I am trying to build a Tokio+Hyper Web server in rust and I am struggling to juggle the requirements of those async/multithread systems.

here are the dependencies of the program:

[dependencies]
hyper = { version = "1", features = ["full"] }
tokio = { version = "1", features = ["full"] }
http-body-util = "0.1"
hyper-util = { version = "0.1", features = ["full"] }

and here is the program:

use std::convert::Infallible;
use std::net::SocketAddr;

use http_body_util::Full;
use hyper::body::Bytes;
use hyper::server::conn::http1;
use hyper::service::service_fn;
use hyper::{Request, Response};
use hyper_util::rt::TokioIo;
use tokio::net::TcpListener;

use std::future::Future;
#[derive(Debug,Clone)]
struct TestStruct {
    a : i32,
}

async fn query_dispatcher_test(_req: Request<hyper::body::Incoming>, _pool : &TestStruct) -> Result<Response<Full<Bytes>>, Infallible>
{
    Ok(Response::new(Full::new(Bytes::from("default API"))))
}

async fn build_service<F, S>(pool : &TestStruct, listener : &TcpListener, f: F)
where
    F: 'static + Fn(Request<hyper::body::Incoming>, &TestStruct) -> S,
    F: Sync + Send + Copy,
    S: Future<Output = Result<Response<Full<Bytes>>, Infallible>> + Send 
{
    let (stream, _) = listener.accept().await.unwrap();
    // Use an adapter to access something implementing `tokio::io` traits as if they implement
    // `hyper::rt` IO traits.
    let io: TokioIo<_> = TokioIo::new(stream);
    let pool_clone = pool.clone();
    let service = service_fn(move |_req : Request<hyper::body::Incoming>| {
        let inner = pool_clone.clone();
        async move {
            f(_req, &inner).await
        }
    });

    // Spawn a tokio task to serve multiple connections concurrently
    tokio::task::spawn(async move {
        // Finally, we bind the incoming connection to our service
        if let Err(err) = http1::Builder::new()
            .serve_connection(io, service)
            .await
        {
            eprintln!("Error serving connection: {:?}", err);
        }
    });
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));

    let listener = TcpListener::bind(addr).await?;
    let pool = TestStruct{
        a : 1,
    };
    // We start a loop to continuously accept incoming connections
    loop {

        build_service(&pool, &listener,query_dispatcher_test);   

    }
}

Here is the error:

error[E0308]: mismatched types
   --> src/main.rs:64:9
    |
64  |         build_service(&pool, &listener,query_dispatcher_test);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
    = note: expected opaque type `impl for<'a> Future<Output = Result<Response<http_body_util::Full<hyper::body::Bytes>>, Infallible>>`
               found opaque type `impl Future<Output = Result<Response<http_body_util::Full<hyper::body::Bytes>>, Infallible>>`
    = help: consider `await`ing on both `Future`s
    = note: distinct uses of `impl Trait` result in different opaque types
note: the lifetime requirement is introduced here
   --> src/main.rs:25:69
    |
25  |     F: 'static + Fn(Request<hyper::body::Incoming>, &TestStruct) -> S,
    |                                                                     ^

Here is where I am struggling: I know that the problem is the pool reference in the f function. If I remove it the program compiles.
Another weird thing is that if I move the content of build_service inside the loop {} in main, and replace f with query_dispatcher_test and remove my call to build_service the program compiles fine.

So I know that the problem is related to the lifetime of my pool in the f function. but because it is moved and cloned, it will live as long as closure provided to service_fn. I don’t understand what lifetime information the compiler needs.

When it comes to the lifetime information I provide to the function it is related to what Tokyo requires for tokio::task::spawn