126 lines
3.6 KiB
Rust
126 lines
3.6 KiB
Rust
use futures_core::ready;
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use futures_core::task::{Context, Poll};
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use futures_io::{AsyncBufRead, AsyncRead};
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use pin_project_lite::pin_project;
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use std::pin::Pin;
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use std::{cmp, io};
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pin_project! {
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/// Reader for the [`take`](super::AsyncReadExt::take) method.
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#[derive(Debug)]
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#[must_use = "readers do nothing unless you `.await` or poll them"]
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pub struct Take<R> {
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#[pin]
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inner: R,
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limit: u64,
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}
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}
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impl<R: AsyncRead> Take<R> {
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pub(super) fn new(inner: R, limit: u64) -> Self {
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Self { inner, limit }
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}
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/// Returns the remaining number of bytes that can be
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/// read before this instance will return EOF.
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///
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/// # Note
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///
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/// This instance may reach `EOF` after reading fewer bytes than indicated by
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/// this method if the underlying [`AsyncRead`] instance reaches EOF.
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///
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/// # Examples
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///
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/// ```
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/// # futures::executor::block_on(async {
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/// use futures::io::{AsyncReadExt, Cursor};
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///
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/// let reader = Cursor::new(&b"12345678"[..]);
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/// let mut buffer = [0; 2];
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///
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/// let mut take = reader.take(4);
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/// let n = take.read(&mut buffer).await?;
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///
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/// assert_eq!(take.limit(), 2);
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/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
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/// ```
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pub fn limit(&self) -> u64 {
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self.limit
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}
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/// Sets the number of bytes that can be read before this instance will
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/// return EOF. This is the same as constructing a new `Take` instance, so
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/// the amount of bytes read and the previous limit value don't matter when
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/// calling this method.
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///
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/// # Examples
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///
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/// ```
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/// # futures::executor::block_on(async {
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/// use futures::io::{AsyncReadExt, Cursor};
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///
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/// let reader = Cursor::new(&b"12345678"[..]);
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/// let mut buffer = [0; 4];
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///
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/// let mut take = reader.take(4);
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/// let n = take.read(&mut buffer).await?;
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///
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/// assert_eq!(n, 4);
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/// assert_eq!(take.limit(), 0);
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///
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/// take.set_limit(10);
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/// let n = take.read(&mut buffer).await?;
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/// assert_eq!(n, 4);
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///
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/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
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/// ```
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pub fn set_limit(&mut self, limit: u64) {
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self.limit = limit
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}
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delegate_access_inner!(inner, R, ());
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}
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impl<R: AsyncRead> AsyncRead for Take<R> {
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fn poll_read(
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self: Pin<&mut Self>,
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cx: &mut Context<'_>,
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buf: &mut [u8],
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) -> Poll<Result<usize, io::Error>> {
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let this = self.project();
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if *this.limit == 0 {
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return Poll::Ready(Ok(0));
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}
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let max = cmp::min(buf.len() as u64, *this.limit) as usize;
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let n = ready!(this.inner.poll_read(cx, &mut buf[..max]))?;
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*this.limit -= n as u64;
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Poll::Ready(Ok(n))
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}
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}
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impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
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fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
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let this = self.project();
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// Don't call into inner reader at all at EOF because it may still block
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if *this.limit == 0 {
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return Poll::Ready(Ok(&[]));
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}
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let buf = ready!(this.inner.poll_fill_buf(cx)?);
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let cap = cmp::min(buf.len() as u64, *this.limit) as usize;
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Poll::Ready(Ok(&buf[..cap]))
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}
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fn consume(self: Pin<&mut Self>, amt: usize) {
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let this = self.project();
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// Don't let callers reset the limit by passing an overlarge value
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let amt = cmp::min(amt as u64, *this.limit) as usize;
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*this.limit -= amt as u64;
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this.inner.consume(amt);
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}
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}
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