如何在注册用户之前检查用户凭据，同时将图像上传到 aws s3

Question

I am trying to implement a registration route in my application. The flow is pretty simple. While using the application, the user has the opportunity to select a profile image (but he doesn't have to). Later on, the user is asked to register and enters an email.

Now, I would like to check on my registration route IF the email already exists BEFORE uploading the image to my S3 bucket. If it does exist, I want to send back a proper error message. If it does NOT exist, I would like to check if the user has send along an image and proceed to upload the image to S3 so I can store the link in my db and proceed to register the user.

The Problem

Im appending both the file and the email to a formData object like so. At this point the file can be empty. That depends if the user has selected a profile image or not.

const formData = new FormData();
formData.append('avatar', this.variables.avatar);
formData.append('email', JSON.stringify(this.email));

The problem is that when making the request, either req.file is undefined or req.body.email is undefined. The reason for this is simple, I cannot acces the req.body.email BEFORE the image is uploaded to my s3 bucket. This would mean that everytime a user registers with an already existing email, the image gets send to my s3 bucket nonetheless.

This is my function to upload to aws:

const avatarImgUpload = multer({
  storage: multerS3({
    s3: s3,
    bucket: process.env.AWS_BUCKET,
    acl: 'public-read',
    key: function (req, file, cb) {
      cb(null, path.basename(file.originalname, path.extname(file.originalname)) + '-' + Date.now() + path.extname(file.originalname))
    }
  }),
}).single('avatar');

And this is my register route:

router.post('/register', (req, res) => {
  //let email = JSON.parse(req.body.email);
  //The email is undefined because I am not using middleware 
  //like multer to be able to 'read' or 'acces' this

  //Ideally I would like to FIRST check if a user exists like so:
  //User.findOne({email: req.body.email})

  //If it does not exists, great! Continue to the 'avatarImgUpload' function that uploads to S3'
  //If not, send back an error message and end the request there.

  avatarImgUpload(req, res, (error) => {
    //Within this function I do have access to req.body.email because it uses multer.
    //However, like I said before this means that the check IF the user already exists
    //has to take place AFTER the image is uploaded to my S3 bucket, which isn't great.
  })
})

Is there a way around this? Can I get acces to req.body.email BEFORE uploading the image to my S3 bucket? Is there a way for example to maybe both send a formData object AND JSON so I can first check the email before continuing with the file upload?

Answer 1

Just split it into 2 requests, let user thinks it's just 1 operation using AJAX:

1. Check User condition
2. If matched, allow to register and upload.

For more secure, Presigned Url works well. Signed url is like a temporary link with temporary permission used to upload to your S3, without this link, user cannot upload to your S3. Basically, the flow will be:

1. User requests to server to check condition and get signed url -> if matched, server responses with an url.

Not sure as if multer supports getting signed url, this code is using aws sdk:

router.post('/register', (req, res) => {
  // Check User exists
  // ...

  // Set custom info for the uploading image
  const fileName = uuid();
  const s3 = new S3();
  const params = {
    Bucket: 'bucket name',
    Key: 'file name',
    ContentType: 'image/*',
    Expires: 60 * 10, // Url is available for 10 mins
    Metadata: {
      'email': 'user@example.com',
      'custom-field': 'custom data',
    },
  };

  res.send(await s3.getSignedUrl('putObject', params));
});

2. User uses the url to upload to S3.

More info:

https://docs.aws.amazon.com/AmazonS3/latest/dev/PresignedUrlUploadObject.html . https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#getSignedUrl-property