1use crate::future::{IntoFuture, TryFutureExt};
2use crate::stream::{Fuse, FuturesOrdered, 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 [`try_buffered`](super::TryStreamExt::try_buffered) method.
13 #[derive(Debug)]
14 #[must_use = "streams do nothing unless polled"]
15 pub struct TryBuffered<St>
16 where
17 St: TryStream,
18 St::Ok: TryFuture,
19 {
20 #[pin]
21 stream: Fuse<IntoStream<St>>,
22 in_progress_queue: FuturesOrdered<IntoFuture<St::Ok>>,
23 max: usize,
24 }
25}
26
27impl<St> TryBuffered<St>
28where
29 St: TryStream,
30 St::Ok: TryFuture,
31{
32 pub(super) fn new(stream: St, n: usize) -> Self {
33 Self {
34 stream: IntoStream::new(stream).fuse(),
35 in_progress_queue: FuturesOrdered::new(),
36 max: n,
37 }
38 }
39
40 delegate_access_inner!(stream, St, (. .));
41}
42
43impl<St> Stream for TryBuffered<St>
44where
45 St: TryStream,
46 St::Ok: TryFuture<Error = St::Error>,
47{
48 type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
49
50 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
51 let mut this = self.project();
52
53 // First up, try to spawn off as many futures as possible by filling up
54 // our queue of futures. Propagate errors from the stream immediately.
55 while this.in_progress_queue.len() < *this.max {
56 match this.stream.as_mut().poll_next(cx)? {
57 Poll::Ready(Some(fut)) => this.in_progress_queue.push_back(fut.into_future()),
58 Poll::Ready(None) | Poll::Pending => break,
59 }
60 }
61
62 // Attempt to pull the next value from the in_progress_queue
63 match this.in_progress_queue.poll_next_unpin(cx) {
64 x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
65 Poll::Ready(None) => {}
66 }
67
68 // If more values are still coming from the stream, we're not done yet
69 if this.stream.is_done() {
70 Poll::Ready(None)
71 } else {
72 Poll::Pending
73 }
74 }
75}
76
77// Forwarding impl of Sink from the underlying stream
78#[cfg(feature = "sink")]
79impl<S, Item, E> Sink<Item> for TryBuffered<S>
80where
81 S: TryStream + Sink<Item, Error = E>,
82 S::Ok: TryFuture<Error = E>,
83{
84 type Error = E;
85
86 delegate_sink!(stream, Item);
87}
88