fix(channel): wrong case clause when alias is inexistent

Fixes #6978 .

src/emqx_channel.erl

@@ -1341,7 +1341,7 @@ process_alias(Packet = #mqtt_packet{
         {ok, Topic} ->
             NPublish = Publish#mqtt_packet_publish{topic_name = Topic},
             {ok, Packet#mqtt_packet{variable = NPublish}, Channel};
-        false -> {error, ?RC_PROTOCOL_ERROR}
+        error -> {error, ?RC_PROTOCOL_ERROR}
     end;
 
 process_alias(#mqtt_packet{
@@ -1685,7 +1685,7 @@ run_hooks(Name, Args, Acc) ->
 
 -compile({inline, [find_alias/3, save_alias/4]}).
 
-find_alias(_, _, undefined) -> false;
+find_alias(_, _, undefined) -> error;
 find_alias(inbound, AliasId, _TopicAliases = #{inbound := Aliases}) ->
     maps:find(AliasId, Aliases);
 find_alias(outbound, Topic, _TopicAliases = #{outbound := Aliases}) ->
@@ -1739,4 +1739,3 @@ flag(false) -> 0.
 set_field(Name, Value, Channel) ->
     Pos = emqx_misc:index_of(Name, record_info(fields, channel)),
     setelement(Pos+1, Channel, Value).
-

test/emqx_channel_SUITE.erl

@@ -674,6 +674,13 @@ t_process_alias(_) ->
     {ok, #mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"t">>}}, _Chan} =
         emqx_channel:process_alias(#mqtt_packet{variable = Publish}, Channel).
 
+t_process_alias_inexistent_alias(_) ->
+    Publish = #mqtt_packet_publish{topic_name = <<>>, properties = #{'Topic-Alias' => 1}},
+    Channel = channel(),
+    ?assertEqual(
+      {error, ?RC_PROTOCOL_ERROR},
+      emqx_channel:process_alias(#mqtt_packet{variable = Publish}, Channel)).
+
 t_packing_alias(_) ->
     Packet1 = #mqtt_packet{variable = #mqtt_packet_publish{
                                          topic_name = <<"x">>,
@@ -710,6 +717,20 @@ t_packing_alias(_) ->
                    #mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"z">>}},
                    channel())).
 
+t_packing_alias_inexistent_alias(_) ->
+    Publish = #mqtt_packet_publish{topic_name = <<>>, properties = #{'Topic-Alias' => 1}},
+    Channel = channel(),
+    Packet = #mqtt_packet{variable = Publish},
+    ExpectedChannel = emqx_channel:set_field(
+                        topic_aliases,
+                        #{ inbound => #{}
+                         , outbound => #{<<>> => 1}
+                         },
+                        Channel),
+    ?assertEqual(
+      {Packet, ExpectedChannel},
+      emqx_channel:packing_alias(Packet, Channel)).
+
 t_check_pub_acl(_) ->
     ok = meck:expect(emqx_zone, enable_acl, fun(_) -> true end),
     Publish = ?PUBLISH_PACKET(?QOS_0, <<"t">>, 1, <<"payload">>),