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use crate::io::AsyncRead;
use std::io;
use std::ops::DerefMut;
use std::pin::Pin;
use std::task::{Context, Poll};
/// Reads bytes asynchronously.
///
/// This trait is analogous to [`std::io::BufRead`], but integrates with
/// the asynchronous task system. In particular, the [`poll_fill_buf`] method,
/// unlike [`BufRead::fill_buf`], will automatically queue the current task for wakeup
/// and return if data is not yet available, rather than blocking the calling
/// thread.
///
/// Utilities for working with `AsyncBufRead` values are provided by
/// [`AsyncBufReadExt`].
///
/// [`std::io::BufRead`]: std::io::BufRead
/// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
/// [`BufRead::fill_buf`]: std::io::BufRead::fill_buf
/// [`AsyncBufReadExt`]: crate::io::AsyncBufReadExt
pub trait AsyncBufRead: AsyncRead {
/// Attempts to return the contents of the internal buffer, filling it with more data
/// from the inner reader if it is empty.
///
/// On success, returns `Poll::Ready(Ok(buf))`.
///
/// If no data is available for reading, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// This function is a lower-level call. It needs to be paired with the
/// [`consume`] method to function properly. When calling this
/// method, none of the contents will be "read" in the sense that later
/// calling [`poll_read`] may return the same contents. As such, [`consume`] must
/// be called with the number of bytes that are consumed from this buffer to
/// ensure that the bytes are never returned twice.
///
/// An empty buffer returned indicates that the stream has reached EOF.
///
/// [`poll_read`]: AsyncRead::poll_read
/// [`consume`]: AsyncBufRead::consume
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>;
/// Tells this buffer that `amt` bytes have been consumed from the buffer,
/// so they should no longer be returned in calls to [`poll_read`].
///
/// This function is a lower-level call. It needs to be paired with the
/// [`poll_fill_buf`] method to function properly. This function does
/// not perform any I/O, it simply informs this object that some amount of
/// its buffer, returned from [`poll_fill_buf`], has been consumed and should
/// no longer be returned. As such, this function may do odd things if
/// [`poll_fill_buf`] isn't called before calling it.
///
/// The `amt` must be `<=` the number of bytes in the buffer returned by
/// [`poll_fill_buf`].
///
/// [`poll_read`]: AsyncRead::poll_read
/// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
fn consume(self: Pin<&mut Self>, amt: usize);
}
macro_rules! deref_async_buf_read {
() => {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
Pin::new(&mut **self.get_mut()).poll_fill_buf(cx)
}
fn consume(mut self: Pin<&mut Self>, amt: usize) {
Pin::new(&mut **self).consume(amt)
}
};
}
impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for Box<T> {
deref_async_buf_read!();
}
impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T {
deref_async_buf_read!();
}
impl<P> AsyncBufRead for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncBufRead,
{
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
self.get_mut().as_mut().poll_fill_buf(cx)
}
fn consume(self: Pin<&mut Self>, amt: usize) {
self.get_mut().as_mut().consume(amt);
}
}
impl AsyncBufRead for &[u8] {
fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
Poll::Ready(Ok(*self))
}
fn consume(mut self: Pin<&mut Self>, amt: usize) {
*self = &self[amt..];
}
}
impl<T: AsRef<[u8]> + Unpin> AsyncBufRead for io::Cursor<T> {
fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
Poll::Ready(io::BufRead::fill_buf(self.get_mut()))
}
fn consume(self: Pin<&mut Self>, amt: usize) {
io::BufRead::consume(self.get_mut(), amt);
}
}