pocketmine\level\format\leveldb\LevelDB::saveLevelData PHP Method

    public function saveLevelData()
    {
        $nbt = new NBT(NBT::LITTLE_ENDIAN);
        $nbt->setData($this->levelData);
        $buffer = $nbt->write();
        file_put_contents($this->getPath() . "level.dat", Binary::writeLInt(3) . Binary::writeLInt(strlen($buffer)) . $buffer);
    }