Using std::sync::RwLock as state for from_fn_with_state ends up in a "trait not satisfied error"

[FelipeLema]

Summary

Not sure if a question or a bug, but using std::sync::RwLock as state for from_fn_with_state ends up in a "trait not satisfied error" that's real hard to decipher

here is a MWE to trigger the error. There's also a cargo build log and rustc --version log

Either not calling state.read() or using tokio::sync::RwLock will solve the issue

use axum::extract;
use axum::http::StatusCode;
use axum::middleware::{from_fn_with_state, Next};
use axum::response;
use axum::routing::method_routing::get;
use axum::Router;
use std::sync::Arc;
use std::sync::RwLock;
//use tokio::sync::RwLock; // change to «use tokio::sync::RwLock;» to fix

pub struct Storage {}

type StorageHandle = Arc<RwLock<Storage>>; // NOTE felo do we need RwLock for actual DB?

async fn get_something(
    extract::State(_s): extract::State<StorageHandle>,
) -> impl response::IntoResponse {
    StatusCode::OK
}
async fn my_layer(
    extract::State(s): extract::State<StorageHandle>,
    req: extract::Request,
    next: Next,
) -> Result<response::Response, StatusCode> {
    // ↓ removing this one line cleans up the error
    let _s_readonly = s.read().map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    Ok(next.run(req).await)
}

#[tokio::main]
async fn main() {
    let state = StorageHandle::new(RwLock::new(Storage {}));
    let app = Router::new()
        .route("/get_something", get(get_something))
        .layer(from_fn_with_state(state, my_layer));
}

axum version

v0.7.2

[davidpdrsn]

It's a bug in rust. It thinks the lock guard is held longer than it actually is. Adding an extra scope fixes it

async fn my_layer(
    extract::State(s): extract::State<StorageHandle>,
    req: extract::Request,
    next: Next,
) -> Result<response::Response, StatusCode> {
    // ↓ removing this one line cleans up the error
    {
        let _s_readonly = s.read().map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;
    }

    Ok(next.run(req).await)
}