#319 Rails Middleware Walkthrough pro

Jan 23, 2012 | 14 minutes | Rack, Code Walkthrough

Here I describe each Rack middleware that is included in a Rails app which will give you a better understanding of what a request goes through behind the scenes before it hits your application.

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Resources

Middleware

ActionDispatch::Static serves static files under "public" directory
Rack::Lock locks the rest of the application to a single thread
ActiveSupport::Cache::Strategy::LocalCache::Middleware flushes memory based store used internally by Rails.cache
Rack::Runtime adds X-Runtime to response header providing number of seconds to process rest of the app
Rack::MethodOverride sets the HTTP request method based on _method parameter
ActionDispatch::RequestId assigns a unique id to the request and adds X-Request-Id response header
Rails::Rack::Logger logs beginning of request and flushes log after request
ActionDispatch::ShowExceptions and ActionDispatch::DebugExceptions catch exceptions and display them on a pretty page
ActionDispatch::RemoteIp captures the remote IP address for later use
ActionDispatch::Reloader reloads classes in development
ActionDispatch::Callbacks provides before/after callback hook
ActiveRecord::ConnectionAdapters::ConnectionManagement clears active database connections
ActiveRecord::QueryCache clears query cache at the end of each request
ActionDispatch::Cookies converts cookies to Set-Cookie HTTP response header.
ActionDispatch::Session::CookieStore converts session into a cookie
ActionDispatch::Flash stores flash in session and sweeps as necessary
ActionDispatch::ParamsParser parses different formatted requests (XML/JSON) into params hash
ActionDispatch::Head strips out response body on HEAD requests
Rack::ConditionalGet and Rack::ETag strips out response body when it has not been modified
ActionDispatch::BestStandardsSupport tells Internet Explorer to use Chrome Frame or latest rendering engine

Production

In the production environment the middleware stack is slightly different. Gone are ActionDispatch::Static and ActionDispatch::Reloader. Added is Rack::Cache which manages HTTP caching.