feat(pool): add a Map pool service type

Author: seanmonstar

src/client/pool/map.rs

@@ -0,0 +1,213 @@
+//! Map pool utilities
+//!
+//! The map isn't a typical `Service`, but rather stand-alone type that can map
+//! requests to a key and  service factory. This is because the service is more
+//! of a router, and cannot determine which inner service to check for
+//! backpressure since it's not know until the request is made.
+//!
+//! The map implementation allows customization of extracting a key, and how to
+//! construct a MakeService for that key.
+//!
+//! # Example
+//!
+//! ```rust,ignore
+//! # async fn run() {
+//! # use hyper_util::client::pool;
+//! # let req = http::Request::new(());
+//! # let some_http1_connector = || {
+//! #     tower::service::service_fn(|_req| async { Ok::<_, &'static str>(()) })
+//! # };
+//! let mut map = pool::map::Map::builder()
+//!     .keys(|uri| (uri.scheme().clone(), uri.authority().clone()))
+//!     .values(|_| {
+//!         some_http1_connector()
+//!     })
+//!     .build();
+//!
+//! let resp = map.service(req.uri()).call(req).await;
+//! # }
+//! ```
+
+use std::collections::HashMap;
+
+// expose the documentation
+#[cfg(docsrs)]
+pub use self::builder::Builder;
+
+/// A map caching `MakeService`s per key.
+///
+/// Create one with the [`Map::builder()`].
+pub struct Map<T, Req>
+where
+    T: target::Target<Req>,
+{
+    map: HashMap<T::Key, T::Service>,
+    targeter: T,
+}
+
+// impl Map
+
+impl Map<builder::StartHere, builder::StartHere> {
+    /// Create a [`Builder`] to configure a new `Map`.
+    pub fn builder<Dst>() -> builder::Builder<Dst, builder::WantsKeyer, builder::WantsServiceMaker>
+    {
+        builder::Builder::new()
+    }
+}
+
+impl<T, Req> Map<T, Req>
+where
+    T: target::Target<Req>,
+{
+    fn new(targeter: T) -> Self {
+        Map {
+            map: HashMap::new(),
+            targeter,
+        }
+    }
+}
+
+impl<T, Req> Map<T, Req>
+where
+    T: target::Target<Req>,
+    T::Key: Eq + std::hash::Hash,
+{
+    /// Get a service after extracting the key from `req`.
+    pub fn service(&mut self, req: &Req) -> &mut T::Service {
+        let key = self.targeter.key(req);
+        self.map
+            .entry(key)
+            .or_insert_with(|| self.targeter.service(req))
+    }
+}
+
+// sealed and unnameable for now
+mod target {
+    pub trait Target<Dst> {
+        type Key;
+        type Service;
+
+        fn key(&self, dst: &Dst) -> Self::Key;
+        fn service(&self, dst: &Dst) -> Self::Service;
+    }
+}
+
+// sealed and unnameable for now
+mod builder {
+    use std::marker::PhantomData;
+
+    /// A builder to configure a `Map`.
+    ///
+    /// # Unnameable
+    ///
+    /// This type is normally unnameable, forbidding naming of the type within
+    /// code. The type is exposed in the documentation to show which methods
+    /// can be publicly called.
+    pub struct Builder<Dst, K, S> {
+        _dst: PhantomData<fn(Dst)>,
+        keys: K,
+        svcs: S,
+    }
+
+    pub struct WantsKeyer;
+    pub struct WantsServiceMaker;
+
+    pub enum StartHere {}
+
+    pub struct Built<K, S> {
+        keys: K,
+        svcs: S,
+    }
+
+    impl<Dst> Builder<Dst, WantsKeyer, WantsServiceMaker> {
+        pub(super) fn new() -> Self {
+            Builder {
+                _dst: PhantomData,
+                keys: WantsKeyer,
+                svcs: WantsServiceMaker,
+            }
+        }
+    }
+
+    impl<Dst, S> Builder<Dst, WantsKeyer, S> {
+        /// Provide a closure that extracts a pool key for the destination.
+        pub fn keys<K, KK>(self, keyer: K) -> Builder<Dst, K, S>
+        where
+            K: Fn(&Dst) -> KK,
+        {
+            Builder {
+                _dst: PhantomData,
+                keys: keyer,
+                svcs: self.svcs,
+            }
+        }
+    }
+
+    impl<Dst, K> Builder<Dst, K, WantsServiceMaker> {
+        /// Provide a closure to create a new `MakeService` for the destination.
+        pub fn values<S, SS>(self, svcs: S) -> Builder<Dst, K, S>
+        where
+            S: Fn(&Dst) -> SS,
+        {
+            Builder {
+                _dst: PhantomData,
+                keys: self.keys,
+                svcs,
+            }
+        }
+    }
+
+    impl<Dst, K, S> Builder<Dst, K, S>
+    where
+        Built<K, S>: super::target::Target<Dst>,
+        <Built<K, S> as super::target::Target<Dst>>::Key: Eq + std::hash::Hash,
+    {
+        /// Build the `Map` pool.
+        pub fn build(self) -> super::Map<Built<K, S>, Dst> {
+            super::Map::new(Built {
+                keys: self.keys,
+                svcs: self.svcs,
+            })
+        }
+    }
+
+    impl super::target::Target<StartHere> for StartHere {
+        type Key = StartHere;
+        type Service = StartHere;
+
+        fn key(&self, _: &StartHere) -> Self::Key {
+            match *self {}
+        }
+
+        fn service(&self, _: &StartHere) -> Self::Service {
+            match *self {}
+        }
+    }
+
+    impl<K, KK, S, SS, Dst> super::target::Target<Dst> for Built<K, S>
+    where
+        K: Fn(&Dst) -> KK,
+        S: Fn(&Dst) -> SS,
+        KK: Eq + std::hash::Hash,
+    {
+        type Key = KK;
+        type Service = SS;
+
+        fn key(&self, dst: &Dst) -> Self::Key {
+            (self.keys)(dst)
+        }
+
+        fn service(&self, dst: &Dst) -> Self::Service {
+            (self.svcs)(dst)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn smoke() {
+        let mut pool = super::Map::builder().keys(|_| "a").values(|_| "b").build();
+        pool.service(&"hello");
+    }
+}

src/client/pool/mod.rs

@@ -1,5 +1,6 @@
 //! Composable pool services
 
 pub mod cache;
+pub mod map;
 pub mod negotiate;
 pub mod singleton;