1use crate::io::AsyncSeek;
2
3use pin_project_lite::pin_project;
4use std::future::Future;
5use std::io::{self, SeekFrom};
6use std::marker::PhantomPinned;
7use std::pin::Pin;
8use std::task::{ready, Context, Poll};
9
10pin_project! {
11 /// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.
12 #[derive(Debug)]
13 #[must_use = "futures do nothing unless you `.await` or poll them"]
14 pub struct Seek<'a, S: ?Sized> {
15 seek: &'a mut S,
16 pos: Option<SeekFrom>,
17 // Make this future `!Unpin` for compatibility with async trait methods.
18 #[pin]
19 _pin: PhantomPinned,
20 }
21}
22
23pub(crate) fn seek<S>(seek: &mut S, pos: SeekFrom) -> Seek<'_, S>
24where
25 S: AsyncSeek + ?Sized + Unpin,
26{
27 Seek {
28 seek,
29 pos: Some(pos),
30 _pin: PhantomPinned,
31 }
32}
33
34impl<S> Future for Seek<'_, S>
35where
36 S: AsyncSeek + ?Sized + Unpin,
37{
38 type Output = io::Result<u64>;
39
40 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
41 let me: Projection<'_, '_, S> = self.project();
42 match me.pos {
43 Some(pos: &mut SeekFrom) => {
44 // ensure no seek in progress
45 ready!(Pin::new(&mut *me.seek).poll_complete(cx))?;
46 match Pin::new(&mut *me.seek).start_seek(*pos) {
47 Ok(()) => {
48 *me.pos = None;
49 Pin::new(&mut *me.seek).poll_complete(cx)
50 }
51 Err(e: Error) => Poll::Ready(Err(e)),
52 }
53 }
54 None => Pin::new(&mut *me.seek).poll_complete(cx),
55 }
56 }
57}
58