Lyo.Notification 1.0.2

Lyo.Notification

In-process publish/subscribe for small domain events. It is not durable, not distributed, and not ordered across machines—only useful when every publisher and handler lives in the same DI container (typical ASP.NET Core host or worker). For cross-service messaging use Lyo.MessageQueue (RabbitMQ, etc.).

Features

• AddLyoNotification registers INotificationPublisher as NotificationPublisher (singleton). The publisher captures IServiceProvider so each publish can resolve the current handler set (supports scoped handlers only if you resolve INotificationPublisher from the same scope that contains scoped handlers—which is fragile; prefer singleton/transient handlers or resolve handlers explicitly in tests).

Examples

Register services

using Lyo.Notification;

builder.Services.AddLyoNotification();
builder.Services.AddSingleton<INotificationHandler<OrderPlacedNotification>, SendEmail>();
builder.Services.AddSingleton<INotificationHandler<OrderPlacedNotification>, UpdateInventoryProjection>();

Publishing

public class CheckoutService(INotificationPublisher bus)
{
    public async Task CompleteAsync(Guid orderId, CancellationToken ct)
    {
        // ... persistence ...
        await bus.PublishAsync(new OrderPlacedNotification(orderId), ct);
    }
}

Why this exists

Sometimes you only need: “when X happens, run these side effects in-process without the feature knowing about each handler.” Full MediatR-style pipelines (behaviors, open generics, pipeline ordering) are intentionally out of scope. You get a marker type, one or more handlers per notification, and a publisher that resolves handlers from DI and awaits them sequentially.

Core types

There is no built-in “stop on first handler” or “only one handler” rule—every matching handler runs every time unless you unregister it.

Registration

• AddLyoNotification registers INotificationPublisher as NotificationPublisher (singleton). The publisher captures IServiceProvider so each publish can resolve the current handler set (supports scoped handlers only if you resolve INotificationPublisher from the same scope that contains scoped handlers—which is fragile; prefer singleton/transient handlers or resolve handlers explicitly in tests).

Publishing

Publish is async void-free: PublishAsync awaits each handler sequentially. There is no parallel fan-out built in.

Error behavior (important)

Inside NotificationPublisher, each handler is wrapped in try/catch: - On exception: the error is logged at Error level (handler type + notification type in the structured log payload). - The remaining handlers still run—failures do not abort the publisher or rethrow. So notifications are best-effort side effects: logging + continue. If you need transactional semantics or fail closed behavior, call handlers explicitly or wrap PublishAsync yourself. Cancellation: CancellationToken is passed through to HandleAsync. If cancelled mid-loop, handlers that observe the token stop; handlers already running complete unless they cancel internally.

When not to use this

• Cross-process or cross-pod events → message bus.
• Guaranteed delivery / retries / dead-letter → queue + outbox patterns.
• Pipelines that must run middleware in order across all handlers → mediator library.
• You need mediator request/response (query objects with return values) → this is publish-only (Task, no aggregate return value from PublishAsync).

See also

• Lyo.MessageQueue — broker-backed messaging.
• Lyo.Discord.Bot — example integration host that pulls in diff and other utilities.

Dependencies

Generated from ProjectReference / PackageReference (same model as docs/Lyo.ProjectGraph.html).

• Lyo.Exceptions — (direct, lyo)
• Microsoft.Extensions.DependencyInjection 10.0.5 — (direct, microsoft)
• Microsoft.Extensions.Logging.Abstractions 10.0.5 — (direct, microsoft)