change activator injection to allow outside dependency replacement

[marmagni]

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Rebus is MIT-licensed. The code submitted in this pull request needs to carry the MIT license too. By leaving this text in, I hereby acknowledge that the code submitted in the pull request has the MIT license and can be merged with the Rebus codebase.

[mookid8000]

Hi @marmagni , your PR looks fine 🙂

What problem does it solve?

[marmagni]

Hi @mookid8000,

Tks feedback, this change can help outside injection replacement to allow custom implementation of IHandlerActivator. This would be useful when we need to change some injection values by transaction, like below example:

1. Configuration:

   
   //Configure Rebus
   services.AddRebus((configure, provider) => ...);

//Replace default handle activator to my custom services.AddSingleton<IHandlerActivator, MyCustomHandlerActivator>();

2. Useful Example:

public class MyCustomHandlerActivator : DependencyInjectionHandlerActivator, IHandlerActivator { //ctor...

public new Task<IEnumerable<IHandleMessages<TMessage>>> GetHandlers<TMessage>(TMessage message, ITransactionContext transactionContext)
{
    //Re-use base implementation
    var handlers = base.GetHandlers(message, transactionContext);

    //Is this better way to get context?
    var stepContext = transactionContext.GetOrNull<IncomingStepContext>(StepContext.StepContextKey);
    var provider = stepContext.Load<IServiceScope>().ServiceProvider;

    //This will change the cross cutting user accesor by transaction
    var userAccessor = provider.GetService<IUserAccessor>();

    var msgHeaders = MessageContext.Current.Headers;
    msgHeaders.TryGetValue("user_id", out userId);

    userAccessor.User = new User(userId);

    return handlers;
}

}

[skwasjer]

@mookid8000 this would solve a (different) use case we have too, when can we have this? ;)

[mookid8000]

Thanks for your PR! 🙂 I've released it as Rebus.ServiceProvider 6.1.0

Sorry for taking so long to process this 😐

[mookid8000]

FYI I've already released Rebus.ServiceProvider 6.2.0 - it has additional targets so it can work with .NET 5