add mqtt_subscription record

include/emqttd.hrl

@@ -55,6 +55,17 @@
 
 -type(mqtt_topic() :: #mqtt_topic{}).
 
+%%--------------------------------------------------------------------
+%% MQTT Subscription
+%%--------------------------------------------------------------------
+-record(mqtt_subscription, {
+    subid :: binary() | atom(),
+    topic :: binary(),
+    qos   :: 0 | 1 | 2
+}).
+
+-type(mqtt_subscription() :: #mqtt_subscription{}).
+
 %%--------------------------------------------------------------------
 %% MQTT Client
 %%--------------------------------------------------------------------