Adding values to header in MassTransit.RabbitMq

If you need to add headers when a message is being sent, you can add middleware components to either the Send or the Publish pipeline as shown below. Note that Send filters will apply to all messages, whereas Publish filters will only apply to messages which are published.

// execute a synchronous delegate on send
cfg.ConfigureSend(x => x.Execute(context => {}));

// execute a synchronous delegate on publish
cfg.ConfigurePublish(x => x.Execute(context => {}));

The middleware can be configured on either the bus or individual receive endpoints, and those configurations are local to where it's configured.

You can also add headers in the consumer class:

public async Task Consume(ConsumeContext<MyMessage> context)
{
    ....
    await context.Publish<MyEvent>(new { Data = data }, c => AddHeaders(c));
}

public static void AddHeaders(PublishContext context)
{
    context.Headers.Set("CausationId", context.MessageId);
}