futures_util/sink/
buffer.rs

1use std::collections::VecDeque;
2
3use futures_core::{Poll, Async, Stream};
4use futures_core::task;
5use futures_sink::Sink;
6
7/// Sink for the `Sink::buffer` combinator, which buffers up to some fixed
8/// number of values when the underlying sink is unable to accept them.
9#[derive(Debug)]
10#[must_use = "sinks do nothing unless polled"]
11pub struct Buffer<S: Sink> {
12    sink: S,
13    buf: VecDeque<S::SinkItem>,
14
15    // Track capacity separately from the `VecDeque`, which may be rounded up
16    cap: usize,
17}
18
19pub fn new<S: Sink>(sink: S, amt: usize) -> Buffer<S> {
20    Buffer {
21        sink: sink,
22        buf: VecDeque::with_capacity(amt),
23        cap: amt,
24    }
25}
26
27impl<S: Sink> Buffer<S> {
28    /// Get a shared reference to the inner sink.
29    pub fn get_ref(&self) -> &S {
30        &self.sink
31    }
32
33    /// Get a mutable reference to the inner sink.
34    pub fn get_mut(&mut self) -> &mut S {
35        &mut self.sink
36    }
37
38    /// Consumes this combinator, returning the underlying sink.
39    ///
40    /// Note that this may discard intermediate state of this combinator, so
41    /// care should be taken to avoid losing resources when this is called.
42    pub fn into_inner(self) -> S {
43        self.sink
44    }
45
46    fn try_empty_buffer(&mut self, cx: &mut task::Context) -> Poll<(), S::SinkError> {
47        try_ready!(self.sink.poll_ready(cx));
48        while let Some(item) = self.buf.pop_front() {
49            self.sink.start_send(item)?;
50            if self.buf.len() != 0 {
51                try_ready!(self.sink.poll_ready(cx));
52            }
53        }
54        Ok(Async::Ready(()))
55    }
56}
57
58// Forwarding impl of Stream from the underlying sink
59impl<S> Stream for Buffer<S> where S: Sink + Stream {
60    type Item = S::Item;
61    type Error = S::Error;
62
63    fn poll_next(&mut self, cx: &mut task::Context) -> Poll<Option<S::Item>, S::Error> {
64        self.sink.poll_next(cx)
65    }
66}
67
68impl<S: Sink> Sink for Buffer<S> {
69    type SinkItem = S::SinkItem;
70    type SinkError = S::SinkError;
71
72    fn poll_ready(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
73        if self.cap == 0 {
74            return self.sink.poll_ready(cx);
75        }
76
77        self.try_empty_buffer(cx)?;
78
79        Ok(if self.buf.len() >= self.cap {
80            Async::Pending
81        } else {
82            Async::Ready(())
83        })
84    }
85
86    fn start_send(&mut self, item: Self::SinkItem) -> Result<(), Self::SinkError> {
87        if self.cap == 0 {
88            self.sink.start_send(item)
89        } else {
90            self.buf.push_back(item);
91            Ok(())
92        }
93    }
94
95    fn poll_flush(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
96        try_ready!(self.try_empty_buffer(cx));
97        debug_assert!(self.buf.is_empty());
98        self.sink.poll_flush(cx)
99    }
100
101    fn poll_close(&mut self, cx: &mut task::Context) -> Poll<(), Self::SinkError> {
102        try_ready!(self.try_empty_buffer(cx));
103        debug_assert!(self.buf.is_empty());
104        self.sink.poll_close(cx)
105    }
106}
futures_util/sink/buffer.rs

futures_util/sink/
buffer.rs
