The Little Server That Could

Have you ever wondered what dark magic happens when you start up your Ruby server? Let’s explore the mysteries of the web universe by writing a tiny web server in Ruby! Writing a web server lets you dig deeper into the Ruby Standard Library and the Rack interface. You’ll get friendlier with I/O, signal trapping, file handles, and threading. You’ll also explore dangers first hand that can be lurking inside your production code- like blocking web requests and shared state with concurrency.

Transcript

1. T h e L i t t l e S e r v e r T h a t C o u l d T h e L i t t l e S e r v e r T h a t C o u l d
2. Stella Cotton | @practice_cactus
3. Stella Cotton | @practice_cactus The Little Server That Could
4. Stella Cotton | @practice_cactus The Little Server That Could Can’t
5. Stella Cotton | @practice_cactus What can it do?
6. Stella Cotton | @practice_cactus Abstractions are Powerful
7. Stella Cotton | @practice_cactus Abstractions are 
 not Magic
8. Stella Cotton | @practice_cactus Servers are an Abstraction
9. Stella Cotton | @practice_cactus Magical
10. Stella Cotton | @practice_cactus Servers are 
 not Magic
11. Stella Cotton | @practice_cactus What else can it do?
12. Stella Cotton | @practice_cactus What’s a server?
13. Stella Cotton | @practice_cactus Production Servers: • Unicorn • Puma • Phusion Passenger • Thin Dev Server: • WEBrick

14. Stella Cotton | @practice_cactus Just a Ruby Program
15. Stella Cotton | @practice_cactus $ ruby server.rb
16. Stella Cotton | @practice_cactus How is it different?
17. Stella Cotton | @practice_cactus 
 1. Interacts with the OS to talk to the outside world
 2. Conforms to a specific API
18. Stella Cotton | @practice_cactus 
 ~4.68 Billion 
 Indexed Web Pages http://www.worldwidewebsize.com/
19. Stella Cotton | @practice_cactus https://en.wikipedia.org/wiki/Usage_share_of_web_browsers Browser Usage Share Chrome 49.82% Safari 13.61% Firefox 7.78% UC Browser 6.67% Opera 5.71% Other 2.43%
20. Stella Cotton | @practice_cactus How is this possible?
21. Stella Cotton | @practice_cactus W3C Worldwide Web Consortium
22. Stella Cotton | @practice_cactus HTTP as an API
23. Stella Cotton | @practice_cactus RFC 2616
24. Stella Cotton | @practice_cactus
25. Stella Cotton | @practice_cactus 1. Initial line 2. Zero or more header lines 3. Blank line 4. Message body (optional) https://www.jmarshall.com/easy/http/ GET /path/to/index.html HTTP/1.0 Host: www.example.com:80 Hello, this is a message body
26. Stella Cotton | @practice_cactus 1. Visiting web page
 2. Telnet
 3. CURL
 4. HTTP Client Libraries
 (e.g. Net::HTTP) Clients:
27. Stella Cotton | @practice_cactus Instructions to Build 
 Your Own API
28. Stella Cotton | @practice_cactus 
 Literal “Spec” & Figurative “Spec”
29. Stella Cotton | @practice_cactus 
 
 GET /path/to/index.html HTTP/1.0
30. Stella Cotton | @practice_cactus 
 
 http://abc.com:80/~smith/home.html http://ABC.com/%7Esmith/home.html http://ABC.com:/%7esmith/home.html https://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html
31. Stella Cotton | @practice_cactus Seth Godin: http://sethgodin.typepad.com/
32. Stella Cotton | @practice_cactus 
 
 $ curl localhost:2222
33. Stella Cotton | @practice_cactus How does it communicate?
34. Stella Cotton | @practice_cactus 1. The Outside World 2. The Application 3. You, the Developer
35. Stella Cotton | @practice_cactus 
 
 Process
36. Stella Cotton | @practice_cactus $ ps aux | grep server.rb
37. Stella Cotton | @practice_cactus
38. Stella Cotton | @practice_cactus 
 
 Ruby Standard Library
39. Stella Cotton | @practice_cactus Open a socket Listen for requests Handle those requests Close the socket
40. Stella Cotton | @practice_cactus 
 
 $ netstat -a
41. Stella Cotton | @practice_cactus 
 
 “File Descriptor”/“File Handle”
42. Stella Cotton | @practice_cactus 
 Defining our Socket:
 1. Addressing Format
 2. Kind of socket
43. Stella Cotton | @practice_cactus 
 UNIX 
 vs 
 INET
44. Stella Cotton | @practice_cactus 
 UNIX: /tmp/my_socket.sock
45. Stella Cotton | @practice_cactus 
 INET: 192.0.1.1:2222
46. Stella Cotton | @practice_cactus 
 Defining our Socket:
 1. Addressing Format
 2. Kind of socket
47. Stella Cotton | @practice_cactus 
 Stream 
 vs 
 Datagram
48. Stella Cotton | @practice_cactus 
 
