src/net/dnsmsg_test.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package net

 import (
 	"encoding/hex"
 	"reflect"
 	"testing"
 )

 func TestStructPackUnpack(t *testing.T) {
 	want := dnsQuestion{
 		Name:   ".",
 		Qtype:  dnsTypeA,
 		Qclass: dnsClassINET,
 	}
 	buf := make([]byte, 50)
 	n, ok := packStruct(&want, buf, 0)
 	if !ok {
 		t.Fatal("packing failed")
 	}
 	buf = buf[:n]
 	got := dnsQuestion{}
 	n, ok = unpackStruct(&got, buf, 0)
 	if !ok {
 		t.Fatal("unpacking failed")
 	}
 	if n != len(buf) {
 		t.Errorf("unpacked different amount than packed: got n = %d, want = %d", n, len(buf))
 	}
 	if !reflect.DeepEqual(got, want) {
 		t.Errorf("got = %+v, want = %+v", got, want)
 	}
 }

 func TestDomainNamePackUnpack(t *testing.T) {
 	tests := []struct {
 		in   string
 		want string
 		ok   bool
 	}{
 		{"", ".", true},
 		{".", ".", true},
 		{"google..com", "", false},
 		{"google.com", "google.com.", true},
 		{"google..com.", "", false},
 		{"google.com.", "google.com.", true},
 		{".google.com.", "", false},
 		{"www..google.com.", "", false},
 		{"www.google.com.", "www.google.com.", true},
 	}

 	for _, test := range tests {
 		buf := make([]byte, 30)
 		n, ok := packDomainName(test.in, buf, 0)
 		if ok != test.ok {
 			t.Errorf("packing of %s: got ok = %t, want = %t", test.in, ok, test.ok)
 			continue
 		}
 		if !test.ok {
 			continue
 		}
 		buf = buf[:n]
 		got, n, ok := unpackDomainName(buf, 0)
 		if !ok {
 			t.Errorf("unpacking for %s failed", test.in)
 			continue
 		}
 		if n != len(buf) {
 			t.Errorf(
 				"unpacked different amount than packed for %s: got n = %d, want = %d",
 				test.in,
 				n,
 				len(buf),
 			)
 		}
 		if got != test.want {
 			t.Errorf("unpacking packing of %s: got = %s, want = %s", test.in, got, test.want)
 		}
 	}
 }

 func TestDNSPackUnpack(t *testing.T) {
 	want := dnsMsg{
 		question: []dnsQuestion{{
 			Name:   ".",
 			Qtype:  dnsTypeAAAA,
 			Qclass: dnsClassINET,
 		}},
 		answer: []dnsRR{},
 		ns:     []dnsRR{},
 		extra:  []dnsRR{},
 	}
 	b, ok := want.Pack()
 	if !ok {
 		t.Fatal("packing failed")
 	}
 	var got dnsMsg
 	ok = got.Unpack(b)
 	if !ok {
 		t.Fatal("unpacking failed")
 	}
 	if !reflect.DeepEqual(got, want) {
 		t.Errorf("got = %+v, want = %+v", got, want)
 	}
 }

 func TestDNSParseSRVReply(t *testing.T) {
 	data, err := hex.DecodeString(dnsSRVReply)
 	if err != nil {
 		t.Fatal(err)
 	}
 	msg := new(dnsMsg)
 	ok := msg.Unpack(data)
 	if !ok {
 		t.Fatal("unpacking packet failed")
 	}
 	_ = msg.String() // exercise this code path
 	if g, e := len(msg.answer), 5; g != e {
 		t.Errorf("len(msg.answer) = %d; want %d", g, e)
 	}
 	for idx, rr := range msg.answer {
 		if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
 			t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
 		}
 		if _, ok := rr.(*dnsRR_SRV); !ok {
 			t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
 		}
 	}
 	for _, name := range [...]string{
 		"_xmpp-server._tcp.google.com.",
 		"_XMPP-Server._TCP.Google.COM.",
 		"_XMPP-SERVER._TCP.GOOGLE.COM.",
 	} {
 		_, addrs, err := answer(name, "foo:53", msg, uint16(dnsTypeSRV))
 		if err != nil {
 			t.Error(err)
 		}
 		if g, e := len(addrs), 5; g != e {
 			t.Errorf("len(addrs) = %d; want %d", g, e)
 			t.Logf("addrs = %#v", addrs)
 		}
 	}
 	// repack and unpack.
 	data2, ok := msg.Pack()
 	msg2 := new(dnsMsg)
 	msg2.Unpack(data2)
 	switch {
 	case !ok:
 		t.Error("failed to repack message")
 	case !reflect.DeepEqual(msg, msg2):
 		t.Error("repacked message differs from original")
 	}
 }

