Securely Uploading Files to AWS S3 from a Node.js Backend

// Install: npm install express multer @aws-sdk/client-s3 @aws-sdk/s3-request-presigner uuid
const express = require('express');
const multer = require('multer');
const { S3Client, PutObjectCommand } = require('@aws-sdk/client-s3');
const { getSignedUrl } = require('@aws-sdk/s3-request-presigner');
const { v4: uuidv4 } = require('uuid'); // For unique file names

const app = express();
const upload = multer({ storage: multer.memoryStorage() }); // Store file in memory temporarily

// AWS S3 Configuration
const s3Client = new S3Client({
  region: 'us-east-1', // Replace with your S3 bucket region
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID, // Use environment variables for security
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
  },
});
const S3_BUCKET_NAME = 'your-unique-s3-bucket-name'; // Replace with your bucket name

app.post('/upload', upload.single('file'), async (req, res) => {
  if (!req.file) {
    return res.status(400).send('No file uploaded.');
  }

  const file = req.file;
  const originalFileName = file.originalname;
  const fileExtension = originalFileName.split('.').pop();
  const s3FileName = `${uuidv4()}.${fileExtension}`; // Generate a unique file name

  const uploadParams = {
    Bucket: S3_BUCKET_NAME,
    Key: `uploads/${s3FileName}`, // Path within the bucket
    Body: file.buffer,
    ContentType: file.mimetype,
    ACL: 'private', // Access Control List: private is generally recommended
  };

  try {
    const command = new PutObjectCommand(uploadParams);
    await s3Client.send(command);

    // Optionally, generate a pre-signed URL for temporary access (e.g., for download)
    const getCommand = new PutObjectCommand({
      Bucket: S3_BUCKET_NAME,
      Key: uploadParams.Key,
    });
    const url = await getSignedUrl(s3Client, getCommand, { expiresIn: 3600 }); // URL valid for 1 hour

    res.status(200).json({
      message: 'File uploaded successfully to S3',
      s3Key: uploadParams.Key,
      fileUrl: url, // Temporary URL for demonstration
    });
  } catch (error) {
    console.error('Error uploading file to S3:', error);
    res.status(500).send('Failed to upload file to S3.');
  }
});

const PORT = process.env.PORT || 3001;
app.listen(PORT, () => {
  console.log(`Server listening on port ${PORT}`);
});