$:/litapp/blog

Functions are going to remove some friction from our code, when the request is set with the appropriate application/json header the parsed json will be available on the request and when we send back an object is automatically serialized and sent back to the client.

The example code of the project can be found at https://github.com/carlo-colombo/serverless-telegram-bot-gc-functions

Prerequisites

• Google Cloud account and a project. https://cloud.google.com/resource-manager/docs/creating-managing-projects
• Enable Google Cloud Functions and RuntimeConfig API from the API manager.
• Get a telegram bot token, ask it to the BotFather.

Warning

• Both Google Cloud Functions and RuntimeConfig are both still in beta.
• Even if the GCP free tier is quite extended some costs can be billed.

The token

# export for local testing 
export TELEGRAM_TOKEN=133545asdasd

# set the token as GC runtime configuration 
gcloud beta runtime-config configs create prod-config
gcloud beta runtime-config configs variables \
    set telegram/token  "$TELEGRAM_TOKEN" \
    --config-name prod-config

The bot

exports.echoBot = function(req, res){
    const {message:{chat, text}} = req.body
    const echo = `echo: ${text}`

    return getToken()
        .then( token => request.post({
            uri: `https://api.telegram.org/bot${token}/sendMessage`,
            json: true,
            body: {text: echo, chat_id: chat.id}
        }))
        .then(resp => res.send(resp))
        .catch(err => res.status(500).send(err))
}

Just an easy bot that echos the received message.

Retrieving the token

This function return a (promise) of a token either from the runtime config api when run online or from an environment variable when run locally. The value is retrieved using fredriks/cloud-functions-runtime-config that wraps the api. NODE_ENV is set to production when the function is run online, thus allowing to discriminate in which environment the function run.

function getToken(){
    if (process.env.NODE_ENV == 'production'){
        return require('cloud-functions-runtime-config')
            .getVariable('prod-config', 'telegram/token')
    }
    return Promise.resolve(process.env.TELEGRAM_TOKEN)
}

Local testing

Google provide a local emulator for Functions feature. It allow to local deploy a function to iterate over it without having to deploy to the google server. It reload the code when changed on the file system so it is not necessary to redeploy after the first time.

npm -g install @google-cloud/functions-emulator

functions start
functions deploy echoBot --trigger-http

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{
     "message": {
       "chat": {
         "id": 1232456
       },
       "text": "hello world"
     }
   }' \
   http://localhost:8010/PROJECT_ID/us-central1/echoBot

# To tail logs
watch functions logs read

Deploying

Before deploy the function is required to create a Cloud Storage bucket where the function will be stored

gsutil mb -c regional -l us-central1 gs://unique-bucket-name

gcloud beta functions deploy function_name \
  --trigger-http \
  --entry-point echoBot \
  --stage-bucket unique-bucket-name

Set up the webhook

Deploying the function with the http trigger will return an url to trigger the function. The url would look like https://<GCP_REGION>-<PROJECT_ID>.cloudfunctions.net/function_name. Use this url to set up a web hook for your bot on telegram. You can check more information on webhook on the Telegram API documentation

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{
     "url": "https://<GCP_REGION>-<PROJECT_ID>.cloudfunctions.net/function_name"
   }' \
   https://api.telegram.org/bot${TELEGRAM_TOKEN}/setWebhook

Conclusions

Setting up a Telegram bot using Google Cloud Functions is quick and easy, and with the HTTP trigger is possible to seamlessy set a webhook endpoint for a bot without having to care about a server and https certificates (http trigger are https).

One last thing to keep in mind is that Functions are stateless and require to be connected to other services to store data or be for example scheduled.