monero_io_mirror/
lib.rs

1#![cfg_attr(docsrs, feature(doc_auto_cfg))]
2#![doc = include_str!("../README.md")]
3#![deny(missing_docs)]
4#![cfg_attr(not(feature = "std"), no_std)]
5
6use core::fmt::Debug;
7use std_shims::{
8  vec,
9  vec::Vec,
10  io::{self, Read, Write},
11};
12
13use curve25519_dalek::{
14  scalar::Scalar,
15  edwards::{EdwardsPoint, CompressedEdwardsY},
16};
17
18const VARINT_CONTINUATION_MASK: u8 = 0b1000_0000;
19
20mod sealed {
21  /// A trait for a number readable/writable as a VarInt.
22  ///
23  /// This is sealed to prevent unintended implementations.
24  pub trait VarInt: TryInto<u64> + TryFrom<u64> + Copy {
25    const BITS: usize;
26  }
27
28  impl VarInt for u8 {
29    const BITS: usize = 8;
30  }
31  impl VarInt for u32 {
32    const BITS: usize = 32;
33  }
34  impl VarInt for u64 {
35    const BITS: usize = 64;
36  }
37  impl VarInt for usize {
38    const BITS: usize = core::mem::size_of::<usize>() * 8;
39  }
40}
41
42/// The amount of bytes this number will take when serialized as a VarInt.
43///
44/// This function will panic if the VarInt exceeds u64::MAX.
45pub fn varint_len<V: sealed::VarInt>(varint: V) -> usize {
46  let varint_u64: u64 = varint.try_into().map_err(|_| "varint exceeded u64").unwrap();
47  ((usize::try_from(u64::BITS - varint_u64.leading_zeros()).unwrap().saturating_sub(1)) / 7) + 1
48}
49
50/// Write a byte.
51///
52/// This is used as a building block within generic functions.
53pub fn write_byte<W: Write>(byte: &u8, w: &mut W) -> io::Result<()> {
54  w.write_all(&[*byte])
55}
56
57/// Write a number, VarInt-encoded.
58///
59/// This will panic if the VarInt exceeds u64::MAX.
60pub fn write_varint<W: Write, U: sealed::VarInt>(varint: &U, w: &mut W) -> io::Result<()> {
61  let mut varint: u64 = (*varint).try_into().map_err(|_| "varint exceeded u64").unwrap();
62  while {
63    let mut b = u8::try_from(varint & u64::from(!VARINT_CONTINUATION_MASK)).unwrap();
64    varint >>= 7;
65    if varint != 0 {
66      b |= VARINT_CONTINUATION_MASK;
67    }
68    write_byte(&b, w)?;
69    varint != 0
70  } {}
71  Ok(())
72}
73
74/// Write a scalar.
75pub fn write_scalar<W: Write>(scalar: &Scalar, w: &mut W) -> io::Result<()> {
76  w.write_all(&scalar.to_bytes())
77}
78
79/// Write a point.
80pub fn write_point<W: Write>(point: &EdwardsPoint, w: &mut W) -> io::Result<()> {
81  w.write_all(&point.compress().to_bytes())
82}
83
84/// Write a list of elements, without length-prefixing.
85pub fn write_raw_vec<T, W: Write, F: Fn(&T, &mut W) -> io::Result<()>>(
86  f: F,
87  values: &[T],
88  w: &mut W,
89) -> io::Result<()> {
90  for value in values {
91    f(value, w)?;
92  }
93  Ok(())
94}
95
96/// Write a list of elements, with length-prefixing.
97pub fn write_vec<T, W: Write, F: Fn(&T, &mut W) -> io::Result<()>>(
98  f: F,
99  values: &[T],
100  w: &mut W,
101) -> io::Result<()> {
102  write_varint(&values.len(), w)?;
103  write_raw_vec(f, values, w)
104}
105
106/// Read a constant amount of bytes.
107pub fn read_bytes<R: Read, const N: usize>(r: &mut R) -> io::Result<[u8; N]> {
108  let mut res = [0; N];
109  r.read_exact(&mut res)?;
110  Ok(res)
111}
112
113/// Read a single byte.
114pub fn read_byte<R: Read>(r: &mut R) -> io::Result<u8> {
115  Ok(read_bytes::<_, 1>(r)?[0])
116}
117
118/// Read a u16, little-endian encoded.
119pub fn read_u16<R: Read>(r: &mut R) -> io::Result<u16> {
120  read_bytes(r).map(u16::from_le_bytes)
121}
122
123/// Read a u32, little-endian encoded.
