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use crate::io::{AsyncRead, ReadBuf};
use pin_project_lite::pin_project;
use std::future::Future;
use std::io;
use std::marker::PhantomPinned;
use std::marker::Unpin;
use std::pin::Pin;
use std::task::{Context, Poll};
/// Tries to read some bytes directly into the given `buf` in asynchronous
/// manner, returning a future type.
///
/// The returned future will resolve to both the I/O stream and the buffer
/// as well as the number of bytes read once the read operation is completed.
pub(crate) fn read<'a, R>(reader: &'a mut R, buf: &'a mut [u8]) -> Read<'a, R>
where
R: AsyncRead + Unpin + ?Sized,
{
Read {
reader,
buf,
_pin: PhantomPinned,
}
}
pin_project! {
/// A future which can be used to easily read available number of bytes to fill
/// a buffer.
///
/// Created by the [`read`] function.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Read<'a, R: ?Sized> {
reader: &'a mut R,
buf: &'a mut [u8],
// Make this future `!Unpin` for compatibility with async trait methods.
#[pin]
_pin: PhantomPinned,
}
}
impl<R> Future for Read<'_, R>
where
R: AsyncRead + Unpin + ?Sized,
{
type Output = io::Result<usize>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
let me = self.project();
let mut buf = ReadBuf::new(me.buf);
ready!(Pin::new(me.reader).poll_read(cx, &mut buf))?;
Poll::Ready(Ok(buf.filled().len()))
}
}