通过Node读取GridFS时如何解码base64文件？

npm install mongodb gridfs-stream

const mongodb = require('mongodb');
const Grid = require('gridfs-stream');
const fs = require('fs');

const MongoClient = mongodb.MongoClient;
const url = 'mongodb://localhost:27017/mydatabase'; // 替换为你的MongoDB连接URL
const dbName = 'mydatabase'; // 替换为你的数据库名称

MongoClient.connect(url, (err, client) => {
  if (err) {
    console.log('MongoDB连接失败:', err);
    return;
  }

  const db = client.db(dbName);
  const gfs = Grid(db, mongodb);
  
  // 在这里进行文件解码操作
});

const fileId = 'your_file_id'; // 替换为你要读取的文件ID

const readStream = gfs.createReadStream({ _id: fileId });
let data = '';

readStream.on('data', (chunk) => {
  data += chunk.toString('base64');
});

readStream.on('end', () => {
  // 解码base64数据
  const decodedData = Buffer.from(data, 'base64');
  
  // 将解码后的数据保存到文件
  fs.writeFile('decoded_file.jpg', decodedData, (err) => {
    if (err) {
      console.log('保存文件失败:', err);
      return;
    }
    console.log('文件解码并保存成功！');
  });
});

readStream.on('error', (err) => {
  console.log('读取文件流失败:', err);
});