feat(users/Profpatsch): add git-db

WIP: currently just a simple setup that creates an empty git repo if
it doesn’t exist yet, and writes a commit to it.

A simple database backed by a bare git repository.

WIP: Will speak a simple interactive protocol to query files and
update them atomically.

It could be made atomic on the git repo level, if a lock is taken
between reading the current commit ref and creating the commit.

Change-Id: I1fd30a046ac977063c3e08c36d96e835b35ff07d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3046
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
This commit is contained in:
Profpatsch 2021-04-19 22:49:15 +02:00
parent 38b3cdebef
commit c1d7714a21
2 changed files with 93 additions and 0 deletions

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{ depot, pkgs, lib, ... }:
depot.nix.writers.rustSimple {
name = "git-db";
dependencies = [
depot.third_party.rust-crates.git2
];
} (builtins.readFile ./git-db.rs)

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extern crate git2;
use std::os::unix::ffi::OsStrExt;
use std::path::PathBuf;
const DEFAULT_BRANCH : &str = "refs/heads/main";
fn main() {
let git_db_dir = std::env::var_os("GIT_DB_DIR").expect("set GIT_DB_DIR");
let git_db = PathBuf::from(git_db_dir).join("git");
std::fs::create_dir_all(&git_db).unwrap();
let repo = git2::Repository::init_opts(
&git_db,
git2::RepositoryInitOptions::new()
.bare(true)
.mkpath(true)
.description("git-db database")
.initial_head(DEFAULT_BRANCH)
).expect(&format!("unable to create or open bare git repo at {}", &git_db.display()));
let mut index = repo.index().expect("cannot get the git index file");
eprintln!("{:#?}", index.version());
index.clear().expect("could not clean the index");
let now = std::time::SystemTime::now()
.duration_since(std::time::SystemTime::UNIX_EPOCH)
.expect("unable to get system time");
let now_git_time = git2::IndexTime::new(
now.as_secs() as i32, // lol
u32::from(now.subsec_nanos()),
);
let data = "hi, its me".as_bytes();
index.add_frombuffer(
&git2::IndexEntry {
mtime: now_git_time,
ctime: now_git_time,
// dont make sense
dev: 0,
ino: 0,
mode: /*libc::S_ISREG*/ 0b1000 << (3+9) | /* read write for owner */ 0o644,
uid: 0,
gid: 0,
file_size: data.len() as u32, // lol again
id: git2::Oid::zero(),
flags: 0,
flags_extended: 0,
path: "hi.txt".as_bytes().to_owned(),
},
data
).expect("could not add data to index");
let oid = index.write_tree().expect("could not write index tree");
let to_add_tree = repo.find_tree(oid)
.expect("we just created this tree, where did it go?");
let parent_commits = match repo.find_reference(DEFAULT_BRANCH) {
Ok(ref_) => vec![
ref_
.peel_to_commit()
.expect(&format!("reference {} does not point to a commit", DEFAULT_BRANCH))
],
Err(err) => match err.code() {
// no commit exists yet
git2::ErrorCode::NotFound => vec![],
_ => panic!("could not read latest commit from {}", DEFAULT_BRANCH),
}
};
repo.commit(
Some(DEFAULT_BRANCH),
&git2::Signature::now("Mr. Authorboy", "author@example.com").unwrap(),
&git2::Signature::now("Mr. Commiterboy", "committer@example.com").unwrap(),
"This is my first commit!\n\
\n\
I wonder if it supports extended commit descriptions?\n",
&to_add_tree,
&parent_commits.iter().collect::<Vec<_>>()[..],
).expect("could not commit the index we just wrote");
}