Transform upload with NodeJS Multer - node.js

Question

I'm currently implementing a file/image upload service for my users. I want to transform these images (resize/optimize) before uploading to my s3 bucket.
What I'm currently doing: Using a multipart form on my frontend (I think the actual implementation doesn't matter here..) and the multer and multer-s3 packages on my backend.
Here my implementation stripped down to the important parts.
// SETUP
var multer = require('multer');
var s3 = require('multer-s3');
var storage = s3({
dirname: 'user/uploads',
bucket: auth.aws.s3.bucket,
secretAccessKey: auth.aws.s3.secretAccessKey,
accessKeyId: auth.aws.s3.accessKeyId,
region: auth.aws.s3.region,
filename: function (req, file, cb) {
cb(null, Date.now());
}
});
var upload = multer({storage: storage}).single('img');
// ROUTE
module.exports = Router()
.post('/', function (req, res, next) {
upload(req, res, function (err) {
if (err) {
return res.status(401).json({err: '...'});
}
return res.json({err:null,url: '..'});
});
});
What I want to do: transform the image before uploading it. I'm not sure if I need to use multer/busboy here or I can just do it with NodeJS (thus I've tagged NodeJS and express as well).
So my question is: where can I intercept the upload and transform it before uploading it to my S3 bucket?

Answer 1

Not sure if you're still looking for an answer to this, but I had the same problem. I decided to extend the multer-s3 package.
I've opened a pull request to the original repository, but for now, you can use my fork.
Here's an example of how to use the extended version:
var upload = multer({
storage: multerS3({
s3: s3,
bucket: 'some-bucket',
shouldTransform: function (req, file, cb) {
cb(null, /^image/i.test(file.mimetype))
},
transforms: [{
id: 'original',
key: function (req, file, cb) {
cb(null, 'image-original.jpg')
},
transform: function (req, file, cb) {
cb(null, sharp().jpg())
}
}, {
id: 'thumbnail',
key: function (req, file, cb) {
cb(null, 'image-thumbnail.jpg')
},
transform: function (req, file, cb) {
cb(null, sharp().resize(100, 100).jpg())
}
}]
})
})
EDIT: My fork is also now available via npm under the name multer-s3-transform.

Answer 2

I've tried using #ItsGreg's fork, but couldn't get it to work. I managed to get this behaviour working by using multer-s3 standard configuration, and inside my file upload endpoint, i.e.,
app.post('/files/upload', upload.single('file'), (req, res) => {...})
I am retrieving the file using request, and passing the Buffer to sharp. The following works (and assumes you are using ~/.aws/credentials):
let request = require('request').defaults({ encoding: null });
let dataURI = `https://s3.amazonaws.com/${process.env.AWS_S3_BUCKET}/${image.defaultUrl}`;
request.get(dataURI, function (error, response, body) {
if (! error && response.statusCode === 200) {
let buffer = new Buffer(body);
const sizes = ['thumbnail', 'medium', 'large'];
sizes.forEach(size => {
sharp(buffer)
.resize(image.sizes[size])
.toBuffer()
.then(data => {
// Upload the resized image Buffer to AWS S3.
let params = {
Body: data,
Bucket: process.env.AWS_S3_BUCKET,
Key: `${image.filePath}${image.names[size]}`,
ServerSideEncryption: "AES256",
};
s3.putObject(params, (err, data) => {
if (err) console.log(err, err.stack); // an error occurred
else console.log(data); // successful response
});
})
})
}
});