1 files changed, 56 insertions, 0 deletions
diff --git a/vendor/gix-index/src/extension/end_of_index_entry/decode.rs b/vendor/gix-index/src/extension/end_of_index_entry/decode.rs
new file mode 100644
index 000000000..f8002ab7c
--- /dev/null
+++ b/vendor/gix-index/src/extension/end_of_index_entry/decode.rs
@@ -0,0 +1,56 @@
+use crate::{
+    decode::header,
+    extension,
+    extension::end_of_index_entry::{MIN_SIZE, MIN_SIZE_WITH_HEADER, SIGNATURE},
+    util::from_be_u32,
+};
+
+/// Decode the end of index entry extension, which is no more than a glorified offset to the first byte of all extensions to allow
+/// loading entries and extensions in parallel.
+///
+/// Itself it's located at the end of the index file, which allows its location to be known and thus addressable.
+/// From there it's possible to traverse the chunks of all set extensions, hash them, and compare that hash with all extensions
+/// stored prior to this one to assure they are correct.
+///
+/// If the checksum wasn't matched, we will ignore this extension entirely.
+pub fn decode(data: &[u8], object_hash: gix_hash::Kind) -> Option<usize> {
+    let hash_len = object_hash.len_in_bytes();
+    if data.len() < MIN_SIZE_WITH_HEADER + hash_len {
+        return None;
+    }
+
+    let start_of_eoie = data.len() - MIN_SIZE_WITH_HEADER - hash_len;
+    let ext_data = &data[start_of_eoie..data.len() - hash_len];
+
+    let (signature, ext_size, ext_data) = extension::decode::header(ext_data);
+    if signature != SIGNATURE || ext_size as usize != MIN_SIZE {
+        return None;
+    }
+
+    let (offset, checksum) = ext_data.split_at(4);
+    let offset = from_be_u32(offset) as usize;
+    if offset < header::SIZE || offset > start_of_eoie || checksum.len() != gix_hash::Kind::Sha1.len_in_bytes() {
+        return None;
+    }
+
+    let mut hasher = gix_features::hash::hasher(gix_hash::Kind::Sha1);
+    let mut last_chunk = None;
+    for (signature, chunk) in extension::Iter::new(&data[offset..data.len() - MIN_SIZE_WITH_HEADER - hash_len]) {
+        hasher.update(&signature);
+        hasher.update(&(chunk.len() as u32).to_be_bytes());
+        last_chunk = Some(chunk);
+    }
+
+    if hasher.digest() != checksum {
+        return None;
+    }
+    // The last-to-this chunk ends where ours starts
+    if last_chunk
+        .map(|s| s.as_ptr_range().end != (&data[start_of_eoie]) as *const _)
+        .unwrap_or(true)
+    {
+        return None;
+    }
+
+    Some(offset)
+}