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use futures_core::future::Future;
use futures_core::task::{Context, Poll};
use futures_io::AsyncBufRead;
use std::io;
use std::pin::Pin;
/// Future for the [`fill_buf`](super::AsyncBufReadExt::fill_buf) method.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct FillBuf<'a, R: ?Sized> {
reader: Option<&'a mut R>,
}
impl<R: ?Sized> Unpin for FillBuf<'_, R> {}
impl<'a, R: AsyncBufRead + ?Sized + Unpin> FillBuf<'a, R> {
pub(super) fn new(reader: &'a mut R) -> Self {
Self { reader: Some(reader) }
}
}
impl<'a, R> Future for FillBuf<'a, R>
where
R: AsyncBufRead + ?Sized + Unpin,
{
type Output = io::Result<&'a [u8]>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = &mut *self;
let reader = this.reader.take().expect("Polled FillBuf after completion");
match Pin::new(&mut *reader).poll_fill_buf(cx) {
// With polonius it is possible to remove this inner match and just have the correct
// lifetime of the reference inferred based on which branch is taken
Poll::Ready(Ok(_)) => match Pin::new(reader).poll_fill_buf(cx) {
Poll::Ready(Ok(slice)) => Poll::Ready(Ok(slice)),
Poll::Ready(Err(err)) => {
unreachable!("reader indicated readiness but then returned an error: {:?}", err)
}
Poll::Pending => {
unreachable!("reader indicated readiness but then returned pending")
}
},
Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
Poll::Pending => {
this.reader = Some(reader);
Poll::Pending
}
}
}
}