 func TestDNSParseCorruptSRVReply(t *testing.T) {
 	data, err := hex.DecodeString(dnsSRVCorruptReply)
 	if err != nil {
 		t.Fatal(err)
 	}
 	msg := new(dnsMsg)
 	ok := msg.Unpack(data)
 	if !ok {
 		t.Fatal("unpacking packet failed")
 	}
 	_ = msg.String() // exercise this code path
 	if g, e := len(msg.answer), 5; g != e {
 		t.Errorf("len(msg.answer) = %d; want %d", g, e)
 	}
 	for idx, rr := range msg.answer {
 		if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
 			t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
 		}
 		if idx == 4 {
 			if _, ok := rr.(*dnsRR_Header); !ok {
 				t.Errorf("answer[%d] = %T; want *dnsRR_Header", idx, rr)
 			}
 		} else {
 			if _, ok := rr.(*dnsRR_SRV); !ok {
 				t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
 			}
 		}
 	}
 	_, addrs, err := answer("_xmpp-server._tcp.google.com.", "foo:53", msg, uint16(dnsTypeSRV))
 	if err != nil {
 		t.Fatalf("answer: %v", err)
 	}
 	if g, e := len(addrs), 4; g != e {
 		t.Errorf("len(addrs) = %d; want %d", g, e)
 		t.Logf("addrs = %#v", addrs)
 	}
 }

 func TestDNSParseTXTReply(t *testing.T) {
 	expectedTxt1 := "v=spf1 redirect=_spf.google.com"
 	expectedTxt2 := "v=spf1 ip4:69.63.179.25 ip4:69.63.178.128/25 ip4:69.63.184.0/25 " +
 		"ip4:66.220.144.128/25 ip4:66.220.155.0/24 " +
 		"ip4:69.171.232.0/25 ip4:66.220.157.0/25 " +
 		"ip4:69.171.244.0/24 mx -all"

 	replies := []string{dnsTXTReply1, dnsTXTReply2}
 	expectedTxts := []string{expectedTxt1, expectedTxt2}

 	for i := range replies {
 		data, err := hex.DecodeString(replies[i])
 		if err != nil {
 			t.Fatal(err)
 		}

 		msg := new(dnsMsg)
 		ok := msg.Unpack(data)
 		if !ok {
 			t.Errorf("test %d: unpacking packet failed", i)
 			continue
 		}

 		if len(msg.answer) != 1 {
 			t.Errorf("test %d: len(rr.answer) = %d; want 1", i, len(msg.answer))
 			continue
 		}

 		rr := msg.answer[0]
 		rrTXT, ok := rr.(*dnsRR_TXT)
 		if !ok {
 			t.Errorf("test %d: answer[0] = %T; want *dnsRR_TXT", i, rr)
 			continue
 		}

 		if rrTXT.Txt != expectedTxts[i] {
 			t.Errorf("test %d: Txt = %s; want %s", i, rrTXT.Txt, expectedTxts[i])
 		}
 	}
 }

 func TestDNSParseTXTCorruptDataLengthReply(t *testing.T) {
 	replies := []string{dnsTXTCorruptDataLengthReply1, dnsTXTCorruptDataLengthReply2}

 	for i := range replies {
 		data, err := hex.DecodeString(replies[i])
 		if err != nil {
 			t.Fatal(err)
 		}

