DNS-over-HTTPS update

My post on DNS-over-HTTPS from last year is getting a fair bit more traffic after a few UK news paper articles (mainly crying that the new UK Government  censoring won’t work if Google roll it out in Chrome… what a shame). The followning article has a good overview [nakedsecurity].

Anyway I tweeted a link to the old post and it started a bit of a discussion and the  question about the other side of system came up. Namely how to use a DNS resolver that pushed traffic over DNS-over-HTTPS rather than provide a HTTPS endpoint that supported queries. The idea being that at the moment only Firefox & Chrome can take advantage of the secure lookups.

I did a bit of poking around and found things like stubby which DNS-over-TLS (another approach to secure DNS lookups) and also Cloudflare have cloudflared which can proxy for DNS-over-HTTPS to Cloudflare’s DNS server (it also is used to set up the VPN tunnel to Cloudflare’s Argo service, which is also worth a good look at.)

Anyway, while there are existing solutions out there I thought I’d have a really quick go at writing my own, to go with the part I’d written last year, just to see how hard it could be.

It turned out a really basic first pass could be done in about 40 lines of Javascript:

const dgram = require('dgram')
const request = require('request')
const dnsPacket = require('dns-packet')

const port = process.env["DNS_PORT"] || 53
//https://cloudflare-dns.com/dns-query
const url = process.env["DNS_URL"] 
    || "https://dns.google.com/experimental" 
const allow_selfSigned = 
    (process.env["DNS_INSECURE"] == 1) 

const server = dgram.createSocket('udp6')

server.on('listening', function(){
  console.log("listening")
})

server.on('message', function(msg, remote){
  var packet = dnsPacket.decode(msg)
  var id = packet.id
  var options = {
    url: url,
    method: 'POST',
    body: msg,
    encoding: null,
    rejectUnauthorized: allow_selfSigned ? false : true,
    headers: {
      'Accept': 'application/dns-message',
      'Content-Type': 'application/dns-message'
    }
  }

  request(options, function(err, resp, body){
    if (!err && resp.statusCode == 200) {
      var respPacket = dnsPacket.decode(body)
      respPacket.id = id
      server.send(body,remote.port)
    } else {
      console.log(err)
    }
  })

})

server.bind(port)

It really could do with some caching and some more error handling and I’d like to add support for Google JSON based lookups as well as the binary DNS format, but I’m going to add it to the github project with the other half and people can help extend it if they want.

The hardest part was working out I needed the encoding: null in the request options to stop it trying to turn the binary response into a string but leaving it as a Buffer.

I’m in the process of migrating my DNS setup to a new machine, I’ll be adding a DNS-over-TLS (using stunnel) & a DNS-over-HTTPS listeners for the public facing sides.

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