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// 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!(),
}
}
}
}