DISCONNECT v5 clients with Server Shutting Down

When RabbitMQ enters maintenance mode / is being drained, all client
connections are closed.

This commit sends a DISCONNECT packet to (Web) MQTT 5.0 clients with
Reason Code "Server shutting down" before the connection is closed.

deps/rabbitmq_mqtt/src/rabbit_mqtt.erl

@@ -71,7 +71,7 @@ emit_connection_info(Items, Ref, AggregatorPid, Pids) ->
               rabbit_mqtt_reader:info(Pid, Items)
       end, Pids).
 
--spec close_local_client_connections(string() | binary()) -> {'ok', non_neg_integer()}.
+-spec close_local_client_connections(atom()) -> {'ok', non_neg_integer()}.
 close_local_client_connections(Reason) ->
     Pids = local_connection_pids(),
     lists:foreach(fun(Pid) ->

deps/rabbitmq_mqtt/src/rabbit_mqtt_internal_event_handler.erl

@@ -27,9 +27,8 @@ handle_event({event, vhost_deleted, Info, _, _}, ?STATE) ->
     rabbit_mqtt_retainer_sup:delete_child_for_vhost(Name),
     {ok, ?STATE};
 handle_event({event, maintenance_connections_closed, _Info, _, _}, ?STATE) ->
-    %% we should close our connections
-    {ok, NConnections} = rabbit_mqtt:close_local_client_connections("node is being put into maintenance mode"),
-    rabbit_log:warning("Closed ~b local MQTT client connections", [NConnections]),
+    {ok, NConnections} = rabbit_mqtt:close_local_client_connections(maintenance),
+    rabbit_log:warning("Closed ~b local (Web) MQTT client connections", [NConnections]),
     {ok, ?STATE};
 handle_event(_Event, ?STATE) ->
     {ok, ?STATE}.

deps/rabbitmq_mqtt/src/rabbit_mqtt_reader.erl

@@ -132,7 +132,11 @@ handle_cast({close_connection, Reason},
             State = #state{conn_name = ConnName, proc_state = PState}) ->
     ?LOG_WARNING("MQTT disconnecting client ~tp with client ID '~ts', reason: ~ts",
                  [ConnName, rabbit_mqtt_processor:info(client_id, PState), Reason]),
-    {stop, {shutdown, server_initiated_close}, State};
+    case Reason of
+        maintenance -> rabbit_mqtt_processor:send_disconnect(?RC_SERVER_SHUTTING_DOWN, PState);
+        _ -> ok
+    end,
+    {stop, {shutdown, {disconnect, server_initiated}}, State};
 
 handle_cast(QueueEvent = {queue_event, _, _},
             State = #state{proc_state = PState0}) ->

deps/rabbitmq_mqtt/test/shared_SUITE.erl

@@ -48,6 +48,7 @@
          http_delete/3]).
 
 %% defined in MQTT v5 (not in v4 or v3)
+-define(RC_SERVER_SHUTTING_DOWN, 16#8B).
 -define(RC_KEEP_ALIVE_TIMEOUT, 16#8D).
 -define(RC_SESSION_TAKEN_OVER, 16#8E).
 
@@ -1131,6 +1132,7 @@ maintenance(Config) ->
     C0 = connect(<<"client-0">>, Config, 0, []),
     C1a = connect(<<"client-1a">>, Config, 1, []),
     C1b = connect(<<"client-1b">>, Config, 1, []),
+    ClientsNode1 = [C1a, C1b],
 
     timer:sleep(500),
 
@@ -1141,12 +1143,14 @@ maintenance(Config) ->
 
     process_flag(trap_exit, true),
     ok = drain_node(Config, 1),
-    [await_exit(Pid) || Pid <- [C1a, C1b]],
+    [await_exit(Pid) || Pid <- ClientsNode1],
+    [assert_v5_disconnect_reason_code(Config, ?RC_SERVER_SHUTTING_DOWN) || _ <- ClientsNode1],
     ok = revive_node(Config, 1),
     ?assert(erlang:is_process_alive(C0)),
 
     ok = drain_node(Config, 0),
     await_exit(C0),
+    assert_v5_disconnect_reason_code(Config, ?RC_SERVER_SHUTTING_DOWN),
     ok = revive_node(Config, 0).
 
 keepalive(Config) ->

deps/rabbitmq_mqtt/test/v5_SUITE.erl

@@ -36,6 +36,7 @@
 -define(RC_DISCONNECT_WITH_WILL, 16#04).
 -define(RC_NO_SUBSCRIPTION_EXISTED, 16#11).
 -define(RC_UNSPECIFIED_ERROR, 16#80).
+-define(RC_SERVER_SHUTTING_DOWN, 16#8B).
 -define(RC_SESSION_TAKEN_OVER, 16#8E).
 
 all() ->
@@ -1672,21 +1673,24 @@ will_delay_node_restart(Config) ->
     Topic = <<"my/topic">>,
     Payload = <<"my-will">>,
 
