dns-eio #

Eio-native DNS client for OCaml.

Single-shot A / AAAA / TXT queries against a configured nameserver, wrapping the dns protocol primitives with an Eio-based UDP transport. Designed for authenticated-channel use cases (ATProto handle resolution, .well-known discovery) where the answer is short and authenticity comes from a higher layer. No caching, no TCP fallback on truncation, no DNSSEC.

Installation #

Install with opam:

$ opam install dns-eio

If opam cannot find the package, it may not yet be released in the public opam-repository. Add the overlay repository, then install it:

$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
$ opam update
$ opam install dns-eio

Usage #

A resolver picks up the nameservers from /etc/resolv.conf, falling back to Cloudflare (1.1.1.1) and Google (8.8.8.8) if that file is missing or empty. The list can be overridden at construction:

# let resolver =
    Dns_eio.create
      ~nameservers:[ Ipaddr.of_string_exn "1.1.1.1" ]
      ~timeout_s:1.0 () in
  List.map Ipaddr.to_string (Dns_eio.nameservers resolver)
- : string list = ["1.1.1.1"]

Each query takes a switch, a net, and a clock so the caller controls socket lifetime. The socket is opened, used for the single query, and closed when the switch ends:

let lookup_txt env name =
  Eio.Switch.run @@ fun sw ->
  let resolver = Dns_eio.create () in
  match
    Dns_eio.txt resolver
      ~sw
      ~net:(Eio.Stdenv.net env)
      ~clock:(Eio.Stdenv.clock env)
      name
  with
  | Ok records -> List.iter print_endline records
  | Error e -> Fmt.pr "DNS error: %a@." Dns_eio.pp_error e

The same pattern applies to Dns_eio.a (IPv4) and Dns_eio.aaaa (IPv6). A name with no matching records returns Ok []; a name that does not exist returns Error \Nxdomain`.

Licence #

ISC