1 use crate::io::AsyncRead; 2 use futures_core::ready; 3 use futures_core::future::Future; 4 use futures_core::task::{Context, Poll}; 5 use std::io; 6 use std::mem; 7 use std::pin::Pin; 8 9 /// Future for the [`read_exact`](super::AsyncReadExt::read_exact) method. 10 #[derive(Debug)] 11 #[must_use = "futures do nothing unless you `.await` or poll them"] 12 pub struct ReadExact<'a, R: ?Sized> { 13 reader: &'a mut R, 14 buf: &'a mut [u8], 15 } 16 17 impl<R: ?Sized + Unpin> Unpin for ReadExact<'_, R> {} 18 19 impl<'a, R: AsyncRead + ?Sized + Unpin> ReadExact<'a, R> { new(reader: &'a mut R, buf: &'a mut [u8]) -> Self20 pub(super) fn new(reader: &'a mut R, buf: &'a mut [u8]) -> Self { 21 Self { reader, buf } 22 } 23 } 24 25 impl<R: AsyncRead + ?Sized + Unpin> Future for ReadExact<'_, R> { 26 type Output = io::Result<()>; 27 poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>28 fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { 29 let this = &mut *self; 30 while !this.buf.is_empty() { 31 let n = ready!(Pin::new(&mut this.reader).poll_read(cx, this.buf))?; 32 { 33 let (_, rest) = mem::replace(&mut this.buf, &mut []).split_at_mut(n); 34 this.buf = rest; 35 } 36 if n == 0 { 37 return Poll::Ready(Err(io::ErrorKind::UnexpectedEof.into())) 38 } 39 } 40 Poll::Ready(Ok(())) 41 } 42 } 43