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Prevent Blocked Numbers from Calling Your Application

Prevent blocked numbers from calling your application. This application would require you to upload a private asset.

// Description
// Prevent blocked numbers from calling your application
// Host blocklist.json as a private Twilio asset

const fs = require('fs');

exports.handler = function (context, event, callback) {
  let twiml = new Twilio.twiml.VoiceResponse();

  // Phone numbers in blocklist.json file are rejected
  // blocklist.json is uploaded to Twilio Assets as a private asset
  // Format of blocklist.json is plain text:
  // ["+14075550100", "+18025550100"]

  let fileName = '/blocklist.json';
  let file = Runtime.getAssets()[fileName].path;
  let text = fs.readFileSync(file);
  let blocklist = JSON.parse(text);
  let blocked = true;

  if (blocklist.length > 0) {
    if (blocklist.indexOf(event.From) === -1) {
      blocked = false;

  if (blocked) {
  } else {
    // if the caller's number is not blocked, redirect to your existing webhook

  return callback(null, twiml);
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