Twilio TWIML nodejs gather sample code control flow - node.js

Question

I was checking this sample on twilio docs (v2.x but v3.x also is similar and my question won't be altered).
// This example uses JavaScript language features present in Node.js 6+
'use strict';
const express = require('express');
const twilio = require('twilio');
const urlencoded = require('body-parser').urlencoded;
let app = express();
// Parse incoming POST params with Express middleware
app.use(urlencoded({ extended: false }));
// Create a route that will handle Twilio webhook requests, sent as an
// HTTP POST to /voice in our application
app.post('/voice', (request, response) => {
// Use the Twilio Node.js SDK to build an XML response
let twiml = new twilio.TwimlResponse();
// Use the <Gather> verb to collect user input
twiml.gather({ numDigits: 1 }, (gatherNode) => {
gatherNode.say('For sales, press 1. For support, press 2.');
});
// If the user doesn't enter input, loop
twiml.redirect('/voice');
// Render the response as XML in reply to the webhook request
response.type('text/xml');
response.send(twiml.toString());
});
// Create an HTTP server and listen for requests on port 3000
app.listen(3000);
So here is the fragment below blocking?
twiml.gather({ numDigits: 1 }, (gatherNode) => {
gatherNode.say('For sales, press 1. For support, press 2.');
});
If yes then assuming user enters something and we then move to
twiml.redirect('/voice');
and other statements execute in sequence.
BUT if its non blocking, then /voice endpoint is called immediately and this continues in an infinite loop.
I was wondering how would the flow work.
EDIT:
The confusion seems to be caused by this comment
// If the user doesn't enter input, loop
If user enters something then also twiml.redirect('/voice') is being called. I am not sure how does that code even work properly?

Answer 1

Ricky from Twilio here.
This code doesn't create an infinite loop, but for a bit of a different reason than blocking vs non-blocking code. The way that you control a Twilio call flow is through TwiML, which is XML containing a set of instructions of what to do with an incoming call. The node code in your /voice route isn't handling the control flow itself, but generating XML that looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<Response>
<Gather numDigits="1">
<Say>For sales, press 1. For support, press 2.</Say>
</Gather>
<Redirect>/voice</Redirect>
</Response>