Re-Graphing the Mental Model of the Rails Router

Rails is incredibly powerful because of its abstractions. For years, developers have been able to hit the ground running and be productive without having to know the in's and out's of the core computer science concepts that fuel this framework. But just because something is hidden away doesn't mean that it's not worth knowing! In this talk, we'll unpack the CS fundamentals that are used in the Rails router. Together, we'll demystify the graph data structure that lies under the hood of the router in order to understand how a simple structure allows for routing to actually work in a Rails app.

Transcript

1. @vaidehijoshi Re-graphing The Mental Model of The Rails Router Vaidehi Joshi
2. @vaidehijoshi hi! i’m vaidehi.
3. @vaidehijoshi i work on
4. @vaidehijoshi four years
5. @vaidehijoshi vaidehi rails
6. @vaidehijoshi off the happy path
7. @vaidehijoshi abstractions
8. @vaidehijoshi rails router
9. @vaidehijoshi routing basics
10. @vaidehijoshi router
11. @vaidehijoshi post office post office router
12. @vaidehijoshi
13. @vaidehijoshi the router knows where to send you
14. @vaidehijoshi $ rails routes
15. @vaidehijoshi $ rails routes 
 Verb URI Pattern Controller#Action GET /articles(.:format) articles#index POST /articles(.:format) articles#create GET /articles/new(.:format) articles#new GET /articles/:id/edit(.:format) articles#edit GET /articles/:id(.:format) articles#show PATCH /articles/:id(.:format) articles#update
 PUT /articles/:id(.:format) articles#update
 DELETE /articles/:id(.:format) articles#destroy
16. @vaidehijoshi routes.rb
17. @vaidehijoshi Rails.application.routes.draw do root 'welcome#home' get 'recipes/:id', to: 'recipes#show' resources :articles end
18. @vaidehijoshi
19. @vaidehijoshi me: where u at bro?
 router:
20. @vaidehijoshi $ rails middleware
21. @vaidehijoshi $ rails middleware 
 use Rack::Sendfile use ActionDispatch::Static use ActionDispatch::Executor
 use ActiveSupport::Cache::Strategy::LocalCache::Middleware
 … use Rack::Head
 use Rack::ConditionalGet
 use Rack::ETag use Rack::TempfileReaper run ExampleApp::Application.routes
22. @vaidehijoshi what’s middleware again?
23. @vaidehijoshi what’s rack again?
24. @vaidehijoshi responds to call (like a proc)
25. @vaidehijoshi { [200, {}, ["Hello World"]] }
26. @vaidehijoshi ProTip™: controller actions are just rack endpoints
27. @vaidehijoshi Rails.application.routes.draw do root 'welcome#home' end root 'welcome#home' root to: proc { [200, {}, [“omg this works!”]] }
28. @vaidehijoshi $ rails middleware 
 use Rack::Sendfile use ActionDispatch::Static use ActionDispatch::Executor
 use ActiveSupport::Cache::Strategy::LocalCache::Middleware
 … use Rack::Head
 use Rack::ConditionalGet
 use Rack::ETag use Rack::TempfileReaper run ExampleApp::Application.routes
29. @vaidehijoshi ExampleApp::Application.routes
30. @vaidehijoshi Application.routes
31. @vaidehijoshi lib/rails/engine.rb
32. @vaidehijoshi def routes #…
 @routes end
33. @vaidehijoshi me: how u route bro? router:
34. @vaidehijoshi get 'recipes/:id', to: ‘recipes#show’ post ‘articles(.:format)’, to: 'articles#create' post 'articles/new', to: ‘articles#new’ get ‘articles/:id', to: ‘articles#new’
 # even more routes here…
35. @vaidehijoshi if request_path =~ /^\articles$/ # go to articles#index
 end
36. @vaidehijoshi if request_path =~ /^\articles$/ # go to articles#index
 elsif request_path =~ /^\recipes$/
 # go to recipes#index elsif
 # etc etc more looping ahhhhhh! else
 # route not found?
 end linear, O(n)
37. @vaidehijoshi
38. @vaidehijoshi
39. @vaidehijoshi
40. @vaidehijoshi
44. @vaidehijoshi where does journey fit in?
45. @vaidehijoshi Application.routes
46. @vaidehijoshi @routes ||=
 ActionDispatch::Routing::RouteSet.new
47. @vaidehijoshi @routes ||=
 ActionDispatch::Routing::RouteSet.new
48. @vaidehijoshi #action_dispatch/routing/route_set.rb
 @set ||= Journey.Routes.new
49. @vaidehijoshi graph
50. @vaidehijoshi node
51. @vaidehijoshi nodes
52. @vaidehijoshi nodes edges (links)
53. @vaidehijoshi edges undirected
54. @vaidehijoshi edges directed
55. @vaidehijoshi
56. @vaidehijoshi 12345 main street
 portland, oregon 97232-1337
 USA
57. @vaidehijoshi
58. @vaidehijoshi Rails.application.routes.draw do root 'welcome#home' resources :articles resources :recipes resources :comments end “/recipes/:id”
