feat: add MPTCP support

infra/conf/cfgcommon/socketcfg/socket.go

@@ -18,6 +18,7 @@ type SocketConfig struct {
 	RxBufSize            uint64 `json:"rxBufSize"`
 	TxBufSize            uint64 `json:"txBufSize"`
 	ForceBufSize         bool   `json:"forceBufSize"`
+	MPTCP                *bool  `json:"mptcp"`
 }
 
 // Build implements Buildable.
@@ -46,6 +47,15 @@ func (c *SocketConfig) Build() (*internet.SocketConfig, error) {
 		tproxy = internet.SocketConfig_Off
 	}
 
+	var mptcpSettings internet.MPTCPState
+	if c.MPTCP != nil {
+		if *c.MPTCP {
+			mptcpSettings = internet.MPTCPState_Enable
+		} else {
+			mptcpSettings = internet.MPTCPState_Disable
+		}
+	}
+
 	return &internet.SocketConfig{
 		Mark:                 c.Mark,
 		Tfo:                  tfoSettings,
@@ -58,5 +68,6 @@ func (c *SocketConfig) Build() (*internet.SocketConfig, error) {
 		TxBufSize:            int64(c.TxBufSize),
 		ForceBufSize:         c.ForceBufSize,
 		BindToDevice:         c.BindToDevice,
+		Mptcp:                mptcpSettings,
 	}, nil
 }

infra/conf/v4/transport_test.go

@@ -38,13 +38,15 @@ func TestSocketConfig(t *testing.T) {
 			Input: `{
 				"mark": 1,
 				"tcpFastOpen": true,
-				"tcpFastOpenQueueLength": 1024
+				"tcpFastOpenQueueLength": 1024,
+				"mptcp": true
 			}`,
 			Parser: createParser(),
 			Output: &internet.SocketConfig{
 				Mark:           1,
 				Tfo:            internet.SocketConfig_Enable,
 				TfoQueueLength: 1024,
+				Mptcp:          internet.MPTCPState_Enable,
 			},
 		},
 	})

transport/internet/config.pb.go

@@ -1,3 +1,9 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.34.2
+// 	protoc        v4.25.3
+// source: transport/internet/config.proto
+
 package internet
 
 import (
@@ -73,6 +79,60 @@ func (TransportProtocol) EnumDescriptor() ([]byte, []int) {
 	return file_transport_internet_config_proto_rawDescGZIP(), []int{0}
 }
 
+// MPTCP is the state of MPTCP settings.
+// Define it here to avoid conflict with TCPFastOpenState.
+type MPTCPState int32
+
+const (
+	// AsIs is to leave the current MPTCP state as is, unmodified.
+	MPTCPState_AsIs MPTCPState = 0
+	// Enable is for enabling MPTCP explictly.
+	MPTCPState_Enable MPTCPState = 1
+	// Disable is for disabling MPTCP explictly.
+	MPTCPState_Disable MPTCPState = 2
+)
+
+// Enum value maps for MPTCPState.
+var (
+	MPTCPState_name = map[int32]string{
+		0: "AsIs",
+		1: "Enable",
+		2: "Disable",
+	}
+	MPTCPState_value = map[string]int32{
+		"AsIs":    0,
+		"Enable":  1,
+		"Disable": 2,
+	}
+)
+
+func (x MPTCPState) Enum() *MPTCPState {
+	p := new(MPTCPState)
+	*p = x
+	return p
+}
+
+func (x MPTCPState) String() string {
+	return protoimpl.X.EnumStringOf(x.Descriptor(), protoreflect.EnumNumber(x))
+}
+
+func (MPTCPState) Descriptor() protoreflect.EnumDescriptor {
+	return file_transport_internet_config_proto_enumTypes[1].Descriptor()
+}
+
+func (MPTCPState) Type() protoreflect.EnumType {
+	return &file_transport_internet_config_proto_enumTypes[1]
+}
+
+func (x MPTCPState) Number() protoreflect.EnumNumber {
+	return protoreflect.EnumNumber(x)
+}
+
+// Deprecated: Use MPTCPState.Descriptor instead.
+func (MPTCPState) EnumDescriptor() ([]byte, []int) {
+	return file_transport_internet_config_proto_rawDescGZIP(), []int{1}
+}
+
 type SocketConfig_TCPFastOpenState int32
 
 const (
@@ -109,11 +169,11 @@ func (x SocketConfig_TCPFastOpenState) String() string {
 }
 
