eth_valkyoth_codec/
rlp.rs

1mod encode;
2mod integer;
3mod list;
4
5#[cfg(test)]
6mod tests;
7
8use crate::{
9    DecodeAccumulator, DecodeError, DecodeLimits, checked_len_add, require_exact_consumption,
10    require_range_in_bounds,
11};
12
13pub use encode::{
14    encode_decoded_integer, encode_decoded_item, encode_decoded_list, encode_decoded_scalar,
15    encode_rlp_integer, encode_rlp_list_payload, encode_rlp_scalar, encoded_rlp_integer_len,
16    encoded_rlp_list_len, encoded_rlp_scalar_len,
17};
18pub use integer::{
19    MAX_RLP_U256_BYTES, RlpInteger, decode_rlp_integer, decode_rlp_integer_partial, decode_rlp_u64,
20    decode_rlp_u128, decode_rlp_u256_bytes,
21};
22pub use list::{
23    MAX_RLP_LIST_TRAVERSAL_DEPTH, RlpItem, RlpList, RlpListForm, RlpListItems, decode_rlp_list,
24    decode_rlp_list_partial,
25};
26
27pub(super) const SHORT_STRING_OFFSET: u8 = 0x80;
28/// Base for computing `len_of_len` in long-string encoding.
29///
30/// This is the last short-string prefix, not the first long-string prefix.
31pub(super) const LONG_STRING_OFFSET: u8 = 0xb7;
32pub(super) const SHORT_LIST_OFFSET: u8 = 0xc0;
33/// Base for computing `len_of_len` in long-list encoding.
34///
35/// This is the last short-list prefix, not the first long-list prefix.
36pub(super) const LONG_LIST_OFFSET: u8 = 0xf7;
37pub(super) const SHORT_STRING_LIMIT: usize = 55;
38pub(super) const LENGTH_RADIX: usize = 256;
39
40/// Canonical RLP scalar form used by the decoder.
41#[derive(Clone, Copy, Debug, Eq, PartialEq)]
42pub enum RlpScalarForm {
43    /// A single byte in `0x00..=0x7f`, encoded as itself.
44    SingleByte,
45    /// A byte string with a one-byte RLP header.
46    ShortString,
47    /// A byte string with a length-of-length RLP header.
48    LongString,
49}
50
51/// Borrowed RLP scalar byte string.
52///
53/// Fields are private so downstream crates cannot construct unvalidated
54/// decoded values and feed them into trusted re-encoding paths.
55#[derive(Clone, Copy, Debug, Eq, PartialEq)]
56pub struct RlpScalar<'a> {
57    payload: &'a [u8],
58    encoded_len: usize,
59    header_len: usize,
60    form: RlpScalarForm,
61}
62
63impl<'a> RlpScalar<'a> {
64    /// Returns the decoded scalar payload bytes.
65    #[must_use]
66    pub const fn payload(self) -> &'a [u8] {
67        self.payload
68    }
69
70    /// Returns the total encoded item length in bytes.
71    #[must_use]
72    pub const fn encoded_len(self) -> usize {
73        self.encoded_len
74    }
75
76    /// Returns the RLP header length in bytes.
77    #[must_use]
78    pub const fn header_len(self) -> usize {
79        self.header_len
80    }
81
82    /// Returns the canonical scalar form that was decoded.
83    #[must_use]
84    pub const fn form(self) -> RlpScalarForm {
85        self.form
86    }
87
88    /// Returns true when the decoded payload is empty.
89    #[must_use]
90    pub const fn is_empty(self) -> bool {
91        self.payload.is_empty()
92    }
93}
94
95/// Decodes exactly one canonical RLP scalar byte string.
96pub fn decode_rlp_scalar<'a>(
97    input: &'a [u8],
98    limits: DecodeLimits,
99) -> Result<RlpScalar<'a>, DecodeError> {
100    let mut accumulator = limits.accumulator();
101    let scalar = decode_rlp_scalar_partial(input, &mut accumulator)?;
102    require_exact_consumption(scalar.encoded_len, input.len())?;
103    Ok(scalar)
104}
105
106/// Decodes one canonical RLP scalar byte string from the start of `input`.
