c# - SignalR - How to perform async Task in hub? -

i trying create signalr application using c# 5 async/await features, whenever code run, throw system.invalidoperationexception. here simplest code reproduce problem.

public class samplehub : hub {     public task<string> getgoogle()     {         var http = new webclient();         return http.downloadstringtaskasync("http://www.google.com");     } } 

exception details:

an asynchronous operation cannot started @ time. asynchronous operations may started within asynchronous handler or module or during events in page lifecycle. if exception occurred while executing page, ensure page marked <%@ page async=\"true\" %>.

stack trace:

at system.web.aspnetsynchronizationcontext.operationstarted() @ system.net.webclient.downloadstringasync(uri address, object usertoken) @ system.net.webclient.downloadstringtaskasync(uri address) @ system.net.webclient.downloadstringtaskasync(string address) 

on client side, javascript looks this.

$.connection.hub.start().done(function () {     $('#google').click(function () {         var google = sample.server.getgoogle();         console.log(google);     }); }); 

what did wrong? there workarounds? keen stick async/await patterns in c# if possible @ all.

i try replacing webclient httpclient. downloadstringtaskasync kind of "bolt-on" support async on existing eap methods, , it's eap methods signalr objecting to. httpclient uses tap directly.