ssh_key/
decode.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
//! Decoder-side implementation of the SSH protocol's data type representations
//! as described in [RFC4251 § 5].
//!
//! [RFC4251 § 5]: https://datatracker.ietf.org/doc/html/rfc4251#section-5

use crate::{reader::Reader, Error, Result};

#[cfg(feature = "alloc")]
use alloc::{string::String, vec::Vec};

/// Maximum size of a `usize` this library will accept.
const MAX_SIZE: usize = 0xFFFFF;

/// Decoder trait.
///
/// This trait describes how to decode a given type.
pub(crate) trait Decode: Sized {
    /// Attempt to decode a value of this type using the provided [`Decoder`].
    fn decode(reader: &mut impl Reader) -> Result<Self>;
}

/// Decode a single `byte` from the input data.
impl Decode for u8 {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        let mut buf = [0];
        reader.read(&mut buf)?;
        Ok(buf[0])
    }
}

/// Decode a `uint32` as described in [RFC4251 § 5]:
///
/// > Represents a 32-bit unsigned integer.  Stored as four bytes in the
/// > order of decreasing significance (network byte order).
/// > For example: the value 699921578 (0x29b7f4aa) is stored as 29 b7 f4 aa.
///
/// [RFC4251 § 5]: https://datatracker.ietf.org/doc/html/rfc4251#section-5
impl Decode for u32 {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        let mut bytes = [0u8; 4];
        reader.read(&mut bytes)?;
        Ok(u32::from_be_bytes(bytes))
    }
}

/// Decode a `uint64` as described in [RFC4251 § 5]:
///
/// > Represents a 64-bit unsigned integer.  Stored as eight bytes in
/// > the order of decreasing significance (network byte order).
///
/// [RFC4251 § 5]: https://datatracker.ietf.org/doc/html/rfc4251#section-5
impl Decode for u64 {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        let mut bytes = [0u8; 8];
        reader.read(&mut bytes)?;
        Ok(u64::from_be_bytes(bytes))
    }
}

/// Decode a `usize`.
///
/// Uses [`Decode`] impl on `u32` and then converts to a `usize`, handling
/// potential overflow if `usize` is smaller than `u32`.
///
/// Enforces a library-internal limit of 1048575, as the main use case for
/// `usize` is length prefixes.
impl Decode for usize {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        let n = usize::try_from(u32::decode(reader)?)?;

        if n <= MAX_SIZE {
            Ok(n)
        } else {
            Err(Error::Length)
        }
    }
}

/// Decodes a byte array from `byte[n]` as described in [RFC4251 § 5]:
///
/// > A byte represents an arbitrary 8-bit value (octet).  Fixed length
/// > data is sometimes represented as an array of bytes, written
/// > byte[n], where n is the number of bytes in the array.
///
/// [RFC4251 § 5]: https://datatracker.ietf.org/doc/html/rfc4251#section-5
impl<const N: usize> Decode for [u8; N] {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        reader.read_nested(|reader| {
            let mut result = [(); N].map(|_| 0);
            reader.read(&mut result)?;
            Ok(result)
        })
    }
}

/// Decodes `Vec<u8>` from `byte[n]` as described in [RFC4251 § 5]:
///
/// > A byte represents an arbitrary 8-bit value (octet).  Fixed length
/// > data is sometimes represented as an array of bytes, written
/// > byte[n], where n is the number of bytes in the array.
///
/// [RFC4251 § 5]: https://datatracker.ietf.org/doc/html/rfc4251#section-5
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
impl Decode for Vec<u8> {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        reader.read_nested(|reader| {
            let mut result = vec![0u8; reader.remaining_len()];
            reader.read(&mut result)?;
            Ok(result)
        })
    }
}

#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
impl Decode for String {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        String::from_utf8(Vec::decode(reader)?).map_err(|_| Error::CharacterEncoding)
    }
}

#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
impl Decode for Vec<String> {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        reader.read_nested(|reader| {
            let mut entries = Self::new();

            while !reader.is_finished() {
                entries.push(String::decode(reader)?);
            }

            Ok(entries)
        })
    }
}