Code Archaeology: Becoming Indiana Jones (PHPConf Asia)

Code archaeology is one of the most important skills you will ever learn as a developer. How many times have you been thrown into legacy projects with no environment setup, no documentation, and little support from coworkers? The ability to hit the ground running on new applications is a sought-after skill for many employers. In this talk, we will take an open-source project that we have never seen before and work through the steps required to get it up and running so we can start contributing today.

Transcript

1. and the Kung Fu Coders @mheap at #PHPCONFASIA
2. Antikythera Mechanism
3. It’s Been Stolen!
4. Why do we want it?
5. 40-80% of a project is maintenance
6. Why so much?
7. Our job is to read code, Not to write it
8. *flying noises*
9. Where do we start?
10. What should be saved?
11. What is dangerous?
12. Who created this?
13. README.md
14. Talk to people
15. Inventory the code
16. Dependencies
17. Build the project
18. Accept you're missing 10%
19. Time to go in!
20. Security!
21. “Incorrect Password”
22. $ grep -lr "Incorrect password" * src/Architect/Security/DoorPasswordValidator.php
23. namespace Architect\Security; class DoorPasswordValidator { private $doorPassword = 'shibboleet'; public function validate($input) { if ($this->doorPassword !== $input) { throw new \Exception("Incorrect password"); } return true; } }
24. We’re in!
25. Navigation
26. Draw a map
28. Read the code
29. Don’t trust the comments
30. namespace Architect\Game; class Roulette { /** * Returns a random number */ private function spinRandom(){ } }
31. Don’t trust the code
32. namespace Architect\Game; class Roulette { /** * Returns a random number */ private function spinRandom(){ return 4; } }
33. Does this code even run?
34. /** * Returns a random number */ private function spinRandom() { die('Yes it does'); return 4; }
35. Look for side effects
36. public function triggerFireAlarm() { $this->startSprinklers(); $this->callFireBrigade(); $this->releaseDoorLocks(); }
37. Naming Things
38. Find intentions
39. Find Patterns
40. Prove you understand it
41. I don’t understand it
42. Debugging
43. use everything
44. Everything goes
45. DDD
46. Die Driven Debugging
47. echo '######################'.PHP_EOL; echo $currentCasinoCapacity; echo '######################'.PHP_EOL;
48. if (!isset($visitors['jenny_wong'])){ var_dump($visitors);die; }
49. echo '######################'.PHP_EOL; var_dump(debug_backtrace()); echo '######################'.PHP_EOL;
50. class MyDoorMan extends DoorMan { public function changeShiftAt($val) { throw new Exception("Changing at $val"); } }
51. XDebug
52. XDebug.scream
53. XDebug_break();
54. if (!isset($visitors['jenny_wong'])){ xdebug_break(); }
55. XHPROF
56. DDD +X Debug + XHProf == WINNING
57. Observer Effect
58. I’m feeling better
59. Project History
60. git log -S <search>
61. git log -S antikythera
62. commit 5288d5804a3fc20dae4f3b2deeaa7f687595aff1 Author: Michael Cheng <michael@example.com> Date: Tue May 24 09:33:59 2016 +0000 Add new secure storage facility. (Closes #42) The existing storage facilities use symmetrical encryption keys which allow anyone with the password to access them. The new storage is more secure and requires both a password and my handprint. There’s nothing in there yet but we’ll put the Antikythera in it as soon as it arrives
63. What’s changed recently?
64. Temporal Coupling
65. Explicit
66. commit 0dc164fb052f4b838a674648aa29d83b60f01fa2 Author: Michael Cheng <michael@example.com> Date: Fri May 20 12:14:55 2016 +0000 Changed from European to American roulette table. Gives the house a better edge 5 2 src/Architect/Game/Roulette.php 14 0 test/Architect/Game/RouletteTest.php
67. Implicit
68. commit 2915dabebc8b87b84ec40fac0f4954fb84f3b7cd Author: Michael Cheng<michael@example.com> Date: Sun May 22 21:27:31 2016 +0000 Removed the corner roulette table as it was crooked. Updated Fire plan to remove table 0 2 src/Architect/FloorPlan.php 0 1 src/Architect/Policy/FireEscape.php
69. Common Causes
70. Code Maat
71. statistic,value number-of-commits,2254 number-of-entities,3179 number-of-entities-changed,9979 number-of-authors,106
72. entity,n-authors,n-revs src/Room/VipLounge.php,26,181 src/Game/Blackjack.php,22,76 src/Controller/CloakroomController.php,21,110 src/People/FloorManager.php,19,91
73. entity,age-months src/Security/PasswordManager.php,1 src/Bar/DrinkPrices.php,1 src/Game/Poker/Stud.php,3 src/Security/RadioChannels.php,7
74. entity,coupled,degree,average-revs src/Manager/FloorManager.php,src/Factory/TableFactory.php,100,19 src/Vendor/Drinks.php,src/Vendor/Snacks.php,60,10 src/Room/VipLounge.php,src/Room/Cloakroom,14,172
75. entity,coupled,degree,average-revs application/config/config.php,application/config/database.php,90,6
76. History Analysis is flawed
77. Leaving a legacy
78. Secure the site
79. Rosetta Stone
80. Logging
81. Name things well
82. Build a knowledge map
83. Leave useful comments
84. // // Dear maintainer: // // Once you are done trying to 'optimize' this routine, // and have realized what a terrible mistake that was, // please increment the following counter as a warning // to the next guy: // // total_hours_wasted_here = 42 // I’ve been @mheap, you’ve been awesome!