ignore duplicated subscriptions

src/emqttd_session.erl

@@ -282,36 +282,40 @@ prioritise_info(Msg, _Len, _State) ->
 handle_call({subscribe, TopicTable0}, _From, Session = #session{client_id = ClientId,
                                                                 subscriptions = Subscriptions}) ->
 
-    TopicTable = emqttd_broker:foldl_hooks('client.subscribe', [ClientId], TopicTable0),
-    
-    %% subscribe first and don't care if the subscriptions have been existed
-    {ok, GrantedQos} = emqttd_pubsub:subscribe(TopicTable),
-
-    emqttd_broker:foreach_hooks('client.subscribe.after', [ClientId, TopicTable]),
-
-    lager:info([{client, ClientId}], "Session(~s): subscribe ~p, Granted QoS: ~p",
-                [ClientId, TopicTable, GrantedQos]),
-
-    Subscriptions1 =
-    lists:foldl(fun({Topic, Qos}, Acc) ->
-                    case lists:keyfind(Topic, 1, Acc) of
-                        {Topic, Qos} ->
-                            lager:warning([{client, ClientId}], "Session(~s): "
-                                            "resubscribe ~s, qos = ~w", [ClientId, Topic, Qos]), Acc;
-                        {Topic, OldQos} ->
-                            lager:warning([{client, ClientId}], "Session(~s): "
-                                            "resubscribe ~s, old qos=~w, new qos=~w", [ClientId, Topic, OldQos, Qos]),
-                            lists:keyreplace(Topic, 1, Acc, {Topic, Qos});
-                        false ->
-                            %%TODO: the design is ugly, rewrite later...:(
-                            %% <MQTT V3.1.1>: 3.8.4
-                            %% Where the Topic Filter is not identical to any existing Subscription’s filter,
-                            %% a new Subscription is created and all matching retained messages are sent.
-                            emqttd_retained:dispatch(Topic, self()),
-                            [{Topic, Qos} | Acc]
-                    end
-                end, Subscriptions, TopicTable),
-    {reply, {ok, GrantedQos}, Session#session{subscriptions = Subscriptions1}};
+    case TopicTable0 -- Subscriptions of
+        [] ->
+            {reply, {ok, [Qos || {_, Qos} <- TopicTable0]}, Session};
+        _  ->
+            TopicTable = emqttd_broker:foldl_hooks('client.subscribe', [ClientId], TopicTable0),
+            %% subscribe first and don't care if the subscriptions have been existed
+            {ok, GrantedQos} = emqttd_pubsub:subscribe(TopicTable),
+
+            emqttd_broker:foreach_hooks('client.subscribe.after', [ClientId, TopicTable]),
+
+            lager:info([{client, ClientId}], "Session(~s): subscribe ~p, Granted QoS: ~p",
+                        [ClientId, TopicTable, GrantedQos]),
+
+            Subscriptions1 =
+            lists:foldl(fun({Topic, Qos}, Acc) ->
+                            case lists:keyfind(Topic, 1, Acc) of
+                                {Topic, Qos} ->
+                                    lager:warning([{client, ClientId}], "Session(~s): "
+                                                    "resubscribe ~s, qos = ~w", [ClientId, Topic, Qos]), Acc;
+                                {Topic, OldQos} ->
+                                    lager:warning([{client, ClientId}], "Session(~s): "
+                                                    "resubscribe ~s, old qos=~w, new qos=~w", [ClientId, Topic, OldQos, Qos]),
+                                    lists:keyreplace(Topic, 1, Acc, {Topic, Qos});
+                                false ->
+                                    %%TODO: the design is ugly, rewrite later...:(
+                                    %% <MQTT V3.1.1>: 3.8.4
+                                    %% Where the Topic Filter is not identical to any existing Subscription’s filter,
+                                    %% a new Subscription is created and all matching retained messages are sent.
+                                    emqttd_retained:dispatch(Topic, self()),
+                                    [{Topic, Qos} | Acc]
+                            end
+                        end, Subscriptions, TopicTable),
+            {reply, {ok, GrantedQos}, Session#session{subscriptions = Subscriptions1}}
+    end;
 
 handle_call({unsubscribe, Topics0}, _From, Session = #session{client_id = ClientId,
                                                              subscriptions = Subscriptions}) ->