tokio_stream/stream_ext/
throttle.rs

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1//! Slow down a stream by enforcing a delay between items.
2
3use crate::Stream;
4use tokio::time::{Duration, Instant, Sleep};
5
6use std::future::Future;
7use std::pin::Pin;
8use std::task::{self, ready, Poll};
9
10use pin_project_lite::pin_project;
11
12pub(super) fn throttle<T>(duration: Duration, stream: T) -> Throttle<T>
13where
14    T: Stream,
15{
16    Throttle {
17        delay: tokio::time::sleep_until(Instant::now() + duration),
18        duration,
19        has_delayed: true,
20        stream,
21    }
22}
23
24pin_project! {
25    /// Stream for the [`throttle`](throttle) function. This object is `!Unpin`. If you need it to
26    /// implement `Unpin` you can pin your throttle like this: `Box::pin(your_throttle)`.
27    #[derive(Debug)]
28    #[must_use = "streams do nothing unless polled"]
29    pub struct Throttle<T> {
30        #[pin]
31        delay: Sleep,
32        duration: Duration,
33
34        // Set to true when `delay` has returned ready, but `stream` hasn't.
35        has_delayed: bool,
36
37        // The stream to throttle
38        #[pin]
39        stream: T,
40    }
41}
42
43impl<T> Throttle<T> {
44    /// Acquires a reference to the underlying stream that this combinator is
45    /// pulling from.
46    pub fn get_ref(&self) -> &T {
47        &self.stream
48    }
49
50    /// Acquires a mutable reference to the underlying stream that this combinator
51    /// is pulling from.
52    ///
53    /// Note that care must be taken to avoid tampering with the state of the stream
54    /// which may otherwise confuse this combinator.
55    pub fn get_mut(&mut self) -> &mut T {
56        &mut self.stream
57    }
58
59    /// Consumes this combinator, returning the underlying stream.
60    ///
61    /// Note that this may discard intermediate state of this combinator, so care
62    /// should be taken to avoid losing resources when this is called.
63    pub fn into_inner(self) -> T {
64        self.stream
65    }
66}
67
68impl<T: Stream> Stream for Throttle<T> {
69    type Item = T::Item;
70
71    fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
72        let mut me = self.project();
73        let dur = *me.duration;
74
75        if !*me.has_delayed && !is_zero(dur) {
76            ready!(me.delay.as_mut().poll(cx));
77            *me.has_delayed = true;
78        }
79
80        let value = ready!(me.stream.poll_next(cx));
81
82        if value.is_some() {
83            if !is_zero(dur) {
84                me.delay.reset(Instant::now() + dur);
85            }
86
87            *me.has_delayed = false;
88        }
89
90        Poll::Ready(value)
91    }
92}
93
94fn is_zero(dur: Duration) -> bool {
95    dur == Duration::from_millis(0)
96}
tokio_stream/stream_ext/throttle.rs

tokio_stream/stream_ext/
throttle.rs
