Intercepting outbound events with LiveView

Phoenix Forum Questions / Help
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Hi all! I’m fairly new to LiveView and am working on a simple game to get started. I’m using Phoenix.Presence to track connected users, which was going great until I wanted to track subscriptions to multiple topics independently. I could use some help orienting myself in the right direction.

My game consists of a lobby from which players pair off to play a game together; when the game ends they’re sent back to the lobby. I want to track users in the lobby for the purpose of maintaining an up-to-date list of idle players; I also want to track players in each game “room” by subscribing them to a game:<id> channel, mostly so that if a user disconnects I can react accordingly. The snag I’m running into is that joins/leaves result in a presence_diff event that doesn’t seem to care which topic it originated from.

What I really want is to override outbound events and differentiate them, which with a channel would look something like this:

intercept ["presence_diff"]

def handle_out("presence_diff", message, socket) do
  # send different events depending on message contents
end

… but without introducing a channel, and I haven’t found a way to do that. Barring that, I’ve considered adding the topic to tracking metadata, and then parsing the topic out in the presence_diff payloads to determine the right behavior… but that feels complex and not really in the spirit of metadata.

Anyway, thanks for reading, and any input would be much appreciated!

1 Like
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Have you thought about using a simple PubSub, whith a different topic for each game and the lobby? Then you could have a separeate LiveView for the lobby, and one for the game. The Lobby could subscribe to the lobby topic on mount, while the game LiveView could subscribte to the given game:<id> topic.

Then you could broadcast messages, and everything would be nicely separated.

3

Thanks for the response! Mounting separate LiveViews for the lobby and games would simplify some aspects (and maybe complicate others), but if I’m understanding right, I think I’d still have the same issue: the presence_diff events that ensue when a player joins or leaves a game wouldn’t differentiate between individual game rooms unless I do something like stick the game ID in the tracking metadata. In other words, if a player leaves game:x, players in game:y will get a presence_diff event. Ideally, I’d like to override tracking behavior so joins/leaves would send a presence_diff_game:<id> event instead, but I don’t know if that’s possible.

I also realized I was misleading in my original post by referring to a ’game:<id> channel" – I’m trying to avoid introducing Phoenix.Channel here, although it’s possible that’s the best way to get what I’m after.

Anyway, I appreciate your response, and I’ll play around with what you suggested!