Debugging Adventures in Rack-land (Fog City Ruby - November 2018)

I ran into a weird bug the other day. Editing an attribute in a web form would kick off an XHR request to the server and update a row in the database. But when the page was refreshed, the attribute on the page had not changed from its original value. Even weirder: refreshing the page a second time caused the attribute to show up correctly—and reflect what was in the database.

I’m not going to spoil the story here, but the issue led me into the internals of Rack middleware. Join me as we explore the details of this strange bug. Together, we’ll learn something about the wonderful world of Rack.

Transcript

1. @panthomakos Debugging Adventures in Rack-land
2. @panthomakos
3. @panthomakos
4. @panthomakos
5. @panthomakos
6. @panthomakos SELECT measurement_preference FROM athletes WHERE id = ?;
7. @panthomakos # app/controllers/settings_controller.rb def athlete Permissions.decorate(current_athlete, self) end
8. @panthomakos pry
9. @panthomakos # app/controllers/settings_controller.rb def athlete binding.pry Permissions.decorate(current_athlete, self) end
10. @panthomakos Ctrl + R
11. @panthomakos From: $HOME/web/app/controllers/settings_controller.rb @ line 313 SettingsController#athlete: 312: def athlete => 313: binding.pry 314: Permissions.decorate(current_athlete, self) 315: end 2.3.3 (...):0 >
12. @panthomakos From: $HOME/web/app/controllers/settings_controller.rb @ line 313 SettingsController#athlete: 312: def athlete => 313: binding.pry 314: Permissions.decorate(current_athlete, self) 315: end 2.3.3 (...):0 > current_athlete.measurement_preference => :meters 2.3.3 (...):0 > Athlete.find(current_athlete.id).measurement_preference => :feet
13. @panthomakos current_athlete vs Athlete.find(current_athlete.id)
14. @panthomakos # app/controllers/application_controller.rb def current_athlete login_from_session || login_remember_cookie end
15. @panthomakos # app/controllers/application_controller.rb def login_from_session ... @session_athlete ||= Athlete.fetch(session[:id]) end
16. @panthomakos From: $HOME/web/app/controllers/settings_controller.rb @ line 313 SettingsController#athlete: 312: def athlete => 313: binding.pry 314: Permissions.decorate(current_athlete, self) 315: end 2.3.3 (...):0 > current_athlete.measurement_preference => :meters 2.3.3 (...):0 > Athlete.find(current_athlete.id).measurement_preference => :feet 2.3.3 (...):0 > Athlete.fetch(current_athlete.id).measurement_preference => :meters
17. @panthomakos # app/models/athlete.rb def self.fetch(id) ::Strava::EntityMap.fetch(self, id) end
18. @panthomakos ::Strava::EntityMap.fetch(self, id)
19. @panthomakos ::Strava::EntityMap
20. @panthomakos Request Level Cache
21. @panthomakos ::Strava::EntityMap.request(Athlete, [1, 2, 3])
22. @panthomakos ::Strava::EntityMap.fetch(Athlete, 1)
23. @panthomakos ::Strava::EntityMap.clear!
24. @panthomakos From: $HOME/web/app/controllers/settings_controller.rb @ line 313 SettingsController#athlete: 312: def athlete => 313: binding.pry 314: Permissions.decorate(current_athlete, self) 315: end 2.3.3 (...):0 > Athlete.fetch(current_athlete.id).measurement_preference => :meters 2.3.3 (...):0 > Strava::EntityMap.clear! => nil 2.3.3 (...):0 > Athlete.fetch(current_athlete.id).measurement_preference => :feet
25. @panthomakos How do we clear the cache in web requests?
26. @panthomakos Each request needs a fresh cache.
27. @panthomakos “For each request”
28. @panthomakos Rack Middleware
29. @panthomakos Rack
30. @panthomakos Web/Application Server Application
31. @panthomakos Rack
32. @panthomakos What makes an HTTP response?
