Store MQTT messages as non-durable if QoS 0

By default, when the 'durable' message container (mc) annotation is unset,
messages are interpreted to be durable.

Prior to this commit, MQTT messages that were sent with QoS 0 were
stored durably in classic queues.
This commit takes the same approach for mc_mqtt as for mc_amqpl and mc_amqp:
If the message is durable, the durable mc annotation will not be set.
If the message is non-durable, the durable mc annotation will be set to false.

deps/rabbitmq_mqtt/src/mc_mqtt.erl

@@ -27,9 +27,9 @@ init(Msg = #mqtt_msg{qos = Qos,
   when is_integer(Qos) ->
     Anns0 = case Qos > 0 of
                 true ->
-                    #{?ANN_DURABLE => true};
+                    #{};
                 false ->
-                    #{}
+                    #{?ANN_DURABLE => false}
             end,
     Anns1 = case Props of
                 #{'Message-Expiry-Interval' := Seconds} ->

deps/rabbitmq_mqtt/test/mc_mqtt_SUITE.erl

@@ -37,7 +37,8 @@ groups() ->
        mqtt_amqpl_alt,
        mqtt_amqp,
        mqtt_amqp_alt,
-       amqp_mqtt
+       amqp_mqtt,
+       is_persistent
       ]}
     ].
 
@@ -501,6 +502,19 @@ amqp_mqtt(_Config) ->
                 }, Mqtt),
     ok.
 
+is_persistent(_Config) ->
+    Msg0 = #mqtt_msg{qos = 0,
+                     topic = <<"my/topic">>,
+                     payload = <<>>},
+    Mc0 = mc:init(mc_mqtt, Msg0, #{}),
+    ?assertNot(mc:is_persistent(Mc0)),
+
+    Msg1 = #mqtt_msg{qos = 1,
+                     topic = <<"my/topic">>,
+                     payload = <<>>},
+    Mc1 = mc:init(mc_mqtt, Msg1, #{}),
+    ?assert(mc:is_persistent(Mc1)).
+
 mqtt_msg() ->
     #mqtt_msg{qos = 0,
               topic = <<"my/topic">>,

deps/rabbitmq_mqtt/test/protocol_interop_SUITE.erl

@@ -23,7 +23,8 @@
 -import(rabbit_ct_broker_helpers,
         [rpc/4]).
 -import(rabbit_ct_helpers,
-        [eventually/3]).
+        [eventually/1,
+         eventually/3]).
 
 all() ->
     [{group, tests}].
@@ -88,7 +89,8 @@ end_per_testcase(Testcase, Config) ->
 mqtt_amqpl_mqtt(Config) ->
     Q = ClientId = atom_to_binary(?FUNCTION_NAME),
     Ch = rabbit_ct_client_helpers:open_channel(Config),
-    #'queue.declare_ok'{} = amqp_channel:call(Ch, #'queue.declare'{queue = Q}),
+    #'queue.declare_ok'{} = amqp_channel:call(Ch, #'queue.declare'{queue = Q,
+                                                                   durable = true}),
     #'queue.bind_ok'{} = amqp_channel:call(Ch, #'queue.bind'{queue = Q,
                                                              exchange = <<"amq.topic">>,
                                                              routing_key = <<"my.topic">>}),
@@ -147,6 +149,14 @@ mqtt_amqpl_mqtt(Config) ->
     after 1000 -> ct:fail("did not receive reply")
     end,
 
+    %% Another message MQTT 5.0 to AMQP 0.9.1, this time with QoS 0
+    ok = emqtt:publish(C, <<"my/topic">>, RequestPayload, [{qos, 0}]),
+    eventually(
+      ?_assertMatch(
+         {#'basic.get_ok'{}, #amqp_msg{payload = RequestPayload,
+                                       props = #'P_basic'{delivery_mode = 1}}},
+         amqp_channel:call(Ch, #'basic.get'{queue = Q}))),
+
     ok = emqtt:disconnect(C).
 
 mqtt_amqp_mqtt(Config) ->