Table of Contents

Producer Behaviors Pipeline

Each message produced by Silverback is processed by a pipeline of behaviors enabling different features and customizations. The SortIndex property of each behavior determines the order in which they are executed and each behavior passes the message along the pipeline to the next behavior.

Default Behaviors

The following table lists the default behaviors that are executed when producing a message.

Name Index Description
ActivityProducerBehavior 100 Starts an Activity and adds the tracing information to the message headers.
HeadersWriterProducerBehavior 200 Maps the properties decorated with the HeaderAttribute to the message headers.
MessageEnricherProducerBehavior 250 Invokes all the IOutboundMessageEnricher configured for the endpoint.
KafkaMessageKeyInitializerProducerBehavior 300 Sets the Kafka key with the value from the properties decorated with the KafkaKeyMemberAttribute, unless a key is already set.
FilterProducerBehavior 400 Applies the configured filters to the message being produced.
BinaryMessageHandlerProducerBehavior 500 Switches to the BinaryMessageSerializer if the message being produced implements the IBinaryMessage interface.
ValidatorProducerBehavior 550 Validates the message being produced.
SerializerProducerBehavior 600 Serializes the message being produced using the configured IMessageSerializer.
EncryptorProducerBehavior 700 Encrypts the message when encryption is enabled.
SequencerProducerBehavior 800 Uses the available implementations of ISequenceWriter (e.g. ChunkSequenceWriter) to set the proper headers and split the published message or messages set to create the sequences.
CustomHeadersMapperProducerBehavior 1000 Applies the custom header name mappings.

Custom Behaviors

It is possible to add custom behaviors to the pipeline to implement cross-cutting concerns, and add new features to Silverback.

A behavior is a class implementing the IProducerBehavior interface. The HandleAsync method is called for each message being produced, allowing the behavior to modify the message or perform additional operations.

The following basic example demonstrates how to set a custom message header on each outbound message.

public class CustomHeadersProducerBehavior : IProducerBehavior
{
    public int SortIndex => 1000;

    public async ValueTask HandleAsync(
        ProducerPipelineContext context,
        ProducerBehaviorHandler next,
        CancellationToken cancellationToken)
    {
        context.Envelope.Headers.Add("generated-by", "silverback");

        await next(context, cancellationToken);
    }
}

The custom behavior must be registered at startup using the AddSingletonBrokerBehavior, or AddTransientBrokerBehavior method. The transient behavior will be resolved once per producer, while the singleton behavior will be shared.

services
    .AddSilverback()
    ...
    .AddSingletonBrokerBehavior<CustomHeadersProducerBehavior>();

Additional services can be injected into the behavior constructor, or resolved via the ServiceProvider from the ProducerPipelineContext if a scoped instance is required.

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