Notification sinks

A sink is a delivery channel for notifications. IPublisher.Publish passes each notification to every registered INotificationSink, one after another.

The default sink, registered by AddAnyMediator, resolves the INotificationHandler<T> implementations from the container and runs them with the configured notification publisher.

Add a channel

Implement INotificationSink to send notifications somewhere else, for example a message broker:

public sealed class ServiceBusSink(ServiceBusSender sender) : INotificationSink
{
    public Task Dispatch<TNotification>(TNotification notification, CancellationToken cancellationToken = default)
        where TNotification : INotification
    {
        var message = new ServiceBusMessage(BinaryData.FromObjectAsJson(notification))
        {
            Subject = typeof(TNotification).Name,
        };
        return sender.SendMessageAsync(message, cancellationToken);
    }
}

Register it next to the default one:

services.AddAnyMediator(cfg => cfg.RegisterServicesFromAssemblyContaining<Program>());
services.AddSingleton<INotificationSink, ServiceBusSink>();

Now every Publish runs the in-process handlers and also sends the message.

Failures

Sinks are isolated from each other: if one throws, the next ones still run. Once all sinks have run, Publish re-throws the failure, or an AggregateException with every failure when several sinks threw.

Inside a sink, TNotification is the type the caller published with; Publish(object) uses the runtime type. When a notification is published through a variable of a base type or interface, TNotification is that type: use notification.GetType() to read the concrete one.

Filtering

A sink receives every notification. To forward only some of them, check the type, or mark the notifications to forward with an interface of your own:

public interface IIntegrationEvent : INotification;

public Task Dispatch<TNotification>(TNotification notification, CancellationToken cancellationToken = default)
    where TNotification : INotification
    => notification is IIntegrationEvent ? Send(notification, cancellationToken) : Task.CompletedTask;