Remove Sync requirement from response bodies

As we learned [in Tonic] bodies don't need to be `Sync` because they can
only be polled from one thread at a time.

This changes axum's bodies to no longer require `Sync` and makes
`BoxBody` an alias for `UnsyncBoxBody<Bytes, axum::Error>`.

[in Tonic]: hyperium/tonic#117

CHANGELOG.md

@@ -34,6 +34,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
     thus wasn't necessary
   - **breaking:** Vendor `AddExtensionLayer` and `AddExtension` to reduce public
     dependencies
+  - **breaking:** `body::BoxBody` is now a type alias for
+    `http_body::combinators::UnsyncBoxBody` and thus is no longer `Sync`. This
+    is because bodies are streams and requiring streams to be `Sync` is
+    unnecessary.
+  - **added:** Implement `IntoResponse` for `http_body::combinators::UnsyncBoxBody`.
 - Routing:
   - Big internal refactoring of routing leading to several improvements ([#363])
     - **added:** Wildcard routes like `.route("/api/users/*rest", service)` are now supported.

Cargo.toml

@@ -29,8 +29,8 @@ bitflags = "1.0"
 bytes = "1.0"
 futures-util = { version = "0.3", default-features = false, features = ["alloc"] }
 http = "0.2"
-http-body = "0.4.3"
-hyper = { version = "0.14", features = ["server", "tcp", "stream"] }
+http-body = "0.4.4"
+hyper = { version = "0.14.14", features = ["server", "tcp", "stream"] }
 matchit = "0.4.4"
 percent-encoding = "2.1"
 pin-project-lite = "0.2.7"

src/body.rs

@@ -20,15 +20,15 @@ pub use bytes::Bytes;
 ///
 /// This is used in axum as the response body type for applications. Its
 /// necessary to unify multiple response bodies types into one.
-pub type BoxBody = http_body::combinators::BoxBody<Bytes, Error>;
+pub type BoxBody = http_body::combinators::UnsyncBoxBody<Bytes, Error>;
 
 /// Convert a [`http_body::Body`] into a [`BoxBody`].
 pub fn box_body<B>(body: B) -> BoxBody
 where
-    B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    B: http_body::Body<Data = Bytes> + Send + 'static,
     B::Error: Into<BoxError>,
 {
-    body.map_err(Error::new).boxed()
+    body.map_err(Error::new).boxed_unsync()
 }
 
 pub(crate) fn empty() -> BoxBody {

src/error_handling/mod.rs

@@ -114,8 +114,8 @@ where
     S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone,
     F: FnOnce(S::Error) -> Res + Clone,
     Res: IntoResponse,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-    ResBody::Error: Into<BoxError> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
+    ResBody::Error: Into<BoxError>,
 {
     type Response = Response<BoxBody>;
     type Error = Infallible;
@@ -181,8 +181,8 @@ pub mod future {
         Fut: Future<Output = Result<Response<B>, E>>,
         F: FnOnce(E) -> Res,
         Res: IntoResponse,
-        B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-        B::Error: Into<BoxError> + Send + Sync + 'static,
+        B: http_body::Body<Data = Bytes> + Send + 'static,
+        B::Error: Into<BoxError>,
     {
         type Output = Result<Response<BoxBody>, Infallible>;
 

src/extract/extractor_middleware.rs

@@ -154,7 +154,7 @@ where
     E: FromRequest<ReqBody> + 'static,
     ReqBody: Default + Send + 'static,
     S: Service<Request<ReqBody>, Response = Response<ResBody>> + Clone,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
     ResBody::Error: Into<BoxError>,
 {
     type Response = Response<BoxBody>;
@@ -213,7 +213,7 @@ where
     E: FromRequest<ReqBody>,
     S: Service<Request<ReqBody>, Response = Response<ResBody>>,
     ReqBody: Default,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
     ResBody::Error: Into<BoxError>,
 {
     type Output = Result<Response<BoxBody>, S::Error>;

src/extract/multipart.rs

@@ -53,7 +53,7 @@ pub struct Multipart {
 impl<B> FromRequest<B> for Multipart
 where
     B: http_body::Body<Data = Bytes> + Default + Unpin + Send + 'static,
-    B::Error: Into<BoxError> + 'static,
+    B::Error: Into<BoxError>,
 {
     type Rejection = MultipartRejection;
 

src/handler/mod.rs

@@ -281,8 +281,8 @@ where
     S::Future: Send,
     T: 'static,
     ReqBody: Send + 'static,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-    ResBody::Error: Into<BoxError> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
+    ResBody::Error: Into<BoxError>,
 {
     type Sealed = sealed::Hidden;
 

src/response/headers.rs

@@ -115,7 +115,7 @@ where
 impl<H, T, K, V> IntoResponse for (Headers<H>, T)
 where
     T: IntoResponse,
-    T::Body: Body<Data = Bytes> + Send + Sync + 'static,
+    T::Body: Body<Data = Bytes> + Send + 'static,
     <T::Body as Body>::Error: Into<BoxError>,
     H: IntoIterator<Item = (K, V)>,
     K: TryInto<HeaderName>,
@@ -141,7 +141,7 @@ where
 impl<H, T, K, V> IntoResponse for (StatusCode, Headers<H>, T)
 where
     T: IntoResponse,
-    T::Body: Body<Data = Bytes> + Send + Sync + 'static,
+    T::Body: Body<Data = Bytes> + Send + 'static,
     <T::Body as Body>::Error: Into<BoxError>,
     H: IntoIterator<Item = (K, V)>,
     K: TryInto<HeaderName>,

