如何使用GridFSBucket逐块处理正在下载的文件

const { MongoClient } = require('mongodb');
const { GridFSBucket } = require('mongodb');

async function downloadFile() {
  const client = await MongoClient.connect('mongodb://localhost:27017');
  const db = client.db('mydb');
  const bucket = new GridFSBucket(db, { bucketName: 'files' });

  // 其他操作...
}

const downloadStream = bucket.openDownloadStreamByName('filename.txt');

downloadStream.on('data', (chunk) => {
  // 处理每个块的数据
});

const fs = require('fs');
const writeStream = fs.createWriteStream('downloaded_file.txt');

downloadStream.pipe(writeStream);

downloadStream.on('end', () => {
  // 下载完成的处理
});