futures_util/stream/stream/
ready_chunks.rs

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1use crate::stream::{Fuse, StreamExt};
2use alloc::vec::Vec;
3use core::pin::Pin;
4use futures_core::stream::{FusedStream, Stream};
5use futures_core::task::{Context, Poll};
6#[cfg(feature = "sink")]
7use futures_sink::Sink;
8use pin_project_lite::pin_project;
9
10pin_project! {
11    /// Stream for the [`ready_chunks`](super::StreamExt::ready_chunks) method.
12    #[derive(Debug)]
13    #[must_use = "streams do nothing unless polled"]
14    pub struct ReadyChunks<St: Stream> {
15        #[pin]
16        stream: Fuse<St>,
17        cap: usize, // https://github.com/rust-lang/futures-rs/issues/1475
18    }
19}
20
21impl<St: Stream> ReadyChunks<St> {
22    pub(super) fn new(stream: St, capacity: usize) -> Self {
23        assert!(capacity > 0);
24
25        Self { stream: stream.fuse(), cap: capacity }
26    }
27
28    delegate_access_inner!(stream, St, (.));
29}
30
31impl<St: Stream> Stream for ReadyChunks<St> {
32    type Item = Vec<St::Item>;
33
34    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
35        let mut this = self.project();
36
37        let mut items: Vec<St::Item> = Vec::new();
38
39        loop {
40            match this.stream.as_mut().poll_next(cx) {
41                // Flush all collected data if underlying stream doesn't contain
42                // more ready values
43                Poll::Pending => {
44                    return if items.is_empty() { Poll::Pending } else { Poll::Ready(Some(items)) }
45                }
46
47                // Push the ready item into the buffer and check whether it is full.
48                // If so, replace our buffer with a new and empty one and return
49                // the full one.
50                Poll::Ready(Some(item)) => {
51                    if items.is_empty() {
52                        items.reserve(*this.cap);
53                    }
54                    items.push(item);
55                    if items.len() >= *this.cap {
56                        return Poll::Ready(Some(items));
57                    }
58                }
59
60                // Since the underlying stream ran out of values, return what we
61                // have buffered, if we have anything.
62                Poll::Ready(None) => {
63                    let last = if items.is_empty() { None } else { Some(items) };
64
65                    return Poll::Ready(last);
66                }
67            }
68        }
69    }
70
71    fn size_hint(&self) -> (usize, Option<usize>) {
72        let (lower, upper) = self.stream.size_hint();
73        let lower = lower / self.cap;
74        (lower, upper)
75    }
76}
77
78impl<St: Stream> FusedStream for ReadyChunks<St> {
79    fn is_terminated(&self) -> bool {
80        self.stream.is_terminated()
81    }
82}
83
84// Forwarding impl of Sink from the underlying stream
85#[cfg(feature = "sink")]
86impl<S, Item> Sink<Item> for ReadyChunks<S>
87where
88    S: Stream + Sink<Item>,
89{
90    type Error = S::Error;
91
92    delegate_sink!(stream, Item);
93}
futures_util/stream/stream/ready_chunks.rs

futures_util/stream/stream/
ready_chunks.rs
