Introduce an `aws-lambda` feature. (#2035)

* Introduce an `aws-lambda` feature.

* Add CHANGELOG

* Use the new and shiny feature syntax to avoid creating an implicit `lambda_http` feature.

* Add `aws-lambda` feature to the Python server. Enable the `aws-lambda` feature in our example. Be explicit in providing an implementation of request rejection for Box<dyn Error>.

* Add an `aws-lambda` feature flag to the generated Python-specific crate. We enable it by default to make sure the Lambda method ends up visible in the final Python wrapper library.

CHANGELOG.next.toml

@@ -487,3 +487,15 @@ message = "Make generated enum `values()` functions callable in const contexts."
 references = ["smithy-rs#2011"]
 meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "all" }
 author = "lsr0"
+
+[[smithy-rs]]
+message = """
+All types that are exclusively relevant within the context of an AWS Lambda function are now gated behind the
+`aws-lambda` feature flag.
+
+This will reduce the number of dependencies (and improve build times) for users that are running their Smithy services
+in non-serverless environments (e.g. via `hyper`).
+"""
+references = ["smithy-rs#2035"]
+meta = { "breaking" = true, "tada" = false, "bug" = false, "target" = "server" }
+author = "LukeMathWalker"

codegen-server/python/src/main/kotlin/software/amazon/smithy/rust/codegen/server/python/smithy/customizations/PythonServerCodegenDecorator.kt

@@ -7,6 +7,7 @@ package software.amazon.smithy.rust.codegen.server.python.smithy.customizations
 
 import software.amazon.smithy.model.neighbor.Walker
 import software.amazon.smithy.rust.codegen.client.smithy.customize.RustCodegenDecorator
+import software.amazon.smithy.rust.codegen.core.rustlang.Feature
 import software.amazon.smithy.rust.codegen.core.rustlang.Writable
 import software.amazon.smithy.rust.codegen.core.rustlang.docs
 import software.amazon.smithy.rust.codegen.core.rustlang.rust
@@ -103,6 +104,21 @@ class PubUsePythonTypesDecorator : RustCodegenDecorator<ServerProtocolGenerator,
         clazz.isAssignableFrom(ServerCodegenContext::class.java)
 }
 
+/**
+ * Decorator adding an `aws-lambda` feature to the generated crate.
+ */
+class PythonFeatureFlagsDecorator : RustCodegenDecorator<ServerProtocolGenerator, ServerCodegenContext> {
+    override val name: String = "PythonFeatureFlagsDecorator"
+    override val order: Byte = 0
+
+    override fun extras(codegenContext: ServerCodegenContext, rustCrate: RustCrate) {
+        rustCrate.mergeFeature(Feature("aws-lambda", true, listOf("aws-smithy-http-server-python/aws-lambda")))
+    }
+
+    override fun supportsCodegenContext(clazz: Class<out CodegenContext>): Boolean =
+        clazz.isAssignableFrom(ServerCodegenContext::class.java)
+}
+
 val DECORATORS = listOf(
     /**
      * Add the [InternalServerError] error to all operations.
@@ -115,4 +131,6 @@ val DECORATORS = listOf(
     PubUsePythonTypesDecorator(),
     // Render the Python shared library export.
     PythonExportModuleDecorator(),
+    // Add the `aws-lambda` feature flag
+    PythonFeatureFlagsDecorator(),
 )

codegen-server/python/src/main/kotlin/software/amazon/smithy/rust/codegen/server/python/smithy/generators/PythonApplicationGenerator.kt

@@ -278,6 +278,7 @@ class PythonApplicationGenerator(
                     self.run_server(py, address, port, backlog, workers)
                 }
                 /// Lambda entrypoint: start the server on Lambda.
+                ##[cfg(feature = "aws-lambda")]
                 ##[pyo3(text_signature = "(${'$'}self)")]
                 pub fn run_lambda(
                     &mut self,

rust-runtime/aws-smithy-http-server-python/Cargo.toml

@@ -12,6 +12,9 @@ Python server runtime for Smithy Rust Server Framework.
 """
 publish = true
 
