WCF Discovery simply doesn't work

Question

I'm trying to add ad-hoc discovery to a simple WCF service-client setup (currently implemented by self hosting in a console app). Debugging using VS2010 on windows 7, and doing whatever I can find in online tutorial, but still - the discovery client simply finds nothing. Needless to say if I open a client to the correct service endpoint I can access the service from the client.

service code:

using (var selfHost = new ServiceHost(typeof(Renderer)))
{
    try
    {
        selfHost.Open();
        ...
        selfHost.Close();

service app.config:

<?xml version="1.0"?>
<configuration>
  <system.serviceModel>
    <services>
      <service name="TestApp.Renderer">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:9000" />
          </baseAddresses>
        </host>
        <endpoint address="ws" binding="wsHttpBinding" contract="TestApp.IRenderer"/>
        <endpoint kind="udpDiscoveryEndpoint"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <serviceDiscovery/>
          <serviceMetadata httpGetEnabled="True"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>

client discovery code:

DiscoveryClient discoveryClient = new DiscoveryClient(new UdpDiscoveryEndpoint());
var criteria = new FindCriteria(typeof(IRenderer)) { Duration = TimeSpan.FromSeconds(5) };
var endpoints = discoveryClient.Find(criteria).Endpoints;

The 'endpoints' collection always comes out empty. I've tried running the service and client from the debugger, from a command line, from an admin command line - everything, but to no avail (all on the local machine, of course, not to mantion I'll need it running on my entire subnet eventually)

Any help would be appreciated :-)

Answer 1

Here is a super simple discovery example. It does not use a config file, it is all c# code, but you can probably port the concepts to a config file.

share this interface between host and client program (copy to each program for now)

[ServiceContract]
public interface IWcfPingTest
{
  [OperationContract]
  string Ping();
}

put this code in the host program

public class WcfPingTest : IWcfPingTest
{
  public const string magicString = "djeut73bch58sb4"; // this is random, just to see if you get the right result
  public string Ping() {return magicString;}
}
public void WcfTestHost_Open()
{
  string hostname = System.Environment.MachineName;
  var baseAddress = new UriBuilder("http", hostname, 7400, "WcfPing");
  var h = new ServiceHost(typeof(WcfPingTest), baseAddress.Uri);

  // enable processing of discovery messages.  use UdpDiscoveryEndpoint to enable listening. use EndpointDiscoveryBehavior for fine control.
  h.Description.Behaviors.Add(new ServiceDiscoveryBehavior());
  h.AddServiceEndpoint(new UdpDiscoveryEndpoint());

  // enable wsdl, so you can use the service from WcfStorm, or other tools.
  var smb = new ServiceMetadataBehavior();
  smb.HttpGetEnabled = true;
  smb.MetadataExporter.PolicyVersion = PolicyVersion.Policy15;
  h.Description.Behaviors.Add(smb);

  // create endpoint
  var binding = new BasicHttpBinding(BasicHttpSecurityMode.None);
  h.AddServiceEndpoint(typeof(IWcfPingTest) , binding,   "");
  h.Open();
  Console.WriteLine("host open");
}

put this code in the client program

private IWcfPingTest channel;
public Uri WcfTestClient_DiscoverChannel()
{
  var dc = new DiscoveryClient(new UdpDiscoveryEndpoint());
  FindCriteria fc = new FindCriteria(typeof(IWcfPingTest));
  fc.Duration = TimeSpan.FromSeconds(5);
  FindResponse fr = dc.Find(fc);
  foreach(EndpointDiscoveryMetadata edm in fr.Endpoints) 
  {
    Console.WriteLine("uri found = " + edm.Address.Uri.ToString());
  }
  // here is the really nasty part
  // i am just returning the first channel, but it may not work.
  // you have to do some logic to decide which uri to use from the discovered uris
  // for example, you may discover "127.0.0.1", but that one is obviously useless.
  // also, catch exceptions when no endpoints are found and try again.
  return fr.Endpoints[0].Address.Uri;  
}
public void WcfTestClient_SetupChannel()
{
  var binding = new BasicHttpBinding(BasicHttpSecurityMode.None);
  var factory = new ChannelFactory<IWcfPingTest>(binding);
  var uri = WcfTestClient_DiscoverChannel();
  Console.WriteLine("creating channel to " + uri.ToString());
  EndpointAddress ea = new EndpointAddress(uri);
  channel = factory.CreateChannel(ea);
  Console.WriteLine("channel created");
  //Console.WriteLine("pinging host");
  //string result = channel.Ping();
  //Console.WriteLine("ping result = " + result);
}
public void WcfTestClient_Ping()
{
  Console.WriteLine("pinging host");
  string result = channel.Ping();
  Console.WriteLine("ping result = " + result);
}

on the host, simply call the WcfTestHost_Open() function, then sleep forever or something.

on the client, run these functions. It takes a little while for a host to open, so there are several delays here.

System.Threading.Thread.Sleep(8000);
this.server.WcfTestClient_SetupChannel();
System.Threading.Thread.Sleep(2000);
this.server.WcfTestClient_Ping();

host output should look like

host open

client output should look like

uri found = http://wilkesvmdev:7400/WcfPing
creating channel to http://wilkesvmdev:7400/WcfPing
channel created
pinging host
ping result = djeut73bch58sb4

this is seriously the minimum I could come up with for a discovery example. This stuff gets pretty complex fast.

Answer 2

Damn! it was the firewall... for some reason all UDP communication was blocked - disabling the firewall solved the problem. Now I only need to figure out the correct firewall configuration...