107///
108/// Warning: this intentionally accepts trailing bytes. Use
109/// [`decode_rlp_scalar`] when the full input must be consumed.
110///
111/// The input-length budget check applies to the full `input` slice, not only
112/// the consumed scalar bytes. Callers that decode from a larger outer buffer
113/// must pre-slice before calling this helper.
114///
115/// This helper does not reject trailing bytes. It is intended for nested
116/// decoders that need to consume one item while sharing cumulative budgets.
117pub fn decode_rlp_scalar_partial<'a>(
118    input: &'a [u8],
119    accumulator: &mut DecodeAccumulator,
120) -> Result<RlpScalar<'a>, DecodeError> {
121    accumulator.check_input_len(input.len())?;
122    accumulator.account_items(1)?;
123
124    let prefix = *input.first().ok_or(DecodeError::Malformed)?;
125    match prefix {
126        0x00..=0x7f => decode_single_byte(input),
127        SHORT_STRING_OFFSET..=LONG_STRING_OFFSET => decode_short_string(input, prefix),
128        0xb8..=0xbf => decode_long_string(input, prefix),
129        SHORT_LIST_OFFSET..=0xff => Err(DecodeError::UnexpectedList),
130    }
131}
132
133fn decode_single_byte(input: &[u8]) -> Result<RlpScalar<'_>, DecodeError> {
134    let payload = input.get(..1).ok_or(DecodeError::OffsetOutOfBounds)?;
135    Ok(RlpScalar {
136        payload,
137        encoded_len: 1,
138        header_len: 0,
139        form: RlpScalarForm::SingleByte,
140    })
141}
142
143pub(super) fn decode_short_string(input: &[u8], prefix: u8) -> Result<RlpScalar<'_>, DecodeError> {
144    let payload_len = usize::from(prefix.saturating_sub(SHORT_STRING_OFFSET));
145    let payload = payload(input, 1, payload_len)?;
146    if payload_len == 1 && payload.first().is_some_and(|byte| *byte <= 0x7f) {
147        return Err(DecodeError::Malformed);
148    }
149    Ok(RlpScalar {
150        payload,
151        encoded_len: checked_len_add(1, payload_len)?,
152        header_len: 1,
153        form: RlpScalarForm::ShortString,
154    })
155}
156
157pub(super) fn decode_long_string(input: &[u8], prefix: u8) -> Result<RlpScalar<'_>, DecodeError> {
158    let len_of_len = usize::from(prefix.saturating_sub(LONG_STRING_OFFSET));
159    let payload_len = parse_payload_len(input, 1, len_of_len)?;
160    if payload_len <= SHORT_STRING_LIMIT {
161        return Err(DecodeError::Malformed);
162    }
163    let header_len = checked_len_add(1, len_of_len)?;
164    let payload = payload(input, header_len, payload_len)?;
165    Ok(RlpScalar {
166        payload,
167        encoded_len: checked_len_add(header_len, payload_len)?,
168        header_len,
169        form: RlpScalarForm::LongString,
170    })
171}
172
173pub(super) fn parse_payload_len(
174    input: &[u8],
175    offset: usize,
176    len: usize,
177) -> Result<usize, DecodeError> {
178    let end = require_range_in_bounds(offset, len, input.len())?;
179    let bytes = input
180        .get(offset..end)
181        .ok_or(DecodeError::OffsetOutOfBounds)?;
182    if bytes.first().is_some_and(|byte| *byte == 0) {
183        return Err(DecodeError::Malformed);
184    }
185
186    let mut value = 0usize;
187    for byte in bytes {
188        value = value
189            .checked_mul(LENGTH_RADIX)
190            .ok_or(DecodeError::LengthOverflow)?;
191        value = value
192            .checked_add(usize::from(*byte))
193            .ok_or(DecodeError::LengthOverflow)?;
194    }
195    Ok(value)
196}
197
198pub(super) fn payload(input: &[u8], offset: usize, len: usize) -> Result<&[u8], DecodeError> {
199    let end = require_range_in_bounds(offset, len, input.len())?;
200    input.get(offset..end).ok_or(DecodeError::OffsetOutOfBounds)
201}
eth_valkyoth_codec/rlp.rs

eth_valkyoth_codec/
rlp.rs
