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use crate::io::AsyncSeek;
use pin_project_lite::pin_project;
use std::future::Future;
use std::io::{self, SeekFrom};
use std::marker::PhantomPinned;
use std::pin::Pin;
use std::task::{Context, Poll};
pin_project! {
/// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Seek<'a, S: ?Sized> {
seek: &'a mut S,
pos: Option<SeekFrom>,
// Make this future `!Unpin` for compatibility with async trait methods.
#[pin]
_pin: PhantomPinned,
}
}
pub(crate) fn seek<S>(seek: &mut S, pos: SeekFrom) -> Seek<'_, S>
where
S: AsyncSeek + ?Sized + Unpin,
{
Seek {
seek,
pos: Some(pos),
_pin: PhantomPinned,
}
}
impl<S> Future for Seek<'_, S>
where
S: AsyncSeek + ?Sized + Unpin,
{
type Output = io::Result<u64>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let me = self.project();
match me.pos {
Some(pos) => match Pin::new(&mut *me.seek).start_seek(cx, *pos) {
Poll::Ready(Ok(())) => {
*me.pos = None;
Pin::new(&mut *me.seek).poll_complete(cx)
}
Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
Poll::Pending => Poll::Pending,
},
None => Pin::new(&mut *me.seek).poll_complete(cx),
}
}
}
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