tower_retry/
future.rs

1//! Future types
2
3use crate::{Policy, Retry};
4use futures_core::ready;
5use pin_project::{pin_project, project};
6use std::future::Future;
7use std::pin::Pin;
8use std::task::{Context, Poll};
9use tower_service::Service;
10
11/// The `Future` returned by a `Retry` service.
12#[pin_project]
13#[derive(Debug)]
14pub struct ResponseFuture<P, S, Request>
15where
16    P: Policy<Request, S::Response, S::Error>,
17    S: Service<Request>,
18{
19    request: Option<Request>,
20    #[pin]
21    retry: Retry<P, S>,
22    #[pin]
23    state: State<S::Future, P::Future>,
24}
25
26#[pin_project]
27#[derive(Debug)]
28enum State<F, P> {
29    /// Polling the future from `Service::call`
30    Called(#[pin] F),
31    /// Polling the future from `Policy::retry`
32    Checking(#[pin] P),
33    /// Polling `Service::poll_ready` after `Checking` was OK.
34    Retrying,
35}
36
37impl<P, S, Request> ResponseFuture<P, S, Request>
38where
39    P: Policy<Request, S::Response, S::Error>,
40    S: Service<Request>,
41{
42    pub(crate) fn new(
43        request: Option<Request>,
44        retry: Retry<P, S>,
45        future: S::Future,
46    ) -> ResponseFuture<P, S, Request> {
47        ResponseFuture {
48            request,
49            retry,
50            state: State::Called(future),
51        }
52    }
53}
54
55impl<P, S, Request> Future for ResponseFuture<P, S, Request>
56where
57    P: Policy<Request, S::Response, S::Error> + Clone,
58    S: Service<Request> + Clone,
59{
60    type Output = Result<S::Response, S::Error>;
61
62    #[project]
63    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
64        let mut this = self.project();
65
66        loop {
67            #[project]
68            match this.state.as_mut().project() {
69                State::Called(future) => {
70                    let result = ready!(future.poll(cx));
71                    if let Some(ref req) = this.request {
72                        match this.retry.policy.retry(req, result.as_ref()) {
73                            Some(checking) => {
74                                this.state.set(State::Checking(checking));
75                            }
76                            None => return Poll::Ready(result),
77                        }
78                    } else {
79                        // request wasn't cloned, so no way to retry it
80                        return Poll::Ready(result);
81                    }
82                }
83                State::Checking(future) => {
84                    this.retry
85                        .as_mut()
86                        .project()
87                        .policy
88                        .set(ready!(future.poll(cx)));
89                    this.state.set(State::Retrying);
90                }
91                State::Retrying => {
92                    // NOTE: we assume here that
93                    //
94                    //   this.retry.poll_ready()
95                    //
96                    // is equivalent to
97                    //
98                    //   this.retry.service.poll_ready()
99                    //
100                    // we need to make that assumption to avoid adding an Unpin bound to the Policy
101                    // in Ready to make it Unpin so that we can get &mut Ready as needed to call
102                    // poll_ready on it.
103                    ready!(this.retry.as_mut().project().service.poll_ready(cx))?;
104                    let req = this
105                        .request
106                        .take()
107                        .expect("retrying requires cloned request");
108                    *this.request = this.retry.policy.clone_request(&req);
109                    this.state.set(State::Called(
110                        this.retry.as_mut().project().service.call(req),
111                    ));
112                }
113            }
114        }
115    }
116}
tower_retry/future.rs

tower_retry/
future.rs
