DNS wireformat support in Elixir?

[darnahsan]

Are there any libs to work with DNS wire format ? I found this lib for erlang not sure how to work with this though

lateio/dnslib

anyone experienced with the format got some questions, working on a side project

I have this code where I can read the incoming application/dns-message body of the request

echo -n 'q80BAAABAAAAAAAAA3d3dwdleGFtcGxlA2NvbQAAAQAB' | base64 | curl -H 'content-type: application/dns-message' --data-binary @- https://cloudflare-dns.com/dns-query -o -

 post "/" do
    {:ok, body, conn} = Plug.Conn.read_body(conn)

    {:ok, query} = String.trim(body) |> Base.url_decode64(padding: false)

    IO.inspect(query, label: "Query")

    conn
    |> put_resp_content_type("application/dns-message")
    |> send_resp(
      200,
      Jason.encode!(%{
        msg: "I don't have a heart but I am alive!"
      })
    )
  end

i am trying to work this out https://developers.cloudflare.com/1.1.1.1/dns-over-https/wireformat

Not sure how to make a request to the upstream DNS from wireformat and return a response I am using GitHub - tungd/elixir-dns: DNS library for Elixir to do the JSON format. Need to know how to get the wireformat to standard domain to send using elixir-dns and then convert the response back to wireformat

[darnahsan]

found this in cloudflare odoh lib it says WireFormat is similar to xdr

cloudflare/odoh-rs

[evadne]

Just a thought but try inet_dns:decode/1 in Erlang as per otp/inet_dns.erl at master · erlang/otp · GitHub and maybe other functions in that module will help you as well.

If it works, you will have the benefit of not having to pull an extra dependency

According to the RFC RFC 8484 - DNS Queries over HTTPS (DoH) the message is formatted as per RFC 1035 which should be what inet_dns:decode/1 accepts

[darnahsan]

Thanks @evadne passed the 1st hurdle , will upate the thread with progress for others if they ever need this info. might ping here if I hit a roadblock

post "/" do
    {:ok, body, conn} = Plug.Conn.read_body(conn)

    IO.inspect(body, label: "body")
    :inet_dns.decode(body) |> IO.inspect(label: "inet_dns.decode")
    conn
    |> put_resp_content_type("application/dns-message")
    |> send_resp(
      200,
      Jason.encode!(%{
        msg: "I don't have a heart but I am alive!"
      })
    )
  end

body: <<171, 205, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 3, 119, 119, 119, 7, 101, 120, 97, 
  109, 112, 108, 101, 3, 99, 111, 109, 0, 0, 1, 0, 1>>
inet_dns.decode: {:ok,
 {:dns_rec,
  {:dns_header, 43981, false, :query, false, false, true, false, false, 0},
  [{:dns_query, 'www.example.com', :a, :in}], [], [], []}}

[darnahsan]

after lack of my erlang understanding I decided to dig into tungd/elixir-dns code out of curiosity to see how it was handling things and it is doing what @evadne suggested and has some nice wrapper around erlang code which i ended up using. elixir-dns/record.ex at master · tungd/elixir-dns · GitHub

Big thanks to the elixir community for being supportive and having a solution to almost everything

[bortzmeyer]

Just for information, my DNS server written in Elixir uses (currently) the elixir-dns library. Because it does not seem actually maintained, I had to fork. My code may give you ideas.

[darnahsan]

Thanks @bortzmeyer , is your fork a drop-in replacement of elixir-dns ?

[bortzmeyer]

Yes. Currently, there is only one small (but important) patch but I will add others, while still trying to allow a merge back to the upstream.

[darnahsan]

doesn’t seem to work out of the box for me by just moving from 2.3.0 → 2.4.0 there is something different

[bortzmeyer]

Strange, I cannot reproduce the problem. IO.inspect DNS.resolve("www.bortzmeyer.org") works for me with the original elixir-dns (tested with 2.3 and 2.4) and my fork (same versions). Could you send me (stephane(at)bortzmeyer.org) the actual files (mix.exs and the program.exs)?