1// Copyright 2018 Brian Smith.
2//
3// Permission to use, copy, modify, and/or distribute this software for any
4// purpose with or without fee is hereby granted, provided that the above
5// copyright notice and this permission notice appear in all copies.
6//
7// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
10// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14
15//! Serialization and deserialization.
16
17use crate::error;
18
19/// A serialized positive integer.
20#[derive(Copy, Clone)]
21pub struct Positive<'a>(untrusted::Input<'a>);
22
23impl<'a> Positive<'a> {
24 #[inline]
25 pub(crate) fn from_be_bytes(input: untrusted::Input<'a>) -> Result<Self, error::Unspecified> {
26 // Empty inputs are not allowed.
27 let &first_byte = input
28 .as_slice_less_safe()
29 .first()
30 .ok_or(error::Unspecified)?;
31 // Zero isn't allowed and leading zeros aren't allowed.
32 if first_byte == 0 {
33 return Err(error::Unspecified);
34 }
35 Ok(Self(input))
36 }
37
38 /// Returns the value, ordered from significant byte to least significant
39 /// byte, without any leading zeros. The result is guaranteed to be
40 /// non-empty.
41 #[inline]
42 pub fn big_endian_without_leading_zero(&self) -> &'a [u8] {
43 self.big_endian_without_leading_zero_as_input()
44 .as_slice_less_safe()
45 }
46
47 #[inline]
48 pub(crate) fn big_endian_without_leading_zero_as_input(&self) -> untrusted::Input<'a> {
49 self.0
50 }
51}
52
53impl Positive<'_> {
54 /// Returns the first byte.
55 ///
56 /// Will not panic because the value is guaranteed to have at least one
57 /// byte.
58 pub fn first_byte(&self) -> u8 {
59 // This won't panic because
60 self.0.as_slice_less_safe()[0]
61 }
62}
63
64#[cfg(test)]
65mod tests {
66 use super::*;
67
68 #[test]
69 fn test_from_be_bytes() {
70 static TEST_CASES: &[(&[u8], Result<&[u8], error::Unspecified>)] = &[
71 // An empty input isn't a number.
72 (&[], Err(error::Unspecified)),
73 // Zero is not positive.
74 (&[0x00], Err(error::Unspecified)),
75 // Minimum value. No leading zero required or allowed.
76 (&[0x00, 0x01], Err(error::Unspecified)),
77 (&[0x01], Ok(&[0x01])),
78 // Maximum first byte. No leading zero required or allowed.
79 (&[0xff], Ok(&[0xff])),
80 (&[0x00, 0xff], Err(error::Unspecified)),
81 // The last byte can be zero.
82 (&[0x01, 0x00], Ok(&[0x01, 0x00])),
83 (&[0x01, 0x00, 0x00], Ok(&[0x01, 0x00, 0x00])),
84 // Having no zero bytes are also allowed.
85 (&[0x01, 0x01], Ok(&[0x01, 0x01])),
86 // A middle byte can be zero.
87 (&[0x01, 0x00, 0x01], Ok(&[0x01, 0x00, 0x01])),
88 (&[0x01, 0x01, 0x01], Ok(&[0x01, 0x01, 0x01])),
89 ];
90 for &(input, result) in TEST_CASES {
91 let input = untrusted::Input::from(input);
92 assert_eq!(
93 Positive::from_be_bytes(input).map(|p| p.big_endian_without_leading_zero()),
94 result
95 );
96 }
97 }
98}
99