Uploading Images to SUSI Server

SUSI Skill CMS is a web app to create and modify SUSI Skills. It needs API Endpoints to function and SUSI Server makes it possible. In this blogpost, we will see how to add a servlet to SUSI Server to upload images and files.

The CreateSkillService.java file is the servlet which handles the process of creating new Skills. It requires different user roles to be implemented and hence it extends the AbstractAPIHandler.

Image upload is only possible via a POST request so we will first override the doPost method in this servlet.

  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  resp.setHeader("Access-Control-Allow-Origin", "*"); // enable CORS

resp.setHeader enables the CORS for the servlet. This is required as POST requests must have CORS enables from the server. This is an important security feature that is provided by the browser.

        Part file = req.getPart("image");
        if (file == null) {
            json.put("accepted", false);
            json.put("message", "Image not given");

Image upload to servers is usually a Multipart Request. So we get the part which is named as “image” in the form data.

When we receive the image file, then we check if the image with the same name exists on the server or not.

Path p = Paths.get(language + File.separator + “images/” + image_name);

        if (image_name == null || Files.exists(p)) {
                json.put("accepted", false);
                json.put("message", "The Image name not given or Image with same name is already present ");

If the same file is present on the server then we return an error to the user requesting to give a unique filename to upload.

Image image = ImageIO.read(filecontent);
BufferedImage bi = this.createResizedCopy(image, 512, 512, true);
if(!Files.exists(Paths.get(language.getPath() + File.separator + "images"))){
   new File(language.getPath() + File.separator + "images").mkdirs();
ImageIO.write(bi, "jpg", new File(language.getPath() + File.separator + "images/" + image_name));

Then we read the content for the image in an Image object. Then we check if images directory exists or not. If there is no image directory in the skill path specified then create a folder named “images”.

We usually prefer square images at the Skill CMS. So we create a resized copy of the image of 512×512 dimensions and save that copy to the directory we created above.

BufferedImage createResizedCopy(Image originalImage, int scaledWidth, int scaledHeight, boolean preserveAlpha) {
        int imageType = preserveAlpha ? BufferedImage.TYPE_INT_RGB : BufferedImage.TYPE_INT_ARGB;
        BufferedImage scaledBI = new BufferedImage(scaledWidth, scaledHeight, imageType);
        Graphics2D g = scaledBI.createGraphics();
        if (preserveAlpha) {
        g.drawImage(originalImage, 0, 0, scaledWidth, scaledHeight, null);
        return scaledBI;

The function above is used to create a  resized copy of the image of specified dimensions. If the image was a PNG then it also preserves the transparency of the image while creating a copy.

Since the SUSI server follows an API centric approach, all servlets respond in JSON.


At last, we set the character encoding and the character set of the output. This helps the clients to parse the data easily.

To see this endpoint in live send a POST request at http://api.susi.ai/cms/createSkill.json.


Apache Docs: https://commons.apache.org/proper/commons-fileupload/using.html

Multipart POST Request Tutorial: http://www.codejava.net/java-se/networking/upload-files-by-sending-multipart-request-programmatically

Java File Upload tutorial: https://ursaj.com/upload-files-in-java-with-servlet-api

Jetty Project: https://github.com/jetty-project/

Flask App to Upload Wallpaper On the Server for Meilix Generator

We had a problem of getting a wallpaper from the user using Meilix Generator and use the wallpaper with the Meilix build scripts to generate the ISO. So, we were required to host the wallpaper on the server and downloaded by Travis CI during the build to include it in the ISO.

A solution is to render HTML templates and access data sent by POST using the request object from the flask. Redirect and url_for will be used to redirect the user once the upload is done and send_from_directory will help us to host the file under the /uploads that the user just uploaded which will be downloaded by the Travis for building the ISO.

We start by creating the HTML form marked with enctype=multipart/form-data.

<form action="upload" method="post" enctype="multipart/form-data">
        <input type="file" name="file"><br /><br />
        <input type="submit" value="Upload">


First, we need imports of modules required. Most important is werkzeug.secure_filename().

import os
from flask import Flask, render_template, request, redirect, url_for, send_from_directory
from werkzeug import secure_file


Now, we’ll define where to upload and the type of file allowed for uploading. The path to upload directory on the server is defined by the extensions in app.config which is uploads/ here.

app.config['UPLOAD_FOLDER'] = 'uploads/'
app.config['ALLOWED_EXTENSIONS'] = set(['png', 'jpg', 'jpeg'])


This functions will check for valid extension for the wallpaper which are png, jpg and jpeg in this case defined above in app.config.

def allowed_file(filename):
    return '.' in filename and \
           filename.rsplit('.', 1)[1] in app.config['ALLOWED_EXTENSIONS']


After, getting the name of uploaded file from the user then using above function check if there are allowed file type and store it in a variable filename after that it move the files to the upload folder to save it.

Upload function check if the file name is safe and remove unsupported characters (line 3) after that moves it from a temporal folder to the upload folder. After moving, it renames the file as wallpaper so that the download link is same always which we have used in Meilix build script to download from server.

def upload():
    file = request.files['file']
    if file and allowed_file(file.filename):
        filename = secure_filename(file.filename)
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
         os.rename(UPLOAD_FOLDER + filename, UPLOAD_FOLDER+'wallpaper')
         filename = 'wallpaper'


At this point, we have only uploaded the wallpaper and renamed the uploaded file to ‘wallpaper’ only. We cannot access the file outside the server it will result in 403 error so to make it available, the uploaded file need to be registered and then hosted using below code snippet.

We can also register uploaded_file as build_only rule and use the SharedDataMiddleware.

def uploaded_file(filename):
    return send_from_directory(app.config['UPLOAD_FOLDER'],filename)

The hosted wallpaper is used by Meilix in Travis CI to generate ISO using the download link which remains same for the uploaded wallpaper.

