Remove PollError from server type parameters (#2457)

## Motivation and Context

#2444

## Description

Remove `PollError` from the implementation and documentation.

Author: hlbarber

CHANGELOG.next.toml

@@ -105,3 +105,13 @@ author = "david-perez"
 references = ["smithy-rs#2676", "smithy-rs#2685"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 
+[[smithy-rs]]
+message = """Remove `PollError` from an operations `Service::Error`.
+
+Any [`tower::Service`](https://docs.rs/tower/latest/tower/trait.Service.html) provided to
+[`Operation::from_service`](https://docs.rs/aws-smithy-http-server/latest/aws_smithy_http_server/operation/struct.Operation.html#method.from_service)
+no longer requires `Service::Error = OperationError<Op::Error, PollError>`, instead requiring just `Service::Error = Op::Error`.
+"""
+references = ["smithy-rs#2457"]
+meta = { "breaking" = true, "tada" = false, "bug" = false, "target" = "server" }
+author = "hlbarber"

rust-runtime/aws-smithy-http-server/src/operation/handler.rs

@@ -10,13 +10,10 @@ use std::{
     task::{Context, Poll},
 };
 
-use futures_util::{
-    future::{Map, MapErr},
-    FutureExt, TryFutureExt,
-};
+use futures_util::{future::Map, FutureExt};
 use tower::Service;
 
-use super::{OperationError, OperationShape};
+use super::OperationShape;
 
 /// A utility trait used to provide an even interface for all operation handlers.
 ///
@@ -143,14 +140,14 @@ where
     H: Handler<Op, Exts>,
 {
     type Response = Op::Output;
-    type Error = OperationError<Op::Error, Infallible>;
-    type Future = MapErr<H::Future, fn(Op::Error) -> Self::Error>;
+    type Error = Op::Error;
+    type Future = H::Future;
 
     fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         Poll::Ready(Ok(()))
     }
 
     fn call(&mut self, (input, exts): (Op::Input, Exts)) -> Self::Future {
-        self.handler.call(input, exts).map_err(OperationError::Model)
+        self.handler.call(input, exts)
     }
 }

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

@@ -84,16 +84,13 @@
 //! ## [`OperationService`]
 //!
 //! Similarly, the [`OperationService`] trait is implemented by all `Service<(Op::Input, ...)>` with
-//! `Response = Op::Output`, and `Error = OperationError<Op::Error, PollError>`.
-//!
-//! We use [`OperationError`], with a `PollError` not constrained by the model, to allow the user to provide a custom
-//! [`Service::poll_ready`](tower::Service::poll_ready) implementation.
+//! `Response = Op::Output`, and `Error = Op::Error`.
 //!
 //! The following are examples of [`Service`](tower::Service)s which implement [`OperationService`]:
 //!
-//! - `Service<CartIdentifier, Response = ShoppingCart, Error = OperationError<Infallible, Infallible>>`.
-//! - `Service<(CartIdentifier, Extension<Context>), Response = ShoppingCart, Error = OperationError<GetShoppingCartError, Infallible>>`.
-//! - `Service<(CartIdentifier, Extension<Context>, Extension<ExtraContext>), Response = ShoppingCart, Error = OperationError<GetShoppingCartError, PollError>)`.
+//! - `Service<CartIdentifier, Response = ShoppingCart, Error = Infallible>`.
+//! - `Service<(CartIdentifier, Extension<Context>), Response = ShoppingCart, Error = GetShoppingCartError>`.
+//! - `Service<(CartIdentifier, Extension<Context>, Extension<ExtraContext>), Response = ShoppingCart, Error = GetShoppingCartError)`.
 //!
 //! Notice the parallels between [`OperationService`] and [`Handler`].
 //!
@@ -116,7 +113,7 @@
 //! #    type Output = ShoppingCart;
 //! #    type Error = GetShoppingError;
 //! # }
-//! # type OpFuture = std::future::Ready<Result<ShoppingCart, OperationError<GetShoppingError, PollError>>>;
+//! # type OpFuture = std::future::Ready<Result<ShoppingCart, GetShoppingError>>;
 //! // Construction of an `Operation` from a `Handler`.
 //!
 //! async fn op_handler(input: CartIdentifier) -> Result<ShoppingCart, GetShoppingError> {
@@ -127,13 +124,11 @@
 //!
 //! // Construction of an `Operation` from a `Service`.
 //!
-//! pub struct PollError;
-//!
 //! pub struct OpService;
 //!
 //! impl Service<CartIdentifier> for OpService {
 //!     type Response = ShoppingCart;
-//!     type Error = OperationError<GetShoppingError, PollError>;
+//!     type Error = GetShoppingError;
 //!     type Future = OpFuture;
 //!
 //!     fn poll_ready(&mut self, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
@@ -155,19 +150,13 @@
 //!
 //! Both [`Handler`] and [`OperationService`] accept and return Smithy model structures. After an [`Operation`] is
 //! constructed they are converted to a canonical form
-//! `Service<(Op::Input, Exts), Response = Op::Output, Error = OperationError<Op::Error, PollError>>`. The
+//! `Service<(Op::Input, Exts), Response = Op::Output, Error = Op::Error>`. The
 //! [`UpgradeLayer`] acts upon such services by converting them to
-//! `Service<http::Request, Response = http::Response, Error = PollError>`.
+//! `Service<http::Request, Response = http::Response, Error = Infallible>`.
 //!
-//! Note that the `PollError` is still exposed, for two reasons:
-//!
-//! - Smithy is agnostic to `PollError` and therefore we have no prescribed way to serialize it to a [`http::Response`]
-//! , unlike the operation errors.
-//! - The intention of `PollError` is to signal that the underlying service is no longer able to take requests, so
-//! should be discarded. See [`Service::poll_ready`](tower::Service::poll_ready).
 //!
 //! The [`UpgradeLayer`] and it's [`Layer::Service`](tower::Layer::Service) [`Upgrade`] are both parameterized by a
-//! protocol. This allows for upgrading to `Service<http::Request, Response = http::Response, Error = PollError>` to be
+//! protocol. This allows for upgrading to `Service<http::Request, Response = http::Response, Error = Infallible>` to be
 //! protocol dependent.
 //!
 //! The [`Operation::upgrade`] will apply [`UpgradeLayer`] to `S` then apply the [`Layer`](tower::Layer) `L`. The
@@ -208,15 +197,15 @@ impl<S, L> Operation<S, L> {
     }
 }
 
