router.re

let router =
  Router.create () |>
  Router.post
    "/"
    (
      fun req body =>
        Cohttp_lwt_body.to_string body >>= (
          fun body => {
            let str =
              switch (Uri.get_query_param (req |> Request.uri) "foo") {
              | None => ""
              | Some x => x
              };
            let json = Yojson.Basic.from_string str;
            let synced_from = json |> Util.member "synced_from" |> Util.to_string;
            let response = Yojson.Basic.to_string (
              `Assoc [
                ("id", `String (Uuidm.to_string (Uuidm.v `V4))),
                ("devices", `String synced_from)
              ]
            );
            Server.respond_string status::`OK body::response ()
          }
        )
    ) |>
  Router.get "/foo" (fun req body => Server.respond_string status::`OK body::"/foo" ()) |>
  Router.get "/bar" (fun req body => Server.respond_string status::`OK body::"/bar" ());