如何在React/Node/Express中将MongoDB缓冲区转换为图像

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

async function getImageFromDB(imageId) {
  const uri = 'your_mongodb_connection_string';
  const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });

  try {
    await client.connect();
    const database = client.db('your_database_name');
    const collection = database.collection('images');
    const image = await collection.findOne({ _id: imageId });
    return image.data; // 返回Buffer对象
  } finally {
    await client.close();
  }
}

const fs = require('fs');

async function saveImageToDisk(buffer, filePath) {
  return new Promise((resolve, reject) => {
    fs.writeFile(filePath, buffer, (err) => {
      if (err) {
        reject(err);
      } else {
        resolve(filePath);
      }
    });
  });
}

const express = require('express');
const app = express();

app.get('/download/:imageId', async (req, res) => {
  const imageId = req.params.imageId;
  try {
    const buffer = await getImageFromDB(imageId);
    const filePath = `./images/${imageId}.jpg`; // 假设图像为JPEG格式
    await saveImageToDisk(buffer, filePath);
    res.download(filePath, (err) => {
      if (err) {
        res.status(500).send('Error downloading image');
      }
    });
  } catch (error) {
    res.status(500).send('Internal Server Error');
  }
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});