aws_smithy_async/future/
timeout.rs

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1/*
2 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
3 * SPDX-License-Identifier: Apache-2.0
4 */
5
6// This code was copied and then modified from Tokio.
7
8/*
9 * Copyright (c) 2021 Tokio Contributors
10 *
11 * Permission is hereby granted, free of charge, to any
12 * person obtaining a copy of this software and associated
13 * documentation files (the "Software"), to deal in the
14 * Software without restriction, including without
15 * limitation the rights to use, copy, modify, merge,
16 * publish, distribute, sublicense, and/or sell copies of
17 * the Software, and to permit persons to whom the Software
18 * is furnished to do so, subject to the following
19 * conditions:
20 *
21 * The above copyright notice and this permission notice
22 * shall be included in all copies or substantial portions
23 * of the Software.
24 *
25 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
26 * ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
27 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
28 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
29 * SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
30 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
31 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
32 * IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
33 * DEALINGS IN THE SOFTWARE.
34 */
35
36//! Provides the [`Timeout`] future for adding a timeout to another future.
37
38use pin_project_lite::pin_project;
39use std::error::Error;
40use std::fmt;
41use std::future::Future;
42use std::pin::Pin;
43use std::task::{Context, Poll};
44
45/// Error returned when [`Timeout`] times out
46#[derive(Debug)]
47pub struct TimedOutError;
48
49impl Error for TimedOutError {}
50
51impl fmt::Display for TimedOutError {
52    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
53        write!(f, "timed out")
54    }
55}
56
57pin_project! {
58    /// Timeout Future
59    #[non_exhaustive]
60    #[must_use = "futures do nothing unless you `.await` or poll them"]
61    #[derive(Debug)]
62    pub struct Timeout<T, S> {
63        #[pin]
64        value: T,
65        #[pin]
66        sleep: S,
67    }
68}
69
70impl<T, S> Timeout<T, S> {
71    /// Create a new future that will race `value` and `sleep`.
72    ///
73    /// If `sleep` resolves first, a timeout error is returned. Otherwise, the value is returned.
74    pub fn new(value: T, sleep: S) -> Timeout<T, S> {
75        Timeout { value, sleep }
76    }
77}
78
79impl<T, S> Future for Timeout<T, S>
80where
81    T: Future,
82    S: Future,
83{
84    type Output = Result<T::Output, TimedOutError>;
85
86    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
87        let me = self.project();
88
89        // First, try polling the future
90        if let Poll::Ready(v) = me.value.poll(cx) {
91            return Poll::Ready(Ok(v));
92        }
93
94        // Now check the timer
95        match me.sleep.poll(cx) {
96            Poll::Ready(_) => Poll::Ready(Err(TimedOutError)),
97            Poll::Pending => Poll::Pending,
98        }
99    }
100}
101
102#[cfg(test)]
103mod tests {
104    use super::{TimedOutError, Timeout};
105    use crate::future::never::Never;
106
107    #[tokio::test]
108    async fn success() {
109        assert!(matches!(
110            Timeout::new(async { Ok::<isize, isize>(5) }, Never).await,
111            Ok(Ok(5))
112        ));
113    }
114
115    #[tokio::test]
116    async fn failure() {
117        assert!(matches!(
118            Timeout::new(async { Err::<isize, isize>(0) }, Never).await,
119            Ok(Err(0))
120        ));
121    }
122
123    #[tokio::test]
124    async fn timeout() {
125        assert!(matches!(
126            Timeout::new(Never, async {}).await,
127            Err(TimedOutError)
128        ));
129    }
130
131    // If the value is available at the same time as the timeout, then return the value
132    #[tokio::test]
133    async fn prefer_value_to_timeout() {
134        assert!(matches!(Timeout::new(async { 5 }, async {}).await, Ok(5)));
135    }
136}
aws_smithy_async/future/timeout.rs

aws_smithy_async/future/
timeout.rs
