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.

2 files changed, 23 insertions, 12 deletions

diff --git a/actioncable/test/stubs/test_connection.rb b/actioncable/test/stubs/test_connection.rb
index 8ba284fdc6..885450dda6 100644
--- a/actioncable/test/stubs/test_connection.rb
+++ b/actioncable/test/stubs/test_connection.rb
@@ -3,24 +3,31 @@ require 'stubs/user'
 class TestConnection
   attr_reader :identifiers, :logger, :current_user, :server, :transmissions
 
-  def initialize(user = User.new("lifo"))
+  delegate :pubsub, to: :server
+
+  def initialize(user = User.new("lifo"), coder: ActiveSupport::JSON, subscription_adapter: SuccessAdapter)
+    @coder = coder
     @identifiers = [ :current_user ]
 
     @current_user = user
     @logger = ActiveSupport::TaggedLogging.new ActiveSupport::Logger.new(StringIO.new)
-    @server = TestServer.new
+    @server = TestServer.new(subscription_adapter: subscription_adapter)
     @transmissions = []
   end
 
-  def pubsub
-    SuccessAdapter.new(server)
+  def transmit(cable_message)
+    @transmissions << encode(cable_message)
   end
 
-  def transmit(data)
-    @transmissions << data
+  def last_transmission
+    decode @transmissions.last if @transmissions.any?
   end
 
-  def last_transmission
-    @transmissions.last
+  def decode(websocket_message)
+    @coder.decode websocket_message
+  end
+
+  def encode(cable_message)
+    @coder.encode cable_message
   end
 end
diff --git a/actioncable/test/stubs/test_server.rb b/actioncable/test/stubs/test_server.rb
index 9e860825f3..b86f422a13 100644
--- a/actioncable/test/stubs/test_server.rb
+++ b/actioncable/test/stubs/test_server.rb
@@ -2,22 +2,26 @@ require 'ostruct'
 
 class TestServer
   include ActionCable::Server::Connections
+  include ActionCable::Server::Broadcasting
 
-  attr_reader :logger, :config
+  attr_reader :logger, :config, :mutex
 
-  def initialize
+  def initialize(subscription_adapter: SuccessAdapter)
     @logger = ActiveSupport::TaggedLogging.new ActiveSupport::Logger.new(StringIO.new)
-    @config = OpenStruct.new(log_tags: [], subscription_adapter: SuccessAdapter)
+
+    @config = OpenStruct.new(log_tags: [], subscription_adapter: subscription_adapter)
     @config.use_faye = ENV['FAYE'].present?
     @config.client_socket_class = if @config.use_faye
                                     ActionCable::Connection::FayeClientSocket
                                   else
                                     ActionCable::Connection::ClientSocket
                                   end
+
+     @mutex = Monitor.new
   end
 
   def pubsub
-    @config.subscription_adapter.new(self)
+    @pubsub ||= @config.subscription_adapter.new(self)
   end
 
   def event_loop