Add middleware to clear context after every Sidekiq job

The error handler is only called after an exception so the context will
carry over from previous jobs that completed successfully.

Fixes getsentry#636

Author: drewish

lib/raven/integrations/sidekiq.rb

@@ -2,7 +2,16 @@
 require 'sidekiq'
 
 module Raven
-  class Sidekiq
+  class SidekiqCleanupMiddleware
+    def call(_worker, _job, _queue)
+      yield
+    ensure
+      Context.clear!
+      BreadcrumbBuffer.clear!
+    end
+  end
+
+  class SidekiqErrorHandler
     ACTIVEJOB_RESERVED_PREFIX = "_aj_".freeze
 
     def call(ex, context)
@@ -13,9 +22,6 @@ def call(ex, context)
         :extra => { :sidekiq => context },
         :culprit => culprit_from_context(context)
       )
-    ensure
-      Context.clear!
-      BreadcrumbBuffer.clear!
     end
 
     private
@@ -59,6 +65,9 @@ def culprit_from_context(context)
 
 if Sidekiq::VERSION > '3'
   Sidekiq.configure_server do |config|
-    config.error_handlers << Raven::Sidekiq.new
+    config.error_handlers << Raven::SidekiqErrorHandler.new
+    config.server_middleware do |chain|
+      chain.add Raven::SidekiqCleanupMiddleware
+    end
   end
 end

spec/raven/integrations/sidekiq_spec.rb

@@ -1,7 +1,7 @@
 require 'spec_helper'
 require 'raven/integrations/sidekiq'
 
-describe Raven::Sidekiq do
+describe Raven::SidekiqErrorHandler do
   before(:all) do
     Raven.configure do |config|
       config.dsn = 'dummy://12345:67890@sentry.localdomain:3000/sentry/42'