src/response/mod.rs

@@ -163,7 +163,7 @@ pub trait IntoResponse {
     /// [`axum::body::Empty<Bytes>`]: crate::body::Empty
     /// [`axum::body::Full<Bytes>`]: crate::body::Full
     /// [`axum::body::BoxBody`]: crate::body::BoxBody
-    type Body: http_body::Body<Data = Bytes, Error = Self::BodyError> + Send + Sync + 'static;
+    type Body: http_body::Body<Data = Bytes, Error = Self::BodyError> + Send + 'static;
 
     /// The error type `Self::Body` might generate.
     ///
@@ -217,7 +217,7 @@ where
 
 impl<B> IntoResponse for Response<B>
 where
-    B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    B: http_body::Body<Data = Bytes> + Send + 'static,
     B::Error: Into<BoxError>,
 {
     type Body = B;
@@ -257,10 +257,22 @@ where
     }
 }
 
+impl<E> IntoResponse for http_body::combinators::UnsyncBoxBody<Bytes, E>
+where
+    E: Into<BoxError> + 'static,
+{
+    type Body = Self;
+    type BodyError = E;
+
+    fn into_response(self) -> Response<Self> {
+        Response::new(self)
+    }
+}
+
 impl<B, F> IntoResponse for MapData<B, F>
 where
-    B: http_body::Body + Send + Sync + 'static,
-    F: FnMut(B::Data) -> Bytes + Send + Sync + 'static,
+    B: http_body::Body + Send + 'static,
+    F: FnMut(B::Data) -> Bytes + Send + 'static,
     B::Error: Into<BoxError>,
 {
     type Body = Self;
@@ -273,8 +285,8 @@ where
 
 impl<B, F, E> IntoResponse for MapErr<B, F>
 where
-    B: http_body::Body<Data = Bytes> + Send + Sync + 'static,
-    F: FnMut(B::Error) -> E + Send + Sync + 'static,
+    B: http_body::Body<Data = Bytes> + Send + 'static,
+    F: FnMut(B::Error) -> E + Send + 'static,
     E: Into<BoxError>,
 {
     type Body = Self;

src/routing/method_not_allowed.rs

@@ -41,7 +41,7 @@ impl<E> fmt::Debug for MethodNotAllowed<E> {
 
 impl<B, E> Service<Request<B>> for MethodNotAllowed<E>
 where
-    B: Send + Sync + 'static,
+    B: Send + 'static,
 {
     type Response = Response<BoxBody>;
     type Error = E;

src/routing/mod.rs

@@ -77,7 +77,7 @@ impl<B> Clone for Router<B> {
 
 impl<B> Default for Router<B>
 where
-    B: Send + Sync + 'static,
+    B: Send + 'static,
 {
     fn default() -> Self {
         Self::new()
@@ -99,7 +99,7 @@ const NEST_TAIL_PARAM_CAPTURE: &str = "/*axum_nest";
 
 impl<B> Router<B>
 where
-    B: Send + Sync + 'static,
+    B: Send + 'static,
 {
     /// Create a new `Router`.
     ///
@@ -240,7 +240,7 @@ where
             + Send
             + 'static,
         <L::Service as Service<Request<LayeredReqBody>>>::Future: Send + 'static,
-        LayeredResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+        LayeredResBody: http_body::Body<Data = Bytes> + Send + 'static,
         LayeredResBody::Error: Into<BoxError>,
     {
         let layer = ServiceBuilder::new()
@@ -361,7 +361,7 @@ where
 
 impl<B> Service<Request<B>> for Router<B>
 where
-    B: Send + Sync + 'static,
+    B: Send + 'static,
 {
     type Response = Response<BoxBody>;
     type Error = Infallible;

src/routing/not_found.rs

@@ -16,7 +16,7 @@ pub(crate) struct NotFound;
 
 impl<B> Service<Request<B>> for NotFound
 where
-    B: Send + Sync + 'static,
+    B: Send + 'static,
 {
     type Response = Response<BoxBody>;
     type Error = Infallible;

src/routing/service_method_routing.rs

@@ -464,7 +464,7 @@ impl<S, F, B> MethodRouter<S, F, B> {
 impl<S, F, B, ResBody> Service<Request<B>> for MethodRouter<S, F, B>
 where
     S: Service<Request<B>, Response = Response<ResBody>> + Clone,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
     ResBody::Error: Into<BoxError>,
     F: Service<Request<B>, Response = Response<BoxBody>, Error = S::Error> + Clone,
 {
@@ -514,7 +514,7 @@ pin_project! {
 impl<S, F, B, ResBody> Future for MethodRouterFuture<S, F, B>
 where
     S: Service<Request<B>, Response = Response<ResBody>> + Clone,
-    ResBody: http_body::Body<Data = Bytes> + Send + Sync + 'static,
+    ResBody: http_body::Body<Data = Bytes> + Send + 'static,
     ResBody::Error: Into<BoxError>,
     F: Service<Request<B>, Response = Response<BoxBody>, Error = S::Error>,
 {