124pub fn read_u32<R: Read>(r: &mut R) -> io::Result<u32> {
125  read_bytes(r).map(u32::from_le_bytes)
126}
127
128/// Read a u64, little-endian encoded.
129pub fn read_u64<R: Read>(r: &mut R) -> io::Result<u64> {
130  read_bytes(r).map(u64::from_le_bytes)
131}
132
133/// Read a canonically-encoded VarInt.
134pub fn read_varint<R: Read, U: sealed::VarInt>(r: &mut R) -> io::Result<U> {
135  let mut bits = 0;
136  let mut res = 0;
137  while {
138    let b = read_byte(r)?;
139    if (bits != 0) && (b == 0) {
140      Err(io::Error::other("non-canonical varint"))?;
141    }
142    if ((bits + 7) >= U::BITS) && (b >= (1 << (U::BITS - bits))) {
143      Err(io::Error::other("varint overflow"))?;
144    }
145
146    res += u64::from(b & (!VARINT_CONTINUATION_MASK)) << bits;
147    bits += 7;
148    b & VARINT_CONTINUATION_MASK == VARINT_CONTINUATION_MASK
149  } {}
150  res.try_into().map_err(|_| io::Error::other("VarInt does not fit into integer type"))
151}
152
153/// Read a canonically-encoded scalar.
154///
155/// Some scalars within the Monero protocol are not enforced to be canonically encoded. For such
156/// scalars, they should be represented as `[u8; 32]` and later converted to scalars as relevant.
157pub fn read_scalar<R: Read>(r: &mut R) -> io::Result<Scalar> {
158  Option::from(Scalar::from_canonical_bytes(read_bytes(r)?))
159    .ok_or_else(|| io::Error::other("unreduced scalar"))
160}
161
162/// Decompress a canonically-encoded Ed25519 point.
163///
164/// Ed25519 is of order `8 * l`. This function ensures each of those `8 * l` points have a singular
165/// encoding by checking points aren't encoded with an unreduced field element, and aren't negative
166/// when the negative is equivalent (0 == -0).
167///
168/// Since this decodes an Ed25519 point, it does not check the point is in the prime-order
169/// subgroup. Torsioned points do have a canonical encoding, and only aren't canonical when
170/// considered in relation to the prime-order subgroup.
171pub fn decompress_point(bytes: [u8; 32]) -> Option<EdwardsPoint> {
172  CompressedEdwardsY(bytes)
173    .decompress()
174    // Ban points which are either unreduced or -0
175    .filter(|point| point.compress().to_bytes() == bytes)
176}
177
178/// Read a canonically-encoded Ed25519 point.
179///
180/// This internally calls `decompress_point` and has the same definition of canonicity. This
181/// function does not check the resulting point is within the prime-order subgroup.
182pub fn read_point<R: Read>(r: &mut R) -> io::Result<EdwardsPoint> {
183  let bytes = read_bytes(r)?;
184  decompress_point(bytes).ok_or_else(|| io::Error::other("invalid point"))
185}
186
187/// Read a canonically-encoded Ed25519 point, within the prime-order subgroup.
188pub fn read_torsion_free_point<R: Read>(r: &mut R) -> io::Result<EdwardsPoint> {
189  read_point(r)
190    .ok()
191    .filter(EdwardsPoint::is_torsion_free)
192    .ok_or_else(|| io::Error::other("invalid point"))
193}
194
195/// Read a variable-length list of elements, without length-prefixing.
196pub fn read_raw_vec<R: Read, T, F: Fn(&mut R) -> io::Result<T>>(
197  f: F,
198  len: usize,
199  r: &mut R,
200) -> io::Result<Vec<T>> {
201  let mut res = vec![];
202  for _ in 0 .. len {
203    res.push(f(r)?);
204  }
205  Ok(res)
206}
207
208/// Read a constant-length list of elements.
209pub fn read_array<R: Read, T: Debug, F: Fn(&mut R) -> io::Result<T>, const N: usize>(
210  f: F,
211  r: &mut R,
212) -> io::Result<[T; N]> {
213  read_raw_vec(f, N, r).map(|vec| vec.try_into().unwrap())
214}
215
216/// Read a length-prefixed variable-length list of elements.
217pub fn read_vec<R: Read, T, F: Fn(&mut R) -> io::Result<T>>(f: F, r: &mut R) -> io::Result<Vec<T>> {
218  read_raw_vec(f, read_varint(r)?, r)
219}
monero_io_mirror/lib.rs

monero_io_mirror/
lib.rs
