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use futures_core::stream::Stream;
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
use core::pin::Pin;
use alloc::collections::VecDeque;
#[derive(Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct Buffer<Si: Sink<Item>, Item> {
sink: Si,
buf: VecDeque<Item>,
capacity: usize,
}
impl<Si: Sink<Item> + Unpin, Item> Unpin for Buffer<Si, Item> {}
impl<Si: Sink<Item>, Item> Buffer<Si, Item> {
unsafe_pinned!(sink: Si);
unsafe_unpinned!(buf: VecDeque<Item>);
unsafe_unpinned!(capacity: usize);
pub(super) fn new(sink: Si, capacity: usize) -> Self {
Buffer {
sink,
buf: VecDeque::with_capacity(capacity),
capacity,
}
}
pub fn get_ref(&self) -> &Si {
&self.sink
}
fn try_empty_buffer(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), Si::SinkError>> {
try_ready!(self.as_mut().sink().poll_ready(cx));
while let Some(item) = self.as_mut().buf().pop_front() {
if let Err(e) = self.as_mut().sink().start_send(item) {
return Poll::Ready(Err(e));
}
if !self.buf.is_empty() {
try_ready!(self.as_mut().sink().poll_ready(cx));
}
}
Poll::Ready(Ok(()))
}
}
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.sink().poll_next(cx)
}
}
impl<Si: Sink<Item>, Item> Sink<Item> for Buffer<Si, Item> {
type SinkError = Si::SinkError;
fn poll_ready(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), Self::SinkError>> {
if self.capacity == 0 {
return self.as_mut().sink().poll_ready(cx);
}
if let Poll::Ready(Err(e)) = self.as_mut().try_empty_buffer(cx) {
return Poll::Ready(Err(e));
}
if self.buf.len() >= self.capacity {
Poll::Pending
} else {
Poll::Ready(Ok(()))
}
}
fn start_send(
mut self: Pin<&mut Self>,
item: Item,
) -> Result<(), Self::SinkError> {
if self.capacity == 0 {
self.as_mut().sink().start_send(item)
} else {
self.as_mut().buf().push_back(item);
Ok(())
}
}
fn poll_flush(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), Self::SinkError>> {
try_ready!(self.as_mut().try_empty_buffer(cx));
debug_assert!(self.as_mut().buf().is_empty());
self.as_mut().sink().poll_flush(cx)
}
fn poll_close(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), Self::SinkError>> {
try_ready!(self.as_mut().try_empty_buffer(cx));
debug_assert!(self.as_mut().buf().is_empty());
self.as_mut().sink().poll_close(cx)
}
}