60 lines
1.2 KiB
Go
60 lines
1.2 KiB
Go
package middleware
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import (
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"bytes"
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"github.com/miekg/dns"
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)
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// Less returns <0 when a is less than b, 0 when they are equal and
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// >0 when a is larger than b.
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// The function orders names in DNSSEC canonical order: RFC 4034s section-6.1
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//
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// See http://bert-hubert.blogspot.co.uk/2015/10/how-to-do-fast-canonical-ordering-of.html
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// for a blog article on this implementation.
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func Less(a, b string) int {
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i := 1
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aj := len(a)
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bj := len(b)
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for {
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ai, oka := dns.PrevLabel(a, i)
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bi, okb := dns.PrevLabel(b, i)
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if oka && okb {
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return 0
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}
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// sadly this []byte will allocate...
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ab := []byte(a[ai:aj])
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toLowerAndDDD(ab)
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bb := []byte(b[bi:bj])
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toLowerAndDDD(bb)
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res := bytes.Compare(ab, bb)
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if res != 0 {
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return res
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}
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i++
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aj, bj = ai, bi
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}
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return 0
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}
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func toLowerAndDDD(b []byte) {
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lb := len(b)
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for i := 0; i < lb; i++ {
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if b[i] >= 'A' && b[i] <= 'Z' {
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b[i] += 32
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continue
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}
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if i+3 < lb && b[i] == '\\' && isDigit(b[i+1]) && isDigit(b[i+2]) && isDigit(b[i+3]) {
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b[i] = dddToByte(b[i:])
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for j := i + 1; j < lb-3; j++ {
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b[j] = b[j+3]
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}
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lb -= 3
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}
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}
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}
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func isDigit(b byte) bool { return b >= '0' && b <= '9' }
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func dddToByte(s []byte) byte { return byte((s[1]-'0')*100 + (s[2]-'0')*10 + (s[3] - '0')) }
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