ZoneParser: error on parsing an IPv6 address in an A record (#923)

* ZoneParser: error on parsing an IPv6 address in an A record

And vice versa for IPv4 with AAAA.

The implementation of isIPv6 is inspired by e341bae08d/src/net/ip.go (L678-L681) .

* Fix benchmarks that try to use ::1 as A record.

* Test A/AAAA parsing via NewRR rather than zone parser.

* Document why we distinguish IPv4 vs IPv6 via existence of ":".

dns_bench_test.go

@@ -233,7 +233,7 @@ func BenchmarkUnpackMX(b *testing.B) {
 }
 
 func BenchmarkPackAAAAA(b *testing.B) {
-	aaaa := testRR(". IN A ::1")
+	aaaa := testRR(". IN AAAA ::1")
 
 	buf := make([]byte, Len(aaaa))
 	b.ReportAllocs()
@@ -244,7 +244,7 @@ func BenchmarkPackAAAAA(b *testing.B) {
 }
 
 func BenchmarkUnpackAAAA(b *testing.B) {
-	aaaa := testRR(". IN A ::1")
+	aaaa := testRR(". IN AAAA ::1")
 
 	buf := make([]byte, Len(aaaa))
 	PackRR(aaaa, buf, 0, nil, false)

scan_rr.go

@@ -133,7 +133,12 @@ func (rr *A) parse(c *zlexer, o, f string) *ParseError {
 	}
 
 	rr.A = net.ParseIP(l.token)
-	if rr.A == nil || l.err {
+	// IPv4 addresses cannot include ":".
+	// We do this rather than use net.IP's To4() because
+	// To4() treats IPv4-mapped IPv6 addresses as being
+	// IPv4.
+	isIPv4 := !strings.Contains(l.token, ":")
+	if rr.A == nil || !isIPv4 || l.err {
 		return &ParseError{f, "bad A A", l}
 	}
 	return slurpRemainder(c, f)
@@ -146,7 +151,10 @@ func (rr *AAAA) parse(c *zlexer, o, f string) *ParseError {
 	}
 
 	rr.AAAA = net.ParseIP(l.token)
-	if rr.AAAA == nil || l.err {
+	// IPv6 addresses must include ":", and IPv4
+	// addresses cannot include ":".
+	isIPv6 := strings.Contains(l.token, ":")
+	if rr.AAAA == nil || !isIPv6 || l.err {
 		return &ParseError{f, "bad AAAA AAAA", l}
 	}
 	return slurpRemainder(c, f)

scan_test.go

@@ -121,6 +121,51 @@ func TestZoneParserIncludeDisallowed(t *testing.T) {
 	}
 }
 
+func TestZoneParserAddressAAAA(t *testing.T) {
+	tests := []struct {
+		record string
+		want   *AAAA
+	}{
+		{
+			record: "1.example.org. 600 IN AAAA ::1",
+			want:   &AAAA{Hdr: RR_Header{Name: "1.example.org."}, AAAA: net.IPv6loopback},
+		},
+		{
+			record: "2.example.org. 600 IN AAAA ::FFFF:127.0.0.1",
+			want:   &AAAA{Hdr: RR_Header{Name: "2.example.org."}, AAAA: net.ParseIP("::FFFF:127.0.0.1")},
+		},
+	}
+
+	for _, tc := range tests {
+		got, err := NewRR(tc.record)
+		if err != nil {
+			t.Fatalf("expected no error, but got %s", err)
+		}
+		aaaa, ok := got.(*AAAA)
+		if !ok {
+			t.Fatalf("expected *AAAA RR, but got %T", aaaa)
+		}
+		if g, w := aaaa.AAAA, tc.want.AAAA; !g.Equal(w) {
+			t.Fatalf("expected AAAA with IP %v, but got %v", g, w)
+		}
+	}
+}
+
+func TestZoneParserAddressBad(t *testing.T) {
+	records := []string{
+		"1.bad.example.org. 600 IN A ::1",
+		"2.bad.example.org. 600 IN A ::FFFF:127.0.0.1",
+		"3.bad.example.org. 600 IN AAAA 127.0.0.1",
+	}
+
+	for _, record := range records {
+		const expect = "bad A"
+		if got, err := NewRR(record); err == nil || !strings.Contains(err.Error(), expect) {
+			t.Errorf("NewRR(%v) = %v, want err to contain %q", record, got, expect)
+		}
+	}
+}
+
 func TestParseTA(t *testing.T) {
 	rr, err := NewRR(` Ta 0 0 0`)
 	if err != nil {