fix(topics-api): respond with correct totals to paged queries

apps/emqx/src/emqx_persistent_session_ds_router.erl

@@ -33,7 +33,10 @@
 ]).
 
 %% Topics API
--export([stream/1]).
+-export([
+    stream/1,
+    stats/1
+]).
 
 -export([cleanup_routes/1]).
 -export([print_routes/1]).
@@ -211,6 +214,14 @@ foldr_routes(FoldFun, AccIn) ->
 stream(MTopic) ->
     emqx_utils_stream:chain(stream(?PS_ROUTER_TAB, MTopic), stream(?PS_FILTERS_TAB, MTopic)).
 
+%% @doc Retrieve router stats.
+%% n_routes: total number of routes, should be equal to the length of `stream('_')`.
+-spec stats(n_routes) -> non_neg_integer().
+stats(n_routes) ->
+    NTopics = ets:info(?PS_ROUTER_TAB, size),
+    NFilters = ets:info(?PS_FILTERS_TAB, size),
+    emqx_maybe:define(NTopics, 0) + emqx_maybe:define(NFilters, 0).
+
 %%--------------------------------------------------------------------
 %% Internal fns
 %%--------------------------------------------------------------------

apps/emqx_management/src/emqx_mgmt_api_topics.erl

@@ -179,6 +179,17 @@ mk_persistent_topic_stream(Spec) ->
             emqx_utils_stream:empty()
     end.
 
+eval_count() ->
+    emqx_router:stats(n_routes) + eval_persistent_count().
+
+eval_persistent_count() ->
+    case emqx_persistent_message:is_persistence_enabled() of
+        true ->
+            emqx_persistent_session_ds_router:stats(n_routes);
+        false ->
+            0
+    end.
+
 eval_topic_query(Stream, QState = #{limit := Limit}, QResult) ->
     case emqx_utils_stream:consume(Limit, Stream) of
         {Rows, NStream} ->
@@ -209,7 +220,7 @@ format_list_response(Meta, Query, QResult = #{rows := RowsAcc}) ->
 format_response_meta(Meta, _Query, #{hasnext := HasNext, complete := true, cursor := Cursor}) ->
     Meta#{hasnext => HasNext, count => Cursor};
 format_response_meta(Meta, _Query = {[], []}, #{hasnext := HasNext}) ->
-    Meta#{hasnext => HasNext, count => emqx_router:stats(n_routes)};
+    Meta#{hasnext => HasNext, count => eval_count()};
 format_response_meta(Meta, _Query, #{hasnext := HasNext}) ->
     Meta#{hasnext => HasNext}.
 

apps/emqx_management/test/emqx_mgmt_api_topics_SUITE.erl

@@ -246,13 +246,21 @@ t_persistent_topics(_Config) ->
         lists:sort(maps:get(<<"data">>, Matched))
     ),
     %% Are results the same when paginating?
-    #{<<"data">> := Page1} = request_json(get, ["topics"], [{"page", "1"}, {"limit", "3"}]),
+    #{<<"data">> := Page1} = R1 = request_json(get, ["topics"], [{"page", "1"}, {"limit", "3"}]),
     #{<<"data">> := Page2} = request_json(get, ["topics"], [{"page", "2"}, {"limit", "3"}]),
     #{<<"data">> := Page3} = request_json(get, ["topics"], [{"page", "3"}, {"limit", "3"}]),
     ?assertEqual(
         lists:sort(Expected),
         lists:sort(Page1 ++ Page2 ++ Page3)
     ),
+    %% Count respects persistent sessions.
+    ?assertMatch(
+        #{
+            <<"meta">> := #{<<"page">> := 1, <<"limit">> := 3, <<"count">> := 8},
+            <<"data">> := [_, _, _]
+        },
+        R1
+    ),
     %% Filtering by node makes no sense for persistent sessions.
     ?assertMatch(
         #{