 		msg := new(dnsMsg)
 		ok := msg.Unpack(data)
 		if ok {
 			t.Errorf("test %d: expected to fail on unpacking corrupt packet", i)
 		}
 	}
 }

 func TestDNSParseTXTCorruptTXTLengthReply(t *testing.T) {
 	replies := []string{dnsTXTCorruptTXTLengthReply1, dnsTXTCorruptTXTLengthReply2}

 	for i := range replies {
 		data, err := hex.DecodeString(replies[i])
 		if err != nil {
 			t.Fatal(err)
 		}

 		msg := new(dnsMsg)
 		ok := msg.Unpack(data)
 		// Unpacking should succeed, but we should just get the header.
 		if !ok {
 			t.Errorf("test %d: unpacking packet failed", i)
 			continue
 		}

 		if len(msg.answer) != 1 {
 			t.Errorf("test %d: len(rr.answer) = %d; want 1", i, len(msg.answer))
 			continue
 		}

 		rr := msg.answer[0]
 		if _, justHeader := rr.(*dnsRR_Header); !justHeader {
 			t.Errorf("test %d: rr = %T; expected *dnsRR_Header", i, rr)
 		}
 	}
 }

 func TestIsResponseTo(t *testing.T) {
 	// Sample DNS query.
 	query := dnsMsg{
 		dnsMsgHdr: dnsMsgHdr{
 			id: 42,
 		},
 		question: []dnsQuestion{
 			{
 				Name:   "www.example.com.",
 				Qtype:  dnsTypeA,
 				Qclass: dnsClassINET,
 			},
 		},
 	}

 	resp := query
 	resp.response = true
 	if !resp.IsResponseTo(&query) {
 		t.Error("got false, want true")
 	}

 	badResponses := []dnsMsg{
 		// Different ID.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       43,
 				response: true,
 			},
 			question: []dnsQuestion{
 				{
 					Name:   "www.example.com.",
 					Qtype:  dnsTypeA,
 					Qclass: dnsClassINET,
 				},
 			},
 		},

 		// Different query name.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       42,
 				response: true,
 			},
 			question: []dnsQuestion{
 				{
 					Name:   "www.google.com.",
 					Qtype:  dnsTypeA,
 					Qclass: dnsClassINET,
 				},
 			},
 		},

 		// Different query type.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       42,
 				response: true,
 			},
 			question: []dnsQuestion{
 				{
 					Name:   "www.example.com.",
 					Qtype:  dnsTypeAAAA,
 					Qclass: dnsClassINET,
 				},
 			},
 		},

 		// Different query class.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       42,
 				response: true,
 			},
 			question: []dnsQuestion{
 				{
 					Name:   "www.example.com.",
 					Qtype:  dnsTypeA,
 					Qclass: dnsClassCSNET,
 				},
 			},
 		},

 		// No questions.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       42,
 				response: true,
 			},
 		},

 		// Extra questions.
 		{
 			dnsMsgHdr: dnsMsgHdr{
 				id:       42,
 				response: true,
 			},
 			question: []dnsQuestion{
 				{
 					Name:   "www.example.com.",
 					Qtype:  dnsTypeA,
 					Qclass: dnsClassINET,
 				},
 				{
 					Name:   "www.golang.org.",
 					Qtype:  dnsTypeAAAA,
 					Qclass: dnsClassINET,
 				},
 			},
 		},
 	}

 	for i := range badResponses {
 		if badResponses[i].IsResponseTo(&query) {
 			t.Errorf("%v: got true, want false", i)
 		}
 	}
 }

 // Valid DNS SRV reply
 const dnsSRVReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
 	"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
 	"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
 	"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
 	"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
 	"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
 	"72016c06676f6f676c6503636f6d00c00c002100010000012c00210014000014950c78" +
 	"6d70702d73657276657231016c06676f6f676c6503636f6d00"

 // Corrupt DNS SRV reply, with its final RR having a bogus length
 // (perhaps it was truncated, or it's malicious) The mutation is the
 // capital "FF" below, instead of the proper "21".
 const dnsSRVCorruptReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
 	"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
 	"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
 	"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
 	"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
 	"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
 	"72016c06676f6f676c6503636f6d00c00c002100010000012c00FF0014000014950c78" +
 	"6d70702d73657276657231016c06676f6f676c6503636f6d00"

