Call 'exhausted' worker method after retries

When the maximum number of retries is hit and the message is about
to be thrown away, give the option of allowing the worker to say
goodbye by defining an 'exhausted' method on the worker.

lib/sidekiq/middleware/server/retry_jobs.rb

@@ -14,7 +14,8 @@ module Sidekiq
       # 3. after a few days, a developer deploys a fix.  the message is
       #    reprocessed successfully.
       # 4. if 3 never happens, sidekiq will eventually give up and throw the
-      #    message away.
+      #    message away. If the worker defines a method called 'exhausted', this
+      #    will be called before throwing the message away.
       #
       # A message looks like:
       #
@@ -82,8 +83,10 @@ module Sidekiq
             end
           else
             # Goodbye dear message, you (re)tried your best I'm sure.
+            worker.exhausted(*msg['args']) if worker.respond_to?(:exhausted)
             logger.debug { "Dropping message after hitting the retry maximum: #{msg}" }
           end
+
           raise e
         end
 

test/test_retry.rb

@@ -167,6 +167,18 @@ class TestRetry < MiniTest::Unit::TestCase
       # MiniTest can't assert that a method call did NOT happen!?
       assert_raises(MockExpectationError) { @redis.verify }
     end
+
+    it 'calls exhausted method on worker after too many retries if available' do
+      msg = {"class"=>"Bob", "args"=>[1, 2, "foo"], "queue"=>"default", "error_message"=>"kerblammo!", "error_class"=>"RuntimeError", "failed_at"=>Time.now.utc, "retry"=>3, "retry_count"=>3}
+      worker = MiniTest::Mock.new
+      worker.expect :exhausted, true, [1, 2, "foo"]
+      handler = Sidekiq::Middleware::Server::RetryJobs.new
+      assert_raises RuntimeError do
+        handler.call(worker, msg, 'default') do
+          raise "kerblammo!"
+        end
+      end
+    end
   end
 
   describe 'poller' do