return error if index < -1

2 files changed, 6 insertions, 1 deletions

diff --git a/dhcpv6/dhcpv6.go b/dhcpv6/dhcpv6.go
index c9e42e2..b424101 100644
--- a/dhcpv6/dhcpv6.go
+++ b/dhcpv6/dhcpv6.go
@@ -153,7 +153,9 @@ func DecapsulateRelayIndex(l DHCPv6, index int) (DHCPv6, error) {
 	if !l.IsRelay() {
 		return l, nil
 	}
-	if index == -1 {
+	if index < -1 {
+		return nil, fmt.Errorf("Invalid index: %d", index)
+	} else if index == -1 {
 		for {
 			d, err := DecapsulateRelay(l)
 			if err != nil {
diff --git a/dhcpv6/dhcpv6_test.go b/dhcpv6/dhcpv6_test.go
index 6b7d2df..2db5649 100644
--- a/dhcpv6/dhcpv6_test.go
+++ b/dhcpv6/dhcpv6_test.go
@@ -74,6 +74,9 @@ func TestDecapsulateRelayIndex(t *testing.T) {
 	require.Equal(t, relay.HopCount(), uint8(0))
 	require.Equal(t, relay.LinkAddr(), net.IPv6linklocalallnodes)
 	require.Equal(t, relay.PeerAddr(), net.IPv6interfacelocalallnodes)
+
+	_, err = DecapsulateRelayIndex(r3, -2)
+	require.Error(t, err)
 }
 
 func TestSettersAndGetters(t *testing.T) {