/// <summary>
/// Parses a telegram received by ReceiveTelegram.
/// </summary>
/// <param name="buffer">Buffer containing the data.</param>
/// <param name="telegramLength">Total length of the telegram in bytes.</param>
/// <param name="isResponse">true if the telegram is a response telegram; false if the telegram is a request telegram.</param>
/// <param name="telegramContext">
/// If isResponse == true: pass the telegramContext returned by CreateTelegram from the request.
/// If isResponse == false: returns the telegramContext from the received request. It must pe passed to the CreateTelegram method for the response.
/// </param>
/// <param name="address">Returns the device address.</param>
/// <param name="fkt">Returns the function code.</param>
/// <param name="dataPos">Returns the offset in buffer of the function code specific data.</param>
/// <param name="dataLength">Returns the length of the function code specific data.</param>
/// <returns>Returns true if this is the matching response according to the telegramContext; else false. If isResponse == false this method should return always true.</returns>
public bool ParseTelegram(byte[] buffer, short telegramLength, bool isResponse, ref object telegramContext, out byte address,
out byte fkt, out short dataPos, out short dataLength)
{
if (telegramLength < 8)
{
throw new ModbusException(ModbusErrorCode.ResponseTooShort);
}
if (isResponse)
{
if (telegramContext is ushort)
{
ushort transactionId = ModbusUtils.ExtractUShort(buffer, 0);
if (transactionId != (ushort)telegramContext)
{
// telegram does not match
address = 0;
fkt = 0;
dataPos = 0;
dataLength = 0;
return(false);
}
}
}
else
{
telegramContext = ModbusUtils.ExtractUShort(buffer, 0);
}
address = buffer[6];
fkt = buffer[7];
dataPos = 8;
dataLength = (short)(telegramLength - 8);
return(true);
}
/// <summary>
/// Waits and receives a telegram.
/// </summary>
/// <param name="buffer">Buffer to write data into.</param>
/// <param name="desiredDataLength">Desired length of the function code specific data in bytes. -1 if length is unknown.</param>
/// <param name="timeout">Timeout in milliseconds to wait for the telegram.</param>
/// <param name="telegramLength">Returns the total length of the telegram in bytes.</param>
/// <returns>Returns true if the telegram was received successfully; false on timeout.</returns>
public bool ReceiveTelegram(byte[] buffer, short desiredDataLength, int timeout, out short telegramLength)
{
if (_Socket == null)
{
throw new ObjectDisposedException("ModbusTcp interface");
}
if (!_Socket.Poll(timeout * 1000, SelectMode.SelectRead) || _Socket.Available == 0)
{
telegramLength = 0;
return(false);
}
// get the 1st 6 bytes, which includes the remaining length
int pos = 0;
while (pos < 6)
{
pos += _Socket.Receive(buffer, pos, 6 - pos, SocketFlags.None);
}
telegramLength = (short)(ModbusUtils.ExtractUShort(buffer, 4) + 6);
// receive remaining data
while (pos < telegramLength)
{
pos += _Socket.Receive(buffer, pos, telegramLength - pos, SocketFlags.None);
}
return(true);
}