Post

What happens if I just point a git server at an object storage bucket?

Back when I was porting agent sandboxes to Go , I built everything on top of billy , a filesystem abstraction for Go. The whole trick of the project was teaching a Tigris bucket to act enough like a filesystem that a shell interpreter and its tools couldn’t tell the difference. Billy was the key layer that made the entire façade fall into place.

After I had gotten things working, I learned that I’m using billy way outside its normal usecase. It was originally made for go-git , a pure-Go implementation of git’s protocols and data formats. It doesn’t rely on the /usr/bin/git binary existing at all. Every method on billy’s filesystem interface exists purely because go-git needs it. This gave me a terrible idea: I already have a bucket that can quack like a filesystem and go-git’s native language is “filesystem”.

If you strip away the porcelain, a git repository is 4 basic things:

Until I started working on this I was under the impression that git stored only the patches done to an empty folder and that was how it reconstructed the history of your repository. It does not. It actually keeps track of the entire files, which explains why big binary blobs fudge the tooling so much. The diff mental model works fine for using git day to day; it’s just wrong at the storage layer, which is the layer this post lives in.

For example, let’s say I just made a new git repository and committed a README.md to it. The tree for the .git folder looks something like this: