custom.cs

public class CustomWebSocketMiddleware
{
  private RequestDelegate m_next;
  private IPAddress m_serviceAddress;
  private int m_servicePort;
  internal static readonly byte[] DefaultServiceAddress = { 127, 0, 0, 1 };

  public CustomWebSocketMiddleware(RequestDelegate next)
  {
    m_next = next;
    m_serviceAddress = new IPAddress(DefaultServiceAddress);
    m_servicePort = 4277;
  }

  public CustomWebSocketMiddleware(RequestDelegate next, 
                                   IPAddress serviceAddress, 
                                   int servicePort = 4277)
  {
    m_next = next;
    m_serviceAddress = serviceAddress;
    m_servicePort = servicePort;
  }

  public CustomWebSocketMiddleware(RequestDelegate next,
                                   string hostNameOrAddress,
                                   int servicePort = 4277)
  {
    m_next = next;
    IPAddress addr = Dns.GetHostAddresses(hostNameOrAddress).FirstOrDefault();
    if (addr == null) throw new Exception($"Host '{hostNameOrAddress}' not found.");
    m_serviceAddress = addr;
    m_servicePort = servicePort;
  }

  public async Task Invoke(HttpContext context)
  {
    if (context.WebSockets.IsWebSocketRequest &&
      context.WebSockets.WebSocketRequestedProtocols.Contains("TXTextControl.Web"))
    {
      var ws = new WebSocketHandler(m_serviceAddress, m_servicePort);
      await ws.Invoke(context);
    }
    else if (m_next != null)
    {
      await m_next.Invoke(context);
    }
  }
}