blob: 9feccb74ba091f8680700adb50ff38c228ade339 [file] [log] [blame]
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
use std::collections::VecDeque;
use std::marker::Unpin;
use std::pin::Pin;
/// Sink for the `Sink::buffer` combinator, which buffers up to some fixed
/// number of values when the underlying sink is unable to accept them.
#[derive(Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct Buffer<Si: Sink> {
sink: Si,
buf: VecDeque<Si::SinkItem>,
// Track capacity separately from the `VecDeque`, which may be rounded up
capacity: usize,
}
impl<Si: Sink + Unpin> Unpin for Buffer<Si> {}
impl<Si: Sink> Buffer<Si> {
unsafe_pinned!(sink: Si);
unsafe_unpinned!(buf: VecDeque<Si::SinkItem>);
unsafe_unpinned!(capacity: usize);
pub(super) fn new(sink: Si, capacity: usize) -> Buffer<Si> {
Buffer {
sink,
buf: VecDeque::with_capacity(capacity),
capacity,
}
}
/// Get a shared reference to the inner sink.
pub fn get_ref(&self) -> &Si {
&self.sink
}
fn try_empty_buffer(
mut self: Pin<&mut Self>,
lw: &LocalWaker
) -> Poll<Result<(), Si::SinkError>> {
try_ready!(self.as_mut().sink().poll_ready(lw));
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(lw));
}
}
Poll::Ready(Ok(()))
}
}
// Forwarding impl of Stream from the underlying sink
impl<S> Stream for Buffer<S> where S: Sink + Stream {
type Item = S::Item;
fn poll_next(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Option<S::Item>> {
self.sink().poll_next(lw)
}
}
impl<Si: Sink> Sink for Buffer<Si> {
type SinkItem = Si::SinkItem;
type SinkError = Si::SinkError;
fn poll_ready(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Result<(), Self::SinkError>> {
if self.capacity == 0 {
return self.as_mut().sink().poll_ready(lw);
}
if let Poll::Ready(Err(e)) = self.as_mut().try_empty_buffer(lw) {
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: Self::SinkItem,
) -> 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>,
lw: &LocalWaker,
) -> Poll<Result<(), Self::SinkError>> {
try_ready!(self.as_mut().try_empty_buffer(lw));
debug_assert!(self.as_mut().buf().is_empty());
self.as_mut().sink().poll_flush(lw)
}
fn poll_close(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Result<(), Self::SinkError>> {
try_ready!(self.as_mut().try_empty_buffer(lw));
debug_assert!(self.as_mut().buf().is_empty());
self.as_mut().sink().poll_close(lw)
}
}