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use crate::io::AsyncRead;
use bytes::BufMut;
use pin_project_lite::pin_project;
use std::future::Future;
use std::io;
use std::marker::PhantomPinned;
use std::pin::Pin;
use std::task::{Context, Poll};
pub(crate) fn read_buf<'a, R, B>(reader: &'a mut R, buf: &'a mut B) -> ReadBuf<'a, R, B>
where
R: AsyncRead + Unpin + ?Sized,
B: BufMut + ?Sized,
{
ReadBuf {
reader,
buf,
_pin: PhantomPinned,
}
}
pin_project! {
/// Future returned by [`read_buf`](crate::io::AsyncReadExt::read_buf).
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct ReadBuf<'a, R: ?Sized, B: ?Sized> {
reader: &'a mut R,
buf: &'a mut B,
#[pin]
_pin: PhantomPinned,
}
}
impl<R, B> Future for ReadBuf<'_, R, B>
where
R: AsyncRead + Unpin + ?Sized,
B: BufMut + ?Sized,
{
type Output = io::Result<usize>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
use crate::io::ReadBuf;
use std::mem::MaybeUninit;
let me = self.project();
if !me.buf.has_remaining_mut() {
return Poll::Ready(Ok(0));
}
let n = {
let dst = me.buf.chunk_mut();
let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
let mut buf = ReadBuf::uninit(dst);
let ptr = buf.filled().as_ptr();
ready!(Pin::new(me.reader).poll_read(cx, &mut buf)?);
// Ensure the pointer does not change from under us
assert_eq!(ptr, buf.filled().as_ptr());
buf.filled().len()
};
// Safety: This is guaranteed to be the number of initialized (and read)
// bytes due to the invariants provided by `ReadBuf::filled`.
unsafe {
me.buf.advance_mut(n);
}
Poll::Ready(Ok(n))
}
}