xapi_ha: add more information to not found errors

When joining a liveset, Not_found errors could be raised, but the users
did not have information on what was that it could not be found. Add
which IP address and which UUID could not be found.

Signed-off-by: Pau Ruiz Safont <pau.safont@vates.tech>

Author: psafont

ocaml/xapi/xapi_ha.ml

@@ -42,6 +42,10 @@ let ha_redo_log =
 (*********************************************************************************************)
 (* Interface with the low-level HA subsystem                                                 *)
 
+exception Address_not_found of string
+
+exception Uuid_not_found of string
+
 (** Returns the current live set info *)
 let query_liveset () =
   let txt = call_script ~log_output:On_failure ha_query_liveset [] in
@@ -104,19 +108,21 @@ let get_uuid_to_ip_mapping () =
     named by UUID. *)
 let address_of_host_uuid uuid =
   let table = get_uuid_to_ip_mapping () in
-  List.assoc_opt uuid table |> Option.to_result ~none:Not_found
+  let uuid_not_found = Uuid_not_found uuid in
+  List.assoc_opt uuid table |> Option.to_result ~none:uuid_not_found
 
 (** Without using the Pool's database, returns the UUID of a particular host named by
     heartbeat IP address. This is only necesary because the liveset info doesn't include
     the host IP address *)
 let uuid_of_host_address address =
   let table = List.map (fun (k, v) -> (v, k)) (get_uuid_to_ip_mapping ()) in
   let invalid_uuid = Invalid_argument "Invalid UUID" in
+  let address_not_found = Address_not_found address in
   let to_uuid str =
     Uuidx.of_string str |> Option.to_result ~none:invalid_uuid
   in
   List.assoc_opt address table
-  |> Option.to_result ~none:Not_found
+  |> Option.to_result ~none:address_not_found
   |> Fun.flip Result.bind to_uuid
 
 let ok_or_raise map_error = function Ok v -> v | Error exn -> map_error exn
@@ -479,9 +485,12 @@ module Monitor = struct
                 |> ok_or_raise (master_uuid_exn __FUNCTION__)
               in
               let open Xha_interface.LiveSetInformation in
+              let uuid_not_found =
+                Uuid_not_found (Uuidx.to_string master_uuid)
+              in
               let master_info =
                 Hashtbl.find_opt liveset.hosts master_uuid
-                |> Option.to_result ~none:Not_found
+                |> Option.to_result ~none:uuid_not_found
                 |> ok_or_raise (master_not_in_liveset_exn __FUNCTION__)
               in
               if master_info.Host.liveness && master_info.Host.master then