Add 'Request::local_cache_async' for use in async request guards.

core/lib/src/request/request.rs

@@ -1,5 +1,6 @@
 use std::sync::{Arc, RwLock, Mutex};
 use std::net::{IpAddr, SocketAddr};
+use std::future::Future;
 use std::fmt;
 use std::str;
 
@@ -564,6 +565,39 @@ impl<'r> Request<'r> {
             })
     }
 
+    /// Retrieves the cached value for type `T` from the request-local cached
+    /// state of `self`. If no such value has previously been cached for this
+    /// request, `fut` is `await`ed to produce the value which is subsequently
+    /// returned.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use rocket::http::Method;
+    /// # use rocket::Request;
+    /// # type User = ();
+    /// async fn current_user<'r>(request: &Request<'r>) -> User {
+    ///     // Validate request for a given user, load from database, etc.
+    /// }
+    ///
+    /// # Request::example(Method::Get, "/uri", |request| rocket::async_test(async {
+    /// let user = request.local_cache_async(async {
+    ///     current_user(request).await
+    /// }).await;
+    /// # }));
+    pub async fn local_cache_async<'a, T, F>(&'a self, fut: F) -> &'a T
+        where F: Future<Output = T>,
+              T: Send + Sync + 'static
+    {
+        match self.state.cache.try_get() {
+            Some(s) => s,
+            None => {
+                self.state.cache.set(fut.await);
+                self.state.cache.get()
+            }
+        }
+    }
+
     /// Retrieves and parses into `T` the 0-indexed `n`th segment from the
     /// request. Returns `None` if `n` is greater than the number of segments.
     /// Returns `Some(Err(T::Error))` if the parameter type `T` failed to be

examples/request_local_state/src/main.rs

@@ -4,8 +4,8 @@
 
 use std::sync::atomic::{AtomicUsize, Ordering};
 
-use rocket::request::{self, Request, FromRequest, State};
 use rocket::outcome::Outcome::*;
+use rocket::request::{self, FromRequest, FromRequestAsync, FromRequestFuture, Request, State};
 
 #[cfg(test)] mod tests;
 
@@ -17,6 +17,8 @@ struct Atomics {
 
 struct Guard1;
 struct Guard2;
+struct Guard3;
+struct Guard4;
 
 impl<'a, 'r> FromRequest<'a, 'r> for Guard1 {
     type Error = ();
@@ -39,15 +41,51 @@ impl<'a, 'r> FromRequest<'a, 'r> for Guard2 {
     }
 }
 
-#[get("/")]
-fn index(_g1: Guard1, _g2: Guard2) {
+impl<'a, 'r> FromRequestAsync<'a, 'r> for Guard3 {
+    type Error = ();
+
+    fn from_request<'fut>(req: &'a Request<'r>) -> FromRequestFuture<'fut, Self, ()>
+        where 'a: 'fut
+    {
+        Box::pin(async move {
+            let atomics = try_outcome!(req.guard::<State<'_, Atomics>>());
+            atomics.uncached.fetch_add(1, Ordering::Relaxed);
+            req.local_cache_async(async {
+                atomics.cached.fetch_add(1, Ordering::Relaxed)
+            }).await;
+
+            Success(Guard3)
+        })
+    }
+}
+
+impl<'a, 'r> FromRequestAsync<'a, 'r> for Guard4 {
+    type Error = ();
+
+    fn from_request<'fut>(req: &'a Request<'r>) -> FromRequestFuture<'fut, Self, ()>
+        where 'a: 'fut
+    {
+        Box::pin(async move {
+            try_outcome!(Guard3::from_request(req).await);
+            Success(Guard4)
+        })
+    }
+}
+
+#[get("/sync")]
+fn r_sync(_g1: Guard1, _g2: Guard2) {
+    // This exists only to run the request guards.
+}
+
+#[get("/async")]
+async fn r_async(_g1: Guard3, _g2: Guard4) {
     // This exists only to run the request guards.
 }
 
 fn rocket() -> rocket::Rocket {
     rocket::ignite()
         .manage(Atomics::default())
-        .mount("/", routes!(index))
+        .mount("/", routes![r_sync, r_async])
 }
 
 fn main() {

examples/request_local_state/src/tests.rs

@@ -6,9 +6,15 @@ use rocket::local::Client;
 #[rocket::async_test]
 async fn test() {
     let client = Client::new(rocket()).unwrap();
-    client.get("/").dispatch().await;
+    client.get("/sync").dispatch().await;
 
     let atomics = client.rocket().state::<Atomics>().unwrap();
     assert_eq!(atomics.uncached.load(Ordering::Relaxed), 2);
     assert_eq!(atomics.cached.load(Ordering::Relaxed), 1);
+
+    client.get("/async").dispatch().await;
+
+    let atomics = client.rocket().state::<Atomics>().unwrap();
+    assert_eq!(atomics.uncached.load(Ordering::Relaxed), 4);
+    assert_eq!(atomics.cached.load(Ordering::Relaxed), 2);
 }