Broadcast Messages to a Specific Topic

If you're using a transport endpoint that supports publishing messages by topic such as this example using Rabbit MQ from the Wolverine tests:

theSender = Host.CreateDefaultBuilder()
    .UseWolverine(opts =>
    {
        opts.UseRabbitMq("host=localhost;port=5672").AutoProvision();
        opts.PublishAllMessages().ToRabbitTopics("wolverine.topics", exchange =>
        {
            exchange.BindTopic("color.green").ToQueue("green");
            exchange.BindTopic("color.blue").ToQueue("blue");
            exchange.BindTopic("color.*").ToQueue("all");
        });

        opts.PublishMessagesToRabbitMqExchange<RoutedMessage>("wolverine.topics", m => m.TopicName);
    }).Start();

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You can explicitly publish a message to a topic through this syntax:

var publisher = theSender.Services
    .GetRequiredService<IMessageBus>();

await publisher.BroadcastToTopicAsync("color.purple", new Message1());

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var publisher = theSender.Services
    .GetRequiredService<IMessageBus>();

await publisher.BroadcastToTopicAsync("color.purple", new Message1());

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Topic Sending as Cascading Message

Wolverine is pretty serious about enabling as many message handlers or HTTP endpoints as possible to be pure functions where the unit testing is easier, so there's an option to broadcast messages to a particular topic as a cascaded message:

public class ManuallyRoutedTopicResponseHandler
{
    public IEnumerable<object> Consume(MyMessage message, Envelope envelope)
    {
        // Go North now at the "direction" queue
        yield return new GoNorth().ToTopic($"direction/{envelope.TenantId}");
    }
}

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