1use core::fmt;
2use core::pin::Pin;
3use futures_core::future::Future;
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`](super::TryStreamExt::try_filter)
13 /// method.
14 #[must_use = "streams do nothing unless polled"]
15 pub struct TryFilter<St, Fut, F>
16 where St: TryStream
17 {
18 #[pin]
19 stream: St,
20 f: F,
21 #[pin]
22 pending_fut: Option<Fut>,
23 pending_item: Option<St::Ok>,
24 }
25}
26
27impl<St, Fut, F> fmt::Debug for TryFilter<St, Fut, F>
28where
29 St: TryStream + fmt::Debug,
30 St::Ok: fmt::Debug,
31 Fut: fmt::Debug,
32{
33 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
34 f.debug_struct("TryFilter")
35 .field("stream", &self.stream)
36 .field("pending_fut", &self.pending_fut)
37 .field("pending_item", &self.pending_item)
38 .finish()
39 }
40}
41
42impl<St, Fut, F> TryFilter<St, Fut, F>
43where
44 St: TryStream,
45{
46 pub(super) fn new(stream: St, f: F) -> Self {
47 Self { stream, f, pending_fut: None, pending_item: None }
48 }
49
50 delegate_access_inner!(stream, St, ());
51}
52
53impl<St, Fut, F> FusedStream for TryFilter<St, Fut, F>
54where
55 St: TryStream + FusedStream,
56 F: FnMut(&St::Ok) -> Fut,
57 Fut: Future<Output = bool>,
58{
59 fn is_terminated(&self) -> bool {
60 self.pending_fut.is_none() && self.stream.is_terminated()
61 }
62}
63
64impl<St, Fut, F> Stream for TryFilter<St, Fut, F>
65where
66 St: TryStream,
67 Fut: Future<Output = bool>,
68 F: FnMut(&St::Ok) -> Fut,
69{
70 type Item = Result<St::Ok, St::Error>;
71
72 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
73 let mut this = self.project();
74
75 Poll::Ready(loop {
76 if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
77 let res = ready!(fut.poll(cx));
78 this.pending_fut.set(None);
79 if res {
80 break this.pending_item.take().map(Ok);
81 }
82 *this.pending_item = None;
83 } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
84 this.pending_fut.set(Some((this.f)(&item)));
85 *this.pending_item = Some(item);
86 } else {
87 break None;
88 }
89 })
90 }
91
92 fn size_hint(&self) -> (usize, Option<usize>) {
93 let pending_len = usize::from(self.pending_fut.is_some());
94 let (_, upper) = self.stream.size_hint();
95 let upper = match upper {
96 Some(x) => x.checked_add(pending_len),
97 None => None,
98 };
99 (0, upper) // can't know a lower bound, due to the predicate
100 }
101}
102
103// Forwarding impl of Sink from the underlying stream
104#[cfg(feature = "sink")]
105impl<S, Fut, F, Item, E> Sink<Item> for TryFilter<S, Fut, F>
106where
107 S: TryStream + Sink<Item, Error = E>,
108{
109 type Error = E;
110
111 delegate_sink!(stream, Item);
112}
113