source: binary-improvements/7dtd-server-fixes/src/AllocsNetTelnetServer.cs@ 101

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Reflection;
using System.Threading;

public class AllocsNetTelnetServer
{
        private static ConsoleSdtd console = null;
        private static Thread telnetThread = null;
        private static TcpListener listener = null;
        private static bool closed = false;
        private static bool authEnabled = false;
        private static List<AllocsTelnetConnection> connections = new List<AllocsTelnetConnection> ();

        public static void init (int port)
        {
                Log.Out ("[7dtd-server-fixes by Alloc] Version: " + Assembly.GetExecutingAssembly ().GetName ().Version);
                authEnabled = GamePrefs.GetString (EnumGamePrefs.TelnetPassword).Length != 0;
                if (authEnabled)
                        listener = new TcpListener (IPAddress.Any, port);
                else
                        listener = new TcpListener (IPAddress.Loopback, port);
                telnetThread = ThreadMaster.Create ("thread Allocs TelnetListenThread", new ThreadStart (telnetListenThread));
                telnetThread.Start ();
                Log.Out ("Started Allocs NetTelnetServer thread on " + port);
        }

        private static void telnetListenThread ()
        {
                try {
                        Log.Out ("Started thread_Allocs_TelnetListenThread()");
                        listener.Start ();
                        while (!closed) {
                                Thread.Sleep (10);
                                if (listener.Pending ()) {
                                        AllocsTelnetConnection c = new AllocsTelnetConnection (listener.AcceptTcpClient (), authEnabled);
                                        connections.Add (c);
                                        Log.Out ("Telnet connection from: " + c.GetEndPoint ());
                                        if (authEnabled) {
                                                c.WriteLine ("Please enter password:");
                                        } else {
                                                LoginMessage (c);
                                        }
                                }

                                foreach (AllocsTelnetConnection c in connections) {
                                        if (c.IsClosed ()) {
                                                c.Close ();
                                                connections.Remove (c);
                                                break;
                                        }
                                        if (c.Read ()) {
                                                string line = lineCorrecter (c.GetLine ());
                                                if (!c.IsAuthenticated ()) {
                                                        if (line.Equals (GamePrefs.GetString (EnumGamePrefs.TelnetPassword))) {
                                                                c.SetAuthenticated ();
                                                                c.WriteLine ("Logon successful.");
                                                                c.WriteLine (string.Empty);
                                                                c.WriteLine (string.Empty);
                                                                c.WriteLine (string.Empty);
                                                                LoginMessage (c);
                                                        } else {
                                                                c.WriteLine ("Password incorrect, please enter password:");
                                                        }
                                                } else {
                                                        if (line.ToLower ().Equals ("exit")) {
                                                                Log.Out ("Telnet connection closed by client: " + c.GetEndPoint ());
                                                                c.Close ();
                                                                connections.Remove (c);
                                                                break;
                                                        }
                                                        Log.Out ("Telnet executed \"" + line + "\" from: " + c.GetEndPoint ());
                                                        console.md000f (line);
                                                }
                                        }
                                }
                        }
                        Log.Out ("Exited thread_Allocs_TelnetListenThread()");
                        ThreadMaster.Remove (Thread.CurrentThread.Name);
                } catch (Exception ex) {
                        Log.Out ("Error in Allocs telnetListenThread: " + ex.Message);
                        Log.Out ("Stack Trace: " + ex.StackTrace);
                }
        }

        private static void LoginMessage (AllocsTelnetConnection c)
        {
                c.WriteLine ("*** Connected with 7DTD server.");
                c.WriteLine ("*** Server version: Alpha 8.7 (b29) Compatibility Version: Alpha 8.7");
                c.WriteLine ("*** Allocs server fixes loaded");
                c.WriteLine (string.Empty);
                c.WriteLine ("Server IP:   " + 
                        ((GamePrefs.GetString (EnumGamePrefs.ServerIP) != null && GamePrefs.GetString (EnumGamePrefs.ServerIP).Length != 0) ? GamePrefs.GetString (EnumGamePrefs.ServerIP) : "Any")
                );
                c.WriteLine ("Server port: " + GamePrefs.GetInt (EnumGamePrefs.ServerPort));
                c.WriteLine ("Max players: " + GamePrefs.GetInt (EnumGamePrefs.ServerMaxPlayerCount));
                c.WriteLine ("Game mode:   " + GamePrefs.GetString (EnumGamePrefs.GameMode));
                c.WriteLine ("World:       " + GamePrefs.GetString (EnumGamePrefs.GameWorld));
                c.WriteLine ("Game name:   " + GamePrefs.GetString (EnumGamePrefs.GameName));
                c.WriteLine ("Difficulty:  " + GamePrefs.GetInt (EnumGamePrefs.GameDifficulty));
                c.WriteLine (string.Empty);
                c.WriteLine ("Press 'help' to get a list of all commands. Press 'exit' to end session.");
                c.WriteLine (string.Empty);
        }

        private static string lineCorrecter (string line)
        {
                string res = "";
                for (int i = 0; i < line.Length; i++) {
                        if (line [i] >= ' ' && line [i] != '\'' && line [i] <= '~') {
                                res += line [i];
                        }
                }
                return res.Trim ();
        }

        public static void Disconnect ()
        {
                closed = true;
                if (listener != null) {
                        listener.Stop ();
                }
                foreach (AllocsTelnetConnection c in connections) {
                        c.Close ();
                }
                Thread.Sleep (100);
        }

        public static void SetConsole (ConsoleSdtd console)
        {
                Log.Out("Telnet SetConsole called");
                AllocsNetTelnetServer.console = console;
        }

        private static void RemoveClosedConnections ()
        {
                foreach (AllocsTelnetConnection c in connections) {
                        if (c.IsClosed ()) {
                                c.Close ();
                        }
                }
        }

        public static void WriteToClient (string line)
        {
                if (line == null) {
                        return;
                }
                RemoveClosedConnections ();
                foreach (AllocsTelnetConnection c in connections) {
                        if (c.IsAuthenticated ())
                                c.WriteLine (line);
                }
        }
}