Using Service Templates with Indigo - Enabling Metadata Exchange
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A metadata exchange endpoint is required to support the dynamic generation of proxy and configuration for client applications. You must explicitly enable metadata exchange by adding the endpoint and enabling the metadata exchange behavior.
A metadata exchange (mex) endpoint is just like any other service endpoint in that it requires an address, contract, and binding. The address for a metadata exchange endpoint requires a base address for the selected binding protocol. The contract must beIMetadataExchange, a predefined service contract belonging to theSystem.ServiceModel.Descriptionnamespace (see Example 1-7).
Example 1-7. IMetadataExchange contract as defined by the service model
[ServiceContract(ConfigurationName="IMetadataExchange",Name=
"IMetadataExchange", Namespace="http://schemas.microsoft.com/ 2006/04/mex")]
public interface IMetadataExchange
{
[OperationContract(Action="http://schemas.xmlsoap.org/ws/2004/ 09/transfer/Get", ReplyAction="http://schemas.xmlsoap.org/ws/ 2004/09/transfer/GetResponse", AsyncPattern=true)]
IAsyncResult BeginGet(Message request,AsyncCallback callback,object state);
Message EndGet(IAsyncResult result);
[OperationContract(Action="http://schemas.xmlsoap.org/ws/2004/ 09/transfer/Get", ReplyAction=http://schemas.xmlsoap.org/ws/ 2004/09/transfer/GetResponse)]
Message Get(Message request);
}
As for the binding, there are several predefined mex bindings, includingMexHttpBinding,MexHttpsBinding,MexTcpBinding, andMexNamedPipeBinding. That means you can expose a mex endpoint over HTTP, HTTPS, TCP, or named pipes and have SvcUtil consume those endpoints.
Like any other endpoint, metadata exchange endpoints can also be consumed at runtime by clients. Applications can call mex endpoints to dynamically generate proxies or just to request information about the associated service.
The following illustrates a service exposing two TCP endpoints: one for the service, another for metadata exchange:
<service behaviorConfiguration="serviceBehavior"
name="HelloIndigo.HelloIndigoService">
<endpoint address="HelloIndigoService" binding="netTcpBinding" name="netTcp"
contract="HelloIndigo.IHelloIndigoService" />
<endpoint binding="mexTcpBinding" name="mex" contract="IMetadataExchange" />
<host>
<baseAddresses>
<add baseAddress="net.tcp:// localhost:9000/HelloIndigo" />
</baseAddresses>
</host>
</service>
Supplying the endpoint is not sufficient on its own. The service metadata behavior must also be enabled. Example 1-5 shows you how to enable the behavior by associating a service behavior to the service and including the<serviceMetadata>element. Once the behavior is enabled, you can use SvcUtil for proxy generation against any mex endpoint. For example, to generate a service proxy and configuration using the TCP endpoint with SvcUtil, you can type this instruction at the command line:
svcutil /d:<YourLearningWCFPath>\Labs\ Chapter1\HelloIndigo\Client /o:serviceproxy.cs
/config:app.config net.tcp://localhost:9000/HelloIndigo/mex
It might seem a little annoying at first that you have to enable metadata exchange before you can generate a client proxy. This opt-in behavior is actually a good thing in the long run. You don't want your services exposing endpoints of which you aren't aware or that you dont want to support.
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter 1 of the book Learning WCF A Hands-on Guide, written by Michele Leroux Bustamante (O'Reilly, 2007; ISBN: 0596101627). Check it out today at your favorite bookstore. Buy this book now.
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