futures_util/stream/try_stream/
try_skip_while.rs

Help
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_skip_while`](super::TryStreamExt::try_skip_while)
13    /// method.
14    #[must_use = "streams do nothing unless polled"]
15    pub struct TrySkipWhile<St, Fut, F> where St: TryStream {
16        #[pin]
17        stream: St,
18        f: F,
19        #[pin]
20        pending_fut: Option<Fut>,
21        pending_item: Option<St::Ok>,
22        done_skipping: bool,
23    }
24}
25
26impl<St, Fut, F> fmt::Debug for TrySkipWhile<St, Fut, F>
27where
28    St: TryStream + fmt::Debug,
29    St::Ok: fmt::Debug,
30    Fut: fmt::Debug,
31{
32    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
33        f.debug_struct("TrySkipWhile")
34            .field("stream", &self.stream)
35            .field("pending_fut", &self.pending_fut)
36            .field("pending_item", &self.pending_item)
37            .field("done_skipping", &self.done_skipping)
38            .finish()
39    }
40}
41
42impl<St, Fut, F> TrySkipWhile<St, Fut, F>
43where
44    St: TryStream,
45    F: FnMut(&St::Ok) -> Fut,
46    Fut: TryFuture<Ok = bool, Error = St::Error>,
47{
48    pub(super) fn new(stream: St, f: F) -> Self {
49        Self { stream, f, pending_fut: None, pending_item: None, done_skipping: false }
50    }
51
52    delegate_access_inner!(stream, St, ());
53}
54
55impl<St, Fut, F> Stream for TrySkipWhile<St, Fut, F>
56where
57    St: TryStream,
58    F: FnMut(&St::Ok) -> Fut,
59    Fut: TryFuture<Ok = bool, Error = St::Error>,
60{
61    type Item = Result<St::Ok, St::Error>;
62
63    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
64        let mut this = self.project();
65
66        if *this.done_skipping {
67            return this.stream.try_poll_next(cx);
68        }
69
70        Poll::Ready(loop {
71            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
72                let res = ready!(fut.try_poll(cx));
73                this.pending_fut.set(None);
74                let skipped = res?;
75                let item = this.pending_item.take();
76                if !skipped {
77                    *this.done_skipping = true;
78                    break item.map(Ok);
79                }
80            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
81                this.pending_fut.set(Some((this.f)(&item)));
82                *this.pending_item = Some(item);
83            } else {
84                break None;
85            }
86        })
87    }
88
89    fn size_hint(&self) -> (usize, Option<usize>) {
90        let pending_len = usize::from(self.pending_item.is_some());
91        let (_, upper) = self.stream.size_hint();
92        let upper = match upper {
93            Some(x) => x.checked_add(pending_len),
94            None => None,
95        };
96        (0, upper) // can't know a lower bound, due to the predicate
97    }
98}
99
100impl<St, Fut, F> FusedStream for TrySkipWhile<St, Fut, F>
101where
102    St: TryStream + FusedStream,
103    F: FnMut(&St::Ok) -> Fut,
104    Fut: TryFuture<Ok = bool, Error = St::Error>,
105{
106    fn is_terminated(&self) -> bool {
107        self.pending_item.is_none() && self.stream.is_terminated()
108    }
109}
110
111// Forwarding impl of Sink from the underlying stream
112#[cfg(feature = "sink")]
113impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>
114where
115    S: TryStream + Sink<Item, Error = E>,
116{
117    type Error = E;
118
119    delegate_sink!(stream, Item);
120}
futures_util/stream/try_stream/try_skip_while.rs

futures_util/stream/try_stream/
try_skip_while.rs
