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use crate::io::{AsyncBufRead, AsyncWrite};
use std::future::Future;
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};
cfg_io_util! {
/// A future that asynchronously copies the entire contents of a reader into a
/// writer.
///
/// This struct is generally created by calling [`copy_buf`][copy_buf]. Please
/// see the documentation of `copy_buf()` for more details.
///
/// [copy_buf]: copy_buf()
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
struct CopyBuf<'a, R: ?Sized, W: ?Sized> {
reader: &'a mut R,
writer: &'a mut W,
amt: u64,
}
/// Asynchronously copies the entire contents of a reader into a writer.
///
/// This function returns a future that will continuously read data from
/// `reader` and then write it into `writer` in a streaming fashion until
/// `reader` returns EOF or fails.
///
/// On success, the total number of bytes that were copied from `reader` to
/// `writer` is returned.
///
/// This is a [`tokio::io::copy`] alternative for [`AsyncBufRead`] readers
/// with no extra buffer allocation, since [`AsyncBufRead`] allow access
/// to the reader's inner buffer.
///
/// [`tokio::io::copy`]: crate::io::copy
/// [`AsyncBufRead`]: crate::io::AsyncBufRead
///
/// # Errors
///
/// The returned future will finish with an error will return an error
/// immediately if any call to `poll_fill_buf` or `poll_write` returns an
/// error.
///
/// # Examples
///
/// ```
/// use tokio::io;
///
/// # async fn dox() -> std::io::Result<()> {
/// let mut reader: &[u8] = b"hello";
/// let mut writer: Vec<u8> = vec![];
///
/// io::copy_buf(&mut reader, &mut writer).await?;
///
/// assert_eq!(b"hello", &writer[..]);
/// # Ok(())
/// # }
/// ```
pub async fn copy_buf<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
where
R: AsyncBufRead + Unpin + ?Sized,
W: AsyncWrite + Unpin + ?Sized,
{
CopyBuf {
reader,
writer,
amt: 0,
}.await
}
}
impl<R, W> Future for CopyBuf<'_, R, W>
where
R: AsyncBufRead + Unpin + ?Sized,
W: AsyncWrite + Unpin + ?Sized,
{
type Output = io::Result<u64>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
loop {
let me = &mut *self;
let buffer = ready!(Pin::new(&mut *me.reader).poll_fill_buf(cx))?;
if buffer.is_empty() {
ready!(Pin::new(&mut self.writer).poll_flush(cx))?;
return Poll::Ready(Ok(self.amt));
}
let i = ready!(Pin::new(&mut *me.writer).poll_write(cx, buffer))?;
if i == 0 {
return Poll::Ready(Err(std::io::ErrorKind::WriteZero.into()));
}
self.amt += i as u64;
Pin::new(&mut *self.reader).consume(i);
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn assert_unpin() {
use std::marker::PhantomPinned;
crate::is_unpin::<CopyBuf<'_, PhantomPinned, PhantomPinned>>();
}
}