1use core::fmt;
2use core::marker::PhantomData;
3use core::pin::Pin;
4use futures_core::ready;
5use futures_core::stream::{FusedStream, Stream};
6use futures_core::task::{Context, Poll};
7use futures_sink::Sink;
8use pin_project_lite::pin_project;
9
10pin_project! {
11 /// Sink for the [`with_flat_map`](super::SinkExt::with_flat_map) method.
12 #[must_use = "sinks do nothing unless polled"]
13 pub struct WithFlatMap<Si, Item, U, St, F> {
14 #[pin]
15 sink: Si,
16 f: F,
17 #[pin]
18 stream: Option<St>,
19 buffer: Option<Item>,
20 _marker: PhantomData<fn(U)>,
21 }
22}
23
24impl<Si, Item, U, St, F> fmt::Debug for WithFlatMap<Si, Item, U, St, F>
25where
26 Si: fmt::Debug,
27 St: fmt::Debug,
28 Item: fmt::Debug,
29{
30 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
31 f&mut DebugStruct<'_, '_>.debug_struct("WithFlatMap")
32 .field("sink", &self.sink)
33 .field("stream", &self.stream)
34 .field(name:"buffer", &self.buffer)
35 .finish()
36 }
37}
38
39impl<Si, Item, U, St, F> WithFlatMap<Si, Item, U, St, F>
40where
41 Si: Sink<Item>,
42 F: FnMut(U) -> St,
43 St: Stream<Item = Result<Item, Si::Error>>,
44{
45 pub(super) fn new(sink: Si, f: F) -> Self {
46 Self { sink, f, stream: None, buffer: None, _marker: PhantomData }
47 }
48
49 delegate_access_inner!(sink, Si, ());
50
51 fn try_empty_stream(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Si::Error>> {
52 let mut this = self.project();
53
54 if this.buffer.is_some() {
55 ready!(this.sink.as_mut().poll_ready(cx))?;
56 let item = this.buffer.take().unwrap();
57 this.sink.as_mut().start_send(item)?;
58 }
59 if let Some(mut some_stream) = this.stream.as_mut().as_pin_mut() {
60 while let Some(item) = ready!(some_stream.as_mut().poll_next(cx)?) {
61 match this.sink.as_mut().poll_ready(cx)? {
62 Poll::Ready(()) => this.sink.as_mut().start_send(item)?,
63 Poll::Pending => {
64 *this.buffer = Some(item);
65 return Poll::Pending;
66 }
67 };
68 }
69 }
70 this.stream.set(None);
71 Poll::Ready(Ok(()))
72 }
73}
74
75// Forwarding impl of Stream from the underlying sink
76impl<S, Item, U, St, F> Stream for WithFlatMap<S, Item, U, St, F>
77where
78 S: Stream + Sink<Item>,
79 F: FnMut(U) -> St,
80 St: Stream<Item = Result<Item, S::Error>>,
81{
82 type Item = S::Item;
83
84 delegate_stream!(sink);
85}
86
87impl<S, Item, U, St, F> FusedStream for WithFlatMap<S, Item, U, St, F>
88where
89 S: FusedStream + Sink<Item>,
90 F: FnMut(U) -> St,
91 St: Stream<Item = Result<Item, S::Error>>,
92{
93 fn is_terminated(&self) -> bool {
94 self.sink.is_terminated()
95 }
96}
97
98impl<Si, Item, U, St, F> Sink<U> for WithFlatMap<Si, Item, U, St, F>
99where
100 Si: Sink<Item>,
101 F: FnMut(U) -> St,
102 St: Stream<Item = Result<Item, Si::Error>>,
103{
104 type Error = Si::Error;
105
106 fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
107 self.try_empty_stream(cx)
108 }
109
110 fn start_send(self: Pin<&mut Self>, item: U) -> Result<(), Self::Error> {
111 let mut this = self.project();
112
113 assert!(this.stream.is_none());
114 this.stream.set(Some((this.f)(item)));
115 Ok(())
116 }
117
118 fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
119 ready!(self.as_mut().try_empty_stream(cx)?);
120 self.project().sink.poll_flush(cx)
121 }
122
123 fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
124 ready!(self.as_mut().try_empty_stream(cx)?);
125 self.project().sink.poll_close(cx)
126 }
127}
128