Function copy_buf 

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

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 a tokio::io::copy alternative for AsyncBufRead readers with no extra buffer allocation, since AsyncBufRead allow access to the reader’s inner buffer.

When to use async alternatives instead of SyncIoBridge

If you are looking to use std::io::copy with a synchronous consumer (like a hasher or compressor), consider using async alternatives instead of wrapping the reader with SyncIoBridge. See the SyncIoBridge documentation for detailed examples and guidance on hashing, compression, and data parsing.

Errors

Errors from poll_fill_buf and poll_write are returned immediately, except io::ErrorKind::Interrupted, which is retried. Errors from flushing the writer are returned without retrying.

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[..]);