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p2p-git — Minimal Git Engine for Embedding

isomorphic-git stripped to a minimal footprint for embedding. Object operations, refs, index, merge, log, walk. No porcelain, no network, no packfiles, no working tree.

Source: bare-for-pear/p2p-git

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What It Does

Git object-level operations as a stripped, embeddable engine. 42 exports from the original 70. 8,336 lines removed, 78 files deleted.

Designed for P2P applications where the object store lives on any pluggable fs backend (bare-fs, Hyperdrive, or other). The embedder provides storage; p2p-git provides git operations.

Transaction Model

Git’s index is the transaction staging area:

1. writeBlob — content into the object store, returns OID
2. updateIndex — stage the change (path → blobOid in the index)
3. Repeat — all changes staged in the index
4. commit — the index becomes a committed tree, transaction closes

The index persists — it survives crashes. Staged but uncommitted changes can be committed later. No working tree, no git add. Blobs created directly, index updated directly.

No Working Tree

The standard git workflow (edit files → add → commit) is replaced by direct object construction. There is no filesystem working tree, no git add reading from disk, no filesystem dependency for git operations. Suitable for environments where the object store lives on Hyperdrive or other P2P storage with no local filesystem.

What Was Removed

• Porcelain — add, checkout, status, clone, fetch, pull, push, stash. The working-tree workflow is not needed for embedded use.
• Network — HTTP transport, smart protocol, remote management. Object exchange is the embedder’s concern.
• Packfiles — loose objects only, each individually addressable.
• Working tree — WORKDIR/STAGE walkers, .gitignore handling.
• Shallow clones — replaced with empty sets.

What Remains

Objects: readBlob, writeBlob, readTree, writeTree, readCommit, writeCommit, readTag, writeTag, readObject, writeObject, hashBlob. Index: updateIndex. Refs: resolveRef, writeRef, expandRef, expandOid, deleteRef, listBranches, listTags, listRefs, currentBranch. Branching: branch, deleteBranch, tag, deleteTag. History: log, findMergeBase, isDescendent. Merge: merge (3-way text). Navigation: walk, TREE. Config and utility: getConfig, setConfig, init, findRoot, listFiles, version.

Design Decisions

Stubs over removal for entangled dependencies. GitPackedRefs and GitRefSpecSet are stubbed rather than removed — GitRefManager references them throughout. Safe because loose-objects-only never has packed refs.

Merge retains the index dependency. Git’s merge uses the index to track 3-way merge state. Removing it would require rewriting merge. Kept as-is.

The stripping was the learning exercise. Every removed file was understood before removal. The dependency structure is mapped. Further stripping can proceed confidently when pressure surfaces.

Current State

Proven under Bare. 42 plumbing operations tested. Not yet exercised: merge, diff, tag operations, the updateIndex → commit flow end-to-end, large repos.