Rails%203%20In%20Action

520 CHAPTER 18 Rack-based applications
PATH_INFO: /
QUERY_STRING: ""
REMOTE_ADDR: 127.0.0.1
REQUEST_METHOD: GET
REQUEST_URI: http://localhost:9292/
...
This output is the YAML-ized version of the env hash, which comes from Rack itself.
Rack parses the incoming request and provides this env hash so that you can determine
how you’d like to respond to the request. You can alter the behavior of the
request using any one of the keys in this hash, 1 but in this case you’ll keep it simple
and use the PATH_INFO key.
A lambda is great for one-liners, but now your Rack application is going to become
more complex, and so you’ve probably outgrown the usefulness of a lambda. You
don’t have to use a lambda though, you only need to pass run an object that has a call
method that responds with that three-element array. Your new code will be a couple of
lines long, and so it’s probably best to define it as a method (called call) on an
object, and what better object to define it on than a class?
A class object would allow you to define other methods, and can be used to
abstract chunks of the call method as well. For good measure, let’s call this class
Application and put it inside a module called Heartbeat, as shown in the following
listing:
Listing 18.1 lib/heartbeat.ru
module Heartbeat
class Application
def self.call(env)
[200, {'Content-Type' => 'text/plain'}, ["Hello World"]
end
end
end
run Heartbeat::Application
Here you’ve defined the Heartbeat::Application to have a call method, which once
again returns OK for any request. On the final line, call run and pass in Heartbeat
::Application, which will work like your first example because Heartbeat
::Application has a call method defined on it. If this looks familiar, it’s because
there’s a similar looking line in your application’s config.ru file that you saw earlier:
run Ticketee::Application
Your Rails application is actually a Rack-based application! Of course, there’s a little
bit more that goes on behind the scenes in your Rails application than in your Rack
application at the moment, but the two are used identically. They both respond in
nearly identical ways with the three-element response array. Your Rack application is
nearly the simplest form you can have.
1 Yes, even the HTTP_USER_AGENT key to send users of a certain browser elsewhere.