der/asn1/
optional.rs

1//! ASN.1 `OPTIONAL` as mapped to Rust's `Option` type
2
3use crate::{Choice, Decode, DerOrd, Encode, Error, Length, Reader, Tag, Writer};
4use core::cmp::Ordering;
5
6impl<'a, T> Decode<'a> for Option<T>
7where
8    T: Choice<'a>, // NOTE: all `Decode + Tagged` types receive a blanket `Choice` impl
9{
10    type Error = T::Error;
11
12    fn decode<R: Reader<'a>>(reader: &mut R) -> Result<Option<T>, Self::Error> {
13        if reader.is_finished() {
14            return Ok(None);
15        }
16
17        if T::can_decode(Tag::peek(reader)?) {
18            return T::decode(reader).map(Some);
19        }
20
21        Ok(None)
22    }
23}
24
25impl<T> DerOrd for Option<T>
26where
27    T: DerOrd,
28{
29    fn der_cmp(&self, other: &Self) -> Result<Ordering, Error> {
30        match (self, other) {
31            (Some(a), Some(b)) => a.der_cmp(b),
32            (Some(_), None) => Ok(Ordering::Greater),
33            (None, Some(_)) => Ok(Ordering::Less),
34            // Both absent: neither contributes any octets.
35            (None, None) => Ok(Ordering::Equal),
36        }
37    }
38}
39
40impl<T> Encode for Option<T>
41where
42    T: Encode,
43{
44    fn encoded_len(&self) -> Result<Length, Error> {
45        (&self).encoded_len()
46    }
47
48    fn encode(&self, writer: &mut impl Writer) -> Result<(), Error> {
49        (&self).encode(writer)
50    }
51}
52
53impl<T> Encode for &Option<T>
54where
55    T: Encode,
56{
57    fn encoded_len(&self) -> Result<Length, Error> {
58        match self {
59            Some(encodable) => encodable.encoded_len(),
60            None => Ok(0u8.into()),
61        }
62    }
63
64    fn encode(&self, writer: &mut impl Writer) -> Result<(), Error> {
65        match self {
66            Some(encodable) => encodable.encode(writer),
67            None => Ok(()),
68        }
69    }
70}
71
72#[cfg(test)]
73mod tests {
74    use crate::DerOrd;
75    use core::cmp::Ordering;
76
77    #[test]
78    fn der_cmp() {
79        let none: Option<u8> = None;
80        assert_eq!(none.der_cmp(&None), Ok(Ordering::Equal));
81        assert_eq!(none.der_cmp(&Some(0)), Ok(Ordering::Less));
82        assert_eq!(Some(0u8).der_cmp(&None), Ok(Ordering::Greater));
83        assert_eq!(Some(1u8).der_cmp(&Some(2)), Ok(Ordering::Less));
84        assert_eq!(Some(2u8).der_cmp(&Some(2)), Ok(Ordering::Equal));
85    }
86}
der/asn1/optional.rs

der/asn1/
optional.rs
