Host WebSocket Server in ASP.NET WebAPI on Console Application

Question

I have built an ASP.NET WebAPI which is hosted on a console application. There are some web apis I had created and worked well. Then I tried to implement web socket service on it. The server side code was like below

[RoutePrefix("api/notification")]
public class NotificationController : ApiController
{
    [HttpGet]
    [Route("")]
    public HttpResponseMessage Get()
    {
        if (HttpContext.Current.IsWebSocketRequest)
        {
            HttpContext.Current.AcceptWebSocketRequest(new NotificationWebSocketHandler());
            return Request.CreateResponse(HttpStatusCode.SwitchingProtocols);
        }
        else
        {
            return Request.CreateResponse(HttpStatusCode.BadRequest);
        }
    }

    public class NotificationWebSocketHandler : WebSocketHandler
    {
        private static WebSocketCollection _clients;

        static NotificationWebSocketHandler()
        {
            _clients = new WebSocketCollection();

            Task.Factory.StartNew(() =>
                {
                    while (true)
                    {
                        Task.Delay(TimeSpan.FromSeconds(5));
                        if (_clients.Count > 0)
                        {
                            _clients.Broadcast(Guid.NewGuid().ToString());
                        }
                    }
                });
        }

        public override void OnOpen()
        {
            _clients.Add(this);
            Console.WriteLine("Web socket client opened, client count = {0}", _clients.Count);
        }

        public override void OnClose()
        {
            _clients.Remove(this);
            Console.WriteLine("Web socket client closed, client count = {0}", _clients.Count);
        }
    }
}

But when I opened the client page (which was built on AngularJS) I got the error message said WebSocket connection to 'ws://10.222.115.220:8080/api/notification/' failed: Error during WebSocket handshake: Unexpected response code: 500

My client side code was

app.shared.controllers.controller('DashboardCtrl', function ($q, $scope) {
    var ws = new WebSocket("ws://10.222.115.220:8080/api/notification/");
    ws.onopen = function () {
        console.log('web socket opened');
    }
    ws.onmessage = function (message) {
        $scope.seed = message;
    };

    $scope.seed = '(empty)';
});

When I attached debug and added a breakpoint at the entry of my Get function, and I found the error 500 was raised without this breakpoint hit. I think this means the error was generated by WebAPI internally.

I'm not sure if anything wrong in my code, or WebSocket feature doesn't support console application host.

user437899 · Accepted Answer · 2014-08-14 14:16:27Z

3

you are using the Web API in "Self Host"-mode? (hosted in the console)

There you have the problem that the object HttpContext.Current is "null". This is a problem of self-hosting. HttpContext.Current is set while using the IIS (web-hosting). This property is not available during self-hosting. I think this could be your problem. (A null-ref-exception is thrown in your web-api-application and returns 500 - internal server error).

answered Aug 14, 2014 at 14:16

user437899

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