1use crate::future::{IntoFuture, TryFutureExt};
2use crate::stream::{Fuse, FuturesUnordered, IntoStream, StreamExt};
3use core::pin::Pin;
4use futures_core::future::TryFuture;
5use futures_core::stream::{Stream, TryStream};
6use futures_core::task::{Context, Poll};
7#[cfg(feature = "sink")]
8use futures_sink::Sink;
9use pin_project_lite::pin_project;
10
11pin_project! {
12 /// Stream for the
13 /// [`try_buffer_unordered`](super::TryStreamExt::try_buffer_unordered) method.
14 #[derive(Debug)]
15 #[must_use = "streams do nothing unless polled"]
16 pub struct TryBufferUnordered<St>
17 where St: TryStream
18 {
19 #[pin]
20 stream: Fuse<IntoStream<St>>,
21 in_progress_queue: FuturesUnordered<IntoFuture<St::Ok>>,
22 max: usize,
23 }
24}
25
26impl<St> TryBufferUnordered<St>
27where
28 St: TryStream,
29 St::Ok: TryFuture,
30{
31 pub(super) fn new(stream: St, n: usize) -> Self {
32 Self {
33 stream: IntoStream::new(stream).fuse(),
34 in_progress_queue: FuturesUnordered::new(),
35 max: n,
36 }
37 }
38
39 delegate_access_inner!(stream, St, (. .));
40}
41
42impl<St> Stream for TryBufferUnordered<St>
43where
44 St: TryStream,
45 St::Ok: TryFuture<Error = St::Error>,
46{
47 type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
48
49 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
50 let mut this = self.project();
51
52 // First up, try to spawn off as many futures as possible by filling up
53 // our queue of futures. Propagate errors from the stream immediately.
54 while this.in_progress_queue.len() < *this.max {
55 match this.stream.as_mut().poll_next(cx)? {
56 Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut.into_future()),
57 Poll::Ready(None) | Poll::Pending => break,
58 }
59 }
60
61 // Attempt to pull the next value from the in_progress_queue
62 match this.in_progress_queue.poll_next_unpin(cx) {
63 x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
64 Poll::Ready(None) => {}
65 }
66
67 // If more values are still coming from the stream, we're not done yet
68 if this.stream.is_done() {
69 Poll::Ready(None)
70 } else {
71 Poll::Pending
72 }
73 }
74}
75
76// Forwarding impl of Sink from the underlying stream
77#[cfg(feature = "sink")]
78impl<S, Item, E> Sink<Item> for TryBufferUnordered<S>
79where
80 S: TryStream + Sink<Item, Error = E>,
81 S::Ok: TryFuture<Error = E>,
82{
83 type Error = E;
84
85 delegate_sink!(stream, Item);
86}
87