 // TXT reply with one <character-string>
 const dnsTXTReply1 = "b3458180000100010004000505676d61696c03636f6d0000100001c00c001000010000012c00" +
 	"201f763d737066312072656469726563743d5f7370662e676f6f676c652e636f6dc00" +
 	"c0002000100025d4c000d036e733406676f6f676c65c012c00c0002000100025d4c00" +
 	"06036e7331c057c00c0002000100025d4c0006036e7333c057c00c0002000100025d4" +
 	"c0006036e7332c057c06c00010001000248b50004d8ef200ac09000010001000248b5" +
 	"0004d8ef220ac07e00010001000248b50004d8ef240ac05300010001000248b50004d" +
 	"8ef260a0000291000000000000000"

 // TXT reply with more than one <character-string>.
 // See https://tools.ietf.org/html/rfc1035#section-3.3.14
 const dnsTXTReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
 	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
 	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
 	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
 	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
 	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
 	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
 	"f0cc0fd0001000100025d15000445abff0c"

 // DataLength field should be sum of all TXT fields. In this case it's less.
 const dnsTXTCorruptDataLengthReply1 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
 	"100000e1000967f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
 	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
 	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
 	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
 	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
 	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
 	"f0cc0fd0001000100025d15000445abff0c"

 // Same as above but DataLength is more than sum of TXT fields.
 const dnsTXTCorruptDataLengthReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
 	"100000e1001227f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
 	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
 	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
 	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
 	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
 	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
 	"f0cc0fd0001000100025d15000445abff0c"

 // TXT Length field is less than actual length.
 const dnsTXTCorruptTXTLengthReply1 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
 	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
 	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
 	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
 	"343a36392e3137312e3233322e302f323520691470343a36362e3232302e3135372e302f32352" +
 	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
 	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
 	"f0cc0fd0001000100025d15000445abff0c"

 // TXT Length field is more than actual length.
 const dnsTXTCorruptTXTLengthReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
 	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
 	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
 	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
 	"343a36392e3137312e3233322e302f323520693370343a36362e3232302e3135372e302f32352" +
 	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
 	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
 	"f0cc0fd0001000100025d15000445abff0c"
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package net

	import (
	"encoding/hex"
	"reflect"
	"testing"
	)

	func TestStructPackUnpack(t *testing.T) {
	want := dnsQuestion{
	Name: ".",
	Qtype: dnsTypeA,
	Qclass: dnsClassINET,
	}
	buf := make([]byte, 50)
	n, ok := packStruct(&want, buf, 0)
	if !ok {
	t.Fatal("packing failed")
	}
	buf = buf[:n]
	got := dnsQuestion{}
	n, ok = unpackStruct(&got, buf, 0)
	if !ok {
	t.Fatal("unpacking failed")
	}
	if n != len(buf) {
	t.Errorf("unpacked different amount than packed: got n = %d, want = %d", n, len(buf))
	}
	if !reflect.DeepEqual(got, want) {
	t.Errorf("got = %+v, want = %+v", got, want)
	}
	}

	func TestDomainNamePackUnpack(t *testing.T) {
	tests := []struct {
	in string
	want string
	ok bool
	}{
	{"", ".", true},
	{".", ".", true},
	{"google..com", "", false},
	{"google.com", "google.com.", true},
	{"google..com.", "", false},
	{"google.com.", "google.com.", true},
	{".google.com.", "", false},
	{"www..google.com.", "", false},
	{"www.google.com.", "www.google.com.", true},
	}

	for _, test := range tests {
	buf := make([]byte, 30)
	n, ok := packDomainName(test.in, buf, 0)
	if ok != test.ok {
	t.Errorf("packing of %s: got ok = %t, want = %t", test.in, ok, test.ok)
	continue
	}
	if !test.ok {
	continue
	}
	buf = buf[:n]
	got, n, ok := unpackDomainName(buf, 0)
	if !ok {
	t.Errorf("unpacking for %s failed", test.in)
	continue
	}
	if n != len(buf) {
	t.Errorf(
	"unpacked different amount than packed for %s: got n = %d, want = %d",
	test.in,
	n,
	len(buf),
	)
	}
	if got != test.want {
	t.Errorf("unpacking packing of %s: got = %s, want = %s", test.in, got, test.want)
	}
	}
	}

