futures_util/stream/stream/
chunks.rs

1use crate::stream::Fuse;
2use alloc::vec::Vec;
3use core::mem;
4use core::pin::Pin;
5use futures_core::ready;
6use futures_core::stream::{FusedStream, Stream};
7use futures_core::task::{Context, Poll};
8#[cfg(feature = "sink")]
9use futures_sink::Sink;
10use pin_project_lite::pin_project;
11
12pin_project! {
13    /// Stream for the [`chunks`](super::StreamExt::chunks) method.
14    #[derive(Debug)]
15    #[must_use = "streams do nothing unless polled"]
16    pub struct Chunks<St: Stream> {
17        #[pin]
18        stream: Fuse<St>,
19        items: Vec<St::Item>,
20        cap: usize, // https://github.com/rust-lang/futures-rs/issues/1475
21    }
22}
23
24impl<St: Stream> Chunks<St> {
25    pub(super) fn new(stream: St, capacity: usize) -> Self {
26        assert!(capacity > 0);
27
28        Self {
29            stream: super::Fuse::new(stream),
30            items: Vec::with_capacity(capacity),
31            cap: capacity,
32        }
33    }
34
35    fn take(self: Pin<&mut Self>) -> Vec<St::Item> {
36        let cap = self.cap;
37        mem::replace(self.project().items, Vec::with_capacity(cap))
38    }
39
40    delegate_access_inner!(stream, St, (.));
41}
42
43impl<St: Stream> Stream for Chunks<St> {
44    type Item = Vec<St::Item>;
45
46    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
47        let mut this = self.as_mut().project();
48        loop {
49            match ready!(this.stream.as_mut().poll_next(cx)) {
50                // Push the item into the buffer and check whether it is full.
51                // If so, replace our buffer with a new and empty one and return
52                // the full one.
53                Some(item) => {
54                    this.items.push(item);
55                    if this.items.len() >= *this.cap {
56                        return Poll::Ready(Some(self.take()));
57                    }
58                }
59
60                // Since the underlying stream ran out of values, return what we
61                // have buffered, if we have anything.
62                None => {
63                    let last = if this.items.is_empty() {
64                        None
65                    } else {
66                        let full_buf = mem::take(this.items);
67                        Some(full_buf)
68                    };
69
70                    return Poll::Ready(last);
71                }
72            }
73        }
74    }
75
76    fn size_hint(&self) -> (usize, Option<usize>) {
77        let chunk_len = usize::from(!self.items.is_empty());
78        let (lower, upper) = self.stream.size_hint();
79        let lower = (lower / self.cap).saturating_add(chunk_len);
80        let upper = match upper {
81            Some(x) => x.checked_add(chunk_len),
82            None => None,
83        };
84        (lower, upper)
85    }
86}
87
88impl<St: FusedStream> FusedStream for Chunks<St> {
89    fn is_terminated(&self) -> bool {
90        self.stream.is_terminated() && self.items.is_empty()
91    }
92}
93
94// Forwarding impl of Sink from the underlying stream
95#[cfg(feature = "sink")]
96impl<S, Item> Sink<Item> for Chunks<S>
97where
98    S: Stream + Sink<Item>,
99{
100    type Error = S::Error;
101
102    delegate_sink!(stream, Item);
103}
futures_util/stream/stream/chunks.rs

futures_util/stream/stream/
chunks.rs
