Properly list Web-MQTT connections in CLI list_mqtt_connections

Before this change only `:not_found` was printed for each connection.

deps/rabbitmq_mqtt/src/rabbit_mqtt.erl

@@ -69,7 +69,13 @@ emit_connection_info(Items, Ref, AggregatorPid, Pids) ->
     rabbit_control_misc:emitting_map_with_exit_handler(
       AggregatorPid, Ref,
       fun(Pid) ->
-              rabbit_mqtt_reader:info(Pid, Items)
+              case rabbit_mqtt_reader:info(Pid, Items) of
+                  {error, not_found} ->
+                      %% a Web-MQTT connection
+                      rabbit_web_mqtt_handler:info(Pid, Items);
+                  Result ->
+                      Result
+              end
       end, Pids).
 
 -spec close_local_client_connections(atom()) -> {'ok', non_neg_integer()}.

deps/rabbitmq_web_mqtt/src/rabbit_web_mqtt_handler.erl

@@ -22,7 +22,8 @@
     terminate/3
 ]).
 
--export([conserve_resources/3]).
+-export([conserve_resources/3,
+         info/2]).
 
 %% cowboy_sub_protocol
 -export([upgrade/4,
@@ -126,6 +127,20 @@ conserve_resources(Pid, _, {_, Conserve, _}) ->
     Pid ! {conserve_resources, Conserve},
     ok.
 
+%% We cannot use a gen_server call, because the handler process is a
+%% special cowboy_websocket process (not a gen_server) which assumes
+%% all gen_server calls are supervisor calls, and does not pass on the
+%% request to this callback module. (see cowboy_websocket:loop/3 and
+%% cowboy_children:handle_supervisor_call/4) However using a generic
+%% gen:call with a special label ?MODULE works fine.
+-spec info(pid(), rabbit_types:info_keys()) ->
+    rabbit_types:infos().
+info(Pid, all) ->
+    info(Pid, ?INFO_ITEMS);
+info(Pid, Items) ->
+    {ok, Res} = gen:call(Pid, ?MODULE, {info, Items}),
+    Res.
+
 -spec websocket_handle(ping | pong | {text | binary | ping | pong, binary()}, State) ->
     {cowboy_websocket:commands(), State} |
     {cowboy_websocket:commands(), State, hibernate}.
@@ -244,6 +259,10 @@ websocket_info(connection_created, State) ->
     rabbit_core_metrics:connection_created(self(), Infos),
     rabbit_event:notify(connection_created, Infos),
     {[], State, hibernate};
+websocket_info({?MODULE, From, {info, Items}}, State) ->
+    Infos = infos(Items, State),
+    gen:reply(From, Infos),
+    {[], State, hibernate};
 websocket_info(Msg, State) ->
     ?LOG_WARNING("Web MQTT: unexpected message ~tp", [Msg]),
     {[], State, hibernate}.