Dns.lookup always throws null error // URL shortener microservice project

#1

hi all, I am working on the URL shortener microservice project, however, it always throws null error as follows:

app.post('/api/shorturl/new',function(req,res){
  const REPLACE_REGEX = /^https?:\/\//i;
  var lookupurl = req.body.url;
  //var removeprotocal = lookupurl.replace(REPLACE_REGEX,'');
  var urlObject = new URL(lookupurl);
  let isValid = false;
  console.log("lookupurl",lookupurl);
  // When options.all is true, the result will be an Array.
  var options = {
    family: 6,
    hints: dns.ADDRCONFIG | dns.V4MAPPED
  };

  //options.all = true;
  //dns.lookup(urlObject.hostname, options, function(err, address, family) {
  dns.lookup(urlObject.hostname, function(err, address, family) {
    //if (err) res.json({ "error": "invalid URL" });
    console.log("err",err);
    if (err != null) isValid = true;
  });
  console.log("isValid",isValid);
  if (isValid) {
    var urlno = shortId.generate;
    Shorturl.create({original_url: lookupurl, short_url: urlno});
    res.json({ "original_url": lookupurl, "short_url": urlno });
  } else {
    res.json({ "error": "invalid URL" });
  }
});

from the log:

lookupurl https://www.freecodecamp.org
isValid false
err null

Whats wrong with my code here? Any help would be highly appreciated.

#2

Hello there,

Are you sure you are passing the correct first argument to dns.loopup? I did not use new URL to construct mine…

#3

here my full code:

'use strict';

var express = require('express');
var mongo = require('mongodb');
var mongoose = require('mongoose');
var dns = require('dns');
var shortId = require('shortid');
var bodyParser = require('body-parser');

var cors = require('cors');

var app = express();

// Basic Configuration 
var port = process.env.PORT || 3000;

/** this project needs a db !! **/ 
mongoose.connect(process.env.DB_URI, {
  useNewUrlParser: true,
  useUnifiedTopology: true
});

var Schema = mongoose.Schema;
var shorturlSchema = new Schema({
  original_url: String,
  short_url: Number
});

var Shorturl  = mongoose.model('Shorturl',shorturlSchema);

app.use(cors());

/** this project needs to parse POST bodies **/
// you should mount the body-parser here
app.use(bodyParser.urlencoded({ extended: false }));
app.use('/public', express.static(process.cwd() + '/public'));

app.get('/', function(req, res){
  res.sendFile(process.cwd() + '/views/index.html');
});

  
// your first API endpoint... 
app.get("/api/hello", function (req, res) {
  res.json({greeting: 'hello API'});
});


app.listen(port, function () {
  console.log('Node.js listening ...');
});


app.post('/api/shorturl/new',function(req,res){
  const REPLACE_REGEX = /^https?:\/\//i;
  var lookupurl = req.body.url;
  //var removeprotocal = lookupurl.replace(REPLACE_REGEX,'');
  var urlObject = new URL(lookupurl);
  let isValid = false;
  console.log("lookupurl",lookupurl);
  // When options.all is true, the result will be an Array.
  var options = {
    family: 6,
    hints: dns.ADDRCONFIG | dns.V4MAPPED
  };

  //options.all = true;
  //dns.lookup(urlObject.hostname, options, function(err, address, family) {
  dns.lookup(urlObject.hostname, function(err, address, family) {
    //if (err) res.json({ "error": "invalid URL" });
    console.log("err",err);
    if (err != null || err != '') isValid = true;
  });
  console.log("isValid",isValid);
  if (isValid) {
    var urlno = shortId.generate;
    Shorturl.create({original_url: lookupurl, short_url: urlno});
    res.json({ "original_url": lookupurl, "short_url": urlno });
  } else {
    res.json({ "error": "invalid URL" });
  }
});

app.get('/:shorturl', function(req,res){
  var shortUrl = Shorturl.findOne({short_url:req.params.url_string});
  if (shortUrl == null) return res.sendStatus(404);
  res.redirect(shortUrl.original_url);
});

And the first argument is correct for dns.loopup

#4

What I mean to clarify is:

  • The first argument should be: www.freecodecamp.org, when the input is https://www.freecodecamp.org
  • I suspect your issue is with this:
if (err != null || err != '') isValid = true;

It should be if (err === null) { isValid = true; }. If there is not an error, it is valid, yes?

Also, I suspect you will have issues with the dns.lookup function being asynchronous. You should probably handle your db logic within the function.

#5

Thanks! I fixed the issue and passed the test.

#6