WCF and Bindings - Metadata Exchange
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A service has two options for publishing its metadata. You can provide the metadata over the HTTP-GET protocol, or you can use a dedicated endpoint, discussed later. WCF can provide the metadata over HTTP-GET automatically for your service; all you need is to enable it by adding an explicit service behavior. Behaviors are described in subsequent chapters. For now, all you need to know is that a behavior is a local aspect of the service, such as whether or not it wants to exchange its metadata over HTTP-GET. You can add this behavior administratively or programmatically. Example 1-10 shows a host application config file, where both hosted services reference a custom behavior section that enables the metadata exchange over HTTP-GET. The address the clients need to use for the HTTP-GET is the registered HTTP base address of the service. You can also specify in the behavior an external URL for this purpose.
Example 1-10. Enabling metadata exchange behavior using a config file
<system.serviceModel>
<services>
<service name = "MyService" behaviorConfiguration = "MEXGET">
<host>
<baseAddresses>
<add baseAddress = "http://localhost:8000/"/>
</baseAddresses>
</host>
...
</service>
<service name = "MyOtherService" behaviorConfiguration = "MEXGET">
<host>
<baseAddresses>
<add baseAddress = "http://localhost:8001/"/>
</baseAddresses>
</host>
...
</service>
</services>
<behaviors>
<serviceBehaviors>
<behavior name = "MEXGET">
<serviceMetadata httpGetEnabled = "true"/>
</behavior>
</serviceBehaviors>
</behaviors>
</system.serviceModel>
Once you have enabled the metadata exchange over HTTP-GET, you can navigate to the HTTP base address (if present) using a browser. If all is well, you will get a confirmation page, such as the one shown in Figure 1-6, letting you know that you have successfully hosted a service. The confirmation page is unrelated to IIS hosting, and you can use a browser to navigate to the service address even when self-hosting.
Enabling Metadata Exchange Programmatically
To programmatically enable the metadata exchange over HTTP-GET, you first need to add the behavior to the collection of behaviors the host maintains for the service type. The ServiceHostBase class offers the Description property of the type ServiceDescription:
public abstract class ServiceHostBase : ...
{
public ServiceDescription Description
{get;}
//More members
}
The service description, as its name implies, is the description of the service with all its aspects and behaviors.ServiceDescription contains a property calledBehaviorsof the typeKeyedByTypeCollection<I>withIServiceBehavioras the generic parameter:
public class KeyedByTypeCollection<I> : KeyedCollection<Type,I>
{
public T Find<T>();
public T Remove<T>();
//More members
}
public class ServiceDescription
{
public KeyedByTypeCollection<IServiceBehavior> Behaviors
{get;}
}
Figure 1-6. A service confirmation page
IServiceBehavior is the interface that all behavior classes and attributes implement.KeyedByTypeCollection<I>offers the generic methodFind<T>(), which returns the requested behavior if it is in the collection, andnull otherwise. A given behavior type can only be found in the collection at most once. Example 1-11 shows how to enable the behavior programmatically.
Example 1-11. Enabling the metadata exchange behavior programmatically
ServiceHost host = new ServiceHost(typeof(MyService));
ServiceMetadataBehavior metadataBehavior; metadataBehavior = host.Description.Behaviors.Find <ServiceMetadataBehavior>();
if(metadataBehavior == null)
{
metadataBehavior = new ServiceMetadataBehavior();
metadataBehavior.HttpGetEnabled = true;
host.Description.Behaviors.Add(metadataBehavior);
}
host.Open();
First the hosting code verifies that no MEX endpoint behavior was provided in the config file by calling theFind<T>()method ofKeyedByTypeCollection<I>usingServiceMetadataBehavioras the type parameter.ServiceMetadataBehavior is defined in theSystem.ServiceModel.Description:
public class ServiceMetadataBehavior : IServiceBehavior
{
public bool HttpGetEnabled
{get;set;}
//More members
}
If the returned behavior isnull, the hosting code creates a newServiceMetadataBehavior, setsHttpGetEnabledtotrue, and adds it to the behaviors in the service description.
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter one of Programming WCF Services, written by Juval Lowry (O'Reilly, 2007; ISBN: 0596526997). Check it out at your favorite bookstore. Buy this book now.
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