How do I find out who is connected to ActionCable?

Question

I have seen ActionCable.server.open_connections_statistics, ActionCable.server.connections.length, ActionCable.server.connections.map(&:s

Answer 1

To be more specific for ActionCable (and to Redis)...

Assuming this channel:

class RoomChannel < ApplicationCable::Channel
end

Get the Redis adapter from ActionCable instead of creating it yourself (you'd need to supply the URL from config/cable.yml otherwise):

pubsub = ActionCable.server.pubsub

Get the channel's name including channel_prefix you may have specified in config/cable.yml:

channel_with_prefix = pubsub.send(:channel_with_prefix, RoomChannel.channel_name)

Get all connected channels from RoomChannel:

# pubsub.send(:redis_connection) actually returns the Redis instance ActionCable uses
channels = pubsub.send(:redis_connection).
  pubsub('channels', "#{channel_with_prefix}:*")

Decode the subscription name:

subscriptions = channels.map do |channel|
   Base64.decode64(channel.match(/^#{Regexp.escape(channel_with_prefix)}:(.*)$/)[1])
end

If you are subscribed to an ActiveRecord object, let's say Room (using stream_for), you can extract the IDs:

# the GID URI looks like that: gid://<app-name>/<ActiveRecordName>/<id>
gid_uri_pattern = /^gid:\/\/.*\/#{Regexp.escape(Room.name)}\/(\d+)$/
chat_ids = subscriptions.map do |subscription|
  subscription.match(gid_uri_pattern)
  # compacting because 'subscriptions' include all subscriptions made from RoomChannel,
  # not just subscriptions to Room records
end.compact.map { |match| match[1] }

Answer 2

If using redis you can see all the pubsub channels.

[2] pry(main)> Redis.new.pubsub("channels", "action_cable/*")
[
    [0] "action_cable/Z2lkOi8vbWFvY290LXByb2plL3QvUmVzcG9uXGVyLzEx",
    [1] "action_cable/Z2lkOi8vbWFvY290LXByb2plL3QvUmVzcG9uXGVyLzI"
]

This will show all websocket connections for all the Puma workers together. And if you have multiple servers it will probably show those here too.