33. @panthomakos Status Code (200, 404, 500)
34. @panthomakos Headers (content-type, etag, set-cookie)
35. @panthomakos Body (html, json, text, image)
36. @panthomakos [status, headers, body]
37. @panthomakos [ 200, { "Content-Type" => "application/json" }, [ { "status": "success" }.to_json ] ]
38. @panthomakos [ 200, { "Content-Type" => "application/json" }, [ '{"status":"success"}' ] ]
39. @panthomakos [ number, hash, [ string, string, string ] ]
40. @panthomakos [ number, hash, &:each ]
41. @panthomakos body.each do |part| res.body << part end
42. @panthomakos [ “<html>”, “<head>...</head>”, “<body>...</body>”, “</html>” ]
43. @panthomakos class Body def each yield “<html>” yield “<head> ... </head>” yield “<body> ... </body>” yield “</html>” end end
44. @panthomakos Buffering & Streaming
45. @panthomakos [status, headers, body]
46. @panthomakos Middleware
47. @panthomakos Rack Handler Ruby Application
48. @panthomakos Rack Handler Ruby Application Rack Middleware Rack Middleware Rack Middleware
49. @panthomakos Rack Handler Ruby Application Rack Middleware Rack Middleware Rack Middleware Req Res
50. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts “Response Time: #{finish - start}ms” response end end
51. @panthomakos # config.ru use MyTimer
52. @panthomakos # app/initializers/use_my_middleware.rb Rails.application.middleware.use MyTimer
53. @panthomakos $ curl localhost:3000/settings ... Response Time: 100ms
54. @panthomakos body.each do |part| res.body << part end
55. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts “Response Time: #{finish - start}ms” response end end
56. @panthomakos class SlowBody def each yield “<head> ... </head>” sleep(2) yield “<body> ... </body>” end end
57. @panthomakos How do we know when our response is complete?
58. @panthomakos #close
59. @panthomakos # lib/rack/handler/webrick.rb def service(req, res) ... status, headers, body = @app.call(env) begin ... body.each { |part| res.body << part } ensure body.close if body.respond_to?(:close) end end
60. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" response end end
61. @panthomakos class BoxyProxy def initialize(body, &close) @body = body @close = close end def each @body.each end def close @body.close if @body.respond_to?(:close) @close.call end end
62. @panthomakos BodyProxy.new(body) do finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" end
63. @panthomakos class MyTimer def call(env) start = ::Timer.cputime status, headers, body = @app.call(env) proxy = BodyProxy.new(body) do finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" end [status, headers, proxy] end end
64. @panthomakos Rack::BodyProxy https://github.com/rack/rack/blob/master/lib/rack/body_proxy.rb
65. @panthomakos Rack Handler Ruby Application Rack Middleware Rack Middleware Rack Middleware
66. @panthomakos Rack Handler Ruby Application Rack Middleware Rack Middleware Rack Middleware Body Body Body Body Req Res
67. @panthomakos Rack Handler Ruby Application Rack Middleware Rack Middleware Rack Middleware Req Res Body Body Body Body #close #close #close #close
68. @panthomakos Rack + Rack Middleware
69. @panthomakos
70. @panthomakos # app/controllers/settings_controller.rb def athlete binding.pry Permissions.decorate(current_athlete, self) end
71. @panthomakos # app/models/athlete.rb def self.fetch(id) ::Strava::EntityMap.fetch(self, id) end
72. @panthomakos From: $HOME/web/app/controllers/settings_controller.rb @ line 313 SettingsController#athlete: 312: def athlete => 313: binding.pry 314: Permissions.decorate(current_athlete, self) 315: end 2.3.3 (...):0 > Athlete.fetch(current_athlete.id).measurement_preference => :meters 2.3.3 (...):0 > Strava::EntityMap.clear! => nil 2.3.3 (...):0 > Athlete.fetch(current_athlete.id).measurement_preference => :feet
73. @panthomakos ::Strava::EntityMap.clear!
