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AddMessageHandlerFallback.cs
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AddMessageHandlerFallback.cs
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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using NUnit.Framework;
using Rebus.Activation;
using Rebus.Bus;
using Rebus.Config;
using Rebus.Handlers;
using Rebus.Retry.Simple;
using Rebus.Tests.Contracts;
using Rebus.Tests.Contracts.Extensions;
using Rebus.Transport;
using Rebus.Transport.InMem;
// ReSharper disable ClassNeverInstantiated.Local
#pragma warning disable CS1998
namespace Rebus.ServiceProvider.Tests.Examples;
[TestFixture]
public class AddMessageHandlerFallback : FixtureBase
{
[Test]
public async Task ItWorks()
{
var events = new ConcurrentQueue<string>();
var services = new ServiceCollection();
services.AddSingleton(events);
services.AddRebus(
configure => configure
.Transport(t => t.UseInMemoryTransport(new(), "whatever"))
.Options(o =>
{
o.RetryStrategy(secondLevelRetriesEnabled: true);
o.MarkAsFallbackHandler<FallbackFailedMessageHandler>();
})
);
services.AddRebusHandler<SomeMessageHandler>();
services.AddRebusHandler<AnotherMessageHandler>();
services.AddRebusHandler<FailedAnotherMessageHandler>();
services.AddRebusHandler<FallbackFailedMessageHandler>();
await using var provider = services.BuildServiceProvider();
provider.StartRebus();
var bus = provider.GetRequiredService<IBus>();
await bus.SendLocal(new SomeMessage());
await bus.SendLocal(new AnotherMessage());
await events.WaitUntil(q => q.Count >= 2);
// additional time to let additional stuff happen
await Task.Delay(TimeSpan.FromSeconds(0.2));
Assert.That(events, Is.EqualTo(new[]
{
"SomeMessage dispatched to FALLBACK message handler",
"AnotherMessage dispatched to failed AnotherMessage message handler"
}));
}
record SomeMessage;
record AnotherMessage;
class SomeMessageHandler : IHandleMessages<SomeMessage>
{
public Task Handle(SomeMessage message) => throw new AccessViolationException("sorry man");
}
class AnotherMessageHandler : IHandleMessages<AnotherMessage>
{
public Task Handle(AnotherMessage message) => throw new AccessViolationException("sorry man");
}
class FailedAnotherMessageHandler : IHandleMessages<IFailed<AnotherMessage>>
{
readonly ConcurrentQueue<string> _events;
public FailedAnotherMessageHandler(ConcurrentQueue<string> events) => _events = events;
public async Task Handle(IFailed<AnotherMessage> message) => _events.Enqueue("AnotherMessage dispatched to failed AnotherMessage message handler");
}
class FallbackFailedMessageHandler : IHandleMessages<IFailed<object>>
{
readonly ConcurrentQueue<string> _events;
public FallbackFailedMessageHandler(ConcurrentQueue<string> events) => _events = events;
public async Task Handle(IFailed<object> message) => _events.Enqueue($"{message.Message.GetType().Name} dispatched to FALLBACK message handler");
}
}
static class FallbackMessageHandlerExtensions
{
/// <summary>
/// Marks handlers of type <typeparamref name="THandler"/> as a "fallback handler", which means that it will
/// only be used in cases where there are no other handlers.
/// </summary>
public static void MarkAsFallbackHandler<THandler>(this OptionsConfigurer configurer) where THandler : IHandleMessages
{
if (configurer == null) throw new ArgumentNullException(nameof(configurer));
configurer.Decorate<IHandlerActivator>(c => new HandlerInvokerRemover<THandler>(c.Get<IHandlerActivator>()));
}
class HandlerInvokerRemover<THandlerType> : IHandlerActivator
{
readonly IHandlerActivator _handlerActivator;
public HandlerInvokerRemover(IHandlerActivator handlerActivator)
{
_handlerActivator = handlerActivator ?? throw new ArgumentNullException(nameof(handlerActivator));
}
public async Task<IEnumerable<IHandleMessages<TMessage>>> GetHandlers<TMessage>(TMessage message, ITransactionContext transactionContext)
{
var handlers = await _handlerActivator.GetHandlers(message, transactionContext);
var handlersList = handlers.ToList();
// if there's more than one handler, there's potential for having included the
// fallback handler without having the need for a fallback
if (handlersList.Count > 1)
{
handlersList.RemoveAll(h => h is THandlerType);
}
return handlersList;
}
}
}