Add Socket#raw_transmit to push data without encoding it

lib/async/cable/socket.rb

@@ -68,6 +68,12 @@ def transmit(data)
 				@output.push(@coder.encode(data))
 			end
 
+			# Enqueue an already-encoded message for asynchronous delivery to the client, bypassing the coder. Useful for "fastlane" broadcasts where the payload is encoded once and shared across many connections.
+			# @parameter data [String] The pre-encoded message to transmit.
+			def raw_transmit(data)
+				@output.push(data)
+			end
+
 			# Close the outbound queue, causing the drain task to terminate once all pending messages have been sent.
 			def close
 				# Console.info(self, "Closing socket.", task: Async::Task.current?)

releases.md

@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Add {ruby Async::Cable::Socket#raw_transmit} for pushing pre-encoded payloads to the client without re-encoding. Enables "fastlane" broadcasts that encode the message once and share it across many connections.
+
 ## v0.3.0
 
   - Filter requests based on path - don't eat all inbound WebSocket connections.

test/async/cable/socket.rb

@@ -56,6 +56,29 @@ def fake_application.env_config; {"rails.test" => true}; end
 		end
 	end
 
+	with "#transmit" do
+		it "encodes data using the coder before enqueueing it" do
+			socket.transmit({type: "ping"})
+			expect(socket.instance_variable_get(:@output).pop).to be == ActiveSupport::JSON.encode({type: "ping"})
+		end
+	end
+
+	with "#raw_transmit" do
+		it "enqueues the data verbatim without encoding it" do
+			payload = ActiveSupport::JSON.encode({type: "ping"})
+			socket.raw_transmit(payload)
+			expect(socket.instance_variable_get(:@output).pop).to be_equal(payload)
+		end
+
+		it "cannot raw_transmit after close" do
+			socket.close
+
+			expect do
+				socket.raw_transmit("already encoded")
+			end.to raise_exception(ClosedQueueError)
+		end
+	end
+
 	with "#run" do
 		include Sus::Fixtures::Async::ReactorContext