1 use crate::io::AsyncBufRead;
2
3 use pin_project_lite::pin_project;
4 use std::future::Future;
5 use std::io;
6 use std::marker::PhantomPinned;
7 use std::pin::Pin;
8 use std::task::{Context, Poll};
9
10 pin_project! {
11 /// Future for the [`fill_buf`](crate::io::AsyncBufReadExt::fill_buf) method.
12 #[derive(Debug)]
13 #[must_use = "futures do nothing unless you `.await` or poll them"]
14 pub struct FillBuf<'a, R: ?Sized> {
15 reader: Option<&'a mut R>,
16 #[pin]
17 _pin: PhantomPinned,
18 }
19 }
20
fill_buf<R>(reader: &mut R) -> FillBuf<'_, R> where R: AsyncBufRead + ?Sized + Unpin,21 pub(crate) fn fill_buf<R>(reader: &mut R) -> FillBuf<'_, R>
22 where
23 R: AsyncBufRead + ?Sized + Unpin,
24 {
25 FillBuf {
26 reader: Some(reader),
27 _pin: PhantomPinned,
28 }
29 }
30
31 impl<'a, R: AsyncBufRead + ?Sized + Unpin> Future for FillBuf<'a, R> {
32 type Output = io::Result<&'a [u8]>;
33
poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>34 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
35 let me = self.project();
36
37 let reader = me.reader.take().expect("Polled after completion.");
38 match Pin::new(&mut *reader).poll_fill_buf(cx) {
39 Poll::Ready(Ok(slice)) => unsafe {
40 // Safety: This is necessary only due to a limitation in the
41 // borrow checker. Once Rust starts using the polonius borrow
42 // checker, this can be simplified.
43 //
44 // The safety of this transmute relies on the fact that the
45 // value of `reader` is `None` when we return in this branch.
46 // Otherwise the caller could poll us again after
47 // completion, and access the mutable reference while the
48 // returned immutable reference still exists.
49 let slice = std::mem::transmute::<&[u8], &'a [u8]>(slice);
50 Poll::Ready(Ok(slice))
51 },
52 Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
53 Poll::Pending => {
54 *me.reader = Some(reader);
55 Poll::Pending
56 }
57 }
58 }
59 }
60