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//! ASN.1 `NULL` support.
use crate::{
asn1::AnyRef, ord::OrdIsValueOrd, BytesRef, DecodeValue, EncodeValue, Error, ErrorKind,
FixedTag, Header, Length, Reader, Result, Tag, Writer,
};
/// ASN.1 `NULL` type.
#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
pub struct Null;
impl_any_conversions!(Null);
impl<'a> DecodeValue<'a> for Null {
fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self> {
if header.length.is_zero() {
Ok(Null)
} else {
Err(reader.error(ErrorKind::Length { tag: Self::TAG }))
}
}
}
impl EncodeValue for Null {
fn value_len(&self) -> Result<Length> {
Ok(Length::ZERO)
}
fn encode_value(&self, _writer: &mut impl Writer) -> Result<()> {
Ok(())
}
}
impl FixedTag for Null {
const TAG: Tag = Tag::Null;
}
impl OrdIsValueOrd for Null {}
impl<'a> From<Null> for AnyRef<'a> {
fn from(_: Null) -> AnyRef<'a> {
AnyRef::from_tag_and_value(Tag::Null, BytesRef::default())
}
}
impl TryFrom<AnyRef<'_>> for () {
type Error = Error;
fn try_from(any: AnyRef<'_>) -> Result<()> {
Null::try_from(any).map(|_| ())
}
}
impl<'a> From<()> for AnyRef<'a> {
fn from(_: ()) -> AnyRef<'a> {
Null.into()
}
}
impl<'a> DecodeValue<'a> for () {
fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self> {
Null::decode_value(reader, header)?;
Ok(())
}
}
impl EncodeValue for () {
fn value_len(&self) -> Result<Length> {
Ok(Length::ZERO)
}
fn encode_value(&self, _writer: &mut impl Writer) -> Result<()> {
Ok(())
}
}
impl FixedTag for () {
const TAG: Tag = Tag::Null;
}
#[cfg(test)]
mod tests {
use super::Null;
use crate::{Decode, Encode};
#[test]
fn decode() {
Null::from_der(&[0x05, 0x00]).unwrap();
}
#[test]
fn encode() {
let mut buffer = [0u8; 2];
assert_eq!(&[0x05, 0x00], Null.encode_to_slice(&mut buffer).unwrap());
assert_eq!(&[0x05, 0x00], ().encode_to_slice(&mut buffer).unwrap());
}
#[test]
fn reject_non_canonical() {
assert!(Null::from_der(&[0x05, 0x81, 0x00]).is_err());
}
}
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