See https://ithoughthecamewithyou.com/post/personal-finger-daemon-for-windows

Program.cs

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

namespace fingerd
{
    static class Program
    {
        private const int FingerPort = 79;
        private const int MaxFingerCommand = 256;
        private const string PlanFile = ".plan";

        private static readonly TcpListener _tcpListener = new TcpListener(
             IPAddress.Any, FingerPort);

        static void Main()
        {
            _tcpListener.Start();

            while (true)
            {
                TcpClient tcpClient = _tcpListener.AcceptTcpClient();
                Thread clientThread = new Thread(ClientThread);
                clientThread.Start(tcpClient);
            }
        }

        static void ClientThread(object client)
        {
            NetworkStream clientStream = null;
            TcpClient tcpClient = client as TcpClient;
            if (tcpClient == null) { return; }

            try
            {
                byte[] command = new byte[MaxFingerCommand];
                clientStream = tcpClient.GetStream();

                int read = clientStream.Read(command, 0, command.Length);
                if (read == 0) { return; }

                ASCIIEncoding asciiEncoding = new ASCIIEncoding();
                string commandText = asciiEncoding.GetString(command);

                int endOfCommand = commandText.IndexOf("\r\n", 
                    StringComparison.InvariantCultureIgnoreCase);
                if (endOfCommand <= 0) { return; }

                string user = commandText.Substring(0, endOfCommand);
                if (string.Compare(user, Environment.UserName, 
                    StringComparison.InvariantCultureIgnoreCase) != 0) { return; }

                string planPath = Path.Combine(Environment.GetFolderPath(
                    Environment.SpecialFolder.UserProfile),
                    PlanFile);
                if (!File.Exists(planPath)) { return; }

                string plan = File.ReadAllText(planPath) + "\r\n";
                byte[] planBytes = asciiEncoding.GetBytes(plan);
                clientStream.Write(planBytes, 0, planBytes.Length);
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
            }
            finally
            {
                if (clientStream != null)
                {
                    clientStream.Close();
                }
                tcpClient.Close();
            }
        }
    }
}