JustSaying.FlexiblePublishers

A set of JustSaying IMessagePublisher replacements to perform different functions

QueuedMessagePublisher

A publisher that queues messages to be published at a later time. This is useful for when you want to publish messages in UoW functionality and you don't want to send the messages until the UoW is committed.

When publishing a message it can be optionally marked as isWhitelisted. When processing the queue, all messages can be sent or only the ones marked as isWhitelisted.

A middleware is provided which add this functionality onto IHandlerAsync<> handlers automatically.

Usage

Either the IQueuedMessagePublisher interface can be registered into DI which wraps the IMessagePublisher instance, OR the IQueuedMessagePublisher can be registered for both IMessagePublisher resolutions and IQueuedMessagePublisher resolutions, which is better as 3rd party code messages will be queued into the UoW as expected.

These examples use SimpleInjector but the theory is the same for all.

Setting up:

// Example for existing IMessagePublisher registration
// container.RegisterSingleton(() => builder.BuildPublisher());

// Approach to wrap the built IMessagePublisher into a QueuedMessagePublisher, then register this as both IMessagePublisher and IQueuedMessagePublisher
var messagingRegistration = Lifestyle.Scoped.CreateRegistration(
    () => new QueuedMessagePublisher(loggerFactory, () => builder.BuildPublisher()),
    container);

container.AddRegistration(typeof(IMessagePublisher), messagingRegistration);
container.AddRegistration(typeof(IQueuedMessagePublisher), messagingRegistration);

Configuring middleware:

x.ForTopic<TestMessage>(
        cfg =>
        {
            cfg.WithMiddlewareConfiguration(m =>
            {
                m.UseQueuedMessagesMiddleware();
                m.UseDefaults<TestMessage>(typeof(TestMessageHandler)); // Add default middleware pipeline
            });
        });

Using in app:

Publish a message normally:

private readonly IMessagePublisher _messagePublisher;

await _messagePublisher.PublishAsync(new TestMessage());

Publish a "isWhitelisted" message - this requires the IQueuedMessageInterface

private readonly IQueuedMessagePublisher _messagePublisher;

await _messagePublisher.PublishAsync(new TestMessage(), isWhitelisted: true);

Additional Notes

If using elsewhere (UoW approach on web controllers), then the queue must be processed at the end of the request handler. If using with a fully manual implementation then the queue must be processed once ready.

There is an example middleware for just with JustSaying 7 in here, and the same approach can be provided to middlewares for Mediator, ASP.NET Core pipelines etc.