MQTT: How to publish to all clients?

[abensoft-williamthome]

Hi!

I successfully subscribe to a topic via template as {% wire type={mqtt topic="my/topic"} action={growl text="hello"} %} or js

cotonic.broker.subscribe("my/topic", () => {
    console.log("hello")
})

In the server

{ok, ClientId} = z_context:client_id(Context),
z_mqtt:publish([<<"bridge">>, ClientId, <<"my">>, <<"topic">>], #{}, Context).

%% or

z_mqtt:publish([<<"~client">>, <<"my">>, <<"topic">>], #{}, Context).

... the current client receives the information on the page, but only the client who fired the event/topic.

How to propagate the event to all clients on the current page? How to, via server, all clientes/pages subscribed in the topic {% wire type={mqtt topic="my/topic"} action={some_action} %} performs some action?
In 0.x we used the ~pagesession namespace, but in 1.x we could not find a way to do this.

Thanks in advance!

[abensoft-alvaro]

Hello,

Complementing the question, we are removing the pubzub library and the same problem occurs when we tried this via .js doing cotonic.broker.subscribe("bridge/origin/server/topic", callback);
and on the server side z_mqtt:publish("server/topic", data).
The subscription is received by the server, but the publish event never arrives to the client.

Our scenario is: a modification generated by one user on a page/URL has to force a refresh to all other users accessing the same page/URL. All users are authenticated.

Any help is appreciated.

[mworrell]

If you to publish to all clients, then all those clients should be subscribed to a topic on the server.

cotonic.broker.subscribe("bridge/origin/my/topic", () => {
    console.log("hello")
})

And then on the server publish to my/topic

Note that all subscribes and publishes are ACL checked, so make certain that your topic can be subscribed to by the client.

For testing you can use the test or public topics, those are publicly available.

cotonic.broker.subscribe("bridge/origin/test/foo/bar", () => {
    console.log("hello")
})

[abensoft-williamthome]

Thanks, @mworrell.
test or public topics work, but I accomplished this using the model topic convention by looking at Cotonic docs and z_mqtt_sessions_runtime:is_allowed/3. Just bridge/origin/my/topic does not work.
My topic looks like so now bridge/origin/model/mymodel/event/my/topic.
Maybe I'm making some mistake, but the Zotonic docs give me this example:

cotonic.broker.subscribe("bridge/origin/foo/#", function(msg, bindings, options) { console.log(msg); });
cotonic.broker.publish("bridge/origin/foo/bar", "hello world");

but I could not make this work as I expected. I think there is some missing explanation about MQTT topics.

UPDATE

Code in my erlang site file:

observe_acl_is_allowed(
    #acl_is_allowed{object = #acl_mqtt{topic = [
        <<"model">>, <<"mymodel">>, <<"event">>, <<"my">>, <<"topic">>
    ]}},
    _Context
) ->
    true;
observe_acl_is_allowed(#acl_is_allowed{}, _Context) ->
    undefined.

[mworrell]

I changed the foo/bar topic in the docs to test/foo.

For the model topics, you need to have use permission on the module that "owns" the model to subscribe.

From z_mqtt_sessions_runtime.erl:

% Model events can be view iff the user has use permission on the module
is_allowed(subscribe, [ <<"model">>, Model, <<"event">> | _ ], Context) ->
    try
        case z_module_indexer:find(model, Model, Context) of
            {ok, #module_index{ module = zotonic_core }} ->
                true;
            {ok, #module_index{ module = Module }} ->
                z_acl:is_allowed(use, Module, Context);
            {error, enoent} ->
                false
        end
    catch
        _:_ ->
            false
    end;

[abensoft-alvaro]

Hello Marc,

That was a question we had yesterday. This model topic refers to the Zotonic model, Cotonic model or is it a new concept?
In the scenario where we have only a button event that should propagate to a set of users and is not related to a specific zotonic model, should we use the module name? As a suggestion, should an "event" topic exist alongside public, test, model, etc? It could call only the is_acl_allowed verification and not the acl use...

Cheers,

[mworrell]

The model is a Zotonic concept that is also used by Cotonic.

In your case, as the topic is not associated with a particular model, I would make a special topic.

It is good to make a list of topics that should be interesting or should have some default access control attached to them.

We have already the model, test, public and user. Top-level topics. Maybe we could add some more convenient topics to these. Especially as adding ACL checks to the code is quite some work (and easy to make errors).