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27 lines
662 B
Go
27 lines
662 B
Go
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package rfc4183
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import (
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"fmt"
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)
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// reverseIPv6 returns the ipv6.arpa string suitable for reverse DNS lookups.
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func reverseIPv6(ip []byte, maskbits int) (arpa string, err error) {
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// Must be IPv6
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if len(ip) != 16 {
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return "", fmt.Errorf("not IPv6")
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}
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buf := []byte("x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.ip6.arpa")
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// Poke hex digits into the template
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pos := 128/4*2 - 2 // Position of the last "x"
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for _, v := range ip {
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buf[pos] = hexDigit[v>>4]
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buf[pos-2] = hexDigit[v&0xF]
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pos = pos - 4
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}
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// Return only the parts without x's
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return string(buf[(128-maskbits)/4*2:]), nil
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}
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const hexDigit = "0123456789abcdef"
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