feat: filter out messages which the source client is banned when delivering the retained message

apps/emqx_retainer/src/emqx_retainer.erl

@@ -22,6 +22,7 @@
 -include_lib("emqx/include/emqx.hrl").
 -include_lib("emqx/include/logger.hrl").
 -include_lib("stdlib/include/ms_transform.hrl").
+-include_lib("snabbkaffe/include/snabbkaffe.hrl").
 
 -logger_header("[Retainer]").
 
@@ -74,11 +75,12 @@ on_session_subscribed(_, Topic, #{rh := Rh, is_new := IsNew}) ->
 
 %% @private
 dispatch(Pid, Topic) ->
-    Msgs = case emqx_topic:wildcard(Topic) of
+    MsgsT = case emqx_topic:wildcard(Topic) of
-               false -> read_messages(Topic);
+                false -> read_messages(Topic);
-               true  -> match_messages(Topic)
+                true  -> match_messages(Topic)
-           end,
+            end,
     Now = erlang:system_time(millisecond),
+    Msgs = drop_banned_messages(MsgsT),
     [Pid ! {deliver, Topic, refresh_timestamp_expiry(Msg, Now)} || Msg  <- sort_retained(Msgs)].
 
 %% RETAIN flag set to 1 and payload containing zero bytes
@@ -332,3 +334,21 @@ refresh_timestamp_expiry(Msg = #message{headers =
 
 refresh_timestamp_expiry(Msg, Now) ->
     Msg#message{timestamp = Now}.
+
+drop_banned_messages(Msgs) ->
+    lists:filter(fun(Msg) ->
+                         case emqx_banned:look_up({clientid, Msg#message.from}) of
+                             [] ->
+                                 true;
+                             _ ->
+                                 ?tp(
+                                    notice,
+                                    ignore_retained_message_deliver,
+                                    #{
+                                      reason => "client is banned",
+                                      clientid => Msg#message.from
+                                     }
+                                   ),
+                                 false
+                         end
+                 end, Msgs).

apps/emqx_retainer/test/emqx_retainer_SUITE.erl

@@ -23,6 +23,7 @@
 
 -include_lib("eunit/include/eunit.hrl").
 -include_lib("common_test/include/ct.hrl").
+-include_lib("snabbkaffe/include/snabbkaffe.hrl").
 
 all() -> emqx_ct:all(?MODULE).
 
@@ -189,6 +190,53 @@ t_stop_publish_clear_msg(_) ->
 
     ok = emqtt:disconnect(C1).
 
+t_deliver_when_banned(_) ->
+    Client1 = <<"c1">>,
+    Client2 = <<"c2">>,
+
+    {ok, C1} = emqtt:start_link([{clientid, Client1}, {clean_start, true}, {proto_ver, v5}]),
+    {ok, _} = emqtt:connect(C1),
+
+    lists:foreach(
+        fun(I) ->
+            Topic = erlang:list_to_binary(io_lib:format("retained/~p", [I])),
+            Msg = emqx_message:make(Client2, 0, Topic, <<"this is a retained message">>),
+            Msg2 = emqx_message:set_flag(retain, Msg),
+            emqx:publish(Msg2)
+        end,
+        lists:seq(1, 3)
+    ),
+
+    Now = erlang:system_time(second),
+    Who = {clientid, Client2},
+
+    emqx_banned:create(#{
+        who => Who,
+        by => <<"test">>,
+        reason => <<"test">>,
+        at => Now,
+        until => Now + 120
+    }),
+    timer:sleep(100),
+
+    snabbkaffe:start_trace(),
+
+    {ok, SubRef} =
+        snabbkaffe_collector:subscribe(?match_event(#{?snk_kind := ignore_retained_message_deliver}),
+                                       _NEvents    = 3,
+                                       _Timeout    = 10000,
+                                       0),
+
+    {ok, #{}, [0]} = emqtt:subscribe(C1, <<"retained/+">>, [{qos, 0}, {rh, 0}]),
+    {ok, Trace} = snabbkaffe_collector:receive_events(SubRef),
+    ?assertEqual(3, length(?of_kind(ignore_retained_message_deliver, Trace))),
+
+    snabbkaffe:stop(),
+
+    emqx_banned:delete(Who),
+    {ok, #{}, [0]} = emqtt:unsubscribe(C1, <<"retained/+">>),
+    ok = emqtt:disconnect(C1).
+
 %%--------------------------------------------------------------------
 %% Helper functions
 %%--------------------------------------------------------------------