+[features]
+aws-lambda = ["aws-smithy-http-server/aws-lambda", "dep:lambda_http"]
+
 [dependencies]
 aws-smithy-http = { path = "../aws-smithy-http" }
 aws-smithy-http-server = { path = "../aws-smithy-http-server" }
@@ -22,7 +25,7 @@ bytes = "1.2"
 futures = "0.3"
 http = "0.2"
 hyper = { version = "0.14.20", features = ["server", "http1", "http2", "tcp", "stream"] }
-lambda_http = "0.7.1"
+lambda_http = { version = "0.7.1", optional = true }
 num_cpus = "1.13.1"
 parking_lot = "0.12.1"
 pin-project-lite = "0.2"

rust-runtime/aws-smithy-http-server-python/src/lib.rs

@@ -3,6 +3,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 //! Rust/Python bindings, runtime and utilities.
 //!
 //! This crates implements all the generic code needed to start and manage

rust-runtime/aws-smithy-http-server-python/src/server.rs

@@ -7,7 +7,7 @@ use std::{collections::HashMap, convert::Infallible, ops::Deref, process, thread
 
 use aws_smithy_http_server::{
     body::{Body, BoxBody},
-    routing::{IntoMakeService, LambdaHandler},
+    routing::IntoMakeService,
     AddExtensionLayer,
 };
 use http::{Request, Response};
@@ -422,7 +422,11 @@ event_loop.add_signal_handler(signal.SIGINT,
     ///
     /// Unlike the `run_server`, `run_lambda_handler` does not spawns other processes,
     /// it starts the Lambda handler on the current process.
+    #[cfg(feature = "aws-lambda")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "aws-lambda")))]
     fn run_lambda_handler(&mut self, py: Python) -> PyResult<()> {
+        use aws_smithy_http_server::routing::LambdaHandler;
+
         let event_loop = self.configure_python_event_loop(py)?;
         let service = self.build_and_configure_service(py, event_loop)?;
         let rt = runtime::Builder::new_multi_thread()

rust-runtime/aws-smithy-http-server/Cargo.toml

@@ -13,6 +13,7 @@ Server runtime for Smithy Rust Server Framework.
 publish = true
 
 [features]
+aws-lambda = ["dep:lambda_http"]
 unredacted-logging = []
 
 [dependencies]
@@ -26,7 +27,7 @@ futures-util = { version = "0.3", default-features = false }
 http = "0.2"
 http-body = "0.4"
 hyper = { version = "0.14.12", features = ["server", "http1", "http2", "tcp", "stream"] }
-lambda_http = "0.7.1"
+lambda_http = { version = "0.7.1", optional = true }
 mime = "0.3"
 nom = "7"
 pin-project-lite = "0.2"

rust-runtime/aws-smithy-http-server/examples/pokemon-service/Cargo.toml

@@ -44,7 +44,7 @@ futures-util = "0.3"
 lambda_http = "0.7.1"
 
 # Local paths
-aws-smithy-http-server = { path = "../../" }
+aws-smithy-http-server = { path = "../../", features = ["aws-lambda"] }
 pokemon-service-server-sdk = { path = "../pokemon-service-server-sdk/" }
 
 [dev-dependencies]

rust-runtime/aws-smithy-http-server/src/lib.rs

@@ -3,10 +3,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 //! HTTP server runtime and utilities, loosely based on [axum].
 //!
 //! [axum]: https://docs.rs/axum/latest/axum/
-
 #[macro_use]
 pub(crate) mod macros;
 

rust-runtime/aws-smithy-http-server/src/rejection.rs

@@ -261,8 +261,9 @@ convert_to_request_rejection!(std::str::Utf8Error, InvalidUtf8);
 // everyone will run a Hyper-based server in their services).
 convert_to_request_rejection!(hyper::Error, HttpBody);
 
-// Required in order to accept Lambda HTTP requests using `Router<lambda_http::Body>`.
-convert_to_request_rejection!(lambda_http::Error, HttpBody);
+// Useful in general, but it also required in order to accept Lambda HTTP requests using
+// `Router<lambda_http::Body>` since `lambda_http::Error` is a type alias for `Box<dyn Error + ..>`.
+convert_to_request_rejection!(Box<dyn std::error::Error + Send + Sync + 'static>, HttpBody);
 
 pub mod any_rejections {
     //! This module hosts enums, up to size 8, which implement [`IntoResponse`] when their variants implement

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

@@ -29,6 +29,8 @@ use tower_http::map_response_body::MapResponseBodyLayer;
 
 mod future;
 mod into_make_service;
+#[cfg(feature = "aws-lambda")]
+#[cfg_attr(docsrs, doc(cfg(feature = "aws-lambda")))]
 mod lambda_handler;
 
 #[doc(hidden)]
@@ -38,6 +40,8 @@ mod route;
 
 pub(crate) mod tiny_map;
 
+#[cfg(feature = "aws-lambda")]
+#[cfg_attr(docsrs, doc(cfg(feature = "aws-lambda")))]
 pub use self::lambda_handler::LambdaHandler;
 pub use self::{future::RouterFuture, into_make_service::IntoMakeService, route::Route};