Add unit tests for MX and A DNS queries

Signed-off-by: Deep Debroy <ddebroy@docker.com>

libnetwork/resolver_test.go

@@ -0,0 +1,167 @@
+package libnetwork
+
+import (
+	"bytes"
+	"net"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+// a simple/null address type that will be used to fake a local address for unit testing
+type tstaddr struct {
+	net string
+}
+
+func (a *tstaddr) Network() string { return "tcp" }
+
+func (a *tstaddr) String() string { return "" }
+
+// a simple writer that implements dns.ResponseWriter for unit testing purposes
+type tstwriter struct {
+	msg *dns.Msg
+}
+
+func (w *tstwriter) WriteMsg(m *dns.Msg) (err error) {
+	w.msg = m
+	return nil
+}
+
+func (w *tstwriter) Write(m []byte) (int, error) { return 0, nil }
+
+func (w *tstwriter) LocalAddr() net.Addr { return new(tstaddr) }
+
+func (w *tstwriter) RemoteAddr() net.Addr { return new(tstaddr) }
+
+func (w *tstwriter) TsigStatus() error { return nil }
+
+func (w *tstwriter) TsigTimersOnly(b bool) {}
+
+func (w *tstwriter) Hijack() {}
+
+func (w *tstwriter) Close() error { return nil }
+
+func (w *tstwriter) GetResponse() *dns.Msg { return w.msg }
+
+func (w *tstwriter) ClearResponse() { w.msg = nil }
+
+func checkNonNullResponse(t *testing.T, m *dns.Msg) {
+	if m == nil {
+		t.Fatal("Null DNS response found. Non Null response msg expected.")
+	}
+}
+
+func checkNullResponse(t *testing.T, m *dns.Msg) {
+	if m != nil {
+		t.Fatal("Non Null DNS response found. Null response msg expected.")
+	}
+}
+
+func checkDNSAnswersCount(t *testing.T, m *dns.Msg, expected int) {
+	answers := len(m.Answer)
+	if answers != expected {
+		t.Fatalf("Expected number of answers in response: %d. Found: %d", expected, answers)
+	}
+}
+
+func checkDNSResponseCode(t *testing.T, m *dns.Msg, expected int) {
+	if m.MsgHdr.Rcode != expected {
+		t.Fatalf("Expected DNS response code: %d. Found: %d", expected, m.MsgHdr.Rcode)
+	}
+}
+
+func checkDNSRRType(t *testing.T, actual, expected uint16) {
+	if actual != expected {
+		t.Fatalf("Expected DNS Rrtype: %d. Found: %d", expected, actual)
+	}
+}
+
+func TestDNSIPQuery(t *testing.T) {
+	c, err := New()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Stop()
+
+	n, err := c.NewNetwork("bridge", "dtnet1", "", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := n.Delete(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	ep, err := n.CreateEndpoint("testep")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sb, err := c.NewSandbox("c1")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() {
+		if err := sb.Delete(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	// we need the endpoint only to populate ep_list for the sandbox as part of resolve_name
+	// it is not set as a target for name resolution and does not serve any other purpose
+	err = ep.Join(sb)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// add service records which are used to resolve names. These are the real targets for the DNS querries
+	n.(*network).addSvcRecords("ep1", "name1", "svc1", net.ParseIP("192.168.0.1"), net.IP{}, true, "test")
+
+	w := new(tstwriter)
+	// the unit tests right now will focus on non-proxyed DNS requests
+	r := NewResolver(resolverIPSandbox, false, sb.Key(), sb.(*sandbox))
+
+	// test name1's IP is resolved correctly with the default A type query
+	q := new(dns.Msg)
+	q.SetQuestion("name1", dns.TypeA)
+	r.(*resolver).ServeDNS(w, q)
+	resp := w.GetResponse()
+	checkNonNullResponse(t, resp)
+	t.Log("Response: ", resp.String())
+	checkDNSResponseCode(t, resp, dns.RcodeSuccess)
+	checkDNSAnswersCount(t, resp, 1)
+	checkDNSRRType(t, resp.Answer[0].Header().Rrtype, dns.TypeA)
+	if answer, ok := resp.Answer[0].(*dns.A); ok {
+		if !bytes.Equal(answer.A, net.ParseIP("192.168.0.1")) {
+			t.Fatalf("IP response in Answer %v does not match 192.168.0.1", answer.A)
+		}
+	} else {
+		t.Fatal("Answer of type A not found")
+	}
+	w.ClearResponse()
+
+	// test MX query with name1 results in Success response with 0 answer records
+	q = new(dns.Msg)
+	q.SetQuestion("name1", dns.TypeMX)
+	r.(*resolver).ServeDNS(w, q)
+	resp = w.GetResponse()
+	checkNonNullResponse(t, resp)
+	t.Log("Response: ", resp.String())
+	checkDNSResponseCode(t, resp, dns.RcodeSuccess)
+	checkDNSAnswersCount(t, resp, 0)
+	w.ClearResponse()
+
+	// test MX query with non existent name results in ServFail response with 0 answer records
+	// since this is a unit test env, we disable proxying DNS above which results in ServFail rather than NXDOMAIN
+	q = new(dns.Msg)
+	q.SetQuestion("nonexistent", dns.TypeMX)
+	r.(*resolver).ServeDNS(w, q)
+	resp = w.GetResponse()
+	checkNonNullResponse(t, resp)
+	t.Log("Response: ", resp.String())
+	checkDNSResponseCode(t, resp, dns.RcodeServerFailure)
+	w.ClearResponse()
+
+}