79 lines
1.8 KiB
Rust
79 lines
1.8 KiB
Rust
//! Macintosh archived format header utilities.
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use crate::bin::*;
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/// Checks for an `AppleSingle` header. Returns offset to the resource fork.
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pub fn check_apple_single(b: &[u8]) -> Option<usize>
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{
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// check magic numbers
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if b.len() < 26 || *b.get(0..8)? != [0, 5, 22, 0, 0, 2, 0, 0] {
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return None;
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}
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let num = usize::from(u16b(&b[24..]));
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if b.len() < 26 + 12 * num {
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return None;
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}
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// get the resource fork (entity 1)
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for i in 0..num {
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let p = 26 + 12 * i;
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let ent = u32b(&b[p..]);
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let ofs = usize_from_u32(u32b(&b[p + 4..]));
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let len = usize_from_u32(u32b(&b[p + 8..]));
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if ent == 1 {
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return if ofs + len > b.len() {None} else {Some(ofs)};
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}
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}
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// no resource fork
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None
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}
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/// Checks for a `MacBinary II` header. Returns offset to the resource fork.
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pub fn check_macbin(b: &[u8]) -> Option<usize>
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{
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// check legacy version, length, zero fill, and macbin2 version
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// I swear this isn't *completely* magic
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if b.len() < 128 || b[0] != 0 || b[1] > 63 || b[74] != 0 || b[123] > 129 {
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return None;
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}
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let mut crc = 0;
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// check header crc
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for &byte in b.iter().take(124) {
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for j in 8..16 {
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let d = u16::from(byte) << j;
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if (d ^ crc) & 0x8000 == 0 {
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crc <<= 1;
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} else {
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crc = crc << 1 ^ 0x1021;
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}
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}
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}
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// if ok, resource fork follows
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if crc == u16b(&b[124..]) {
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Some(128)
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} else {
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None
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}
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}
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/// Reads a `MacBin` or `AppleSingle` header if there is one and returns the
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/// offset from the start of the header to the resource fork (if one is found.)
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pub fn try_mac_header(b: &[u8]) -> usize
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{
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if let Some(ofs) = check_macbin(b) {
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ofs
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} else {
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check_apple_single(b).unwrap_or(0)
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}
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}
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// EOF
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