1use core::pin::Pin;
2use futures_core::ready;
3use futures_core::stream::{FusedStream, Stream, TryStream};
4use futures_core::task::{Context, Poll};
5#[cfg(feature = "sink")]
6use futures_sink::Sink;
7use pin_project_lite::pin_project;
8
9pin_project! {
10 /// Stream for the [`try_flatten`](super::TryStreamExt::try_flatten) method.
11 #[derive(Debug)]
12 #[must_use = "streams do nothing unless polled"]
13 pub struct TryFlatten<St>
14 where
15 St: TryStream,
16 {
17 #[pin]
18 stream: St,
19 #[pin]
20 next: Option<St::Ok>,
21 }
22}
23
24impl<St> TryFlatten<St>
25where
26 St: TryStream,
27 St::Ok: TryStream,
28 <St::Ok as TryStream>::Error: From<St::Error>,
29{
30 pub(super) fn new(stream: St) -> Self {
31 Self { stream, next: None }
32 }
33
34 delegate_access_inner!(stream, St, ());
35}
36
37impl<St> FusedStream for TryFlatten<St>
38where
39 St: TryStream + FusedStream,
40 St::Ok: TryStream,
41 <St::Ok as TryStream>::Error: From<St::Error>,
42{
43 fn is_terminated(&self) -> bool {
44 self.next.is_none() && self.stream.is_terminated()
45 }
46}
47
48impl<St> Stream for TryFlatten<St>
49where
50 St: TryStream,
51 St::Ok: TryStream,
52 <St::Ok as TryStream>::Error: From<St::Error>,
53{
54 type Item = Result<<St::Ok as TryStream>::Ok, <St::Ok as TryStream>::Error>;
55
56 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
57 let mut this: Projection<'_, St> = self.project();
58
59 Poll::Ready(loop {
60 if let Some(s: Pin<&mut impl TryStream + From<…>>) = this.next.as_mut().as_pin_mut() {
61 if let Some(item: > as TryStream>::Ok) = ready!(s.try_poll_next(cx)?) {
62 break Some(Ok(item));
63 } else {
64 this.next.set(None);
65 }
66 } else if let Some(s: impl TryStream + From>) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
67 this.next.set(Some(s));
68 } else {
69 break None;
70 }
71 })
72 }
73}
74
75// Forwarding impl of Sink from the underlying stream
76#[cfg(feature = "sink")]
77impl<S, Item> Sink<Item> for TryFlatten<S>
78where
79 S: TryStream + Sink<Item>,
80{
81 type Error = <S as Sink<Item>>::Error;
82
83 delegate_sink!(stream, Item);
84}
85