index.js

'use strict'

const Assert = require('assert')
const Dns = require('dns')
const Http = require('http')
const Https = require('https')
const IPRangeCheck = require('ip-range-check')

const lookup = function (settings) {
  Assert(settings.type === 'whitelist' || settings.type === 'blacklist', 'type must be whitelist or blacklist')

  const filter = function (hostname, options, callback) {
    if (arguments.length === 2) {
      callback = options
      options = {}
    }

    Dns.lookup(hostname, options, (err, address, family) => {
      if (err) {
        callback(err)
        return
      }

      const ipTest = IPRangeCheck(address, settings.iplist)

      if (ipTest && settings.type === 'whitelist') { // IP on whitelist, pass
        callback(err, address, family)
        return
      }

      if (!ipTest && settings.type === 'blacklist') { // IP not on blacklist, pass
        callback(err, address, family)
        return
      }
      // Fail

      callback(new Error(`Connection to IP ${address} not allowed`))
    })
  }

  return filter
}

exports.http = function (settings) {
  const httpAgent = new Http.Agent(settings.agent)

  httpAgent._oldCreateConnection_ = httpAgent.createConnection
  httpAgent.createConnection = function (options, ...args) {
    options.lookup = lookup(settings)

    return this._oldCreateConnection_(options, ...args)
  }

  return httpAgent
}

exports.https = function (settings) {
  const httpsAgent = new Https.Agent(settings.agent)

  httpsAgent._oldCreateConnection_ = httpsAgent.createConnection
  httpsAgent.createConnection = function (options, ...args) {
    options.lookup = lookup(settings)

    return this._oldCreateConnection_(options, ...args)
  }

  return httpsAgent
}