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}
104