Programming WCF Services, 2nd Edition

Intercepting Client Calls

To intercept client-side calls WCF provides the interface IClientMessageInspector, defined as:

public interface IClientMessageInspector
{
   object BeforeSendRequest(ref Message request,IClientChannel channel);
   void AfterReceiveReply(ref Message reply,object correlationState);
}

The BeforeSendRequest( ) method is called just before the message is sent down the wire, allowing you to affect the request message. Similarly, the AfterReceiveReply( ) method is your chance to interact with the reply message for post-call processing.

The client runtime represented by the ClientRuntime class contains a collection of message inspectors:

public sealed class ClientRuntime
{
   public SynchronizedCollection<IClientMessageInspector> MessageInspectors
   {get;}

  //More members
}

You can add your message inspector to the collection by associating the proxy with an endpoint behavior. That behavior needs to add the inspector in the ApplyClientBehavior( ) method:

public interface IEndpointBehavior
{
   void ApplyClientBehavior(ServiceEndpoint endpoint,ClientRuntime clientRuntime);
   //More members
}

To encapsulate these steps I wrote the class InterceptorClientBase<T> defined in Example E-4.

Example E-4. The InterceptorClientBase<T> class

public abstract class InterceptorClientBase<T> : ClientBase<T> where T : class { public InterceptorClientBase( ) { Endpoint.Behaviors.Add(new ClientInterceptor(this)); } public InterceptorClientBase(string endpointName) : base(endpointName) { Endpoint.Behaviors.Add(new ...