Add Channel model to track subscribers

app/models/solid_cable/channel.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module SolidCable
+  class Channel < SolidCable::Record
+    scope :for, ->(channel) { where(channel_hash: channel_hash_for(channel)) }
+
+    def increment_subscribers!
+      update!(subscribers: subscribers + 1)
+    end
+
+    def decrement_subscribers!
+      update!(subscribers: [ subscribers - 1, 0 ].max)
+    end
+  end
+end

app/models/solid_cable/channel_hash.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module ChannelHash
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def channel_hashes_for(channels)
+      channels.map { |channel| channel_hash_for(channel) }
+    end
+
+    # Need to unpack this as a signed integer since Postgresql and SQLite
+    # don't support unsigned integers
+    def channel_hash_for(channel)
+      Digest::SHA256.digest(channel.to_s).unpack1("q>")
+    end
+  end
+end

app/models/solid_cable/message.rb

@@ -2,6 +2,9 @@
 
 module SolidCable
   class Message < SolidCable::Record
+    has_one :channel_record, class_name: "::SolidCable::Channel",
+      foreign_key: :channel_hash, primary_key: :channel_hash
+
     scope :trimmable, lambda {
       where(created_at: ...::SolidCable.message_retention.ago)
     }
@@ -14,16 +17,8 @@ class << self
       def broadcast(channel, payload)
         insert({ created_at: Time.current, channel:, payload:,
           channel_hash: channel_hash_for(channel) })
-      end
-
-      def channel_hashes_for(channels)
-        channels.map { |channel| channel_hash_for(channel) }
-      end
 
-      # Need to unpack this as a signed integer since Postgresql and SQLite
-      # don't support unsigned integers
-      def channel_hash_for(channel)
-        Digest::SHA256.digest(channel.to_s).unpack1("q>")
+        channel_record&.subscribers.to_i
       end
     end
   end

app/models/solid_cable/record.rb

@@ -2,6 +2,8 @@
 
 module SolidCable
   class Record < ActiveRecord::Base
+    include ChannelHash
+
     self.abstract_class = true
 
     connects_to(**SolidCable.connects_to) if SolidCable.connects_to.present?

lib/action_cable/subscription_adapter/solid_cable.rb

@@ -15,9 +15,9 @@ def initialize(*)
       end
 
       def broadcast(channel, payload)
-        ::SolidCable::Message.broadcast(channel, payload)
-
-        ::SolidCable::TrimJob.perform_now if ::SolidCable.autotrim?
+        ::SolidCable::Message.broadcast(channel, payload).tap do
+          ::SolidCable::TrimJob.perform_now if ::SolidCable.autotrim?
+        end
       end
 
       def subscribe(channel, callback, success_callback = nil)
@@ -64,11 +64,13 @@ def shutdown
 
           def add_channel(channel, on_success)
             channels.add(channel)
+            ::SolidCable::Channel.for(channel).first_or_create.increment_subscribers!
             event_loop.post(&on_success) if on_success
           end
 
           def remove_channel(channel)
             channels.delete(channel)
+            ::SolidCable::Channel.for(channel).first_or_create.decrement_subscribers!
           end
 
           def invoke_callback(*)

lib/generators/solid_cable/add_channels/USAGE

@@ -0,0 +1,5 @@
+Description:
+    Adds Solid Cable channel migration
+
+Example:
+    bin/rails generate solid_cable:add_channels

lib/generators/solid_cable/add_channels/add_channels_generator.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require "rails/generators"
+require "rails/generators/active_record"
+
+class SolidCable::AddChannelsGenerator < Rails::Generators::Base
+  include ActiveRecord::Generators::Migration
+
+  source_root File.expand_path("templates", __dir__)
+
+  def copy_files
+    migration_template "db/migrate/create_channels.rb",
+                       "db/cable_migrate/create_channels.rb"
+  end
+end

lib/generators/solid_cable/add_channels/templates/db/migrate/create_channels.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class CreateChannels < ActiveRecord::Migration[7.2]
+  def change
+    create_table "solid_cable_channels", force: :cascade do |t|
+      t.integer "channel_hash", limit: 8, null: false
+      t.integer "subscribers", default: 0, null: false
+      t.datetime "created_at", null: false
+      t.index ["channel_hash"], name: "index_solid_cable_channels_on_channel_hash"
+    end
+  end
+end

lib/tasks/solid_cable_tasks.rake

@@ -9,4 +9,8 @@ namespace :solid_cable do
   task :update do
     Rails::Command.invoke :generate, [ "solid_cable:update" ]
   end
+
+  task :add_channels do
+    Rails::Command.invoke :generate, [ "solid_cable:add_channels" ]
+  end
 end

test/dummy/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2024_09_12_130854) do
+ActiveRecord::Schema[7.2].define(version: 2024_10_11_202426) do
   create_table "solid_cable_messages", force: :cascade do |t|
     t.binary "channel", limit: 1024, null: false
     t.binary "payload", limit: 536870912, null: false
@@ -20,4 +20,11 @@
     t.index ["channel_hash"], name: "index_solid_cable_messages_on_channel_hash"
     t.index ["created_at"], name: "index_solid_cable_messages_on_created_at"
   end
+
+  create_table "solid_cable_channels", force: :cascade do |t|
+    t.integer "channel_hash", limit: 8, null: false
+    t.integer "subscribers", default: 0, null: false
+    t.datetime "created_at", null: false
+    t.index ["channel_hash"], name: "index_solid_cable_channels_on_channel_hash"
+  end
 end