状态共享

use axum::AddExtensionLayer;

// ...

let app = Router::new()
        .route("/", get(handler::index))
        .layer(AddExtensionLayer::new(Arc::new(AppState { pool }));

新版本的写法

use axum::extract::Extension;

// ...

let app = Router::new()
        .route("/", get(handler::index))
        .layer(Extension(Arc::new(AppState { pool }));