diff --git a/engine/parse.go b/engine/parse.go
index f83649a..20ee46f 100644
--- a/engine/parse.go
+++ b/engine/parse.go
@@ -9,6 +9,7 @@ import (
 	"github.com/xjasonlyu/tun2socks/device"
 	"github.com/xjasonlyu/tun2socks/device/tun"
 	"github.com/xjasonlyu/tun2socks/proxy"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 )
 
 func parseDevice(s string, mtu uint32) (device.Device, error) {
@@ -34,7 +35,7 @@ func parseDevice(s string, mtu uint32) (device.Device, error) {
 
 func parseProxy(s string) (proxy.Proxy, error) {
 	if !strings.Contains(s, "://") {
-		s = proxy.Socks5Proto.String() + "://" + s /* default protocol */
+		s = proto.Socks5.String() + "://" + s /* default protocol */
 	}
 
 	u, err := url.Parse(s)
@@ -42,17 +43,17 @@ func parseProxy(s string) (proxy.Proxy, error) {
 		return nil, err
 	}
 
-	proto := strings.ToLower(u.Scheme)
+	protocol := strings.ToLower(u.Scheme)
 
-	switch proto {
-	case proxy.DirectProto.String():
+	switch protocol {
+	case proto.Direct.String():
 		return proxy.NewDirect(), nil
-	case proxy.Socks5Proto.String():
+	case proto.Socks5.String():
 		return proxy.NewSocks5(parseSocks(u))
-	case proxy.ShadowsocksProto.String():
+	case proto.Shadowsocks.String():
 		return proxy.NewShadowsocks(parseShadowsocks(u))
 	default:
-		return nil, fmt.Errorf("unsupported protocol: %s", proto)
+		return nil, fmt.Errorf("unsupported protocol: %s", protocol)
 	}
 }
 
diff --git a/proxy/base.go b/proxy/base.go
index ca5cb90..2185404 100755
--- a/proxy/base.go
+++ b/proxy/base.go
@@ -6,24 +6,26 @@ import (
 	"net"
 
 	"github.com/xjasonlyu/tun2socks/common/adapter"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 )
 
 var _ Proxy = (*Base)(nil)
 
 type Base struct {
-	addr string
+	addr  string
+	proto proto.Proto
 }
 
-func NewBase(addr string) *Base {
-	return &Base{addr: addr}
+func NewBase(addr string, proto proto.Proto) *Base {
+	return &Base{addr: addr, proto: proto}
 }
 
 func (b *Base) Addr() string {
 	return b.addr
 }
 
-func (b *Base) Proto() string {
-	return ""
+func (b *Base) Proto() proto.Proto {
+	return b.proto
 }
 
 func (b *Base) DialContext(context.Context, *adapter.Metadata) (net.Conn, error) {
diff --git a/proxy/direct.go b/proxy/direct.go
index aa577de..6880c1f 100755
--- a/proxy/direct.go
+++ b/proxy/direct.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/xjasonlyu/tun2socks/common/adapter"
 	"github.com/xjasonlyu/tun2socks/component/dialer"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 )
 
 var _ Proxy = (*Direct)(nil)
@@ -16,14 +17,12 @@ type Direct struct {
 
 func NewDirect() *Direct {
 	return &Direct{
-		Base: &Base{},
+		Base: &Base{
+			proto: proto.Direct,
+		},
 	}
 }
 
