use futures_core::ready;
use pin_project_lite::pin_project;
use std::{
fmt,
future::Future,
pin::Pin,
task::{Context, Poll},
};
use tower_service::Service;
pin_project! {
#[derive(Debug)]
pub struct Oneshot<S: Service<Req>, Req> {
#[pin]
state: State<S, Req>,
}
}
pin_project! {
#[project = StateProj]
enum State<S: Service<Req>, Req> {
NotReady {
svc: S,
req: Option<Req>,
},
Called {
#[pin]
fut: S::Future,
},
Done,
}
}
impl<S: Service<Req>, Req> State<S, Req> {
const fn not_ready(svc: S, req: Option<Req>) -> Self {
Self::NotReady { svc, req }
}
const fn called(fut: S::Future) -> Self {
Self::Called { fut }
}
}
impl<S, Req> fmt::Debug for State<S, Req>
where
S: Service<Req> + fmt::Debug,
Req: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
State::NotReady {
svc,
req: Some(req),
} => f
.debug_tuple("State::NotReady")
.field(svc)
.field(req)
.finish(),
State::NotReady { req: None, .. } => unreachable!(),
State::Called { .. } => f.debug_tuple("State::Called").field(&"S::Future").finish(),
State::Done => f.debug_tuple("State::Done").finish(),
}
}
}
impl<S, Req> Oneshot<S, Req>
where
S: Service<Req>,
{
#[allow(missing_docs)]
pub const fn new(svc: S, req: Req) -> Self {
Oneshot {
state: State::not_ready(svc, Some(req)),
}
}
}
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 Context<'_>) -> Poll<Self::Output> {
let mut this = self.project();
loop {
match this.state.as_mut().project() {
StateProj::NotReady { svc, req } => {
let _ = ready!(svc.poll_ready(cx))?;
let f = svc.call(req.take().expect("already called"));
this.state.set(State::called(f));
}
StateProj::Called { fut } => {
let res = ready!(fut.poll(cx))?;
this.state.set(State::Done);
return Poll::Ready(Ok(res));
}
StateProj::Done => panic!("polled after complete"),
}
}
}
}