Telnet connection using .net

Question

Our office currently uses telnet to query an external server. The procedure is something like this.

1. Connect - telnet opent 128........ 25000
2. Query - we paste the query and then hit alt + 019
3. Response - We receive the response as text in the telnet window

So I’m trying to make this queries automatic using a c# app. My code is the following

First the connection. (No exceptions)

    SocketClient = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    String szIPSelected = txtIPAddress.Text;
    String szPort = txtPort.Text;
    int alPort = System.Convert.ToInt16(szPort, 10);

    System.Net.IPAddress remoteIPAddress = System.Net.IPAddress.Parse(szIPSelected);
    System.Net.IPEndPoint remoteEndPoint = new System.Net.IPEndPoint(remoteIPAddress, alPort);
    SocketClient.Connect(remoteEndPoint);

Then I send the query (No exceptions)

    string data ="some query";
    byte[] byData = System.Text.Encoding.ASCII.GetBytes(data);
    SocketClient.Send(byData);

Then I try to receive the response

    byte[] buffer = new byte[10];
    Receive(SocketClient, buffer, 0, buffer.Length, 10000);
    string str = Encoding.ASCII.GetString(buffer, 0, buffer.Length);
    txtDataRx.Text = str;

public static void Receive(Socket socket, byte[] buffer, int offset, int size, int timeout)
{
  int startTickCount = Environment.TickCount;
  int received = 0;  // how many bytes is already received
  do
  {
    if (Environment.TickCount > startTickCount + timeout)
      throw new Exception("Timeout.");
    try
    {
      received += socket.Receive(buffer, offset + received, size - received, SocketFlags.None);
    }
    catch (SocketException ex)
    {
      if (ex.SocketErrorCode == SocketError.WouldBlock ||
          ex.SocketErrorCode == SocketError.IOPending ||
          ex.SocketErrorCode == SocketError.NoBufferSpaceAvailable)
      {
        // socket buffer is probably empty, wait and try again
        Thread.Sleep(30);
      }
      else
        throw ex;  // any serious error occurr
    }
  } while (received < size);
}

Every time I try to receive the response I get "an exsiting connetion has forcibly closed by the remote host" if open telnet and send the same query I get a response right away

Any ideas, or suggestions?

Answer 1

Based on the comment exchange between you and I, it would seem that you need to append Ascii code 19 (0x13) to the end of your query.