Function default_read_buf 

#[doc(hidden)]
pub(crate) fn default_read_buf<F>(
    read: F,
    cursor: BorrowedCursor<'_, u8>,
) -> Result<(), Error>
where
    F: FnOnce(&mut [u8]) -> Result<usize, Error>,

🔬This is a nightly-only experimental API. (core_io_internals)