Rails%203%20In%20Action

524 CHAPTER 18 Rack-based applications
A keen eye may have noticed that you’ve nested the paths to the heartbeat responses
underneath a path called test. This is because when you build your combined class
application, you’ll make your Heartbeat::Application sit under the /test route.
When do you do this? Right now!
18.2.2 Running a combined Rack application
You’re now going to change the lib/heartbeat/config.ru file to now create a Rack application
that uses both of your classes for different functionality. For this, you’re going to
use the Rack::Builder class, which lets you build Rack applications from different
parts. Let’s fill lib/heartbeat/config.ru with the content shown in the following listing.
Listing 18.5 lib/heartbeat/config.ru
heartbeat_root = File.expand_path(File.dirname(__FILE__))
require heartbeat_root + '/application'
require heartbeat_root + '/test_application'
app = Rack::Builder.app do
map '/test' do
run Heartbeat::Application
end
map '/' do
run Heartbeat::TestApplication
end
end
run app
Rather than calling run Heartbeat::Application here, you’re compiling a multifaceted
Rack application using Rack::Builder.app. The run method you’ve been
using all this time is defined inside the Rack::Builder class, actually. A *.ru file is usually
evaluated within the instance of a Rack::Builder object by the code the rackup
command uses, and so you are able to use the run method without having to call
Rack::Builder.new before it or wrapping .ru code in a Rack::Builder.app block.
This time, you’re being implicit and building a new Rack::Builder instance using
Rack::Builder.app. Inside this instance, you’ll declare two routes using the map
method. Within a block given to each of your map calls, you’re calling the run method
again, passing it one of your two application classes.
When a request comes into this application beginning with the path /test, it will be
served by the Heartbeat::Application class. All other requests will be served by the
Heartbeat::TestApplication class. This is not unlike the way certain requests in
your Rails application beginning with /tickets are routed to the TicketsController
and others beginning with /projects go to ProjectsController. 2
Let’s start this application and see what it can do by running this command:
rackup lib/heartbeat/config.ru
2 In fact, the similarities are astounding.