GitHub - runxiyu/furgit: Low-level Git plumbing library in pure Go

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builds.sr.ht status Go Reference

Furgit is a low-level Git library in Go.

Status

Goals

  • General-purpose Git plumbing library for UNIX-like systems
  • Aim for extremely clear and modular architecture
  • Then aim for high performance
  • Expect familiarity with Git internals

Finding your way around

If you are working with a normal on-disk repository, start with repository.Open(...). It opens the repository and wires together the refs storage, object storage, and fetcher. Note that it requires either a bare repository or a .git directory. Then,

  • repo.Refs() is for branch names, tags, HEAD, and ref updates.

    • Use it when you are starting from names rather than object IDs.
    • A common pattern is to resolve a ref first, then pass the resulting object ID to the fetcher.

  • repo.Fetcher() is the main object-facing API for most callers.

    • Use it when you want commits, trees, blobs, or tags as typed values.
    • It also handles peeling through annotated tags, resolving objects to the type you actually want, and walking paths inside trees.
    • It even allows you to access a tree as an io/fs.FS.
    • If your goal is "show me this commit", "read this tree", "follow this tag", or "get me the file at this path", this is usually the right layer.

  • repo.Objects() is the storage layer underneath Fetcher.

    • Use it when you need to read object headers, read raw object contents, stream object data, or otherwise look up objects directly by ID.
    • Most callers who want to work with Git objects as commits, trees, blobs, or tags should prefer the fetcher instead.
    • However, checking an object ID's size and type are somewhat common operations that should be done here.

Note that:

  • object contains parsed Git object values such as blobs, trees, commits, and tags. These are the decoded contents of Git objects and do not tell you anything about the object's identity.

  • object/stored wraps a parsed object together with the object ID it was loaded from. This is used when you need both the parsed value and the identity it was loaded under.

As a rule of thumb:

  • If you have a ref name, start with repo.Refs().
  • If you want typed objects or path-based access, use repo.Fetcher().
  • If you need raw object lookup by ID, object headers, or object streams, use repo.Objects().

Some useful operations are separate and are meant to be constructed over the stores that Repository already exposes:

  • To check whether one revision is an ancestor of another, or to compute merge bases, construct a commitquery.Query over repo.Objects(). If you already have a commit-graph reader, pass it in as well for performance.

  • To walk commits or all reachable objects from a set of starting points, construct a reachability.Reachability over repo.Objects(). This is useful for tasks such as connectivity checks and computing the object set that a fetch or push needs to account for.

  • To accept pushes on the server side, construct network/receivepack or network/receivepack/service with the repository's ref store, object store, and object ID algorithm.

    • Push handling also needs the repository's object storage root so incoming objects can be quarantined and later promoted.
    • Repository does not currently expose that root directly (we'll consider possible solutions sometime later), so a push server usually keeps the repository path or object root handle alongside the Repository value.
    • Hook-based checks are just Go functions; then, a fast-forward check can use commitquery over the existing and quarantined object stores. Some hooks are provided.

Alternatives

Not endorsements.

Community

See the CONTRIBUTING document for bug reports and patch submissions.

Acknowledgements

Partly inspired by upstream Git, OpenBSD's Game of Trees, and 9front Git.

License

This project is licensed under the GNU Affero General Public License, Version 3.0 only.

Pursuant to Section 14 of the GNU Affero General Public License, Version 3.0, Runxi Yu is hereby designated as the proxy who is authorized to issue a public statement accepting any future version of the GNU Affero General Public License for use with this Program.

Therefore, notwithstanding the specification that this Program is licensed under the GNU Affero General Public License, Version 3.0 only, a public acceptance by the Designated Proxy of any subsequent version of the GNU Affero General Public License shall permanently authorize the use of that accepted version for this Program.