How to Implement Memory like Servlets in SUSI.AI

In this blog, I’ll be discussing about how a server gets previous messages from the Log files in SUSI server. SUSI AI clients, Android, iOS and web chat, follow a very simple rule. Whenever a user logs in to the app, the app makes a http GET call to the server in the background and in response, server returns the chat history.

Link to the API endpoint ->

But parsing a lot of data might depend on the connection speed. If the connection is poor or lacking speed, the history would cost user’s time. To prevent this, server by default returns last 10 pair of messages. It is up to the client that how many messages they want to render. So for example, if the client requests last 5 messages, then the client has to make a GET request and pass the cognitions parameter. Hence the modified end point will be :

But how does the server process it? Let us see.
Browse to susi_server/src/ai/susi/server/api/susi/ file. This is the main working servlet. If you are new and wondering how servlets for susi are implemented, Please go through this first how-to-add-a-new-servletapi-to-susi-server
This is how serviceImpl() method looks like :

    public ServiceResponse serviceImpl(Query post, HttpServletResponse response, Authorization user, final JsonObjectWithDefault permissions) throws APIException {

        int cognitionsCount = Math.min(10, post.get("cognitions", 10));
        String client = user.getIdentity().getClient();
        List<SusiCognition> cognitions = DAO.susi.getMemories().getCognitions(client);
        JSONArray coga = new JSONArray();
        for (SusiCognition cognition: cognitions) {
            if (--cognitionsCount <= 0) break;
        JSONObject json = new JSONObject(true);
        json.put("cognitions", coga);
        return new ServiceResponse(json);

In the first step, we find the minimum of default value (i.e. 10) and the value of cognitions received as GET parameter. Messages equivalent to minimum variable are encoded in JSONArray and sent to the client.

Whenever the server receives a valid signup request, It makes a directory with the name “email_emailid”. In this directory, a log.txt file is maintained which stores all the queries along with the other details associated with it. For example if user has signed up with the email id [email protected], Then the path of this directory will be [email protected]. If a user queries “”,  then

	"query": "flip a coin",
	"count": 1,
	"client_id": "",
	"query_date": "2017-06-30T12:22:05.918Z",
	"answers": [{
		"data": [{
			"0": "flip a coin",
			"token_original": "coin",
			"token_canonical": "coin",
			"token_categorized": "coin",
			"timezoneOffset": "-330",
			"answer": "tails",

			"skill": "/susi_skill_data/models/general/entertainment/en/flip_coin.txt",
			"_etherpad_dream": "cricket"
		"metadata": {
			"count": 1
		"actions": [{
			"type": "answer",
			"expression": "tails"
		"skills": ["/susi_skill_data/models/general/entertainment/en/flip_coin.txt"]
	"answer_date": "2017-06-30T12:22:05.928Z",
	"answer_time": 10,
	"language": "en"

The server has user’s identity. It will use this identity and store (will be appended) in the respective log file.

The next steps in retrieving the message are pretty easy and includes getting the identity of the current user session. Use this identity to populate the JSONArray named coga. This is finally encoded in a JSONObject along with other basic details and returned to the clients where they render the data received, and show the messages in an appropriate way.