feat(secondary): add fallthrough support (#8041)

test/secondary_test.go

@@ -10,6 +10,143 @@ import (
 	"github.com/miekg/dns"
 )
 
+func TestSecondaryFallthrough(t *testing.T) {
+	// Create zone file for primary - has www.example.org A 127.0.0.1
+	primaryZone, rm1, err := test.TempFile(".", `$ORIGIN example.org.
+@ 3600 IN SOA  sns.dns.icann.org. noc.dns.icann.org. (
+        2017042745 ; serial
+        7200       ; refresh (2 hours)
+        3600       ; retry (1 hour)
+        1209600    ; expire (2 weeks)
+        3600       ; minimum (1 hour)
+)
+
+  3600 IN NS   a.iana-servers.net.
+  3600 IN NS   b.iana-servers.net.
+
+www    IN A    127.0.0.1
+`)
+	if err != nil {
+		t.Fatalf("Failed to create primary zone: %s", err)
+	}
+	defer rm1()
+
+	// Create zone file for fallback server - has other.example.org A 10.10.10.10
+	fallbackZone, rm2, err := test.TempFile(".", `$ORIGIN example.org.
+@ 3600 IN SOA  sns.dns.icann.org. noc.dns.icann.org. (
+        2017042745 ; serial
+        7200       ; refresh (2 hours)
+        3600       ; retry (1 hour)
+        1209600    ; expire (2 weeks)
+        3600       ; minimum (1 hour)
+)
+
+  3600 IN NS   a.iana-servers.net.
+  3600 IN NS   b.iana-servers.net.
+
+other  IN A    10.10.10.10
+`)
+	if err != nil {
+		t.Fatalf("Failed to create fallback zone: %s", err)
+	}
+	defer rm2()
+
+	// Start primary server (serves zone via AXFR)
+	primaryCorefile := `example.org:0 {
+		file ` + primaryZone + `
+		transfer {
+			to *
+		}
+	}`
+	primary, _, primaryTCP, err := CoreDNSServerAndPorts(primaryCorefile)
+	if err != nil {
+		t.Fatalf("Could not get primary CoreDNS instance: %s", err)
+	}
+	defer primary.Stop()
+
+	// Start fallback server (answers queries forwarded by secondary)
+	fallbackCorefile := `example.org:0 {
+		file ` + fallbackZone + `
+	}`
+	fallback, fallbackUDP, _, err := CoreDNSServerAndPorts(fallbackCorefile)
+	if err != nil {
+		t.Fatalf("Could not get fallback CoreDNS instance: %s", err)
+	}
+	defer fallback.Stop()
+
+	// Start secondary with fallthrough + forward to fallback
+	secondaryCorefile := `example.org:0 {
+		secondary {
+			transfer from ` + primaryTCP + `
+			fallthrough
+		}
+		forward . ` + fallbackUDP + `
+	}`
+	sec, secUDP, _, err := CoreDNSServerAndPorts(secondaryCorefile)
+	if err != nil {
+		t.Fatalf("Could not get secondary CoreDNS instance: %s", err)
+	}
+	defer sec.Stop()
+
+	// Wait for zone transfer to complete
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeSOA)
+	var r *dns.Msg
+	for range 10 {
+		r, _ = dns.Exchange(m, secUDP)
+		if r != nil && len(r.Answer) != 0 {
+			break
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	if r == nil || len(r.Answer) == 0 {
+		t.Fatal("Zone transfer did not complete")
+	}
+
+	// Test 1: www.example.org exists in secondary zone - should return answer from zone
+	m = new(dns.Msg)
+	m.SetQuestion("www.example.org.", dns.TypeA)
+	r, err = dns.Exchange(m, secUDP)
+	if err != nil {
+		t.Fatalf("Expected to receive reply for www.example.org, but got error: %s", err)
+	}
+	if r.Rcode != dns.RcodeSuccess {
+		t.Fatalf("Expected NOERROR for www.example.org, got %s", dns.RcodeToString[r.Rcode])
+	}
+	if len(r.Answer) != 1 {
+		t.Fatalf("Expected 1 answer for www.example.org, got %d", len(r.Answer))
+	}
+	a, ok := r.Answer[0].(*dns.A)
+	if !ok {
+		t.Fatalf("Expected A record for www.example.org, got %T", r.Answer[0])
+	}
+	if a.A.String() != "127.0.0.1" {
+		t.Fatalf("Expected www.example.org to be 127.0.0.1, got %s", a.A.String())
+	}
+
+	// Test 2: other.example.org does NOT exist in secondary zone
+	// With fallthrough, query should pass to forward plugin which queries fallback server
+	m = new(dns.Msg)
+	m.SetQuestion("other.example.org.", dns.TypeA)
+	r, err = dns.Exchange(m, secUDP)
+	if err != nil {
+		t.Fatalf("Expected to receive reply for other.example.org, but got error: %s", err)
+	}
+	if r.Rcode != dns.RcodeSuccess {
+		t.Fatalf("Expected NOERROR for fallthrough query other.example.org, got %s", dns.RcodeToString[r.Rcode])
+	}
+	if len(r.Answer) != 1 {
+		t.Fatalf("Expected 1 answer from fallback for other.example.org, got %d", len(r.Answer))
+	}
+	a, ok = r.Answer[0].(*dns.A)
+	if !ok {
+		t.Fatalf("Expected A record from fallback for other.example.org, got %T", r.Answer[0])
+	}
+	if a.A.String() != "10.10.10.10" {
+		t.Fatalf("Expected fallback answer 10.10.10.10, got %s", a.A.String())
+	}
+}
+
 func TestEmptySecondaryZone(t *testing.T) {
 	// Corefile that fails to transfer example.org.
 	corefile := `example.org:0 {