2015-08-24 21:02:32 +00:00
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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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2015-08-25 05:52:56 +00:00
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// The lowest TTL of any duplicates is used in the remaining one.
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2015-08-25 07:39:43 +00:00
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//
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// TODO(miek): This function will be extended to also look for CNAMEs and DNAMEs.
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// if found, it will prune rrs from the "other data" that can exist. Example:
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// if it finds a: a.miek.nl. CNAME foo, all other RRs with the ownername a.miek.nl.
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2015-08-25 08:30:43 +00:00
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// will be removed. When a DNAME is found all RRs with an ownername below that of
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// the DNAME will be removed.
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2015-08-25 09:32:08 +00:00
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// Note that the class of the CNAME/DNAME is *not* taken into account. TODO(miek)?
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2015-08-24 21:02:32 +00:00
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func Dedup(rrs []RR) []RR {
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m := make(map[string]RR)
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2015-08-25 05:52:56 +00:00
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keys := make([]string, 0, len(rrs))
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2015-08-24 21:02:32 +00:00
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2015-08-25 09:32:08 +00:00
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/*
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make separate step that remove cname, dname
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2015-08-25 08:30:43 +00:00
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switch r.Header().Rrtype {
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case TypeCNAME:
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2015-08-25 09:32:08 +00:00
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cname = append(cname, strings.ToLower(r.Header().Name))
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2015-08-25 08:30:43 +00:00
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case TypeDNAME:
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2015-08-25 09:32:08 +00:00
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dname = append(dname, strings.ToLower(r.Header().Name))
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2015-08-25 08:30:43 +00:00
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default:
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2015-08-25 09:32:08 +00:00
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if len(cname) == 0 && len(dname) == 0 {
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break
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}
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if strings.EqualFold
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2015-08-25 08:30:43 +00:00
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}
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2015-08-25 09:32:08 +00:00
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*/
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2015-08-25 08:30:43 +00:00
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2015-08-25 09:32:08 +00:00
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for _, r := range rrs {
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2015-08-24 21:02:32 +00:00
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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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2015-08-25 05:52:56 +00:00
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// it means they were all different. We can then just return the original rrset.
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2015-08-24 21:02:32 +00:00
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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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