fix(emqx_channel): return Receive-Maximum in CONNACK when no error

apps/emqx/src/emqx_channel.erl

@@ -2007,14 +2007,15 @@ merge_default_subopts(SubOpts) ->
 %%--------------------------------------------------------------------
 %% Enrich ConnAck Caps
 
-enrich_connack_caps(
-    AckProps,
-    ?IS_MQTT_V5 = #channel{
+enrich_connack_caps(AckProps, ?IS_MQTT_V5 = Channel) ->
+    #channel{
         clientinfo = #{
             zone := Zone
+        },
+        conninfo = #{
+            receive_maximum := ReceiveMaximum
         }
-    }
-) ->
+    } = Channel,
     #{
         max_packet_size := MaxPktSize,
         max_qos_allowed := MaxQoS,
@@ -2029,7 +2030,8 @@ enrich_connack_caps(
         'Topic-Alias-Maximum' => MaxAlias,
         'Wildcard-Subscription-Available' => flag(Wildcard),
         'Subscription-Identifier-Available' => 1,
-        'Shared-Subscription-Available' => flag(Shared)
+        'Shared-Subscription-Available' => flag(Shared),
+        'Receive-Maximum' => ReceiveMaximum
     },
     %% MQTT 5.0 - 3.2.2.3.4:
     %% It is a Protocol Error to include Maximum QoS more than once,

apps/emqx/test/emqx_client_SUITE.erl

@@ -72,7 +72,7 @@ groups() ->
             t_dollar_topics,
             t_sub_non_utf8_topic
         ]},
-        {mqttv5, [non_parallel_tests], [t_basic_with_props_v5]},
+        {mqttv5, [non_parallel_tests], [t_basic_with_props_v5, t_v5_receive_maximim_in_connack]},
         {others, [non_parallel_tests], [
             t_username_as_clientid,
             t_certcn_as_clientid_default_config_tls,
@@ -103,14 +103,14 @@ end_per_testcase(_Case, _Config) ->
 %%--------------------------------------------------------------------
 
 t_basic_v3(_) ->
-    t_basic([{proto_ver, v3}]).
+    run_basic([{proto_ver, v3}]).
 
 %%--------------------------------------------------------------------
 %% Test cases for MQTT v4
 %%--------------------------------------------------------------------
 
 t_basic_v4(_Config) ->
-    t_basic([{proto_ver, v4}]).
+    run_basic([{proto_ver, v4}]).
 
 t_cm(_) ->
     emqx_config:put_zone_conf(default, [mqtt, idle_timeout], 1000),
@@ -335,19 +335,30 @@ t_sub_non_utf8_topic(_) ->
 %% Test cases for MQTT v5
 %%--------------------------------------------------------------------
 
-t_basic_with_props_v5(_) ->
-    t_basic([
+v5_conn_props(ReceiveMaximum) ->
+    [
         {proto_ver, v5},
-        {properties, #{'Receive-Maximum' => 4}}
-    ]).
+        {properties, #{'Receive-Maximum' => ReceiveMaximum}}
+    ].
+
+t_basic_with_props_v5(_) ->
+    run_basic(v5_conn_props(4)).
+
+t_v5_receive_maximim_in_connack(_) ->
+    ReceiveMaximum = 7,
+    {ok, C} = emqtt:start_link(v5_conn_props(ReceiveMaximum)),
+    {ok, Props} = emqtt:connect(C),
+    ?assertMatch(#{'Receive-Maximum' := ReceiveMaximum}, Props),
+    ok = emqtt:disconnect(C),
+    ok.
 
 %%--------------------------------------------------------------------
 %% General test cases.
 %%--------------------------------------------------------------------
 
-t_basic(_Opts) ->
+run_basic(Opts) ->
     Topic = nth(1, ?TOPICS),
-    {ok, C} = emqtt:start_link([{proto_ver, v4}]),
+    {ok, C} = emqtt:start_link(Opts),
     {ok, _} = emqtt:connect(C),
     {ok, _, [1]} = emqtt:subscribe(C, Topic, qos1),
     {ok, _, [2]} = emqtt:subscribe(C, Topic, qos2),

changes/ce/fix-12492.en.md

@@ -0,0 +1,4 @@
+Return `Receive-Maximum` in `CONNACK` for MQTT v5 clients.
+
+EMQX takes the min value of client's `Receive-Maximum` and server's `max_inflight` config as the max number of inflight (unacknowledged) messages allowed.
+Prior to this fix, the value was not sent back to the client in `CONNACK` message.