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 
7 /// Future for the [`fill_buf`](super::AsyncBufReadExt::fill_buf) method.
8 #[derive(Debug)]
9 #[must_use = "futures do nothing unless you `.await` or poll them"]
10 pub struct FillBuf<'a, R: ?Sized> {
11     reader: Option<&'a mut R>,
12 }
13 
14 impl<R: ?Sized> Unpin for FillBuf<'_, R> {}
15 
16 impl<'a, R: AsyncBufRead + ?Sized + Unpin> FillBuf<'a, R> {
new(reader: &'a mut R) -> Self17     pub(super) fn new(reader: &'a mut R) -> Self {
18         Self { reader: Some(reader) }
19     }
20 }
21 
22 impl<'a, R> Future for FillBuf<'a, R>
23     where R: AsyncBufRead + ?Sized + Unpin,
24 {
25     type Output = io::Result<&'a [u8]>;
26 
poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>27     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
28         let this = &mut *self;
29         let reader = this.reader.take().expect("Polled FillBuf after completion");
30 
31         match Pin::new(&mut *reader).poll_fill_buf(cx) {
32             // With polinius it is possible to remove this inner match and just have the correct
33             // lifetime of the reference inferred based on which branch is taken
34             Poll::Ready(Ok(_)) => match Pin::new(reader).poll_fill_buf(cx) {
35                 Poll::Ready(Ok(slice)) => Poll::Ready(Ok(slice)),
36                 Poll::Ready(Err(err)) => {
37                     unreachable!("reader indicated readiness but then returned an error: {:?}", err)
38                 }
39                 Poll::Pending => {
40                     unreachable!("reader indicated readiness but then returned pending")
41                 }
42             },
43             Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
44             Poll::Pending => {
45                 this.reader = Some(reader);
46                 Poll::Pending
47             }
48         }
49     }
50 }
51