1 use crate::stream::{Fuse, StreamExt};
2 use alloc::vec::Vec;
3 use core::pin::Pin;
4 use futures_core::stream::{FusedStream, Stream};
5 use futures_core::task::{Context, Poll};
6 #[cfg(feature = "sink")]
7 use futures_sink::Sink;
8 use pin_project_lite::pin_project;
9 
10 pin_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 
21 impl<St: Stream> ReadyChunks<St> {
new(stream: St, capacity: usize) -> Self22     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 
31 impl<St: Stream> Stream for ReadyChunks<St> {
32     type Item = Vec<St::Item>;
33 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>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 
size_hint(&self) -> (usize, Option<usize>)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 
78 impl<St: Stream> FusedStream for ReadyChunks<St> {
is_terminated(&self) -> bool79     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")]
86 impl<S, Item> Sink<Item> for ReadyChunks<S>
87 where
88     S: Stream + Sink<Item>,
89 {
90     type Error = S::Error;
91 
92     delegate_sink!(stream, Item);
93 }
94