private void codeHandler(Code sign, SocketChannel channel) throws Exception {
        switch (sign) {

        // client return message
        case CLIENT_HEARTBEAT:

            // in alive channels
            handlerAlive(channel);
            break;
        case SYSTEM_CHANNEL:

            // as system channels
            addChannel(channel);

            // in alive channels
            handlerAlive(channel);
            break;
        case OPT_DOWNLOAD:
            handlerDownload(channel);
            break;
        case OPT_DOWNLOAD_FOUND_FILE:
            handlerDownloadOver(channel);
            break;
        case SERVER_SYNC_SHARED_INDEX_FILE_SUCCESS:
            handlerSharedSync(channel);
            break;
        case SERVER_SYNC_SHARED_INDEX_FILE_EMPTY:
            handlerSharedSyncEmpty(channel);
            break;
        case REPLICATION_SYNC_SHARED:
            handlerRepliSync(channel);
            break;
        case SHARED_RECEIVE_SYNC_AND_SEND_REPLICATION:
            handlerRepliSyncServerReceive(channel);
            break;
        case REPLICATION_RECEIVE_SHARED_SUCCESS:
            handlerRepliSyncSuccess(channel);
        default:
            break;
        }
    }