title: How to detect if ActionCable subscription request failed
body: <p>I've recently deployed a Rails app, and have heard back from a few users that it doesn't work in their work environments. It's clear that Websockets are blocked for them.</p>
  
  <p>I've hunted through the Rails documentation on this but can't find any information on how to go about detecting if this has happened. My best guess would be to send an AJAX request out for an ActionCable broadcast, and when that broadcast is not received after a certain timeout, to conclude that Websockets must be blocked.</p>
  
  <p>Are there any easy answers here, perhaps already part of the Rails API, to determine Websocket connectivity?</p>