rars-format 0.1.0

RAR archive format parser and writer implementation used by rars.
Documentation 
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

use crate::version::ArchiveFamily;

pub const RAR13_SIGNATURE: &[u8; 4] = b"RE~^";
pub const RAR15_SIGNATURE: &[u8; 7] = b"Rar!\x1a\x07\x00";
pub const RAR50_SIGNATURE: &[u8; 8] = b"Rar!\x1a\x07\x01\x00";

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[non_exhaustive]
pub struct ArchiveSignature {
    pub family: ArchiveFamily,
    pub offset: usize,
    pub length: usize,
}

pub fn detect_archive_family(input: &[u8]) -> Option<ArchiveSignature> {
    detect_at(input, 0)
}

pub fn find_archive_start(input: &[u8], max_scan: usize) -> Option<ArchiveSignature> {
    let limit = input.len().min(max_scan);
    (0..=limit).find_map(|offset| detect_at(input, offset))
}

fn detect_at(input: &[u8], offset: usize) -> Option<ArchiveSignature> {
    let tail = input.get(offset..)?;

    if tail.starts_with(RAR50_SIGNATURE) {
        Some(ArchiveSignature {
            family: ArchiveFamily::Rar50Plus,
            offset,
            length: RAR50_SIGNATURE.len(),
        })
    } else if tail.starts_with(RAR15_SIGNATURE) {
        Some(ArchiveSignature {
            family: ArchiveFamily::Rar15To40,
            offset,
            length: RAR15_SIGNATURE.len(),
        })
    } else if tail.starts_with(RAR13_SIGNATURE) {
        Some(ArchiveSignature {
            family: ArchiveFamily::Rar13,
            offset,
            length: RAR13_SIGNATURE.len(),
        })
    } else {
        None
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn detects_all_known_signatures() {
        assert_eq!(
            detect_archive_family(b"RE~^").unwrap().family,
            ArchiveFamily::Rar13
        );
        assert_eq!(
            detect_archive_family(b"Rar!\x1a\x07\x00").unwrap().family,
            ArchiveFamily::Rar15To40
        );
        assert_eq!(
            detect_archive_family(b"Rar!\x1a\x07\x01\x00")
                .unwrap()
                .family,
            ArchiveFamily::Rar50Plus
        );
    }

    #[test]
    fn finds_sfx_prefixed_archive() {
        let sig = find_archive_start(b"stub bytes RE~^payload", 128).unwrap();
        assert_eq!(sig.family, ArchiveFamily::Rar13);
        assert_eq!(sig.offset, 11);
    }

    #[test]
    fn rejects_unknown_and_truncated_signatures() {
        assert_eq!(detect_archive_family(b""), None);
        assert_eq!(detect_archive_family(b"RAR!"), None);
        assert_eq!(detect_archive_family(b"Rar!\x1a\x07"), None);
        assert_eq!(find_archive_start(b"not an archive", 128), None);
    }

    #[test]
    fn scan_limit_bounds_sfx_detection() {
        let input = b"stub bytes RE~^payload";

        assert_eq!(find_archive_start(input, 10), None);

        let sig = find_archive_start(input, 11).unwrap();
        assert_eq!(sig.family, ArchiveFamily::Rar13);
        assert_eq!(sig.offset, 11);
        assert_eq!(sig.length, RAR13_SIGNATURE.len());
    }
}