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use crate::stream::{Fuse, FuturesOrdered, StreamExt};
use futures_core::future::Future;
use futures_core::ready;
use futures_core::stream::Stream;
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project_lite::pin_project;
use core::fmt;
use core::pin::Pin;
pin_project! {
#[must_use = "streams do nothing unless polled"]
pub struct Buffered<St>
where
St: Stream,
St::Item: Future,
{
#[pin]
stream: Fuse<St>,
in_progress_queue: FuturesOrdered<St::Item>,
max: usize,
}
}
impl<St> fmt::Debug for Buffered<St>
where
St: Stream + fmt::Debug,
St::Item: Future,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Buffered")
.field("stream", &self.stream)
.field("in_progress_queue", &self.in_progress_queue)
.field("max", &self.max)
.finish()
}
}
impl<St> Buffered<St>
where
St: Stream,
St::Item: Future,
{
pub(super) fn new(stream: St, n: usize) -> Self {
Self {
stream: super::Fuse::new(stream),
in_progress_queue: FuturesOrdered::new(),
max: n,
}
}
delegate_access_inner!(stream, St, (.));
}
impl<St> Stream for Buffered<St>
where
St: Stream,
St::Item: Future,
{
type Item = <St::Item as Future>::Output;
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Self::Item>> {
let mut this = self.project();
while this.in_progress_queue.len() < *this.max {
match this.stream.as_mut().poll_next(cx) {
Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut),
Poll::Ready(None) | Poll::Pending => break,
}
}
let res = this.in_progress_queue.poll_next_unpin(cx);
if let Some(val) = ready!(res) {
return Poll::Ready(Some(val))
}
if this.stream.is_done() {
Poll::Ready(None)
} else {
Poll::Pending
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let queue_len = self.in_progress_queue.len();
let (lower, upper) = self.stream.size_hint();
let lower = lower.saturating_add(queue_len);
let upper = match upper {
Some(x) => x.checked_add(queue_len),
None => None,
};
(lower, upper)
}
}
#[cfg(feature = "sink")]
impl<S, Item> Sink<Item> for Buffered<S>
where
S: Stream + Sink<Item>,
S::Item: Future,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}