Time Required: 20 minutes.
Technologies: Express, Node.js, JavaScript.
Prerequisites:

• Basic knowledge of Express, Node.js, and JavaScript.
• Node.js and npm are installed.

This tutorial will go over how to build a bot that will respond to pings (i.e. @), and send messages to a chat room. On a high level, the bot will run on an express server, and receive pings via an HTTP endpoint. Responses to pings will be sent synchronously through a payload in the HTTP response, while bot-initiated messages will be sent asynchronously using the Google Hangout Chat API.

Outline

1. Environment setup.
2. Get bot to respond to pings.
3. Send bot-initiated messages.
4. Deploy.

Environment Setup

Create a new project with the file ‘app.js’.
Open command line/terminal, and navigate to your project directory. Run ‘npm init’, and press enter until package.json is created. Next, install the following dependencies:

• express: npm install express --save
• body-parser:  npm install body-parser --save
• googleapis: npm install googleapis --save
• unirest:  npm install unirest --save

In ‘app.js’, let’s setup our server:

const express = require('express');
const bodyParser = require('body-parser');
const {google} = require('googleapis');

const app = express();

app.use(bodyParser.urlencoded({
    extended: false
}));

app.use(bodyParser.json());

app.listen(8100, () => {
    console.log('App listening on port 8100.');
});

Running ‘node app.js’ will now create a local server on port 8100.

Responding to Pings

The bot will respond to pings through a HTTP POST endpoint. Create one with express:

app.post('/', (req, res) => {
    console.log('someone pinged @');

    if (req.body.type === 'MESSAGE') {
        return res.json({
	    text: 'sleeping...'
	});
    }
});

The bot will respond with the text: ‘sleeping…’.

Synchronously responding to messages simply requires us to return a response to Google. The downside to this is the 30 second time limit before Google no longer accepts responses to the request. For instance, this would be a problem if you were building some kind of reminder app; the bot wouldn’t be able to synchronously respond after 30 seconds. This is where async responses come in.

Bot-initiated Messages

To show this, we will have our bot post to a chat room every 1 minute.

Sending async messages to Google API requires a Service Account for authentication. Once authenticated, we can make a POST request to a Google API URL that will create a message.

So first, create a Google Service Account following these steps. Take the downloaded JSON file and put it in the root directory of your project. Here, we renamed it to googlekeys.json:

const gkeys = require("./googlekeys.json");

We will be making POST requests using Unirest:

const unirest = require('unirest');

Now generate a JWT that will be used in our POST request:

function getJWT() {
    return new Promise((resolve, reject) => {
        let jwtClient = new google.auth.JWT(
	    gkeys.client_email,
	    null,
	    gkeys.private_key, ['https://www.googleapis.com/auth/chat.bot']);

	jwtClient.authorize((err, tokens) => {
	    if (err) {
	        console.log('Error create JWT hangoutchat');
		reject(err);
	    } else {
	        resolve(tokens.access_token);
	    }
	});
    });
}

Here is our function for posting messages. ROOM-ID can be found in the URL of the hangout chat room page i.e.: https://chat.google.com/u/0/room/.

function postMessage(count) {
    return new Promise((resolve, reject) => {
        getJWT().then((token) => {
	    unirest.post('https://chat.googleapis.com/v1/spaces/' +  + '/messages')
	        .headers({
		    "Content-Type": "application/json",
		    "Authorization": "Bearer " + token
		})
		.send(JSON.stringify({
		    'text': 'Hello! This is message number ' + count,
		}))
		.end((res) => {
		    resolve();
		});
        }).catch((err) => {
	    reject(err);
	});
    });
}

Finally, add the code that will repeat our post every minute.

const timer = require('timers');

app.listen(8100, () => {
    console.log('App listening on port 8100.');

    let count = 0;
    timer.setInterval(() => {
        postMessage(count += 1);
    }, 60000);
});

Deploy

Expose your local server to public (we used ngrok).

Login to developer console. Create a new project, and enable Hangout Chat API. Under configuration, set:

• status: live
• bot name (this is how you will add and ping the bot)
• avatar
• description
• functionality: rooms
• connection settings – bot URL:
• permission: everyone in your domain

Restart your local server, and that’s it! Make sure you have your bot added to the chat room, and you can ping it by sending @. The bot will also post to the chat room every minute.

There are a lot of different ways to further extend this bot, such as setting reminders/notifications, making to-do lists, displaying server logs, and interacting with API’s.