Extended ServiceHost class not getting Description object initialized

Question

I'm having a small problem, should be simple but I cant seemt o figure it out.

My console host:

Code Snippet

class Program {
    static void Main(string[] args) {

      using (ServiceHost<QueueManager> host = new ServiceHost<QueueManager>()) {       
        host.Open();
        Console.ReadKey();
        host.Close();         
      }

      //using (ServiceHost host = new ServiceHost(typeof(QueueManager))) {
      //  host.Open();

      //  Console.ReadKey();
      //  host.Close();
      //}
    }
  }

My derived class:

Code Snippet

 class ServiceHost<T> : ServiceHost
  {
    protected override void OnOpening()
    {
      foreach (ServiceEndpoint p in Description.Endpoints) {
        //check and create the queue mentioned in the endpoints if type msmq binding
        QueuedServiceHelper.VerifyQueue(p);
      }
      base.OnOpening();
    }
  }

I get an invalidoperation exception when I open the host


after debugging I found that in the ServiceHost<T> class in the OnOpening implementation the Description object is null and does not get populated from the base ServiceHost

although if I create and host the base ServiceHost object directly, it works without any issues. Any suggestions ?

my config section is below is below:

Code Snippet

<system.serviceModel>
    <services>
      <service name="xxx.QueueManager" behaviorConfiguration="xxx.QueueManagerBehavior">
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8000/QueueManager/service"/>
          </baseAddresses>
        </host>
        <!-- Service Endpoints -->
        <endpoint address="" binding="wsHttpBinding" contract="xxx.IQueueManager">
          <identity>
            <dns value="localhost"/>
          </identity>
        </endpoint>
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="xxx.QueueManagerBehavior">
          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <netMsmqBinding>
        <binding name="noMSMQSecurity">
          <security mode="None" />
        </binding>
      </netMsmqBinding>
    </bindings>
  </system.serviceModel>

Answer 1

This error is probably occuring in the Open() method.  YOu should not be using a "using" statement here because of how the Dispose method is implemented.   See this blog post for a full explaination and recommentations about what you should do:
http://www.danrigsby.com/blog/index.php/2008/02/26/dont-wrap-wcf-service-hosts-or-clients-in-a-using-statement/.

Have you looked at the stack trace for that exception or looked at the call stack?  I bet under the invalidoperation you will find some other exception, quite possibly an exception that derives from CommunicationException, and could be about not being able to setup the channels correctly from the Open() method.  In the OnOpening method, the endpoints probably arent set yet.

Answer 2

You probalby want to override the OnOpened method if you want to look at the endpoints after they have been added from the app.config file.  OnOpening would occur right before it does the work of Open(), while OnOpened occurs after all of the work from Open().

Answer 3

Thanks Dan,

Good blog post on not to use the using statement, I tried your suggestion of overriding the OnOpened method instead. But I'm getting the same InvalidOperationException, there is no inner exception with it.

my stack trace with the OnOpened implamentation:

   at System.ServiceModel.ServiceHostBase.InitializeRuntime()
   at System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Open()
   at TestHost.Program.Main(String[] args) in D:\Projects\VTLS\Main\Source\VTLS\Source\Upload\WebClient\QueueManagerHost\TestHost.cs:line 19

stack trace with OnOpening implementation:

   at Services.QueueManagerHost.ServiceHost`1.OnOpening() in D:\Projects\VTLS\Main\Source\VTLS\Source\Upload\WebClient\QueueManagerHost\GenericServiceHost.cs:line 14
   at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Open()
   at TestHost.Program.Main(String[] args) in D:\Projects\VTLS\Main\Source\VTLS\Source\Upload\WebClient\QueueManagerHost\TestHost.cs:line 19


my implementation is based on the book :

Programming WCF Services

By Juval Lowy

...............................................

Publisher: O'Reilly

Pub Date: February 20, 2007

ISBN-10: 0-596-52699-7

ISBN-13: 978-0-596-52699-3

section 9.2 "Queued Calls"

please note that it seems to work fine if I implement the base ServiceHost, It sems like a good pattern, but it doesnt work... , although it should. weird

following is my complete implementation of the code:

 

Code Snippet

class ServiceHost<T> : ServiceHost {
    protected override void OnOpening() {
      foreach (ServiceEndpoint p in Description.Endpoints) {
        //check and create the queue mentioned in the endpoints if type msmq binding
        QueuedServiceHelper.VerifyQueue(p);
      }
      base.OnOpened();
    }

    protected override void OnClosing() {
      PurgeQueues();
      base.OnClosing();
    }

    [Conditional("DEBUG")]
    private void PurgeQueues() {
      foreach (ServiceEndpoint p in Description.Endpoints) {
        QueuedServiceHelper.PurgeQueue(p);
      }
    }
  }

  public static class QueuedServiceHelper {
    public static void VerifyQueue(ServiceEndpoint endpoint) {
      if (endpoint.Binding is NetMsmqBinding) {
        string queue = GetQueueFromUri(endpoint.Address.Uri);
        if (MessageQueue.Exists(queue) == false) {
          MessageQueue.Create(queue, true);
        }
      }
    }

    public static void VerifyQueue<T>(string endpointName) where T : class {
      ChannelFactory<T> factory = new ChannelFactory<T>(endpointName);
      VerifyQueue(factory.Endpoint);
    }
    public static void VerifyQueue<T>() where T : class {
      VerifyQueue<T>("");
    }


    //Parses the queue name out of the address
    static string GetQueueFromUri(Uri uri) {
      string[] pathFragments = uri.Segments;      

      //return the last uri segment, it would be the queue name
      return pathFragments[pathFragments.Length - 1];
    }

    //purge the queue while in debug , otherwise it makes debugging difficult    
    public static void PurgeQueue(ServiceEndpoint endpoint) {
      if (endpoint.Binding is NetMsmqBinding) {
        string queueName = GetQueueFromUri(endpoint.Address.Uri);
        if (MessageQueue.Exists(queueName) == true) {
          MessageQueue queue = new MessageQueue(queueName);
          queue.Purge();
        }
      }
    }

  }

Answer 4

Sorry to reply to an old thread, but I ran into the exact same problem today.  A search pulled up this thread, so I thought to post a solution for anyone else finding their way here.  The problem is that you are not calling the base class's constructor.  Add the following code:

public class ServiceHost<T> : ServiceHost
{
	public ServiceHost() : base(typeof(T))
	{
	}
	...
}