blob: c57753e3d0e0df9cc2539e6045c9958afc9ccab4 [file] [log] [blame]
use crate::io::AsyncRead;
use futures_core::future::Future;
use futures_core::task::{self, Poll};
use std::io;
use std::marker::Unpin;
use std::mem::{self, PinMut};
/// A future which can be used to easily read exactly enough bytes to fill
/// a buffer.
///
/// Created by the [`read_exact`] function.
///
/// [`read_exact`]: fn.read_exact.html
#[derive(Debug)]
pub struct ReadExact<'a, R: ?Sized + 'a> {
reader: &'a mut R,
buf: &'a mut [u8],
}
impl<R: ?Sized> Unpin for ReadExact<'_, R> {}
impl<'a, R: AsyncRead + ?Sized> ReadExact<'a, R> {
pub(super) fn new(reader: &'a mut R, buf: &'a mut [u8]) -> Self {
ReadExact { reader, buf }
}
}
fn eof() -> io::Error {
io::Error::new(io::ErrorKind::UnexpectedEof, "early eof")
}
impl<R: AsyncRead + ?Sized> Future for ReadExact<'_, R> {
type Output = io::Result<()>;
fn poll(mut self: PinMut<Self>, cx: &mut task::Context) -> Poll<Self::Output> {
let this = &mut *self;
while !this.buf.is_empty() {
let n = try_ready!(this.reader.poll_read(cx, this.buf));
{
let (_, rest) = mem::replace(&mut this.buf, &mut []).split_at_mut(n);
this.buf = rest;
}
if n == 0 {
return Poll::Ready(Err(eof()))
}
}
Poll::Ready(Ok(()))
}
}