 Stream sockets 

49. Stella Cotton | @practice_cactus 
 TCP 
 Three-Way Handshake
50. Stella Cotton | @practice_cactus created by unlimicon from the Noun Project Client Server Syn Ack Syn, Ack
51. Stella Cotton | @practice_cactus created by unlimicon from the Noun Project Client Server Ack Data Pkt 1 Ack Data Pkt 2
52. Stella Cotton | @practice_cactus 
 
 Datagram sockets 

53. Stella Cotton | @practice_cactus created by unlimicon from the Noun Project Client Server Data Pkt 10 Data Pkt 4 Data Pkt 4
54. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 create_server_socket
 end
 
 def create_server_socket
 Socket.new(:INET, :STREAM, 0) #create socket
 end
55. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 create_server_socket
 end
 
 def create_server_socket
 socket = Socket.new(:INET, :STREAM, 0) #create socket
 sockaddr = Addrinfo.tcp("127.0.0.1", 2222) #create an address
 end
56. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 create_server_socket
 end
 
 def create_server_socket
 socket = Socket.new(:INET, :STREAM, 0) #create socket
 sockaddr = Addrinfo.tcp("127.0.0.1", 2222) #create an address
 socket.bind(sockaddr) #bind socket to that address
 end
57. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 create_server_socket
 end
 
 def create_server_socket
 socket = Socket.new(:INET, :STREAM, 0) #create socket
 sockaddr = Addrinfo.tcp("127.0.0.1", 2222) #create an address
 socket.bind(sockaddr) #bind socket to that address
 socket.listen(5) #listen on the socket
 socket #return the socket
 end
58. Stella Cotton | @practice_cactus Open a socket Listen for requests Handle those requests Close the socket
59. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do client_socket, client_addrinfo = server.accept end
 end
60. Stella Cotton | @practice_cactus 
 
 $ curl localhost:2222
61. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do client_socket, client_addrinfo = server.accept # returns new sockets end
 end
62. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do client_socket, client_addrinfo = server.accept request = client_socket.recv(1056) end
 end
63. Stella Cotton | @practice_cactus Open a socket Listen for requests Handle those requests Close the socket
64. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end
 def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code
 end
 end

65. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end
66. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end
67. Stella Cotton | @practice_cactus Open a socket Listen for requests Handle those requests Close the socket
68. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end
69. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end
70. Stella Cotton | @practice_cactus 1. The Outside World 2. The Application 3. You, the Developer
71. Stella Cotton | @practice_cactus Parser
72. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end we never 
 actually use this
 request
73. Stella Cotton | @practice_cactus 
 Parser extracts… Header fields and values Content-Length Request method Response status code Transfer-Encoding HTTP version Request URL Message body
74. Stella Cotton | @practice_cactus 
 
 Ragel Parser (.rl)
75. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end let’s modify this!
76. Stella Cotton | @practice_cactus Rack Interface
77. Stella Cotton | @practice_cactus 1. Ruby Object
 2. Responds to “.call”
 3. Takes 1 argument (env hash)
 4. Returns a response with 
 status, header, body Rack Interface:
78. Stella Cotton | @practice_cactus class RackApp
 def call(environment)
 [
 '200',
 {'Content-Type' => 'text/html'},
 ["Hello world for reals"]
 ]
 end
 end
 
 Rack::Handler.register('server', 'Rack::Handler::Server')
 Rack::Handler::Server.run(RackApp.new)

79. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 def run_application_code
 app_response = "Hello World!\n"
 server_response = "HTTP/1.1 200 OK\r\n" +
 "Content-Type: text/plain\r\n" +
 "Content-Length: #{app_response.bytesize}\r\n” +
 "Connection: close\r\n" +
 "\r\n" +
 app_response
 end let’s modify this!
80. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end def run_application_code
 status, headers, body = app.call({})
 
 server_response = "HTTP/1.1 #{status}\r\n" +
 "#{headers}" +
 "\r\n" +
 "#{body}"
 end
 Rack interface!
81. Stella Cotton | @practice_cactus class RackApp
 def call(environment)
 [
 '200',
 {'Content-Type' => 'text/html'},
 ["Hello world for reals"]
 ]
 end
 end
 
 Rack::Handler.register('server', 'Rack::Handler::Server')
 Rack::Handler::Server.run(RackApp.new)

82. Stella Cotton | @practice_cactus
83. Stella Cotton | @practice_cactus class RackApp
 def call(environment)
 maru_gif = get_maru_gif_from_giphy_api
 [
 '200',
 {'Content-Type' => 'text/html'},
 [ maru_gif ]
 ]
 end
 end
 
