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

# Function tokio::io::copy [−] [src]

    pub async fn copy<'a, R: ?Sized, W: ?Sized>(
        reader: &'a mut R,
        writer: &'a mut W
    ) -> Result<u64> where
        R: AsyncRead + 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.

This is an asynchronous version of `std::io::copy`.

# Errors

The returned future will finish with an error will return an error immediately if any call to `poll_read` or `poll_write` returns an error.

# Examples

    use tokio::io;

    let mut reader: &[u8] = b"hello";
    let mut writer: Vec<u8> = vec![];

    io::copy(&mut reader, &mut writer).await?;

    assert_eq!(&b"hello"[..], &writer[..]);