-func (d *Direct) Proto() string {
-	return DirectProto.String()
-}
-
 func (d *Direct) DialContext(ctx context.Context, metadata *adapter.Metadata) (net.Conn, error) {
 	c, err := dialer.DialContext(ctx, "tcp", metadata.DestinationAddress())
 	if err != nil {
diff --git a/proxy/proto.go b/proxy/proto/proto.go
similarity index 60%
rename from proxy/proto.go
rename to proxy/proto/proto.go
index 64c859b..4f7286d 100644
--- a/proxy/proto.go
+++ b/proxy/proto/proto.go
@@ -1,22 +1,22 @@
-package proxy
+package proto
 
 import "fmt"
 
 const (
-	DirectProto Proto = iota
-	ShadowsocksProto
-	Socks5Proto
+	Direct Proto = iota
+	Shadowsocks
+	Socks5
 )
 
 type Proto uint8
 
 func (proto Proto) String() string {
 	switch proto {
-	case DirectProto:
+	case Direct:
 		return "direct"
-	case ShadowsocksProto:
+	case Shadowsocks:
 		return "ss"
-	case Socks5Proto:
+	case Socks5:
 		return "socks5"
 	default:
 		return fmt.Sprintf("proto(%d)", proto)
diff --git a/proxy/proxy.go b/proxy/proxy.go
index d9dadf5..df36883 100755
--- a/proxy/proxy.go
+++ b/proxy/proxy.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/xjasonlyu/tun2socks/common/adapter"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 )
 
 const (
@@ -25,7 +26,7 @@ type Dialer interface {
 type Proxy interface {
 	Dialer
 	Addr() string
-	Proto() string
+	Proto() proto.Proto
 }
 
 // SetDialer sets default Dialer.
diff --git a/proxy/shadowsocks.go b/proxy/shadowsocks.go
index cef2bb2..d8de273 100755
--- a/proxy/shadowsocks.go
+++ b/proxy/shadowsocks.go
@@ -10,6 +10,7 @@ import (
 	"github.com/xjasonlyu/tun2socks/component/dialer"
 	obfs "github.com/xjasonlyu/tun2socks/component/simple-obfs"
 	"github.com/xjasonlyu/tun2socks/component/socks5"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 
 	"github.com/Dreamacro/go-shadowsocks2/core"
 )
@@ -32,17 +33,16 @@ func NewShadowsocks(addr, method, password, obfsMode, obfsHost string) (*Shadows
 	}
 
 	return &Shadowsocks{
-		Base:     NewBase(addr),
+		Base: &Base{
+			addr:  addr,
+			proto: proto.Shadowsocks,
+		},
 		cipher:   cipher,
 		obfsMode: obfsMode,
 		obfsHost: obfsHost,
 	}, nil
 }
 
-func (ss *Shadowsocks) Proto() string {
-	return ShadowsocksProto.String()
-}
-
 func (ss *Shadowsocks) DialContext(ctx context.Context, metadata *adapter.Metadata) (c net.Conn, err error) {
 	c, err = dialer.DialContext(ctx, "tcp", ss.Addr())
 	if err != nil {
diff --git a/proxy/socks5.go b/proxy/socks5.go
index 2792b41..7ccbbe6 100755
--- a/proxy/socks5.go
+++ b/proxy/socks5.go
@@ -10,6 +10,7 @@ import (
 	"github.com/xjasonlyu/tun2socks/common/adapter"
 	"github.com/xjasonlyu/tun2socks/component/dialer"
 	"github.com/xjasonlyu/tun2socks/component/socks5"
+	"github.com/xjasonlyu/tun2socks/proxy/proto"
 )
 
 var _ Proxy = (*Socks5)(nil)
@@ -23,16 +24,15 @@ type Socks5 struct {
 
 func NewSocks5(addr, user, pass string) (*Socks5, error) {
 	return &Socks5{
-		Base: NewBase(addr),
+		Base: &Base{
+			addr:  addr,
+			proto: proto.Socks5,
+		},
 		user: user,
 		pass: pass,
 	}, nil
 }
 
-func (ss *Socks5) Proto() string {
-	return Socks5Proto.String()
-}
-
 func (ss *Socks5) DialContext(ctx context.Context, metadata *adapter.Metadata) (c net.Conn, err error) {
 	c, err = dialer.DialContext(ctx, "tcp", ss.Addr())
 	if err != nil {