Retry if connection fails

README.md

@@ -86,6 +86,8 @@ The options are:
 - `silence_polling` - whether to silence Active Record logs emitted when polling (Defaults to true)
 - `use_skip_locked` - whether to use `FOR UPDATE SKIP LOCKED` when performing trimming. This will be automatically detected in the future, and for now, you'd only need to set this to `false` if your database doesn't support it. For MySQL, that'd be versions < 8, and for PostgreSQL, versions < 9.5. If you use SQLite, this has no effect, as writes are sequential. (Defaults to true)
 - `trim_batch_size` - the batch size to use when deleting old records (default: `100`)
+- `reconnect_attempts` - Supports a number of connection attempts or an array of
+  durations to wait between attempts. (Defaults to 1 retry attempt)
 
 
 ## Trimming

lib/action_cable/subscription_adapter/solid_cable.rb

@@ -39,6 +39,7 @@ def listener
         end
 
         class Listener < ::ActionCable::SubscriptionAdapter::SubscriberMap
+          CONNECTION_ERRORS = [ ActiveRecord::ConnectionFailed ]
           Stop = Class.new(Exception)
 
           def initialize(event_loop)
@@ -51,11 +52,17 @@ def initialize(event_loop)
             # for specific sections of code, rather than acquired.
             @critical = Concurrent::Semaphore.new(0)
 
+            @reconnect_attempt = 0
+
             @thread = Thread.new do
               Thread.current.name = "solid_cable_listener"
               Thread.current.report_on_exception = true
 
-              listen
+              begin
+                listen
+              rescue *CONNECTION_ERRORS
+                retry if retry_connecting?
+              end
             end
           end
 
@@ -107,6 +114,7 @@ def invoke_callback(*)
           private
             attr_reader :event_loop, :thread
             attr_writer :last_id
+            attr_accessor :reconnect_attempt
 
             def last_id
               @last_id ||= last_message_id
@@ -146,6 +154,22 @@ def with_polling_volume
                 yield
               end
             end
+
+            def reconnect_attempts
+              @reconnect_attempts ||= ::SolidCable.reconnect_attempts
+            end
+
+            def retry_connecting?
+              self.reconnect_attempt += 1
+
+              return false if reconnect_attempt > reconnect_attempts.size
+
+              sleep_t = reconnect_attempts[reconnect_attempt - 1]
+
+              sleep(sleep_t) if sleep_t > 0
+
+              true
+            end
         end
     end
   end

lib/solid_cable.rb

@@ -48,6 +48,12 @@ def trim_chance
       2
     end
 
+    def reconnect_attempts
+      attempts = cable_config.fetch(:reconnect_attempts, 1)
+      attempts = Array.new(attempts, 0) if attempts.is_a?(Integer)
+      attempts
+    end
+
     private
       def cable_config
         Rails.application.config_for("cable")

test/lib/action_cable/subscription_adapter/solid_cable_test.rb

@@ -175,6 +175,30 @@ class ActionCable::SubscriptionAdapter::SolidCableTest < ActionCable::TestCase
     end
   end
 
+  test "retries after a connection failure and keeps listening" do
+    with_cable_config reconnect_attempts: [0] do
+      raised = false
+      original = SolidCable::Message.method(:broadcastable)
+
+      SolidCable::Message.stub(:broadcastable, lambda { |channels, last_id|
+        if raised
+          original.call(channels, last_id)
+        else
+          raised = true
+          raise ActiveRecord::ConnectionFailed, "boom"
+        end
+      }) do
+        subscribe_as_queue("reconnect-channel") do |queue|
+          @tx_adapter.broadcast("reconnect-channel", "hello")
+
+          assert_equal "hello", next_message_in_queue(queue)
+        end
+      end
+
+      assert raised
+    end
+  end
+
   private
     def cable_config
       { adapter: "solid_cable", message_retention: "1.second",

test/solid_cable_test.rb

@@ -46,4 +46,20 @@ class SolidCableTest < ActiveSupport::TestCase
       assert_equal 42, SolidCable.trim_batch_size
     end
   end
+
+  test "reconnect_attempts defaults to a single zero" do
+    assert_equal [ 0 ], SolidCable.reconnect_attempts
+  end
+
+  test "reconnect_attempts accepts an integer" do
+    with_cable_config reconnect_attempts: 3 do
+      assert_equal [ 0, 0, 0 ], SolidCable.reconnect_attempts
+    end
+  end
+
+  test "reconnect_attempts accepts an array" do
+    with_cable_config reconnect_attempts: [ 0, 1, 2 ] do
+      assert_equal [ 0, 1, 2 ], SolidCable.reconnect_attempts
+    end
+  end
 end