Trying to serve static files and custom endpoints and lifetime error

[modern olive]

Hello folks, I'm trying to find a way to solve my issue, I tried with routing but it's inconsistent, and I'm now trying with middlewares but I'm ending up in types hell...

Basically, I'm trying to have 2 scopes: "/api" for manually configured routes on the rust side, and "/*" fallback to frontend files embedded in the binary with the static_files crate and its generated functions crate::generate(). I am flexible in my structure so I could change dependencies etc if necessary, but I lack a lot of knowledge on the Actix side to know how to do it "the quick way".
For the middleware part, I tried using wrap_fn or copy/pasting&adapting the middleware examples on Actix web docs, but failed for type hell again.

Basically, this is what I'd like to do (of course it doesn't work like that, but still):

App::new()
// ... .app_data() calls
.wrap_fn(|req: ServiceRequest, srv /* : &AppRouting */ | async {
    let path = req.path().to_string();
    let asset: Option<HttpResponse> = http::admin::frontend_assets(path.clone()); // That's my code, the one that checks whether the resource exists, and if it does, we get the associated HTTP response with proper Content-Type

    if asset.is_some() {
        println!("response: asset exists");
        let r: ServiceResponse = req.into_response(asset.unwrap());
        return Ok(r);
    }

    println!("response: asset does not exist");
    let r: ServiceResponse = srv.call(req).await.unwrap();
    Ok(r)
})
// API routes

With the Rust-complex-typing-system newbie I am, compiling this code triggers a lifetime error that I have ever seen and I don't understand

error: lifetime may not live long enough
   --> src\serve\mod.rs:95:70
    |
95  |               .wrap_fn(|req: ServiceRequest, srv /* : &AppRouting */ | async {
    |  ____________________________________________---_____________________-_^
    | |                                            |                       |
    | |                                            |                       return type of closure `[async block@src\serve\mod.rs:95:70: 108:14]` contains a lifetime `'2`
    | |                                            has type `&'1 actix_web::app_service::AppRouting`
96  | |                 let path = req.path().to_string();
97  | |                 let asset: Option<HttpResponse> = http::admin::frontend_assets(path.clone()); 
98  | |
...   |
107 | |                 Ok(r)
108 | |             })
    | |_____________^ returning this value requires that `'1` must outlive `'2`

Screenshot of the error for visual readability:

Trying to serve static files and custom endpoints and lifetime error

Okay, solved! ✅

I just tried some code based on the HTTP-to-HTTPS example on the repository (here: https://github.com/actix/examples/blob/master/middleware/middleware-http-to-https/src/main.rs#L51-L60 )

Doing exactly the same thing but returning a response coming from my own code:

.wrap_fn(|sreq, srv | {
    let path = sreq.path().to_string();
    let asset: Option<HttpResponse> = http::admin::frontend_assets(path.clone());

    if asset.is_none() {
        println!("response: asset does not exist");
        Either::Left(srv.call(sreq).map(|res| res))
    } else {
        println!("response: asset exists");
        let res: HttpResponse = asset.unwrap();
        return Either::Right(future::ready(Ok(sreq.into_response(res))));
    }
})

Be super careful with your IDE importing Either: it must come from the futures_util::future::Either and not actix_web::Either, else it won't work