59. @vaidehijoshi $ rails routes 
 Verb URI Pattern Controller#Action GET /articles(.:format) articles#index POST /articles(.:format) articles#create GET /articles/new(.:format) articles#new GET /articles/:id/edit(.:format) articles#edit GET /articles/:id(.:format) articles#show PATCH /articles/:id(.:format) articles#update
 PUT /articles/:id(.:format) articles#update
 DELETE /articles/:id(.:format) articles#destroy
60. @vaidehijoshi Rails.application.routes.draw do root 'welcome#home' resources :articles resources :recipes resources :comments end “/recipes/:id”
61. @vaidehijoshi
62. @vaidehijoshi me: how u read bro? router:
63. @vaidehijoshi The cow jumped over the moon.
64. @vaidehijoshi The cow jumped over the moon.
65. @vaidehijoshi “/recipes/:id”
66. @vaidehijoshi tokenization
67. @vaidehijoshi “/recipes/:id”
68. @vaidehijoshi hi. i’m a scanner!
69. @vaidehijoshi $ rails console
 > scanner = ActionDispatch::Journey::Scanner.new > scanner.scan_setup(“/recipes/:id”)
70. @vaidehijoshi > scanner.next_token
 => [:SLASH, “/“] > scanner.next_token
 => [:LITERAL, "recipes"] 
 > scanner.next_token
 => [:SLASH, “/"]
 > scanner.next_token
 => [:SYMBOL, ":id"]
71. @vaidehijoshi :SLASH, :LITERAL, :SYMBOL, :LPAREN, :RPAREN, :DOT, :OR,
 :STAR. Tokens I know:
72. @vaidehijoshi half the battle
73. @vaidehijoshi stars — they’re just like us! stars computers
74. @vaidehijoshi hi. i’m a parser!
75. @vaidehijoshi syntax tree
76. @vaidehijoshi The cow jumped over the moon.
77. @vaidehijoshi jumped The cow over the moon over the moon
78. @vaidehijoshi jumped The cow over the moon over the moon noun phrase verb prepositional phrase
79. @vaidehijoshi recipes :id / :format . / () “/recipes/:id(.:format)”
80. @vaidehijoshi recipes :id / (.:format) / “/recipes/:id(.:format)”
81. @vaidehijoshi recipes / :id(.:format) / “/recipes/:id(.:format)”
82. @vaidehijoshi recipes /:id(.:format) / “/recipes/:id(.:format)”
83. @vaidehijoshi recipes/:id(.:format) / “/recipes/:id(.:format)”
84. @vaidehijoshi /recipes/:id(.:format) “/recipes/:id(.:format)”
85. @vaidehijoshi $ rails console
 > parser = ActionDispatch::Journey::Parser.new > syntax_tree = parser.parse(“/recipes/:id(.:format)”)
86. @vaidehijoshi intermediate step
87. @vaidehijoshi + + = graph
88. @vaidehijoshi + + = generalized
 transition graph (GTG)
89. @vaidehijoshi + + = state
 machine
90. @vaidehijoshi 0 0 0 0 0 0 1 2 3 4
91. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
92. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
93. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
94. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
95. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
96. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
97. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json ✅
98. @vaidehijoshi get 'recipes/:id', to: ‘recipes#show’ get ‘articles(.:format)’, to: 'articles#index' post 'articles/new', to: ‘articles#new’ get ‘articles/:id', to: ‘articles#new’
 # even more routes here…
99. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
100. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
101. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
102. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
103. @vaidehijoshi 0 0 0 0 0 0 1 2 4 5 / articles / (?-mix:[^./?]+) 0 3 0 … . /articles.json
104. @vaidehijoshi nondeterministic finite automaton (NFA) just a fancy state machine!
105. @vaidehijoshi two possible outcomes
106. @vaidehijoshi we find a valid route
107. @vaidehijoshi or we don’t
108. @vaidehijoshi “accepted” state valid, acceptable route dispatch to corresponding controller action
109. @vaidehijoshi
110. @vaidehijoshi
111. @vaidehijoshi “rejected” state invalid, unacceptable route cause an error
112. @vaidehijoshi
113. @vaidehijoshi
114. @vaidehijoshi $ rails console
 > nfa = Rails.application.routes.router.visualizer
115. @vaidehijoshi well this has been quite a ~journey~
116. @vaidehijoshi but we learned so many things!
117. @vaidehijoshi tokenization scanning trees & graphs automatons
118. @vaidehijoshi you don’t need to think about abstractions every day.
119. @vaidehijoshi but if you find yourself wanting or need to learn them, don’t be afraid!
120. @vaidehijoshi
121. @vaidehijoshi
122. @vaidehijoshi basecs.org ✨
123. @vaidehijoshi ✨ basecs.org thank you!