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- package dns
-
- // Dedup removes identical RRs from rrs. It preserves the original ordering.
- // The lowest TTL of any duplicates is used in the remaining one. Dedup modifies
- // rrs.
- // m is used to store the RRs temporary. If it is nil a new map will be allocated.
- func Dedup(rrs []RR, m map[string]RR) []RR {
-
- if m == nil {
- m = make(map[string]RR)
- }
- // Save the keys, so we don't have to call normalizedString twice.
- keys := make([]*string, 0, len(rrs))
-
- for _, r := range rrs {
- key := normalizedString(r)
- keys = append(keys, &key)
- if mr, ok := m[key]; ok {
- // Shortest TTL wins.
- rh, mrh := r.Header(), mr.Header()
- if mrh.Ttl > rh.Ttl {
- mrh.Ttl = rh.Ttl
- }
- continue
- }
-
- m[key] = r
- }
- // If the length of the result map equals the amount of RRs we got,
- // it means they were all different. We can then just return the original rrset.
- if len(m) == len(rrs) {
- return rrs
- }
-
- j := 0
- for i, r := range rrs {
- // If keys[i] lives in the map, we should copy and remove it.
- if _, ok := m[*keys[i]]; ok {
- delete(m, *keys[i])
- rrs[j] = r
- j++
- }
-
- if len(m) == 0 {
- break
- }
- }
-
- return rrs[:j]
- }
-
- // normalizedString returns a normalized string from r. The TTL
- // is removed and the domain name is lowercased. We go from this:
- // DomainName<TAB>TTL<TAB>CLASS<TAB>TYPE<TAB>RDATA to:
- // lowercasename<TAB>CLASS<TAB>TYPE...
- func normalizedString(r RR) string {
- // A string Go DNS makes has: domainname<TAB>TTL<TAB>...
- b := []byte(r.String())
-
- // find the first non-escaped tab, then another, so we capture where the TTL lives.
- esc := false
- ttlStart, ttlEnd := 0, 0
- for i := 0; i < len(b) && ttlEnd == 0; i++ {
- switch {
- case b[i] == '\\':
- esc = !esc
- case b[i] == '\t' && !esc:
- if ttlStart == 0 {
- ttlStart = i
- continue
- }
- if ttlEnd == 0 {
- ttlEnd = i
- }
- case b[i] >= 'A' && b[i] <= 'Z' && !esc:
- b[i] += 32
- default:
- esc = false
- }
- }
-
- // remove TTL.
- copy(b[ttlStart:], b[ttlEnd:])
- cut := ttlEnd - ttlStart
- return string(b[:len(b)-cut])
- }
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