Stuck in the Middle: Leverage the power of Rack::Middleware

Before a request ever hits your Rails application, it winds its way through a series of pieces of Rack middleware. Middleware sets session cookies, writes your logs, and enables the functionality in many gems such as Warden.

With Rails or any Rack app, you can easily insert your own custom middleware, allowing you to log, track, redirect, and alter the incoming request before it hits your application.

You will leave this talk confident in writing your own custom middleware, better able to troubleshoot gems that rely on middleware and with an understanding of how your Rails app functions.

Transcript

1. Stuck in the Middle Leverage the power of Rack::Middleware
2. §  What? §  How? §  Why? §  Who…?
3. What?
4. Rack
5. Your Application
6. CGI
7. http://www.whynot.io/ruby/what-is-rack-in-ruby/
8. Rack ¤ Incoming Request: ¤ the “environment” hash ¤ Outgoing Response: ¤ Status code ¤ Headers ¤ Content body
10. Rack
11. Rack::Middleware
12. http://www.whynot.io/ruby/what-is-rack-in- ruby/
14. Handler
15. Handler Adapter
16. Handler Adapter Middlewares
17. Middleware in Rails q  ActionDispatch::Static q  Rails::Rack::Logger q  ActionDispatch::Cookies q  ActionDispatch::Flash q  ActionDispatch::ParamsParser
18. How?
19. A very basic Middleware Ping!
20. # lib/middleware/ping.rb
21. # lib/middleware/ping.rb class Ping end
22. # lib/middleware/ping.rb module Middleware class Ping end end
23. # Middleware::Ping def initialize(app) @app = app end
24. # Middleware::Ping def initialize(app) @app = app end def call(env) end
25. # Middleware::Ping def initialize(app) @app = app end def call(env) [‘200’, {}, [“Pong!”]] end
26. # Middleware::Ping def call(env) request = Rack::Request.new(env) [‘200’, {}, [“Pong!”]] end
27. { "PATH_INFO" => "/ping.json", "QUERY_STRING" => "", "REQUEST_METHOD" => "GET", "REQUEST_URI" => "http://localhost:3000/ping.json", "REQUEST_PATH" => "/ping.json" ... }
28. # Middleware::Ping def call(env) request = Rack::Request.new(env) return @app.call(env) unless request.path == ‘/ping’ [‘200’, {}, [“Pong!”]] end
29. A less basic middleware Request response time logging
30. # lib/middleware/request_time_logging.rb module Middleware class RequestTimeLogging end end
31. # Middleware::RequestTimeLogging def initialize(app) @app = app end
32. # Middleware::RequestTimeLogging def call(env) end
33. # Middleware::RequestTimeLogging def call(env) @app.call(env) end
34. # Middleware::RequestTimeLogging def call(env) start = Time.now @app.call(env) end
35. # Middleware::RequestTimeLogging def call(env) start = Time.now @app.call(env) elapsed = Time.now - start end
36. # Middleware::RequestTimeLogging def call(env) start = Time.now @app.call(env) elapsed = Time.now - start [status, headers, response] end
37. # Middleware::RequestTimeLogging def call(env) start = Time.now @app.call(env) elapsed = Time.now - start [status, headers, response] end
38. # Middleware::RequestTimeLogging def call(env) start = Time.now status, headers, response = @app.call(env) elapsed = Time.now - start [status, headers, response] end
39. # Middleware::RequestTimeLogging def call(env) start = Time.now status, headers, response = @app.call(env) elapsed = Time.now - start [status, headers, response] end
40. # Middleware::RequestTimeLogging def call(env) start = Time.now status, headers, response = @app.call(env) elapsed = Time.now - start log_response_time( elapsed ) [status, headers, response] end
41. # Middleware::RequestTimeLogging def call(env) start = Time.now status, headers, response = @app.call(env) elapsed = Time.now - start request = Rack::Request.new(env) log_response_time( elapsed, request ) [status, headers, response] end
42. # Middleware::RequestTimeLogging private def log_response_time(elapsed_time, request) end
43. # Middleware::RequestTimeLogging private def log_response_time(elapsed_time, request) end
44. # Middleware::RequestTimeLogging def log_response_time(elapsed_time, request) end
45. # Middleware::RequestTimeLogging def log_response_time(elapsed_time, request) { response_time_secs: elapsed_time, path: request.path } end
46. # Middleware::RequestTimeLogging def log_response_time(elapsed_time, request) payload = { response_time_secs: elapsed_time, path: request.path } SplunkLogger.log(‘request.response_time’, payload) end
47. Throttling https://github.com/bendiken/rack-throttle
48. lib/rack/throttle/limiter.rb
49. lib/rack/throttle/limiter.rb
50. lib/rack/throttle/limiter.rb
51. Why?
52. Middleware can simplify your application
53. addons.heroku.com
54. elements.heroku.com
55. Middleware can protect your application
56. Middleware sees both the request & response object
57. Middleware can be a code sharing mechanism
58. Who...? Things that will trigger your successors to `git blame` your code
59. Order
60. > rake middleware
61. Order use Rack::Sendfile use ActionDispatch::Static … run MyApp::Application.routes
62. Order use Rack::Sendfile use ActionDispatch::Static … use ActionDispatch::RequestId use Rails::Rack::Logger … run MyApp::Application.routes
63. Order use ActionDispatch::RequestId use Rails::Rack::Logger … use Rack::Sendfile use ActionDispatch::Static run MyApp::Application.routes
64. Order use OmniAuth::Builder use Warden::Manager use WardenOmniAuth … use ActionDispatch::Session::ActiveRecordStore … run MyApp::Application.routes
65. github.com/hassox/warden/wiki/Setup
66. Order use ActionDispatch::Session::ActiveRecordStore … use OmniAuth::Builder use Warden::Manager use WardenOmniAuth … run MyApp::Application.routes
67. Application Logic
68. Application Logic
69. Some Red Flags §  Modifying the request §  Awareness of business logic §  Awareness of models
70. Mitigation Strategies §  Use app/middlewares §  Use app/hacks or lib/hacks §  Keyword comments
71. Always return a response
72. Thread Safety (if you set instance variables)
73. # Middleware::Ping def initialize(app) @app = app end def call(env) [‘200’, {}, [“Pong!”]] end
74. # Middleware::Ping def call(env) dup._call(env) end private def _call(env) [‘200’, {}, [“Pong!”]] end
75. # Middleware::Ping def call(env) dup._call(env) end private def _call(env) [‘200’, {}, [“Pong!”]] end
76. Stuck in the Middle Leverage the power of Rack::Middleware
77. Thank You! @cdwort