Rails%203%20In%20Action

538 CHAPTER 18 Rack-based applications
def directory_exist?(path)
full_path = File.join(@file_server.root, ::Rack::Utils.unescape(path))
File.directory?(full_path) && File.readable?(full_path)
end
It performs basically the same function as the file_exist? method, except that it uses
File.directory? to check for the directory rather than File.file?. If this directory
does exist, then the cached_path variable is set to /projects/index in your case. The
second line in this else references the ::ActionController::Base.page_cache
_extension, which is a string that defaults to .html and makes your cached_path variable
now projects/index.html, the alternate path where the page for /projects may be
cached.
If this file exists, then the middleware sets env["PATH_INFO"] to be this path so
that the Rack::File instance knows what’s being requested, and then it makes a call
to the @fileserver.call method and returns the response it gives back.
If everything fails and there’s no file at the path you’ve requested, the middleware
gives up and passes the request to the next piece of middleware by using this line:
@app.call(env)
The request then continues on down the chain of middleware until it hits a middleware
that serves that request or the Ticketee::Application.routes endpoint. Either
way, the browser (or whatever makes the request) is basically guaranteed to get a
response from a piece of middleware or the application itself. For the first situation, a
middleware can return a response itself:
return [200, { "Content-Type" => "text/html" }, ["Oh happy day!"]]
Or it can pass the buck to the next piece with the call method, passing through the
(possibly modified) env variable representing this request’s environment:
@app.call(env)
Now that you’ve got a nice grasp of how one piece of middleware works, let’s build
your own!
18.4.3 Crafting middleware
Soon you’ll have your own piece of middleware that you can put into the middleware
stack of a Rails or Rack application. This middleware will allow the request to run all
the way down the chain to the application and then will modify the body, replacing
specific letters in the text for links with other, equally specific letters. Create a new file
for your middleware at lib/link_jumbler.rb and fill it with the content shown in the following
listing.
Listing 18.11 lib/link_jumbler.rb
require 'nokogiri'
class LinkJumbler
def initialize(app, letters)