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use std::mem; use std::pin::Pin; use std::future::Future; use crate::io::{self, Read}; use crate::task::{Context, Poll}; #[doc(hidden)] #[allow(missing_debug_implementations)] pub struct ReadExactFuture<'a, T: Unpin + ?Sized> { pub(crate) reader: &'a mut T, pub(crate) buf: &'a mut [u8], } impl<T: Read + Unpin + ?Sized> Future for ReadExactFuture<'_, T> { type Output = io::Result<()>; fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { let Self { reader, buf } = &mut *self; while !buf.is_empty() { let n = futures_core::ready!(Pin::new(&mut *reader).poll_read(cx, buf))?; let (_, rest) = mem::replace(buf, &mut []).split_at_mut(n); *buf = rest; if n == 0 { return Poll::Ready(Err(io::ErrorKind::UnexpectedEof.into())); } } Poll::Ready(Ok(())) } }