check topic alias

src/emqx_mqtt_caps.erl

@@ -43,7 +43,9 @@
                        {mqtt_wildcard_subscription, true}]).
 
 -define(PUBCAP_KEYS, [max_qos_allowed,
-                      mqtt_retain_available]).
+                      mqtt_retain_available,
+                      mqtt_topic_alias
+                     ]).
 -define(SUBCAP_KEYS, [max_qos_allowed,
                       max_topic_levels,
                       mqtt_shared_subscription,
@@ -60,6 +62,11 @@ do_check_pub(Props = #{qos := QoS}, [{max_qos_allowed, MaxQoS}|Caps]) ->
         true  -> {error, ?RC_QOS_NOT_SUPPORTED};
         false -> do_check_pub(Props, Caps)
     end;
+do_check_pub(Props = #{ topic_alias := TopicAlias}, [{max_topic_alias, MaxTopicAlias}| Caps]) ->
+    case TopicAlias =< MaxTopicAlias andalso TopicAlias > 0 of
+        false -> {error, ?RC_TOPIC_ALIAS_INVALID};
+        true -> do_check_pub(Props, Caps)
+    end;
 do_check_pub(#{retain := true}, [{mqtt_retain_available, false}|_Caps]) ->
     {error, ?RC_RETAIN_NOT_SUPPORTED};
 do_check_pub(Props, [{mqtt_retain_available, _}|Caps]) ->
@@ -136,4 +143,3 @@ with_env(Zone, Key, InitFun) ->
                      Caps;
         ZoneCaps  -> ZoneCaps
     end.
-

src/emqx_protocol.erl

@@ -631,9 +631,11 @@ check_publish(Packet, PState) ->
     run_check_steps([fun check_pub_caps/2,
                      fun check_pub_acl/2], Packet, PState).
 
-check_pub_caps(#mqtt_packet{header = #mqtt_packet_header{qos = QoS, retain = R}},
+check_pub_caps(#mqtt_packet{header = #mqtt_packet_header{qos = QoS, retain = Retain},
+                            variable = #mqtt_packet_publish{ properties = Properties}},
                #pstate{zone = Zone}) ->
-    emqx_mqtt_caps:check_pub(Zone, #{qos => QoS, retain => R}).
+    #{'Topic-Alias' := TopicAlias} = Properties,
+    emqx_mqtt_caps:check_pub(Zone, #{qos => QoS, retain => Retain, topic_alias => TopicAlias}).
 
 check_pub_acl(_Packet, #pstate{is_super = IsSuper, enable_acl = EnableAcl})
     when IsSuper orelse (not EnableAcl) ->