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use std::io::{self, SeekFrom};
use std::ops::DerefMut;
use std::pin::Pin;
use std::task::{Context, Poll};
pub trait AsyncSeek {
fn start_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
position: SeekFrom,
) -> Poll<io::Result<()>>;
fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>>;
}
macro_rules! deref_async_seek {
() => {
fn start_seek(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<()>> {
Pin::new(&mut **self).start_seek(cx, pos)
}
fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
Pin::new(&mut **self).poll_complete(cx)
}
};
}
impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for Box<T> {
deref_async_seek!();
}
impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for &mut T {
deref_async_seek!();
}
impl<P> AsyncSeek for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncSeek,
{
fn start_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<()>> {
self.get_mut().as_mut().start_seek(cx, pos)
}
fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
self.get_mut().as_mut().poll_complete(cx)
}
}
impl<T: AsRef<[u8]> + Unpin> AsyncSeek for io::Cursor<T> {
fn start_seek(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<io::Result<()>> {
Poll::Ready(io::Seek::seek(&mut *self, pos).map(drop))
}
fn poll_complete(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<u64>> {
Poll::Ready(Ok(self.get_mut().position()))
}
}