Implement socket expr (#222)

Signed-off-by: black-desk <me@black-desk.cn>

expr/socket.go

@@ -0,0 +1,89 @@
+// Copyright 2023 Google LLC. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package expr
+
+import (
+	"encoding/binary"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/google/nftables/binaryutil"
+	"github.com/mdlayher/netlink"
+)
+
+type Socket struct {
+	Key      SocketKey
+	Level    uint32
+	Register uint32
+}
+
+type SocketKey uint32
+
+const (
+	// TODO, Once the constants below are available in golang.org/x/sys/unix, switch to use those.
+	NFTA_SOCKET_KEY   = 1
+	NFTA_SOCKET_DREG  = 2
+	NFTA_SOCKET_LEVEL = 3
+
+	NFT_SOCKET_TRANSPARENT = 0
+	NFT_SOCKET_MARK        = 1
+	NFT_SOCKET_WILDCARD    = 2
+	NFT_SOCKET_CGROUPV2    = 3
+
+	SocketKeyTransparent SocketKey = NFT_SOCKET_TRANSPARENT
+	SocketKeyMark        SocketKey = NFT_SOCKET_MARK
+	SocketKeyWildcard    SocketKey = NFT_SOCKET_WILDCARD
+	SocketKeyCgroupv2    SocketKey = NFT_SOCKET_CGROUPV2
+)
+
+func (e *Socket) marshal(fam byte) ([]byte, error) {
+	// NOTE: Socket.Level is only used when Socket.Key == SocketKeyCgroupv2. But `nft` always encoding it. Check link below:
+	// http://git.netfilter.org/nftables/tree/src/netlink_linearize.c?id=0583bac241ea18c9d7f61cb20ca04faa1e043b78#n319
+	exprData, err := netlink.MarshalAttributes(
+		[]netlink.Attribute{
+			{Type: NFTA_SOCKET_DREG, Data: binaryutil.BigEndian.PutUint32(e.Register)},
+			{Type: NFTA_SOCKET_KEY, Data: binaryutil.BigEndian.PutUint32(uint32(e.Key))},
+			{Type: NFTA_SOCKET_LEVEL, Data: binaryutil.BigEndian.PutUint32(uint32(e.Level))},
+		},
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return netlink.MarshalAttributes([]netlink.Attribute{
+		{Type: unix.NFTA_EXPR_NAME, Data: []byte("socket\x00")},
+		{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: exprData},
+	})
+}
+
+func (e *Socket) unmarshal(fam byte, data []byte) error {
+	ad, err := netlink.NewAttributeDecoder(data)
+	if err != nil {
+		return err
+	}
+
+	ad.ByteOrder = binary.BigEndian
+	for ad.Next() {
+		switch ad.Type() {
+		case NFTA_SOCKET_DREG:
+			e.Register = ad.Uint32()
+		case NFTA_SOCKET_KEY:
+			e.Key = SocketKey(ad.Uint32())
+		case NFTA_SOCKET_LEVEL:
+			e.Level = ad.Uint32()
+		}
+	}
+	return ad.Err()
+}

expr/socket_test.go

@@ -0,0 +1,100 @@
+// Copyright 2023 Google LLC. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package expr
+
+import (
+	"encoding/binary"
+	"reflect"
+	"testing"
+
+	"github.com/mdlayher/netlink"
+	"golang.org/x/sys/unix"
+)
+
+func TestSocket(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name   string
+		socket Socket
+	}{
+		{
+			name: "Unmarshal `socket transparent`",
+			socket: Socket{
+				Key:      SocketKeyTransparent,
+				Level:    0,
+				Register: 1,
+			},
+		},
+		{
+			name: "Unmarshal `socket cgroup level 5`",
+			socket: Socket{
+				Key:      SocketKeyCgroupv2,
+				Level:    5,
+				Register: 1,
+			},
+		},
+		{
+			name: "Unmarshal `socket cgroup level 1`",
+			socket: Socket{
+				Key:      SocketKeyCgroupv2,
+				Level:    1,
+				Register: 1,
+			},
+		},
+		{
+			name: "Unmarshal `socket wildcard`",
+			socket: Socket{
+				Key:      SocketKeyWildcard,
+				Level:    0,
+				Register: 1,
+			},
+		},
+		{
+			name: "Unmarshal `socket mark`",
+			socket: Socket{
+				Key:      SocketKeyMark,
+				Level:    0,
+				Register: 1,
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nSocket := Socket{}
+			data, err := tt.socket.marshal(0 /* don't care in this test */)
+			if err != nil {
+				t.Fatalf("marshal error: %+v", err)
+
+			}
+			ad, err := netlink.NewAttributeDecoder(data)
+			if err != nil {
+				t.Fatalf("NewAttributeDecoder() error: %+v", err)
+			}
+			ad.ByteOrder = binary.BigEndian
+			for ad.Next() {
+				if ad.Type() == unix.NFTA_EXPR_DATA {
+					if err := nSocket.unmarshal(0, ad.Bytes()); err != nil {
+						t.Errorf("unmarshal error: %+v", err)
+						break
+					}
+				}
+			}
+			if !reflect.DeepEqual(tt.socket, nSocket) {
+				t.Fatalf("original %+v and recovered %+v Socket structs are different", tt.socket, nSocket)
+			}
+		})
+	}
+}