der/
decode.rs

1//! Trait definition for [`Decode`].
2
3use crate::{FixedTag, Header, Reader, Result, SliceReader};
4use core::marker::PhantomData;
5
6#[cfg(feature = "pem")]
7use crate::{pem::PemLabel, PemReader};
8
9#[cfg(doc)]
10use crate::{Length, Tag};
11
12#[cfg(feature = "alloc")]
13use alloc::boxed::Box;
14
15/// Decoding trait.
16///
17/// This trait provides the core abstraction upon which all decoding operations
18/// are based.
19pub trait Decode<'a>: Sized {
20    /// Attempt to decode this message using the provided decoder.
21    fn decode<R: Reader<'a>>(decoder: &mut R) -> Result<Self>;
22
23    /// Parse `Self` from the provided DER-encoded byte slice.
24    fn from_der(bytes: &'a [u8]) -> Result<Self> {
25        let mut reader = SliceReader::new(bytes)?;
26        let result = Self::decode(&mut reader)?;
27        reader.finish(result)
28    }
29}
30
31impl<'a, T> Decode<'a> for T
32where
33    T: DecodeValue<'a> + FixedTag,
34{
35    fn decode<R: Reader<'a>>(reader: &mut R) -> Result<T> {
36        let header = Header::decode(reader)?;
37        header.tag.assert_eq(T::TAG)?;
38        T::decode_value(reader, header)
39    }
40}
41
42/// Dummy implementation for [`PhantomData`] which allows deriving
43/// implementations on structs with phantom fields.
44impl<'a, T> Decode<'a> for PhantomData<T>
45where
46    T: ?Sized,
47{
48    fn decode<R: Reader<'a>>(_reader: &mut R) -> Result<PhantomData<T>> {
49        Ok(PhantomData)
50    }
51}
52
53/// Marker trait for data structures that can be decoded from DER without
54/// borrowing any data from the decoder.
55///
56/// This is primarily useful for trait bounds on functions which require that
57/// no data is borrowed from the decoder, for example a PEM decoder which needs
58/// to first decode data from Base64.
59///
60/// This trait is inspired by the [`DeserializeOwned` trait from `serde`](https://docs.rs/serde/latest/serde/de/trait.DeserializeOwned.html).
61pub trait DecodeOwned: for<'a> Decode<'a> {}
62
63impl<T> DecodeOwned for T where T: for<'a> Decode<'a> {}
64
65/// PEM decoding trait.
66///
67/// This trait is automatically impl'd for any type which impls both
68/// [`DecodeOwned`] and [`PemLabel`].
69#[cfg(feature = "pem")]
70pub trait DecodePem: DecodeOwned + PemLabel {
71    /// Try to decode this type from PEM.
72    fn from_pem(pem: impl AsRef<[u8]>) -> Result<Self>;
73}
74
75#[cfg(feature = "pem")]
76impl<T: DecodeOwned + PemLabel> DecodePem for T {
77    fn from_pem(pem: impl AsRef<[u8]>) -> Result<Self> {
78        let mut reader = PemReader::new(pem.as_ref())?;
79        Self::validate_pem_label(reader.type_label())?;
80        T::decode(&mut reader)
81    }
82}
83
84/// Decode the value part of a Tag-Length-Value encoded field, sans the [`Tag`]
85/// and [`Length`].
86pub trait DecodeValue<'a>: Sized {
87    /// Attempt to decode this message using the provided [`Reader`].
88    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self>;
89}
90
91#[cfg(feature = "alloc")]
92impl<'a, T> DecodeValue<'a> for Box<T>
93where
94    T: DecodeValue<'a>,
95{
96    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self> {
97        Ok(Box::new(T::decode_value(reader, header)?))
98    }
99}
der/decode.rs

der/
decode.rs
