write server mode

backend/src/engine.cpp

@@ -451,4 +451,8 @@ std::vector<std::string> BookStoreEngineClass::ExecuteReport(
     return ret;
   }
   return std::vector<std::string>();
+}
+
+std::string BookStoreEngineClass::QueryUserInfo(const std::string &user_name) {
+  return user_name + std::to_string(user_data_base.GetPrevilege(user_name));
 }