 func (SocketConfig_TCPFastOpenState) Descriptor() protoreflect.EnumDescriptor {
-	return file_transport_internet_config_proto_enumTypes[1].Descriptor()
+	return file_transport_internet_config_proto_enumTypes[2].Descriptor()
 }
 
 func (SocketConfig_TCPFastOpenState) Type() protoreflect.EnumType {
-	return &file_transport_internet_config_proto_enumTypes[1]
+	return &file_transport_internet_config_proto_enumTypes[2]
 }
 
 func (x SocketConfig_TCPFastOpenState) Number() protoreflect.EnumNumber {
@@ -161,11 +221,11 @@ func (x SocketConfig_TProxyMode) String() string {
 }
 
 func (SocketConfig_TProxyMode) Descriptor() protoreflect.EnumDescriptor {
-	return file_transport_internet_config_proto_enumTypes[2].Descriptor()
+	return file_transport_internet_config_proto_enumTypes[3].Descriptor()
 }
 
 func (SocketConfig_TProxyMode) Type() protoreflect.EnumType {
-	return &file_transport_internet_config_proto_enumTypes[2]
+	return &file_transport_internet_config_proto_enumTypes[3]
 }
 
 func (x SocketConfig_TProxyMode) Number() protoreflect.EnumNumber {
@@ -410,17 +470,18 @@ type SocketConfig struct {
 	Tproxy SocketConfig_TProxyMode `protobuf:"varint,3,opt,name=tproxy,proto3,enum=v2ray.core.transport.internet.SocketConfig_TProxyMode" json:"tproxy,omitempty"`
 	// ReceiveOriginalDestAddress is for enabling IP_RECVORIGDSTADDR socket
 	// option. This option is for UDP only.
-	ReceiveOriginalDestAddress bool   `protobuf:"varint,4,opt,name=receive_original_dest_address,json=receiveOriginalDestAddress,proto3" json:"receive_original_dest_address,omitempty"`
-	BindAddress                []byte `protobuf:"bytes,5,opt,name=bind_address,json=bindAddress,proto3" json:"bind_address,omitempty"`
-	BindPort                   uint32 `protobuf:"varint,6,opt,name=bind_port,json=bindPort,proto3" json:"bind_port,omitempty"`
-	AcceptProxyProtocol        bool   `protobuf:"varint,7,opt,name=accept_proxy_protocol,json=acceptProxyProtocol,proto3" json:"accept_proxy_protocol,omitempty"`
-	TcpKeepAliveInterval       int32  `protobuf:"varint,8,opt,name=tcp_keep_alive_interval,json=tcpKeepAliveInterval,proto3" json:"tcp_keep_alive_interval,omitempty"`
-	TfoQueueLength             uint32 `protobuf:"varint,9,opt,name=tfo_queue_length,json=tfoQueueLength,proto3" json:"tfo_queue_length,omitempty"`
-	TcpKeepAliveIdle           int32  `protobuf:"varint,10,opt,name=tcp_keep_alive_idle,json=tcpKeepAliveIdle,proto3" json:"tcp_keep_alive_idle,omitempty"`
-	BindToDevice               string `protobuf:"bytes,11,opt,name=bind_to_device,json=bindToDevice,proto3" json:"bind_to_device,omitempty"`
-	RxBufSize                  int64  `protobuf:"varint,12,opt,name=rx_buf_size,json=rxBufSize,proto3" json:"rx_buf_size,omitempty"`
-	TxBufSize                  int64  `protobuf:"varint,13,opt,name=tx_buf_size,json=txBufSize,proto3" json:"tx_buf_size,omitempty"`
-	ForceBufSize               bool   `protobuf:"varint,14,opt,name=force_buf_size,json=forceBufSize,proto3" json:"force_buf_size,omitempty"`
+	ReceiveOriginalDestAddress bool       `protobuf:"varint,4,opt,name=receive_original_dest_address,json=receiveOriginalDestAddress,proto3" json:"receive_original_dest_address,omitempty"`
+	BindAddress                []byte     `protobuf:"bytes,5,opt,name=bind_address,json=bindAddress,proto3" json:"bind_address,omitempty"`
+	BindPort                   uint32     `protobuf:"varint,6,opt,name=bind_port,json=bindPort,proto3" json:"bind_port,omitempty"`
+	AcceptProxyProtocol        bool       `protobuf:"varint,7,opt,name=accept_proxy_protocol,json=acceptProxyProtocol,proto3" json:"accept_proxy_protocol,omitempty"`
+	TcpKeepAliveInterval       int32      `protobuf:"varint,8,opt,name=tcp_keep_alive_interval,json=tcpKeepAliveInterval,proto3" json:"tcp_keep_alive_interval,omitempty"`
+	TfoQueueLength             uint32     `protobuf:"varint,9,opt,name=tfo_queue_length,json=tfoQueueLength,proto3" json:"tfo_queue_length,omitempty"`
+	TcpKeepAliveIdle           int32      `protobuf:"varint,10,opt,name=tcp_keep_alive_idle,json=tcpKeepAliveIdle,proto3" json:"tcp_keep_alive_idle,omitempty"`
+	BindToDevice               string     `protobuf:"bytes,11,opt,name=bind_to_device,json=bindToDevice,proto3" json:"bind_to_device,omitempty"`
+	RxBufSize                  int64      `protobuf:"varint,12,opt,name=rx_buf_size,json=rxBufSize,proto3" json:"rx_buf_size,omitempty"`
+	TxBufSize                  int64      `protobuf:"varint,13,opt,name=tx_buf_size,json=txBufSize,proto3" json:"tx_buf_size,omitempty"`
+	ForceBufSize               bool       `protobuf:"varint,14,opt,name=force_buf_size,json=forceBufSize,proto3" json:"force_buf_size,omitempty"`
+	Mptcp                      MPTCPState `protobuf:"varint,15,opt,name=mptcp,proto3,enum=v2ray.core.transport.internet.MPTCPState" json:"mptcp,omitempty"`
 }
 
