tokio/io/util/
copy_buf.rs

1use crate::io::{AsyncBufRead, AsyncWrite};
2use std::future::Future;
3use std::io;
4use std::pin::Pin;
5use std::task::{ready, Context, Poll};
6
7cfg_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    /// # When to use async alternatives instead of `SyncIoBridge`
37    ///
38    /// If you are looking to use [`std::io::copy`] with a synchronous consumer
39    /// (like a `hasher` or compressor), consider using async alternatives instead of
40    /// wrapping the reader with [`SyncIoBridge`]. See the [`SyncIoBridge`]
41    /// documentation for detailed examples and guidance on hashing, compression,
42    /// and data parsing.
43    ///
44    /// [`tokio::io::copy`]: crate::io::copy
45    /// [`AsyncBufRead`]: crate::io::AsyncBufRead
46    /// [`SyncIoBridge`]: https://docs.rs/tokio-util/latest/tokio_util/io/struct.SyncIoBridge.html
47    ///
48    /// # Errors
49    ///
50    /// The returned future will finish with an error will return an error
51    /// immediately if any call to `poll_fill_buf` or `poll_write` returns an
52    /// error.
53    ///
54    /// # Examples
55    ///
56    /// ```
57    /// use tokio::io;
58    ///
59    /// # async fn dox() -> std::io::Result<()> {
60    /// let mut reader: &[u8] = b"hello";
61    /// let mut writer: Vec<u8> = vec![];
62    ///
63    /// io::copy_buf(&mut reader, &mut writer).await?;
64    ///
65    /// assert_eq!(b"hello", &writer[..]);
66    /// # Ok(())
67    /// # }
68    /// ```
69    pub async fn copy_buf<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
70    where
71        R: AsyncBufRead + Unpin + ?Sized,
72        W: AsyncWrite + Unpin + ?Sized,
73    {
74        CopyBuf {
75            reader,
76            writer,
77            amt: 0,
78        }.await
79    }
80}
81
82impl<R, W> Future for CopyBuf<'_, R, W>
83where
84    R: AsyncBufRead + Unpin + ?Sized,
85    W: AsyncWrite + Unpin + ?Sized,
86{
87    type Output = io::Result<u64>;
88
89    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
90        loop {
91            let me = &mut *self;
92            let buffer = ready!(Pin::new(&mut *me.reader).poll_fill_buf(cx))?;
93            if buffer.is_empty() {
94                ready!(Pin::new(&mut self.writer).poll_flush(cx))?;
95                return Poll::Ready(Ok(self.amt));
96            }
97
98            let i = ready!(Pin::new(&mut *me.writer).poll_write(cx, buffer))?;
99            if i == 0 {
100                return Poll::Ready(Err(std::io::ErrorKind::WriteZero.into()));
101            }
102            self.amt += i as u64;
103            Pin::new(&mut *self.reader).consume(i);
104        }
105    }
106}
107
108#[cfg(test)]
109mod tests {
110    use super::*;
111
112    #[test]
113    fn assert_unpin() {
114        use std::marker::PhantomPinned;
115        crate::is_unpin::<CopyBuf<'_, PhantomPinned, PhantomPinned>>();
116    }
117}
tokio/io/util/copy_buf.rs

tokio/io/util/
copy_buf.rs
