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use core::fmt;
use core::pin::Pin;
use futures_core::future::TryFuture;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream, TryStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project_lite::pin_project;
pin_project! {
/// Stream for the [`try_take_while`](super::TryStreamExt::try_take_while)
/// method.
#[must_use = "streams do nothing unless polled"]
pub struct TryTakeWhile<St, Fut, F>
where
St: TryStream,
{
#[pin]
stream: St,
f: F,
#[pin]
pending_fut: Option<Fut>,
pending_item: Option<St::Ok>,
done_taking: bool,
}
}
impl<St, Fut, F> fmt::Debug for TryTakeWhile<St, Fut, F>
where
St: TryStream + fmt::Debug,
St::Ok: fmt::Debug,
Fut: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TryTakeWhile")
.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, Fut, F> TryTakeWhile<St, Fut, F>
where
St: TryStream,
F: FnMut(&St::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = St::Error>,
{
pub(super) fn new(stream: St, f: F) -> Self {
Self { stream, f, pending_fut: None, pending_item: None, done_taking: false }
}
delegate_access_inner!(stream, St, ());
}
impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F>
where
St: TryStream,
F: FnMut(&St::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = St::Error>,
{
type Item = Result<St::Ok, St::Error>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let mut this = self.project();
if *this.done_taking {
return Poll::Ready(None);
}
Poll::Ready(loop {
if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
let res = ready!(fut.try_poll(cx));
this.pending_fut.set(None);
let take = res?;
let item = this.pending_item.take();
if take {
break item.map(Ok);
} else {
*this.done_taking = true;
break None;
}
} else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
this.pending_fut.set(Some((this.f)(&item)));
*this.pending_item = Some(item);
} else {
break None;
}
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
if self.done_taking {
return (0, Some(0));
}
let pending_len = usize::from(self.pending_item.is_some());
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 TryTakeWhile<St, Fut, F>
where
St: TryStream + FusedStream,
F: FnMut(&St::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = St::Error>,
{
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, E> Sink<Item> for TryTakeWhile<S, Fut, F>
where
S: TryStream + Sink<Item, Error = E>,
{
type Error = E;
delegate_sink!(stream, Item);
}