futures_util/io/
fill_buf.rs

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1use futures_core::future::Future;
2use futures_core::task::{Context, Poll};
3use futures_io::AsyncBufRead;
4use std::io;
5use std::pin::Pin;
6use std::slice;
7
8/// Future for the [`fill_buf`](super::AsyncBufReadExt::fill_buf) method.
9#[derive(Debug)]
10#[must_use = "futures do nothing unless you `.await` or poll them"]
11pub struct FillBuf<'a, R: ?Sized> {
12    reader: Option<&'a mut R>,
13}
14
15impl<R: ?Sized> Unpin for FillBuf<'_, R> {}
16
17impl<'a, R: AsyncBufRead + ?Sized + Unpin> FillBuf<'a, R> {
18    pub(super) fn new(reader: &'a mut R) -> Self {
19        Self { reader: Some(reader) }
20    }
21}
22
23impl<'a, R> Future for FillBuf<'a, R>
24where
25    R: AsyncBufRead + ?Sized + Unpin,
26{
27    type Output = io::Result<&'a [u8]>;
28
29    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
30        let this = &mut *self;
31        let reader = this.reader.take().expect("Polled FillBuf after completion");
32
33        match Pin::new(&mut *reader).poll_fill_buf(cx) {
34            Poll::Ready(Ok(slice)) => {
35                // With polonius it is possible to remove this lifetime transmutation and just have
36                // the correct lifetime of the reference inferred based on which branch is taken
37                let slice: &'a [u8] = unsafe { slice::from_raw_parts(slice.as_ptr(), slice.len()) };
38                Poll::Ready(Ok(slice))
39            }
40            Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
41            Poll::Pending => {
42                this.reader = Some(reader);
43                Poll::Pending
44            }
45        }
46    }
47}
futures_util/io/fill_buf.rs

futures_util/io/
fill_buf.rs
