Add web::ReqData<T> extractor (#1748)

Co-authored-by: Jonas Platte <jonas@lumeo.com>

src/request_data.rs

@@ -0,0 +1,175 @@
+use std::{any::type_name, ops::Deref};
+
+use actix_http::error::{Error, ErrorInternalServerError};
+use futures_util::future;
+
+use crate::{dev::Payload, FromRequest, HttpRequest};
+
+/// Request-local data extractor.
+///
+/// Request-local data is arbitrary data attached to an individual request, usually
+/// by middleware. It can be set via `extensions_mut` on [`HttpRequest`][htr_ext_mut]
+/// or [`ServiceRequest`][srv_ext_mut].
+///
+/// Unlike app data, request data is dropped when the request has finished processing. This makes it
+/// useful as a kind of messaging system between middleware and request handlers. It uses the same
+/// types-as-keys storage system as app data.
+///
+/// # Mutating Request Data
+/// Note that since extractors must output owned data, only types that `impl Clone` can use this
+/// extractor. A clone is taken of the required request data and can, therefore, not be directly
+/// mutated in-place. To mutate request data, continue to use [`HttpRequest::extensions_mut`] or
+/// re-insert the cloned data back into the extensions map. A `DerefMut` impl is intentionally not
+/// provided to make this potential foot-gun more obvious.
+///
+/// # Example
+/// ```rust,no_run
+/// # use actix_web::{web, HttpResponse, HttpRequest, Responder};
+///
+/// #[derive(Debug, Clone, PartialEq)]
+/// struct FlagFromMiddleware(String);
+///
+/// /// Use the `ReqData<T>` extractor to access request data in a handler.
+/// async fn handler(
+///     req: HttpRequest,
+///     opt_flag: Option<web::ReqData<FlagFromMiddleware>>,
+/// ) -> impl Responder {
+///     // use an optional extractor if the middleware is
+///     // not guaranteed to add this type of requests data
+///     if let Some(flag) = opt_flag {
+///         assert_eq!(&flag.into_inner(), req.extensions().get::<FlagFromMiddleware>().unwrap());
+///     }
+///     
+///     HttpResponse::Ok()
+/// }
+/// ```
+///
+/// [htr_ext_mut]: crate::HttpRequest::extensions_mut
+/// [srv_ext_mut]: crate::dev::ServiceRequest::extensions_mut
+#[derive(Debug, Clone)]
+pub struct ReqData<T: Clone + 'static>(T);
+
+impl<T: Clone + 'static> ReqData<T> {
+    /// Consumes the `ReqData`, returning it's wrapped data.
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T: Clone + 'static> Deref for ReqData<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
+impl<T: Clone + 'static> FromRequest for ReqData<T> {
+    type Config = ();
+    type Error = Error;
+    type Future = future::Ready<Result<Self, Error>>;
+
+    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
+        if let Some(st) = req.extensions().get::<T>() {
+            future::ok(ReqData(st.clone()))
+        } else {
+            log::debug!(
+                "Failed to construct App-level ReqData extractor. \
+                 Request path: {:?} (type: {})",
+                req.path(),
+                type_name::<T>(),
+            );
+            future::err(ErrorInternalServerError(
+                "Missing expected request extension data",
+            ))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{cell::RefCell, rc::Rc};
+
+    use futures_util::TryFutureExt as _;
+
+    use super::*;
+    use crate::{
+        dev::Service,
+        http::{Method, StatusCode},
+        test::{init_service, TestRequest},
+        web, App, HttpMessage, HttpResponse,
+    };
+
+    #[actix_rt::test]
+    async fn req_data_extractor() {
+        let mut srv = init_service(
+            App::new()
+                .wrap_fn(|req, srv| {
+                    if req.method() == Method::POST {
+                        req.extensions_mut().insert(42u32);
+                    }
+
+                    srv.call(req)
+                })
+                .service(web::resource("/test").to(
+                    |req: HttpRequest, data: Option<ReqData<u32>>| {
+                        if req.method() != Method::POST {
+                            assert!(data.is_none());
+                        }
+
+                        if let Some(data) = data {
+                            assert_eq!(*data, 42);
+                            assert_eq!(
+                                Some(data.into_inner()),
+                                req.extensions().get::<u32>().copied()
+                            );
+                        }
+
+                        HttpResponse::Ok()
+                    },
+                )),
+        )
+        .await;
+
+        let req = TestRequest::get().uri("/test").to_request();
+        let resp = srv.call(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+
+        let req = TestRequest::post().uri("/test").to_request();
+        let resp = srv.call(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+    }
+
+    #[actix_rt::test]
+    async fn req_data_internal_mutability() {
+        let mut srv = init_service(
+            App::new()
+                .wrap_fn(|req, srv| {
+                    let data_before = Rc::new(RefCell::new(42u32));
+                    req.extensions_mut().insert(data_before);
+
+                    srv.call(req).map_ok(|res| {
+                        {
+                            let ext = res.request().extensions();
+                            let data_after = ext.get::<Rc<RefCell<u32>>>().unwrap();
+                            assert_eq!(*data_after.borrow(), 53u32);
+                        }
+
+                        res
+                    })
+                })
+                .default_service(web::to(|data: ReqData<Rc<RefCell<u32>>>| {
+                    assert_eq!(*data.borrow(), 42);
+                    *data.borrow_mut() += 11;
+                    assert_eq!(*data.borrow(), 53);
+
+                    HttpResponse::Ok()
+                })),
+        )
+        .await;
+
+        let req = TestRequest::get().uri("/test").to_request();
+        let resp = srv.call(req).await.unwrap();
+        assert_eq!(resp.status(), StatusCode::OK);
+    }
+}