blob: 3e1d5b36b9d7bd7e322335fac262ed980bc64050 [file] [log] [blame]
use crate::stream::{StreamExt, Fuse};
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A `Stream` that implements a `peek` method.
///
/// The `peek` method can be used to retrieve a reference
/// to the next `Stream::Item` if available. A subsequent
/// call to `poll` will return the owned item.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Peekable<St: Stream> {
stream: Fuse<St>,
peeked: Option<St::Item>,
}
impl<St: Stream + Unpin> Unpin for Peekable<St> {}
impl<St: Stream> Peekable<St> {
unsafe_pinned!(stream: Fuse<St>);
unsafe_unpinned!(peeked: Option<St::Item>);
pub(super) fn new(stream: St) -> Peekable<St> {
Peekable {
stream: stream.fuse(),
peeked: None
}
}
/// Peek retrieves a reference to the next item in the stream.
///
/// This method polls the underlying stream and return either a reference
/// to the next item if the stream is ready or passes through any errors.
pub fn peek<'a>(
mut self: Pin<&'a mut Self>,
lw: &LocalWaker,
) -> Poll<Option<&'a St::Item>> {
if self.peeked.is_some() {
let this: &Self = self.into_ref().get_ref();
return Poll::Ready(this.peeked.as_ref())
}
match ready!(self.as_mut().stream().poll_next(lw)) {
None => Poll::Ready(None),
Some(item) => {
*self.as_mut().peeked() = Some(item);
let this: &Self = self.into_ref().get_ref();
Poll::Ready(this.peeked.as_ref())
}
}
}
}
impl<St: Stream> FusedStream for Peekable<St> {
fn is_terminated(&self) -> bool {
self.peeked.is_none() && self.stream.is_terminated()
}
}
impl<S: Stream> Stream for Peekable<S> {
type Item = S::Item;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker
) -> Poll<Option<Self::Item>> {
if let Some(item) = self.as_mut().peeked().take() {
return Poll::Ready(Some(item))
}
self.as_mut().stream().poll_next(lw)
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S> Sink for Peekable<S>
where S: Sink + Stream
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/