plugin/file: Fix panic on zero-valued SOA refresh (#8276)

This PR fixes panic with zero-valued SOA refresh

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/file/secondary.go

@@ -152,9 +152,9 @@ Restart:
 		return nil
 	}
 	soa := z.getSOA()
-	refresh := time.Second * time.Duration(soa.Refresh)
+	refresh := time.Second * time.Duration(max(soa.Refresh, 1))
-	retry := time.Second * time.Duration(soa.Retry)
+	retry := time.Second * time.Duration(max(soa.Retry, 1))
-	expire := time.Second * time.Duration(soa.Expire)
+	expire := time.Second * time.Duration(max(soa.Expire, 1))
 
 	refreshTicker := time.NewTicker(refresh)
 	retryTicker := time.NewTicker(retry)

plugin/file/secondary_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
 	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/plugin/transfer"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -166,3 +167,23 @@ func newRequest(_zone string, _qtype uint16) request.Request {
 	m.SetEdns0(4097, true)
 	return request.Request{W: &test.ResponseWriter{}, Req: m}
 }
+
+func TestUpdateWithZeroSOATimers(t *testing.T) {
+	z := NewZone(testZone, "test")
+	z.SOA = test.SOA(
+		fmt.Sprintf("%s IN SOA bla. bla. 1 0 0 0 0", testZone),
+	)
+
+	updateShutdown := make(chan bool)
+	time.AfterFunc(10*time.Millisecond, func() {
+		close(updateShutdown)
+	})
+
+	if err := z.UpdateWithTransfer(
+		updateShutdown,
+		nil,
+		func(*Zone, *transfer.Transfer) error { return nil },
+	); err != nil {
+		t.Fatalf("Unexpected update error: %v", err)
+	}
+}