futures_util/stream/try_stream/
try_buffered.rs

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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}
futures_util/stream/try_stream/try_buffered.rs

futures_util/stream/try_stream/
try_buffered.rs
