Question

Im building a WPF 3.5 desktop app that has a self-hosted WCF service.

The service has an PollingDuplexHttpBinding endpoint defined like so:

public static void StartService()
    {
        var selfHost = new ServiceHost(Singleton, new Uri("http://localhost:1155/"));

        selfHost.AddServiceEndpoint(
            typeof(IMyService), 
            new PollingDuplexHttpBinding(PollingDuplexMode.MultipleMessagesPerPoll) {ReceiveTimeout = new TimeSpan(1,0,0,0)},
            "MyService"
        );

        ServiceMetadataBehavior smb = new ServiceMetadataBehavior();
        smb.HttpGetEnabled = true;
        selfHost.Description.Behaviors.Add(smb);

        selfHost.AddServiceEndpoint(typeof(IPolicyRetriever), new WebHttpBinding(), "").Behaviors.Add(new WebHttpBehavior());

        selfHost.Open();
    }

Note: the IPolicyRetriever is a service that enables me to define a policy file

This works and I can see my service in my client Silverlight application. I then create a reference to the proxy in the Silverlight code like so:

        EndpointAddress address = new EndpointAddress("http://localhost:1155/MyService");

        PollingDuplexHttpBinding binding = new PollingDuplexHttpBinding(PollingDuplexMode.MultipleMessagesPerPoll);
        binding.ReceiveTimeout = new TimeSpan(1, 0, 0, 0);
        _proxy = new MyServiceClient(binding, address);
        _proxy.ReceiveReceived += MessageFromServer;
        _proxy.OrderAsync("Test", 4);

And this also works fine, the communication works!

But if I leave it alone (i.e. dont sent messages from the server) for longer than 1 minute, then try to send a message to the client from the WPF server application, I get timeout errors like so:

The IOutputChannel timed out attempting to send after 00:01:00. Increase the timeout value passed to the call to Send or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout.

Its all running on localhost and there really should not be a delay, let alone a 1 minute delay. I dont know why, but the channel seems to be closed or lost or something…

I have also tried removing the timeouts on the bindings and I get errors like this

The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it has been Aborted

How can I try to find out whats wrong here?

Answer 1

WPF uses wsDualHttpBinding, Silverlight – Polling Duplex.
WPF solution is simple; Silverlight requires ServiceHostFactory and a bit more code. Also, Silverlight Server never sends messages, rather Client polls the server and retrieves its messages.

After many problems with PollingDuplexHttpBinding I have decided to use CustomBinding without MultipleMessagesPerPoll.

web.config

<system.serviceModel>
    <behaviors>
        <serviceBehaviors>
            <behavior name="SlApp.Web.DuplexServiceBehavior">
                <serviceMetadata httpGetEnabled="true" />
                <serviceDebug includeExceptionDetailInFaults="true" />
            </behavior>
        </serviceBehaviors>
    </behaviors>

  <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />

    <services>
        <service behaviorConfiguration="SlApp.Web.DuplexServiceBehavior" name="SlApp.Web.DuplexService">
            <endpoint address="WS" binding="wsDualHttpBinding" contract="SlApp.Web.DuplexService" />
            <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
        </service>
    </services>      
</system.serviceModel>

DuplexService.svc:

<%@ ServiceHost Language="C#" Debug="true" Service="SlApp.Web.DuplexService" Factory="SlApp.Web.DuplexServiceHostFactory" %>

DuplexServiceHostFactory.cs:

    public class DuplexServiceHostFactory : ServiceHostFactoryBase
    {
        public override ServiceHostBase CreateServiceHost(string constructorString, Uri[] baseAddresses)
        {
            return new DuplexServiceHost(baseAddresses);
        }
    }

    class DuplexServiceHost : ServiceHost
    {
        public DuplexServiceHost(params Uri[] addresses)
        {
            base.InitializeDescription(typeof(DuplexService), new UriSchemeKeyedCollection(addresses));
        }

        protected override void InitializeRuntime()
        {
            PollingDuplexBindingElement pdbe = new PollingDuplexBindingElement()
            {
                ServerPollTimeout = TimeSpan.FromSeconds(3),
                //Duration to wait before the channel is closed due to inactivity
                InactivityTimeout = TimeSpan.FromHours(24)
            };

            this.AddServiceEndpoint(typeof(DuplexService),
                new CustomBinding(
                    pdbe,
                    new BinaryMessageEncodingBindingElement(),
                    new HttpTransportBindingElement()), string.Empty);

            base.InitializeRuntime();
        }
    }

Silverlight client code:

address = new EndpointAddress("http://localhost:43000/DuplexService.svc");
binding = new CustomBinding(
            new PollingDuplexBindingElement(),
            new BinaryMessageEncodingBindingElement(),
            new HttpTransportBindingElement()
        );
proxy = new DuplexServiceClient(binding, address);