# tokio::io::copy_buf - Rust
API documentation for the Rust `copy_buf` fn in crate `tokio`.
Keywords: rust, rustlang, rust-lang, copy_buf

# Function tokio::io::copy_buf [−] [src]

    pub async fn copy_buf<'a, R: ?Sized, W: ?Sized>(
        reader: &'a mut R,
        writer: &'a mut W
    ) -> Result<u64> where
        R: AsyncBufRead + Unpin,
        W: AsyncWrite + Unpin,

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.

On success, the total number of bytes that were copied from `reader` to `writer` is returned.

# 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;

    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[..]);