From 8f95e125341fc56916b9513062dbddb8ff3f63d8 Mon Sep 17 00:00:00 2001
From: zhanghongtong <rory-z@outlook.com>
Date: Thu, 23 Jul 2020 15:46:53 +0800
Subject: [PATCH] fix(emqx_channel): EMQ X replaces MQTT properties when node
 connects using "topic-alias-maximum" property

---
 src/emqx_channel.erl        | 17 ++++++++++++++---
 test/emqx_channel_SUITE.erl | 20 +++++++++++++++++---
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/src/emqx_channel.erl b/src/emqx_channel.erl
index d0f951596..450492852 100644
--- a/src/emqx_channel.erl
+++ b/src/emqx_channel.erl
@@ -1239,14 +1239,21 @@ process_alias(_Packet, Channel) -> {ok, Channel}.
 %% Packing Topic Alias
 
 packing_alias(Packet = #mqtt_packet{
-                            variable = #mqtt_packet_publish{topic_name = Topic} = Publish
+                            variable = #mqtt_packet_publish{
+                                          topic_name = Topic,
+                                          properties = Prop
+                                         } = Publish
                         },
               Channel = ?IS_MQTT_V5 = #channel{topic_aliases = TopicAliases, alias_maximum = Limits}) ->
     case find_alias(outbound, Topic, TopicAliases) of
         {ok, AliasId} -> 
+            NProp = case Prop of
+                undefined -> #{'Topic-Alias' => AliasId};
+                _ -> maps:merge(Prop, #{'Topic-Alias' => AliasId})
+            end,
             NPublish = Publish#mqtt_packet_publish{
                             topic_name = <<>>,
-                            properties = #{'Topic-Alias' => AliasId}
+                            properties = NProp
                             },
             {Packet#mqtt_packet{variable = NPublish}, Channel};
         error ->
@@ -1257,9 +1264,13 @@ packing_alias(Packet = #mqtt_packet{
                 true ->
                     NTopicAliases = save_alias(outbound, AliasId, Topic, TopicAliases),
                     NChannel = Channel#channel{topic_aliases = NTopicAliases},
+                    NProp = case Prop of
+                        undefined -> #{'Topic-Alias' => AliasId};
+                        _ -> maps:merge(Prop, #{'Topic-Alias' => AliasId})
+                    end,
                     NPublish = Publish#mqtt_packet_publish{
                                     topic_name = Topic,
-                                    properties = #{'Topic-Alias' => AliasId}
+                                    properties = NProp
                                     },
                     {Packet#mqtt_packet{variable = NPublish}, NChannel};
                 false -> {Packet, Channel}
diff --git a/test/emqx_channel_SUITE.erl b/test/emqx_channel_SUITE.erl
index 2dba03dfb..506dd2812 100644
--- a/test/emqx_channel_SUITE.erl
+++ b/test/emqx_channel_SUITE.erl
@@ -532,15 +532,29 @@ t_process_alias(_) ->
         emqx_channel:process_alias(#mqtt_packet{variable = Publish}, Channel).
 
 t_packing_alias(_) ->
-    Packet1 = #mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"x">>}},
+    Packet1 = #mqtt_packet{variable = #mqtt_packet_publish{
+                                         topic_name = <<"x">>,
+                                         properties = #{'User-Property' => [{<<"k">>, <<"v">>}]}
+                                        }},
     Packet2 = #mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"y">>}},
     Channel = emqx_channel:set_field(alias_maximum, #{outbound => 1}, channel()),
 
     {RePacket1, NChannel1} = emqx_channel:packing_alias(Packet1, Channel),
-    ?assertEqual(#mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"x">>, properties = #{'Topic-Alias' => 1}}}, RePacket1),
+    ?assertEqual(#mqtt_packet{variable = #mqtt_packet_publish{
+                                            topic_name = <<"x">>,
+                                            properties = #{
+                                                'Topic-Alias' => 1,
+                                                'User-Property' => [{<<"k">>, <<"v">>}]
+                                             }
+                                           }}, RePacket1),
 
     {RePacket2, NChannel2} = emqx_channel:packing_alias(Packet1, NChannel1),
-    ?assertEqual(#mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<>>, properties = #{'Topic-Alias' => 1}}}, RePacket2),
+    ?assertEqual(#mqtt_packet{variable = #mqtt_packet_publish{
+                                            topic_name = <<>>,
+                                            properties = #{
+                                                'Topic-Alias' => 1,
+                                                'User-Property' => [{<<"k">>, <<"v">>}]
+                                             }}}, RePacket2),
 
     {RePacket3, _} = emqx_channel:packing_alias(Packet2, NChannel2),
     ?assertEqual(#mqtt_packet{variable = #mqtt_packet_publish{topic_name = <<"y">>, properties = undefined}}, RePacket3),