In previous versions of Silverlight, the browser handled all the HTTP communication for the Silverlight plug-in. The browser HTTP stack works well but has some limitations including the HTTP methods you can use and the response codes that are accepted. In Silverlight 3, you can opt-in to have the Silverlight client perform the HTTP handling. By opt-in, I mean, if you don't specifically choose the client to perform HTTP processing, it will be done by the browser, just like it always has been. However, if you decide you need to call REST services, you can easily do this with Silverlight3 by opting in to the client HTTP stack.
Here’s a table that summarizes some of the basic HTTP capabilities of Silverlight 3 and whether browser or client HTTP handling supports the capability.
Specifying the HTTP stack is easy. You simply call the WebRequest.RegisterPrefix method, passing the ClientHttp object to specify client HTTP handling or a BrowserHttp object to specify browser HTTP handling. You do this before you make any web requests. One important thing to remember is that once you have specified the client or browser HTTP stack for a particular domain or scheme, you can’t change it.
The following code shows how to specify client handling all HTTP and HTTPS requests and responses.
bool httpResult = WebRequest.RegisterPrefix("http://", WebRequestCreator.ClientHttp);
bool httpsResult = WebRequest.RegisterPrefix("https://", WebRequestCreator.ClientHttp);
You can also use the WebRequest.RegisterPrefix method to register a specific domain. The following code shows and example of how to do this.
HttpWebRequest request = (HttpWebRequest)WebRequestCreator.ClientHttp.Create(new Uri( http://api.search.live.net/qson.aspx?query=Silverlight));
For more details (and VB code) on specifying Client or browser HTTP handling, see How to: Specify Client or Browser HTTP Handling.
For more details on general HTTP capabilities and how to make HTTP requests with Silverlight, plus some security considerations if you are hosting Web services for Silverlight clients, see HTTP Communication and Security with Silverlight.