Hooking into wcf pipeline

Question

Is there way inspect wcf method call. I means anything equal to HttpModule in asp.net.

I want execute a method before any method call.

Answer 1

WCF has a very extensible architecture. It is possible to intercept and customize a lot of WCF functionality to do your own thing.

For your case you will have to write appropriate Service or Endpoint Behavior. The process between receiving a message from the transport channels and invoking your service method is called as dispatching. WCF uses a set of Behaviors to do the dispatching. You can provide your own Behavior to inspect the method calls.

This article provides an excellent overview and examples - Extending WCF with Custom Behaviors.

I would also suggest that you go through this WCF architecture overview http://msdn.microsoft.com/en-us/library/aa480210.aspx

Answer 2

The IOperationInvoker might have been what you were looking for:

public class MyOperationInvoker : IOperationInvoker
{
    IOperationInvoker originalInvoker;
    public MyOperationInvoker(IOperationInvoker originalInvoker)
    {
        this.originalInvoker = originalInvoker;
    }

    public bool IsSynchronous { get { return originalInvoker.IsSynchronous; } }

    public object[] AllocateInputs() { return originalInvoker.AllocateInputs(); }

    public object Invoke(object instance, object[] inputs, out object[] outputs)
    {
        //Do stuff before call
        var res = this.originalInvoker.Invoke(instance, inputs, out outputs);
        //stuff after call
        return res;
    }

    public IAsyncResult InvokeBegin(object instance, object[] inputs,
                AsyncCallback callback, object state)
    {
        //Do stuff before async call
        var res = this.originalInvoker.InvokeBegin(instance, inputs, callback, state);
        return res;
    }

    public object InvokeEnd(object instance, out object[] outputs, IAsyncResult result)
    {
        var res = this.InvokeEnd(instance, out outputs, result);
        //Do stuff after async call
        return res;
    }
}

Implemented as an attribute for all operations in the service:

public class MyBehaviorAttribute : Attribute, IServiceBehavior, IOperationBehavior
{
    //IOperationBehavior
    public void ApplyDispatchBehavior(OperationDescription operationDescription,
            DispatchOperation dispatchOperation)
    {
        dispatchOperation.Invoker = new MyOperationInvoker(dispatchOperation.Invoker);
    }

    public void AddBindingParameters(OperationDescription operationDescription,
            BindingParameterCollection bindingParameters) { /*Do nothing*/ }

    public void ApplyClientBehavior(OperationDescription operationDescription,
            ClientOperation clientOperation) { /*Do nothing*/ }

    public void Validate(OperationDescription operationDescription) { /*Do nothing*/ }

    //IServiceBehavior
    public void Validate(ServiceDescription serviceDescription,
                ServiceHostBase serviceHostBase) { /*Do nothing*/ }

    public void AddBindingParameters(ServiceDescription serviceDescription,
                ServiceHostBase serviceHostBase,
                Collection<ServiceEndpoint> endpoints,
                BindingParameterCollection bindingParameters) { /*Do nothing*/ }

    public void ApplyDispatchBehavior(ServiceDescription serviceDescription,
                ServiceHostBase serviceHostBase)
    {
        foreach (ServiceEndpoint endpoint in serviceHostBase.Description.Endpoints)
        {
            foreach (var operation in endpoint.Contract.Operations)
            {
                operation.Behaviors.Add(this);
            }
        }
    }

And the service:

[MyBehavior]
public class HelloService : IHelloService
{
    ...
}

Answer 3

It depends what you want to check or modify in message at what level. If you'd like to modify something at Encoding level, you can opt for Custom Message Encoder, if it's before request get deserialize or before sending reply to client, use Custom Message Inspector.

HTH.