1 files changed, 95 insertions, 0 deletions
diff --git a/actioncable/app/javascript/action_cable/connection_monitor.js b/actioncable/app/javascript/action_cable/connection_monitor.js
new file mode 100644
index 0000000000..0cc675fa94
--- /dev/null
+++ b/actioncable/app/javascript/action_cable/connection_monitor.js
@@ -0,0 +1,95 @@
+# Responsible for ensuring the cable connection is in good health by validating the heartbeat pings sent from the server, and attempting
+# revival reconnections if things go astray. Internal class, not intended for direct user manipulation.
+class ActionCable.ConnectionMonitor
+  @pollInterval:
+    min: 3
+    max: 30
+
+  @staleThreshold: 6 # Server::Connections::BEAT_INTERVAL * 2 (missed two pings)
+
+  constructor: (@connection) ->
+    @reconnectAttempts = 0
+
+  start: ->
+    unless @isRunning()
+      @startedAt = now()
+      delete @stoppedAt
+      @startPolling()
+      document.addEventListener("visibilitychange", @visibilityDidChange)
+      ActionCable.log("ConnectionMonitor started. pollInterval = #{@getPollInterval()} ms")
+
+  stop: ->
+    if @isRunning()
+      @stoppedAt = now()
+      @stopPolling()
+      document.removeEventListener("visibilitychange", @visibilityDidChange)
+      ActionCable.log("ConnectionMonitor stopped")
+
+  isRunning: ->
+    @startedAt? and not @stoppedAt?
+
+  recordPing: ->
+    @pingedAt = now()
+
+  recordConnect: ->
+    @reconnectAttempts = 0
+    @recordPing()
+    delete @disconnectedAt
+    ActionCable.log("ConnectionMonitor recorded connect")
+
+  recordDisconnect: ->
+    @disconnectedAt = now()
+    ActionCable.log("ConnectionMonitor recorded disconnect")
+
+  # Private
+
+  startPolling: ->
+    @stopPolling()
+    @poll()
+
+  stopPolling: ->
+    clearTimeout(@pollTimeout)
+
+  poll: ->
+    @pollTimeout = setTimeout =>
+      @reconnectIfStale()
+      @poll()
+    , @getPollInterval()
+
+  getPollInterval: ->
+    {min, max} = @constructor.pollInterval
+    interval = 5 * Math.log(@reconnectAttempts + 1)
+    Math.round(clamp(interval, min, max) * 1000)
+
+  reconnectIfStale: ->
+    if @connectionIsStale()
+      ActionCable.log("ConnectionMonitor detected stale connection. reconnectAttempts = #{@reconnectAttempts}, pollInterval = #{@getPollInterval()} ms, time disconnected = #{secondsSince(@disconnectedAt)} s, stale threshold = #{@constructor.staleThreshold} s")
+      @reconnectAttempts++
+      if @disconnectedRecently()
+        ActionCable.log("ConnectionMonitor skipping reopening recent disconnect")
+      else
+        ActionCable.log("ConnectionMonitor reopening")
+        @connection.reopen()
+
+  connectionIsStale: ->
+    secondsSince(@pingedAt ? @startedAt) > @constructor.staleThreshold
+
+  disconnectedRecently: ->
+    @disconnectedAt and secondsSince(@disconnectedAt) < @constructor.staleThreshold
+
+  visibilityDidChange: =>
+    if document.visibilityState is "visible"
+      setTimeout =>
+        if @connectionIsStale() or not @connection.isOpen()
+          ActionCable.log("ConnectionMonitor reopening stale connection on visibilitychange. visbilityState = #{document.visibilityState}")
+          @connection.reopen()
+      , 200
+
+  now = ->
+    new Date().getTime()
+
+  secondsSince = (time) ->
+    (now() - time) / 1000
+
+  clamp = (number, min, max) ->
+    Math.max(min, Math.min(max, number))