From eec9d66e22faf142537941954cd48263464f25c2 Mon Sep 17 00:00:00 2001
From: Konstantine <kbabuadze@yahoo.com>
Date: Sun, 17 Oct 2021 03:15:57 +0300
Subject: [PATCH] fix encodeIPAsFqdn to return alt-domain when requested, added
 test case

---
 agent/dns.go      |   9 ++--
 agent/dns_test.go | 104 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 4 deletions(-)

diff --git a/agent/dns.go b/agent/dns.go
index 937c32d08..c003305a4 100644
--- a/agent/dns.go
+++ b/agent/dns.go
@@ -1551,13 +1551,14 @@ func findWeight(node structs.CheckServiceNode) int {
 	}
 }
 
-func (d *DNSServer) encodeIPAsFqdn(dc string, ip net.IP) string {
+func (d *DNSServer) encodeIPAsFqdn(questionName string, dc string, ip net.IP) string {
 	ipv4 := ip.To4()
+	respDomain := d.getResponseDomain(questionName)
 	if ipv4 != nil {
 		ipStr := hex.EncodeToString(ip)
-		return fmt.Sprintf("%s.addr.%s.%s", ipStr[len(ipStr)-(net.IPv4len*2):], dc, d.domain)
+		return fmt.Sprintf("%s.addr.%s.%s", ipStr[len(ipStr)-(net.IPv4len*2):], dc, respDomain)
 	} else {
-		return fmt.Sprintf("%s.addr.%s.%s", hex.EncodeToString(ip), dc, d.domain)
+		return fmt.Sprintf("%s.addr.%s.%s", hex.EncodeToString(ip), dc, respDomain)
 	}
 }
 
@@ -1681,7 +1682,7 @@ func (d *DNSServer) makeRecordFromIP(dc string, addr net.IP, serviceNode structs
 	}
 
 	if q.Qtype == dns.TypeSRV {
-		ipFQDN := d.encodeIPAsFqdn(dc, addr)
+		ipFQDN := d.encodeIPAsFqdn(q.Name, dc, addr)
 		answers := []dns.RR{
 			&dns.SRV{
 				Hdr: dns.RR_Header{
diff --git a/agent/dns_test.go b/agent/dns_test.go
index 7bcab1cea..e658c58f4 100644
--- a/agent/dns_test.go
+++ b/agent/dns_test.go
@@ -2502,6 +2502,110 @@ func TestDNS_ServiceLookup_ServiceAddress_A(t *testing.T) {
 	}
 }
 
+func TestDNS_AltDomain_ServiceLookup_ServiceAddress_A(t *testing.T) {
+	if testing.Short() {
+		t.Skip("too slow for testing.Short")
+	}
+
+	t.Parallel()
+	a := NewTestAgent(t, `
+		alt_domain = "test-domain"
+	`)
+	defer a.Shutdown()
+	testrpc.WaitForLeader(t, a.RPC, "dc1")
+
+	// Register a node with a service.
+	{
+		args := &structs.RegisterRequest{
+			Datacenter: "dc1",
+			Node:       "foo",
+			Address:    "127.0.0.1",
+			Service: &structs.NodeService{
+				Service: "db",
+				Tags:    []string{"primary"},
+				Address: "127.0.0.2",
+				Port:    12345,
+			},
+		}
+
+		var out struct{}
+		if err := a.RPC("Catalog.Register", args, &out); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+	}
+
+	// Register an equivalent prepared query.
+	var id string
+	{
+		args := &structs.PreparedQueryRequest{
+			Datacenter: "dc1",
+			Op:         structs.PreparedQueryCreate,
+			Query: &structs.PreparedQuery{
+				Name: "test",
+				Service: structs.ServiceQuery{
+					Service: "db",
+				},
+			},
+		}
+		if err := a.RPC("PreparedQuery.Apply", args, &id); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+	}
+
+	// Look up the service directly and via prepared query.
+	questions := []struct {
+		ask        string
+		wantDomain string
+	}{
+		{"db.service.consul.", "consul."},
+		{id + ".query.consul.", "consul."},
+		{"db.service.test-domain.", "test-domain."},
+		{id + ".query.test-domain.", "test-domain."},
+	}
+	for _, question := range questions {
+		m := new(dns.Msg)
+		m.SetQuestion(question.ask, dns.TypeSRV)
+
+		c := new(dns.Client)
+		in, _, err := c.Exchange(m, a.DNSAddr())
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+
+		if len(in.Answer) != 1 {
+			t.Fatalf("Bad: %#v", in)
+		}
+
+		srvRec, ok := in.Answer[0].(*dns.SRV)
+		if !ok {
+			t.Fatalf("Bad: %#v", in.Answer[0])
+		}
+		if srvRec.Port != 12345 {
+			t.Fatalf("Bad: %#v", srvRec)
+		}
+		if srvRec.Target != "7f000002.addr.dc1."+question.wantDomain {
+			t.Fatalf("Bad: %#v", srvRec)
+		}
+		if srvRec.Hdr.Ttl != 0 {
+			t.Fatalf("Bad: %#v", in.Answer[0])
+		}
+
+		aRec, ok := in.Extra[0].(*dns.A)
+		if !ok {
+			t.Fatalf("Bad: %#v", in.Extra[0])
+		}
+		if aRec.Hdr.Name != "7f000002.addr.dc1."+question.wantDomain {
+			t.Fatalf("Bad: %#v", in.Extra[0])
+		}
+		if aRec.A.String() != "127.0.0.2" {
+			t.Fatalf("Bad: %#v", in.Extra[0])
+		}
+		if aRec.Hdr.Ttl != 0 {
+			t.Fatalf("Bad: %#v", in.Extra[0])
+		}
+	}
+}
+
 func TestDNS_ServiceLookup_ServiceAddress_SRV(t *testing.T) {
 	if testing.Short() {
 		t.Skip("too slow for testing.Short")