source: binary-improvements/7dtd-server-fixes/src/NetConnections/Servers/Telnet/Telnet.cs@ 185

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 TcpListener listener = null;
                private bool authEnabled = false;
                private List<TelnetConnection> connections = new List<TelnetConnection> ();

                public Telnet ()
                {
                        try {
                                if (!GamePrefs.GetBool (EnumGamePrefs.TelnetEnabled)) {
                                        return;
                                }

                                int port = GamePrefs.GetInt (EnumGamePrefs.TelnetPort);

                                authEnabled = GamePrefs.GetString (EnumGamePrefs.TelnetPassword).Length != 0;
                                if (authEnabled)
                                        listener = new TcpListener (IPAddress.Any, port);
                                else
                                        listener = new TcpListener (IPAddress.Loopback, port);

                                listener.Start ();
                                listener.BeginAcceptTcpClient (new AsyncCallback (AcceptClient), null);

                                NetTelnetServer.RegisterServer (this);

                                Log.Out ("Started Telnet on " + port);
                        } catch (Exception e) {
                                Log.Out ("Error in Telnet.ctor: " + e);
                        }
                }

                public void FailedLogins ()
                {
                }

                private void AcceptClient (IAsyncResult asyncResult)
                {
                        if (listener.Server.IsBound) {
                                TelnetConnection c = new TelnetConnection (this, listener.EndAcceptTcpClient (asyncResult), authEnabled);
                                connections.Add (c);
                                listener.BeginAcceptTcpClient (new AsyncCallback (AcceptClient), null);
                        }
                }

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

                private void RemoveClosedConnections ()
                {
                        try {
                                List<TelnetConnection> toRemove = new List<TelnetConnection> ();
                                foreach (TelnetConnection c in connections) {
                                        if (c.IsClosed ())
                                                toRemove.Add (c);
                                }
                                foreach (TelnetConnection c in toRemove) {
                                        connections.Remove (c);
                                }
                        } 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);
                                }
                        }
                }

        }
}