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//! ASN.1 DER headers.
use crate::{Decode, DerOrd, Encode, ErrorKind, Length, Reader, Result, Tag, Writer};
use core::cmp::Ordering;
/// ASN.1 DER headers: tag + length component of TLV-encoded values
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct Header {
/// Tag representing the type of the encoded value
pub tag: Tag,
/// Length of the encoded value
pub length: Length,
}
impl Header {
/// Create a new [`Header`] from a [`Tag`] and a specified length.
///
/// Returns an error if the length exceeds the limits of [`Length`].
pub fn new(tag: Tag, length: impl TryInto<Length>) -> Result<Self> {
let length = length.try_into().map_err(|_| ErrorKind::Overflow)?;
Ok(Self { tag, length })
}
}
impl<'a> Decode<'a> for Header {
fn decode<R: Reader<'a>>(reader: &mut R) -> Result<Header> {
let tag = Tag::decode(reader)?;
let length = Length::decode(reader).map_err(|e| {
if e.kind() == ErrorKind::Overlength {
ErrorKind::Length { tag }.into()
} else {
e
}
})?;
Ok(Self { tag, length })
}
}
impl Encode for Header {
fn encoded_len(&self) -> Result<Length> {
self.tag.encoded_len()? + self.length.encoded_len()?
}
fn encode(&self, writer: &mut impl Writer) -> Result<()> {
self.tag.encode(writer)?;
self.length.encode(writer)
}
}
impl DerOrd for Header {
fn der_cmp(&self, other: &Self) -> Result<Ordering> {
match self.tag.der_cmp(&other.tag)? {
Ordering::Equal => self.length.der_cmp(&other.length),
ordering => Ok(ordering),
}
}
}
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