The Great Migration: From Merb to Rails 3 at Typekit

Transcript

1. THE GREAT
   MIGRATION
   David Demaree
   [email protected] • @ddemaree
   ChicagoRuby
   October 4, 2011
   

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3. http://j.mp/q2jl54
   

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4. Merb to Rails 3
   

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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
   

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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
   

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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
    

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11. M E R B C O M M U N I T Y c a . 2 0 1 1
    

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13. Fork and maintain Merb
    Move to Rails 3
    

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14. Move to Rails 3
    Fork and maintain Merb
    Move to Rails 3
    

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15. D A V I D V S . M E R B
    

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16. S E T U P
    

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17. http://cl.ly/AebP
    

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18. MERB
    config/init.rb
    config/router.rb
    RAILS
    config/application.rb
    config/routes.rb
    Shared Config Directory
    

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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
    

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20. app/
    controllers/
    antiques.rb
    application.rb
    application_controller.rb
    exceptions.rb
    novelties_controller.rb
    MERB & RAILS CONTROLLERS, TOGETHER AT LAST
    

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21. class Application < Merb::Controller
    ...
    include Typekit::MerbExtensions::RailsHelper
    include Typekit::MerbExtensions::CsrfSupport
    ...
    end
    Bridging Merb to Rails
    

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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
    ...
    

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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
    

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24. R O U T I N G
    

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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
    

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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
    

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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
    

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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"
    

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29. Next-Level Routing Tricks
    

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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
    

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31. class FlipperConstraint
    def initialize(flag)
    @flag = flag
    end
    def matches?(request)
    request.env['flipper.manager'].flag_enabled?(@flag)
    end
    end
    

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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
    

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33. M I D D L E W A R E
    

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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
    

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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
    

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36. Cookies, Sessions, & the Rails Flash
    

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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
    

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38. # In a middleware
    session['user.id'] = 1234
    #=> 1234
    # In a Rails controller
    session['user.id']
    #=> nil
    

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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
    

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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
    

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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
    

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42. Cross-Site Request Forgery (CSRF)
    Protection
    

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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
    

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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
    

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45. T E S T I N G
    

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47. A test suite should
    be a trusted system.
    

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49. Custom Example Groups
    Our solution:
    

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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
    

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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
    

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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
    

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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
    

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54. Cucumber
    Merb legacy request specs
    Rails integration specs
    Capybara-driven acceptance specs
    Choose your tools wisely
    

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55. Q&A
    to make up for your speaker’s woeful lack of preparation
    

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56. S T R AT E G Y
    

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57. Merb and Rails co-exist
    for the foreseeable future
    

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58. New work should
    be done in Rails
    

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59. Favor small iterations
    over big rewrites
    

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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
    

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61. Build bridges between
    Rails & Merb when necessary
    

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62. Use Rack
    

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63. Use integration tests
    

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64. When in doubt,
    read the source code
    

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