cannot call async method in route

[thinkingInWorldByNull]

Bug Report

Version

v0.5.1

Platform

Darwin 16-MacBookPro 21.4.0 Darwin Kernel Version 21.4.0: Fri Mar 18 00:46:32 PDT 2022; root:xnu-8020.101.4~15/RELEASE_ARM64_T6000 arm64

Description

Cannot call async method in handle. code example as follow.

1. compiler error when call async_method in get_image_byte
2. it's ok for block_method in get_image_byte

#[derive(Serialize, Deserialize, Debug)]
struct Param{
    spec:String,
    origin_url: String,
}

type Cache = Arc<Mutex<LruCache<u64, Bytes>>>;

#[tokio::main]
async fn main() {
    tracing_subscriber::fmt::init();
    let cache:Cache = Arc::new(Mutex::new(LruCache::new(1024)));
    let app = Router::new()
        .route("/image/:spec/:origin_url", get(handler))
        .layer(ServiceBuilder::new().layer(AddExtensionLayer::new(cache)));

    let addr = SocketAddr::from(([127, 0, 0, 1], 13000));
    tracing::debug!("listening on {}", addr);
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
    info!("start ok listener on 13000");
}


async fn handler(Path(Param{spec, origin_url}):Path<Param>, Extension(cache):Extension<Cache>) -> Result<Bytes, StatusCode>{
    let image_bytes = get_image_byte(origin_url.borrow(), cache).await
        .map_err(|_|StatusCode::BAD_REQUEST)?;

    Err(StatusCode::NOT_FOUND)
}

#[instrument(level = "info", skip(cache))]
async fn get_image_byte(origin_url:&str, cache: Cache) -> Result<Bytes> {
    let mut hasher = DefaultHasher::new();
    hasher.write(origin_url.as_bytes());
    let url_hash = hasher.finish();
    let g = &mut cache.lock().unwrap();

    let data = match g.get(&url_hash) {
        Some(v) => {
            info!("get from cache{}", url_hash);
            v.to_owned()
        }
        None => {
            info!("fetch image it");
            //❓open this will case " the trait `Handler<_, _>` is not implemented for ..."
            async_method().await?

            //❗️but block method is ok
            // block_method()?
        }
    };

    Ok(data)
}


fn block_method() -> Result<Bytes>{
    Ok(Bytes::from("123"))
}

async fn async_method() -> Result<Bytes>{
    Ok(Bytes::from("123"))
}

[davidpdrsn]

What is the compile error 👀 ?

If its something with Handler not being implemented have a look at https://docs.rs/axum/latest/axum/handler/index.html#debugging-handler-type-errors

[thinkingInWorldByNull]

Thanks,

the compiler error tip as follow

error[E0277]: the trait bound `fn(axum::extract::Path<Param>, Extension<Arc<std::sync::Mutex<LruCache<u64, axum::body::Bytes>>>>) -> impl Future {handler}: Handler<_, _>` is not satisfied
   --> image_server/examples/image-server.rs:45:48
    |
45  |         .route("/image/:spec/:origin_url", get(handler))
    |                                                ^^^^^^^ the trait `Handler<_, _>` is not implemented for `fn(axum::extract::Path<Param>, Extension<Arc<std::sync::Mutex<LruCache<u64, axum::body::Bytes>>>>) -> impl Future {handler}`
    |
note: required by a bound in `axum::routing::get`
   --> /Users/wanggang/.cargo/registry/src/mirrors.sjtug.sjtu.edu.cn-7a04d2510079875b/axum-0.5.1/src/routing/method_routing.rs:394:1
    |
394 | top_level_handler_fn!(get, GET);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `axum::routing::get`
    = note: this error originates in the macro `top_level_handler_fn` (in Nightly builds, run with -Z macro-backtrace for more info)

The strange thing is that calling method block_method is ok for cargo build and startup, but error for async_method.

[davidpdrsn]

Did you look at https://docs.rs/axum/latest/axum/handler/index.html#debugging-handler-type-errors?

[thinkingInWorldByNull]

Thank you for reminding 😄 , finally i get answer from #[debug_handler]