use futures_util::ready;
use pin_project_lite::pin_project;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use tower_service::Service;
pin_project! {
#[project = OneshotProj]
#[derive(Debug)]
pub enum Oneshot<S: Service<Req>, Req> {
NotReady {
svc: S,
req: Option<Req>,
},
Called {
#[pin]
fut: S::Future,
},
Done,
}
}
impl<S, Req> Oneshot<S, Req>
where
S: Service<Req>,
{
pub(crate) const fn new(svc: S, req: Req) -> Self {
Oneshot::NotReady {
svc,
req: Some(req),
}
}
}
impl<S, Req> Future for Oneshot<S, Req>
where
S: Service<Req>,
{
type Output = Result<S::Response, S::Error>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
loop {
let this = self.as_mut().project();
match this {
OneshotProj::NotReady { svc, req } => {
let _ = ready!(svc.poll_ready(cx))?;
let fut = svc.call(req.take().expect("already called"));
self.set(Oneshot::Called { fut });
}
OneshotProj::Called { fut } => {
let res = ready!(fut.poll(cx))?;
self.set(Oneshot::Done);
return Poll::Ready(Ok(res));
}
OneshotProj::Done => panic!("polled after complete"),
}
}
}
}