Rack middleware is a simply bigger thing then rails. It’s look-alike rack application that you can use to filter, process, or otherwise mess with responses.There is middleware like warden - devise, to work on catch and log exceptions, deal with cookies, SSO, and pretty much anything else you can think of. And in case you missed it, rails is a rack application. Create a new rails app and run

{% highlight ruby %} rake middleware {% endhighlight %}

It will display results like this :

{% highlight ruby %} use Rack::Cors use Rack::Sendfile use ActionDispatch::Static use Rack::Lock use #ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x00000007238168 use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::Migration::CheckPending use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use Remotipart::Middleware use Rack::Head use Rack::ConditionalGet use Rack::ETag run Banana::Application.routes {% endhighlight %}

Okay so what’s the problem?

let’s you have an middleware say AwesomeMe. The AwesomeMe is calculated after the response time is injected, so that’s fine (imagine if the etag middleware was at the bottom). What about poor ExceptionNotifier? What if there is an exception thrown in the ResponseTimeInjector or AwesomeMe middleware? ExceptionNotifier isn’t going to catch it! The ExceptionNotifier middleware doesn’t modify anything in the response, so it needs to be up higher; it needs to be first.

Solution

You can add a new middleware to the middleware stack using any of the following methods:

• config.middleware.use(new_middleware, args) - Adds the new middleware at the bottom of the middleware stack.

• config.middleware.insert_before(existing_middleware, new_middleware, args) - Adds the new middleware before the specified existing middleware in the middleware stack.

• config.middleware.insert_after(existing_middleware, new_middleware, args) - Adds the new middleware after the specified existing middleware in the middleware stack.

{% highlight ruby %}

config/application.rb

Push Rack::BounceFavicon at the bottom

config.middleware.use Rack::BounceFavicon

Add Lifo::Cache after ActiveRecord::QueryCache.

Pass { page_cache: false } argument to Lifo::Cache.

config.middleware.insert_after ActiveRecord::QueryCache, Lifo::Cache, page_cache: false {% endhighlight %}

And if you get stuck… Ask Here

^{email me rajeevsharma86@gmail.com}