	func TestDNSPackUnpack(t *testing.T) {
	want := dnsMsg{
	question: []dnsQuestion{{
	Name: ".",
	Qtype: dnsTypeAAAA,
	Qclass: dnsClassINET,
	}},
	answer: []dnsRR{},
	ns: []dnsRR{},
	extra: []dnsRR{},
	}
	b, ok := want.Pack()
	if !ok {
	t.Fatal("packing failed")
	}
	var got dnsMsg
	ok = got.Unpack(b)
	if !ok {
	t.Fatal("unpacking failed")
	}
	if !reflect.DeepEqual(got, want) {
	t.Errorf("got = %+v, want = %+v", got, want)
	}
	}

	func TestDNSParseSRVReply(t *testing.T) {
	data, err := hex.DecodeString(dnsSRVReply)
	if err != nil {
	t.Fatal(err)
	}
	msg := new(dnsMsg)
	ok := msg.Unpack(data)
	if !ok {
	t.Fatal("unpacking packet failed")
	}
	_ = msg.String() // exercise this code path
	if g, e := len(msg.answer), 5; g != e {
	t.Errorf("len(msg.answer) = %d; want %d", g, e)
	}
	for idx, rr := range msg.answer {
	if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
	t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
	}
	if _, ok := rr.(*dnsRR_SRV); !ok {
	t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
	}
	}
	for _, name := range [...]string{
	"_xmpp-server._tcp.google.com.",
	"_XMPP-Server._TCP.Google.COM.",
	"_XMPP-SERVER._TCP.GOOGLE.COM.",
	} {
	_, addrs, err := answer(name, "foo:53", msg, uint16(dnsTypeSRV))
	if err != nil {
	t.Error(err)
	}
	if g, e := len(addrs), 5; g != e {
	t.Errorf("len(addrs) = %d; want %d", g, e)
	t.Logf("addrs = %#v", addrs)
	}
	}
	// repack and unpack.
	data2, ok := msg.Pack()
	msg2 := new(dnsMsg)
	msg2.Unpack(data2)
	switch {
	case !ok:
	t.Error("failed to repack message")
	case !reflect.DeepEqual(msg, msg2):
	t.Error("repacked message differs from original")
	}
	}

	func TestDNSParseCorruptSRVReply(t *testing.T) {
	data, err := hex.DecodeString(dnsSRVCorruptReply)
	if err != nil {
	t.Fatal(err)
	}
	msg := new(dnsMsg)
	ok := msg.Unpack(data)
	if !ok {
	t.Fatal("unpacking packet failed")
	}
	_ = msg.String() // exercise this code path
	if g, e := len(msg.answer), 5; g != e {
	t.Errorf("len(msg.answer) = %d; want %d", g, e)
	}
	for idx, rr := range msg.answer {
	if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
	t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
	}
	if idx == 4 {
	if _, ok := rr.(*dnsRR_Header); !ok {
	t.Errorf("answer[%d] = %T; want *dnsRR_Header", idx, rr)
	}
	} else {
	if _, ok := rr.(*dnsRR_SRV); !ok {
	t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
	}
	}
	}
	_, addrs, err := answer("_xmpp-server._tcp.google.com.", "foo:53", msg, uint16(dnsTypeSRV))
	if err != nil {
	t.Fatalf("answer: %v", err)
	}
	if g, e := len(addrs), 4; g != e {
	t.Errorf("len(addrs) = %d; want %d", g, e)
	t.Logf("addrs = %#v", addrs)
	}
	}

