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
121
122
123
124
125
126
127
128
129
130
131
132
133
134

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;

/// Sink for the [`buffer`](super::SinkExt::buffer) method.
#[derive(Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct Buffer<Si: Sink<Item>, Item> {
    sink: Si,
    buf: VecDeque<Item>,

    // Track capacity separately from the `VecDeque`, which may be rounded up
    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,
        }
    }

    /// Get a shared reference to the inner sink.
    pub fn get_ref(&self) -> &Si {
        &self.sink
    }

    /// Get a mutable reference to the inner sink.
    pub fn get_mut(&mut self) -> &mut Si {
        &mut self.sink
    }

    /// Get a pinned mutable reference to the inner sink.
    pub fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut Si> {
        self.sink()
    }

    /// Consumes this combinator, returning the underlying sink.
    ///
    /// Note that this may discard intermediate state of this combinator, so
    /// care should be taken to avoid losing resources when this is called.
    pub fn into_inner(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(()))
    }
}

// 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.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)
    }
}