Rails%203%20In%20Action

534 CHAPTER 18 Rack-based applications
You can run the rake middleware command within your Rails
application’s directory to see the list of middleware currently in
use by your Rails application:
use ActionDispatch::Static
use Rack::Lock
use ActiveSupport::Cache::Strategy::LocalCache
use Rack::Runtime
...
use ActionDispatch::BestStandardsSupport
use Warden::Manager
run Ticketee::Application.routes
Each of these middleware pieces performs its own individual function.
For instance, the first middleware ActionDispatch::Static
intercepts requests for static files such as images, JavaScript files,
or stylesheets found in public and serves them immediately, without
the request to them falling through to the rest of the stack. It’s
important to note that this middleware is only active in the development
environment, as in production your web server (such as
nginx) is better suited for serving static assets.
Other middleware, such as ActionDispatch::BestStandards-
Support, sets additional headers on your request. This particular piece of middleware
sets the X-UA-Compatible header to IE=Edge,chrome=1, which tells Microsoft Internet
Explorer to “display content in the highest mode available” that is “equivalent to IE9
mode,” meaning your pages should render in a “best standards” fashion. 6 The
chrome=1 part of this header is for the Google Chrome Frame, which again will support
“best standards” rendering on a page.
Let’s look at both of these middleware pieces now.
18.4.1 Middleware in Rails
Browser
Web Server
In the case of the ActionDispatch::Static middleware, a response is returned when
it finds a file to serve, and the request stops there. In the case of Action-
Dispatch::BestStandardsSupport, the request is modified and allowed to continued
down the chain of middleware until it hits Ticketee::Application.routes, which
will serve the request using the routes and code in your application. The process of
ActionDispatch::Static can be seen in figure 18.4.
When a request is made to /images/rails.png, the middleware checks to see if the
public/images/rails.png file exists. If it does, then it is returned as the response of
this request. This middleware will also check for cached pages. If you make a request
to /projects, Rails (by default) will first check to see if a public/projects.html file
exists before sending the request to the rest of the stack. This type of request is
shown in figure 18.5.
6 For more information about IE=Edge and the X-UA-Compatible header, see http://msdn.microsoft.com/
en-us/library/cc288325(v=vs.85).aspx.
Rack
Application Stack
Middleware
...
Middleware
Application
Figure 18.3 Full
request stack, redux