ip6[16-i/4-1] = byte(n2<<4) | byte(n&0x0f)
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}
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return ip6
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}
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// ipReverse - reverse IP address: 1.0.0.127 -> 127.0.0.1
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func ipReverse(ip net.IP) net.IP {
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n := len(ip)
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r := make(net.IP, n)
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for i := 0; i != n; i++ {
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r[i] = ip[n-i-1]
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}
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return r
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}
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// DNSUnreverseAddr - convert reversed ARPA address to a normal IP address
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func DNSUnreverseAddr(s string) net.IP {
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const arpaV4 = ".in-addr.arpa"
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const arpaV6 = ".ip6.arpa"
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if strings.HasSuffix(s, arpaV4) {
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ip := strings.TrimSuffix(s, arpaV4)
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ip4 := net.ParseIP(ip).To4()
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if ip4 == nil {
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return nil
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}
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return ipReverse(ip4)
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} else if strings.HasSuffix(s, arpaV6) {
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ip := strings.TrimSuffix(s, arpaV6)
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return ipParseArpa6(ip)
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}
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return nil // unknown suffix
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}
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