feat: custom dispatcher for Presence handle_diff broadcast #6500
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josevalim
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Oct 4, 2025
| use Phoenix.Presence, | ||
| otp_app: :my_app, | ||
| pubsub_server: MyApp.PubSub, | ||
| dispatcher: MyApp.CustomDispatcher |
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We need some documentation or links on what is the dispatch and how a custom implementation would look like. I don't know if we want to link to the endpoint, Elixir's Registry or what else, but we just need a bit more context here. :)
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Makes sense! I added a link to https://hexdocs.pm/phoenix_pubsub/2.1.3/Phoenix.PubSub.html#module-custom-dispatching
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josevalim
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Hi there!
I've started a discussion in the Elixir forum about this change but then I noticed that the change in the end was pretty straightforward so I decided to open a PR as well.
If someone is using a non-standard metadata when subscribing to the topic it’s not possible to specify a custom dispatcher module. It will always use the
Phoenix.Channel.Server.dispatch/3function.At Realtime we use a custom metadata but our custom dispatcher can't be used as
Phoenix.Presencealways usePhoenix.Channel.Serveras dispatcher. We considered having our ownPresencemodule but it felt heavy handed given that we only needed a custom dispatcher in the end.Can totally understand if we don't want to expose this as a function but I thought I would try anyway 😅