Post to PubSub subscribers outside a Phoenix.Channel controller

[simonp...@gmail.com]

Hi,

I want to know if there is a way to broadcast a message to a topic that will be catch by every subscriber of the topic.

As this issue (https://github.com/phoenixframework/phoenix/issues/671) mentionned, there is no way to list all subscribers anymore.

My use case is simple. An action in a web controller should send a message to a topic and every subscribers should receive it.

I read the docs and tried several things but nothing seems to work :/

Thanks!

[Chris McCord]

That’s exactly what the broadcast functions do today. They broadcast a message on a topic, and all subscribers to that topic receive the message. So it works as you want, but what that issue outline, is you can’t get a list of pids of the subscribers, but you *can* broadcast to all of hem. Make sense?

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[Adam Kittelson]

How are you trying to receive the messages? If your subscribing processes are genservers you should be able receive your message via the handle_info callback. To debug you could create a handle_info callback that catches everything to help you catch if the issue is that the messages aren't quite the format you were expecting, e.g.

def handle_info(message, state) do

  # some debugging stuff here, IO.puts, IEx.pry etc  

  {:noreply, state}

end

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[simonp...@gmail.com]

Sorry for the noob question but the handle_info should be in the controller? Or on the socket processes directly?

Thanks for the quick responses guys :)

[Adam Kittelson]

I think I misunderstood what you're trying to do, if you're using Channels (as opposed to just PubSub) you can broadcast to those from anywhere with something like:

YourApp.Endpoint.broadcast! "some topic", "some event", %{some: "message"}

I think the info at http://hexdocs.pm/phoenix/Phoenix.Channel.html under "Broadcasting to an external topic" might be what you're looking for if I'm understanding what you're trying to do correctly.

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[simonp...@gmail.com]

Ah thanks! That’s exactly what I want to do, I don’t know how I skipped this part of the doc