74. @panthomakos Rails 3 -> 4
75. @panthomakos IdentityMap http://api.rubyonrails.org/v3.1/classes/ActiveRecord/IdentityMap.html
76. @panthomakos # activerecord/lib/active_record/identity_map.rb class Middleware def initialize(app) @app = app end def call(env) status, headers, body = @app.call(env) [status, headers, BodyProxy.new(body)] end end
77. @panthomakos # activerecord/lib/active_record/identity_map.rb class Middleware class BodyProxy def initialize(target) @target = target end def each(&block) @target.each(&block) end def close @target.close if @target.respond_to?(:close) ensure IdentityMap.clear end end end
78. @panthomakos # lib/strava/entity_map_middleware.rb module Strava class EntityMapMiddleware def initialize(app) @app = app end def call(env) status, headers, body = @app.call(env) [status, headers, BodyProxy.new(body)] end end end
79. @panthomakos # lib/strava/entity_map_middleware.rb module Strava class EntityMapMiddleware class BodyProxy def initialize(target) @target = target end def each(&block) @target.each(&block) end def close @target.close if @target.respond_to?(:close) ensure ::Strava::EntityMap.clear! end end end end
80. @panthomakos binding.pry
81. @panthomakos def close @target.close if @target.respond_to?(:close) ensure ::Strava::EntityMap.clear! end
82. @panthomakos def close binding.pry @target.close if @target.respond_to?(:close) ensure ::Strava::EntityMap.clear! end
83. @panthomakos Ctrl + R
84. @panthomakos
85. @panthomakos def close binding.pry @target.close if @target.respond_to?(:close) ensure ::Strava::EntityMap.clear! end
86. @panthomakos def close raise 'This is supposed to happen!' @target.close if @target.respond_to?(:close) ensure ::Strava::EntityMap.clear! end
87. @panthomakos Ctrl + R
88. @panthomakos
89. @panthomakos github.com/rack/rack
90. @panthomakos What version of rack are we using again?
91. @panthomakos $ bundle show rack
92. @panthomakos $ bundle show rack ~/.rbenv/.../lib/ruby/gems/2.3.0/gems/rack-1.6.10
93. @panthomakos $ cd $(bundle show rack)
94. @panthomakos $ cd $(bundle show rack) $ vim lib/rack/handler/webrick.rb
95. @panthomakos $ bundle open rack
96. @panthomakos $ cd $(bundle show rack) $ vim lib/rack/handler/webrick.rb
97. @panthomakos # lib/rack/handler/webrick.rb def service(req, res) ... status, headers, body = @app.call(env) begin ... body.each { |part| res.body << part } ensure body.close if body.respond_to?(:close) end end
98. @panthomakos # lib/rack/handler/webrick.rb def service(req, res) ... status, headers, body = @app.call(env) begin ... body.each { |part| res.body << part } ensure binding.pry body.close if body.respond_to?(:close) end end
99. @panthomakos
100. @panthomakos From: .../lib/rack/handler/webrick.rb @ line 75 Rack::Handler::WEBrick#service: 70: } 71: body.each { |part| 72: res.body << part 73: } 74: ensure => 75: binding.pry 76: body.close if body.respond_to? :close 77: end 78: end 79: end 80: end 2.3.3 (...):0 >
101. @panthomakos 2.3.3 (...):0 > body
102. @panthomakos 2.3.3 (...):0 > body => #<Rack::BodyProxy:0x0055b6af04bad0 @block=#<Proc:0x0055b6af04baa8@.../rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af04c318 @block= #<Proc:0x0055b6af04c2c8@.../action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121566960060, @original_cache_value=false, @target=["{\"success\":true}"]>, @testing=false>, @closed=false>, @closed=false>
103. @panthomakos 2.3.3 (...):0 > body => #<Rack::BodyProxy:0x0055b6af04bad0 @block=#<Proc:0x0055b6af04baa8@.../rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af04c318 @block= #<Proc:0x0055b6af04c2c8@.../action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121566960060, @original_cache_value=false, @target=["{\"success\":true}"]>, @testing=false>, @closed=false>, @closed=false>
104. @panthomakos 2.3.3 (...):0 > body => #<Rack::BodyProxy:0x0055b6af04bad0 @block=#<Proc:0x0055b6af04baa8@.../rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af04c318 @block= #<Proc:0x0055b6af04c2c8@.../action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121566960060, @original_cache_value=false, @target=["{\"success\":true}"]>, @testing=false>, @closed=false>, @closed=false>
105. @panthomakos Where’s my middleware?
