How to detect connectivity to my server using Silverlight 4 - silverlight-4.0

Question

The users of my Silverlight application will access the server via a VPN connection. Thus, the built in NetworkInterface.GetIsNetworkAvailable is of no use.
I tried 2 different methods for checking connection to my server; WebClient and a WCF service.
As for the service, I tried the following method. I can't see how I would use a regular service call since the return handler would never hit.
var ping = new PingServiceClient();
ping.InnerChannel.Open( new TimeSpan(1500) );
var result = ping.State == CommunicationState.Opened;
Using WebClient, I tried this:
var client = new WebClient();
client.OpenReadCompleted += (s, e) => { MessageBox.Show( "Returned from server" ); };
client.OpenReadAsync( new PingServiceClient().Endpoint.Address.Uri );
In both cases, the results were the same (indicates connected) whether or not I was connected to the server (I pushed the samples to the live server and connected/disconnected using the VPN client.
The next thing I would try is sockets, but just getting a working sample is beyond difficult. Before going down that road any further, is there some other way of accomplishing this?

Answer 1

The WebClient will probably return completed regardless. You'll need to check if there was an error in the request.
var client = new WebClient();
client.OpenReadCompleted += (s,e) =>
{
if (e.Error == null)
{
MessageBox.Show("Returned from server");
}
}
client.OpenReadAsync( new PingServiceClient().Endpoint.Address.Uri );

Answer 2

I placed a small text file on the server and read it's contents. So this test worked reliably [edit: see comment]:
var client = new WebClient();
client.OpenReadCompleted += (s, e) =>
{
if ( e.Error == null )
{
var bytesReceived = new byte[ e.Result.Length ];
e.Result.Read( bytesReceived, 0, 50 );
var result = Encoding.UTF8.GetString( bytesReceived, 0, bytesReceived.Length );
if ( result.Contains( "pingback" ) )
{
MessageBox.Show("Server up");
}
else
{
MessageBox.Show( "Server down" );
}
}
else
{
MessageBox.Show("Server down");
}
};
var uri = string.Format( "{0}{1}{2}{3}{4}{5}", App.Current.Host.Source.Scheme, "://", App.Current.Host.Source.DnsSafeHost, ":", App.Current.Host.Source.Port, "/Ping.txt" );
client.OpenReadAsync( new Uri(uri) );