How can I use an API to detect if an IP address is a VPN in OCaml?

To detect if an IP address is a VPN using IP2Location.io in OCaml, you can use the IP2Location.io API to retrieve geolocation and related data.

1. We'll assume that you have already installed OCaml and we won't cover that here. You will also need a paid subscription to the Security plan. Subscribe now!
2. In the command line, run the commands below to create a new executable project called example and navigate into the folder created.
   Bash

   
   dune init proj example
   cd example
   			

3. In the command line, run the command below to install the dependencies using opam if you don't have them installed.
   Bash

   
   opam install lwt cohttp cohttp-lwt-unix yojson
   			

4. Edit the bin/dune file and replace the code with the below codes
   OCaml

   
   (executable
    (public_name example)
    (name main)
    (libraries example lwt cohttp cohttp-lwt-unix yojson))
   			

5. Edit the bin/main.ml file and replace the code with the below codes
   OCaml

   
   open Printf
   open Lwt
   open Cohttp
   open Cohttp_lwt_unix
   open Yojson
   
   let () =
     let ip = "8.8.8.8" in
     let key = "YOUR_API_KEY" in
     let uri =
       Uri.of_string
         ("https://api.ip2location.io/?format=json&key=" ^ key ^ "&ip=" ^ ip)
     in
     Lwt_main.run
       ( Client.get uri >>= fun (resp, body) ->
         let code = resp |> Response.status |> Code.code_of_status in
         let json_promise = body |> Cohttp_lwt.Body.to_string in
         json_promise >|= fun json_string ->
         let json = Basic.from_string json_string in
         let open Yojson.Basic.Util in
         match code with
         | 200 when member "proxy" json <> `Null -> (
             match json |> member "proxy" |> member "is_vpn" |> to_bool with
             | true -> printf "The IP %s is a VPN.\n" ip
             | _ -> printf "The IP %s is NOT a VPN.\n" ip)
         | 200 ->
             printf
               "ERROR: The is_vpn field requires a paid subscription to the \
                Security plan.\n"
         | (400 | 401) when member "error" json <> `Null ->
             json |> member "error" |> member "error_message" |> to_string
             |> printf "ERROR: %s\n"
         | _ -> printf "HTTP Code: %d\n" code )
   			

6. In the command line, run the below commands to compile and run the codes.
   Bash

   
   dune build
   dune exec example
   			

This script will check if the specified IP address is a VPN. Make sure to replace 8.8.8.8 with the IP address you want and replace YOUR_API_KEY to your own API key.

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