52 lines
1.4 KiB
Go
52 lines
1.4 KiB
Go
package dnsutil
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import (
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"time"
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"github.com/coredns/coredns/plugin/pkg/response"
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"github.com/miekg/dns"
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)
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// MinimalTTL scans the message returns the lowest TTL found taking into the response.Type of the message.
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func MinimalTTL(m *dns.Msg, mt response.Type) time.Duration {
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if mt != response.NoError && mt != response.NameError && mt != response.NoData {
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return MinimalDefaultTTL
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}
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// No records or OPT is the only record, return a short ttl as a fail safe.
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if len(m.Answer)+len(m.Ns) == 0 &&
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(len(m.Extra) == 0 || (len(m.Extra) == 1 && m.Extra[0].Header().Rrtype == dns.TypeOPT)) {
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return MinimalDefaultTTL
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}
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minTTL := MaximumDefaulTTL
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for _, r := range m.Answer {
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if r.Header().Ttl < uint32(minTTL.Seconds()) {
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minTTL = time.Duration(r.Header().Ttl) * time.Second
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}
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}
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for _, r := range m.Ns {
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if r.Header().Ttl < uint32(minTTL.Seconds()) {
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minTTL = time.Duration(r.Header().Ttl) * time.Second
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}
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}
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for _, r := range m.Extra {
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if r.Header().Rrtype == dns.TypeOPT {
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// OPT records use TTL field for extended rcode and flags
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continue
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}
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if r.Header().Ttl < uint32(minTTL.Seconds()) {
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minTTL = time.Duration(r.Header().Ttl) * time.Second
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}
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}
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return minTTL
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}
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const (
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// MinimalDefaultTTL is the absolute lowest TTL we use in CoreDNS.
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MinimalDefaultTTL = 5 * time.Second
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// MaximumDefaulTTL is the maximum TTL was use on RRsets in CoreDNS.
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MaximumDefaulTTL = 1 * time.Hour
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)
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