106. @panthomakos 2.3.3 (...):0 > exit
107. @panthomakos Ctrl + R
108. @panthomakos From: .../lib/rack/handler/webrick.rb @ line 75 Rack::Handler::WEBrick#service: 70: } 71: body.each { |part| 72: res.body << part 73: } 74: ensure => 75: binding.pry 76: body.close if body.respond_to? :close 77: end 78: end 79: end 80: end 2.3.3 (...):0 >
109. @panthomakos 2.3.3 (...):0 > body
110. @panthomakos 2.3.3 (#<Rack::Handler::WEBrick:0x0055b6ae171168>):0 > body => #<Rack::BodyProxy:0x0055b6af109b70 @block=#<Proc:0x0055b6af109b48@...lib/rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af10a368 @block= #<Proc:0x0055b6af10a318@...lib/action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121546748840, @original_cache_value=false, @target= ["<!DOCTYPE html>\n<html class='logged-in clean s-minifeed old-login' dir='ltr' lang='en-US'..."]
111. @panthomakos 2.3.3 (#<Rack::Handler::WEBrick:0x0055b6ae171168>):0 > body => #<Rack::BodyProxy:0x0055b6af109b70 @block=#<Proc:0x0055b6af109b48@...lib/rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af10a368 @block= #<Proc:0x0055b6af10a318@...lib/action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121546748840, @original_cache_value=false, @target= ["<!DOCTYPE html>\n<html class='logged-in clean s-minifeed old-login' dir='ltr' lang='en-US'..."]
112. @panthomakos 2.3.3 (#<Rack::Handler::WEBrick:0x0055b6ae171168>):0 > body => #<Rack::BodyProxy:0x0055b6af109b70 @block=#<Proc:0x0055b6af109b48@...lib/rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6af10a368 @block= #<Proc:0x0055b6af10a318@...lib/action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x00... @connection_id=47121546748840, @original_cache_value=false, @target= ["<!DOCTYPE html>\n<html class='logged-in clean s-minifeed old-login' dir='ltr' lang='en-US'..."]
113. @panthomakos 2.3.3 (...):0 > exit
114. @panthomakos From: .../lib/rack/handler/webrick.rb @ line 75 Rack::Handler::WEBrick#service: 70: } 71: body.each { |part| 72: res.body << part 73: } 74: ensure => 75: binding.pry 76: body.close if body.respond_to? :close 77: end 78: end 79: end 80: end 2.3.3 (...):0 >
115. @panthomakos WTF is this request?
116. @panthomakos 2.3.3 (...):0 > env['REQUEST_PATH']
117. @panthomakos 2.3.3 (...):0 > env['REQUEST_PATH'] => "/assets/application.css"
118. @panthomakos 2.3.3 (...):0 > body
119. @panthomakos 2.3.3 (#<Rack::Handler::WEBrick:0x0055b6ae6ca100>):0 > body => #<Rack::BodyProxy:0x0055b6ae31a1e0 @block=#<Proc:0x0055b6ae31a1b8@...lib/rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6ae31a898 @block= #<Proc:0x0055b6ae31a820@...lib/action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x0055b6ae31a960 @connection_id=47121546748840, @original_cache_value=false, @target= #<Strava::EntityMapMiddleware::BodyProxy:0x00... @target=[]>>, @testing=false>, @closed=false>, @closed=false>
120. @panthomakos 2.3.3 (#<Rack::Handler::WEBrick:0x0055b6ae6ca100>):0 > body => #<Rack::BodyProxy:0x0055b6ae31a1e0 @block=#<Proc:0x0055b6ae31a1b8@...lib/rack/lock.rb:16>, @body= #<ActionDispatch::BodyProxy:0x0055b6ae31a898 @block= #<Proc:0x0055b6ae31a820@...lib/action_dispatch/middleware/reloader.rb:66>, @body= #<ActiveRecord::ConnectionAdapters::ConnectionManagement::Proxy:0x00... @body= #<ActiveRecord::QueryCache::BodyProxy:0x0055b6ae31a960 @connection_id=47121546748840, @original_cache_value=false, @target= #<Strava::EntityMapMiddleware::BodyProxy:0x00... @target=[]>>, @testing=false>, @closed=false>, @closed=false>
121. @panthomakos 2.3.3 (...):0 > env['REQUEST_PATH'] => "/assets/application.css" 2.3.3 (...):0 > env['REQUEST_PATH'] => "/assets/strava/i18n/locales/en-US.js"
122. @panthomakos Why is my middleware not present in AJAX/HTML requests?
