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9dc7194321
See https://github.com/hashicorp/consul/issues/3977 While trying to improve furthermore #3948 (This pull request is still valid since we are not using Compression to compute the result anyway). I saw a strange behaviour of dns library. Basically, msg.Len() and len(msg.Pack()) disagree on Message len. Thus, calculation of DNS response is false consul relies on msg.Len() instead of the result of Pack() This is linked to miekg/dns#453 and a fix has been provided with miekg/dns#454 Would it be possible to upgrade miekg/dns to a more recent function ? Consul might for instance upgrade to a post 1.0 release such as https://github.com/miekg/dns/releases/tag/v1.0.4
85 lines
2.0 KiB
Go
85 lines
2.0 KiB
Go
package dns
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// Dedup removes identical RRs from rrs. It preserves the original ordering.
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// The lowest TTL of any duplicates is used in the remaining one. Dedup modifies
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// rrs.
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// m is used to store the RRs temporary. If it is nil a new map will be allocated.
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func Dedup(rrs []RR, m map[string]RR) []RR {
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if m == nil {
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m = make(map[string]RR)
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}
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// Save the keys, so we don't have to call normalizedString twice.
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keys := make([]*string, 0, len(rrs))
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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 rrset.
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if len(m) == len(rrs) {
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return rrs
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}
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j := 0
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for i, r := range rrs {
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// If keys[i] lives in the map, we should copy and remove it.
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if _, ok := m[*keys[i]]; ok {
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delete(m, *keys[i])
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rrs[j] = r
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j++
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}
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if len(m) == 0 {
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break
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}
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}
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return rrs[:j]
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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. We go from this:
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// DomainName<TAB>TTL<TAB>CLASS<TAB>TYPE<TAB>RDATA to:
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// lowercasename<TAB>CLASS<TAB>TYPE...
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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 where the TTL lives.
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esc := false
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ttlStart, ttlEnd := 0, 0
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for i := 0; i < len(b) && ttlEnd == 0; i++ {
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switch {
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case b[i] == '\\':
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esc = !esc
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case b[i] == '\t' && !esc:
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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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}
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case b[i] >= 'A' && b[i] <= 'Z' && !esc:
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b[i] += 32
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default:
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esc = false
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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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