generate index header

Author: Sidney Douw

git-index/src/lib.rs

@@ -22,6 +22,8 @@ pub mod decode;
 
 pub mod verify;
 
+pub mod write;
+
 /// All known versions of a git index file.
 #[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]
 #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]

git-index/src/write.rs

@@ -0,0 +1,21 @@
+use bstr::{BString, ByteVec};
+
+use crate::Version;
+
+pub fn header(version: Version, num_entries: i32) -> BString {
+    let mut header = BString::from("");
+
+    const SIGNATURE: &[u8; 4] = b"DIRC";
+
+    let version = match version {
+        Version::V2 => 2_i32.to_be_bytes(),
+        Version::V3 => 3_i32.to_be_bytes(),
+        Version::V4 => 4_i32.to_be_bytes(),
+    };
+
+    header.push_str(SIGNATURE);
+    header.push_str(version);
+    header.push_str(num_entries.to_be_bytes());
+
+    header
+}