Document the remaining parts of the Channel setup.

1 files changed, 47 insertions, 0 deletions

diff --git a/lib/action_cable/channel/streams.rb b/lib/action_cable/channel/streams.rb
index 9ff2f85fa1..6a3dc76c1d 100644
--- a/lib/action_cable/channel/streams.rb
+++ b/lib/action_cable/channel/streams.rb
@@ -1,5 +1,50 @@
 module ActionCable
   module Channel
+    # Streams allow channels to route broadcastings to the subscriber. A broadcasting is an discussed elsewhere a pub/sub queue where any data
+    # put into it is automatically sent to the clients that are connected at that time. It's purely an online queue, though. If you're not 
+    # streaming a broadcasting at the very moment it sends out an update, you'll not get that update when connecting later.
+    #
+    # Most commonly, the streamed broadcast is sent straight to the subscriber on the client-side. The channel just acts as a connector between
+    # the two parties (the broadcaster and the channel subscriber). Here's an example of a channel that allows subscribers to get all new
+    # comments on a given page:
+    #
+    #   class CommentsChannel < ApplicationCable::Channel
+    #     def follow(data)
+    #       stream_from "comments_for_#{data['recording_id']}"
+    #     end
+    #   
+    #     def unfollow
+    #       stop_all_streams
+    #     end
+    #   end
+    #
+    # So the subscribers of this channel will get whatever data is put into the, let's say, `comments_for_45` broadcasting as soon as it's put there.
+    # That looks like so from that side of things:
+    #
+    #   ActionCable.server.broadcast "comments_for_45", author: 'DHH', content: 'Rails is just swell'
+    #
+    # If you don't just want to parlay the broadcast unfiltered to the subscriber, you can supply a callback that let's you alter what goes out. 
+    # Example below shows how you can use this to provide performance introspection in the process:
+    #
+    #   class ChatChannel < ApplicationCable::Channel
+    #    def subscribed
+    #      @room = Chat::Room[params[:room_number]]
+    #  
+    #      stream_from @room.channel, -> (message) do
+    #        message = ActiveSupport::JSON.decode(m)
+    #  
+    #        if message['originated_at'].present?
+    #          elapsed_time = (Time.now.to_f - message['originated_at']).round(2)
+    #  
+    #          ActiveSupport::Notifications.instrument :performance, measurement: 'Chat.message_delay', value: elapsed_time, action: :timing
+    #          logger.info "Message took #{elapsed_time}s to arrive"
+    #        end
+    #  
+    #        transmit message
+    #      end
+    #    end
+    #
+    # You can stop streaming from all broadcasts by calling #stop_all_streams.
     module Streams
       extend ActiveSupport::Concern
 
@@ -7,6 +52,8 @@ module ActionCable
         on_unsubscribe :stop_all_streams
       end
 
+      # Start streaming from the named <tt>broadcasting</tt> pubsub queue. Optionally, you can pass a <tt>callback</tt> that'll be used
+      # instead of the default of just transmitting the updates straight to the subscriber.
       def stream_from(broadcasting, callback = nil)
         callback ||= default_stream_callback(broadcasting)