No working way for UseCase Aspire+MassTransit+RabbitMq+MessagePackSerializer

[migoldfinger]

Describe the bug

Hi,
I am in dire need of a working example of how to get the Weather Forecast template running with MassTransit.
I got it to work without MassTransit already, so the Messages are working fine.
I hit dead ends all the time. I think I have found a way for the Consumer side but the website gives me a headache.
I use the Packages

    <PackageReference Include="CommunityToolkit.Aspire.MassTransit.RabbitMQ" Version="9.4.0" />
    <PackageReference Include="MassTransit.MessagePack" Version="8.4.0" />
    <PackageReference Include="MessagePack" Version="3.1.3" />

I have defined 2 Messages WeatherRequestMessage and WeatherResponseMessage.
My Problem on the Webapplication
I want to use a specific Exchange and RoutingKey when I send the RequestMessage
This code should be enough if the rest is configured correctly

namespace My.Web;

using MassTransit;
using Messages.Weather;

public sealed class WeatherApiClient(ILogger<WeatherApiClient> logger, IRequestClient<WeatherRequestMessage> requestClient)
{
	public async Task<WeatherResponse[]> GetWeatherAsync(int maxItems = 10, CancellationToken cancellationToken = default)
	{
		Response<WeatherResponseMessage> response = await requestClient.GetResponse<WeatherResponseMessage>(new WeatherRequestMessage(), cancellationToken).ConfigureAwait(false);
		logger.LogInformation("Published message to requestClient");

		return response.Message.WeatherForecastArray;
	}
}
}

in Program.cs i tried something like this but that gives me errors

builder.AddMassTransitRabbitMq("MessageBus",
                               static settings => { settings.DisableTelemetry = false; },
                               static config =>
                               {
	                               config.UsingRabbitMq(static (context, cfg) =>
	                                                    {
		                                                    var configuration = context.GetRequiredService<IConfiguration>();
		                                                    string? host = configuration["RabbitMQ:Host"];
		                                                    cfg.Host(host);
		                                                    cfg.UseMessagePackSerializer();
		                                                    cfg.AddPublishMessageTypes([typeof(WeatherRequestMessage)],
		                                                                               (configurator, type) =>
		                                                                               {
			                                                                               configurator
				                                                                               .BindQueue(configuration["RabbitMQ:RequestExchange"]!,
					                                                                               configuration["RabbitMQ:RequestRoutingKey"]);
		                                                                               });
	                                                    });
                               });

Regression

No response

Steps to reproduce

All examples found that uses Aspire+MassTransit do not even mention the builder.AddMassTransitRabbitMq extension.

Expected behavior

A working example for this common use case.

Screenshots

No response

IDE and version

VS 2022

IDE version

No response

Nuget packages

<PackageReference Include="CommunityToolkit.Aspire.MassTransit.RabbitMQ" Version="9.4.0" />
  <PackageReference Include="MassTransit.MessagePack" Version="8.4.0" />
  <PackageReference Include="MessagePack" Version="3.1.3" />

Additional context

No response

Help us help you

No, just wanted to report this

[migoldfinger]

Partial success I was able to register MassTransitSerializer, I just had to write an own custom extension

public static class CustomExtensions
{
	public static void AddMassTransitRabbitMq(this IHostApplicationBuilder builder,
		string name,
		Action<MassTransitRabbitMqSettings>? configureOptions = null,
		Action<IBusRegistrationConfigurator>? massTransitConfiguration = null,
		Action<IRabbitMqBusFactoryConfigurator>? rabbitMqConfiguration = null
	)
	{
		AddMassTransitRabbitMq<IBus>(builder, name, configureOptions, massTransitConfiguration, rabbitMqConfiguration);
	}

	public static void AddMassTransitRabbitMq<TBus>(this IHostApplicationBuilder builder,
		string name,
		Action<MassTransitRabbitMqSettings>? configureOptions = null,
		Action<IBusRegistrationConfigurator>? massTransitConfiguration = null,
		Action<IRabbitMqBusFactoryConfigurator>? rabbitMqConfiguration = null
	)
		where TBus : class, IBus
	{
		ArgumentNullException.ThrowIfNull(builder);
		ArgumentNullException.ThrowIfNull(name);
		ArgumentException.ThrowIfNullOrWhiteSpace(name);

		var options = new MassTransitRabbitMqSettings();
		configureOptions?.Invoke(options);
		string? rabbitMqConnectionString = builder.Configuration["ConnectionStrings:" + name];

		if (string.IsNullOrWhiteSpace(rabbitMqConnectionString))
		{
			throw new InvalidOperationException("RabbitMQ connection string is missing or empty in configuration.");
		}

		GlobalTopology.Send.UseRoutingKeyFormatter<WeatherRequestMessage>(static x => string.Empty);
		GlobalTopology.Send.TryAddConvention(new RoutingKeySendTopologyConvention());

		builder.Services.AddMassTransit<TBus>(x =>
		                                      {
			                                      x.SetKebabCaseEndpointNameFormatter();
			                                      x.SetInMemorySagaRepositoryProvider();
			                                      var entryAssembly = Assembly.GetEntryAssembly();
			                                      x.AddSagaStateMachines(entryAssembly);
			                                      x.AddSagas(entryAssembly);
			                                      x.AddActivities(entryAssembly);

			                                      massTransitConfiguration?.Invoke(x);

			                                      x.UsingRabbitMq((context, cfg) =>
			                                                      {
				                                                      cfg.Host(new Uri(rabbitMqConnectionString));
				                                                      cfg.ConfigureEndpoints(context);
				                                                      rabbitMqConfiguration?.Invoke(cfg);
			                                                      });
		                                      });

		if (!options.DisableTelemetry)
		{
			builder.Services
			       .AddOpenTelemetry()
			       .WithMetrics(static b => b.AddMeter(DiagnosticHeaders.DefaultListenerName))
			       .WithTracing(static providerBuilder => { providerBuilder.AddSource(DiagnosticHeaders.DefaultListenerName); });
		}
	}
}

I then could call in Program.cs

builder.AddMassTransitRabbitMq("MessageBus",
                                massTransitConfiguration: static configurator =>
                                                          {
configurator.AddRequestClient<WeatherRequestMessage>();
                                                          },
                                rabbitMqConfiguration: static configurator =>
                                                       {
	                                                       configurator.UseMessagePackSerializer();
                                                       });

After that, MessagePack was used. I still struggle to find a way to use existing Exchanges and Queues.

[aaronpowell]

I've converted this to a discussion as it's not a bug but more a request for how to use the libraries.

[migoldfinger]

I see your point. But right now it looks like it's a missing feature instead of a how to use problem.