 func (x *SocketConfig) Reset() {
@@ -553,6 +614,13 @@ func (x *SocketConfig) GetForceBufSize() bool {
 	return false
 }
 
+func (x *SocketConfig) GetMptcp() MPTCPState {
+	if x != nil {
+		return x.Mptcp
+	}
+	return MPTCPState_AsIs
+}
+
 var File_transport_internet_config_proto protoreflect.FileDescriptor
 
 var file_transport_internet_config_proto_rawDesc = []byte{
@@ -605,7 +673,7 @@ var file_transport_internet_config_proto_rawDesc = []byte{
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@@ -646,27 +714,34 @@ var file_transport_internet_config_proto_rawDesc = []byte{
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 }
 
 var (
@@ -681,32 +756,34 @@ func file_transport_internet_config_proto_rawDescGZIP() []byte {
 	return file_transport_internet_config_proto_rawDescData
 }
 
-var file_transport_internet_config_proto_enumTypes = make([]protoimpl.EnumInfo, 3)
+var file_transport_internet_config_proto_enumTypes = make([]protoimpl.EnumInfo, 4)
 var file_transport_internet_config_proto_msgTypes = make([]protoimpl.MessageInfo, 4)
-var file_transport_internet_config_proto_goTypes = []interface{}{
+var file_transport_internet_config_proto_goTypes = []any{
 	(TransportProtocol)(0),             // 0: v2ray.core.transport.internet.TransportProtocol
-	(SocketConfig_TCPFastOpenState)(0), // 1: v2ray.core.transport.internet.SocketConfig.TCPFastOpenState
-	(SocketConfig_TProxyMode)(0),       // 2: v2ray.core.transport.internet.SocketConfig.TProxyMode
-	(*TransportConfig)(nil),            // 3: v2ray.core.transport.internet.TransportConfig
-	(*StreamConfig)(nil),               // 4: v2ray.core.transport.internet.StreamConfig
-	(*ProxyConfig)(nil),                // 5: v2ray.core.transport.internet.ProxyConfig
-	(*SocketConfig)(nil),               // 6: v2ray.core.transport.internet.SocketConfig
-	(*anypb.Any)(nil),                  // 7: google.protobuf.Any
+	(MPTCPState)(0),                    // 1: v2ray.core.transport.internet.MPTCPState
+	(SocketConfig_TCPFastOpenState)(0), // 2: v2ray.core.transport.internet.SocketConfig.TCPFastOpenState
+	(SocketConfig_TProxyMode)(0),       // 3: v2ray.core.transport.internet.SocketConfig.TProxyMode
+	(*TransportConfig)(nil),            // 4: v2ray.core.transport.internet.TransportConfig
+	(*StreamConfig)(nil),               // 5: v2ray.core.transport.internet.StreamConfig
+	(*ProxyConfig)(nil),                // 6: v2ray.core.transport.internet.ProxyConfig
+	(*SocketConfig)(nil),               // 7: v2ray.core.transport.internet.SocketConfig
+	(*anypb.Any)(nil),                  // 8: google.protobuf.Any
 }
 var file_transport_internet_config_proto_depIdxs = []int32{
 	0, // 0: v2ray.core.transport.internet.TransportConfig.protocol:type_name -> v2ray.core.transport.internet.TransportProtocol
-	7, // 1: v2ray.core.transport.internet.TransportConfig.settings:type_name -> google.protobuf.Any
+	8, // 1: v2ray.core.transport.internet.TransportConfig.settings:type_name -> google.protobuf.Any
 	0, // 2: v2ray.core.transport.internet.StreamConfig.protocol:type_name -> v2ray.core.transport.internet.TransportProtocol
-	3, // 3: v2ray.core.transport.internet.StreamConfig.transport_settings:type_name -> v2ray.core.transport.internet.TransportConfig
-	7, // 4: v2ray.core.transport.internet.StreamConfig.security_settings:type_name -> google.protobuf.Any
