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

use crate::fns::FnMut1;
use core::fmt;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project_lite::pin_project;

pin_project! {
    /// Stream for the [`filter`](super::StreamExt::filter) method.
    #[must_use = "streams do nothing unless polled"]
    pub struct Filter<St, Fut, F>
        where St: Stream,
    {
        #[pin]
        stream: St,
        f: F,
        #[pin]
        pending_fut: Option<Fut>,
        pending_item: Option<St::Item>,
    }
}

impl<St, Fut, F> fmt::Debug for Filter<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("Filter")
            .field("stream", &self.stream)
            .field("pending_fut", &self.pending_fut)
            .field("pending_item", &self.pending_item)
            .finish()
    }
}

#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
impl<St, Fut, F> Filter<St, Fut, F>
where
    St: Stream,
    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
    Fut: Future<Output = bool>,
{
    pub(super) fn new(stream: St, f: F) -> Self {
        Self { stream, f, pending_fut: None, pending_item: None }
    }

    delegate_access_inner!(stream, St, ());
}

impl<St, Fut, F> FusedStream for Filter<St, Fut, F>
where
    St: Stream + FusedStream,
    F: FnMut(&St::Item) -> Fut,
    Fut: Future<Output = bool>,
{
    fn is_terminated(&self) -> bool {
        self.pending_fut.is_none() && self.stream.is_terminated()
    }
}

#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
impl<St, Fut, F> Stream for Filter<St, Fut, F>
where
    St: Stream,
    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
    Fut: Future<Output = bool>,
{
    type Item = St::Item;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
        let mut this = self.project();
        Poll::Ready(loop {
            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
                let res = ready!(fut.poll(cx));
                this.pending_fut.set(None);
                if res {
                    break this.pending_item.take();
                }
                *this.pending_item = None;
            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
                this.pending_fut.set(Some(this.f.call_mut(&item)));
                *this.pending_item = Some(item);
            } else {
                break None;
            }
        })
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        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
    }
}

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

    delegate_sink!(stream, Item);
}