1 use crate::future::{IntoFuture, TryFutureExt};
2 use crate::stream::{Fuse, FuturesUnordered, IntoStream, StreamExt};
3 use core::pin::Pin;
4 use futures_core::future::TryFuture;
5 use futures_core::stream::{Stream, TryStream};
6 use futures_core::task::{Context, Poll};
7 #[cfg(feature = "sink")]
8 use futures_sink::Sink;
9 use pin_project_lite::pin_project;
10 
11 pin_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 
26 impl<St> TryBufferUnordered<St>
27 where
28     St: TryStream,
29     St::Ok: TryFuture,
30 {
new(stream: St, n: usize) -> Self31     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 
42 impl<St> Stream for TryBufferUnordered<St>
43 where
44     St: TryStream,
45     St::Ok: TryFuture<Error = St::Error>,
46 {
47     type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
48 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>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")]
78 impl<S, Item, E> Sink<Item> for TryBufferUnordered<S>
79 where
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