-	6, // 5: v2ray.core.transport.internet.StreamConfig.socket_settings:type_name -> v2ray.core.transport.internet.SocketConfig
-	1, // 6: v2ray.core.transport.internet.SocketConfig.tfo:type_name -> v2ray.core.transport.internet.SocketConfig.TCPFastOpenState
-	2, // 7: v2ray.core.transport.internet.SocketConfig.tproxy:type_name -> v2ray.core.transport.internet.SocketConfig.TProxyMode
-	8, // [8:8] is the sub-list for method output_type
-	8, // [8:8] is the sub-list for method input_type
-	8, // [8:8] is the sub-list for extension type_name
-	8, // [8:8] is the sub-list for extension extendee
-	0, // [0:8] is the sub-list for field type_name
+	4, // 3: v2ray.core.transport.internet.StreamConfig.transport_settings:type_name -> v2ray.core.transport.internet.TransportConfig
+	8, // 4: v2ray.core.transport.internet.StreamConfig.security_settings:type_name -> google.protobuf.Any
+	7, // 5: v2ray.core.transport.internet.StreamConfig.socket_settings:type_name -> v2ray.core.transport.internet.SocketConfig
+	2, // 6: v2ray.core.transport.internet.SocketConfig.tfo:type_name -> v2ray.core.transport.internet.SocketConfig.TCPFastOpenState
+	3, // 7: v2ray.core.transport.internet.SocketConfig.tproxy:type_name -> v2ray.core.transport.internet.SocketConfig.TProxyMode
+	1, // 8: v2ray.core.transport.internet.SocketConfig.mptcp:type_name -> v2ray.core.transport.internet.MPTCPState
+	9, // [9:9] is the sub-list for method output_type
+	9, // [9:9] is the sub-list for method input_type
+	9, // [9:9] is the sub-list for extension type_name
+	9, // [9:9] is the sub-list for extension extendee
+	0, // [0:9] is the sub-list for field type_name
 }
 
 func init() { file_transport_internet_config_proto_init() }
@@ -715,7 +792,7 @@ func file_transport_internet_config_proto_init() {
 		return
 	}
 	if !protoimpl.UnsafeEnabled {
-		file_transport_internet_config_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+		file_transport_internet_config_proto_msgTypes[0].Exporter = func(v any, i int) any {
 			switch v := v.(*TransportConfig); i {
 			case 0:
 				return &v.state
@@ -727,7 +804,7 @@ func file_transport_internet_config_proto_init() {
 				return nil
 			}
 		}
-		file_transport_internet_config_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+		file_transport_internet_config_proto_msgTypes[1].Exporter = func(v any, i int) any {
 			switch v := v.(*StreamConfig); i {
 			case 0:
 				return &v.state
@@ -739,7 +816,7 @@ func file_transport_internet_config_proto_init() {
 				return nil
 			}
 		}
-		file_transport_internet_config_proto_msgTypes[2].Exporter = func(v interface{}, i int) interface{} {
+		file_transport_internet_config_proto_msgTypes[2].Exporter = func(v any, i int) any {
 			switch v := v.(*ProxyConfig); i {
 			case 0:
 				return &v.state
@@ -751,7 +828,7 @@ func file_transport_internet_config_proto_init() {
 				return nil
 			}
 		}
-		file_transport_internet_config_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
+		file_transport_internet_config_proto_msgTypes[3].Exporter = func(v any, i int) any {
 			switch v := v.(*SocketConfig); i {
 			case 0:
 				return &v.state
@@ -769,7 +846,7 @@ func file_transport_internet_config_proto_init() {
 		File: protoimpl.DescBuilder{
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_transport_internet_config_proto_rawDesc,
-			NumEnums:      3,
+			NumEnums:      4,
 			NumMessages:   4,
 			NumExtensions: 0,
 			NumServices:   0,

