showip/app.js

const express = require('express')
const { Resolver } = require('dns').promises

const app = express()
const r = new Resolver()
r.setServers(['1.1.1.1'])

app.get('/', async (req, res) => {
  res.header('Content-type: text/plain')
  let ip, host
  try {
    ip = /.*:([^:]+)$/.exec(req.connection.remoteAddress)[1]
  } catch(err) {
    console.log(err.message)
    ip = 'ERR'
  }
  try {
    host = await r.reverse(ip)
  } catch(err) {
    console.log(err.message)
    host = 'ERR'
  }
  res.send(`${ip}\n${host}\n`)
})

app.listen(18080)