main.rs

use axum::{
    async_trait,
    extract::{FromRequestParts, Request},
    http::{request::Parts, StatusCode},
    middleware::Next,
    routing::get,
    Router,
};

#[derive(Debug)]
struct Foo(i32);

fn new_foo() -> Foo {
    Foo(rand::random())
}

#[async_trait]
impl<S> FromRequestParts<S> for Foo
where
    S: Send + Sync,
{
    type Rejection = StatusCode;

    async fn from_request_parts(_: &mut Parts, _: &S) -> Result<Self, Self::Rejection> {
        println!("extractor run");
        Ok(new_foo())
    }
}

#[tokio::main]
async fn main() {
    // build our application with a single route
    let app = Router::new()
        .route(
            "/",
            get(|foo: Foo| async move {
                println!("hello from handler: {foo:?}");
                format!("Hello, {foo:?}!")
            }),
        )
        .layer(axum::middleware::from_fn(
            |foo: Foo, req: Request, next: Next| async move {
                println!("hello from layer: {foo:?}");
                next.run(req).await
            },
        ));

    // run our app with hyper, listening globally on port 3000
    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
    axum::serve(listener, app).await.unwrap();
}