Messaging: queues and pub/sub

Send work to a competing-consumers queue, and broadcast events to a fan-out topic.

What you'll build

A host using SquidStd.Messaging: an IMessageQueue (one consumer handles each message) and an IMessageTopic (every subscriber receives each message). The same APIs work over RabbitMQ via SquidStd.Messaging.RabbitMq.

Prerequisites

.NET 10 SDK
dotnet add package SquidStd.Messaging (or SquidStd.Messaging.RabbitMq)

Steps

1. Register in-memory messaging


bootstrap.ConfigureServices(container => container.RegisterCoreServices().AddInMemoryMessaging());

2. Queue: competing consumers

Subscribe a listener and PublishAsync to a named queue. Each message is handled by exactly one consumer.


var queue = bootstrap.Resolve<IMessageQueue>();

using (queue.Subscribe("orders", new OrderListener()))
{
    await queue.PublishAsync("orders", new OrderPlaced("order-1"));
    await Task.Delay(200);
}

3. Topic: fan-out pub/sub

A topic delivers each published message to every current subscriber.


var topic = bootstrap.Resolve<IMessageTopic>();

using (topic.Subscribe<OrderPlaced>(
           "order-events",
           (order, _) =>
           {
               Console.WriteLine($"topic saw {order.Id}");

               return Task.CompletedTask;
           }
       ))
{
    await topic.PublishAsync("order-events", new OrderPlaced("order-2"));
    await Task.Delay(200);
}

Run it

dotnet run --project samples/SquidStd.Samples.Messaging

Prints queue handled order-1 and topic saw order-2.

How it works

Queues use competing-consumers with retry and dead-lettering (MessagingOptions); topics use transient fan-out (at-most-once). Swap AddInMemoryMessaging() for AddRabbitMqMessaging(...) for a durable broker - the IMessageQueue/IMessageTopic code is unchanged.

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