private void sendFile(IWebSocketConnection webSocket, string filename)
        {
            if (!File.Exists(filename))
            {
                Log(webSocket, filename + " not exists");
                return;
            }
            List <string> param = new List <string>();

            param.Add(Path.GetFileName(filename));
            param.Add(RSA_Unit.Base64EncodeBytes(rsa.Encode(File.ReadAllBytes(filename))));
            param.Add(HashTool.SHA256File(new FileStream(filename, FileMode.Open)));
            Operation op = new Operation()
            {
                op    = "send_file",
                param = param
            };

            Log(string.Format("{0} {1}", param[0], param[2]));
            send(webSocket, JsonConvert.SerializeObject(op));
        }