Gitlet Design Document

Classes

• Blob:represents file contents snapshot, stores id (hash) and content.
• Tree:represents directory snapshot, simplified flat map (filename → blobId).
• Commit:represents commit object with id, parent commit, tree id, message, and timestamp.
• Index:staging area (map of file path → blob id).
• Repository:controller class, manages .gitlet structure, implements commands like init, add, commit, checkout, etc.
• Utils:helper methods (hashing, serialization, file IO).
• Main:CLI entry point, parses user commands and delegates to Repository.

.gitlet directory

.gitlet/
├── HEAD          # a plain text file that says what branch you are on, e.g., e.g. ref: refs/heads/master
├── index         # a binary file of the list of file paths pointing to blob objects, e.g., hello.txt -> e965407...
├── objects/      # database for all gitlet objects: blob, tree, commit, dividing into subfolders based on the SHA-1 hash prefix (first 2 hex digits)
├── refs/         # plain text files containing commit hash
|    └── heads/   # the latest commit hash for each local branch (branch tips), e.g., master, feature-x, etc.
│  
└── logs/
    ├── HEAD      # history of what HEAD had pointed at over time
    └── refs/     # history for each brach

Gitlet commands and algorithms

• java gitlet.Main init
• java gitlet.Main add [file name]
• java gitlet.Main commit [message]
• java gitlet.Main rm [file name]
• java gitlet.Main log
• java gitlet.Main global-log
• java gitlet.Main find [commit message]
• java gitlet.Main status
• java gitlet.Main checkout -- [file name]
• java gitlet.Main checkout [commit id] -- [file name]
• java gitlet.Main checkout [branch name]
• java gitlet.Main branch [branch name]
• java gitlet.Main rm-branch [branch name]
• java gitlet.Main reset [commit id]
• java gitlet.Main merge [branch name]

Comparing to Git

• In index, a file path points to other metadata as well in git, but gets ignored in getlet
• In Tree object, a directory tree is simplified as a list in gitlet, i.e., it's always a flat directory without subdirectory
• In objects, Git "packs" objects when the repo grows big.