Cable message encoding

* Introduce a connection coder responsible for encoding Cable messages
  as WebSocket messages, defaulting to `ActiveSupport::JSON` and duck-
  typing to any object responding to `#encode` and `#decode`.
* Consolidate encoding responsibility to the connection. No longer
  explicitly JSON-encode from channels or other sources. Pass Cable
  messages as Hashes to `#transmit` and rely on it to encode.
* Introduce stream encoders responsible for decoding pubsub messages.
  Preserve the currently raw encoding, but make it easy to use JSON.
  Same duck type as the connection encoder.
* Revert recent data normalization/quoting (#23649) which treated
  `identifier` and `data` values as nested JSON objects rather than as
  opaque JSON-encoded strings. That dealt us an awkward hand where we'd
  decode JSON strings… or not, but always encode as JSON. Embedding
  JSON object values directly is preferably, no extra JSON encoding,
  but that should be a purposeful protocol version change rather than
  ambiguously, inadvertently supporting multiple message formats.

1 files changed, 10 insertions, 9 deletions

diff --git a/actioncable/lib/action_cable/server/broadcasting.rb b/actioncable/lib/action_cable/server/broadcasting.rb
index 98025f27f2..8f93564113 100644
--- a/actioncable/lib/action_cable/server/broadcasting.rb
+++ b/actioncable/lib/action_cable/server/broadcasting.rb
@@ -19,27 +19,28 @@ module ActionCable
     #       new Notification data['title'], body: data['body']
     module Broadcasting
       # Broadcast a hash directly to a named <tt>broadcasting</tt>. This will later be JSON encoded.
-      def broadcast(broadcasting, message)
-        broadcaster_for(broadcasting).broadcast(message)
+      def broadcast(broadcasting, message, coder: ActiveSupport::JSON)
+        broadcaster_for(broadcasting, coder: coder).broadcast(message)
       end
 
       # Returns a broadcaster for a named <tt>broadcasting</tt> that can be reused. Useful when you have an object that
       # may need multiple spots to transmit to a specific broadcasting over and over.
-      def broadcaster_for(broadcasting)
-        Broadcaster.new(self, String(broadcasting))
+      def broadcaster_for(broadcasting, coder: ActiveSupport::JSON)
+        Broadcaster.new(self, String(broadcasting), coder: coder)
       end
 
       private
         class Broadcaster
-          attr_reader :server, :broadcasting
+          attr_reader :server, :broadcasting, :coder
 
-          def initialize(server, broadcasting)
-            @server, @broadcasting = server, broadcasting
+          def initialize(server, broadcasting, coder:)
+            @server, @broadcasting, @coder = server, broadcasting, coder
           end
 
           def broadcast(message)
-            server.logger.info "[ActionCable] Broadcasting to #{broadcasting}: #{message}"
-            server.pubsub.broadcast broadcasting, ActiveSupport::JSON.encode(message)
+            server.logger.info "[ActionCable] Broadcasting to #{broadcasting}: #{message.inspect}"
+            encoded = coder ? coder.encode(message) : message
+            server.pubsub.broadcast broadcasting, encoded
           end
         end
     end