How do I use Rc inside middleware?

[squeaktoy]

Summary

Hey fellow axumates. I'm working on a project at https://git.sr.ht/~latex/streamlist
The xrust library uses Rc for its RNode object that I'm trying to use in a middleware.
This is not allowed because middlewares are Send.
Do any of you know any ideas how I can work around this issue?
Here are some ideas I and fellow Rustaceans at ##rust on libera.chat came up with:

1. Make xrust thread-safe. I opened a bug report for xrust Using RNode in async code doesn't work because of Rc ballsteve/xrust#123
2. Spawn a new thread that handles all interactions with xrust
3. Somehow make the middleware not Send, e.g. by using Tokio in non-work-stealing mode.

Preferably I don't want to use yet another thread just for xrust. Is it even possible to make the middleware non-Send? Does axum even support that or not? What about actix-web?

axum version

0.7.7

[jplatte]

Using a non-Send type inside of an async fn does not automatically make its future type non-Send. That only happens when you declare a binding of such a type before the last .await point (roughly speaking).

If you don't need to hold the RNode across a .await point, the best solution is probably to move all the xrust logic into a regular fn that is called by your async fn. I took a brief look at your code and think this should work there.

[squeaktoy]

So I think I might have fixed the Rc thingy. But using the request inside the middleware is still a mystery for me, but I opened a new discussion for that: #3022