send method

@override Future<ModbusResponseCode> send(ModbusRequest request)

Sends the modbus requests. A ModbusResponseCode is returned as a future.

If request has its own unitId defined, then it will override this client unitId (see getUnitId).

If request has its own responseTimeout defined, then it will override this client responseTimeout (see getResponseTimeout).

Implementation

@override
Future<ModbusResponseCode> send(ModbusRequest request) async {
  var res = await _lock.synchronized(() async {
    // Connect if needed
    try {
      if (connectionMode != ModbusConnectionMode.doNotConnect) {
        await connect();
      }
      if (!isConnected) {
        return ModbusResponseCode.connectionFailed;
      }
    } catch (ex) {
      ModbusAppLogger.severe(
          "Unexpected exception in sending TCP message", ex);
      return ModbusResponseCode.connectionFailed;
    }

    // Flushes any old pending data
    await _socket!.flush();

    // Create the new response handler
    var transactionId = _getNextTransactionId();
    _currentResponse = _TcpResponse(request,
        transactionId: transactionId, timeout: getResponseTimeout(request));

    // Reset this request in case it was already used before
    request.reset();

    // Create request data
    int pduLen = request.protocolDataUnit.length;
    var header = Uint8List(pduLen + 7);
    ByteData.view(header.buffer)
      ..setUint16(0, transactionId) // Transaction ID
      ..setUint16(2, 0) // Protocol ID = 0
      ..setUint16(4, pduLen + 1) // PDU Length + Unit ID byte
      ..setUint8(6, getUnitId(request)); // Unit ID
    header.setAll(7, request.protocolDataUnit);

    // Send the request data
    _socket!.add(header);

    // Wait for the response code
    return await request.responseCode;
  });
  // Need to disconnect?
  if (connectionMode == ModbusConnectionMode.autoConnectAndDisconnect) {
    await disconnect();
  }
  return res;
}