-impl<Op, S, PollError> Operation<Normalize<Op, S, PollError>> {
+impl<Op, S> Operation<Normalize<Op, S>> {
     /// Creates an [`Operation`] from a [`Service`](tower::Service).
     pub fn from_service<Exts>(inner: S) -> Self
     where
         Op: OperationShape,
-        S: OperationService<Op, Exts, PollError>,
+        S: OperationService<Op, Exts>,
     {
         Self {
-            inner: inner.canonicalize(),
+            inner: inner.normalize(),
             layer: Identity::new(),
         }
     }
@@ -235,12 +224,3 @@ impl<Op, H> Operation<IntoService<Op, H>> {
         }
     }
 }
-
-/// The operation [`Service`](tower::Service) has two classes of failure modes - those specified by the Smithy model
-/// and those associated with [`Service::poll_ready`](tower::Service::poll_ready).
-pub enum OperationError<ModelError, PollError> {
-    /// An error modelled by the Smithy model occurred.
-    Model(ModelError),
-    /// A [`Service::poll_ready`](tower::Service::poll_ready) failure occurred.
-    PollReady(PollError),
-}

rust-runtime/aws-smithy-http-server/src/operation/operation_service.rs

@@ -10,7 +10,7 @@ use std::{
 
 use tower::Service;
 
-use super::{OperationError, OperationShape};
+use super::OperationShape;
 
 /// A utility trait used to provide an even interface for all operation services.
 ///
@@ -19,8 +19,7 @@ use super::{OperationError, OperationShape};
 /// [`IntoService`](super::IntoService).
 ///
 /// See [`operation`](crate::operation) documentation for more info.
-pub trait OperationService<Op, Exts, PollError>:
-    Service<Self::Normalized, Response = Op::Output, Error = OperationError<Op::Error, PollError>>
+pub trait OperationService<Op, Exts>: Service<Self::Normalized, Response = Op::Output, Error = Op::Error>
 where
     Op: OperationShape,
 {
@@ -31,10 +30,10 @@ where
 }
 