	func TestDNSParseTXTReply(t *testing.T) {
	expectedTxt1 := "v=spf1 redirect=_spf.google.com"
	expectedTxt2 := "v=spf1 ip4:69.63.179.25 ip4:69.63.178.128/25 ip4:69.63.184.0/25 " +
	"ip4:66.220.144.128/25 ip4:66.220.155.0/24 " +
	"ip4:69.171.232.0/25 ip4:66.220.157.0/25 " +
	"ip4:69.171.244.0/24 mx -all"

	replies := []string{dnsTXTReply1, dnsTXTReply2}
	expectedTxts := []string{expectedTxt1, expectedTxt2}

	for i := range replies {
	data, err := hex.DecodeString(replies[i])
	if err != nil {
	t.Fatal(err)
	}

	msg := new(dnsMsg)
	ok := msg.Unpack(data)
	if !ok {
	t.Errorf("test %d: unpacking packet failed", i)
	continue
	}

	if len(msg.answer) != 1 {
	t.Errorf("test %d: len(rr.answer) = %d; want 1", i, len(msg.answer))
	continue
	}

	rr := msg.answer[0]
	rrTXT, ok := rr.(*dnsRR_TXT)
	if !ok {
	t.Errorf("test %d: answer[0] = %T; want *dnsRR_TXT", i, rr)
	continue
	}

	if rrTXT.Txt != expectedTxts[i] {
	t.Errorf("test %d: Txt = %s; want %s", i, rrTXT.Txt, expectedTxts[i])
	}
	}
	}

	func TestDNSParseTXTCorruptDataLengthReply(t *testing.T) {
	replies := []string{dnsTXTCorruptDataLengthReply1, dnsTXTCorruptDataLengthReply2}

	for i := range replies {
	data, err := hex.DecodeString(replies[i])
	if err != nil {
	t.Fatal(err)
	}

	msg := new(dnsMsg)
	ok := msg.Unpack(data)
	if ok {
	t.Errorf("test %d: expected to fail on unpacking corrupt packet", i)
	}
	}
	}

	func TestDNSParseTXTCorruptTXTLengthReply(t *testing.T) {
	replies := []string{dnsTXTCorruptTXTLengthReply1, dnsTXTCorruptTXTLengthReply2}

	for i := range replies {
	data, err := hex.DecodeString(replies[i])
	if err != nil {
	t.Fatal(err)
	}

	msg := new(dnsMsg)
	ok := msg.Unpack(data)
	// Unpacking should succeed, but we should just get the header.
	if !ok {
	t.Errorf("test %d: unpacking packet failed", i)
	continue
	}

	if len(msg.answer) != 1 {
	t.Errorf("test %d: len(rr.answer) = %d; want 1", i, len(msg.answer))
	continue
	}

	rr := msg.answer[0]
	if _, justHeader := rr.(*dnsRR_Header); !justHeader {
	t.Errorf("test %d: rr = %T; expected *dnsRR_Header", i, rr)
	}
	}
	}

	func TestIsResponseTo(t *testing.T) {
	// Sample DNS query.
	query := dnsMsg{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	},
	question: []dnsQuestion{
	{
	Name: "www.example.com.",
	Qtype: dnsTypeA,
	Qclass: dnsClassINET,
	},
	},
	}

	resp := query
	resp.response = true
	if !resp.IsResponseTo(&query) {
	t.Error("got false, want true")
	}

	badResponses := []dnsMsg{
	// Different ID.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 43,
	response: true,
	},
	question: []dnsQuestion{
	{
	Name: "www.example.com.",
	Qtype: dnsTypeA,
	Qclass: dnsClassINET,
	},
	},
	},

	// Different query name.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	response: true,
	},
	question: []dnsQuestion{
	{
	Name: "www.google.com.",
	Qtype: dnsTypeA,
	Qclass: dnsClassINET,
	},
	},
	},

	// Different query type.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	response: true,
	},
	question: []dnsQuestion{
	{
	Name: "www.example.com.",
	Qtype: dnsTypeAAAA,
	Qclass: dnsClassINET,
	},
	},
	},

	// Different query class.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	response: true,
	},
	question: []dnsQuestion{
	{
	Name: "www.example.com.",
	Qtype: dnsTypeA,
	Qclass: dnsClassCSNET,
	},
	},
	},

