1 use futures_core::future::Future;
2 use futures_core::task::{Context, Poll};
3 use futures_io::AsyncBufRead;
4 use std::io;
5 use std::pin::Pin;
6 use 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"]
11 pub struct FillBuf<'a, R: ?Sized> {
12     reader: Option<&'a mut R>,
13 }
14 
15 impl<R: ?Sized> Unpin for FillBuf<'_, R> {}
16 
17 impl<'a, R: AsyncBufRead + ?Sized + Unpin> FillBuf<'a, R> {
new(reader: &'a mut R) -> Self18     pub(super) fn new(reader: &'a mut R) -> Self {
19         Self { reader: Some(reader) }
20     }
21 }
22 
23 impl<'a, R> Future for FillBuf<'a, R>
24 where
25     R: AsyncBufRead + ?Sized + Unpin,
26 {
27     type Output = io::Result<&'a [u8]>;
28 
poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>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 }
48