Support NACK on exceptions

It’s crucial to me to nack a message if I didn’t handle it. Currently if my application crashes the message just dissapears. I have read the documentation that says

If your subscription callback throws an exception, EasyNetQ will take the message that was being consumed and wrap it in a special error message. The error message will be published to the EasyNetQ error queue (named EasyNetQ_Default_Error_Queue). You should monitor the error queue for any messages. The error message includes all the information necessary to re-publish the original message as well as the exception’s type, message and stack trace. You can use the EasyNetQ.Hosepipe utility to re-publish error messages. See the section on EasyNetQ.Hosepipe below.

But shouldn’t it be default? It’s suprising to me that I have to create yet another queue and republish messages manually when it’s simply shouldn’t be ack’ed.

My problem is that I must preserve messages order. If some message throws an exception then the whole queue should wait until this message gets processed. But it’s not possible if exception just makes this message to go into another queue.

[Pzixel]

Sorry for late response, I have suddenly been burrowed under tons of others tasks.

I have been tested following code:

using System;
using System.Threading.Tasks;
using EasyNetQ;
using EasyNetQ.Consumer;
using static System.Console;

namespace Console
{
    public static class Program
    {
        public static void Main()
        {
            Task.Run(async () =>
            {
                using (var bus = RabbitHutch
                                 .CreateBus(
                                     "host=myhost:5672;username=reader;password=mypass;requestedHeartbeat=20;prefetchcount=20;timeout=1000;publisherConfirms=true",
                                     x => x.Register<IConsumerErrorStrategy>(_ => new AlwaysRequeueErrorStrategy())
                                 ).Advanced)
                {
                    using (var _ = await ConsumeBus(bus, "blockchain", async () =>
                    {
                        WriteLine("Got new message");
                        throw new Exception();
                    }))
                    {
                        WriteLine("Listening for messages. Hit <return> to quit.");

                        ReadKey();
                    }
                }
            }).Wait();
        }

        private static async Task<IDisposable> ConsumeBus(IAdvancedBus bus, string queueName,
                                                          Func<Task> messageConsumptionTask)
        {
            var queue = await bus.QueueDeclareAsync(queueName, true).ConfigureAwait(false);
            return bus.Consume(queue,
                               (body, properties, info) =>
                                   messageConsumptionTask());
        }
    }

    public sealed class AlwaysRequeueErrorStrategy : IConsumerErrorStrategy
    {
        public void Dispose()
        {
        }

        public AckStrategy HandleConsumerError(ConsumerExecutionContext context, Exception exception)
        {
            return AckStrategies.NackWithRequeue;
        }

        public AckStrategy HandleConsumerCancelled(ConsumerExecutionContext context)
        {
            return AckStrategies.NackWithRequeue;
        }
    }
}

And it worked as expected.

Thank you, it really solves the problem. All bad messages stays in the queue and are requested a bit later

[Pzixel]

And still it works as expected. What versions of EasyNetQ and RabbitMQ are you using?

3.0.0 and 3.7.5 respectively.

Well, it’s a friday, and I have to go. Let’s continue our great talk at monday. I wish you a happy weekend.