ring/io/
positive.rs

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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}
ring/io/positive.rs

ring/io/
positive.rs
