1 use crate::io::{AsyncBufRead, AsyncWrite};
2 use std::future::Future;
3 use std::io;
4 use std::pin::Pin;
5 use std::task::{ready, Context, Poll};
6 
7 cfg_io_util! {
8     /// A future that asynchronously copies the entire contents of a reader into a
9     /// writer.
10     ///
11     /// This struct is generally created by calling [`copy_buf`][copy_buf]. Please
12     /// see the documentation of `copy_buf()` for more details.
13     ///
14     /// [copy_buf]: copy_buf()
15     #[derive(Debug)]
16     #[must_use = "futures do nothing unless you `.await` or poll them"]
17     struct CopyBuf<'a, R: ?Sized, W: ?Sized> {
18         reader: &'a mut R,
19         writer: &'a mut W,
20         amt: u64,
21     }
22 
23     /// Asynchronously copies the entire contents of a reader into a writer.
24     ///
25     /// This function returns a future that will continuously read data from
26     /// `reader` and then write it into `writer` in a streaming fashion until
27     /// `reader` returns EOF or fails.
28     ///
29     /// On success, the total number of bytes that were copied from `reader` to
30     /// `writer` is returned.
31     ///
32     /// This is a [`tokio::io::copy`] alternative for [`AsyncBufRead`] readers
33     /// with no extra buffer allocation, since [`AsyncBufRead`] allow access
34     /// to the reader's inner buffer.
35     ///
36     /// [`tokio::io::copy`]: crate::io::copy
37     /// [`AsyncBufRead`]: crate::io::AsyncBufRead
38     ///
39     /// # Errors
40     ///
41     /// The returned future will finish with an error will return an error
42     /// immediately if any call to `poll_fill_buf` or `poll_write` returns an
43     /// error.
44     ///
45     /// # Examples
46     ///
47     /// ```
48     /// use tokio::io;
49     ///
50     /// # async fn dox() -> std::io::Result<()> {
51     /// let mut reader: &[u8] = b"hello";
52     /// let mut writer: Vec<u8> = vec![];
53     ///
54     /// io::copy_buf(&mut reader, &mut writer).await?;
55     ///
56     /// assert_eq!(b"hello", &writer[..]);
57     /// # Ok(())
58     /// # }
59     /// ```
60     pub async fn copy_buf<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
61     where
62         R: AsyncBufRead + Unpin + ?Sized,
63         W: AsyncWrite + Unpin + ?Sized,
64     {
65         CopyBuf {
66             reader,
67             writer,
68             amt: 0,
69         }.await
70     }
71 }
72 
73 impl<R, W> Future for CopyBuf<'_, R, W>
74 where
75     R: AsyncBufRead + Unpin + ?Sized,
76     W: AsyncWrite + Unpin + ?Sized,
77 {
78     type Output = io::Result<u64>;
79 
poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>80     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
81         loop {
82             let me = &mut *self;
83             let buffer = ready!(Pin::new(&mut *me.reader).poll_fill_buf(cx))?;
84             if buffer.is_empty() {
85                 ready!(Pin::new(&mut self.writer).poll_flush(cx))?;
86                 return Poll::Ready(Ok(self.amt));
87             }
88 
89             let i = ready!(Pin::new(&mut *me.writer).poll_write(cx, buffer))?;
90             if i == 0 {
91                 return Poll::Ready(Err(std::io::ErrorKind::WriteZero.into()));
92             }
93             self.amt += i as u64;
94             Pin::new(&mut *self.reader).consume(i);
95         }
96     }
97 }
98 
99 #[cfg(test)]
100 mod tests {
101     use super::*;
102 
103     #[test]
assert_unpin()104     fn assert_unpin() {
105         use std::marker::PhantomPinned;
106         crate::is_unpin::<CopyBuf<'_, PhantomPinned, PhantomPinned>>();
107     }
108 }
109