tegdb 0.4.0

The name TegridyDB (short for TegDB) is inspired by the Tegridy Farm in South Park and tries to correct some of the wrong database implementations, such as null support, implicit conversion support, etc.
Documentation 
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use std::fs::{File, OpenOptions};
use std::io::{Read, Seek, SeekFrom, Write};

use tempfile::TempDir;

const MAGIC: &[u8] = b"TEGDB\0";
const HEADER_SIZE: usize = 64;

#[test]
fn writes_header_on_create() {
    let tmp = TempDir::new().unwrap();
    let db_path = tmp.path().join("tegdb").with_extension("teg");
    let identifier = format!("file://{}", db_path.to_string_lossy());

    {
        // Create database
        let mut db = tegdb::Database::open(&identifier).unwrap();
        db.execute("CREATE TABLE t (id INTEGER PRIMARY KEY, name TEXT(32))")
            .unwrap();
    } // drop

    let mut f = File::open(&db_path).unwrap();
    let mut header = vec![0u8; HEADER_SIZE];
    f.read_exact(&mut header).unwrap();
    assert_eq!(&header[0..MAGIC.len()], MAGIC);
    // version == 2
    assert_eq!(u16::from_be_bytes([header[6], header[7]]), 2);
    assert_eq!(header.len(), HEADER_SIZE);
}

#[test]
fn rejects_missing_or_wrong_magic() {
    let tmp = TempDir::new().unwrap();
    let db_path = tmp.path().join("bad").with_extension("teg");
    {
        let mut f = OpenOptions::new()
            .create(true)
            .truncate(true)
            .write(true)
            .open(&db_path)
            .unwrap();
        // Write bogus header of correct size but wrong magic (6 bytes)
        let mut bogus = vec![0u8; HEADER_SIZE];
        bogus[0..6].copy_from_slice(b"BADDB!");
        f.write_all(&bogus).unwrap();
        f.flush().unwrap();
    }
    let identifier = format!("file://{}", db_path.to_string_lossy());
    let res = tegdb::Database::open(&identifier);
    assert!(res.is_err());
    let msg = format!("{}", res.err().unwrap());
    assert!(msg.contains("Invalid storage file magic"));
}

#[test]
fn reads_entries_after_header() {
    let tmp = TempDir::new().unwrap();
    let db_path = tmp.path().join("entries").with_extension("teg");
    let identifier = format!("file://{}", db_path.to_string_lossy());

    {
        let mut db = tegdb::Database::open(&identifier).unwrap();
        db.execute("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT(32))")
            .unwrap();
        db.execute("INSERT INTO users (id, name) VALUES (1, 'Alice')")
            .unwrap();
    }

    {
        let mut db = tegdb::Database::open(&identifier).unwrap();
        let result = db.query("SELECT name FROM users WHERE id = 1").unwrap();
        assert_eq!(result.rows().len(), 1);
        assert_eq!(result.get_cell_text(0, 0).as_deref(), Some("Alice"));
    }
}

#[cfg(feature = "dev")]
#[test]
fn compaction_preserves_header() {
    use tegdb::storage_engine::StorageEngine;

    let tmp = TempDir::new().unwrap();
    let db_path = tmp.path().join("compact").with_extension("teg");

    // Use low-level engine API
    let mut engine = StorageEngine::new(db_path.clone()).unwrap();
    // write some data
    engine.set(b"k1", b"v1".to_vec()).unwrap();
    engine.set(b"k2", b"v2".to_vec()).unwrap();
    engine.del(b"k1").unwrap();

    // Compact
    engine.compact().unwrap();
    drop(engine);

    // Verify header still present and correct
    let mut f = File::open(&db_path).unwrap();
    let mut header = vec![0u8; HEADER_SIZE];
    f.read_exact(&mut header).unwrap();
    assert_eq!(&header[0..MAGIC.len()], MAGIC);
    assert_eq!(u16::from_be_bytes([header[6], header[7]]), 2);

    // Also ensure remaining data starts after header
    f.seek(SeekFrom::Start(HEADER_SIZE as u64)).unwrap();
    let mut rest = Vec::new();
    f.read_to_end(&mut rest).unwrap();
    assert!(!rest.is_empty());
}