Transform upload with NodeJS Multer

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.

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                        });                    })            })        }    });