Fixed unsoundness in .and_then()/.then() service combinators

actix-service/src/then.rs

@@ -1,5 +1,6 @@
 use std::future::Future;
 use std::pin::Pin;
+use std::rc::Rc;
 use std::task::{Context, Poll};
 
 use super::{Service, ServiceFactory};
@@ -8,11 +9,8 @@ use crate::cell::Cell;
 /// Service for the `then` combinator, chaining a computation onto the end of
 /// another service.
 ///
-/// This is created by the `ServiceExt::then` method.
-pub struct ThenService<A, B> {
-    a: A,
-    b: Cell<B>,
-}
+/// This is created by the `Pipeline::then` method.
+pub(crate) struct ThenService<A, B>(Cell<(A, B)>);
 
 impl<A, B> ThenService<A, B> {
     /// Create new `.then()` combinator
@@ -21,19 +19,13 @@ impl<A, B> ThenService<A, B> {
         A: Service,
         B: Service<Request = Result<A::Response, A::Error>, Error = A::Error>,
     {
-        Self { a, b: Cell::new(b) }
+        Self(Cell::new((a, b)))
     }
 }
 
-impl<A, B> Clone for ThenService<A, B>
-where
-    A: Clone,
-{
+impl<A, B> Clone for ThenService<A, B> {
     fn clone(&self) -> Self {
-        ThenService {
-            a: self.a.clone(),
-            b: self.b.clone(),
-        }
+        ThenService(self.0.clone())
     }
 }
 
@@ -47,9 +39,10 @@ where
     type Error = B::Error;
     type Future = ThenServiceResponse<A, B>;
 
-    fn poll_ready(&mut self, ctx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        let not_ready = !self.a.poll_ready(ctx)?.is_ready();
-        if !self.b.get_mut().poll_ready(ctx)?.is_ready() || not_ready {
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let srv = self.0.get_mut();
+        let not_ready = !srv.0.poll_ready(cx)?.is_ready();
+        if !srv.1.poll_ready(cx)?.is_ready() || not_ready {
             Poll::Pending
         } else {
             Poll::Ready(Ok(()))
@@ -58,13 +51,13 @@ where
 
     fn call(&mut self, req: A::Request) -> Self::Future {
         ThenServiceResponse {
-            state: State::A(self.a.call(req), Some(self.b.clone())),
+            state: State::A(self.0.get_mut().0.call(req), Some(self.0.clone())),
         }
     }
 }
 
 #[pin_project::pin_project]
-pub struct ThenServiceResponse<A, B>
+pub(crate) struct ThenServiceResponse<A, B>
 where
     A: Service,
     B: Service<Request = Result<A::Response, A::Error>>,
@@ -79,7 +72,7 @@ where
     A: Service,
     B: Service<Request = Result<A::Response, A::Error>>,
 {
-    A(#[pin] A::Future, Option<Cell<B>>),
+    A(#[pin] A::Future, Option<Cell<(A, B)>>),
     B(#[pin] B::Future),
     Empty,
 }
@@ -101,7 +94,7 @@ where
                 Poll::Ready(res) => {
                     let mut b = b.take().unwrap();
                     this.state.set(State::Empty); // drop fut A
-                    let fut = b.get_mut().call(res);
+                    let fut = b.get_mut().1.call(res);
                     this.state.set(State::B(fut));
                     self.poll(cx)
                 }
@@ -117,10 +110,7 @@ where
 }
 
 /// `.then()` service factory combinator
-pub struct ThenServiceFactory<A, B> {
-    a: A,
-    b: B,
-}
+pub(crate) struct ThenServiceFactory<A, B>(Rc<(A, B)>);
 
 impl<A, B> ThenServiceFactory<A, B>
 where
@@ -135,7 +125,7 @@ where
 {
     /// Create new `AndThen` combinator
     pub(crate) fn new(a: A, b: B) -> Self {
-        Self { a, b }
+        Self(Rc::new((a, b)))
     }
 }
 
@@ -160,28 +150,19 @@ where
     type Future = ThenServiceFactoryResponse<A, B>;
 
     fn new_service(&self, cfg: A::Config) -> Self::Future {
-        ThenServiceFactoryResponse::new(
-            self.a.new_service(cfg.clone()),
-            self.b.new_service(cfg),
-        )
+        let srv = &*self.0;
+        ThenServiceFactoryResponse::new(srv.0.new_service(cfg.clone()), srv.1.new_service(cfg))
     }
 }
 
-impl<A, B> Clone for ThenServiceFactory<A, B>
-where
-    A: Clone,
-    B: Clone,
-{
+impl<A, B> Clone for ThenServiceFactory<A, B> {
     fn clone(&self) -> Self {
-        Self {
-            a: self.a.clone(),
-            b: self.b.clone(),
-        }
+        Self(self.0.clone())
     }
 }
 
 #[pin_project::pin_project]
-pub struct ThenServiceFactoryResponse<A, B>
+pub(crate) struct ThenServiceFactoryResponse<A, B>
 where
     A: ServiceFactory,
     B: ServiceFactory<