The Great Migration: From Merb to Rails 3 at Typekit

Late in 2008 the Rails and Merb development teams merged to create Rails 3, the most robust, most extensible, best release of everyone's favorite Ruby web framework. But while those competing teams merged, their frameworks didn't. Though Rails 3 shows plenty of influence from Merb and its creators, today Merb itself is a legacy framework, with no clear, supported path for Merb apps to move forward to Rails 3 without significant effort.

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1. THE GREAT MIGRATION David Demaree david@typekit.com • @ddemaree ChicagoRuby October 4, 2011
3. http://j.mp/q2jl54
4. Merb to Rails 3
8. Also, the Merb guys aren’t just abandoning the existing Merb user base and their applications. They’ll still be doing bug fixes, security fixes, and work on easing the upgrade path to Rails 3. This will all progress in a nice, orderly fashion. David Heinemeier Hansson DECEMBER 23, 2008
9. Merb folks will not be left out in the cold. We will continue to support … the merb 1.0.x line. And we will provide a clear upgrade path to Rails 3.0 for merb apps. Ezra Zygmuntowicz DECEMBER 23, 2008
10. We will also release versions of Merb specifically designed to help ease the transition to Rails 3 … with deprecation notices and other transitional mechanisms to assist developers in tracking down the changes that will come between Merb 1.x and Rails 3. Yehuda Katz DECEMBER 23, 2008
11. M E R B C O M M U N I T Y c a . 2 0 1 1
13. Fork and maintain Merb Move to Rails 3
14. Move to Rails 3 Fork and maintain Merb Move to Rails 3
15. D A V I D V S . M E R B
16. S E T U P
17. http://cl.ly/AebP
18. MERB config/init.rb config/router.rb RAILS config/application.rb config/routes.rb Shared Config Directory
19. module Typekit class Application < Rails::Application ... config.before_initialize do Merb.push_path(:view, "#{config.root}/app/views") end config.after_initialize do Merb.start_environment(:environment => Rails.env.to_s) end ... end end
20. app/ controllers/ antiques.rb application.rb application_controller.rb exceptions.rb novelties_controller.rb MERB & RAILS CONTROLLERS, TOGETHER AT LAST
21. class Application < Merb::Controller ... include Typekit::MerbExtensions::RailsHelper include Typekit::MerbExtensions::CsrfSupport ... end Bridging Merb to Rails
22. module Typekit module MerbExtensions module RailsHelper extend ActiveSupport::Concern included do |base| base.class_eval do # Include Rails routes into Merbland include Rails.application.routes.url_helpers # Alias resource/url routes as merb_resource/merb_url, # for API consistency with the Rails app alias merb_resource resource alias merb_url url end end ...
23. # app/helpers/typekit/merb_transition_helper.rb module Typekit module MerbTransitionHelper include AssetBundles def merb_url(named_url, *args) Merb::Router.url(named_url, *args) end ... # app/controllers/application_controller.rb class ApplicationController < ActionController::Base include Typekit::MerbTransitionHelper ... Bridging Rails to Merb
24. R O U T I N G
25. module RackApplication def self.new Rack::Builder.new do use Middleware::ExceptionCatcher map "#{host}/api/v1" do # Sinatra-based API app run Api::V1::Application.new end map "#{host}/" do # Merb app run Merb::Rack::Application.new end end end end
26. module RackApplication def self.new Rack::Builder.new do use Middleware::ExceptionCatcher map "#{host}/" do # Rails app run Typekit::Application end end end end
27. Typekit::Application.routes.draw do # Sinatra app mount Api::V1::Application => "/api/v1" # .. Rails routes here .. # # Merb app match "*wildcard" => Merb::Rack::Application.new # Home page (Rails controller) root :to => "static_pages#home" end config/routes.rb
28. # Passes through entire URI get "/api/v1" => Api::V1::Application # Only passes through the segment after # the given prefix, e.g. /api/v1/foo is # handled by the Sinatra app as /foo mount Api::V1::Application => "/api/v1"
29. Next-Level Routing Tricks
30. constraints(FlipperConstraint.new(:new_browse_ui)) do get "/fonts" => "browse/families#index", :as => :browse_families end # If the :new_browse_ui flag is false, requests # for /fonts are served by the Merb app CONSTRAINTS
31. class FlipperConstraint def initialize(flag) @flag = flag end def matches?(request) request.env['flipper.manager'].flag_enabled?(@flag) end end
32. # config/routes.rb # /backend is normally served by the Merb app get "/backend" => "backend/home#index" # app/controllers/backend/home_controller.rb class Backend::HomeController < ApplicationController def index # The X-Cascade header tells Rack to skip this # endpoint and look for the next suitable one, # which in this case would be the Merb app head :ok, "X-Cascade" => "pass" end end X-CASCADE: PASS
33. M I D D L E W A R E
