Cannot read data sent from TCP client on python to TCP server in C#

Question

I have a windows service written in C# which has opens a TCP socket. I've connected and tested this TCP socket through telnet, and I am able to send and receive messages to the socket through putty with the telnet protocol. When connecting with a small python script, the script is able to receive messages, but unable to send them such that they are received by the C# server. The code for the server is:

IPAddress ipAddress = IPAddress.Parse("127.0.0.1");
TcpListener listener = new TcpListener(ipAddress, 5555);
listener.Start();


Thread whileThread = new Thread(() =>
{
    while (true)
    {
        TcpClient client = listener.AcceptTcpClient();
        Thread childThread = new Thread(() =>
        {

            NetworkStream stream = client.GetStream();
            StreamReader streamreader = new StreamReader(client.GetStream(), Encoding.ASCII);
            string line = null;
            WriteToNetworkStream(stream, "Connected to the service");
            eventLog1.WriteEntry("TCP Socket opened");
            eventLog1.WriteEntry((GetState(client) == TcpState.Established).ToString()); //this does return True.
            while ((line = streamreader.ReadLine()) != "<EOF>" && GetState(client) == TcpState.Established)
            {
                eventLog1.WriteEntry(line);
            }
            eventLog1.WriteEntry("TCP Socket closed");

            stream.Close();
            client.Close();
        });

        childThread.Start();

    } 
});
whileThread.Start();

The python script on the other side is:

import socket
import time

TCP_IP = '127.0.0.1'
TCP_PORT = 5555
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
time.sleep(1)
s.send("this is a test")
time.sleep(10)
data = s.recv(BUFFER_SIZE)
print(data)

The message "this is a test" is never received by the other side, but "TCP Socket closed" isn't logged until after after the time.sleep(10) is done, showing the C# does recognize some sort of prolonged connection. Also, the data variable does contain "Connected to the service" as expected, showing the server can send data to the client. Like I said earlier, when trying to send and receive messages using telnet with putty, this does work correctly.

insane_developer insane_developer · Accepted Answer · 2020-08-13T18:15:04

Have you tried reading the bytes from the network stream? I can't say whether it will make a difference but it's worth a try to check if actual bytes are coming in:

NetworkStream stream = client.GetStream();
Byte[] bytes = new Byte[256]; //whatever size is appropriate
int bytesRead;
string data;
while ((bytesRead = stream.Read(bytes, 0, bytes.Length)) != 0)
{
    data = System.Text.Encoding.ASCII.GetString(bytes, 0, bytesRead);
    // ......
}

Cannot read data sent from TCP client on python to TCP server in C#

1 Answers