-    Sub1a = connect(<<"sub1">>, Config, 0, [{properties, #{'Session-Expiry-Interval' => 900}}]),
-    {ok, _, [0]} = emqtt:subscribe(Sub1a, Topic),
-    Sub2 = connect(<<"sub2">>, Config, 1, []),
-    {ok, _, [0]} = emqtt:subscribe(Sub2, Topic),
+    Sub0a = connect(<<"sub0">>, Config, 0, [{properties, #{'Session-Expiry-Interval' => 900}}]),
+    {ok, _, [0]} = emqtt:subscribe(Sub0a, Topic),
+    Sub1 = connect(<<"sub1">>, Config, 1, []),
+    {ok, _, [0]} = emqtt:subscribe(Sub1, Topic),
     WillDelaySecs = 10,
-    Ca = connect(<<"will">>, Config, 0,
+    C0a = connect(<<"will">>, Config, 0,
                   [{properties, #{'Session-Expiry-Interval' => 900}},
                    {will_props, #{'Will-Delay-Interval' => WillDelaySecs}},
                    {will_topic, Topic},
                    {will_qos, 0},
                    {will_payload, Payload}]),
-    unlink(Sub1a),
-    unlink(Ca),
+    ClientsNode0 = [Sub0a, C0a],
+    [unlink(C) || C <- ClientsNode0],
     T = erlang:monotonic_time(millisecond),
     ok = rabbit_ct_broker_helpers:drain_node(Config, 0),
+    [receive {disconnected, ?RC_SERVER_SHUTTING_DOWN, #{}} -> ok
+     after 10_000 -> ct:fail("server did not disconnect us")
+     end || _ <- ClientsNode0],
     ok = rabbit_ct_broker_helpers:stop_node(Config, 0),
     ElapsedMs = erlang:monotonic_time(millisecond) - T,
     SleepMs = max(0, timer:seconds(WillDelaySecs) - ElapsedMs),
@@ -1695,20 +1699,20 @@ will_delay_node_restart(Config) ->
     assert_nothing_received(),
     ok = rabbit_ct_broker_helpers:start_node(Config, 0),
     %% After node 0 restarts, we should receive the Will Message promptly on both nodes 0 and 1.
-    receive {publish, #{client_pid := Sub2,
+    receive {publish, #{client_pid := Sub1,
                         payload := Payload}} -> ok
     after 1000 -> ct:fail("did not receive Will Message on node 1")
     end,
-    Sub1b = connect(<<"sub1">>, Config, 0, [{clean_start, false}]),
-    receive {publish, #{client_pid := Sub1b,
+    Sub0b = connect(<<"sub0">>, Config, 0, [{clean_start, false}]),
+    receive {publish, #{client_pid := Sub0b,
                         payload := Payload}} -> ok
     after 1000 -> ct:fail("did not receive Will Message on node 0")
     end,
 
-    ok = emqtt:disconnect(Sub1b),
-    ok = emqtt:disconnect(Sub2),
-    Cb = connect(<<"will">>, Config),
-    ok = emqtt:disconnect(Cb).
+    ok = emqtt:disconnect(Sub0b),
+    ok = emqtt:disconnect(Sub1),
+    C0b = connect(<<"will">>, Config),
+    ok = emqtt:disconnect(C0b).
 
 session_migrate_v3_v5(Config) ->
     session_switch_v3_v5(Config, true).

deps/rabbitmq_web_mqtt/src/rabbit_web_mqtt_handler.erl

@@ -45,6 +45,7 @@
 
 %% Close frame status codes as defined in https://www.rfc-editor.org/rfc/rfc6455#section-7.4.1
 -define(CLOSE_NORMAL, 1000).
+-define(CLOSE_SERVER_GOING_DOWN, 1001).
 -define(CLOSE_PROTOCOL_ERROR, 1002).
 -define(CLOSE_UNACCEPTABLE_DATA_TYPE, 1003).
 
@@ -167,7 +168,14 @@ websocket_info({'$gen_cast', {close_connection, Reason}}, State = #state{ proc_s
                                                                          conn_name = ConnName}) ->
     ?LOG_WARNING("Web MQTT disconnecting client with ID '~s' (~p), reason: ~s",
                  [rabbit_mqtt_processor:info(client_id, ProcState), ConnName, Reason]),
-    stop(State);
+    case Reason of
+        maintenance ->
+            rabbit_mqtt_processor:send_disconnect(?RC_SERVER_SHUTTING_DOWN, ProcState),
+            defer_close(?CLOSE_SERVER_GOING_DOWN),
+            {[], State};
+        _ ->
+            stop(State)
+    end;
 websocket_info({'$gen_cast', {force_event_refresh, Ref}}, State0) ->
     Infos = infos(?EVENT_KEYS, State0),
     rabbit_event:notify(connection_created, Infos, Ref),