1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_project::{pin_project, project};
use core::pin::Pin;
use alloc::collections::VecDeque;

/// Sink for the [`buffer`](super::SinkExt::buffer) method.
#[pin_project]
#[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 {
        Buffer {
            sink,
            buf: VecDeque::with_capacity(capacity),
            capacity,
        }
    }

    delegate_access_inner!(sink, Si, ());

    #[project]
    fn try_empty_buffer(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Result<(), Si::Error>> {
        #[project]
        let Buffer { mut sink, buf, .. } = self.project();
        ready!(sink.as_mut().poll_ready(cx))?;
        while let Some(item) = buf.pop_front() {
            sink.as_mut().start_send(item)?;
            if !buf.is_empty() {
                ready!(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(())
        }
    }

    #[allow(clippy::debug_assert_with_mut_call)]
    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)
    }

    #[allow(clippy::debug_assert_with_mut_call)]
    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)
    }
}