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};
#[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,
}
}
pub fn get_ref(&self) -> &St {
&self.stream
}
pub fn get_mut(&mut self) -> &mut St {
&mut self.stream
}
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
self.stream()
}
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) }
}
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()
}
}
#[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);
}