Repository: tokio-rs/tokio
File: tokio/src/io/util/copy.rs (Rust)

Code before:

/// A future that asynchronously copies the entire contents of a reader into a
/// writer.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
struct Copy<'a, R: ?Sized, W: ?Sized> {
    reader: &'a mut R,
    writer: &'a mut W,
    buf: CopyBuffer,
}

cfg_io_util! {
    /// 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 an asynchronous version of [`std::io::copy`][std].
    ///
    /// A heap-allocated buffer with 8 KB is created to take data from the
    /// reader to the writer, check [`copy_buf`] if you want an alternative
    /// for [`AsyncBufRead`].
    ///
    /// [std]: std::io::copy
    /// [`copy_buf`]: crate::io::copy_buf
    /// [`AsyncBufRead`]: crate::io::AsyncBufRead
    ///
    /// # Errors
    ///
    /// The returned future will return an error immediately if any call to
    /// `poll_read` 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(&mut reader, &mut writer).await?;
    ///
    /// assert_eq!(&b"hello"[..], &writer[..]);
    /// # Ok(())
    /// # }
    /// ```

Review comment (suggestion):
It might be nice to mention that to change the size of the buffer, you can use a `BufReader` together with `copy_buf`.

Code after:

/// A future that asynchronously copies the entire contents of a reader into a
/// writer.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
struct Copy<'a, R: ?Sized, W: ?Sized> {
    reader: &'a mut R,
    writer: &'a mut W,
    buf: CopyBuffer,
}

cfg_io_util! {
    /// 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 an asynchronous version of [`std::io::copy`][std].
    ///
    /// A heap-allocated copy buffer with 8 KB is created to take data from the
    /// reader to the writer, check [`copy_buf`] if you want an alternative for
    /// [`AsyncBufRead`]. You can use `copy_buf` with [`BufReader`] to change the
    /// buffer capacity.
    ///
    /// [std]: std::io::copy
    /// [`copy_buf`]: crate::io::copy_buf
    /// [`AsyncBufRead`]: crate::io::AsyncBufRead
    /// [`BufReader`]: crate::io::BufReader
    ///
    /// # Errors
    ///
    /// The returned future will return an error immediately if any call to
    /// `poll_read` 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(&mut reader, &mut writer).await?;
    ///
    /// assert_eq!(&b"hello"[..], &writer[..]);
    /// # Ok(())