123. @panthomakos Why is my middleware present in ASSET requests?
124. @panthomakos binding.pry
125. @panthomakos $ bundle exec rake middleware
126. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
127. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
128. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
129. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
130. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
131. @panthomakos insert_before
132. @panthomakos Rails.application.config.middleware.insert_before( ::ActionDispatch::BestStandardsSupport, ::Strava::EntityMapMiddleware )
133. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use ActionDispatch::BestStandardsSupport use Strava::EntityMapMiddleware run Strava::Application.routes
134. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use Strava::EntityMapMiddleware use ActionDispatch::BestStandardsSupport run Strava::Application.routes
135. @panthomakos Ctrl + R
136. @panthomakos bug...
137. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use Strava::EntityMapMiddleware use ActionDispatch::BestStandardsSupport run Strava::Application.routes
138. @panthomakos Rails.application.config.middleware.insert_before( ::Rack::ETag, ::Strava::EntityMapMiddleware )
139. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Rack::ETag use Strava::EntityMapMiddleware use ActionDispatch::BestStandardsSupport run Strava::Application.routes
140. @panthomakos $ bundle exec rake middleware use Rack::Cors use Airbrake::UserInformer use ActionDispatch::Static use Rack::Lock use Rack::Runtime use Rack::MethodOverride use ActionDispatch::RequestId use Rails::Rack::Logger use ActionDispatch::ShowExceptions use ActionDispatch::DebugExceptions use BetterErrors::Middleware use Airbrake::Rails::Middleware use ActionDispatch::RemoteIp use ActionDispatch::Reloader use ActionDispatch::Callbacks use ActiveRecord::ConnectionAdapters::ConnectionManagement use ActiveRecord::QueryCache use ActionDispatch::Cookies use ActionDispatch::Session::CookieStore use ActionDispatch::Flash use ActionDispatch::ParamsParser use ActionDispatch::Head use Rack::ConditionalGet use Strava::EntityMapMiddleware use Rack::ETag use ActionDispatch::BestStandardsSupport run Strava::Application.routes
141. @panthomakos Ctrl + R
142. @panthomakos fixed!
143. @panthomakos Rack::ETag
144. @panthomakos $ cd $(bundle show rack) $ vim lib/rack/etag.rb
145. @panthomakos def call(env) status, headers, body = @app.call(env) if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) digest, body = digest_body(body) headers['ETag'] = %("#{digest}") if digest end unless headers['Cache-Control'] if digest headers['Cache-Control'] = @cache_control if @cache_control else headers['Cache-Control'] = @no_cache_control if @no_cache_control end end [status, headers, body] end
146. @panthomakos def call(env) status, headers, body = @app.call(env) if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) digest, body = digest_body(body) headers['ETag'] = %("#{digest}") if digest end unless headers['Cache-Control'] if digest headers['Cache-Control'] = @cache_control if @cache_control else headers['Cache-Control'] = @no_cache_control if @no_cache_control end end [status, headers, body] end
147. @panthomakos private def digest_body(body) parts = [] body.each { |part| parts << part } string_body = parts.join digest = Digest::MD5.hexdigest(string_body) unless string_body.empty? [digest, parts] end
148. @panthomakos private def digest_body(body) parts = [] body.each { |part| parts << part } string_body = parts.join digest = Digest::MD5.hexdigest(string_body) unless string_body.empty? [digest, parts] end
149. @panthomakos close!?
150. @panthomakos private def digest_body(body) parts = [] body.each { |part| parts << part } string_body = parts.join digest = Digest::MD5.hexdigest(string_body) unless string_body.empty? [digest, parts] end
151. @panthomakos close!
152. @panthomakos def call(env) status, headers, body = @app.call(env) if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) digest, body = digest_body(body) headers['ETag'] = %("#{digest}") if digest end unless headers['Cache-Control'] if digest headers['Cache-Control'] = @cache_control if @cache_control else headers['Cache-Control'] = @no_cache_control if @no_cache_control end end [status, headers, body] end
153. @panthomakos close!
