using (EngineIOServer server = new EngineIOServer(new EngineIOServerOption(1009, AllowEIO3: true, VerificationTimeout: 1001)))
{
    Console.WriteLine("Listening on " + server.Option.Port);
    server.OnConnecting((obj) =>
    {
        var token = obj.Item1["token2"];
        if (string.IsNullOrWhiteSpace(token))
        {
            Console.WriteLine($"{DateTime.Now:HH:mm:ss.fff} The authentication fails and the connection is denied");
        }
        server.VerificationResult.TryAdd(obj.Item2, string.IsNullOrWhiteSpace(token));
    });
    server.OnConnection((socket) =>
    {
        Console.WriteLine($"{DateTime.Now:HH:mm:ss.fff} Client connected!");
    });

    server.Start();
}

public static readonly EngineIOException CONNECTIONREFUSED = new EngineIOException("ConnectionRefused");//401/403
private static readonly EngineIOException[] VALUES = new EngineIOException[] { CONNECTIONREFUSED }

public EngineIOServer OnConnecting(Action<Tuple<System.Collections.Specialized.NameValueCollection, string>> Callback)
{
	return On(Event.CONNECTING, (Client) => Callback(Client as Tuple<System.Collections.Specialized.NameValueCollection, string>));
}
public static class Event
{
	public static readonly string CONNECTING = "connecting";
}

public static void SendErrorMessage(HttpListenerRequest Request, HttpListenerResponse Response, EngineIOException Exception)
{
    using (Response)
    {
        ......
        if (EngineIOServer.Exceptions.Contains(Exception))
        {
            ......
            Response.StatusCode = 400;
            Response.Headers["ServerResponse"] = Message;
            Response.StatusCode = Exception == EngineIOServer.Exceptions.CONNECTIONREFUSED ? 401 : 400;
        }
        else
        {
            ......
        }

        ......
    }
}

public ulong VerificationTimeout { get; private set; }
public EngineIOServerOption(ulong VerificationTimeout = 1000)
{
	this.VerificationTimeout = VerificationTimeout;
}

/// <summary>
/// Verification result: If no entry is made within 1000ms, it is regarded as passed
/// </summary>
public readonly ConcurrentDictionary<string, bool> VerificationResult = new ConcurrentDictionary<string, bool>();
private EngineIOException Verify(NameValueCollection QueryString, NameValueCollection Headers, EngineIOTransportType ExpectedTransportType)
{
    ......
    else if (EngineIOHttpManager.GetTransport(QueryString).Equals(ExpectedTransportType.ToString()))
    {
        ......
        if (IsPolling || IsWebSocket)
        {
            if (EngineIOHttpManager.IsValidHeader(EngineIOHttpManager.GetOrigin(Headers)))
            {
                Exception = null;
                #region connection verification
				if (string.IsNullOrWhiteSpace(EngineIOHttpManager.GetSID(QueryString)))
				{
					var abortId = $"{QueryString}&k={DateTime.Now.Ticks}";
					Emit(Event.CONNECTING, new Tuple<NameValueCollection, string>(Headers, abortId));

#if NET45_OR_GREATER
				//var task = System.Threading.Tasks.Task.Run(() => { while (!VerificationResult.ContainsKey(abortId)) { continue; } });
				//System.Threading.Tasks.Task.WaitAny(new System.Threading.Tasks.Task[] { task }, TimeSpan.FromMilliseconds(Option.VerificationTimeout));

				var cts = new System.Threading.CancellationTokenSource(TimeSpan.FromMilliseconds(Option.VerificationTimeout));
				while (!VerificationResult.ContainsKey(abortId) && !cts.IsCancellationRequested) { continue; }
#else
					var cts = new System.Threading.CancellationTokenSource();
					var waitTimer = new System.Timers.Timer(Option.VerificationTimeout) { AutoReset = false };
					waitTimer.Elapsed += (aa, bb) => cts.Cancel();
					waitTimer.Start();
					while (!VerificationResult.ContainsKey(abortId) && !cts.IsCancellationRequested) { continue; }
#endif
					if (VerificationResult.TryGetValue(abortId, out var result))
					{
						VerificationResult.TryRemove(abortId, out _);
						if (result) Exception = Exceptions.CONNECTIONREFUSED;
					}
				}
				#endregion
            }
            else
            {
                Exception = Exceptions.BAD_REQUEST;
            }
        }
    }

    return Exception;
}

using EngineIOSharp.Client;
using EngineIOSharp.Common.Enum;

