Function read_exactish_async 

pub async fn read_exactish_async(
    reader: &mut (impl AsyncRead + Unpin),
    buf: &mut [u8],
) -> Result<bool>

This function reads the exact amount of bytes required to fill the buffer, possibly performing multiple reads to do so (and also retrying if required to deal with EINTR).

This is the async version of read_exactish().