Send subscription confirmation from server to the client to avoid race conditions.

Without this, it's very easy to send messages over a subscription even before the
redis pubsub has been fully initialized.

Now we delay calling the subscription#connected method on the client side until we
receive a subscription confirmation message from the server.

1 files changed, 9 insertions, 3 deletions

diff --git a/lib/action_cable/channel/streams.rb b/lib/action_cable/channel/streams.rb
index 9fffdf1789..b5ffa17f72 100644
--- a/lib/action_cable/channel/streams.rb
+++ b/lib/action_cable/channel/streams.rb
@@ -69,12 +69,18 @@ module ActionCable
       # 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)
+        # Hold off the confirmation until pubsub#subscribe is successful
+        defer_subscription_confirmation!
 
+        callback ||= default_stream_callback(broadcasting)
         streams << [ broadcasting, callback ]
-        EM.next_tick { pubsub.subscribe broadcasting, &callback }
 
-        logger.info "#{self.class.name} is streaming from #{broadcasting}"
+        EM.next_tick do
+          pubsub.subscribe(broadcasting, &callback).callback do |reply|
+            transmit_subscription_confirmation
+            logger.info "#{self.class.name} is streaming from #{broadcasting}"
+          end
+        end
       end
 
       # Start streaming the pubsub queue for the <tt>model</tt> in this channel. Optionally, you can pass a