Added Other expression type to support types that are not explicitly supported.

This replaces the previous behaviour of silently ignoring unkown types
when decoding

expr/other.go

@@ -0,0 +1,50 @@
+package expr
+
+import (
+	"encoding/binary"
+
+	"github.com/mdlayher/netlink"
+	"golang.org/x/sys/unix"
+)
+
+// Other is a nft expression that this library don't know
+// It can unmarshal/marshal it as list of attributes
+type Other struct {
+	Type       string // the type (name) of the expression
+	Attributes []OtherAttribute
+}
+
+// OtherAttribute is one of the attributes in an Other
+type OtherAttribute struct {
+	Type uint16
+	Data []byte
+}
+
+func (e *Other) marshal() ([]byte, error) {
+	attrs := make([]netlink.Attribute, len(e.Attributes))
+	for i, a := range e.Attributes {
+		attrs[i].Type = a.Type
+		attrs[i].Data = a.Data
+	}
+
+	data, err := netlink.MarshalAttributes(attrs)
+	if err != nil {
+		return nil, err
+	}
+	return netlink.MarshalAttributes([]netlink.Attribute{
+		{Type: unix.NFTA_EXPR_NAME, Data: []byte(e.Type + "\x00")},
+		{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: data},
+	})
+}
+
+func (e *Other) unmarshal(data []byte) error {
+	ad, err := netlink.NewAttributeDecoder(data)
+	if err != nil {
+		return err
+	}
+	ad.ByteOrder = binary.BigEndian
+	for ad.Next() {
+		e.Attributes = append(e.Attributes, OtherAttribute{Type: ad.Type(), Data: ad.Bytes()})
+	}
+	return ad.Err()
+}

expr/other_test.go

@@ -0,0 +1,54 @@
+package expr
+
+import (
+	"encoding/binary"
+	"reflect"
+	"testing"
+
+	"github.com/mdlayher/netlink"
+	"golang.org/x/sys/unix"
+)
+
+func TestOther(t *testing.T) {
+	orig := &Other{
+		Type: "testing",
+		Attributes: []OtherAttribute{
+			{1, []byte{66, 5}},
+			{5, []byte("test")},
+		},
+	}
+
+	data, err := Marshal(orig)
+	if err != nil {
+		t.Fatal("Error marshalling other: ", err)
+	}
+
+	ad, err := netlink.NewAttributeDecoder(data)
+	if err != nil {
+		t.Fatalf("NewAttributeDecoder() error: %+v", err)
+	}
+	ad.ByteOrder = binary.BigEndian
+	if !ad.Next() {
+		t.Fatal("too short")
+	}
+	if ad.Type() != unix.NFTA_EXPR_NAME || ad.String() != orig.Type {
+		t.Fatalf("wrong name %d:%q", ad.Type(), ad.String())
+	}
+
+	if !ad.Next() {
+		t.Fatal("too short")
+	}
+	decoded := &Other{Type: "testing"}
+	if ad.Type() != unix.NFTA_EXPR_DATA {
+		t.Fatal("Wrong type for data:", ad.Type())
+	}
+	if err := Unmarshal(ad.Bytes(), decoded); err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(orig, decoded) {
+		t.Errorf("Wrong structure decoded: %+v vs %+v", decoded, orig)
+	}
+	if ad.Next() {
+		t.Error("Got extra attribute: ", ad.Type())
+	}
+}

rule.go

@@ -248,11 +248,8 @@ func exprsFromMsg(b []byte) ([]expr.Any, error) {
 						e = &expr.Limit{}
 					case "dynset":
 						e = &expr.Dynset{}
-					}
+					default:
-					if e == nil {
+						e = &expr.Other{Type: name}
-						// TODO: introduce an opaque expression type so that users know
-						// something is here.
-						continue // unsupported expression type
 					}
 
 					ad.Do(func(b []byte) error {