Why should we use secure secure_filename() function?

just imagine someone sends the following information as the filename to your app.

filename = "../../../../home/username/.sh"


If the number of ../ is correct and you would join this with your UPLOAD_FOLDER the hacker might have the ability to modify a file on the server’s filesystem that he or she should not modify.

Now, let’s look how the function works.


Improving the uploads

We can add validation to the size of the file to be uploaded so that in case a user tries to upload a file too much big that may increase load on the server.

from flask import Flask, Request
app = Flask(__name__)
app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024


Uploading Images via APIs in the Open Event Server

APIs help us to send and receive data in some particular data format that can then be used individually or integrated with a frontend UI. In our case, the entire API server is used to manage all the requests from the frontend and send back the necessary response. Usually, the application is to send simple form data which is then stored into the backend database and a valid jsonapi response is shown. However other than normal text, url, datetime data one very important data is media files, in our case event images, user images, slides, etc. In this blog, we will particularly deal with how we can upload images in the server using API.

Sending Data

Firstly, we need to decide how do we send the data in the post request of the API. So we are sending a base64 encoded string representing the image along with the image extension appended to it, for example, data:image/png;base64,iVBORw0KGgoAAAANS. This is a widely used format for showing images over the web. So when we send a POST request we send a json encoded body like:

    "data": "data:image/png;base64,iVBORw0KGgoAAAANS"

Converting Base64 Data to Image

There are 2 parts of the data in the string that we receive. The first part basically tells us the format of the image(.gif in this case) and string encoding(base64 in this case), the second part gives us the encoded string. So, from the first part, we extract the file extension for the image file to be created. We use uuid.uuid4() for a random filename.

filename = '{}.{}'.format(str(uuid.uuid4()).data.split(";")[0].split("/")[1])

Now to write the base64 encoded string as an image file, we first need to get only the encoded string part from the data and then decode it. We use string decode function of python for the decoding purpose. Then we write the data to the image file and save it.


API Response

Finally using whatever logic you are using for serving your static files, you generate the static file path for the image saved. And then create another json encoded response which returns you the url for the saved image in the server.

    "url": "https://xyz.storage.com/asd/fgh/hjk/1233456.png"

And there you have your image uploaded and served.

File upload progress in a Node app using Socket.io

If you look at the webapp generator, you’ll see that there is an option to upload a zip file containing event data. We wanted to give visual cue to the user when he is uploading to see how much file has uploaded.

We are uploading the file, and giving the generate start command via socket.io events instead of POST requests here.

To observe file upload progress on socket (when sending file using a Buffer), there is an awesome node module available called socketio-upload-progress.

In our webapp you can see we implemented it on the frontend here in the form.js and here in the backend in app.js

Basically on the backend you should add the socketio-file-upload module as a middleware to express

var siofu = require("socketio-file-upload");
var app = express()

After a socket is opened, set up the upload directory and start listening for uploads

io.on("connection", function(socket){
    var uploader = new siofu();
    uploader.dir = "/path/to/save/uploads";

On the frontend, we’ll listen for an input change on an file input type element whose id is siofu_upload

var socket = io.connect();
var uploader = new SocketIOFileUpload(socket);

One thing to note here is that, if you observe percentage of upload on frontend, it’ll give you false values. The correct values of how much data is actually transferred can be found in the backend. So observe progress in backend, and send percentage to frontend using the same socket.

  uploader.on('progress', function(event) {
    console.log(event.file.bytesLoaded / event.file.size)
    socket.emit('upload.progress', {
      percentage:(event.file.bytesLoaded / event.file.size) * 100


Handling file uploading in HTML5 and Express

The Open Event Webapp Generator has a pure HTML front end form, and Express based backend.


We needed an option where users can upload their own JSON files to create a schedule page for it.

On the HTML form that’s easy. As you can see here we simple add input tags with type=”file”

<input type="file" name="sponsorfile" id="sponsorfile">

In our express app, we need to use multer to be able to handle file uploads.

We create a middleware called uploadedFiles, and pass the middleware to the get() block


var express = require('express');
var multer = require('multer');
var app = express();

var upload = multer({dest: 'uploads/'});

var uploadedFiles = upload.fields([
  {name: 'speakerfile', maxCount: 1},
  {name: 'sessionfile', maxCount: 1},
  {name: 'trackfile', maxCount: 1},
  {name: 'sponsorfile', maxCount: 1},
  {name: 'eventfile', maxCount: 1},
  {name: 'locationfile', maxCount: 1}

app.post('/live', uploadedFiles, function(req, res) {
         // req.files has the files
         // req.body has the POST body params

Now we can access the files inside req.files (that will have a path to the temporary location of the file, you’ll have to use some filesystem module to read the files)

File Uploading in Flask

Last week I took up an issue of adding upload functionality to the open-event server. I had to implement the upload in 3 places – one in the sponsor table to upload images, another in the user profile page and the third is to upload slides in the session form. However the basic function behind it remains the same. File upload makes use of the inbuilt werkzeug FileStorage class. A code snippet will help understand how it works:


So  on selecting the file it gets stored in the request.files object. It is temporarily stored in the FileStorage in werkzeug. Now we access the file’s name using request.files[‘files’] and then using the inbuilt save()  function in flask it gets saved to the folder specified by us. There are some frameworks available for file uploading in Flask but all this can be done using the standard libraries also and there is no such need of the frameworks.

However instead of storing just the direct name of the file we make use of the secure_filename of werkzeug to save it.Capture2.PNG

Thus the secure_filename stores the file in the format given in the image and makes uploading easier by converting the long url/image path to an easier one.