global: snapshot

crates/brk_reader/src/scan.rs

@@ -0,0 +1,73 @@
+use std::ops::ControlFlow;
+
+use brk_types::{BlkMetadata, BlkPosition};
+
+use crate::{XORBytes, XORIndex};
+
+const MAGIC_BYTES: [u8; 4] = [249, 190, 180, 217];
+
+pub fn find_magic(bytes: &[u8], xor_i: &mut XORIndex, xor_bytes: XORBytes) -> Option<usize> {
+    let mut window = [0u8; 4];
+    for (i, &b) in bytes.iter().enumerate() {
+        window.rotate_left(1);
+        window[3] = xor_i.byte(b, xor_bytes);
+        if window == MAGIC_BYTES {
+            return Some(i + 1);
+        }
+    }
+    None
+}
+
+pub struct ScanResult {
+    pub first_magic: Option<usize>,
+    pub interrupted: bool,
+}
+
+/// Scans `buf` for blocks. `file_offset` is the absolute position of `buf[0]` in the file.
+/// Calls `on_block` for each complete block found.
+pub fn scan_bytes(
+    buf: &mut [u8],
+    blk_index: u16,
+    file_offset: usize,
+    xor_bytes: XORBytes,
+    mut on_block: impl FnMut(BlkMetadata, Vec<u8>, XORIndex) -> ControlFlow<()>,
+) -> ScanResult {
+    let mut xor_i = XORIndex::default();
+    xor_i.add_assign(file_offset);
+    let mut first_magic = None;
+    let mut i = 0;
+
+    while let Some(off) = find_magic(&buf[i..], &mut xor_i, xor_bytes) {
+        let before = i;
+        i += off;
+        first_magic.get_or_insert(before + off.saturating_sub(4));
+        if i + 4 > buf.len() {
+            break;
+        }
+        let len = u32::from_le_bytes(
+            xor_i
+                .bytes(&mut buf[i..i + 4], xor_bytes)
+                .try_into()
+                .unwrap(),
+        ) as usize;
+        i += 4;
+        if i + len > buf.len() {
+            break;
+        }
+        let position = BlkPosition::new(blk_index, (file_offset + i) as u32);
+        let metadata = BlkMetadata::new(position, len as u32);
+        if on_block(metadata, buf[i..i + len].to_vec(), xor_i).is_break() {
+            return ScanResult {
+                first_magic,
+                interrupted: true,
+            };
+        }
+        i += len;
+        xor_i.add_assign(len);
+    }
+
+    ScanResult {
+        first_magic,
+        interrupted: false,
+    }
+}