What is Rails ? What is Rack ? What happens between the time you type bundle exec rails s and when you view localhost:3000 in a browser

1. Rails
From the beginning to … well .. the beginning

2. What is Rails ?

3. What is Rack ?

4. What are gems ?

5. bundle exec rails s

6. $ which rails
#!/usr/bin/env ruby_executable_hooks
!
require 'rubygems'
!
version = ">= 0"
!
…….
!
gem 'railties', version
load Gem.bin_path('railties', 'rails', version)

7. script/rails
APP_PATH = File.expand_path('../../config/application', __FILE__)
require File.expand_path('../../config/boot', __FILE__)
require 'rails/commands'

8. config/boot.rb
require 'rubygems'
!
# Set up gems listed in the Gemfile.
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
!
require 'bundler/setup' if File.exists?(ENV['BUNDLE_GEMFILE'])

9. rails/commands
ARGV << '--help' if ARGV.empty?
aliases = {
"g" => "generate",
"d" => "destroy",
"c" => "console",
"s" => "server",
"db" => "dbconsole",
"r" => "runner"
}
command = ARGV.shift
command = aliases[command] || command
require 'rails/commands/commands_tasks'
Rails::CommandsTasks.new(ARGV).run_command!(command)

10. COMMAND_WHITELIST = %(plugin server console … help)
def run_command!(command)
if COMMAND_WHITELIST.include?(command)
send(command)
else
write_error_message(command)
end
end
‘rails/commands/commands_tasks'

11. The happy scenario
def set_application_directory!
Dir.chdir(File.expand_path('../../', APP_PATH)) unless
File.exist?(File.expand_path("config.ru"))
end
def server
set_application_directory!
require_command!("server")
Rails::Server.new.tap do |server|
require APP_PATH
Dir.chdir(Rails.application.root)
server.start
end
end
def require_command!(command)
require "rails/commands/#{command}"
end

12. config/application.rb!
!
!
!
require File.expand_path(‘../../preinitializer', __FILE__)
require File.expand_path('../boot', __FILE__)
!
# Pick the frameworks you want:
require “active_record/railtie"
!
if defined?(Bundler)
Bundler.require(*Rails.groups(:assets => %w(development test)))
end
!
module Share
class Application < Rails::Application
….
end
end

13. require “rails/commands/server"
def start
print_boot_information
trap(:INT) { exit }
create_tmp_directories
log_to_stdout if options[:log_stdout]
super
...
end

14. print_boot_information
def print_boot_information
...
puts "=> Run `rails server -h` for more startup options"
puts "=> Ctrl-C to shutdown server" unless options[:daemonize]
end

15. create_tmp_directories
def create_tmp_directories
%w(cache pids sessions sockets).each do |dir_to_make|
FileUtils.mkdir_p(File.join(Rails.root, 'tmp', dir_to_make))
end
end

16. log_to_stdout
def log_to_stdout
wrapped_app # touch the app so the logger is set up
console = ActiveSupport::Logger.new($stdout)
console.formatter = Rails.logger.formatter
console.level = Rails.logger.level
Rails.logger.extend(ActiveSupport::Logger.broadcast(console))
end

17. Rack::Server
def start &blk
…
wrapped_app
…
server.run wrapped_app, options, &blk
end

18. wrapped_app
• Sets up the config.ru
• Sets up the config/environment.rb
• Loads up config/environments/RAILS_ENV.rb

19. config.ru
require ::File.expand_path('../config/environment', __FILE__)
!
….

20. config/environment.rb
• This file initialises the application via
• Name::Application.initialize!
• This actually calls railties/lib/rails/application.rb

21. railties/lib/rails/application.rb
def initialize!(group=:default) #:nodoc:
raise "Application has been already initialized." if @initialized
run_initializers(group, self)
@initialized = true
self
end

22. run_initializers(group, self)
def run_initializers(group=:default, *args)
return if instance_variable_defined?(:@ran)
initializers.tsort_each do |initializer|
initializer.run(*args) if initializer.belongs_to?(group)
end
@ran = true
end

23. order of initialisers
• You can define order of run
• 01_something will be run before 02_something

24. middlewares
• At this point, the rails app itself is a middleware
• And now any written middle ware is called
• middleware written in config/initializers
• called via config/application.rb

25. routes
• The default routes are now loaded
• along with the custom routes in config/routes.rb

26. All files loaded
• At this point load order is done
• App servers like thin look for public directory to
load from unless routes overloads it and points
at other file.

27. Questions ?
PLZKTHXBYE

28. Bonus - Load order
|“load boot"
|“end loading boot"
|“load application.rb"
|“end loading application.rb”
!
[WEBrick|Thin|Puma] SERVER START
!
|“load config.ru"
|_ “load config/environment.rb"
|__ “load config/environments/development.rb"
|__ “end loading config/environments/development.rb"
|__ "load an initialiser"
|__ “finish loading initialiser”
|__ “load routes”
|__ “end loading routes"
|_ “end loading config/environment.rb"
|“end loading config.ru"