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//! Slow down a stream by enforcing a delay between items.
use crate::Stream;
use tokio::time::{Duration, Instant, Sleep};
use std::future::Future;
use std::pin::Pin;
use std::task::{self, Poll};
use pin_project_lite::pin_project;
pub(super) fn throttle<T>(duration: Duration, stream: T) -> Throttle<T>
where
T: Stream,
{
Throttle {
delay: tokio::time::sleep_until(Instant::now() + duration),
duration,
has_delayed: true,
stream,
}
}
pin_project! {
/// Stream for the [`throttle`](throttle) function. This object is `!Unpin`. If you need it to
/// implement `Unpin` you can pin your throttle like this: `Box::pin(your_throttle)`.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
#[pin]
delay: Sleep,
duration: Duration,
// Set to true when `delay` has returned ready, but `stream` hasn't.
has_delayed: bool,
// The stream to throttle
#[pin]
stream: T,
}
}
impl<T> Throttle<T> {
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &T {
&self.stream
}
/// Acquires a mutable reference to the underlying stream that this combinator
/// is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the stream
/// which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut T {
&mut self.stream
}
/// Consumes this combinator, returning the underlying stream.
///
/// Note that this may discard intermediate state of this combinator, so care
/// should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> T {
self.stream
}
}
impl<T: Stream> Stream for Throttle<T> {
type Item = T::Item;
fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
let mut me = self.project();
let dur = *me.duration;
if !*me.has_delayed && !is_zero(dur) {
ready!(me.delay.as_mut().poll(cx));
*me.has_delayed = true;
}
let value = ready!(me.stream.poll_next(cx));
if value.is_some() {
if !is_zero(dur) {
me.delay.reset(Instant::now() + dur);
}
*me.has_delayed = false;
}
Poll::Ready(value)
}
}
fn is_zero(dur: Duration) -> bool {
dur == Duration::from_millis(0)
}
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