title: Adding a custom middleware to Rails 4
body: <p>I have a Rails 4 sample project (Blog) and I have created a simple middleware called 'request_timer' in <code>config/initializers/request_timer.rb</code></p>
  
  <pre><code>  #config/initializers/request_timer.rb
    class RequestTimer                                                                                                                                         
  
      def initialize(app)                                                                                                                                      
       @app = app                                                                                                                                              
      end                                                                                                                                                      
  
      def call(env)                                                                                                                                            
        start_time = Time.now                                                                                                                                  
        status, headers, response = @app.call(env)                                                                                                             
        stop_time = Time.now                                                                                                                                   
        [status, headers, response.body]                                                                                                                       
      end                                                                                                                                                      
  
    end 
  </code></pre>
  
  <p>and I have added my middleware in <code>config/application.rb</code> in two ways</p>
  
  <p><strong>1 ) Adding as a constant</strong></p>
  
  <pre><code>#config/application.rb
  module Blog                                                                                                                                                  
    class Application &lt; Rails::Application                                                                                                                     
      config.middleware.use RequestTimer                                                                                                                       
    end                                                                                                                                                        
  end
  </code></pre>
  
  <p>this way when I try to run my rails app I'm getting the error </p>
  
  <pre><code>/Users/sameera/workspace/ruby-rack/blog/config/application.rb:9:in `require': cannot load such file -- request_timer (LoadError)
      from /Users/sameera/workspace/ruby-rack/blog/config/application.rb:9:in `&lt;top (required)&gt;'
      from /Users/sameera/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.2/lib/rails/commands.rb:74:in `require'
      from /Users/sameera/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.2/lib/rails/commands.rb:74:in `block in &lt;top (required)&gt;'
      from /Users/sameera/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.2/lib/rails/commands.rb:71:in `tap'
      from /Users/sameera/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.2/lib/rails/commands.rb:71:in `&lt;top (required)&gt;'
      from bin/rails:4:in `require'
      from bin/rails:4:in `&lt;main&gt;'
  </code></pre>
  
  <p><strong>2 ) Then I added my middleware as a string</strong></p>
  
  <pre><code>#config/application.rb
  module Blog                                                                                                                                                  
    class Application &lt; Rails::Application                                                                                                                     
      config.middleware.use "RequestTimer"                                                                                                                       
    end                                                                                                                                                        
  end
  </code></pre>
  
  <p>This ways, it allows me to run the rails server, but when I access <code>localhost:3000</code>, it errors saying</p>
  
  <pre><code>NoMethodError (undefined method `each' for #&lt;String:0x007fdf649b0028&gt;):
    rack (1.5.2) lib/rack/etag.rb:58:in `digest_body'
    rack (1.5.2) lib/rack/etag.rb:26:in `call'
    rack (1.5.2) lib/rack/conditionalget.rb:25:in `call'
    rack (1.5.2) lib/rack/head.rb:11:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/flash.rb:241:in `call'
    rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
    rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/cookies.rb:486:in `call'
    activerecord (4.0.2) lib/active_record/query_cache.rb:36:in `call'
    activerecord (4.0.2) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
    activerecord (4.0.2) lib/active_record/migration.rb:369:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
    activesupport (4.0.2) lib/active_support/callbacks.rb:373:in `_run__2755475928771109453__call__callbacks'
    activesupport (4.0.2) lib/active_support/callbacks.rb:80:in `run_callbacks'
    actionpack (4.0.2) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/reloader.rb:64:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
    railties (4.0.2) lib/rails/rack/logger.rb:38:in `call_app'
    railties (4.0.2) lib/rails/rack/logger.rb:20:in `block in call'
    activesupport (4.0.2) lib/active_support/tagged_logging.rb:67:in `block in tagged'
    activesupport (4.0.2) lib/active_support/tagged_logging.rb:25:in `tagged'
    activesupport (4.0.2) lib/active_support/tagged_logging.rb:67:in `tagged'
    railties (4.0.2) lib/rails/rack/logger.rb:20:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/request_id.rb:21:in `call'
    rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
    rack (1.5.2) lib/rack/runtime.rb:17:in `call'
    activesupport (4.0.2) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
    rack (1.5.2) lib/rack/lock.rb:17:in `call'
    actionpack (4.0.2) lib/action_dispatch/middleware/static.rb:64:in `call'
    rack (1.5.2) lib/rack/sendfile.rb:112:in `call'
    railties (4.0.2) lib/rails/engine.rb:511:in `call'
    railties (4.0.2) lib/rails/application.rb:97:in `call'
    rack (1.5.2) lib/rack/lock.rb:17:in `call'
    rack (1.5.2) lib/rack/content_length.rb:14:in `call'
    rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service'
    /Users/sameera/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
    /Users/sameera/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
    /Users/sameera/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'
  </code></pre>
  
  <p>What would be the reason? I'm using Rails <code>4.0.2</code> and <code>rack-1.5.2</code> and <code>ruby 2.0.0p247</code>.</p>