Allow for zero-length ND_LLADDR

Fixes #199
This change allows for neighbor entries with a
zero-length LLADDR attribute.
This has the side-effect that consumers of this
module might have to filter this entry, depending
on their usage.

Signed-off-by: Jeroen Simonetti <[email protected]>

Author: jsimonetti

neigh.go

@@ -194,7 +194,7 @@ func (a *NeighAttributes) decode(ad *netlink.AttributeDecoder) error {
 			// Allow IEEE 802 MAC-48, EUI-48, EUI-64, or 20-octet
 			// IP over InfiniBand link-layer addresses
 			l := len(ad.Bytes())
-			if l != 6 && l != 8 && l != 20 {
+			if l != 0 && l != 6 && l != 8 && l != 20 {
 				return errInvalidNeighMessageAttr
 			}
 			a.LLAddress = ad.Bytes()

neigh_test.go

@@ -3,9 +3,9 @@ package rtnetlink
 import (
 	"bytes"
 	"net"
-	"reflect"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
 	"github.com/jsimonetti/rtnetlink/internal/unix"
 )
 
@@ -167,6 +167,29 @@ func TestNeighMessageUnmarshalBinary(t *testing.T) {
 				Type:  unix.NTF_PROXY,
 			},
 		},
+		{
+			name: "zero-length attributes",
+			m: &NeighMessage{
+				Index: 2,
+				State: 64,
+				Type:  unix.NTF_PROXY,
+				Attributes: &NeighAttributes{
+					Address:   net.ParseIP("0.0.0.0"),
+					LLAddress: []byte{},
+					IfIndex:   0,
+				},
+			},
+			b: []byte{
+				0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00,
+				0x40, 0x00, 0x00, 0x08, 0x06, 0x00, 0x00, 0x00,
+				0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x01, 0x00,
+				0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+				0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00,
+				0x04, 0x00, 0x02, 0x00,
+				0x00, 0x00, 0x08, 0x00, 0x08, 0x00,
+				0x00, 0x00, 0x00, 0x00,
+			},
+		},
 	}
 
 	for _, tt := range tests {
@@ -180,9 +203,8 @@ func TestNeighMessageUnmarshalBinary(t *testing.T) {
 			if err != nil {
 				return
 			}
-
-			if want, got := tt.m, m; !reflect.DeepEqual(want, got) {
-				t.Fatalf("unexpected Message:\n- want: %#v\n-  got: %#v", want, got)
+			if diff := cmp.Diff(tt.m, m); diff != "" {
+				t.Fatalf("unexpected parsed messages (-want +got):\n%s", diff)
 			}
 		})
 	}