 Rack::Handler.register('server', 'Rack::Handler::Server')
 Rack::Handler::Server.run(RackApp.new) External API call
84. Stella Cotton | @practice_cactus
85. Stella Cotton | @practice_cactus Client 1 waits 5 seconds Server Two Clients Slowly 
 downloading 
 cat gifs
86. Stella Cotton | @practice_cactus Server Two Clients Client 2 waits almost 10 seconds Slowly 
 downloading 
 cat gifs
87. Stella Cotton | @practice_cactus Forking
88. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept request = client_socket.recv(1056)
 response = run_application_code client_socket.print response client_socket.close
 end
 end
 code that 
 handles request
89. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept handle_request(client_socket) client_socket.close
 end
 end
 def handle_request
 request = client_socket.recv(1056)
 response = run_application_code
 client_socket.print response
 end code that 
 handles request
90. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept fork do handle_request(client_socket) end client_socket.close
 end
 end
 def handle_request
 request = client_socket.recv(1056)
 response = run_application_code
 client_socket.print response
 end code that 
 handles request
91. Stella Cotton | @practice_cactus Still slowly 
 downloading 
 cat gifs Server Two Clients Client 2 only waits 5 seconds
92. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept fork do handle_request(client_socket) end client_socket.close
 end
 end
 def handle_request
 request = client_socket.recv(1056)
 response = run_application_code
 client_socket.print response
 end be sure to close this!
93. Stella Cotton | @practice_cactus 
 Killing Zombies: sudo lsof -i -n -P | grep 2222 ps aux | grep [process id] kill [process id]

94. Stella Cotton | @practice_cactus Parent Process fork do Child Process fork do Child Process fork do Child Process
95. Stella Cotton | @practice_cactus 
 
 Wait…won’t fork double my memory that I’m consuming?
96. Stella Cotton | @practice_cactus 
 
 “Copy on Write”
97. Stella Cotton | @practice_cactus Parent Process fork do Child Process fork do Child Process fork do Child Process
98. Stella Cotton | @practice_cactus Pre- Ruby 2.0
 :(
99. Stella Cotton | @practice_cactus Garbage Collection
100. Stella Cotton | @practice_cactus 
 
 cat_gifs = “awesome”
101. Stella Cotton | @practice_cactus Pre- Ruby 2.0
 :( *technically a patched version of Ruby 1.8 existed, but wasn’t in the core
102. Stella Cotton | @practice_cactus Parent Process fork do Child Process fork do Child Process fork do Child Process
103. Stella Cotton | @practice_cactus Parent Process fork do fork do Child Process Child Process
104. Stella Cotton | @practice_cactus 
 
 Ruby 2.0
 :) http://patshaughnessy.net/2012/3/23/
 why-you-should-be-excited-about-garbage-collection-in-ruby-2-0
105. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 end def loop_and_listen_for_client_requests(server)
 loop do
 client_socket, client_addrinfo = server.accept fork do handle_request(client_socket) end client_socket.close
 end
 end
 def handle_request
 request = client_socket.recv(1056)
 response = run_application_code
 client_socket.print response
 end
106. Stella Cotton | @practice_cactus Threading
107. Stella Cotton | @practice_cactus Parent Process Thread.new Child Thread Child Thread Child Thread Thread.new Thread.new Shared Memory
108. Stella Cotton | @practice_cactus Benefits of Threading:
 - Uses less memory
 -Threads die with process
 - Much faster to communicate
109. Stella Cotton | @practice_cactus GIL
 Global Interpreter Lock
110. Stella Cotton | @practice_cactus def purchase_cat_toys
 if @available_cat_toys > 0
 buy_cat_toy
 else
 cat_toy_unavailable
 end
 end

111. Stella Cotton | @practice_cactus def purchase_cat_toys
 if @available_cat_toys > 0 
 #context switch 
 #buy a cat toy that #doesn’t exist :( buy_cat_toy
 else
 cat_toy_unavailable
 end
 end def purchase_cat_toys 
 if @available_cat_toys > 0
 #buy last cat toy
 buy_cat_toy 
 else
 cat_toy_unavailable
 end
 end #context switch Thread 1 Thread 2
112. Stella Cotton | @practice_cactus GIL
 Global Interpreter Lock
113. Stella Cotton | @practice_cactus Why use a multi-threaded 
 server with MRI?
114. Stella Cotton | @practice_cactus Downsides of Threading:
 - Your code has to be thread safe
 - Your gems have to be thread safe
115. Stella Cotton | @practice_cactus 1. The Outside World 2. The Application 3. You, the Developer
116. Stella Cotton | @practice_cactus 
 
 Signals
117. Stella Cotton | @practice_cactus 
 
 kill -l
118. Stella Cotton | @practice_cactus 
 
 ctrl + c
119. Stella Cotton | @practice_cactus require 'socket'
 
 def server
 trap_interrupt
 socket = create_server_socket
 loop_and_listen_for_client_requests(socket)
 socket.close
 end
 
 def trap_interrupt
 Signal.trap("INT") do
 puts "\nTerminating..."
 exit 130
 end
 end
120. Stella Cotton | @practice_cactus 
 
 SIGKILL
121. Stella Cotton | @practice_cactus Our Little Server 
 ❤
122. Stella Cotton | @practice_cactus 11am - 2pm Saturday