How to change EntityNameAttribute to custom NameAttribute in Masstransit (RabbitMq)

Question

in my Applications I use different Interfaces to handle Messages. To avoid multiple Implementations and to reduce the maintenance of the same DTO, I want to use a Custom Attribute to handle the Exchange name of the Masstransit part. Also I want to reduce the dependencies to Masstransit in these common software parts.

So my Question is " How to change the EntityNameAttribute to a custom NameAttribute in Masstransit. (RabbitMq Version 7.3.1) "

I Have tried to Overwrite the EntityNameFormatter for the MessageTopology.

cfg.MessageTopology.SetEntityNameFormatter(new CustomExchangeNameFormatter(cfg.MessageTopology.EntityNameFormatter));  

If the Application publish a Message an error occurs.

_asyncApi.PublishMessage<CustomMessage>(new CustomMessage(){Content = "TestMessage"});

... RabbitMQ.Client.Exceptions.OperationInterruptedException: The AMQP operation was interrupted: AMQP close-reason, initiated by Peer, code=403, text='ACCESS_REFUSED - operation not permitted on the default exchange', classId=40, methodId=10 ...

public class CustomExchangeNameFormatter: IEntityNameFormatter
{
    private IEntityNameFormatter _original;

    public CustomExchangeNameFormatter(IEntityNameFormatter original)
    {
        _original = original;
    }

    //Used to rename the exchanges
    public string FormatEntityName<T>()
    {
        string entityName;

        var exchangeNameAttribute = typeof(T).GetCustomAttribute<ExchangeNameAttribute>();
        if (exchangeNameAttribute != null)
        {
            entityName = exchangeNameAttribute.ExchangName;
        }
        else
        {
            entityName = _original.FormatEntityName<T>();
        }

        return entityName;
    }
}

Answer 1

Hi fixed the Problem by moving the SetEntityNameFormatter method call under the line cfg.SetMessageSerializer(.. and cfg.AddMessageDeserializer(... I don't know why, but if the method is called before these two lines it throws the described error.

   public static IServiceCollection AddRabbitMqApi(this IServiceCollection services, IConfiguration configuration)
    {
        return services.AddMassTransit(busCfg =>
            {
                busCfg.UsingRabbitMq((ctx, cfg) =>
                {
                    cfg.Host(...); 

                    //Setup the NamespaceSpecificStrings
                    var (nssMappingForSerialization, nssMappingForDeserialization) = GetNssMappings(assemblies);

                    //serialization and deserialization
                    cfg.SetMessageSerializer(() => new CustomJsonMessageSerializer(nssMappingForSerialization));
                    cfg.AddMessageDeserializer(CustomJsonMessageSerializer.JsonContentType, () => new CustomJsonMessageDeserializer(CustomJsonMessageSerializer.Deserializer, nssMappingForDeserialization));

                    //entity name formatter
                    cfg.MessageTopology.SetEntityNameFormatter(new CustomExchangeNameFormatter(cfg.MessageTopology.EntityNameFormatter));

                    cfg.ConfigureJsonSerializer(settings =>
                    {
                        settings.DefaultValueHandling = DefaultValueHandling.Include;
                        return settings;
                    });
                    
                    cfg.Publish<CustomMessage>(x => { x.ExchangeType = ExchangeType.Topic; });
                });
            })
            .AddMassTransitHostedService();
    }