ActionCable should not raise when a connection is already open

[itsmeduncan]

ActionCable was throwing a "Existing connection must be closed before
opening" exception which was being picked up as a production issue in
our error monitoring software. Since this happens pretty often on any
device that allows the browser to sleep (mobile) this error was getting
triggered often.

This change removes the exception, but keeps logging the occurrence. We
now return false to let the caller now that open failed.

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @schneems (or someone else) soon.

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[itsmeduncan]

The discussion related to this change is #26503. Happy for some guidance on how to unit test this change.

[maclover7]

r? @javan

[itsmeduncan]

@javan Anything else needed here?

[javan]

Mind adding a test? This change should fail without your change and pass with it:

--- a/actioncable/test/javascript/src/unit/consumer_test.coffee
+++ b/actioncable/test/javascript/src/unit/consumer_test.coffee
@@ -2,9 +2,12 @@
 {consumerTest} = ActionCable.TestHelpers
 
 module "ActionCable.Consumer", ->
-  consumerTest "#connect", connect: false, ({consumer, server, done}) ->
-    server.on("connection", done)
-    consumer.connect()
+  consumerTest "#connect", connect: false, ({consumer, server, assert, done}) ->
+    server.on "connection", ->
+      assert.equal consumer.connect(), false
+      done()
+
+    assert.equal consumer.connect(), true

[itsmeduncan]

@javan What release of Rails was/will this be in?

[javan]

You can view the commit to see: 23e3e2b

[itsmeduncan]

Thanks! Looking forward to these errors being a little quieter.