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aacs: fix stale mkb_version offset doc comment

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The doc comment claimed the version was a BE u32 at offset 8 of the
record body (offset 12 from pos), but the code correctly reads pos+8
(body offset 4): a 4-byte record header at pos, the Type field at body
offset 0, then the version at body offset 4. Rewrite the comment to
match the actual read so a maintainer does not 'correct' the offset and
break MKB version parsing. Clarify the matching test comment too.
This commit is contained in:
Matthew Jackson
2026-06-23 02:28:34 -07:00
parent 24ed1d1d19
commit 8e6d494e54
1 changed files with 6 additions and 2 deletions
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src/aacs/keys.rs
+6 -2
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@@ -562,7 +562,10 @@ pub fn trim_mkb(mut mkb: Vec<u8>) -> Vec<u8> {
} }
/// Get MKB version from Type and Version Record (type 0x10). /// Get MKB version from Type and Version Record (type 0x10).
/// Version is a BE u32 at offset 8 of the record body (offset 12 from `pos`). /// Layout: 4-byte record header at `pos` (type + BE24 length), then the
/// record body starts at `pos + 4`. The body holds the BE u32 Type field at
/// body offset 0 (`pos + 4`), then the BE u32 version at body offset 4
/// (`pos + 8`).
pub fn mkb_version(mkb: &[u8]) -> Option<u32> { pub fn mkb_version(mkb: &[u8]) -> Option<u32> {
let mut pos = 0; let mut pos = 0;
while pos + 4 <= mkb.len() { while pos + 4 <= mkb.len() {
@@ -2542,7 +2545,8 @@ mod tests {
#[test] #[test]
fn mkb_version_uses_be24_length_and_reads_offset_8() { fn mkb_version_uses_be24_length_and_reads_offset_8() {
// Type 0x10, BE24 length 0x0C (12), version u32 at body offset 8. // Type 0x10, BE24 length 0x0C (12). Body starts at pos+4: Type field
// u32 at body offset 0, version u32 at body offset 4 (pos+8).
// Confirm a length encoded in the high BE24 byte is honored. // Confirm a length encoded in the high BE24 byte is honored.
let mkb = [ let mkb = [
0x10, 0x00, 0x00, 0x0C, 0x11, 0x22, 0x33, 0x44, 0x01, 0x02, 0x03, 0x04, 0x10, 0x00, 0x00, 0x0C, 0x11, 0x22, 0x33, 0x44, 0x01, 0x02, 0x03, 0x04,