soundc

I have been looking for a nice implementation of XML-RPC for silverlight for a while now. There are a few good resources out there such as XML-RPC.NET, but they don’t really work on Silverlight.

Silverlight is different, that it only has asynchronous network calls and you can’t really imitate sync calls, which makes the use of a RPC a little weird.

I have written a small XML-RPC library for Silverlight. Actually its just a single C# file which users can just drag and drop into their projects. The library is still under development, presently I am hacking together a parser, making sure it works with the most common scenarios.

Here is what the usage of this library looks like. You instantiate a service class, and then instantiate query requests as shown below:

XmlRpcService service
            = new XmlRpcService ("http://betty.userland.com/RPC2");
XmlRpcRequest req
            = new XmlRpcRequest (service, "examples.getStateName",
                     new object [] { 10 });
req.XmlRpcCallCompleteHandler
            += new XmlRpcCallComplete (req_XmlRpcCallCompleteHandler);

req.Execute (null);

Once your call completes or some error occurs, your event handler is invoked (Here I am just assuming that the call succeeded):

void req_XmlRpcCallCompleteHandler (XmlRpcResponse response, object userState) {
    string result = (string)response.TryCast (typeof (string));
    System.Diagnostics.Debug.WriteLine ("Result: " + result);
}

You try to cast the response into a string, if it cannot be casted you get back a null or the default value for value types. TryCast is pretty powerful, you can declare a class and have TryCast map the returned struct (associative array) to that class. E.g. lets say we have this fault class:

public class Fault {
    public int FaultCode;
    public string FaultString;

    public override string  ToString() {
                 return "Fault Code: " + FaultCode.ToString ()
                     + ", Fault String: " + FaultString;
    }
}

You can use TryCast to map a fault response to this class. Note that, the names of the members here actually match with those returned when a fault occurs (see XML-RPC spec), case is not important though. You can use your own classes to map with struct returned as XML-RPC responses, this should be pretty handy. I will include more details when I actually release the library.

So a more fault tolerant event handler would look something like this:

Fault f = (Fault)response.TryCast (typeof (Fault));
if (f != null) {
    Debug.WriteLine ("Fault occured: " + f.ToString ());
    if (f.FaultCode == -1) {
        Debug.WriteLine ("OMG! -1 ERROR!");
    }
}
else {
    string result = (string)response.TryCast (typeof (string));
    Debug.WriteLine ("Result: " + result);
}

I am still working on a few things with this library, I will post it up here as soon as I am done, I promise!

Stay tuned!

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