tower/util/
oneshot.rs

1use futures_core::ready;
2use pin_project_lite::pin_project;
3use std::{
4    fmt,
5    future::Future,
6    pin::Pin,
7    task::{Context, Poll},
8};
9use tower_service::Service;
10
11pin_project! {
12    /// A [`Future`] consuming a [`Service`] and request, waiting until the [`Service`]
13    /// is ready, and then calling [`Service::call`] with the request, and
14    /// waiting for that [`Future`].
15    #[derive(Debug)]
16    pub struct Oneshot<S: Service<Req>, Req> {
17        #[pin]
18        state: State<S, Req>,
19    }
20}
21
22pin_project! {
23    #[project = StateProj]
24    enum State<S: Service<Req>, Req> {
25        NotReady {
26            svc: S,
27            req: Option<Req>,
28        },
29        Called {
30            #[pin]
31            fut: S::Future,
32        },
33        Done,
34    }
35}
36
37impl<S: Service<Req>, Req> State<S, Req> {
38    const fn not_ready(svc: S, req: Option<Req>) -> Self {
39        Self::NotReady { svc, req }
40    }
41
42    const fn called(fut: S::Future) -> Self {
43        Self::Called { fut }
44    }
45}
46
47impl<S, Req> fmt::Debug for State<S, Req>
48where
49    S: Service<Req> + fmt::Debug,
50    Req: fmt::Debug,
51{
52    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
53        match self {
54            State::NotReady {
55                svc,
56                req: Some(req),
57            } => f
58                .debug_tuple("State::NotReady")
59                .field(svc)
60                .field(req)
61                .finish(),
62            State::NotReady { req: None, .. } => unreachable!(),
63            State::Called { .. } => f.debug_tuple("State::Called").field(&"S::Future").finish(),
64            State::Done => f.debug_tuple("State::Done").finish(),
65        }
66    }
67}
68
69impl<S, Req> Oneshot<S, Req>
70where
71    S: Service<Req>,
72{
73    #[allow(missing_docs)]
74    pub const fn new(svc: S, req: Req) -> Self {
75        Oneshot {
76            state: State::not_ready(svc, Some(req)),
77        }
78    }
79}
80
81impl<S, Req> Future for Oneshot<S, Req>
82where
83    S: Service<Req>,
84{
85    type Output = Result<S::Response, S::Error>;
86
87    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
88        let mut this = self.project();
89        loop {
90            match this.state.as_mut().project() {
91                StateProj::NotReady { svc, req } => {
92                    let _ = ready!(svc.poll_ready(cx))?;
93                    let f = svc.call(req.take().expect("already called"));
94                    this.state.set(State::called(f));
95                }
96                StateProj::Called { fut } => {
97                    let res = ready!(fut.poll(cx))?;
98                    this.state.set(State::Done);
99                    return Poll::Ready(Ok(res));
100                }
101                StateProj::Done => panic!("polled after complete"),
102            }
103        }
104    }
105}
tower/util/oneshot.rs

tower/util/
oneshot.rs
