Introduce per-channel consumers limit (by @illotum, AWS)

deps/rabbit/priv/schema/rabbit.schema

@@ -903,6 +903,24 @@ end}.
  end
 }.
 
+%% Set the max allowed number of consumers per channel.
+%% `infinity` means "no limit".
+%%
+%% {consumer_max_per_channel, infinity},
+
+{mapping, "consumer_max_per_channel", "rabbit.consumer_max_per_channel",
+  [{datatype, [{atom, infinity}, integer]}]}.
+
+{translation, "rabbit.consumer_max_per_channel",
+ fun(Conf) ->
+  case cuttlefish:conf_get("consumer_max_per_channel", Conf, undefined) of
+      undefined -> cuttlefish:unset();
+      infinity  -> infinity;
+      Val when is_integer(Val) andalso Val > 0 -> Val;
+      _         -> cuttlefish:invalid("should be positive integer or 'infinity'")
+  end
+ end
+}.
 
 %% Set the max permissible number of client connections per node.
 %% `infinity` means "no limit".

deps/rabbit/src/rabbit_channel.erl

@@ -105,6 +105,7 @@
           consumer_prefetch,
           consumer_timeout,
           authz_context,
+          max_consumers,  % taken from rabbit.consumer_max_per_channel
           %% defines how ofter gc will be executed
           writer_gc_threshold
          }).
@@ -507,6 +508,7 @@ init([Channel, ReaderPid, WriterPid, ConnPid, ConnName, Protocol, User, VHost,
     ConsumerTimeout = get_consumer_timeout(),
     OptionalVariables = extract_variable_map_from_amqp_params(AmqpParams),
     {ok, GCThreshold} = application:get_env(rabbit, writer_gc_threshold),
+    MaxConsumers = application:get_env(rabbit, consumer_max_per_channel, infinity),
     State = #ch{cfg = #conf{state = starting,
                             protocol = Protocol,
                             channel = Channel,
@@ -523,6 +525,7 @@ init([Channel, ReaderPid, WriterPid, ConnPid, ConnName, Protocol, User, VHost,
                             consumer_prefetch = Prefetch,
                             consumer_timeout = ConsumerTimeout,
                             authz_context = OptionalVariables,
+                            max_consumers = MaxConsumers,
                             writer_gc_threshold = GCThreshold
                            },
                 limiter = Limiter,
@@ -1313,8 +1316,13 @@ handle_method(#'basic.consume'{queue        = <<"amq.rabbitmq.reply-to">>,
                                no_ack       = NoAck,
                                nowait       = NoWait},
               _, State = #ch{reply_consumer   = ReplyConsumer,
+                             cfg = #conf{max_consumers = MaxConsumers},
                              consumer_mapping = ConsumerMapping}) ->
+    CurrentConsumers = maps:size(ConsumerMapping),
     case maps:find(CTag0, ConsumerMapping) of
+        error when CurrentConsumers >= MaxConsumers ->  % false when MaxConsumers is 'infinity'
+            rabbit_misc:protocol_error(
+              not_allowed, "reached maximum (~ts) of consumers per channel", [MaxConsumers]);
         error ->
             case {ReplyConsumer, NoAck} of
                 {none, true} ->
@@ -1363,12 +1371,17 @@ handle_method(#'basic.consume'{queue        = QueueNameBin,
                                nowait       = NoWait,
                                arguments    = Args},
               _, State = #ch{cfg = #conf{consumer_prefetch = ConsumerPrefetch,
+                                         max_consumers = MaxConsumers,
                                          user = User,
                                          virtual_host = VHostPath,
                                          authz_context = AuthzContext},
                              consumer_mapping  = ConsumerMapping
                             }) ->
+    CurrentConsumers = length(maps:keys(ConsumerMapping)),
     case maps:find(ConsumerTag, ConsumerMapping) of
+        error when CurrentConsumers >= MaxConsumers ->  % false when MaxConsumers is 'infinity'
+        rabbit_misc:protocol_error(
+              not_allowed, "reached maximum (~ts) of consumers per channel", [MaxConsumers]);
         error ->
             QueueName = qbin_to_resource(QueueNameBin, VHostPath),
             check_read_permitted(QueueName, User, AuthzContext),

deps/rabbit/test/config_schema_SUITE_data/rabbit.snippets

@@ -404,6 +404,14 @@ tcp_listen_options.exit_on_close = false",
   "channel_max_per_node = infinity",
   [{rabbit,[{channel_max_per_node, infinity}]}],
   []},
+ {consumer_max_per_channel,
+  "consumer_max_per_channel = 16",
+  [{rabbit,[{consumer_max_per_channel, 16}]}],
+  []},
+ {consumer_max_per_channel,
+  "consumer_max_per_channel = infinity",
+  [{rabbit,[{consumer_max_per_channel, infinity}]}],
+  []},
  {max_message_size,
   "max_message_size = 131072",
   [{rabbit, [{max_message_size, 131072}]}],

