1use core::marker::PhantomData;
2use core::pin::Pin;
3
4use futures_core::ready;
5use futures_core::stream::{FusedStream, Stream, TryStream};
6use futures_core::task::{Context, Poll};
7#[cfg(feature = "sink")]
8use futures_sink::Sink;
9
10use pin_project_lite::pin_project;
11
12use crate::future::Either;
13use crate::stream::stream::flatten_unordered::{
14 FlattenUnorderedWithFlowController, FlowController, FlowStep,
15};
16use crate::stream::IntoStream;
17use crate::TryStreamExt;
18
19delegate_all!(
20 /// Stream for the [`try_flatten_unordered`](super::TryStreamExt::try_flatten_unordered) method.
21 TryFlattenUnordered<St>(
22 FlattenUnorderedWithFlowController<NestedTryStreamIntoEitherTryStream<St>, PropagateBaseStreamError<St>>
23 ): Debug + Sink + Stream + FusedStream + AccessInner[St, (. .)]
24 + New[
25 |stream: St, limit: impl Into<Option<usize>>|
26 FlattenUnorderedWithFlowController::new(
27 NestedTryStreamIntoEitherTryStream::new(stream),
28 limit.into()
29 )
30 ]
31 where
32 St: TryStream,
33 St::Ok: TryStream,
34 St::Ok: Unpin,
35 <St::Ok as TryStream>::Error: From<St::Error>
36);
37
38pin_project! {
39 /// Emits either successful streams or single-item streams containing the underlying errors.
40 /// This's a wrapper for `FlattenUnordered` to reuse its logic over `TryStream`.
41 #[derive(Debug)]
42 #[must_use = "streams do nothing unless polled"]
43 pub struct NestedTryStreamIntoEitherTryStream<St>
44 where
45 St: TryStream,
46 St::Ok: TryStream,
47 St::Ok: Unpin,
48 <St::Ok as TryStream>::Error: From<St::Error>
49 {
50 #[pin]
51 stream: St
52 }
53}
54
55impl<St> NestedTryStreamIntoEitherTryStream<St>
56where
57 St: TryStream,
58 St::Ok: TryStream + Unpin,
59 <St::Ok as TryStream>::Error: From<St::Error>,
60{
61 fn new(stream: St) -> Self {
62 Self { stream }
63 }
64
65 delegate_access_inner!(stream, St, ());
66}
67
68/// Emits a single item immediately, then stream will be terminated.
69#[derive(Debug, Clone)]
70pub struct Single<T>(Option<T>);
71
72impl<T> Single<T> {
73 /// Constructs new `Single` with the given value.
74 fn new(val: T) -> Self {
75 Self(Some(val))
76 }
77
78 /// Attempts to take inner item immediately. Will always succeed if the stream isn't terminated.
79 fn next_immediate(&mut self) -> Option<T> {
80 self.0.take()
81 }
82}
83
84impl<T> Unpin for Single<T> {}
85
86impl<T> Stream for Single<T> {
87 type Item = T;
88
89 fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
90 Poll::Ready(self.0.take())
91 }
92
93 fn size_hint(&self) -> (usize, Option<usize>) {
94 self.0.as_ref().map_or((0, Some(0)), |_| (1, Some(1)))
95 }
96}
97
98/// Immediately propagates errors occurred in the base stream.
99#[derive(Debug, Clone, Copy)]
100pub struct PropagateBaseStreamError<St>(PhantomData<St>);
101
102type BaseStreamItem<St> = <NestedTryStreamIntoEitherTryStream<St> as Stream>::Item;
103type InnerStreamItem<St> = <BaseStreamItem<St> as Stream>::Item;
104
105impl<St> FlowController<BaseStreamItem<St>, InnerStreamItem<St>> for PropagateBaseStreamError<St>
106where
107 St: TryStream,
108 St::Ok: TryStream + Unpin,
109 <St::Ok as TryStream>::Error: From<St::Error>,
110{
111 fn next_step(item: BaseStreamItem<St>) -> FlowStep<BaseStreamItem<St>, InnerStreamItem<St>> {
112 match item {
113 // A new successful inner stream received
114 st: Either>, …> @ Either::Left(_) => FlowStep::Continue(st),
115 // An error encountered
116 Either::Right(mut err: Single as TryStream>::Ok, …>>) => FlowStep::Return(err.next_immediate().unwrap()),
117 }
118 }
119}
120
121type SingleStreamResult<St> = Single<Result<<St as TryStream>::Ok, <St as TryStream>::Error>>;
122
123impl<St> Stream for NestedTryStreamIntoEitherTryStream<St>
124where
125 St: TryStream,
126 St::Ok: TryStream + Unpin,
127 <St::Ok as TryStream>::Error: From<St::Error>,
128{
129 // Item is either an inner stream or a stream containing a single error.
130 // This will allow using `Either`'s `Stream` implementation as both branches are actually streams of `Result`'s.
131 type Item = Either<IntoStream<St::Ok>, SingleStreamResult<St::Ok>>;
132
133 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
134 let item = ready!(self.project().stream.try_poll_next(cx));
135
136 let out = match item {
137 Some(res) => match res {
138 // Emit successful inner stream as is
139 Ok(stream) => Either::Left(stream.into_stream()),
140 // Wrap an error into a stream containing a single item
141 err @ Err(_) => {
142 let res = err.map(|_: St::Ok| unreachable!()).map_err(Into::into);
143
144 Either::Right(Single::new(res))
145 }
146 },
147 None => return Poll::Ready(None),
148 };
149
150 Poll::Ready(Some(out))
151 }
152}
153
154impl<St> FusedStream for NestedTryStreamIntoEitherTryStream<St>
155where
156 St: TryStream + FusedStream,
157 St::Ok: TryStream + Unpin,
158 <St::Ok as TryStream>::Error: From<St::Error>,
159{
160 fn is_terminated(&self) -> bool {
161 self.stream.is_terminated()
162 }
163}
164
165// Forwarding impl of Sink from the underlying stream
166#[cfg(feature = "sink")]
167impl<St, Item> Sink<Item> for NestedTryStreamIntoEitherTryStream<St>
168where
169 St: TryStream + Sink<Item>,
170 St::Ok: TryStream + Unpin,
171 <St::Ok as TryStream>::Error: From<<St as TryStream>::Error>,
172{
173 type Error = <St as Sink<Item>>::Error;
174
175 delegate_sink!(stream, Item);
176}
177