fix: reject non tunnel request & reject duplicated port

main.go

@@ -9,12 +9,16 @@ import (
 
 func main() {
 	sshConfig := &ssh.ServerConfig{
-		NoClientAuth: true,
+		NoClientAuth:  true,
+		ServerVersion: "SSH-2.0-TunnlPls-1.0",
 		PasswordCallback: func(conn ssh.ConnMetadata, password []byte) (*ssh.Permissions, error) {
 			return nil, nil
 		},
 	}
 
+	log.SetOutput(os.Stdout)
+	log.SetFlags(log.LstdFlags | log.Lshortfile)
+
 	privateBytes, err := os.ReadFile("id_rsa")
 	if err != nil {
 		log.Fatal("Failed to load private key (./id_rsa)")