Live Visit Count for website or page. ActionCable, Turbo Broadcasts, Kredis

It’s amazing that now you can add advanced javascript/websockets features like “Live visitor count” without writing a single extra line of javascript!

A “live visitor count” feature can give users a “you are not alone” feeling. For example, when watching a live stream on youtube:

Another example - see other people that have the same google doc open:

“live visitor count” can also boost urgency (booking website example):

By the end of this article you will have created:

• live counter of all visitors on the app
• live conter of all visitors on a specific page or “inside a Room” (like google doc or youtube live video)

Explanation of the above GIF:

• I have 2 browsers open. Each browser = different session.
• When I open the website in the second browser, the visitor count goes from 1 to 2.
• If the user closes the browser tab, visitor count will decrease by 1.
• When I open a specific Room page, the visitor count goes from 1 to 2 for this particular Room.
• If a user leaves the Room (closes tab or redirects), visitor count will decrease by 1.

Technologies we will need to implement the “live visitor count”:

• ActionCable - the core technology, that lets us to establish a websockets connection, and see if a user connected or disconnected.
• turbo/streams_channel.rb - a way to link a turbo stream with an ActionCable channel.
• gem Kredis - a Redis adapter for Rails, where we will store the visitor ids (session_id).

1. Count all current visitors on your website

In this example we will not implement user authentication. We will identify separate users by sessions. One browser = one session.

To make session_id available within an ActionCable Channel, you have to add it inside Connection. The Connection has access to request and cookie data.

# app/channels/application_cable/connection.rb
module ApplicationCable
  class Connection < ActionCable::Connection::Base
    identified_by :session_user
    def connect
      self.session_user = request.session.id
    end
  end
end

Next, add a turbo_stream_from broadcast to your application layout.

Importantly, append the channel: VisitorChannel to connect to an ActionCable channel.

Add a placeholder div visitors-counter where we will update the number of current visitors.

# app/views/layouts/application.html.erb
<%= turbo_stream_from :visitors, channel: VisitorChannel %>

Current website visitors: 
<span id="visitors-counter"></span>

Create an action cable channel. Don’t use the generator, because you will not need the other extra files and code that rails g channel visitor would give you. It has to inherit from Turbo::StreamsChannel. Add super. That way you will have streams_form automatically imported. You will have access to verified_stream_name_from_params that is :visitors for our current case.

In this case verified_stream_name_from_params = :visitors.

Create a redis unique list and add the session_user on subscribed, remove the user on unsubscribed.

Send a turbo stream broadcast to update this count in everyones views with Turbo::StreamsChannel.broadcast_update_to.

# app/channels/visitor_channel.rb
# class VisitorChannel < ApplicationCable::Channel
class VisitorChannel < Turbo::StreamsChannel
  def subscribed
    super
    visitors_online = Kredis.unique_list "visitors_online"
    visitors_online << session_user
    update_visitors_count(visitors_online)
  end

  def unsubscribed
    visitors_online = Kredis.unique_list "visitors_online"
    visitors_online.remove session_user
    update_visitors_count(visitors_online)
  end

  private

  def update_visitors_count(visitors_online)
    Turbo::StreamsChannel.broadcast_update_to(
      verified_stream_name_from_params,
      target: 'visitors-counter',
      html: visitors_online.elements.count
    )
  end
end

Success! Now every visitor of your application will see the visitor count!

Try opening/closing pages in your app from 2 different browsers and see the visitor_count change.

2. Count current visitors on a specific page

Maybe a more useful feature would be to see the quantity of users on a specific page. For example, we have a scaffold of Room and each room has a #show page.

In this case we will pass an additional room_id param to the turbo_stream_from.

Make the target also unique based on the room_id:

# app/views/rooms/show.html.erb
<%= turbo_stream_from @room, channel: RoomChannel, params: { room_id: @room.id } %>
<%#= turbo_stream_from @room, channel: RoomChannel, data: { room_id: @room.id } %>

People inside this room: <span id="room-<%= params[:room_id]%>-counter"></span>

Now we can access params[:room_id] from our room_channel.rb:

# app/channels/room_channel.rb
class RoomChannel < Turbo::StreamsChannel
  def subscribed
    super
    room_visitors = Kredis.unique_list "room_visitors"
    room_visitors << session_user
    target = "room-#{params[:room_id]}-counter"
    update_visitors_count(room_visitors, target)
  end

  def unsubscribed
    room_visitors = Kredis.unique_list "room_visitors"
    room_visitors.remove session_user
    target = "room-#{params[:room_id]}-counter"
    update_visitors_count(room_visitors, target)
  end

  private

  def update_visitors_count(room_visitors, target)
    Turbo::StreamsChannel.broadcast_update_to(
      verified_stream_name_from_params,
      target:,
      html: room_visitors.elements.count
    )
  end
end

Success! Now when you open a specific room page, it will register a new connection. See the “People inside this room” counter get updated:

That’s it. See you in the next one!