Add chain#add_before and chain#add_after to facilitate insertion into the middle of the Middleware chains.

lib/sidekiq/middleware/chain.rb

@@ -23,6 +23,22 @@ module Sidekiq
   #   end
   # end
   #
+  # To insert immediately preceding another entry:
+  #
+  # Sidekiq.configure_client do |config|
+  #   config.client_middleware do |chain|
+  #     chain.add_before ActiveRecord, MyClientHook
+  #   end
+  # end
+  #
+  # To insert immediately after another entry:
+  #
+  # Sidekiq.configure_client do |config|
+  #   config.client_middleware do |chain|
+  #     chain.add_after ActiveRecord, MyClientHook
+  #   end
+  # end
+  #
   # This is an example of a minimal server middleware:
   #
   # class MyServerHook
@@ -60,6 +76,16 @@ module Sidekiq
         entries << Entry.new(klass, *args) unless exists?(klass)
       end
 
+      def add_before(oldklass, newklass, *args)
+        i = entries.find_index { |entry| entry.klass == oldklass } || 0
+        entries.insert(i, Entry.new(klass, *args)) unless exists?(klass)
+      end
+
+      def add_after(oldklass, newklass, *args)
+        i = entries.find_index { |entry| entry.klass == oldklass } || entries.count - 1
+        entries.insert(i+1, Entry.new(klass, *args)) unless exists?(klass)
+      end
+
       def exists?(klass)
         entries.any? { |entry| entry.klass == klass }
       end

test/test_middleware.rb

@@ -41,6 +41,32 @@ class TestMiddleware < MiniTest::Unit::TestCase
       def call(*args)
       end
     end
+    
+    class AnotherCustomMiddleware
+      def initialize(name, recorder)
+        @name = name
+        @recorder = recorder
+      end
+
+      def call(*args)
+        @recorder << [@name, 'before']
+        yield
+        @recorder << [@name, 'after']
+      end
+    end
+
+    class YetAnotherCustomMiddleware
+      def initialize(name, recorder)
+        @name = name
+        @recorder = recorder
+      end
+
+      def call(*args)
+        @recorder << [@name, 'before']
+        yield
+        @recorder << [@name, 'after']
+      end
+    end
 
     it 'executes middleware in the proper order' do
       msg = Sidekiq.dump_json({ 'class' => CustomWorker.to_s, 'args' => [$recorder] })
@@ -48,6 +74,8 @@ class TestMiddleware < MiniTest::Unit::TestCase
       Sidekiq.server_middleware do |chain|
         # should only add once, second should be ignored
         2.times { |i| chain.add CustomMiddleware, i.to_s, $recorder }
+        chain.add_before CustomMiddleware, AnotherCustomMiddleware, '2', $recorder
+        chain.add_after AnotherCustomMiddleware, YetAnotherCustomMiddleware, '3', $recorder
       end
 
       boss = MiniTest::Mock.new
@@ -56,7 +84,7 @@ class TestMiddleware < MiniTest::Unit::TestCase
       actor.expect(:processor_done, nil, [processor])
       boss.expect(:async, actor, [])
       processor.process(msg, 'default')
-      assert_equal %w(0 before work_performed 0 after), $recorder.flatten
+      assert_equal %w(2 before 3 before 0 before work_performed 0 after 3 after 2 after), $recorder.flatten
     end
 
     it 'allows middleware to abruptly stop processing rest of chain' do