34. # send all exceptions to hoptoad use Rack::Hoptoad, HOPTOAD_API_KEY do |notifier| notifier.environment_filters << %w(warden rack.session) end # run offline jobs after each request when a # separate process isn't used. use Middleware::OfflineJobRunner # reload the application after each request if # rails is configured to do so. use Middleware::RailsAutoload app/racks/rack_application.rb
35. config/initializers/middleware.rb Rails.application.config.middleware.tap do |m| # send all exceptions to hoptoad m.use Rack::Hoptoad, HOPTOAD_API_KEY do |notifier| notifier.environment_filters << %w(warden rack.session) end # run offline jobs after each request when a # separate process isn't used. m.use Middleware::OfflineJobRunner # reload the application after each request if # rails is configured to do so. m.use Middleware::RailsAutoload end
36. Cookies, Sessions, & the Rails Flash
37. module RackApplication def self.new Rack::Builder.new do use Middleware::ExceptionCatcher use Rack::Session::Cookie, :key => ::Merb::Config[:session_cookie_name], :secret => ::Merb::Config[:session_secret_key], :domain => typekit_cookie_domain, :httponly => true ... end end end app/racks/rack_application.rb Stage 1: Rack sessions
38. # In a middleware session['user.id'] = 1234 #=> 1234 # In a Rails controller session['user.id'] #=> nil
39. # Initialize Rails cookie store use Middleware::SecretToken, "sekrit token here" use ActionDispatch::Cookies # Enable Rails session storage for all endpoints use ActionDispatch::Session::CookieStore, :key => Merb::Config[:session_cookie_name], :domain => typekit_cookie_domain, :httponly => true # Enable Rails flash use ActionDispatch::Flash Stage 2: Port Rails session middlewares to RackApplication
40. module Middleware class SecretToken TOKEN_KEY = "action_dispatch.secret_token".freeze def initialize(app, secret) @app = app; @secret = secret end def call(env) env[TOKEN_KEY] ||= @secret return @app.call(env) end end end
41. Stage 3: Switch to standard Rails sessions # config/initializers/session_store.rb Typekit::Application.config.session_store :cookie_store, :key => Typekit.config.session_cookie_name, :domain => typekit_cookie_domain, :httponly => true
42. Cross-Site Request Forgery (CSRF) Protection
43. module Typekit module MerbExtensions module CsrfSupport extend ActiveSupport::Concern def verified_request? request.method == :get || form_authenticity_token == params[csrf_param_name] || form_authenticity_token == request.env['HTTP_X_CSRF_TOKEN'] end def verify_csrf_token unless verified_request? raise Merb::Controller::PreconditionFailed end end end end end
44. module Middleware class CsrfToken def initialize(app) @app = app end def call(env) env['rack.session'][:_csrf_token] ||= SecureRandom.base64(32) @app.call(env) end end end
45. T E S T I N G
47. A test suite should be a trusted system.
49. Custom Example Groups Our solution:
50. module Typekit module LegacyRequestExampleGroup extend ActiveSupport::Concern # Include Merb request stuff include Merb::Test::RouteHelper include Merb::Test::RequestHelper include Merb::Test::MultipartRequestHelper ... end end Defining a custom example group
51. RSpec.configure do |config| config.include Typekit::LegacyRequestExampleGroup, :type => :legacy_request, :example_group => { :file_path => config.escaped_path(%w[spec requests]) } end Adding a custom example group to RSpec
52. # BTW, specs in spec/requests are automatically tagged thusly describe "GET /login over non-SSL", :type => :legacy_request do it "should redirect to SSL" do # Returns a Merb::Test::MakeRequest struct object @response = request("/login") @response.should redirect_to("https://secure.example.org/login") end end
53. describe "GET /login over non-SSL", :type => :legacy_request do it "should redirect to SSL" do # Returns a Merb::Test::MakeRequest struct object @response = request("/login") @response.should redirect_to("https://secure.example.org/login") end end describe "GET /login over SSL", :type => :legacy_request do it "should be successful" do # Returns an ActionDispatch::Request object @response = request(path_over_ssl("/login")).body @response.status.should == 200 end end
54. Cucumber Merb legacy request specs Rails integration specs Capybara-driven acceptance specs Choose your tools wisely
55. Q&A to make up for your speaker’s woeful lack of preparation
56. S T R AT E G Y
57. Merb and Rails co-exist for the foreseeable future
58. New work should be done in Rails
59. Favor small iterations over big rewrites
60. Try to change just one thing at a time Trustworthy test coverage, passing before and after Code review Merge and deploy once tests are passing Big, complex features can be migrated in stages
61. Build bridges between Rails & Merb when necessary
62. Use Rack
63. Use integration tests
64. When in doubt, read the source code