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

// Copyright (c) The Diem Core Contributors
// Copyright (c) The Move Contributors
// SPDX-License-Identifier: Apache-2.0

/// Determine if a character is an allowed eye-visible (printable) character.
///
/// The only allowed printable characters are the printable ascii characters (SPACE through ~) and
/// tabs. All other characters are invalid and we return false.
pub fn is_permitted_printable_char(c: char) -> bool {
    let x = c as u32;
    let is_above_space = x >= 0x20; // Don't allow meta characters
    let is_below_tilde = x <= 0x7E; // Don't allow DEL meta character
    let is_tab = x == 0x09; // Allow tabs
    (is_above_space && is_below_tilde) || is_tab
}

/// Determine if a character is a permitted newline lf character.
///
/// The only permitted newline lf character is \n All others are invalid.
pub fn is_permitted_newline_lf_char(c: char) -> bool {
    let x = c as u32;
    x == 0x0A // \n
}

/// Determine if a character is a permitted newline crlf character.
///
/// The only permitted newline character is \r\n. All others are invalid.
pub fn is_permitted_newline_crlf_chars(c1: char, c2: char) -> bool {
    let x1 = c1 as u32;
    let x2 = c2 as u32;
    let is_cr = x1 == 0x0D; // \r
    let is_lf = x2 == 0x0A; // \n
    is_cr && is_lf
}

/// Determine if a character is permitted character.
///
/// A permitted character is either a permitted printable character, or a permitted
/// newline. Any other characters are disallowed from appearing in the file.
pub fn is_permitted_char(c: char) -> bool {
    is_permitted_printable_char(c) || is_permitted_newline_lf_char(c)
}

/// Determine if the characters is permitted characters.
///
/// A permitted characters is either a permitted printable character, or a permitted
/// newlines. Any other characters are disallowed from appearing in the file.
pub fn is_permitted_chars(chars: &[u8], idx: usize) -> bool {
    let c1 = chars[idx] as char;

    if is_permitted_char(c1) {
        return true;
    }

    if idx + 1 >= chars.len() {
        return false;
    }

    let c2 = chars[idx + 1] as char;
    is_permitted_newline_crlf_chars(c1, c2)
}

#[cfg(test)]
mod tests {
    #[test]
    fn test_permitted_characters() {
        let mut good_chars = (0x20..=0x7E).collect::<Vec<u8>>();
        good_chars.push(0x0D); // \r
        good_chars.push(0x0A); // \n
        good_chars.push(0x09); // \t

        for idx in 0..good_chars.len() {
            assert!(super::is_permitted_chars(&good_chars, idx));
        }
    }

    #[test]
    fn test_forbidden_last_lf_characters() {
        let mut good_chars = (0x20..=0x7E).collect::<Vec<u8>>();
        good_chars.push(0x0D); // \r

        assert!(!super::is_permitted_chars(
            &good_chars,
            good_chars.len() - 1
        ));
    }

    #[test]
    fn test_forbidden_characters() {
        let mut bad_chars = (0x0..0x09).collect::<Vec<u8>>();
        bad_chars.append(&mut (0x0B..=0x1F).collect::<Vec<u8>>());
        bad_chars.push(0x7F);

        for idx in 0..bad_chars.len() {
            assert!(!super::is_permitted_chars(&bad_chars, idx));
        }
    }
}