EngineIOClient client = new EngineIOClient(new EngineIOClientOption(EngineIOScheme.http, "localhost", 1009)));

client.Connect();

client.Close();

client.Dispose();

client.OnOpen(() =>
{
  Console.WriteLine("Conencted!");
});

client.OnMessage((Packet) =>
{
  Console.WriteLine("Server : " + Packet.Data);
});

client.OnClose((Exception Description) =>
{
  Console.WriteLine("Disconnected!");
  
  if (Description != null)
  {
    Console.WriteLine(Description);
  }
});

client.On(EngineIOClient.Event.FLUSH, () =>
{
  Console.WriteLine("Flushed!");
});

public static class Event
{
  public static readonly string OPEN = "open";
  public static readonly string HANDSHAKE = "handshake";

  public static readonly string ERROR = "error";
  public static readonly string CLOSE = "close";

  public static readonly string PACKET = "packet";
  public static readonly string MESSAGE = "message";

  public static readonly string PACKET_CREATE = "packetCreate";
  public static readonly string FLUSH = "flush";
  public static readonly string DRAIN = "drain";

  public static readonly string UPGRADE = "upgrade";
  public static readonly string UPGRADING = "upgrading";
  public static readonly string UPGRADE_ERROR = "upgradeError";
}

client.Send("This is string value.");
client.Send("String value with callback.", () => Console.WriteLine("Flushed!"));

client.send(new byte[] { 1, 2, 3, 4, 5 });
client.send(new byte[] { 6, 7, 8, 9, 0 }, () => Console.WriteLine("Bytes flushed!"));

using EngineIOSharp.Server;

EngineIOServer server = new EngineIOServer(new EngineIOServerOption(1009));

server.Start();

server.Stop();

server.Dispose();

server.OnConnection((EngineIOSocket socket) =>
{
  Console.WriteLine("Client connected!");

  socket.OnMessage((Packet) =>
  {
    Console.WriteLine(Packet.Data);

    if (Packet.IsText)
    {
      socket.Send(Packet.Data);
    }
    else
    {
      socket.Send(Packet.RawData);
    }
  });

  socket.OnClose(() =>
  {
    Console.WriteLine("Client disconnected!");
  });

  socket.Send("Hello client!");
  socket.Send(new byte[] { 0, 1, 2, 3, 4, 5, 6 });
});

socket.Close();

socket.Dispose();

socket.OnMessage((Packet) =>
{
  Console.WriteLine("Server : " + Packet.Data);
});

socket.OnClose((string Messsage, Exception Description) =>
{
  Console.WriteLine("Disconnected!");
  
  if (Message != null) 
  {
    Console.WriteLine(Message);
  }
  
  if (Description != null)
  {
    Console.WriteLine(Description);
  }
});

socket.On(EngineIOSocket.Event.FLUSH, () =>
{
  Console.WriteLine("Flushed!");
});

public static class Event
{
  public static readonly string OPEN = "open";
  public static readonly string HEARTBEAT = "heartbeat";

  public static readonly string ERROR = "error";
  public static readonly string CLOSE = "close";

  public static readonly string PACKET = "packet";
  public static readonly string MESSAGE = "message";

  public static readonly string PACKET_CREATE = "packetCreate";
  public static readonly string FLUSH = "flush";
  public static readonly string DRAIN = "drain";

  public static readonly string UPGRADE = "upgrade";
  public static readonly string UPGRADING = "upgrading";
  public static readonly string UPGRADE_ERROR = "upgradeError";
}

socket.Send("This is string value.");
socket.Send("String value with callback.", () => Console.WriteLine("Flushed!"));

socket.send(new byte[] { 1, 2, 3, 4, 5 });
socket.send(new byte[] { 6, 7, 8, 9, 0 }, () => Console.WriteLine("Bytes flushed!"));

server.Braodcast("This is string value.");
server.Braodcast("String value with callback.", () => Console.WriteLine("Braodcasted!"));

server.Braodcast(new byte[] { 1, 2, 3, 4, 5 });
server.Braodcast(new byte[] { 6, 7, 8, 9, 0 }, () => Console.WriteLine("Bytes braodcasted!"));