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use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};
use pin_project_lite::pin_project;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::{cmp, io};
pin_project! {
/// Stream for the [`take`](super::AsyncReadExt::take) method.
#[derive(Debug)]
#[must_use = "streams do nothing unless you `.await` or poll them"]
#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
pub struct Take<R> {
#[pin]
inner: R,
// Add '_' to avoid conflicts with `limit` method.
limit_: u64,
}
}
pub(super) fn take<R: AsyncRead>(inner: R, limit: u64) -> Take<R> {
Take {
inner,
limit_: limit,
}
}
impl<R: AsyncRead> Take<R> {
/// Returns the remaining number of bytes that can be
/// read before this instance will return EOF.
///
/// # Note
///
/// This instance may reach `EOF` after reading fewer bytes than indicated by
/// this method if the underlying [`AsyncRead`] instance reaches EOF.
pub fn limit(&self) -> u64 {
self.limit_
}
/// Sets the number of bytes that can be read before this instance will
/// return EOF. This is the same as constructing a new `Take` instance, so
/// the amount of bytes read and the previous limit value don't matter when
/// calling this method.
pub fn set_limit(&mut self, limit: u64) {
self.limit_ = limit
}
/// Gets a reference to the underlying reader.
pub fn get_ref(&self) -> &R {
&self.inner
}
/// Gets a mutable reference to the underlying reader.
///
/// Care should be taken to avoid modifying the internal I/O state of the
/// underlying reader as doing so may corrupt the internal limit of this
/// `Take`.
pub fn get_mut(&mut self) -> &mut R {
&mut self.inner
}
/// Gets a pinned mutable reference to the underlying reader.
///
/// Care should be taken to avoid modifying the internal I/O state of the
/// underlying reader as doing so may corrupt the internal limit of this
/// `Take`.
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> {
self.project().inner
}
/// Consumes the `Take`, returning the wrapped reader.
pub fn into_inner(self) -> R {
self.inner
}
}
impl<R: AsyncRead> AsyncRead for Take<R> {
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<Result<(), io::Error>> {
if self.limit_ == 0 {
return Poll::Ready(Ok(()));
}
let me = self.project();
let mut b = buf.take(*me.limit_ as usize);
let buf_ptr = b.filled().as_ptr();
ready!(me.inner.poll_read(cx, &mut b))?;
assert_eq!(b.filled().as_ptr(), buf_ptr);
let n = b.filled().len();
// We need to update the original ReadBuf
unsafe {
buf.assume_init(n);
}
buf.advance(n);
*me.limit_ -= n as u64;
Poll::Ready(Ok(()))
}
}
impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
let me = self.project();
// Don't call into inner reader at all at EOF because it may still block
if *me.limit_ == 0 {
return Poll::Ready(Ok(&[]));
}
let buf = ready!(me.inner.poll_fill_buf(cx)?);
let cap = cmp::min(buf.len() as u64, *me.limit_) as usize;
Poll::Ready(Ok(&buf[..cap]))
}
fn consume(self: Pin<&mut Self>, amt: usize) {
let me = self.project();
// Don't let callers reset the limit by passing an overlarge value
let amt = cmp::min(amt as u64, *me.limit_) as usize;
*me.limit_ -= amt as u64;
me.inner.consume(amt);
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn assert_unpin() {
crate::is_unpin::<Take<()>>();
}
}