futures_util/stream/try_stream/
try_filter.rs

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}
futures_util/stream/try_stream/try_filter.rs

futures_util/stream/try_stream/
try_filter.rs
