blob: 142512421b0b6332f391a62320d4d129196fe6c1 [file] [log] [blame]
use std::io;
use std::mem;
use futures::{Poll, Future};
use AsyncRead;
/// 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, T> {
state: State<A, T>,
}
#[derive(Debug)]
enum State<A, T> {
Reading {
a: A,
buf: T,
pos: usize,
},
Empty,
}
/// Creates a future which will read exactly enough bytes to fill `buf`,
/// returning an error if EOF is hit sooner.
///
/// The returned future will resolve to both the I/O stream as well as the
/// buffer once the read operation is completed.
///
/// In the case of an error the buffer and the object will be discarded, with
/// the error yielded. In the case of success the object will be destroyed and
/// the buffer will be returned, with all data read from the stream appended to
/// the buffer.
pub fn read_exact<A, T>(a: A, buf: T) -> ReadExact<A, T>
where A: AsyncRead,
T: AsMut<[u8]>,
{
ReadExact {
state: State::Reading {
a: a,
buf: buf,
pos: 0,
},
}
}
fn eof() -> io::Error {
io::Error::new(io::ErrorKind::UnexpectedEof, "early eof")
}
impl<A, T> Future for ReadExact<A, T>
where A: AsyncRead,
T: AsMut<[u8]>,
{
type Item = (A, T);
type Error = io::Error;
fn poll(&mut self) -> Poll<(A, T), io::Error> {
match self.state {
State::Reading { ref mut a, ref mut buf, ref mut pos } => {
let buf = buf.as_mut();
while *pos < buf.len() {
let n = try_nb!(a.read(&mut buf[*pos..]));
*pos += n;
if n == 0 {
return Err(eof())
}
}
}
State::Empty => panic!("poll a ReadExact after it's done"),
}
match mem::replace(&mut self.state, State::Empty) {
State::Reading { a, buf, .. } => Ok((a, buf).into()),
State::Empty => panic!(),
}
}
}