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.

3 files changed, 12 insertions, 6 deletions

diff --git a/lib/assets/javascripts/cable.coffee b/lib/assets/javascripts/cable.coffee
index 0bd1757505..476d90ef72 100644
--- a/lib/assets/javascripts/cable.coffee
+++ b/lib/assets/javascripts/cable.coffee
@@ -3,6 +3,8 @@
 
 @Cable =
   PING_IDENTIFIER: "_ping"
+  INTERNAL_MESSAGES:
+    SUBSCRIPTION_CONFIRMATION: 'confirm_subscription'
 
   createConsumer: (url) ->
     new Cable.Consumer url
diff --git a/lib/assets/javascripts/cable/connection.coffee b/lib/assets/javascripts/cable/connection.coffee
index 90d8fac3e1..33159130c7 100644
--- a/lib/assets/javascripts/cable/connection.coffee
+++ b/lib/assets/javascripts/cable/connection.coffee
@@ -52,8 +52,14 @@ class Cable.Connection
 
   events:
     message: (event) ->
-      {identifier, message} = JSON.parse(event.data)
-      @consumer.subscriptions.notify(identifier, "received", message)
+      {identifier, message, type} = JSON.parse(event.data)
+
+      if type?
+        switch type
+          when Cable.INTERNAL_MESSAGES.SUBSCRIPTION_CONFIRMATION
+            @consumer.subscriptions.notify(identifier, "connected")
+      else
+        @consumer.subscriptions.notify(identifier, "received", message)
 
     open: ->
       @disconnected = false
diff --git a/lib/assets/javascripts/cable/subscriptions.coffee b/lib/assets/javascripts/cable/subscriptions.coffee
index eeaa697081..4efb384ee2 100644
--- a/lib/assets/javascripts/cable/subscriptions.coffee
+++ b/lib/assets/javascripts/cable/subscriptions.coffee
@@ -21,13 +21,11 @@ class Cable.Subscriptions
   add: (subscription) ->
     @subscriptions.push(subscription)
     @notify(subscription, "initialized")
-    if @sendCommand(subscription, "subscribe")
-      @notify(subscription, "connected")
+    @sendCommand(subscription, "subscribe")
 
   reload: ->
     for subscription in @subscriptions
-      if @sendCommand(subscription, "subscribe")
-        @notify(subscription, "connected")
+      @sendCommand(subscription, "subscribe")
 
   remove: (subscription) ->
     @subscriptions = (s for s in @subscriptions when s isnt subscription)