You may wish to block certain numbers from contacting or spamming your application's phone number. Creating a block list and using a Function that compares the incoming number to its contents will allow you to decide whether to Reject an incoming call, or Redirect it to your actual application.
The following examples will show a couple of approaches to this problem. To get started, use the following directions to create two new Functions that will form the base of this application: /filter-calls
and /welcome
.
In order to run any of the following examples, you will first need to create a Function into which you can paste the example code. You can create a Function using the Twilio Console or the Serverless Toolkit as explained below:
If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps:
https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>
test-function-3548.twil.io/hello-world
.
Your Function is now ready to be invoked by HTTP requests, set as the webhook of a Twilio phone number, invoked by a Twilio Studio Run Function Widget, and more!
To introduce the logic and TwiML involved without extra complications, this example code for /filter-calls
includes a sample block list hard-coded into its body.
The Function compares the incoming phone number, provided as From
when this Function is connected to your Twilio phone number as a webhook, to the contents of the block list. The resulting boolean is then used to determine whether the result should be a rejection, or a redirect to the /welcome
Function.
The /welcome
Function returns a welcome message to the user and primarily serves as an example of how you can still leverage Redirect verbs even within a Serverless project such as this. You're able to use the relative URL '/welcome'
since the same Service contains both Functions.
To test this out, copy and paste both samples into their respective Functions, and add your personal phone number to the block list in E.164 format. Save and deploy your Service, and use the following directions to set /filter-calls
as the A Call Comes In webhook handler for your Twilio phone number. The application will immediately reject your calls. If you remove your number from the block list and re-deploy, you will instead get the welcome message.
Sample code for /filter-calls
_22exports.handler = (context, event, callback) => {_22 // Prepare a new Voice TwiML object that will control Twilio's response_22 // to the incoming call_22 const twiml = new Twilio.twiml.VoiceResponse();_22 // The incoming phone number is provided by Twilio as the `From` property_22 const incomingNumber = event.From;_22_22 // This is an example of a blocklist hard-coded into the Function_22 const blockList = ['+14075550100', '+18025550100'];_22_22 const isBlocked = blockList.length > 0 && blockList.includes(incomingNumber);_22_22 if (isBlocked) {_22 twiml.reject();_22 } else {_22 // If the number is not blocked, redirect call to the webhook that_22 // handles allowed callers_22 twiml.redirect('/welcome');_22 }_22_22 return callback(null, twiml);_22};
Sample code for /welcome
_10exports.handler = (context, event, callback) => {_10 const twiml = new Twilio.twiml.VoiceResponse();_10 twiml.say("Hello, congratulations! You aren't blocked!");_10 return callback(null, twiml);_10};
In order for your Function to react to incoming SMS and/or voice calls, it must be set as a webhook for your Twilio number. There are a variety of methods to set a Function as a webhook, as detailed below:
You can use the Twilio Console UI as a straightforward way of connecting your Function as a webhook:
ui
unless you have created
custom domains
), and finally
Function Path
of your Function from the respective dropdown menus.
To keep your block list separate from and independent of your Function's code, one recommendation is to store the list as JSON in a private Asset. Your Function will read and parse the contents of this file using methods provided by the Runtime Client, and achieve the same functionality with more separation of concerns.
First, create a new private Asset named blocklist.json
, populate it with the sample contents (and your personal number like before, to verify the blocking works), and save the Asset. Ensure that this Asset is private in order to protect its contents and to enable helper methods such as Runtime.getAssets, which can only retrieve private Assets.
Next, update the existing /filter-calls
Function with the highlighted changes. This new code replaces the hard-coded block list array with a synchronous read of blocklist.json
, and a quick JSON.parse
to convert the file contents to a usable array.
Save your changes to the Function, and deploy your updated Service. Subsequent calls to your Twilio phone number will behave exactly as before!
Save as blocklist.json
_10["+14075550100", "+18025550100"]
Updates to /filter-calls
_24exports.handler = (context, event, callback) => {_24 // Prepare a new Voice TwiML object that will control Twilio's response_24 // to the incoming call_24 const twiml = new Twilio.twiml.VoiceResponse();_24 // The incoming phone number is provided by Twilio as the `From` property_24 const incomingNumber = event.From;_24_24 // Open the contents of the private Asset containing the blocklist_24 const blockListJson = Runtime.getAssets()['/blocklist.json'].open();_24 // Parse the string, such as "["+14075550100", "+18025550100"]", to an array_24 const blockList = JSON.parse(blockListJson);_24_24 const isBlocked = blockList.length > 0 && blockList.includes(incomingNumber);_24_24 if (isBlocked) {_24 twiml.reject();_24 } else {_24 // If the number is not blocked, redirect call to the webhook that_24 // handles allowed callers_24 twiml.redirect('/welcome');_24 }_24_24 return callback(null, twiml);_24};
Ensure that you write the Asset name as '/blocklist.json'
and not 'blocklist.json'
; the leading slash is necessary, as described in the Runtime.getAssets documentation.