source: binary-improvements/7dtd-server-fixes/src/NetConnections/Servers/Telnet/Telnet.cs@ 143

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

namespace AllocsFixes.NetConnections.Servers.Telnet
{
        public class Telnet : IServer
        {
                private static Thread telnetThread = null;
                private static TcpListener listener = null;
                private static bool closed = false;
                private static bool authEnabled = false;
                private static List<TelnetConnection> connections = new List<TelnetConnection> ();

                public Telnet (int port)
                {
                        try {
                                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 TelnetListenThread", new ThreadStart (telnetListenThread));
                                telnetThread.Start ();
                                Log.Out ("Started Telnet thread on " + port);
                        } catch (Exception e) {
                                Log.Out ("Error in Telnet.ctor: " + e);
                        }
                }

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

                                        foreach (TelnetConnection 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 ());
                                                                ConsoleOutputSeparator.QueueNetCommand (line, c);
                                                        }
                                                }
                                        }
                                }
                                Log.Out ("Exited thread_TelnetListenThread()");
                                ThreadMaster.Remove (Thread.CurrentThread.Name);
                        } catch (Exception ex) {
                                Log.Out ("Error in TelnetListenThread: " + ex.Message);
                                Log.Out ("Stack Trace: " + ex.StackTrace);
                        }
                }

                private void LoginMessage (TelnetConnection c)
                {
                        c.WriteLine ("*** Connected with 7DTD server.");
                        c.WriteLine ("*** Dedicated server only build");
                        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 string lineCorrecter (string line)
                {
                        string res = "";
                        for (int i = 0; i < line.Length; i++) {
                                if (line [i] >= ' ' && line [i] != '\'') {
                                        res += line [i];
                                }
                        }
                        return res.Trim ();
                }

                public void Disconnect ()
                {
                        try {
                                closed = true;
                                if (listener != null) {
                                        listener.Stop ();
                                }
                                foreach (TelnetConnection c in connections) {
                                        c.Close ();
                                }
                                Thread.Sleep (100);
                        } catch (Exception e) {
                                Log.Out ("Error in Telnet.Disconnect: " + e);
                        }
                }

                private void RemoveClosedConnections ()
                {
                        try {
                                foreach (TelnetConnection c in connections) {
                                        if (c.IsClosed ()) {
                                                c.Close ();
                                        }
                                }
                        } catch (Exception e) {
                                Log.Out ("Error in Telnet.RemoveClosedConnections: " + e);
                        }
                }

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

                public void WriteToClient_Single (string line, IConnection client)
                {
                        if (line == null) {
                                return;
                        }
                        RemoveClosedConnections ();
                        foreach (TelnetConnection con in connections) {
                                if (con == client) {
                                        if (con.IsAuthenticated ())
                                                con.WriteLine (line);
                                }
                        }
                }

        }
}