77 lines
1.5 KiB
Go
77 lines
1.5 KiB
Go
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package dns
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// Dedup removes identical RRs from rrs. It preserves the original ordering.
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// TODO(miek): CNAME, DNAME 'n stuff.
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func Dedup(rrs []RR) []RR {
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m := make(map[string]RR)
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keys := []string{}
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for _, r := range rrs {
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key := normalizedString(r)
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keys = append(keys, key)
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if _, ok := m[key]; ok {
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// Shortest TTL wins.
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if m[key].Header().Ttl > r.Header().Ttl {
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m[key].Header().Ttl = r.Header().Ttl
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}
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continue
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}
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m[key] = r
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}
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// If the length of the result map equals the amount of RRs we got,
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// it means they were all different. We can then just return the original
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// rrset.
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if len(m) == len(rrs) {
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return rrs
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}
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var i = 0
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for i, _ = range rrs {
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if len(m) == 0 {
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break
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}
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// We saved the key for each RR.
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delete(m, keys[i])
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}
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return rrs[:i]
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}
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// normalizedString returns a normalized string from r. The TTL
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// is removed and the domain name is lowercased.
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func normalizedString(r RR) string {
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// A string Go DNS makes has: domainname<TAB>TTL<TAB>...
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b := []byte(r.String())
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// find the first non-escaped tab, then another, so we capture
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// where the TTL lives.
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esc := false
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ttlStart, ttlEnd := 0, 0
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for i, c := range b {
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if c == '\\' {
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esc = true
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continue
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}
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if esc {
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esc = false
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continue
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}
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if c == '\t' {
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if ttlStart == 0 {
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ttlStart = i
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continue
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}
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if ttlEnd == 0 {
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ttlEnd = i
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break
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}
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}
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if c >= 'A' && c <= 'Z' {
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b[i] = c + 32
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}
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}
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// remove TTL.
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copy(b[ttlStart:], b[ttlEnd:])
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cut := ttlEnd - ttlStart
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return string(b[:len(b)-cut])
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}
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