Cloning Git in Go - GopherCon India 2017

Gitgo began as an experiment: how would programming today be different if Git had been written in Go instead of C?

The result: an implementation of Git that is compatible with existing Git repositories, but simpler, more portable, and fast enough to be used as a general-purpose data store. With Gitgo, Git is no longer just for managing source control. Go makes Git a practical choice for content distribution, distributed build systems, establishing consensus, and more.

This talk was given on Feb 25, 2017 at GopherCon India in Pune.

Transcript

1. Cloning Git in Go Aditya Mukerjee Risk & Systems Engineer at Stripe @chimeracoder
2. Why write Gitgo? •Git operations from Go applications •Portability •Simplicity •…why not? @chimeracoder
3. The dirty secret about Git •Git wasn’t always meant to be a version control system •Git is a decentralized, userland filesystem for preserving historical state and synchronizing data @chimeracoder
4. What We’ve Enabled •Backup •Content management •Distributed build systems •Establishing consensus @chimeracoder
5. Have you ever seen a “friend’s” computer that looked like this? @chimeracoder
6. @chimeracoder 107724969b2af751a1ffd74e3f38d0d76cb8aa55
7. @chimeracoder commits trees blobs objects
8. Discovery #1: Layered interfaces are more flexible than union types @chimeracoder commits trees blobs objects
9. Bootstrapping Git in Go “We can just use the real .git directory for our tests, right?” @chimeracoder …nope.
10. hash(“I love Go”) != hash(“I love Go!”) @chimeracoder Packfiles
11. Reference: Unpacking Git Packfiles Reference: Implementing Git’s Compression Algorithm in Go binarydiff(1, 2, 3) 1. “I love Go” 2. “I love Go!” 3. “You love Go, and so do I!” “I love Go” <string 1> + “!”
12. Discovery #2: Pay attention to interface contracts @chimeracoder zlib data <arbitrary data> zlib data <arbitrary data>
13. @chimeracoder type Reader interface { Read(p []byte) (n int, err error) } Object 1 Object 2 Object 3 Object 4 …
14. • Discovery #3: Use concurrency to define state machines, and use channels for the input/output @chimeracoder f1 f3 f2 g g1 if f g2
15. • Discovery #4: Treat errors as values, and ask how they behave @chimeracoder httpdir.Open() ParsePackfile() GitFetch()
16. • Discovery #5: Well-architected interfaces perform very well @chimeracoder
17. #1: Layered interfaces are more flexible than union types #2: Pay attention to interface contracts #3: Use concurrency to define state machines, and use channels for the input/output #4: Treat errors as values, and ask how they behave #5: Well-architected interfaces perform very well @chimeracoder
18. Aditya Mukerjee @chimeracoder https://github.com/ChimeraCoder
19. Further References • “Unpacking Git Packfiles”: https://codewords.recurse.com/issues/three/unpacking-git-packfiles/ • “Implementing Git’s Compression Algorithm in Go”: https://blog.gopheracademy.com/advent- 2016/implementing_gits-compression_algorithm_in_go/ • Gitgo: https://github.com/ChimeraCoder/gitgo/ • “Git from the Inside Out”: https://codewords.recurse.com/issues/two/git-from-the-inside-out @chimeracoder