1 use futures_core::future::Future;
2 use futures_core::ready;
3 use futures_core::task::{Context, Poll};
4 use futures_io::{AsyncBufRead, AsyncWrite};
5 use pin_project_lite::pin_project;
6 use std::io;
7 use std::pin::Pin;
8
9 /// Creates a future which copies all the bytes from one object to another.
10 ///
11 /// The returned future will copy all the bytes read from this `AsyncBufRead` into the
12 /// `writer` specified. This future will only complete once the `reader` has hit
13 /// EOF and all bytes have been written to and flushed from the `writer`
14 /// provided.
15 ///
16 /// On success the number of bytes is returned.
17 ///
18 /// # Examples
19 ///
20 /// ```
21 /// # futures::executor::block_on(async {
22 /// use futures::io::{self, AsyncWriteExt, Cursor};
23 ///
24 /// let reader = Cursor::new([1, 2, 3, 4]);
25 /// let mut writer = Cursor::new(vec![0u8; 5]);
26 ///
27 /// let bytes = io::copy_buf(reader, &mut writer).await?;
28 /// writer.close().await?;
29 ///
30 /// assert_eq!(bytes, 4);
31 /// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
32 /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
33 /// ```
copy_buf<R, W>(reader: R, writer: &mut W) -> CopyBuf<'_, R, W> where R: AsyncBufRead, W: AsyncWrite + Unpin + ?Sized,34 pub fn copy_buf<R, W>(reader: R, writer: &mut W) -> CopyBuf<'_, R, W>
35 where
36 R: AsyncBufRead,
37 W: AsyncWrite + Unpin + ?Sized,
38 {
39 CopyBuf { reader, writer, amt: 0 }
40 }
41
42 pin_project! {
43 /// Future for the [`copy_buf()`] function.
44 #[derive(Debug)]
45 #[must_use = "futures do nothing unless you `.await` or poll them"]
46 pub struct CopyBuf<'a, R, W: ?Sized> {
47 #[pin]
48 reader: R,
49 writer: &'a mut W,
50 amt: u64,
51 }
52 }
53
54 impl<R, W> Future for CopyBuf<'_, R, W>
55 where
56 R: AsyncBufRead,
57 W: AsyncWrite + Unpin + ?Sized,
58 {
59 type Output = io::Result<u64>;
60
poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>61 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
62 let mut this = self.project();
63 loop {
64 let buffer = ready!(this.reader.as_mut().poll_fill_buf(cx))?;
65 if buffer.is_empty() {
66 ready!(Pin::new(&mut this.writer).poll_flush(cx))?;
67 return Poll::Ready(Ok(*this.amt));
68 }
69
70 let i = ready!(Pin::new(&mut this.writer).poll_write(cx, buffer))?;
71 if i == 0 {
72 return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
73 }
74 *this.amt += i as u64;
75 this.reader.as_mut().consume(i);
76 }
77 }
78 }
79