futures_util/stream/try_stream/
try_filter_map.rs

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}
futures_util/stream/try_stream/try_filter_map.rs

futures_util/stream/try_stream/
try_filter_map.rs
