header-mutation-between-retries.cs

using System;
using System.Threading.Tasks;
using NServiceBus;
using NServiceBus.Logging;
using NServiceBus.MessageMutator;

namespace RabbitMutatorTest
{
    class Program
    {
        static void Main(string[] args)
        {
            Start().GetAwaiter().GetResult();
        }
        static async Task Start()
        {
            LogManager.Use<DefaultFactory>().Level(LogLevel.Error);

            var config = new EndpointConfiguration("RabbitMutatorTest");
            config.UsePersistence<InMemoryPersistence>();
            config.SendFailedMessagesTo("error");
            config.EnableInstallers();
            config.RegisterMessageMutator(new Mutator());
            config.Recoverability().Delayed(d => d.NumberOfRetries(0));

            var transport = config.UseTransport<RabbitMQTransport>();
            transport.ConnectionString("host=localhost");
            transport.UseConventionalRoutingTopology();

            //config.UseTransport<LearningTransport>();

            var endpoint = await Endpoint.Start(config);

            Console.WriteLine("Press <enter> to send a message");
            while (true)
            {
                Console.ReadLine();
                await endpoint.SendLocal(new MutatorMessage());
            }
        }
    }

    class MutatorMessageHandler : IHandleMessages<MutatorMessage>
    {
        public Task Handle(MutatorMessage message, IMessageHandlerContext context)
        {
            var header = context.MessageHeaders["Test"];
            Console.WriteLine($"Test header value is: {header}");

            throw new Exception("Simulated");
        }
    }

    public class Mutator : IMutateIncomingTransportMessages
    {
        public Task MutateIncoming(MutateIncomingTransportMessageContext context)
        {
            var attempt = context.Headers.TryGetValue("Test", out string value) 
                ? int.Parse(value) 
                : 0;

            attempt++;
            context.Headers["Test"] = attempt.ToString();
            return Task.CompletedTask;
        }
    }

    class MutatorMessage : IMessage
    {

    }
}