transport/internet/config.proto

@@ -53,6 +53,17 @@ message ProxyConfig {
   bool transportLayerProxy = 2;
 }
 
+// MPTCP is the state of MPTCP settings.
+// Define it here to avoid conflict with TCPFastOpenState.
+enum MPTCPState {
+  // AsIs is to leave the current MPTCP state as is, unmodified.
+  AsIs = 0;
+  // Enable is for enabling MPTCP explictly.
+  Enable = 1;
+  // Disable is for disabling MPTCP explictly.
+  Disable = 2;
+}
+
 // SocketConfig is options to be applied on network sockets.
 message SocketConfig {
   // Mark of the connection. If non-zero, the value will be set to SO_MARK.
@@ -103,4 +114,7 @@ message SocketConfig {
   int64 rx_buf_size = 12;
   int64 tx_buf_size = 13;
   bool force_buf_size = 14;
+
+
+  MPTCPState mptcp = 15;
 }

transport/internet/sockopt_test.go

@@ -39,3 +39,33 @@ func TestTCPFastOpen(t *testing.T) {
 		t.Fatal(r)
 	}
 }
+
+// Currently, Multipath TCP is only supported on Linux.
+// We test the Multipath TCP Settings on other platforms for ensure code will not have any negative impact on other platforms.
+func TestMultipathTCP(t *testing.T) {
+	tcpServer := tcp.Server{
+		MsgProcessor: func(b []byte) []byte {
+			return b
+		},
+	}
+	dest, err := tcpServer.StartContext(context.Background(), &SocketConfig{Mptcp: MPTCPState_Enable})
+	common.Must(err)
+	defer tcpServer.Close()
+
+	ctx := context.Background()
+	dialer := DefaultSystemDialer{}
+	conn, err := dialer.Dial(ctx, nil, dest, &SocketConfig{
+		Mptcp: MPTCPState_Enable,
+	})
+	common.Must(err)
+	defer conn.Close()
+
+	_, err = conn.Write([]byte("abcd"))
+	common.Must(err)
+
+	b := buf.New()
+	common.Must2(b.ReadFrom(conn))
+	if r := cmp.Diff(b.Bytes(), []byte("abcd")); r != "" {
+		t.Fatal(r)
+	}
+}

transport/internet/system_dialer.go

@@ -73,6 +73,15 @@ func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest ne
 		KeepAlive: goStdKeepAlive,
 	}
 
+	if sockopt != nil {
+		switch sockopt.Mptcp {
+		case MPTCPState_Enable:
+			dialer.SetMultipathTCP(true)
+		case MPTCPState_Disable:
+			dialer.SetMultipathTCP(false)
+		}
+	}
+
 	if sockopt != nil || len(d.controllers) > 0 {
 		dialer.Control = func(network, address string, c syscall.RawConn) error {
 			return c.Control(func(fd uintptr) {

transport/internet/system_listener.go

@@ -69,8 +69,17 @@ func (dl *DefaultListener) Listen(ctx context.Context, addr net.Addr, sockopt *S
 		network = addr.Network()
 		address = addr.String()
 		lc.Control = getControlFunc(ctx, sockopt, dl.controllers)
-		if sockopt != nil && (sockopt.TcpKeepAliveInterval != 0 || sockopt.TcpKeepAliveIdle != 0) {
-			lc.KeepAlive = time.Duration(-1)
+		if sockopt != nil {
+			switch sockopt.Mptcp {
+			case MPTCPState_Enable:
+				lc.SetMultipathTCP(true)
+			case MPTCPState_Disable:
+				lc.SetMultipathTCP(false)
+			}
+
+			if sockopt.TcpKeepAliveInterval != 0 || sockopt.TcpKeepAliveIdle != 0 {
+				lc.KeepAlive = time.Duration(-1)
+			}
 		}
 	case *net.UnixAddr:
 		lc.Control = nil