Asp.net – Receiving Data from Pathology Machine using Socket

There is no generic way on how systems exchange data.
Instead, there are different protocols for different kinds of applications or use cases, i.e. thinks like HTTP (web), TLS (transport encryption), SMTP (mail), ….
You need to adhere to the protocol expected by the peer both for requesting data, transporting data, reconnecting, …
It is unknown what protocol this is in your specific case, so one cannot recommend you a specific approach. Check documentation, vendor support etc. for the protocol documentation you need.

If you are dealing with TCP/IP communication, using a NetworkStream (as commented) along with a StreamReader can simplify the process of reading incoming data.
That would abstract away some of the lower-level byte handling (and the code is simpler).

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;

IPAddress ipAddress = IPAddress.Parse(SERVER_IP);
IPEndPoint localEndpoint = new IPEndPoint(ipAddress, PORT_NO);

using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
    try
    {
        socket.Connect(localEndpoint);

        using (NetworkStream networkStream = new NetworkStream(socket))
        using (StreamReader streamReader = new StreamReader(networkStream, Encoding.ASCII))
        {
            string message = string.Empty;
            while (!message.EndsWith("<EOF>"))
            {
                message += streamReader.ReadLine(); // Assuming each message ends with a newline
            }
            // Process the received message
        }
    }
    catch (Exception ex)
    {
        // Handle exceptions
    }
}

The "Process the received message" part means understanding the protocol used by your pathology machine. If the machine uses a standard protocol (HTTP, TLS, SMTP, etc.), you should use a library or framework that supports that protocol out of the box. That way, you will be able to handle messages according to the protocol’s specifications, including reconnections and data transmission.

For protocols that do not support signaling for "send next message," you might indeed need to close and reopen the connection. But this should be considered a last resort, as it is not efficient and might not be supported by all devices.

As commented, considering asynchronous communication (e.g., using BeginReceive and EndReceive or async/await with NetworkStream) to improve performance and responsiveness, especially if you are dealing with large volumes of data.
See also "Using Asynchronous Methods in ASP.NET 4.5"

using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

async Task ReceiveDataAsync(string serverIp, int portNo)
{
    IPAddress ipAddress = IPAddress.Parse(serverIp);
    IPEndPoint localEndpoint = new IPEndPoint(ipAddress, portNo);

    using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
    {
        await socket.ConnectAsync(localEndpoint);

        using (NetworkStream networkStream = new NetworkStream(socket))
        using (StreamReader streamReader = new StreamReader(networkStream, Encoding.ASCII))
        {
            StringBuilder completeMessage = new StringBuilder();
            char[] buffer = new char[2048];
            int bytesRead;

            while (true)
            {
                bytesRead = await streamReader.ReadAsync(buffer, 0, buffer.Length);
                completeMessage.Append(buffer, 0, bytesRead);
                string message = completeMessage.ToString();
                if (message.IndexOf("<EOF>") > -1)
                {
                    // Process the message up to <EOF>
                    break;
                }
            }

            // Process the received message
            Console.WriteLine("Received message: " + completeMessage.ToString());
        }
    }
}