c2pa_structured_text/
embed.rs

1const BEGIN: &str = "-----BEGIN C2PA MANIFEST-----";
2const END: &str = "-----END C2PA MANIFEST-----";
3const B64_CHARS: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
4
5pub enum ManifestRef<'a> {
6    Url(&'a str),
7    Embedded(&'a [u8]),
8}
9
10pub fn embed_manifest(
11    text: &str,
12    manifest: ManifestRef<'_>,
13    comment_prefix: &str,
14    comment_suffix: Option<&str>,
15) -> String {
16    let reference = match manifest {
17        ManifestRef::Url(url) => url.to_string(),
18        ManifestRef::Embedded(bytes) => {
19            format!("data:application/c2pa;base64,{}", base64_encode(bytes))
20        }
21    };
22
23    let suffix = comment_suffix.unwrap_or("");
24    let manifest_line = format!(
25        "{comment_prefix} {BEGIN} {reference} {END} {suffix}"
26    ).trim_end().to_string();
27
28    format!("{manifest_line}\n{text}")
29}
30
31fn base64_encode(input: &[u8]) -> String {
32    let mut out = Vec::with_capacity((input.len() + 2) / 3 * 4);
33    for chunk in input.chunks(3) {
34        let b0 = chunk[0] as u32;
35        let b1 = if chunk.len() > 1 { chunk[1] as u32 } else { 0 };
36        let b2 = if chunk.len() > 2 { chunk[2] as u32 } else { 0 };
37        let triple = (b0 << 16) | (b1 << 8) | b2;
38        out.push(B64_CHARS[((triple >> 18) & 0x3F) as usize]);
39        out.push(B64_CHARS[((triple >> 12) & 0x3F) as usize]);
40        if chunk.len() > 1 {
41            out.push(B64_CHARS[((triple >> 6) & 0x3F) as usize]);
42        } else {
43            out.push(b'=');
44        }
45        if chunk.len() > 2 {
46            out.push(B64_CHARS[(triple & 0x3F) as usize]);
47        } else {
48            out.push(b'=');
49        }
50    }
51    String::from_utf8(out).unwrap()
52}
53
54#[cfg(test)]
55mod tests {
56    use super::*;
57
58    #[test]
59    fn embed_url_python() {
60        let text = "print('hello')\n";
61        let result = embed_manifest(text, ManifestRef::Url("https://example.com/m.c2pa"), "#", None);
62        assert!(result.starts_with("# -----BEGIN C2PA MANIFEST-----"));
63        assert!(result.contains("https://example.com/m.c2pa"));
64        assert!(result.contains("-----END C2PA MANIFEST-----"));
65        assert!(result.ends_with("print('hello')\n"));
66    }
67
68    #[test]
69    fn embed_url_css() {
70        let result = embed_manifest("body {}", ManifestRef::Url("https://example.com/m.c2pa"), "/*", Some("*/"));
71        assert!(result.starts_with("/* -----BEGIN C2PA MANIFEST-----"));
72        assert!(result.contains("-----END C2PA MANIFEST----- */"));
73    }
74
75    #[test]
76    fn embed_data_uri() {
77        let bytes = b"test manifest";
78        let result = embed_manifest("content", ManifestRef::Embedded(bytes), "#", None);
79        assert!(result.contains("data:application/c2pa;base64,"));
80    }
81
82    #[test]
83    fn base64_known_vectors() {
84        assert_eq!(base64_encode(b""), "");
85        assert_eq!(base64_encode(b"f"), "Zg==");
86        assert_eq!(base64_encode(b"fo"), "Zm8=");
87        assert_eq!(base64_encode(b"foo"), "Zm9v");
88        assert_eq!(base64_encode(b"foob"), "Zm9vYg==");
89        assert_eq!(base64_encode(b"fooba"), "Zm9vYmE=");
90        assert_eq!(base64_encode(b"foobar"), "Zm9vYmFy");
91    }
92}
c2pa_structured_text/embed.rs

c2pa_structured_text/
embed.rs
