Vendor `AddExtensionLayer` and `AddExtension` (#414)

This remove tower-http from axum's public API. I would like to be able
to make breaking releases of tower-http without also having to ship a
breaking release of axum.

CHANGELOG.md

@@ -32,6 +32,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     public because `Router` is internally boxed ([#404])
   - **breaking:** Remove `routing::Layered` as it didn't actually do anything and
     thus wasn't necessary
+  - **breaking:** Vendor `AddExtensionLayer` and `AddExtension` to reduce public
+    dependencies
 - Routing:
   - Big internal refactoring of routing leading to several improvements ([#363])
     - **added:** Wildcard routes like `.route("/api/users/*rest", service)` are now supported.

src/add_extension.rs

@@ -0,0 +1,70 @@
+// this is vendored from tower-http to reduce public dependencies
+
+use http::Request;
+use std::task::{Context, Poll};
+use tower_layer::Layer;
+use tower_service::Service;
+
+/// [`Layer`] for adding some shareable value to [request extensions].
+///
+/// See [Sharing state with handlers](index.html#sharing-state-with-handlers)
+/// for more details.
+///
+/// [request extensions]: https://docs.rs/http/latest/http/struct.Extensions.html
+#[derive(Clone, Copy, Debug)]
+pub struct AddExtensionLayer<T> {
+    value: T,
+}
+
+impl<T> AddExtensionLayer<T> {
+    /// Create a new [`AddExtensionLayer`].
+    pub fn new(value: T) -> Self {
+        AddExtensionLayer { value }
+    }
+}
+
+impl<S, T> Layer<S> for AddExtensionLayer<T>
+where
+    T: Clone,
+{
+    type Service = AddExtension<S, T>;
+
+    fn layer(&self, inner: S) -> Self::Service {
+        AddExtension {
+            inner,
+            value: self.value.clone(),
+        }
+    }
+}
+
+/// Middleware for adding some shareable value to [request extensions].
+///
+/// See [Sharing state with handlers](index.html#sharing-state-with-handlers)
+/// for more details.
+///
+/// [request extensions]: https://docs.rs/http/latest/http/struct.Extensions.html
+#[derive(Clone, Copy, Debug)]
+pub struct AddExtension<S, T> {
+    inner: S,
+    value: T,
+}
+
+impl<ResBody, S, T> Service<Request<ResBody>> for AddExtension<S, T>
+where
+    S: Service<Request<ResBody>>,
+    T: Clone + Send + Sync + 'static,
+{
+    type Response = S::Response;
+    type Error = S::Error;
+    type Future = S::Future;
+
+    #[inline]
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.inner.poll_ready(cx)
+    }
+
+    fn call(&mut self, mut req: Request<ResBody>) -> Self::Future {
+        req.extensions_mut().insert(self.value.clone());
+        self.inner.call(req)
+    }
+}

src/extract/connect_info.rs

@@ -5,6 +5,7 @@
 //! [`Router::into_make_service_with_connect_info`]: crate::routing::Router::into_make_service_with_connect_info
 
 use super::{Extension, FromRequest, RequestParts};
+use crate::{AddExtension, AddExtensionLayer};
 use async_trait::async_trait;
 use hyper::server::conn::AddrStream;
 use std::future::ready;
@@ -15,7 +16,7 @@ use std::{
     net::SocketAddr,
     task::{Context, Poll},
 };
-use tower_http::add_extension::AddExtension;
+use tower_layer::Layer;
 use tower_service::Service;
 
 /// A [`MakeService`] created from a router.
@@ -91,7 +92,7 @@ where
 
     fn call(&mut self, target: T) -> Self::Future {
         let connect_info = ConnectInfo(C::connect_info(target));
-        let svc = AddExtension::new(self.svc.clone(), connect_info);
+        let svc = AddExtensionLayer::new(connect_info).layer(self.svc.clone());
         ResponseFuture {
             future: ready(Ok(svc)),
         }

src/lib.rs

@@ -1238,6 +1238,7 @@
 #[macro_use]
 pub(crate) mod macros;
 
+mod add_extension;
 mod clone_box_service;
 mod error;
 #[cfg(feature = "json")]
@@ -1254,14 +1255,13 @@ pub mod routing;
 #[cfg(test)]
 mod tests;
 
+pub use add_extension::{AddExtension, AddExtensionLayer};
 #[doc(no_inline)]
 pub use async_trait::async_trait;
 #[doc(no_inline)]
 pub use http;
 #[doc(no_inline)]
 pub use hyper::Server;
-#[doc(no_inline)]
-pub use tower_http::add_extension::{AddExtension, AddExtensionLayer};
 
 #[doc(inline)]
 #[cfg(feature = "json")]