git-go

A small Git implementation written in Go.

The main goals of this project were to learn about Git internals and Go. This small Git implementation is capable of initializing a repository, creating commits and cloning a public repository.

Features

Commands

Basic commands:

• init: Initialize the git directory structure
• commit: Record changes to the repository
• log: Show commit logs for a commit ID

Plumbing commands:

• cat-file: Provide content or type and size information for repository objects
• hash-object: Compute object ID and optionally creates a blob from a file
• ls-tree: List the contents of a tree object
• write-tree: Create a tree object from the current working directory
• commit-tree: Create a new commit object

Remote commands:

• clone: Clone a repository into a new directory
• ls-remote: List references in a remote repository

Clone

Clone command is implemented using the smart HTTP protocol only. What it does:

1. Discover references in the remote repository
2. Negotiate packfile transfer
3. Transfer and unpack packfile (with deltas unpacking)

Clone uses loose objects, unpacking the packfile fully to .git/objects.

Build and test

Build

$ go build -o git-go
$ ./git-go
Usage: git-go <command> [<args>...]

Commands:
    init        Initialize the git directory structure
    cat-file    Provide content or type and size information for repository objects
    hash-object Compute object ID and optionally creates a blob from a file
    ls-tree     List the contents of a tree object
    write-tree  Create a tree object from the current working directory
    commit-tree Create a new commit object
    clone       Clone a repository into a new directory
    ls-remote   List references in a remote repository
    log         Show commit logs for a commit ID
    commit      Record changes to the repository

Test

$ ./testsuite.sh
Build successful
=== Running cat_file.sh ===
Initialized empty Git repository in /tmp/tmp.X9EiYylEQ5/.git/
[OK] good output
=> tests/cat_file.sh passed
...

Example

$ mkdir test_repo
$ cd test_repo
$ git-go init
Initialized empty Git repository in /tmp/tmp.XpIeQSf7Ns/test_repo/.git/
$ git-go commit -m "first"
[70dbd5eedb3c888ee6be6f1dc00e45f190a8a856] first
$ git-go log
commit 70dbd5eedb3c888ee6be6f1dc00e45f190a8a856
Author:	william <mygit>
Date: 	Thu Jun 13 00:11:03 2024 +0200

	first

$ git-go cat-file -p 70dbd5eedb3c888ee6be6f1dc00e45f190a8a856
tree 581caa0fe56cf01dc028cc0b089d364993e046b6
author william <mygit> 1718230263 +0200
committer william <mygit> 1718230263 +0200

first
$ echo 'test' > test.txt
$ git-go hash-object test.txt
9daeafb9864cf43055ae93beb0afd6c7d144bfa4
$ git-go ls-tree 581caa0fe56cf01dc028cc0b089d364993e046b6
100644 blob 980a0d5f19a64b4b30a87d4206aade58726b60e3	hello.txt
$ cd $(mktemp -d)
$ git-go init
Initialized empty Git repository in /tmp/tmp.rl0ccY5hyN/.git/
$ echo 'hello world' > hello.txt
$ echo 'test' > test.txt
$ echo 'draft' > draft
$ git-go write-tree
16e7f5e6e626c055a249af61ff9631f863f0b5a7
$ cd $(mktemp -d)
$ git-go clone https://github.com/githubtraining/hellogitworld
Cloning into 'hellogitworld'...
remote: Number of objects: 1147
remote: Resolving deltas: 418
$ ls hellogitworld
build.gradle  fix.txt  pom.xml  README.txt  resources  runme.sh  src

Resources

• Pro Git Book
• Git Internals Plumbing and Porcelain
• Git Internals - git objects
• Git’s database internals I: packed object store
• Git Smart HTTP Transfer protocol doc
• Git Smart HTTP Transfer protocol stackoverflow
• Git clone in haskell from the bottom up
• Unpacking git packfiles
• gitprotocol-pack.txt
• man gitformat-pack
• Git from the Bottom Up
• CodeCrafters Challenge