LMDB `DUP_SORT` `cursor.put(CURRENT)` different value size bug

test_lmdb_dup_sort_update_in_place.rs

use lmdb::{Cursor, Transaction};

fn test_lmdb_dup_sort_update_in_place() -> anyhow::Result<()> {
    let db_dir = "lmdb-dir";

    if let Err(err) = std::fs::remove_dir_all(db_dir) {
        if err.kind() != std::io::ErrorKind::NotFound {
            return Err(err.try_into()?);
        }
    }
    std::fs::create_dir_all(db_dir)?;

    let env = {
        let builder = lmdb::Environment::new();
        builder.open(std::path::Path::new(db_dir)).unwrap()
    };

    let db = env.create_db(
        None,
        lmdb::DatabaseFlags::INTEGER_KEY | lmdb::DatabaseFlags::DUP_SORT,
    )?;

    let key = 0x3003_0000_0000_003d_u64;
    eprintln!("Input key: {:#x}", key);

    let key_bytes = key.to_ne_bytes();
    // cursor.put(..., CURRENT) BUG: when new val len is less than old val len
    let val1 = "新建"; // "新建".len() = 3 * 2 = 6
    let val2 = "123456";

    let mut txn = env.begin_rw_txn()?;
    txn.put(db, &key_bytes, &val1, lmdb::WriteFlags::empty())?;

    let val = txn.get(db, &key_bytes)?;
    assert_eq!(val, val1.as_bytes());

    let mut cursor = txn.open_rw_cursor(db)?;
    for it in cursor.iter_from(key_bytes) {
        let (it_key, it_val) = it?;
        assert_eq!(it_key, key_bytes);
        assert_eq!(it_val, val1.as_bytes());

        cursor.put(&it_key, &val2, lmdb::WriteFlags::CURRENT)?;

        // HOWTO fix:
        //cursor.del(lmdb::WriteFlags::empty())?;
        //cursor.put(&it_key, &val2, lmdb::WriteFlags::empty())?;

        break;
    }
    drop(cursor);
    txn.commit()?;

    let txn = env.begin_ro_txn()?;
    let mut cursor = txn.open_ro_cursor(db)?;
    let mut count = 0;
    for it in cursor.iter_from(key_bytes) {
        let (it_key, it_val) = it?;

        let a = u64::from_ne_bytes(it_key.try_into()?);
        let b = std::str::from_utf8(it_val)?;

        eprintln!(" Read key: {:#x}", a);
        eprintln!(" Read val: {}", b);

        count += 1;

        assert_eq!(count, 1);
        assert_eq!(a, key, "{:#x} vs {:#x}", a, key);
        assert_eq!(b, val2);
    }
    drop(cursor);
    txn.abort();

    assert_eq!(count, 1);

    let txn = env.begin_ro_txn()?;
    let val = txn.get(db, &key_bytes)?;
    assert_eq!(val, val2.as_bytes());
    txn.abort();

    Ok(())
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    test_lmdb_dup_sort_update_in_place()?;
    eprintln!("OK!");
    Ok(())
}

Reproduce

Change let val1 = "新建"; to

• let val1 = "新建_";
• let val1 = "新建__";
• let val1 = "新建___";

See

https://github.com/leiless/lmdb
leiless/lmdb#1
meilisearch/lmdb#2