Interoperation with mirage/ocaml-ipaddr

[RyanGibb]

A number of libraries use https://github.com/mirage/ocaml-ipaddr. Using EIO with these libraries requires translating an Eio.Net.Ipaddr to an Ipaddr [0]:

let convert_eio_addr_to_ipaddr (ip : Eio.Net.Ipaddr.t) ->
    let src = (ip :> string) in
    Eio.Net.Ipaddr.fold
      ~v4:(fun _v4 -> Ipaddr.V4 (Result.get_ok @@ Ipaddr.V4.of_octets src))
      ~v6:(fun _v6 -> Ipaddr.V6 (Result.get_ok @@ Ipaddr.V6.of_octets src))
      ip

I imagine adding mirage/ocaml-ipaddr as a dependency of eio is not desirable (and vice versa) but perhaps this is worth documenting?

Also, with mirage/ocaml-ipaddr#115 changing the internal representation of Ipaddr.V6.t to a Bytes (Ipaddr.V4.t is a int32) I imagine there is a more efficient and/or elegant way to do this.

[0] https://github.com/RyanGibb/aeon/blob/4adbb7be231c3cc6a1c22cc3f3dae71e89f9e06a/src/server.ml#L4-L15 (thanks to @patricoferris for this)

[RyanGibb]

And similar with the reverse:

let convert_ipaddr_to_eio (addr : Ipaddr.t) =
  (match addr with
  | Ipaddr.V4 v4 -> Ipaddr.V4.to_octets v4
  | Ipaddr.V6 v6 -> Ipaddr.V6.to_octets v6
  ) |> Eio.Net.Ipaddr.of_raw

[talex5]

If Ipaddr adds to_raw/from_raw then the conversion would be very simple. The "raw" format is what Unix uses (internally, though it doesn't expose this unfortunately).

[RyanGibb]

Do you mean something like?

In ocaml-ipaddr's ipaddr.ml:

let of_octets_exn ?(off = 0) bs =
  match String.length bs - off with
    | 4 -> V4.of_octets_exn off bs
    | 16 -> V6.of_octets_exn off bs
    | _ -> raise (Parse_error ("octets must be of length 4 or 16", bs))

let of_octets ?off bs = try_with_result (of_octets_exn ?off) bs

let to_octets i = function
    | V4 p -> V4.Prefix.to_octets p
    | V6 p -> V6.Prefix.to_octets p

Which would then be used with:

let convert_eio_addr_to_ipaddr (ip : Eio.Net.Ipaddr.t) ->
  Ipaddr.of_octets (ip :> string)

let convert_ipaddr_to_eio (addr : Ipaddr.t) =
  Ipaddr.to_octets addr |> Eio.Net.Ipaddr.of_raw

[talex5]

Yes, exactly.

[RyanGibb]

Great! I've created a PR here: mirage/ocaml-ipaddr#117

[avsm]

Relevant Ipaddr release now heading into opam-repository; ocaml/opam-repository#23602

[RyanGibb]

Thanks @avsm! Do you think this is worth documenting @talex5, or shall I close the issue?

[talex5]

Do you think this is worth documenting @talex5, or shall I close the issue?

Up to you. Mentioning Ipaddr (and Eio_unix.Ipaddr) in Eio.Net.Ipaddr seems reasonable to me.

[RyanGibb]

I've created a PR documenting this here: #492