craigfe / ocaml-git

Pure OCaml Git format and protocol

ocaml-git -- Git format and protocol in pure OCaml

Support for on-disk and in-memory Git stores. Can read and write all the Git objects: the usual blobs, trees, commits and tags but also the pack files, pack indexes and the index file (where the staging area lives).

All the objects share a consistent API, and convenience functions are provided to manipulate the different objects. For instance, it is possible to make a pack file position independent (as the Zlib compression might change the relative offsets between the packed objects), to generate pack indexes from pack files, or to expand the filesystem of a given commit.

The library comes with some command-line tools called ogit-* as a Proof-of-concept of the core library which shares a similar interface with git, but where all operations are mapped to the API exposed ocaml-git (and hence using only OCaml code). However, these tools are not done to be use. They are just examples of how to use ocaml-git.

The API documentation is available online.

Build and Install Instructions

To build and install the project, simply run:

$ opam install git

What is supported

• The loose object files can be read and written;

  • blobs (files)
  • trees (directories)
  • commits (revision history)
  • tags (annotated tags)
  • references (branch names)

• The pack files (collections of compressed loose objects using a binary-diff representation) and pack indexes (indexes of pack files) can be read and written). The binary diff hunks are exposed using a high-level position-independent representation so that they can be manipulated more easily. Pack file can be created and is compressed.

• The index file (used as for managing the staging area) are fully supported. Which means that git diff and git status will work as expected on a repository created by the library.

• Cloning and fetching (using various options) are fully supported for the Git protocol, the smart-HTTP protocol and git+ssh. A subset of the protocol capabilities are implemented (mainly thin-pack, ofs-delta, side-band-64k and allow-reachable-sha1-in-want).

• Pushing is still experimental and needs more testing.

• An abstraction for Git Store Is available. Various store implementations are available:

  • An in-memory implementation;
  • A unix filesystem implementation;
  • A mirageOS implementation, requiring a Mirage_fs_lwt implementation.

What is not supported

• No server-side operations are currently supported.
• No GC.
• Updates, merge and rebase are not supported. Use irmin instead.

Performance

Performance is comparable to the Git tool.

Example

# #require "git.unix";;
# open Git_unix;;
# module Search = Git.Search.Make(FS);;

# let read filename =
    let open Lwt_result.Infix in
    Store.v (Fpath.v ".") >>= fun t ->
    Store.Ref.resolve Store.Reference.master >>= fun head ->
    let open Lwt.Infix in
    Search.find t head (`Commit (`Path filename)) >|= function
    | None -> Lwt.return (Error `Not_found)
    | Some hash -> Store.read t hash
val read : string list -> (Store.Value.t, Store.error) Lwt_result.t
    
# let pp =
    let ok ppf = function
      | Store.Value.Blob blob ->
        Fmt.string ppf (Store.Value.Blob.to_string blob)
      | _ -> Fmt.string ppf "#git-object" in
    Fmt.pp_result ~ok ~error:Store.pp_error
val pp : (Store.Value.t, Store.error) Fmt.t

# Lwt_main.run Lwt.Infix.(read [ "README.md" ] >|= pp Fmt.stdout)

ocaml-git -- Git format and protocol in pure OCaml

Support for on-disk and in-memory Git stores. Can read and write all
the Git objects: the usual blobs, trees, commits and tags but also
the pack files, pack indexes and the index file (where the staging area
lives).

[...]

License

MIT, see LICENSE.md file for its text.