Configure a telegram bot webhook into an existing express app

Recently I wrote about How to build a telegram bot using node.js and heroku. In the article we use polling to listen to incoming messages. This approach has few problems though…

1. heroku may/will shut down the web-server after a period of inactivity that will result in your polling loop to shut down too – hence missing incoming traffic.

2. polling loop is slightly naive in handling/discarding incoming messages. (see infinite loop issue).

3. user message will have a delay in processing up to the interval specified (seconds at least) which may become annoying in message-heavy bots.

Webhook

Luckily solution is easy. With webhooks telegram does you the favor of calling into your API whenever a new message comes. and it does it in a fairly reliable fashion. (at least far more reliable that what a polling loop does).

In our case we already have an express web app and so wish to add an api end-point for the webhook and configure telegram to use it.

Simply change the setup of your express web app to include the following:

var bodyParser = require('body-parser');
app.use(bodyParser.json());

app.post('/' + token, function (req, res) {
  bot.processUpdate(req.body);
  res.sendStatus(200);
});

The first two line enables the json body parser to allow reading payload on incoming request with content-type=application/json. (note that telegram makes a POST request to the api with the standard message metadata as request body in json format).

Then we listen to the /<token> path for POST requests and simply call into the bot’s message handler.

Next, we need to configure webhook on our telegram bot:

var bot = new Bot(token);
bot.setWebHook('https://my-web-root.com/' + bot.token);

This line will let telegram know about the api you wish messages be sent to.

Development vs Production

As cool as webhooks are, unfortunately you can’t utilize them on development machine – given telegram servers can’t make a request to the local server running on your machine.

The solution I came up with is to fall-back to the polling model for the development environment:

var bot;

if(process.env.NODE_ENV === 'production') {
  bot = new Bot(token);
  bot.setWebHook('https://my-web-root.com/' + bot.token);
}
else {
  bot = new Bot(token, { polling: true });
}

when heroku starts the app, NODE_ENV environment variable is set to production and therefore the if block is hit.

Conclusion

Although the node-telegram-bot-api library supports wiring up an http(s) listener (via webhook: true option), I decided to hook the bot into my own express app for various reasons:

1. I already have a web-app for monitoring/health-checking purposes, plus I may add some additional functionality for my app via a web-interface.

2. most importantly, I have two bots that I wish to wire-up in the same app (they have a lot to share) and as of today, the library doesn’t support joining up multiple bots to share the same https server.

Therefore I decided to pass empty options to the bot and call into it from my express api handler.

P.S.

A complete source code of this tutorial can be found on the following GitHub repository:

https://github.com/mvalipour/telegram-bot-webhook