1use core::fmt;
2use core::pin::Pin;
3use futures_core::future::TryFuture;
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;
9use pin_project_lite::pin_project;
10
11pin_project! {
12 /// Stream for the [`try_filter_map`](super::TryStreamExt::try_filter_map)
13 /// method.
14 #[must_use = "streams do nothing unless polled"]
15 pub struct TryFilterMap<St, Fut, F> {
16 #[pin]
17 stream: St,
18 f: F,
19 #[pin]
20 pending: Option<Fut>,
21 }
22}
23
24impl<St, Fut, F> fmt::Debug for TryFilterMap<St, Fut, F>
25where
26 St: fmt::Debug,
27 Fut: fmt::Debug,
28{
29 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
30 f.debug_struct("TryFilterMap")
31 .field("stream", &self.stream)
32 .field("pending", &self.pending)
33 .finish()
34 }
35}
36
37impl<St, Fut, F> TryFilterMap<St, Fut, F> {
38 pub(super) fn new(stream: St, f: F) -> Self {
39 Self { stream, f, pending: None }
40 }
41
42 delegate_access_inner!(stream, St, ());
43}
44
45impl<St, Fut, F, T> FusedStream for TryFilterMap<St, Fut, F>
46where
47 St: TryStream + FusedStream,
48 Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
49 F: FnMut(St::Ok) -> Fut,
50{
51 fn is_terminated(&self) -> bool {
52 self.pending.is_none() && self.stream.is_terminated()
53 }
54}
55
56impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>
57where
58 St: TryStream,
59 Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
60 F: FnMut(St::Ok) -> Fut,
61{
62 type Item = Result<T, St::Error>;
63
64 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
65 let mut this = self.project();
66
67 Poll::Ready(loop {
68 if let Some(p) = this.pending.as_mut().as_pin_mut() {
69 // We have an item in progress, poll that until it's done
70 let res = ready!(p.try_poll(cx));
71 this.pending.set(None);
72 let item = res?;
73 if item.is_some() {
74 break item.map(Ok);
75 }
76 } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
77 // No item in progress, but the stream is still going
78 this.pending.set(Some((this.f)(item)));
79 } else {
80 // The stream is done
81 break None;
82 }
83 })
84 }
85
86 fn size_hint(&self) -> (usize, Option<usize>) {
87 let pending_len = usize::from(self.pending.is_some());
88 let (_, upper) = self.stream.size_hint();
89 let upper = match upper {
90 Some(x) => x.checked_add(pending_len),
91 None => None,
92 };
93 (0, upper) // can't know a lower bound, due to the predicate
94 }
95}
96
97// Forwarding impl of Sink from the underlying stream
98#[cfg(feature = "sink")]
99impl<S, Fut, F, Item> Sink<Item> for TryFilterMap<S, Fut, F>
100where
101 S: Sink<Item>,
102{
103 type Error = S::Error;
104
105 delegate_sink!(stream, Item);
106}
107