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use crate::future::Either;
use crate::stream::{Fuse, StreamExt};
use core::fmt;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
#[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,
}
}
pub fn get_ref(&self) -> &St {
self.stream.get_ref()
}
pub fn get_mut(&mut self) -> &mut St {
self.stream.get_mut()
}
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
self.stream().get_pin_mut()
}
pub fn into_inner(self) -> St {
self.stream.into_inner()
}
pub fn peek(self: Pin<&mut Self>) -> Peek<'_, St> {
Peek { inner: Some(self) }
}
fn do_poll_peek(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Either<Pin<&mut Self>, Option<&St::Item>> {
if self.peeked.is_some() {
let this: &Self = self.into_ref().get_ref();
return Either::Right(this.peeked.as_ref());
}
match self.as_mut().stream().poll_next(cx) {
Poll::Ready(None) => Either::Right(None),
Poll::Ready(Some(item)) => {
*self.as_mut().peeked() = Some(item);
let this: &Self = self.into_ref().get_ref();
Either::Right(this.peeked.as_ref())
}
_ => Either::Left(self),
}
}
pub fn poll_peek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<&St::Item>> {
match self.do_poll_peek(cx) {
Either::Left(_) => Poll::Pending,
Either::Right(poll) => Poll::Ready(poll),
}
}
}
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>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
if let Some(item) = self.as_mut().peeked().take() {
return Poll::Ready(Some(item));
}
self.as_mut().stream().poll_next(cx)
}
fn size_hint(&self) -> (usize, Option<usize>) {
let peek_len = if self.peeked.is_some() { 1 } else { 0 };
let (lower, upper) = self.stream.size_hint();
let lower = lower.saturating_add(peek_len);
let upper = match upper {
Some(x) => x.checked_add(peek_len),
None => None,
};
(lower, upper)
}
}
#[cfg(feature = "sink")]
impl<S, Item> Sink<Item> for Peekable<S>
where
S: Sink<Item> + Stream,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}
#[must_use = "futures do nothing unless polled"]
pub struct Peek<'a, St: Stream> {
inner: Option<Pin<&'a mut Peekable<St>>>,
}
impl<St: Stream> Unpin for Peek<'_, St> {}
impl<St> fmt::Debug for Peek<'_, St>
where
St: Stream + fmt::Debug,
St::Item: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Peek")
.field("inner", &self.inner)
.finish()
}
}
impl<St: Stream> FusedFuture for Peek<'_, St> {
fn is_terminated(&self) -> bool {
self.inner.is_none()
}
}
impl<'a, St> Future for Peek<'a, St>
where
St: Stream,
{
type Output = Option<&'a St::Item>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
if let Some(peekable) = self.inner.take() {
match peekable.do_poll_peek(cx) {
Either::Left(peekable) => {
self.inner = Some(peekable);
Poll::Pending
}
Either::Right(peek) => Poll::Ready(peek),
}
} else {
panic!("Peek polled after completion")
}
}
}