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use core::fmt;
use core::pin::Pin;
use futures_core::future::TryFuture;
use futures_core::stream::{Stream, TryStream, FusedStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project::pin_project;
#[pin_project]
#[must_use = "streams do nothing unless polled"]
pub struct TrySkipWhile<St, Fut, F> where St: TryStream {
#[pin]
stream: St,
f: F,
#[pin]
pending_fut: Option<Fut>,
pending_item: Option<St::Ok>,
done_skipping: bool,
}
impl<St, Fut, F> fmt::Debug for TrySkipWhile<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("TrySkipWhile")
.field("stream", &self.stream)
.field("pending_fut", &self.pending_fut)
.field("pending_item", &self.pending_item)
.field("done_skipping", &self.done_skipping)
.finish()
}
}
impl<St, Fut, F> TrySkipWhile<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) -> TrySkipWhile<St, Fut, F> {
TrySkipWhile {
stream,
f,
pending_fut: None,
pending_item: None,
done_skipping: false,
}
}
delegate_access_inner!(stream, St, ());
}
impl<St, Fut, F> Stream for TrySkipWhile<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_skipping {
return this.stream.try_poll_next(cx);
}
Poll::Ready(loop {
if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
let skipped = ready!(fut.try_poll(cx)?);
let item = this.pending_item.take();
this.pending_fut.set(None);
if !skipped {
*this.done_skipping = true;
break item.map(Ok);
}
} 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>) {
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)
}
}
impl<St, Fut, F> FusedStream for TrySkipWhile<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.pending_item.is_none() && self.stream.is_terminated()
}
}
#[cfg(feature = "sink")]
impl<S, Fut, F, Item, E> Sink<Item> for TrySkipWhile<S, Fut, F>
where S: TryStream + Sink<Item, Error = E>,
{
type Error = E;
delegate_sink!(stream, Item);
}