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