1 files changed, 46 insertions, 0 deletions
diff --git a/vendor/gix-index/src/decode/header.rs b/vendor/gix-index/src/decode/header.rs
new file mode 100644
index 000000000..04c3bfd98
--- /dev/null
+++ b/vendor/gix-index/src/decode/header.rs
@@ -0,0 +1,46 @@
+pub(crate) const SIZE: usize = 4 /*signature*/ + 4 /*version*/ + 4 /* num entries */;
+
+use crate::{util::from_be_u32, Version};
+
+pub(crate) const SIGNATURE: &[u8] = b"DIRC";
+
+mod error {
+
+    /// The error produced when failing to decode an index header.
+    #[derive(Debug, thiserror::Error)]
+    #[allow(missing_docs)]
+    pub enum Error {
+        #[error("{0}")]
+        Corrupt(&'static str),
+        #[error("Index version {0} is not supported")]
+        UnsupportedVersion(u32),
+    }
+}
+pub use error::Error;
+
+pub(crate) fn decode(data: &[u8], object_hash: gix_hash::Kind) -> Result<(Version, u32, &[u8]), Error> {
+    if data.len() < (3 * 4) + object_hash.len_in_bytes() {
+        return Err(Error::Corrupt(
+            "File is too small even for header with zero entries and smallest hash",
+        ));
+    }
+
+    let (signature, data) = data.split_at(4);
+    if signature != SIGNATURE {
+        return Err(Error::Corrupt(
+            "Signature mismatch - this doesn't claim to be a header file",
+        ));
+    }
+
+    let (version, data) = data.split_at(4);
+    let version = match from_be_u32(version) {
+        2 => Version::V2,
+        3 => Version::V3,
+        4 => Version::V4,
+        unknown => return Err(Error::UnsupportedVersion(unknown)),
+    };
+    let (entries, data) = data.split_at(4);
+    let entries = from_be_u32(entries);
+
+    Ok((version, entries, data))
+}