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//! ASN.1 `OPTIONAL` as mapped to Rust's `Option` type
use crate::{Choice, Decode, DerOrd, Encode, Length, Reader, Result, Tag, Writer};
use core::cmp::Ordering;
impl<'a, T> Decode<'a> for Option<T>
where
T: Choice<'a>, // NOTE: all `Decode + Tagged` types receive a blanket `Choice` impl
{
fn decode<R: Reader<'a>>(reader: &mut R) -> Result<Option<T>> {
if let Some(byte) = reader.peek_byte() {
if T::can_decode(Tag::try_from(byte)?) {
return T::decode(reader).map(Some);
}
}
Ok(None)
}
}
impl<T> DerOrd for Option<T>
where
T: DerOrd,
{
fn der_cmp(&self, other: &Self) -> Result<Ordering> {
match self {
Some(a) => match other {
Some(b) => a.der_cmp(b),
None => Ok(Ordering::Greater),
},
None => Ok(Ordering::Less),
}
}
}
impl<T> Encode for Option<T>
where
T: Encode,
{
fn encoded_len(&self) -> Result<Length> {
(&self).encoded_len()
}
fn encode(&self, writer: &mut impl Writer) -> Result<()> {
(&self).encode(writer)
}
}
impl<T> Encode for &Option<T>
where
T: Encode,
{
fn encoded_len(&self) -> Result<Length> {
match self {
Some(encodable) => encodable.encoded_len(),
None => Ok(0u8.into()),
}
}
fn encode(&self, encoder: &mut impl Writer) -> Result<()> {
match self {
Some(encodable) => encodable.encode(encoder),
None => Ok(()),
}
}
}
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