git-rust is a simplified Git implementation built from scratch in Rust. It mimics core Git functionality such as init, hash-object, and cat-file, and serves both as a learning project and a functional Git-like CLI.
This project explores how Git works under the hood — from creating repositories and hashing objects, to writing Git-compliant blob files and reading them back from the .git/objects directory.
git-rust init — Initialize a new Git-like repository. Does not re-initialize a repo.
git-rust hash-object -w <file> — Hash and write blob objects to .git/objects
git-rust cat-file -p <hash> — Decode and print stored objects
Fully compatible object format (blob <size>\0<content>) using zlib compression
Built with safety, performance, and testability in mind using idiomatic Rust
This project is ideal if you want to:
Understand Git internals by building them yourself
Learn about SHA-1 hashing, zlib compression, and Git’s object model
Practice building command-line tools and file-based data structures in Rust
Todo
Todo
It uses a binary layour (raw bytes) and always big-endian format. The index has a header that is 12 bytes, a record of entries (files/blobs) added to the staging area and a checksum (SHA-1) of all the content (header + entries). The entries are not a fixed length, but a multiple of 8 bytes:
- 62 bytes of fixed-size metadata (ctime, mtime, mode, sha1, etc.).
- Variable-length path (the filename or relative path), which follows the metadata.
- 1–8 bytes of padding to ensure the total size of the entry is a multiple of 8 bytes.
Example of the Header:
| Field | Size (Bytes) | Description | Example (Hex) |
|---|---|---|---|
dircache DIRC |
4 | Always set as "DIRC" | 44 49 52 43 |
Version |
4 | Version 2, 3 or 4. 2 is most common | 00 00 00 00 |
Entries |
4 | Number of entries | 00 00 00 20 |
Example of an entry:
| Field | Size (Bytes) | Description | Example (Hex) |
|---|---|---|---|
ctime |
4 | Created time (seconds) | 5E 2D 5A 80 |
ctime_nanos |
4 | Created time (nanoseconds) | 00 00 00 00 |
mtime |
4 | Modified time (seconds) | 5E 2D 5A 90 |
mtime_nanos |
4 | Modified time (nanoseconds) | 00 00 00 00 |
dev |
4 | Device ID (from stat(2)) |
00 00 00 15 |
ino |
4 | Inode number | 00 00 00 01 |
mode |
4 | File mode (includes type and permissions) | 00 00 81 A4 |
uid |
4 | User ID | 00 00 03 E8 |
gid |
4 | Group ID | 00 00 03 E8 |
file_size |
4 | File size in bytes | 00 00 00 04 |
sha1 |
20 | SHA-1 hash of the file contents | 12 34 ... EF |
flags |
2 | Bitfield with name length, stage, and flags | 00 0A |
path |
N (variable) | File path (UTF-8 bytes, not null-terminated) | "main.rs" = 6D 61 69 6E 2E 72 73 |
padding |
0–7 | Null bytes to align total entry size to multiple of 8 | 00 00 00 (example) |