Improve Plugin toolkit (#2003)

Co-authored-by: Julian Antonielli <[email protected]>
Co-authored-by: Luca Palmieri <[email protected]>

rust-runtime/aws-smithy-http-server/src/plugin/closure.rs

@@ -0,0 +1,61 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+use tower::layer::util::Stack;
+
+use crate::operation::{Operation, OperationShape};
+
+use super::Plugin;
+
+/// An adapter to convert a `Fn(&'static str) -> Layer` closure into a [`Plugin`]. See [`plugin_from_operation_name_fn`] for more details.
+pub struct OperationNameFn<F> {
+    f: F,
+}
+
+impl<P, Op, S, ExistingLayer, NewLayer, F> Plugin<P, Op, S, ExistingLayer> for OperationNameFn<F>
+where
+    F: Fn(&'static str) -> NewLayer,
+    Op: OperationShape,
+{
+    type Service = S;
+    type Layer = Stack<ExistingLayer, NewLayer>;
+
+    fn map(&self, input: Operation<S, ExistingLayer>) -> Operation<Self::Service, Self::Layer> {
+        input.layer((self.f)(Op::NAME))
+    }
+}
+
+/// Constructs a [`Plugin`] using a closure over the operation name `F: Fn(&'static str) -> L` where `L` is a HTTP
+/// [`Layer`](tower::Layer).
+///
+/// # Example
+///
+/// ```rust
+/// use aws_smithy_http_server::plugin::plugin_from_operation_name_fn;
+/// use tower::layer::layer_fn;
+///
+/// // A `Service` which prints the operation name before calling `S`.
+/// struct PrintService<S> {
+///     operation_name: &'static str,
+///     inner: S
+/// }
+///
+/// // A `Layer` applying `PrintService`.
+/// struct PrintLayer {
+///     operation_name: &'static str
+/// }
+///
+/// // Defines a closure taking the operation name to `PrintLayer`.
+/// let f = |operation_name| PrintLayer { operation_name };
+///
+/// // This plugin applies the `PrintService` middleware around every operation.
+/// let plugin = plugin_from_operation_name_fn(f);
+/// ```
+pub fn plugin_from_operation_name_fn<L, F>(f: F) -> OperationNameFn<F>
+where
+    F: Fn(&'static str) -> L,
+{
+    OperationNameFn { f }
+}

rust-runtime/aws-smithy-http-server/src/plugin/layer.rs

@@ -0,0 +1,25 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+use tower::layer::util::Stack;
+
+use crate::operation::Operation;
+
+use super::Plugin;
+
+/// A [`Plugin`] which appends a HTTP [`Layer`](tower::Layer) `L` to the existing `Layer` in [`Operation<S, Layer>`](Operation).
+pub struct HttpLayer<L>(pub L);
+
+impl<P, Op, S, ExistingLayer, NewLayer> Plugin<P, Op, S, ExistingLayer> for HttpLayer<NewLayer>
+where
+    NewLayer: Clone,
+{
+    type Service = S;
+    type Layer = Stack<ExistingLayer, NewLayer>;
+
+    fn map(&self, input: Operation<S, ExistingLayer>) -> Operation<Self::Service, Self::Layer> {
+        input.layer(self.0.clone())
+    }
+}

rust-runtime/aws-smithy-http-server/src/plugin/mod.rs

@@ -3,15 +3,19 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+mod closure;
 mod filter;
 mod identity;
+mod layer;
 mod pipeline;
 mod stack;
 
 use crate::operation::Operation;
 
+pub use closure::{plugin_from_operation_name_fn, OperationNameFn};
 pub use filter::{filter_by_operation_name, FilterByOperationName};
 pub use identity::IdentityPlugin;
+pub use layer::HttpLayer;
 pub use pipeline::PluginPipeline;
 pub use stack::PluginStack;