External creation of ILifetimeScope

[srogovtsev]

I have a particular configuration (i.e., hosting OWIN in plain vanilla asp.net application in IIS) that requires me to "inject" ILifetimeScope from outside OWIN middleware instead of creating it inside. So what I want to have is:

1. asp.net's Application_BeginRequest creates a per-request lifetime scope and saves it to HttpRequest properties
2. OWIN injector middleware, instead of creating its own lifetime scope, calls external "factory", which simply extracts lifetime scope from HttpRequest properties
3. further OWIN pipeline proceeds as before
4. because lifetime scope was created externally, OWIN injector middleware does not dispose it
5. asp.net's Application_EndRequest gets lifetime scope from HttpRequest properties and disposes it

Is this a feasible approach? I can provide a create a pull-request for this quite quickly and I don't think this would be a breaking change.

[tillig]

Why not just insert your own middleware that creates the lifetime scope into the pipeline before the Autofac middleware runs? OWIN won't create a lifetime scope if it's already present.

You could basically copy/paste the AutofacMiddleware class, have it call your factory, and then add it to the pipeline prior to the AutofacMiddleware itself being added.

[srogovtsev]

Constants.OwinLifetimeScopeKey is internal, so I can't inject the scope myself (same with InjectorRegisteredKey).

(yes, actually the minimal change that allows me to fix the problem is to simply make them public)

[tillig]

What if we added context.SetAutofacLifetimeScope(ILifetimeScope scope)?

[srogovtsev]

This would be nice! But UseMiddlewareFromContainer checks for injector registration, so you'd have to provide something like app.MarkInjectorAsRegistered as well - which is not a problem by me, of course.

So the whole startup would look like this:

app
   .Use((ctx, next) =>
   {
      ctx.SetAutofacLifetimeScope(myScopeGetter());
      return next();
   }
   .MarkInjectorRegistered()
   .UseMiddlewareFromContainer<MyMiddleware>();

[tillig]

Couldn't we just add a null check here? Like, if lifetime scope isn't already set, create it; otherwise just don't do anything.

[tillig]

Also, when did you want to dispose of the scope? If you set your own scope, would that mean you're responsible for disposing it? (I'm guessing so.) In that case, it'd be like "if the scope is set, just await next() otherwise do the using/create lifetime scope thing."

[srogovtsev]

Yes, I want to be responsible for scope disposal. So, you mean the startup would look like

app
   .Use((ctx, next) =>
   {
      ctx.SetAutofacLifetimeScope(myScopeGetter());
      return next();
   }
   .UseAutofacLifetimeScopeInjector(rootContainer)
   .UseMiddlewareFromContainer<MyMiddleware>();

...and UseAutofacLifetimeScopeInjector (RegisterAutofacLifetimeScopeInjector, in fact) will check whether the scope exists, and if it does, will simply call next() instead of creating/disposing its own scope?

Totally fine by me.

[srogovtsev]

Should I draft up a pull-request for this?

[tillig]

Sure, that'd rock.