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use crate::io::util::vec_with_initialized::{into_read_buf_parts, VecU8, VecWithInitialized};
use crate::io::{AsyncRead, ReadBuf};
use pin_project_lite::pin_project;
use std::future::Future;
use std::io;
use std::marker::PhantomPinned;
use std::mem::{self, MaybeUninit};
use std::pin::Pin;
use std::task::{Context, Poll};
pin_project! {
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct ReadToEnd<'a, R: ?Sized> {
reader: &'a mut R,
buf: VecWithInitialized<&'a mut Vec<u8>>,
// The number of bytes appended to buf. This can be less than buf.len() if
// the buffer was not empty when the operation was started.
read: usize,
// Make this future `!Unpin` for compatibility with async trait methods.
#[pin]
_pin: PhantomPinned,
}
}
pub(crate) fn read_to_end<'a, R>(reader: &'a mut R, buffer: &'a mut Vec<u8>) -> ReadToEnd<'a, R>
where
R: AsyncRead + Unpin + ?Sized,
{
ReadToEnd {
reader,
buf: VecWithInitialized::new(buffer),
read: 0,
_pin: PhantomPinned,
}
}
pub(super) fn read_to_end_internal<V: VecU8, R: AsyncRead + ?Sized>(
buf: &mut VecWithInitialized<V>,
mut reader: Pin<&mut R>,
num_read: &mut usize,
cx: &mut Context<'_>,
) -> Poll<io::Result<usize>> {
loop {
let ret = ready!(poll_read_to_end(buf, reader.as_mut(), cx));
match ret {
Err(err) => return Poll::Ready(Err(err)),
Ok(0) => return Poll::Ready(Ok(mem::replace(num_read, 0))),
Ok(num) => {
*num_read += num;
}
}
}
}
/// Tries to read from the provided [`AsyncRead`].
///
/// The length of the buffer is increased by the number of bytes read.
fn poll_read_to_end<V: VecU8, R: AsyncRead + ?Sized>(
buf: &mut VecWithInitialized<V>,
read: Pin<&mut R>,
cx: &mut Context<'_>,
) -> Poll<io::Result<usize>> {
// 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. When the vector is full with its starting
// capacity, we first try to read into a small buffer to see if we reached
// an EOF. This only happens when the starting capacity is >= NUM_BYTES, since
// we allocate at least NUM_BYTES each time. This avoids the unnecessary
// allocation that we attempt before reading into the vector.
const NUM_BYTES: usize = 32;
let try_small_read = buf.try_small_read_first(NUM_BYTES);
// Get a ReadBuf into the vector.
let mut read_buf;
let poll_result;
let n = if try_small_read {
// Read some bytes using a small read.
let mut small_buf: [MaybeUninit<u8>; NUM_BYTES] = [MaybeUninit::uninit(); NUM_BYTES];
let mut small_read_buf = ReadBuf::uninit(&mut small_buf);
poll_result = read.poll_read(cx, &mut small_read_buf);
let to_write = small_read_buf.filled();
// Ensure we have enough space to fill our vector with what we read.
read_buf = buf.get_read_buf();
if to_write.len() > read_buf.remaining() {
buf.reserve(NUM_BYTES);
read_buf = buf.get_read_buf();
}
read_buf.put_slice(to_write);
to_write.len()
} else {
// Ensure we have enough space for reading.
buf.reserve(NUM_BYTES);
read_buf = buf.get_read_buf();
// Read data directly into vector.
let filled_before = read_buf.filled().len();
poll_result = read.poll_read(cx, &mut read_buf);
// Compute the number of bytes read.
read_buf.filled().len() - filled_before
};
// Update the length of the vector using the result of poll_read.
let read_buf_parts = into_read_buf_parts(read_buf);
buf.apply_read_buf(read_buf_parts);
match poll_result {
Poll::Pending => {
// In this case, nothing should have been read. However we still
// update the vector in case the poll_read call initialized parts of
// the vector's unused capacity.
debug_assert_eq!(n, 0);
Poll::Pending
}
Poll::Ready(Err(err)) => {
debug_assert_eq!(n, 0);
Poll::Ready(Err(err))
}
Poll::Ready(Ok(())) => Poll::Ready(Ok(n)),
}
}
impl<A> Future for ReadToEnd<'_, A>
where
A: AsyncRead + ?Sized + Unpin,
{
type Output = io::Result<usize>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let me = self.project();
read_to_end_internal(me.buf, Pin::new(*me.reader), me.read, cx)
}
}