New tcpclient().connected throws null reference

See more:

.NET3.5

C#

TCP/IP

Hey,

I have written a bespoke "latency checker". There is a client and server. Client is Console App and service is a Service. I am restricted to .Net 3.5.

So this all works locally fine, but on the clients main server it throws an error:

while (!client.Connected && retry-- > 0)

Null ref exception
at TcpClient.Get_Connected (points to the line above)

I don't get it. I only just instantiated it. The most it might be is closed.

here is the code for this method.

private int GetPort(long taskLength, bool isReport = false)
{
    IPEndPoint endPoint = new IPEndPoint(_address, _port);
    TcpClient client = new TcpClient();
    int port = 0;


    int retry = retries;

    while (!client.Connected && retry-- > 0)
    {
        try
        {
            client.Connect(endPoint);

            using (var stream = client.GetStream())
            using (StreamReader reader = new StreamReader(stream))
            using (StreamWriter writer = new StreamWriter(stream))
            {
                writer.AutoFlush = true;
                if (isReport)
                {
                    writer.WriteLine($"report:{taskLength}");
                }
                else
                {
                    writer.WriteLine($"port request:{taskLength}");
                }
                string portString = reader.ReadLine();
                if (!string.IsNullOrEmpty(portString) && int.TryParse(portString, out port))
                    return port;
                throw new BadResponseException("Port format incorrect");
            }
        }
        catch (BadResponseException)
        {
            //retry
        }
        catch (SocketException)
        {
            //retry
        }
        finally
        {
            client.Close();
        }
    }
    return port;
}

For the first call: taskLength = 1 and isReport = false.


Any ideas on what could've caused this would help ^_^

Thanks

What I have tried:

I tested the client and server locally and the server is running both locally to it. This is the first test before I put the client on another machine.

The Server has 1 port held open for requests from clients. It opens a port async, sets it to receive a specific number of bytes and replies back saying what the port number is.

I only have 1 client running atm which is single threaded.