	// No questions.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	response: true,
	},
	},

	// Extra questions.
	{
	dnsMsgHdr: dnsMsgHdr{
	id: 42,
	response: true,
	},
	question: []dnsQuestion{
	{
	Name: "www.example.com.",
	Qtype: dnsTypeA,
	Qclass: dnsClassINET,
	},
	{
	Name: "www.golang.org.",
	Qtype: dnsTypeAAAA,
	Qclass: dnsClassINET,
	},
	},
	},
	}

	for i := range badResponses {
	if badResponses[i].IsResponseTo(&query) {
	t.Errorf("%v: got true, want false", i)
	}
	}
	}

	// Valid DNS SRV reply
	const dnsSRVReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
	"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
	"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
	"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
	"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
	"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
	"72016c06676f6f676c6503636f6d00c00c002100010000012c00210014000014950c78" +
	"6d70702d73657276657231016c06676f6f676c6503636f6d00"

	// Corrupt DNS SRV reply, with its final RR having a bogus length
	// (perhaps it was truncated, or it's malicious) The mutation is the
	// capital "FF" below, instead of the proper "21".
	const dnsSRVCorruptReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
	"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
	"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
	"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
	"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
	"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
	"72016c06676f6f676c6503636f6d00c00c002100010000012c00FF0014000014950c78" +
	"6d70702d73657276657231016c06676f6f676c6503636f6d00"

	// TXT reply with one <character-string>
	const dnsTXTReply1 = "b3458180000100010004000505676d61696c03636f6d0000100001c00c001000010000012c00" +
	"201f763d737066312072656469726563743d5f7370662e676f6f676c652e636f6dc00" +
	"c0002000100025d4c000d036e733406676f6f676c65c012c00c0002000100025d4c00" +
	"06036e7331c057c00c0002000100025d4c0006036e7333c057c00c0002000100025d4" +
	"c0006036e7332c057c06c00010001000248b50004d8ef200ac09000010001000248b5" +
	"0004d8ef220ac07e00010001000248b50004d8ef240ac05300010001000248b50004d" +
	"8ef260a0000291000000000000000"

	// TXT reply with more than one <character-string>.
	// See https://tools.ietf.org/html/rfc1035#section-3.3.14
	const dnsTXTReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
	"f0cc0fd0001000100025d15000445abff0c"

	// DataLength field should be sum of all TXT fields. In this case it's less.
	const dnsTXTCorruptDataLengthReply1 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
	"100000e1000967f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
	"f0cc0fd0001000100025d15000445abff0c"

	// Same as above but DataLength is more than sum of TXT fields.
	const dnsTXTCorruptDataLengthReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
	"100000e1001227f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
	"343a36392e3137312e3233322e302f323520692e70343a36362e3232302e3135372e302f32352" +
	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
	"f0cc0fd0001000100025d15000445abff0c"

	// TXT Length field is less than actual length.
	const dnsTXTCorruptTXTLengthReply1 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
	"343a36392e3137312e3233322e302f323520691470343a36362e3232302e3135372e302f32352" +
	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
	"f0cc0fd0001000100025d15000445abff0c"

	// TXT Length field is more than actual length.
	const dnsTXTCorruptTXTLengthReply2 = "a0a381800001000100020002045f7370660866616365626f6f6b03636f6d0000100001c00c0010000" +
	"100000e1000af7f763d73706631206970343a36392e36332e3137392e3235206970343a36392e" +
	"36332e3137382e3132382f3235206970343a36392e36332e3138342e302f3235206970343a363" +
	"62e3232302e3134342e3132382f3235206970343a36362e3232302e3135352e302f3234206970" +
	"343a36392e3137312e3233322e302f323520693370343a36362e3232302e3135372e302f32352" +
	"06970343a36392e3137312e3234342e302f3234206d78202d616c6cc0110002000100025d1500" +
	"070161026e73c011c0110002000100025d1500040162c0ecc0ea0001000100025d15000445abe" +
	"f0cc0fd0001000100025d15000445abff0c"