pub trait WasiDir: WasiNode {
// Required method
fn get_readdir(
&self,
start: u64,
) -> Result<Vec<(String, u64, FileType)>, Errno>;
// Provided method
fn fd_readdir(
&self,
cursor: usize,
write_buf: &mut [u8],
) -> Result<usize, Errno> { ... }
}