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use futures_core::future::Future;
use futures_core::ready;
use futures_core::task::{Context, Poll};
use futures_io::AsyncRead;
use std::io;
use std::pin::Pin;
use std::vec::Vec;
/// Future for the [`read_to_end`](super::AsyncReadExt::read_to_end) method.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct ReadToEnd<'a, R: ?Sized> {
reader: &'a mut R,
buf: &'a mut Vec<u8>,
start_len: usize,
}
impl<R: ?Sized + Unpin> Unpin for ReadToEnd<'_, R> {}
impl<'a, R: AsyncRead + ?Sized + Unpin> ReadToEnd<'a, R> {
pub(super) fn new(reader: &'a mut R, buf: &'a mut Vec<u8>) -> Self {
let start_len = buf.len();
Self { reader, buf, start_len }
}
}
struct Guard<'a> {
buf: &'a mut Vec<u8>,
len: usize,
}
impl Drop for Guard<'_> {
fn drop(&mut self) {
unsafe {
self.buf.set_len(self.len);
}
}
}
// This uses an adaptive system to extend the vector when it fills. We want to
// avoid paying to allocate and zero a huge chunk of memory if the reader only
// has 4 bytes while still making large reads if the reader does have a ton
// of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
// time is 4,500 times (!) slower than this if the reader has a very small
// amount of data to return.
//
// Because we're extending the buffer with uninitialized data for trusted
// readers, we need to make sure to truncate that if any of this panics.
pub(super) fn read_to_end_internal<R: AsyncRead + ?Sized>(
mut rd: Pin<&mut R>,
cx: &mut Context<'_>,
buf: &mut Vec<u8>,
start_len: usize,
) -> Poll<io::Result<usize>> {
let mut g = Guard { len: buf.len(), buf };
loop {
if g.len == g.buf.len() {
unsafe {
g.buf.reserve(32);
let capacity = g.buf.capacity();
g.buf.set_len(capacity);
super::initialize(&rd, &mut g.buf[g.len..]);
}
}
let buf = &mut g.buf[g.len..];
match ready!(rd.as_mut().poll_read(cx, buf)) {
Ok(0) => return Poll::Ready(Ok(g.len - start_len)),
Ok(n) => {
// We can't allow bogus values from read. If it is too large, the returned vec could have its length
// set past its capacity, or if it overflows the vec could be shortened which could create an invalid
// string if this is called via read_to_string.
assert!(n <= buf.len());
g.len += n;
}
Err(e) => return Poll::Ready(Err(e)),
}
}
}
impl<A> Future for ReadToEnd<'_, A>
where
A: AsyncRead + ?Sized + Unpin,
{
type Output = io::Result<usize>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = &mut *self;
read_to_end_internal(Pin::new(&mut this.reader), cx, this.buf, this.start_len)
}
}