deps/rabbit/test/per_node_limit_SUITE.erl

@@ -23,6 +23,7 @@ groups() ->
      {limit_tests, [], [
                         node_connection_limit,
                         vhost_limit,
+                        channel_consumers_limit,
                         node_channel_limit
                        ]}
     ].
@@ -62,13 +63,15 @@ init_per_testcase(Testcase, Config) ->
 
 end_per_testcase(vhost_limit = Testcase, Config) ->
     set_node_limit(Config, vhost_max, infinity),
-    set_node_limit(Config, channel_max_per_node, 0),
+    set_node_limit(Config, channel_max_per_node, infinity),
+    set_node_limit(Config, consumer_max_per_channel, infinity),
     set_node_limit(Config, connection_max, infinity),
     [rabbit_ct_broker_helpers:delete_vhost(Config, integer_to_binary(I)) || I <- lists:seq(1,4)],
     rabbit_ct_helpers:testcase_finished(Config, Testcase);
 end_per_testcase(Testcase, Config) ->
     set_node_limit(Config, vhost_max, infinity),
-    set_node_limit(Config, channel_max_per_node, 0),
+    set_node_limit(Config, channel_max_per_node, infinity),
+    set_node_limit(Config, consumer_max_per_channel, infinity),
     set_node_limit(Config, connection_max, infinity),
     rabbit_ct_helpers:testcase_finished(Config, Testcase).
 
@@ -111,12 +114,13 @@ vhost_limit(Config) ->
 node_channel_limit(Config) ->
     set_node_limit(Config, channel_max_per_node, 5),
 
-    VHost = <<"foobar">>,
+    VHost = <<"node_channel_limit">>,
     User = <<"guest">>,
     ok = rabbit_ct_broker_helpers:add_vhost(Config, VHost),
     ok = rabbit_ct_broker_helpers:set_full_permissions(Config, User, VHost),
     Conn1 = rabbit_ct_client_helpers:open_unmanaged_connection(Config, 0, VHost),
     Conn2 = rabbit_ct_client_helpers:open_unmanaged_connection(Config, 0, VHost),
+    0 = count_channels_per_node(Config),
 
     lists:foreach(fun(N) when (N band 1) == 1 -> {ok, _} = open_channel(Conn1);
                      (_) -> {ok,_ } = open_channel(Conn2)
@@ -137,6 +141,30 @@ node_channel_limit(Config) ->
 
     %% Now all connections are closed, so there should be 0 open connections
     0 = count_channels_per_node(Config),
+    close_all_connections([Conn1, Conn2]),
+
+    rabbit_ct_broker_helpers:delete_vhost(Config, VHost),
+
+    ok.
+
+channel_consumers_limit(Config) ->
+    set_node_limit(Config, consumer_max_per_channel, 2),
+
+    VHost = <<"channel_consumers_limit">>,
+    User = <<"guest">>,
+    ok = rabbit_ct_broker_helpers:add_vhost(Config, VHost),
+    ok = rabbit_ct_broker_helpers:set_full_permissions(Config, User, VHost),
+    Conn1 = rabbit_ct_client_helpers:open_unmanaged_connection(Config, 0, VHost),
+    {ok, Ch} = open_channel(Conn1),
+    Q = <<"Q">>, Tag = <<"Tag">>,
+
+    {ok, _} = consume(Ch, Q, <<"Tag1">>),
+    {ok, _} = consume(Ch, Q, <<"Tag2">>),
+    {error, not_allowed_crash} = consume(Ch, Q, <<"Tag3">>),  % Third consumer should fail
+
+    close_all_connections([Conn1]),
+    rabbit_ct_broker_helpers:delete_vhost(Config, VHost),
+
     ok.
 
 %% -------------------------------------------------------------------
@@ -157,6 +185,15 @@ set_node_limit(Config, Type, Limit) ->
                                  application,
                                  set_env, [rabbit, Type, Limit]).
 
+consume(Ch, Q, Tag) ->
+    #'queue.declare_ok'{queue = Q} = amqp_channel:call(Ch, #'queue.declare'{queue = Q}),
+    try amqp_channel:call(Ch, #'basic.consume'{queue = Q, consumer_tag = Tag}) of
+      #'basic.consume_ok'{} = OK -> {ok, OK};
+      NotOk -> {error, NotOk}
+    catch
+      _:_Error -> {error, not_allowed_crash}
+   end.
+
 open_channel(Conn) when is_pid(Conn) ->
     try amqp_connection:open_channel(Conn) of
       {ok, Ch} -> {ok, Ch};