 // `Service<Op::Input>`
-impl<Op, S, PollError> OperationService<Op, (), PollError> for S
+impl<Op, S> OperationService<Op, ()> for S
 where
     Op: OperationShape,
-    S: Service<Op::Input, Response = Op::Output, Error = OperationError<Op::Error, PollError>>,
+    S: Service<Op::Input, Response = Op::Output, Error = Op::Error>,
 {
     type Normalized = Op::Input;
 
@@ -44,10 +43,10 @@ where
 }
 
 // `Service<(Op::Input, Ext0)>`
-impl<Op, Ext0, S, PollError> OperationService<Op, (Ext0,), PollError> for S
+impl<Op, Ext0, S> OperationService<Op, (Ext0,)> for S
 where
     Op: OperationShape,
-    S: Service<(Op::Input, Ext0), Response = Op::Output, Error = OperationError<Op::Error, PollError>>,
+    S: Service<(Op::Input, Ext0), Response = Op::Output, Error = Op::Error>,
 {
     type Normalized = (Op::Input, Ext0);
 
@@ -57,10 +56,10 @@ where
 }
 
 // `Service<(Op::Input, Ext0, Ext1)>`
-impl<Op, Ext0, Ext1, S, PollError> OperationService<Op, (Ext0, Ext1), PollError> for S
+impl<Op, Ext0, Ext1, S> OperationService<Op, (Ext0, Ext1)> for S
 where
     Op: OperationShape,
-    S: Service<(Op::Input, Ext0, Ext1), Response = Op::Output, Error = OperationError<Op::Error, PollError>>,
+    S: Service<(Op::Input, Ext0, Ext1), Response = Op::Output, Error = Op::Error>,
 {
     type Normalized = (Op::Input, Ext0, Ext1);
 
@@ -70,55 +69,52 @@ where
 }
 
 /// An extension trait of [`OperationService`].
-pub trait OperationServiceExt<Op, Exts, PollError>: OperationService<Op, Exts, PollError>
+pub trait OperationServiceExt<Op, Exts>: OperationService<Op, Exts>
 where
     Op: OperationShape,
 {
     /// Convert the [`OperationService`] into a canonicalized [`Service`].
-    fn canonicalize(self) -> Normalize<Op, Self, PollError>
+    fn normalize(self) -> Normalize<Op, Self>
     where
         Self: Sized,
     {
         Normalize {
             inner: self,
             _operation: PhantomData,
-            _poll_error: PhantomData,
         }
     }
 }
 
-impl<F, Op, Exts, PollError> OperationServiceExt<Op, Exts, PollError> for F
+impl<F, Op, Exts> OperationServiceExt<Op, Exts> for F
 where
     Op: OperationShape,
-    F: OperationService<Op, Exts, PollError>,
+    F: OperationService<Op, Exts>,
 {
 }
 
 /// A [`Service`] normalizing the request type of a [`OperationService`].
 #[derive(Debug)]
-pub struct Normalize<Op, S, PollError> {
+pub struct Normalize<Op, S> {
     inner: S,
     _operation: PhantomData<Op>,
-    _poll_error: PhantomData<PollError>,
 }
 
-impl<Op, S, PollError> Clone for Normalize<Op, S, PollError>
+impl<Op, S> Clone for Normalize<Op, S>
 where
     S: Clone,
 {
     fn clone(&self) -> Self {
         Self {
             inner: self.inner.clone(),
             _operation: PhantomData,
-            _poll_error: PhantomData,
         }
     }
 }
 
-impl<Op, S, Exts, PollError> Service<(Op::Input, Exts)> for Normalize<Op, S, PollError>
+impl<Op, S, Exts> Service<(Op::Input, Exts)> for Normalize<Op, S>
 where
     Op: OperationShape,
-    S: OperationService<Op, Exts, PollError>,
+    S: OperationService<Op, Exts>,
 {
     type Response = S::Response;
     type Error = S::Error;

rust-runtime/aws-smithy-http-server/src/operation/shape.rs

@@ -33,9 +33,9 @@ pub trait OperationShapeExt: OperationShape {
     }
 
     /// Creates a new [`Operation`] for well-formed [`Service`](tower::Service)s.
-    fn from_service<S, Exts, PollError>(svc: S) -> Operation<Normalize<Self, S, PollError>>
+    fn from_service<S, Exts>(svc: S) -> Operation<Normalize<Self, S>>
     where
-        S: OperationService<Self, Exts, PollError>,
+        S: OperationService<Self, Exts>,
         Self: Sized,
     {
         Operation::from_service(svc)