1use alloc::collections::VecDeque;
2use core::pin::Pin;
3use futures_core::ready;
4use futures_core::stream::{FusedStream, Stream};
5use futures_core::task::{Context, Poll};
6use futures_sink::Sink;
7use pin_project_lite::pin_project;
8
9pin_project! {
10 /// Sink for the [`buffer`](super::SinkExt::buffer) method.
11 #[derive(Debug)]
12 #[must_use = "sinks do nothing unless polled"]
13 pub struct Buffer<Si, Item> {
14 #[pin]
15 sink: Si,
16 buf: VecDeque<Item>,
17
18 // Track capacity separately from the `VecDeque`, which may be rounded up
19 capacity: usize,
20 }
21}
22
23impl<Si: Sink<Item>, Item> Buffer<Si, Item> {
24 pub(super) fn new(sink: Si, capacity: usize) -> Self {
25 Self { sink, buf: VecDeque::with_capacity(capacity), capacity }
26 }
27
28 delegate_access_inner!(sink, Si, ());
29
30 fn try_empty_buffer(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
31 let mut this: Projection<'_, Si, Item> = self.project();
32 ready!(this.sink.as_mut().poll_ready(cx))?;
33 while let Some(item: Item) = this.buf.pop_front() {
34 this.sink.as_mut().start_send(item)?;
35 if !this.buf.is_empty() {
36 ready!(this.sink.as_mut().poll_ready(cx))?;
37 }
38 }
39 Poll::Ready(Ok(()))
40 }
41}
42
43// Forwarding impl of Stream from the underlying sink
44impl<S, Item> Stream for Buffer<S, Item>
45where
46 S: Sink<Item> + Stream,
47{
48 type Item = S::Item;
49
50 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
51 self.project().sink.poll_next(cx)
52 }
53
54 fn size_hint(&self) -> (usize, Option<usize>) {
55 self.sink.size_hint()
56 }
57}
58
59impl<S, Item> FusedStream for Buffer<S, Item>
60where
61 S: Sink<Item> + FusedStream,
62{
63 fn is_terminated(&self) -> bool {
64 self.sink.is_terminated()
65 }
66}
67
68impl<Si: Sink<Item>, Item> Sink<Item> for Buffer<Si, Item> {
69 type Error = Si::Error;
70
71 fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
72 if self.capacity == 0 {
73 return self.project().sink.poll_ready(cx);
74 }
75
76 let _ = self.as_mut().try_empty_buffer(cx)?;
77
78 if self.buf.len() >= self.capacity {
79 Poll::Pending
80 } else {
81 Poll::Ready(Ok(()))
82 }
83 }
84
85 fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
86 if self.capacity == 0 {
87 self.project().sink.start_send(item)
88 } else {
89 self.project().buf.push_back(item);
90 Ok(())
91 }
92 }
93
94 fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
95 ready!(self.as_mut().try_empty_buffer(cx))?;
96 debug_assert!(self.buf.is_empty());
97 self.project().sink.poll_flush(cx)
98 }
99
100 fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
101 ready!(self.as_mut().try_empty_buffer(cx))?;
102 debug_assert!(self.buf.is_empty());
103 self.project().sink.poll_close(cx)
104 }
105}
106