ip2name

.gitignore

node_modules/

index.js

dns = require('dns');

const reverse = ip => new Promise((resolve, reject) => {
  dns.reverse(ip, (err, hostnames) => {
    if (err) {
      reject(err);
    } else {
      resolve(hostnames);
    }
  });
});

const resolve = name => new Promise((resolve, reject) => {
  dns.resolve4(name, (err, result) => {
    if (err) {
      reject(err);
    } else {
      resolve(result);
    }
  });
});

/**
 * Get the hostname corresponding to the given IP.  This hostname
 * must be the only hostname to which that IP resolves in reverse DNS (via
 * PTR records), and the hostname must only resolve to the given IP.
 */
module.exports = ip => {
  return reverse(ip).then(hostnames => {
    if (hostnames.length > 1) {
      throw new Error(`Several hostnames found for ${ip}`);
    } else if (hostnames.length === 0) {
      throw new Error(`No hostnames found for ${ip}`);
    }
    return resolve(hostnames[0]).then(result => {
      if (result.length > 1) {
        throw new Error(`Hostname for ${ip} maps back to several IPs`);
      } else if (result.length === 0 || result[0] !== ip) {
        throw new Error(`Hostname for ${ip} does not map back to ${ip}`);
      }
      return hostnames[0]; // success!
    });
  }).catch(err => {
    console.error(err);
  });
};

package.json

{
  "name": "ip2name",
  "version": "1.0.0",
  "description": "Convert an IP to a name checking forward and reverse resolution",
  "main": "index.js",
  "files": [
    "index.js"
  ],
  "scripts": {
    "test": "mocha --ui tdd test.js"
  },
  "author": "Dustin J. Mitchell",
  "license": "MPL-2.0"
}

test.js

require('mocha');
assert = require('assert');
ip2name = require('./index');

suite("convert", function() {
  test("8.8.8.8", function() {
    return ip2name('8.8.8.8').then(name => {
      assert.equal(name, 'google-public-dns-a.google.com');
    });
  });
});