alkblobs/tests/git_interop.rs

//! The load-bearing interop test (ADR-002; POC #1 findings 4/5's
//! standard): byte-exact derivation against the `git hash-object` CLI
//! for both algorithms — validated against git, not just hardcoded
//! vectors — plus the external-oid round-trip into pool keys.
//!
//! Harness detail (POC finding 4, empirically learned): in current
//! git, `--object-format` is not a `hash-object` flag; the object
//! format is set on the repo (`git init --object-format=sha256`) and
//! the hash-object runs inside that repo. Repos are created fresh in
//! a per-call temp directory, with global/system config detached.

use std::fs;
use std::path::{Path, PathBuf};
use std::process::Command;
use std::time::{SystemTime, UNIX_EPOCH};

use alkblobs::{Algorithm, Digest, Key};

/// Content cases: empty, short text, binary-with-NULs, and a
/// multi-KiB case (75 KiB, deterministic).
fn content_cases() -> Vec<(&'static str, Vec<u8>)> {
    vec![
        ("empty", Vec::new()),
        ("short", b"hello".to_vec()),
        (
            "binary-nuls",
            vec![0u8, 1, 255, 0, 10, 13, 0, 7, 255, 255, 0, 0],
        ),
        (
            "multi-kib",
            (0..75 * 1024).map(|i| (i % 251) as u8).collect::<Vec<u8>>(),
        ),
    ]
}

fn scratch_dir(tag: &str) -> PathBuf {
    let nanos = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .expect("system clock before epoch")
        .as_nanos();
    let dir = std::env::temp_dir().join(format!(
        "alkblobs-git-interop-{}-{}-{}",
        tag,
        std::process::id(),
        nanos
    ));
    fs::create_dir_all(&dir).expect("temp dir creation");
    dir
}

fn detached_config(command: &mut Command) {
    let devnull = if cfg!(windows) { "NUL" } else { "/dev/null" };
    command
        .env("GIT_CONFIG_GLOBAL", devnull)
        .env("GIT_CONFIG_SYSTEM", devnull);
}

/// Initialize a fresh repo of the requested object format and return
/// the oid hex `git hash-object --stdin` prints for `content`.
fn git_hash_object(content: &[u8], sha256: bool) -> (PathBuf, String) {
    let dir = scratch_dir("repo");
    let mut init = Command::new("git");
    detached_config(&mut init);
    init.arg("init").arg("-q").current_dir(&dir);
    if sha256 {
        init.arg("--object-format=sha256");
    }
    let out = init.output().expect("git init spawn");
    assert!(
        out.status.success(),
        "git init failed: {}",
        String::from_utf8_lossy(&out.stderr)
    );

    let mut hash = Command::new("git");
    detached_config(&mut hash);
    hash.arg("-C").arg(&dir).arg("hash-object").arg("--stdin");
    use std::io::Write as _;
    let mut child = hash
        .stdin(std::process::Stdio::piped())
        .stdout(std::process::Stdio::piped())
        .spawn()
        .expect("git hash-object spawn");
    child
        .stdin
        .as_mut()
        .expect("stdin piped")
        .write_all(content)
        .expect("stdin write");
    let out = child.wait_with_output().expect("git hash-object output");
    assert!(
        out.status.success(),
        "git hash-object failed: {}",
        String::from_utf8_lossy(&out.stderr)
    );
    let oid = String::from_utf8(out.stdout)
        .expect("git output utf8")
        .trim()
        .to_owned();
    (dir, oid)
}

fn drop_dir(dir: &Path) {
    let _ = fs::remove_dir_all(dir);
}

/// The load-bearing test: `Digest`'s derivation matches the git CLI
/// byte-exact, both algorithms, small and multi-KiB content.
#[test]
fn derivation_is_byte_exact_against_git_hash_object() {
    for (tag, content) in content_cases() {
        let (dir, oid) = git_hash_object(&content, false);
        drop_dir(&dir);
        assert_eq!(oid.len(), 40, "git printed a sha1 oid");
        assert_eq!(
            Digest::from_git_oid_hex(&oid),
            Ok(Algorithm::GitBlobSha1.derive(&content, content.len() as u64)),
            "sha1 {tag}: derived digest != git hash-object",
        );

        let (dir, oid) = git_hash_object(&content, true);
        drop_dir(&dir);
        assert_eq!(oid.len(), 64, "git printed a sha256 oid");
        assert_eq!(
            Digest::from_git_oid_hex(&oid),
            Ok(Digest::derive(&content, content.len() as u64)),
            "sha256 {tag}: derived digest != git hash-object",
        );
    }
}

/// The external-oid round-trip (POC finding 4 corollary, key level):
/// an oid produced by external git (`from_git_oid_hex` →
/// `as_bytes` → `from_bytes`) becomes exactly the pool key the store
/// core would derive — no mapping layer.
#[test]
fn external_oid_round_trips_into_pool_keys() {
    for sha256 in [false, true] {
        let content = b"external producer blob \0 bytes";
        let (dir, oid) = git_hash_object(content, sha256);
        drop_dir(&dir);

        let external: Key = Digest::from_git_oid_hex(&oid)
            .expect("external oid decodes")
            .into();
        let derived: Key = {
            let len = content.len() as u64;
            Digest::derive(content, len).into()
        };
        if sha256 {
            assert_eq!(external, derived, "sha256: external oid == derived key");
        } else {
            assert_eq!(
                external,
                Key::from(Algorithm::GitBlobSha1.derive(content, content.len() as u64)),
                "sha1: external oid == derived key"
            );
        }
        let decoded = Key::from_bytes(&external.as_bytes()).expect("physical encoding decodes");
        assert_eq!(decoded, external);
        assert_eq!(decoded.as_bytes(), external.as_bytes());
    }
}

/// Tagged-key coexistence (POC finding 5): git oids of both formats
/// address the same flat key universe from one external producer.
#[test]
fn both_oid_formats_coexist_in_one_pool() {
    let content = b"same content, two formats";
    let (dir1, oid1) = git_hash_object(content, false);
    drop_dir(&dir1);
    let (dir2, oid2) = git_hash_object(content, true);
    drop_dir(&dir2);

    let mut pool = std::collections::BTreeSet::new();
    pool.insert(
        Key::from_bytes(
            &Key::from(Digest::from_git_oid_hex(&oid1).expect("sha1 oid decodes")).as_bytes(),
        )
        .expect("sha1 external key decodes"),
    );
    pool.insert(
        Key::from_bytes(
            &Key::from(Digest::from_git_oid_hex(&oid2).expect("sha256 oid decodes")).as_bytes(),
        )
        .expect("sha256 external key decodes"),
    );
    assert_eq!(pool.len(), 2, "both algorithms coexist in one flat pool");
}