Biocaml 0.4-dev : Biocaml_internal_utils.Url.unescape

let unescape s ~error =

  (* ?(error= fun s -> `wrong_url_string s) s =; *)

  let buf = Buffer.create (String.length s) in

  let rec loop pos =

   match String.lfindi s ~pos ~f:(fun _ c -> (=) '%' c) with

   | None ->

    Buffer.add_substring buf s pos String.(length s - pos)

   | Some idx ->

    if String.length s >= idx + 2 then (

     let char = Scanf.sscanf (String.sub s (idx + 1) 2) "%x" ident in

     Buffer.add_substring buf s pos String.(idx - pos);

     Buffer.add_char buf (Char.of_int_exn char);

     loop (idx + 3)

    ) else (

     failwith "A"

    )

 in

  try loop 0; Ok (Buffer.contents buf) with

  | e -> Error (error s)