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use alloc::collections::VecDeque;
use core::pin::Pin;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_project_lite::pin_project;
pin_project! {
/// Sink for the [`buffer`](super::SinkExt::buffer) method.
#[derive(Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct Buffer<Si, Item> {
#[pin]
sink: Si,
buf: VecDeque<Item>,
// Track capacity separately from the `VecDeque`, which may be rounded up
capacity: usize,
}
}
impl<Si: Sink<Item>, Item> Buffer<Si, Item> {
pub(super) fn new(sink: Si, capacity: usize) -> Self {
Self { sink, buf: VecDeque::with_capacity(capacity), capacity }
}
delegate_access_inner!(sink, Si, ());
fn try_empty_buffer(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
let mut this = self.project();
ready!(this.sink.as_mut().poll_ready(cx))?;
while let Some(item) = this.buf.pop_front() {
this.sink.as_mut().start_send(item)?;
if !this.buf.is_empty() {
ready!(this.sink.as_mut().poll_ready(cx))?;
}
}
Poll::Ready(Ok(()))
}
}
// Forwarding impl of Stream from the underlying sink
impl<S, Item> Stream for Buffer<S, Item>
where
S: Sink<Item> + Stream,
{
type Item = S::Item;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
self.project().sink.poll_next(cx)
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.sink.size_hint()
}
}
impl<S, Item> FusedStream for Buffer<S, Item>
where
S: Sink<Item> + FusedStream,
{
fn is_terminated(&self) -> bool {
self.sink.is_terminated()
}
}
impl<Si: Sink<Item>, Item> Sink<Item> for Buffer<Si, Item> {
type Error = Si::Error;
fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
if self.capacity == 0 {
return self.project().sink.poll_ready(cx);
}
let _ = self.as_mut().try_empty_buffer(cx)?;
if self.buf.len() >= self.capacity {
Poll::Pending
} else {
Poll::Ready(Ok(()))
}
}
fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
if self.capacity == 0 {
self.project().sink.start_send(item)
} else {
self.project().buf.push_back(item);
Ok(())
}
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().try_empty_buffer(cx))?;
debug_assert!(self.buf.is_empty());
self.project().sink.poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().try_empty_buffer(cx))?;
debug_assert!(self.buf.is_empty());
self.project().sink.poll_close(cx)
}
}
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