154. @panthomakos def call(env) status, headers, body = @app.call(env) # if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) # digest, body = digest_body(body) # headers['ETag'] = %("#{digest}") if digest # end unless headers['Cache-Control'] if digest headers['Cache-Control'] = @cache_control if @cache_control else headers['Cache-Control'] = @no_cache_control if @no_cache_control end end [status, headers, body] end
155. @panthomakos rack/rack @ master
156. @panthomakos def call(env) status, headers, body = @app.call(env) if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) original_body = body digest, new_body = digest_body(body) body = Rack::BodyProxy.new(new_body) do original_body.close if original_body.respond_to?(:close) end headers[ETAG_STRING] = %(W/"#{digest}") if digest end unless headers[CACHE_CONTROL] if digest headers[CACHE_CONTROL] = @cache_control if @cache_control else headers[CACHE_CONTROL] = @no_cache_control if @no_cache_control end end [status, headers, body] end
157. @panthomakos def call(env) status, headers, body = @app.call(env) if etag_status?(status) && etag_body?(body) && !skip_caching?(headers) original_body = body digest, new_body = digest_body(body) body = Rack::BodyProxy.new(new_body) do original_body.close if original_body.respond_to?(:close) end headers[ETAG_STRING] = %(W/"#{digest}") if digest end unless headers[CACHE_CONTROL] if digest headers[CACHE_CONTROL] = @cache_control if @cache_control else headers[CACHE_CONTROL] = @no_cache_control if @no_cache_control end end [status, headers, body] end
158. @panthomakos ETag middleware now conforms to body close SPEC https://github.com/rack/rack/commit/4d9e1b228dacbcf1552c68e2ab2f21274fdcecb4
159. @panthomakos Next
160. @panthomakos $ bundle update rack
161. @panthomakos Rails.application.config.middleware.insert_before( ::Rack::ETag, ::Strava::EntityMapMiddleware )
162. @panthomakos module Strava class EntityMapMiddleware def initialize(app) @app = app end def call(env) status, headers, body = @app.call(env) [status, headers, BodyProxy.new(body)] end end end
163. @panthomakos module Strava class EntityMapMiddleware def initialize(app) @app = app end def call(env) ::Strava::EntityMap.clear! @app.call(env) end end end
164. @panthomakos Options
165. @panthomakos Is the Rack API error-prone?
166. @panthomakos Malicious Middleware
167. @panthomakos Forgetful Middleware
168. @panthomakos Is the Rack API Ruby-like?
169. @panthomakos [status, headers, body]
170. @panthomakos response.status response.headers response.body
171. @panthomakos [status, headers, body]
172. @panthomakos #close
173. @panthomakos Body #each and #close
174. @panthomakos #each is the response
175. @panthomakos #close is the lifecycle
176. @panthomakos [ status, headers, body, &close ]
177. @panthomakos Definitely Not Backwards Compatible
178. @panthomakos [ status, headers, body, &close ]
179. @panthomakos [ status, headers, body, &close ]
180. @panthomakos Ignores other lifecycle events
181. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" response end end
182. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" response end end
183. @panthomakos class MyTimer def initialize(app) @app = app end def call(env) start = ::Timer.cputime response = @app.call(env) finish = ::Timer.cputime puts "Response Time: #{finish - start}ms" response end end
184. @panthomakos before_all before after after_all
185. @panthomakos ActionDispatch::Callbacks http://api.rubyonrails.org/v5.0.3/classes/ActionDispatch/Callbacks.html
186. @panthomakos ::ActionDispatch::Callbacks.before do ::Strava::EntityMap.clear! end
187. @panthomakos ::ActionDispatch::Callbacks.before do @start = Timer.cputime end
188. @panthomakos Rails Only
189. @panthomakos Order Dependency (timers, exception trackers, cache clearing)
190. @panthomakos Rack.before(::Strava::Application) do ::Strava::EntityMap.clear! end
191. @panthomakos class MyTimer def before(_request) @start = Timer.cputime end def after(_response) @finish = Timer.cputime puts "Response Time: #{@finish - @start}ms" end end
192. @panthomakos before_all before after after_all
193. @panthomakos Hooks that manage the underlying middleware complexity for you.
194. @panthomakos Probably Backwards Compatible
195. @panthomakos Middleware Lite Miller Lite Beer Mat / Roger W / CC BY-SA 2.0
196. @panthomakos Double Refresh Bug
197. @panthomakos @panthomakos