How to upload image to S3 using Node

I am writing an Express app that takes in a base64 encoded string that represents an image. Right now, i'm not really sure how I can take that string and upload the image to AWS S3, so i'm reading in the encoded image string data, decoding it, writing a file using fs, and then trying to upload. I have this working for an endpoint that just takes in a raw file, and all of its content is correctly uploaded to AWS s3.

Now when I try to do what I described above, i'm able to upload to S3, but the file has 0kb and is empty, and i'm not sure why. I tested just taking the stringData and writing a file to a test file, and it works. However, when I try uploading to s3, the file shows but it's empty. Here is my code:

router.post('/images/tags/nutritionalInformation/image/base64encoded', function (req, res) {
    console.log(req.body.imageString);
    var base64Stream = req.body.imageString;
    var imgDecodedBuffer = decodeBase64Image(base64Stream);
    console.log(imgDecodedBuffer);
    // write to image file
    var prefix = guid().toString() + ".jpg";
    var filePath = './uploads/' + prefix;
    console.log(filePath);


    fs.writeFile(filePath, imgDecodedBuffer.data, function(err) {
        console.log(err);
    });

    var stream = fs.createReadStream(filePath);


    console.log(stream);

    return s3fsImpl.writeFile(prefix, stream).then(function () {
        fs.unlink(filePath, function (err) {
            if (err) {
                console.error(err);
            }
        });
    });
})

Here are the relevant import statements:

var fs = require('fs');
var s3fs = require('s3fs');
var multiparty = require('connect-multiparty'),
    multipartyMidleware = multiparty();

var s3fsImpl = new s3fs('blahblah', {
    accessKeyId: 'ACCESS_KEY_ID',
    secretAccessKey: 'SECRET'
});

Any help would be greatly appreciated!