Expose the internal behavior in order to decorate it

[danielmarbach]

Let's consider this example:

https://github.com/Particular/NServiceBus/blob/develop/src/NServiceBus.AcceptanceTests/PipelineExt/FilteringWhatGetsAudited.cs

The problem of the replace is that you need to reimplement the existing auditing behavior by copy pasting the code. It would be awesome if the pipeline allows to decorate existing behaviors without knowing the concrete class of the core behavior. This could for example be achieved with the follwowing syntactic sugar:

class FilteringAuditBehavior : IBehavior<IncomingContext>
            {
                public void Invoke(IncomingContext context, Action next)
                {
                    var auditBehavior = context.Get<IBehavior<IncomingContext>>(WellKnownSteps.AuditBehavior);
                    var auditResult = new AuditFilterResult();
                    context.Set(auditResult);
                    next();

                    //note: and rule operating on the raw TransportMessage can be applied here if needed.
                    // Access to the message is through: context.PhysicalMessage. Eg:  context.PhysicalMessage.Headers.ContainsKey("NServiceBus.ControlMessage")
                    if (auditResult.DoNotAuditMessage)
                    {
                        return;
                    }
                    auditBehavior.Invoke(context, next);
                }

                //here we inject our behavior
                class AuditFilteringOverride : INeedInitialization
                {
                    public void Customize(BusConfiguration configuration)
                    {
configuration.Pipeline.Replace(WellKnownStep.AuditProcessedMessage, typeof(FilteringAuditBehavior), "A new audit forwarder that has filtering");
                    }
                }
            }

The classes can be left internal but it allows the user to decorate existing behaviors. Thoughts?

[andreasohlund]

I like it!

[SimonCropp]

confused. how is this any different than the currently supported "wrapping a behaviour"?

[SimonCropp]

i now understand and withdraw my objection

[danielmarbach]

Cool!

[danielmarbach]

This could be solved with the internal service bag pretty easily.