futures_util/stream/try_stream/
try_take_while.rs

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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_take_while`](super::TryStreamExt::try_take_while)
13    /// method.
14    #[must_use = "streams do nothing unless polled"]
15    pub struct TryTakeWhile<St, Fut, F>
16    where
17        St: TryStream,
18    {
19        #[pin]
20        stream: St,
21        f: F,
22        #[pin]
23        pending_fut: Option<Fut>,
24        pending_item: Option<St::Ok>,
25        done_taking: bool,
26    }
27}
28
29impl<St, Fut, F> fmt::Debug for TryTakeWhile<St, Fut, F>
30where
31    St: TryStream + fmt::Debug,
32    St::Ok: fmt::Debug,
33    Fut: fmt::Debug,
34{
35    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
36        f.debug_struct("TryTakeWhile")
37            .field("stream", &self.stream)
38            .field("pending_fut", &self.pending_fut)
39            .field("pending_item", &self.pending_item)
40            .field("done_taking", &self.done_taking)
41            .finish()
42    }
43}
44
45impl<St, Fut, F> TryTakeWhile<St, Fut, F>
46where
47    St: TryStream,
48    F: FnMut(&St::Ok) -> Fut,
49    Fut: TryFuture<Ok = bool, Error = St::Error>,
50{
51    pub(super) fn new(stream: St, f: F) -> Self {
52        Self { stream, f, pending_fut: None, pending_item: None, done_taking: false }
53    }
54
55    delegate_access_inner!(stream, St, ());
56}
57
58impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
59where
60    St: TryStream,
61    F: FnMut(&St::Ok) -> Fut,
62    Fut: TryFuture<Ok = bool, Error = St::Error>,
63{
64    type Item = Result<St::Ok, St::Error>;
65
66    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
67        let mut this = self.project();
68
69        if *this.done_taking {
70            return Poll::Ready(None);
71        }
72
73        Poll::Ready(loop {
74            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
75                let res = ready!(fut.try_poll(cx));
76                this.pending_fut.set(None);
77                let take = res?;
78                let item = this.pending_item.take();
79                if take {
80                    break item.map(Ok);
81                } else {
82                    *this.done_taking = true;
83                    break None;
84                }
85            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
86                this.pending_fut.set(Some((this.f)(&item)));
87                *this.pending_item = Some(item);
88            } else {
89                break None;
90            }
91        })
92    }
93
94    fn size_hint(&self) -> (usize, Option<usize>) {
95        if self.done_taking {
96            return (0, Some(0));
97        }
98
99        let pending_len = usize::from(self.pending_item.is_some());
100        let (_, upper) = self.stream.size_hint();
101        let upper = match upper {
102            Some(x) => x.checked_add(pending_len),
103            None => None,
104        };
105        (0, upper) // can't know a lower bound, due to the predicate
106    }
107}
108
109impl<St, Fut, F> FusedStream for TryTakeWhile<St, Fut, F>
110where
111    St: TryStream + FusedStream,
112    F: FnMut(&St::Ok) -> Fut,
113    Fut: TryFuture<Ok = bool, Error = St::Error>,
114{
115    fn is_terminated(&self) -> bool {
116        self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
117    }
118}
119
120// Forwarding impl of Sink from the underlying stream
121#[cfg(feature = "sink")]
122impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F>
123where
124    S: TryStream + Sink<Item, Error = E>,
125{
126    type Error = E;
127
128    delegate_sink!(stream, Item);
129}
futures_util/stream/try_stream/try_take_while.rs

futures_util/stream/try_stream/
try_take_while.rs
