You have been using Silverlight for a while and by now you figure it out that to communicate outside your domain you need the crossdomain.xml file on the root directory of the domain you want to talk to, otherwise if Silverlight does not read that file with the policies, will return an exception on the request.

{System.Reflection.TargetInvocationException: An exception occurred during the operation, making the result invalid.  Check InnerException for exception details. ---> System.Security.SecurityException ---> System.Security.SecurityException: Security error.
   at System.Net.BrowserHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)

This is a restriction added in Silverlight that should be removed in my opinion as the work around is pretty simple and just slows down the request. Consuming data from the Internet is now with all social networks the most common task for an application. Restricting the user with making sure the crossdomain.xml is added into the domain just makes it frustrating for developers.

In order to avoid problems like that I added a proxy to consume any data from any domain with with a crossdomain file that looks like this:

<?xml version="1.0" encoding="utf-8" ?>
<cross-domain-policy>
    <allow-access-from domain="*" />
</cross-domain-policy>

 Creating the Cloud proxy

Open VS2008 and create a new cloud project, make sure, of course, that you installed the Azure SDK and Tools for Visual Studio 2008.

Just create a generic handler on the Web Role for the proxy code and publish the solution to your cloud account.

Click run and could take more than 5 minutes to start the application.

Once started, check the temp website url is working, then you can promote it to your production website by clicking the icon in the middle of both.

To make sure is working check http://al.cloudapp.net/ for a simple html page.

You are welcome to use it.

I added into Azure for anybody that wants to use it, this way, first I’ll be testing the Azure cloud as providing a service to fellow developers. I’ll leave the app running there indefinitely. So use that huge pipe to free yourself away from cross domain requests.

Add the to the beginning of your url path: http://al.cloudapp.net/proxy.ashx?

So to download an xml file from the web you do:

http://al.cloudapp.net/proxy.ashx?http://domain.com/page.xml

Please make sure to use it only for Silverlight development requests.

Vote NO on crossdomain policies for Silverlight.

If you want to vote no, please leave a comment on this blog. Enough people complains may the big guys up in their offices change their minds. In the mid time, use the proxy that will never return an exception for policy errors. As well you are helping test Azure and the speed of the cloud. With time, they would be many services installed there.

The C# Code

Just a normal proxy, nothing special here:

[WebService(Namespace = "http://tempuri.org/")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] public class Proxy : IHttpHandler { public void ProcessRequest(HttpContext context) { string uri = context.Request.QueryString[0]; if (uri.IndexOf("http://") == -1) { uri = context.Request.Url.Query.Substring(1); } System.Net.WebRequest req = System.Net.WebRequest.Create(new Uri(uri));

 req.Method = context.Request.HttpMethod; // Set body of request for POST requests if (context.Request.InputStream.Length > 0) { byte[] bytes = new byte[context.Request.InputStream.Length]; context.Request.InputStream.Read(bytes, 0, (int)context.Request.InputStream.Length); req.ContentLength = bytes.Length; req.ContentType = "application/x-www-form-urlencoded"; System.IO.Stream outputStream = req.GetRequestStream(); outputStream.Write(bytes, 0, bytes.Length); outputStream.Close(); } System.Net.WebResponse res = req.GetResponse(); context.Response.ContentType = res.ContentType; System.IO.StreamReader sr = new System.IO.StreamReader(res.GetResponseStream());

 string strResponse = sr.ReadToEnd(); context.Response.Write(strResponse);

 context.Response.End(); }

Related posts

The cloud for a fast deployment of proof of concepts

Having problems with Windows Azure Tools for Microsoft Visual Studio CTP, do you want a invitation for Azure?

Improve the performance of your ASP.NET application with Silverlight 2.0

Moving Community Server to the Cloud

Cheers

Al

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