feat: add ThinData wrapper

actix-web/Cargo.toml

@@ -151,6 +151,7 @@ encoding_rs = "0.8"
 futures-core = { version = "0.3.17", default-features = false }
 futures-util = { version = "0.3.17", default-features = false }
 itoa = "1"
+impl-more = "0.1.4"
 language-tags = "0.3"
 log = "0.4"
 mime = "0.3"

actix-web/src/lib.rs

@@ -104,6 +104,7 @@ mod scope;
 mod server;
 mod service;
 pub mod test;
+mod thin_data;
 pub(crate) mod types;
 pub mod web;
 

actix-web/src/thin_data.rs

@@ -0,0 +1,121 @@
+use std::any::type_name;
+
+use actix_utils::future::{ready, Ready};
+
+use crate::{dev::Payload, error, FromRequest, HttpRequest};
+
+/// Application data wrapper and extractor for cheaply-cloned types.
+///
+/// Similar to the [`Data`] wrapper but for `Clone`/`Copy` types that are already an `Arc` internally,
+/// share state using some other means when cloned, or is otherwise static data that is very cheap
+/// to clone.
+///
+/// Unlike `Data`, this wrapper clones `T` during extraction. Therefore, it is the user's
+/// responsibility to ensure that clones of `T` do actually share the same state, otherwise state
+/// may be unexpectedly different across multiple requests.
+///
+/// Note that if your type is literally an `Arc<T>` then it's recommended to use the
+/// [`Data::from(arc)`][data_from_arc] conversion instead.
+///
+/// # Examples
+///
+/// ```
+/// use actix_web::{
+///     web::{self, ThinData},
+///     App, HttpResponse, Responder,
+/// };
+///
+/// // Use the `ThinData<T>` extractor to access a database connection pool.
+/// async fn index(ThinData(db_pool): ThinData<DbPool>) -> impl Responder {
+///     // database action ...
+///
+///     HttpResponse::Ok()
+/// }
+///
+/// # type DbPool = ();
+/// let db_pool = DbPool::default();
+///
+/// App::new()
+///     .app_data(ThinData(db_pool.clone()))
+///     .service(web::resource("/").get(index))
+/// # ;
+/// ```
+///
+/// [`Data`]: crate::web::Data
+/// [data_from_arc]: crate::web::Data#impl-From<Arc<T>>-for-Data<T>
+#[derive(Debug, Clone)]
+pub struct ThinData<T>(pub T);
+
+impl_more::impl_as_ref!(ThinData<T> => T);
+impl_more::impl_as_mut!(ThinData<T> => T);
+impl_more::impl_deref_and_mut!(<T> in ThinData<T> => T);
+
+impl<T: Clone + 'static> FromRequest for ThinData<T> {
+    type Error = crate::Error;
+    type Future = Ready<Result<Self, Self::Error>>;
+
+    #[inline]
+    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
+        ready(req.app_data::<Self>().cloned().ok_or_else(|| {
+            log::debug!(
+                "Failed to extract `ThinData<{}>` for `{}` handler. For the ThinData extractor to work \
+                correctly, wrap the data with `ThinData()` and pass it to `App::app_data()`. \
+                Ensure that types align in both the set and retrieve calls.",
+                type_name::<T>(),
+                req.match_name().unwrap_or(req.path())
+            );
+
+            error::ErrorInternalServerError(
+                "Requested application data is not configured correctly. \
+                View/enable debug logs for more details.",
+            )
+        }))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::{Arc, Mutex};
+
+    use super::*;
+    use crate::{
+        http::StatusCode,
+        test::{call_service, init_service, TestRequest},
+        web, App, HttpResponse,
+    };
+
+    type TestT = Arc<Mutex<u32>>;
+
+    #[actix_rt::test]
+    async fn thin_data() {
+        let test_data = TestT::default();
+
+        let app = init_service(App::new().app_data(ThinData(test_data.clone())).service(
+            web::resource("/").to(|td: ThinData<TestT>| {
+                *td.lock().unwrap() += 1;
+                HttpResponse::Ok()
+            }),
+        ))
+        .await;
+
+        for _ in 0..3 {
+            let req = TestRequest::default().to_request();
+            let resp = call_service(&app, req).await;
+            assert_eq!(resp.status(), StatusCode::OK);
+        }
+
+        assert_eq!(*test_data.lock().unwrap(), 3);
+    }
+
+    #[actix_rt::test]
+    async fn thin_data_missing() {
+        let app = init_service(
+            App::new().service(web::resource("/").to(|_: ThinData<u32>| HttpResponse::Ok())),
+        )
+        .await;
+
+        let req = TestRequest::default().to_request();
+        let resp = call_service(&app, req).await;
+        assert_eq!(resp.status(), StatusCode::INTERNAL_SERVER_ERROR);
+    }
+}

actix-web/src/web.rs

@@ -3,6 +3,7 @@
 //! # Request Extractors
 //! - [`Data`]: Application data item
 //! - [`ReqData`]: Request-local data item
+//! - [`ThinData`]: Request-local data item
 //! - [`Path`]: URL path parameters / dynamic segments
 //! - [`Query`]: URL query parameters
 //! - [`Header`]: Typed header
@@ -22,7 +23,8 @@ use actix_router::IntoPatterns;
 pub use bytes::{Buf, BufMut, Bytes, BytesMut};
 
 pub use crate::{
-    config::ServiceConfig, data::Data, redirect::Redirect, request_data::ReqData, types::*,
+    config::ServiceConfig, data::Data, redirect::Redirect, request_data::ReqData,
+    thin_data::ThinData, types::*,
 };
 use crate::{
     error::BlockingError, http::Method, service::WebService, FromRequest, Handler, Resource,