Feature: Support Open Generic Notification Handlers (Global Notification Pipeline) #47

Summary

Currently, DispatchR supports open generic pipeline behaviors for requests (e.g., IPipelineBehavior<TRequest, TResponse>), allowing for global/intercepting logic across all request or stream types. However, there is no equivalent for generic notification handlers – all notification handlers must be registered for specific notification types.

Problem

• There is currently no way to register a global INotificationHandler<TNotification> (open generic notification handler) that would handle all notifications, regardless of the actual notification type.
• Developers might want to implement cross-cutting logic (such as logging, auditing, or metrics) for all notifications in a single place, just as with generic pipeline behaviors.

Proposal

• Support registration and correct resolution of open generic notification handlers, such as:

  public class GlobalNotificationLogger<TNotification> : INotificationHandler<TNotification> where TNotification : INotification
  {
      public ValueTask Handle(TNotification notification, CancellationToken token) { /* ... */ }
  }

• When a notification is published, any applicable open generic notification handlers should be resolved and invoked along with type-specific handlers.
• This would bring the notification pipeline on par with the existing pipeline behavior mechanism for requests.

Possible Solution

• Extend ServiceRegistrator.RegisterNotification to detect and register open generic notification handlers.
• At publish time, resolve both specific and open generic handlers for the notification type.
• Follow a similar resolution logic as current pipeline behavior to avoid duplicates and support ordering if needed.

Motivation / Use cases

• Centralized notification logging/auditing
• Adding metrics, distributed tracing, or global fallback logic
• Writing less repetitive code when applying the same operation to all notifications

References

• This feature is common in some mediator/messaging frameworks (both MediatR and pipeline support are already in DispatchR for requests)

Thank you for considering this enhancement!