Check Mailbox in a Loop, Read Email and Create PDF - node.js

Question

I have a code that reads unseen emails and creates pdf.
The problem is;
I cannot pull email if any new unseen email exist without executing code again.
var Imap = require('imap');
const MailParser = require('mailparser').MailParser;
var pdf = require('html-pdf');
var fs = require('fs');
var Promise = require("bluebird");
Promise.longStackTraces();
var imapConfig = {
user: '*****',
password: '*****',
host: 'imap.gmail.com',
port: 993,
tls: true
};
var imap = new Imap(imapConfig);
Promise.promisifyAll(imap);
imap.once("ready", execute);
imap.once("error", function(err) {
log.error("Connection error: " + err.stack);
});
imap.connect();
function execute() {
imap.openBox("INBOX", false, function(err, mailBox) {
if (err) {
console.error(err);
return;
}
imap.search(["UNSEEN"], function(err, results) {
if(!results || !results.length){console.log("No unread mails");imap.end();return;}
var f = imap.fetch(results, { bodies: "" });
f.on("message", processMessage);
f.once("error", function(err) {
return Promise.reject(err);
});
f.once("end", function() {
console.log("Done fetching all unseen messages.");
imap.end();
});
});
});
}
const options = { format: 'A2', width:"19in", height:"17in", orientation: "portrait" };
function processMessage(msg, seqno) {
console.log("Processing msg #" + seqno);
// console.log(msg);
var parser = new MailParser();
parser.on("headers", function(headers) {
console.log("Header: " + JSON.stringify(headers));
});
parser.on('data', data => {
if (data.type === 'text') {
console.log(seqno);
console.log(data.html); /* data.html*/
var test = data.html
pdf.create(test, options).toStream(function(err, stream){
stream.pipe(fs.createWriteStream('./foo.pdf'));
});
}
});
msg.on("body", function(stream) {
stream.on("data", function(chunk) {
parser.write(chunk.toString("utf8"));
});
});
msg.once("end", function() {
// console.log("Finished msg #" + seqno);
parser.end();
});
}
Also I have tried to use setInterval to check new unseen emails but I get
'Error: Not authenticated'
How can I pull new unseen emails in a loop and create pdf from that email?

Answer 1

Your observation is correct. You must poll your IMAP (or POP3) server on a regular schedule to keep up with incoming messages. Depending on your requirements, a schedule of once every few minutes is good.
continous polling, or polling every second or so, is very rude. The operator of the IMAP server may block your application if you try to do that: it looks to them like an attempt to overload the server.