How to know which queue a message is received on?

[jorgenbosman]

In my program, I register multiple queues using services.AddRebus(... ,key="<name>"). They all use the same message handler.
In my message handler, I need to know on which queue the message was received, so I would like know the "key" of that rebus queue. Is that possible somehow?

[mookid8000]

Unfortunately no – at least not at the moment.

Being able to host multiple Rebus instances in the same container instance is a fairly new thing, so it has never really been relevant to provide this information anywhere, but I can definitely see how it could be useful in some cases.

To fix your issue right away, you can extend your Rebus instances with a small plugin that makes the queue name available. It can be done like this – first, create a nice extension method that adds the queue name to the incoming step context in the form of an InputQueueName object:

public static class NiftyRebusConfigurationExtensions
{
    public static void AddInputQueueNameToStepContext(this OptionsConfigurer configurer)
    {
        configurer.Decorate<IPipeline>(c =>
        {
            var pipeline = c.Get<IPipeline>();
            var inputQueueName = c.Get<ITransport>().Address;
            var step = new AddInputQueueNameToPipelineStep(new(inputQueueName));

            return new PipelineStepInjector(pipeline)
                .OnReceive(step, PipelineRelativePosition.After, typeof(DefaultRetryStep));
        });
    }

    [StepDocumentation("Adds the bus' own input queue name to the incoming step context in the form of an InputQueueName object containing the queue name.")]
    class AddInputQueueNameToPipelineStep : IIncomingStep
    {
        readonly InputQueueName _inputQueueName;

        public AddInputQueueNameToPipelineStep(InputQueueName inputQueueName) => _inputQueueName = inputQueueName;

        public async Task Process(IncomingStepContext context, Func<Task> next)
        {
            context.Save(_inputQueueName);

            await next();
        }
    }
}

and then be sure to enable it on your Rebus instances:

services.AddRebus(
	configure => configure
		.(...)
		.Options(o => o.AddInputQueueNameToStepContext())
);

With that done, you can retrieve the input queue name via IMessageContext by having it injected and retrieving it from the incoming step context:

public class MyMessageHandler : IHandleMessages<MyMessage>
{
	readonly IMessageContext _messageContext;

	public MyMessageHandler(IMessageContext messageContext) => _messageContext = messageContext;

	public async Task Handle(MyMessage message) 
	{
		var incomingStepContext = _messageContext.IncomingStepContext;
		var queueName = incomingStepContext.Load<InputQueueName>()?.QueueName 
						?? throw new ApplicationException("Did not find the expected queue name object in the step context");

	}
}

You can see a working (but slightly different) example here: https://github.com/rebus-org/Rebus/blob/master/Rebus.Tests/Examples/AddInputQueueNameToIncomingStepContext.cs