Use copy instead of loop in EDNS0_SUBNET.unpack (#825)

edns.go

@@ -273,22 +273,16 @@ func (e *EDNS0_SUBNET) unpack(b []byte) error {
 		if e.SourceNetmask > net.IPv4len*8 || e.SourceScope > net.IPv4len*8 {
 			return errors.New("dns: bad netmask")
 		}
-		addr := make([]byte, net.IPv4len)
-		for i := 0; i < net.IPv4len && 4+i < len(b); i++ {
-			addr[i] = b[4+i]
-		}
-		e.Address = net.IPv4(addr[0], addr[1], addr[2], addr[3])
+		addr := make(net.IP, net.IPv4len)
+		copy(addr, b[4:])
+		e.Address = addr.To16()
 	case 2:
 		if e.SourceNetmask > net.IPv6len*8 || e.SourceScope > net.IPv6len*8 {
 			return errors.New("dns: bad netmask")
 		}
-		addr := make([]byte, net.IPv6len)
-		for i := 0; i < net.IPv6len && 4+i < len(b); i++ {
-			addr[i] = b[4+i]
-		}
-		e.Address = net.IP{addr[0], addr[1], addr[2], addr[3], addr[4],
-			addr[5], addr[6], addr[7], addr[8], addr[9], addr[10],
-			addr[11], addr[12], addr[13], addr[14], addr[15]}
+		addr := make(net.IP, net.IPv6len)
+		copy(addr, b[4:])
+		e.Address = addr
 	default:
 		return errors.New("dns: bad address family")
 	}

edns_test.go

@@ -1,6 +1,9 @@
 package dns
 
-import "testing"
+import (
+	"net"
+	"testing"
+)
 
 func TestOPTTtl(t *testing.T) {
 	e := &OPT{}
@@ -63,8 +66,8 @@ func TestOPTTtl(t *testing.T) {
 
 	e.SetExtendedRcode(42)
 	// ExtendedRcode has the last 4 bits set to 0.
-	if e.ExtendedRcode() != 42 & 0xFFFFFFF0 {
-		t.Errorf("set 42, expected %d, got %d", 42 & 0xFFFFFFF0, e.ExtendedRcode())
+	if e.ExtendedRcode() != 42&0xFFFFFFF0 {
+		t.Errorf("set 42, expected %d, got %d", 42&0xFFFFFFF0, e.ExtendedRcode())
 	}
 
 	// This will reset the 8 upper bits of the extended rcode
@@ -73,3 +76,36 @@ func TestOPTTtl(t *testing.T) {
 		t.Errorf("Setting a non-extended rcode is expected to set extended rcode to 0, got: %d", e.ExtendedRcode())
 	}
 }
+
+func TestEDNS0_SUBNETUnpack(t *testing.T) {
+	for _, ip := range []net.IP{
+		net.IPv4(0xde, 0xad, 0xbe, 0xef),
+		net.ParseIP("192.0.2.1"),
+		net.ParseIP("2001:db8::68"),
+	} {
+		var s1 EDNS0_SUBNET
+		s1.Address = ip
+
+		if ip.To4() == nil {
+			s1.Family = 2
+			s1.SourceNetmask = net.IPv6len * 8
+		} else {
+			s1.Family = 1
+			s1.SourceNetmask = net.IPv4len * 8
+		}
+
+		b, err := s1.pack()
+		if err != nil {
+			t.Fatalf("failed to pack: %v", err)
+		}
+
+		var s2 EDNS0_SUBNET
+		if err := s2.unpack(b); err != nil {
+			t.Fatalf("failed to unpack: %v", err)
+		}
+
+		if !ip.Equal(s2.Address) {
+			t.Errorf("address different after unpacking; expected %s, got %s", ip, s2.Address)
+		}
+	}
+}