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