Add condition to handle when mqx_topic_alias do not exist

src/emqx_mqtt_caps.erl

@@ -69,6 +69,8 @@ do_check_pub(Props = #{ topic_alias := TopicAlias}, [{max_topic_alias, MaxTopicA
     end;
 do_check_pub(#{retain := true}, [{mqtt_retain_available, false}|_Caps]) ->
     {error, ?RC_RETAIN_NOT_SUPPORTED};
+do_check_pub(Props, [{max_topic_alias, _} | Caps]) ->
+    do_check_pub(Props, Caps);
 do_check_pub(Props, [{mqtt_retain_available, _}|Caps]) ->
     do_check_pub(Props, Caps).
 

src/emqx_protocol.erl

@@ -33,36 +33,36 @@
 -export([shutdown/2]).
 
 -record(pstate, {
-                 zone,
-                 sendfun,
-                 peername,
-                 peercert,
-                 proto_ver,
-                 proto_name,
-                 ackprops,
-                 client_id,
-                 is_assigned,
-                 conn_pid,
-                 conn_props,
-                 ack_props,
-                 username,
-                 session,
-                 clean_start,
-                 topic_aliases,
-                 packet_size,
-                 will_topic,
-                 will_msg,
-                 keepalive,
-                 mountpoint,
-                 is_super,
-                 is_bridge,
-                 enable_ban,
-                 enable_acl,
-                 recv_stats,
-                 send_stats,
-                 connected,
-                 connected_at
-                }).
+         zone,
+         sendfun,
+         peername,
+         peercert,
+         proto_ver,
+         proto_name,
+         ackprops,
+         client_id,
+         is_assigned,
+         conn_pid,
+         conn_props,
+         ack_props,
+         username,
+         session,
+         clean_start,
+         topic_aliases,
+         packet_size,
+         will_topic,
+         will_msg,
+         keepalive,
+         mountpoint,
+         is_super,
+         is_bridge,
+         enable_ban,
+         enable_acl,
+         recv_stats,
+         send_stats,
+         connected,
+         connected_at
+        }).
 
 -type(state() :: #pstate{}).
 -export_type([state/0]).

test/emqx_mqtt_caps_SUITE.erl

@@ -63,10 +63,12 @@ t_check_pub(_) ->
     {ok, _} = emqx_zone:start_link(),
     PubCaps = #{
         max_qos_allowed => ?QOS_1,
-        mqtt_retain_available => false
+        mqtt_retain_available => false,
+        max_topic_alias => 4
     },
     emqx_zone:set_env(zone, '$mqtt_pub_caps', PubCaps),
     timer:sleep(100),
+    ct:log("~p", [emqx_mqtt_caps:get_caps(zone, publish)]),
     BadPubProps1 = #{
         qos => ?QOS_2,
         retain => false
@@ -77,6 +79,12 @@ t_check_pub(_) ->
         retain => true
     },
     {error, ?RC_RETAIN_NOT_SUPPORTED} = emqx_mqtt_caps:check_pub(zone, BadPubProps2),
+    BadPubProps3 = #{
+        qos => ?QOS_1,
+        retain => false,
+        topic_alias => 5
+    },
+    {error, ?RC_TOPIC_ALIAS_INVALID} = emqx_mqtt_caps:check_pub(zone, BadPubProps3),
     PubProps = #{
         qos => ?QOS_1,
         retain => false