dns: no negative TTL

Author: Snawoot

go.mod

@@ -15,6 +15,7 @@ require (
 	github.com/miekg/dns v1.1.58 // indirect
 	github.com/natefinch/atomic v1.0.1 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
+	golang.org/x/exp v0.0.0-20240119083558-1b970713d09a // indirect
 	golang.org/x/mod v0.14.0 // indirect
 	golang.org/x/net v0.20.0 // indirect
 	golang.org/x/sync v0.6.0 // indirect

go.sum

@@ -16,6 +16,8 @@ github.com/spf13/cobra v1.8.0 h1:7aJaZx1B85qltLMc546zn58BxxfZdR/W22ej9CFoEf0=
 github.com/spf13/cobra v1.8.0/go.mod h1:WXLWApfZ71AjXPya3WOlMsY9yMs7YeiHhFVlvLyhcho=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+golang.org/x/exp v0.0.0-20240119083558-1b970713d09a h1:Q8/wZp0KX97QFTc2ywcOE0YRjZPVIx+MXInMzdvQqcA=
+golang.org/x/exp v0.0.0-20240119083558-1b970713d09a/go.mod h1:idGWGoKP1toJGkd5/ig9ZLuPcZBC3ewk7SzmH0uou08=
 golang.org/x/mod v0.14.0 h1:dGoOF9QVLYng8IHTm7BAyWqCqSheQ5pYWGhzW00YJr0=
 golang.org/x/mod v0.14.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/net v0.20.0 h1:aCL9BSgETF1k+blQaYUBx9hJ9LOGP3gAVemcZlf1Kpo=

output/dns.go

@@ -187,7 +187,7 @@ func (o *DNSServer) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 		now := time.Now()
 		for _, item := range items {
 			netAddr := item.Address().Unmap()
-			ttl := uint32(item.ExpiresAt().Sub(now).Seconds())
+			ttl := uint32(util.Max(item.ExpiresAt().Sub(now).Seconds(), 0))
 			switch qtype {
 			case dns.TypeA:
 				if netAddr.Is4() {

util/util.go

@@ -9,6 +9,7 @@ import (
 	"net/netip"
 	"strings"
 
+	"golang.org/x/exp/constraints"
 	"gopkg.in/yaml.v3"
 )
 
@@ -117,3 +118,17 @@ func ResolveInterface(spec string) (*net.Interface, error) {
 	}
 	return nil, errors.New("specified interface not found")
 }
+
+func Max[T constraints.Ordered](x, y T) T {
+	if x >= y {
+		return x
+	}
+	return y
+}
+
+func Min[T constraints.Ordered](x, y T) T {
+	if x <= y {
+		return x
+	}
+	return y
+}