Question

I have a list of IP’s that keep crawling our live site which throw exceptions when they use certain URL’s with no parameters (because of the MVC routing). I want to block those IP addresses and return a 404 not found page as soon as they can be picked up, but I don’t want to do it in IIS as I want to log the encounters within our application.

I’ve written a catch-all type routehandler that uses a custom MvcHandler to check the list and modify the response:

public class ApplicationRouteHandler : IRouteHandler
{
    public IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        BlacklistedIPAddressHandler handler = new BlacklistedIPAddressHandler(Cache.WebsiteCache.GetBlacklistedIPList(), requestContext);

        return handler;
    }
}

public class BlacklistedIPAddressHandler : MvcHandler
{
    List<IPBlacklistModel> blacklist;

    public BlacklistedIPAddressHandler(List<IPBlacklistModel> Blacklist, RequestContext requestContext) : base(requestContext)
    {
        blacklist = Blacklist;
    }

    protected override IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state)
    {
        var ip = httpContext.Request.UserHostAddress;

        if (blacklist != null &&
            blacklist.Where(x => x.IP_ADDRESS.Contains(ip)).Count() > 0)
        {

            httpContext.Response.ClearHeaders();
            httpContext.Response.Clear();

            httpContext.Response.StatusCode = 404;
            httpContext.Response.SuppressContent = true;
            httpContext.Response.End();
        }

        return base.BeginProcessRequest(httpContext, callback, state);
    }
}

It’s then implemented as follows:

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.MapRoute(
            "Default",
            "{controller}/{action}/{id}",
            new { controller = "Home", action = "Index", id = UrlParameter.Optional },
            new { controller = @"[^\.]*" }
        ).RouteHandler = new Helpers.Routing.ApplicationRouteHandler();
    }

I keep getting a Server cannot append header after HTTP headers have been sent error when I do this. Anybody perhaps know why?

Answer 1

I suppose you should remove httpContext.Response.End(); statement from your handler – as the request is passed for further processing, it should not be terminated now.

HttpResponse.End method description from MSDN:

Sends all currently buffered output to the client, stops execution of
the page, and raises the EndRequest event.