1 files changed, 73 insertions, 0 deletions
diff --git a/third_party/rust/hyper/src/service/oneshot.rs b/third_party/rust/hyper/src/service/oneshot.rs
new file mode 100644
index 0000000000..2697af8f4c
--- /dev/null
+++ b/third_party/rust/hyper/src/service/oneshot.rs
@@ -0,0 +1,73 @@
+// TODO: Eventually to be replaced with tower_util::Oneshot.
+
+use pin_project_lite::pin_project;
+use tower_service::Service;
+
+use crate::common::{task, Future, Pin, Poll};
+
+pub(crate) fn oneshot<S, Req>(svc: S, req: Req) -> Oneshot<S, Req>
+where
+    S: Service<Req>,
+{
+    Oneshot {
+        state: State::NotReady { svc, req },
+    }
+}
+
+pin_project! {
+    // A `Future` consuming a `Service` and request, waiting until the `Service`
+    // is ready, and then calling `Service::call` with the request, and
+    // waiting for that `Future`.
+    #[allow(missing_debug_implementations)]
+    pub struct Oneshot<S: Service<Req>, Req> {
+        #[pin]
+        state: State<S, Req>,
+    }
+}
+
+pin_project! {
+    #[project = StateProj]
+    #[project_replace = StateProjOwn]
+    enum State<S: Service<Req>, Req> {
+        NotReady {
+            svc: S,
+            req: Req,
+        },
+        Called {
+            #[pin]
+            fut: S::Future,
+        },
+        Tmp,
+    }
+}
+
+impl<S, Req> Future for Oneshot<S, Req>
+where
+    S: Service<Req>,
+{
+    type Output = Result<S::Response, S::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        let mut me = self.project();
+
+        loop {
+            match me.state.as_mut().project() {
+                StateProj::NotReady { ref mut svc, .. } => {
+                    ready!(svc.poll_ready(cx))?;
+                    // fallthrough out of the match's borrow
+                }
+                StateProj::Called { fut } => {
+                    return fut.poll(cx);
+                }
+                StateProj::Tmp => unreachable!(),
+            }
+
+            match me.state.as_mut().project_replace(State::Tmp) {
+                StateProjOwn::NotReady { mut svc, req } => {
+                    me.state.set(State::Called { fut: svc.call(req) });
+                }
+                _ => unreachable!(),
+            }
+        }
+    }
+}