Rails%203%20In%20Action

Middleware
def call(env)
path = env['PATH_INFO'].chomp('/')
method = env['REQUEST_METHOD']
if FILE_METHODS.include?(method)
The env variable here is the same sort of style as the env variable that you used back in
your Rack application. Rack middleware and Rack applications are actually designed
almost identically. You saw the env["PATH_INFO"] key before—that’s the one that contains
the path of the request, something such as /images/rails.png. By calling chomp
on this, it strips off any trailing forward-slashes on the end of this URL.
The env["REQUEST_METHOD"] key contains the HTTP request method used in this
request. If this method is either GET or HEAD, then the code inside the if runs here.
The next line after this one checks for the presence of a file:
if file_exist?(path)
This method is defined further down in this file, like this:
def file_exist?(path)
full_path = File.join(@file_server.root, ::Rack::Utils.unescape(path))
File.file?(full_path) && File.readable?(full_path)
end
This method uses the root method, which returns the fill path to the public directory
of your application. This method then uses File.join to join the path to the public
directory and the unescaped name of the file that’s being requested. Finally, this
method uses the File.file? and File.readable? methods to determine if the path
specified is actually a file and if that file is readable. If it is indeed a file and is indeed
readable, then this line is executed:
return @file_server.call(env)
This calls the call method on the Rack::File instance, which then (after some additional
processing) serves the file.
So far, this has been the process this piece of middleware uses for an existing file. If
the file doesn’t exist, then it goes into the else for the if File.exists? line, which
results in the following code being run:
cached_path = directory_exist?(path) ? "#{path}/index" : path
cached_path += ::ActionController::Base.page_cache_extension
if file_exist?(cached_path)
env['PATH_INFO'] = cached_path
return @file_server.call(env)
end
The first line here checks for a directory with the same name as the path you’ve
requested. Imagine your request is now /projects and you have a public/projects directory.
This directory_exists? method would then return true because this directory
exists. The directory_exists? method is defined like this:
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