fix(actix): process request in other middleware using correct Hub

[lcian]

Extensions are a feature of Actix-web to pass request-local data.
With this change, we pass the Hub that we create with each Actix request in the extensions, so that other middleware can access it and use it to capture events within the correct hub.

Closes #624

[Swatinem]

Suggested change

	//! .get::<Arc<Hub>>()
	//! .unwrap_or(&Hub::current()) // should never happen
	//! .clone();
	//! .get::<Arc<Hub>>()
	//! .cloned()
	//! .unwrap_or(Hub::current()); // should never happen

If this is just the same as Hub::current(), I wonder what purpose this serves?

[lcian]

Are you referring to the clone or what?

[lcian]

I've updated it to just use unwrap, if we apply our middleware first it's guaranteed to be there anyways.

[Swatinem]

I mean what is the purpose of storing this in the request extensions at all, if its the same value as is available from Hub::current()?

[lcian]

Yeah that was misleading, it was just for the sake of not unwrapping.
The whole reason this PR exists is because Hub::current() and the hub stored in the extension are different.

To explain better why we need to pass the per-request hub in the extensions:
when we do svc.call here

sentry-rust/sentry-actix/src/lib.rs

Line 403 in a6f1db2

let fut = svc.call(req).bind_hub(hub.clone());

it first processes the request through all middleware, and then returns us a future that refers only to the response half of the processing (i.e. handler execution + middleware processing of the response).
So, during request processing, we need to use extensions to pass the correct hub to the subsequent middleware.

Let me know if you see a better solution that I might have missed.

[Swatinem]

oh, so the svc.call part does not run in the current hub?
well in that case, we have to activate the hub within the function that calls svc.call, as well as binding it to the future like we do right now.

[lcian]

Oh I see. Fixed it now:

sentry-rust/sentry-actix/src/lib.rs

Line 341 in ae8c91d

let fut = Hub::run(hub.clone(), || svc.call(req)).bind_hub(hub.clone());

Thanks, that's much better! Obviously it doesn't require using the extensions.