[codec] Add Zeroed type #1703
Description
A type that represents a sequence of zeroed bytes. Similar to [0; N] but required to be all-zeroes. Doesn't actually need to store the array, could just be a single usize instead. This is useful for padding or zeroing out a buffer. Should return an error on read_cfg(...) if the bytes are not zeroed
pub struct Zeroed {
n: usize,
}
impl Zeroed {
pub fn new(n: usize) -> Self {
Self { n }
}
}
impl Read for Zeroed {
type Cfg = usize;
fn read_cfg(buf: &mut impl Buf, n: &Self::Cfg) -> Result<Self, Error> {
at_least(buf, *n)?;
let mut bytes = vec![0; *n];
buf.copy_to_slice(&mut bytes);
if bytes.iter().any(|&b| b != 0) {
return Err(Error::Invalid("Zeroed", "bytes are not zero"));
}
Ok(Self { n: *n })
}
}
impl Write for Zeroed {
fn write(&self, buf: &mut impl BufMut) {
buf.put_bytes(0, self.n);
}
}
impl EncodeSize for Zeroed {
fn encode_size(&self) -> usize {
self.n
}
}