add go-tun2socks code

proxy/echo/tcp.go

@@ -0,0 +1,26 @@
+package echo
+
+import (
+	"io"
+	"net"
+
+	"github.com/xjasonlyu/tun2socks/core"
+)
+
+// An echo proxy, do nothing but echo back data to the sender, the handler was
+// created for testing purposes, it may causes issues when more than one clients
+// are connecting the handler simultaneously.
+type tcpHandler struct{}
+
+func NewTCPHandler() core.TCPConnHandler {
+	return &tcpHandler{}
+}
+
+func (h *tcpHandler) echoBack(conn net.Conn) {
+	io.Copy(conn, conn)
+}
+
+func (h *tcpHandler) Handle(conn net.Conn, target *net.TCPAddr) error {
+	go h.echoBack(conn)
+	return nil
+}