Topics

A topic handler receives one message at a time, from a subscription of the topic:

using Hardened.Functions.Runtime.Attributes;

public class OrderEventHandlers {

    [Topic("order-events")]
    public void OnOrderEvent(OrderEvent orderEvent, IProjection projection) => projection.Apply(orderEvent);
}

Packages

<PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="2.1.0" />
<PackageReference Include="Hardened.Azure.Functions.Runtime" Version="0.38.0-rc1000" />
<PackageReference Include="Hardened.Azure.Functions.ServiceBus" Version="0.38.0-rc1000" />
<PackageReference Include="Hardened.Azure.Functions.SourceGenerator" Version="0.38.0-rc1000" PrivateAssets="all" />

The same package serves [Queue]; the delivery, the headers and the settlement are the ones Queues describes.

dotnet new hardened-function --host azure --trigger topic writes this shape with tests.

The subscription is the module's

Service Bus reads a topic through a subscription, and a subscription is named for the consumer, so it is not something a handler that names the topic can know. It is written once on the application:

[HardenedModule]
[ServiceBusModule(Subscription = "projection")]
public partial class Application;

Every [Topic] handler in the application reads through that subscription. Leaving it out is HRDAZ003 at build, naming the property and where to write it, because the binding cannot be generated without it. The value has to be a literal: the host reads it from metadata the build writes, not from the compiled attribute, and a constant from another class is HRDAZ004.

[Topic("order-events")] becomes Topic_order_events, bound by [ServiceBusTrigger("order-events", "projection", IsBatched = true)] and routed as TOPIC /order-events. Two applications reading the same topic are two subscriptions, one each.

Deploying

az servicebus topic create --namespace-name orders-ns --resource-group orders --name order-events
az servicebus topic subscription create --namespace-name orders-ns --resource-group orders \
    --topic-name order-events --name projection

The connection is AzureWebJobsServiceBus, set as Queues shows, or the setting [ServiceBusModule(Connection = "...")] names.

What a failure means

The same as a queue's: the batch is abandoned and delivered again unless ReportsItemFailures is on, and then only the refused messages come back. The subscription's MaxDeliveryCount is where they stop.

Testing

[HardenedTest]
public async Task AnEventIsProjected(Application.Topics topics, IProjection projection) {
    await topics.OrderEvents(new OrderEvent { Id = "A-1" });

    Assert.Contains("A-1", projection.Applied);
}

The façade is named for the topic. Under [assembly: AzureFunctionsTesting] the message is the ServiceBusReceivedMessage the worker would bind, and MetadataAgreement checks that the subscription the build wrote into functions.metadata is the one the generated provider tells the host. See Testing Azure handlers.

Next

• Queues: the delivery, the headers and the settlement in full
• Events: Event Grid, for events that are not Service Bus messages