1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164

use core::fmt;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};

/// Stream for the [`take_while`](super::StreamExt::take_while) method.
#[must_use = "streams do nothing unless polled"]
pub struct TakeWhile<St: Stream , Fut, F> {
    stream: St,
    f: F,
    pending_fut: Option<Fut>,
    pending_item: Option<St::Item>,
    done_taking: bool,
}

impl<St: Unpin + Stream, Fut: Unpin, F> Unpin for TakeWhile<St, Fut, F> {}

impl<St, Fut, F> fmt::Debug for TakeWhile<St, Fut, F>
where
    St: Stream + fmt::Debug,
    St::Item: fmt::Debug,
    Fut: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("TakeWhile")
            .field("stream", &self.stream)
            .field("pending_fut", &self.pending_fut)
            .field("pending_item", &self.pending_item)
            .field("done_taking", &self.done_taking)
            .finish()
    }
}

impl<St: Stream, Fut, F> TakeWhile<St, Fut, F> {
    unsafe_pinned!(stream: St);
    unsafe_unpinned!(f: F);
    unsafe_pinned!(pending_fut: Option<Fut>);
    unsafe_unpinned!(pending_item: Option<St::Item>);
    unsafe_unpinned!(done_taking: bool);
}

impl<St, Fut, F> TakeWhile<St, Fut, F>
    where St: Stream,
          F: FnMut(&St::Item) -> Fut,
          Fut: Future<Output = bool>,
{
    pub(super) fn new(stream: St, f: F) -> TakeWhile<St, Fut, F> {
        TakeWhile {
            stream,
            f,
            pending_fut: None,
            pending_item: None,
            done_taking: false,
        }
    }

    /// Acquires a reference to the underlying stream that this combinator is
    /// pulling from.
    pub fn get_ref(&self) -> &St {
        &self.stream
    }

    /// Acquires a mutable reference to the underlying stream that this
    /// combinator is pulling from.
    ///
    /// Note that care must be taken to avoid tampering with the state of the
    /// stream which may otherwise confuse this combinator.
    pub fn get_mut(&mut self) -> &mut St {
        &mut self.stream
    }

    /// Acquires a pinned mutable reference to the underlying stream that this
    /// combinator is pulling from.
    ///
    /// Note that care must be taken to avoid tampering with the state of the
    /// stream which may otherwise confuse this combinator.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
        self.stream()
    }

    /// Consumes this combinator, returning the underlying stream.
    ///
    /// Note that this may discard intermediate state of this combinator, so
    /// care should be taken to avoid losing resources when this is called.
    pub fn into_inner(self) -> St {
        self.stream
    }
}

impl<St, Fut, F> Stream for TakeWhile<St, Fut, F>
    where St: Stream,
          F: FnMut(&St::Item) -> Fut,
          Fut: Future<Output = bool>,
{
    type Item = St::Item;

    fn poll_next(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<St::Item>> {
        if self.done_taking {
            return Poll::Ready(None);
        }

        if self.pending_item.is_none() {
            let item = match ready!(self.as_mut().stream().poll_next(cx)) {
                Some(e) => e,
                None => return Poll::Ready(None),
            };
            let fut = (self.as_mut().f())(&item);
            self.as_mut().pending_fut().set(Some(fut));
            *self.as_mut().pending_item() = Some(item);
        }

        let take = ready!(self.as_mut().pending_fut().as_pin_mut().unwrap().poll(cx));
        self.as_mut().pending_fut().set(None);
        let item = self.as_mut().pending_item().take().unwrap();

        if take {
            Poll::Ready(Some(item))
        } else {
            *self.as_mut().done_taking() = true;
            Poll::Ready(None)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        if self.done_taking {
            return (0, Some(0));
        }

        let pending_len = if self.pending_item.is_some() { 1 } else { 0 };
        let (_, upper) = self.stream.size_hint();
        let upper = match upper {
            Some(x) => x.checked_add(pending_len),
            None => None,
        };
        (0, upper) // can't know a lower bound, due to the predicate
    }
}

impl<St, Fut, F> FusedStream for TakeWhile<St, Fut, F>
    where St: FusedStream,
          F: FnMut(&St::Item) -> Fut,
          Fut: Future<Output = bool>,
{
    fn is_terminated(&self) -> bool {
        self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
    }
}

// Forwarding impl of Sink from the underlying stream
#[cfg(feature = "sink")]
impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F>
    where S: Stream + Sink<Item>,
{
    type Error = S::Error;

    delegate_sink!(stream, Item);
}