fix(emqx_slow_subs_api): return error when the module is not enable

apps/emqx_plugin_libs/src/emqx_slow_subs/emqx_slow_subs_api.erl

@@ -50,27 +50,7 @@ clear_history(_Bindings, _Params) ->
     return(ok).
 
 get_history(_Bindings, _Params) ->
-    Nodes = ekka_mnesia:running_nodes(),
+    execute_when_enabled(fun do_get_history/0).
-      Fun = fun(Node, Acc) ->
-                    NodeRankL = rpc_call(Node,
-                                         ?MODULE,
-                                         ?FUNCTION_NAME,
-                                         [],
-                                         [],
-                                         ?DEFAULT_RPC_TIMEOUT),
-                    NodeRankL ++ Acc
-            end,
-
-    RankL = lists:foldl(Fun, [], Nodes),
-
-    SortFun = fun(#{timespan := A}, #{timespan := B}) ->
-                      A > B
-              end,
-
-    SortedL = lists:sort(SortFun, RankL),
-    SortedL2 = lists:sublist(SortedL, ?MAX_SIZE),
-
-    return({ok, SortedL2}).
 
 get_history() ->
     Node = node(),
@@ -84,10 +64,36 @@ get_history() ->
                        , timespan => TimeSpan
                        , last_update_time => LastUpdateTime
                        }
-           end,
+              end,
 
     lists:map(ConvFun, RankL).
 
+%%--------------------------------------------------------------------
+%% Internal functions
+%%--------------------------------------------------------------------
+do_get_history() ->
+    Nodes = ekka_mnesia:running_nodes(),
+    Fun = fun(Node, Acc) ->
+                  NodeRankL = rpc_call(Node,
+                                       ?MODULE,
+                                       get_history,
+                                       [],
+                                       [],
+                                       ?DEFAULT_RPC_TIMEOUT),
+                  NodeRankL ++ Acc
+          end,
+
+    RankL = lists:foldl(Fun, [], Nodes),
+
+    SortFun = fun(#{timespan := A}, #{timespan := B}) ->
+                      A > B
+              end,
+
+    SortedL = lists:sort(SortFun, RankL),
+    SortedL2 = lists:sublist(SortedL, ?MAX_SIZE),
+
+    return({ok, SortedL2}).
+
 rpc_call(Node, M, F, A, _ErrorR, _T) when Node =:= node() ->
     erlang:apply(M, F, A);
 
@@ -96,3 +102,15 @@ rpc_call(Node, M, F, A, ErrorR, T) ->
         {badrpc, _} -> ErrorR;
         Res -> Res
     end.
+
+-ifdef(EMQX_ENTERPRISE).
+execute_when_enabled(Fun) ->
+    Fun().
+-else.
+%% this code from emqx_mod_api_topics_metrics:execute_when_enabled
+execute_when_enabled(Fun) ->
+    case emqx_modules:find_module(emqx_mod_slow_subs) of
+        [{_, true}] -> Fun();
+        _ -> return({error, module_not_loaded})
+    end.
+-endif.