Practical tips for dealing with projects involving legacy code. Covers investigating past projects, static analysis of existing code, and methods for changing legacy code. Presented at PHP Benelux '10

1. ving
Li
with
Legacy
Code

2. @rowan_m

3. @rowan_m
Plusnet
Ibuildings

4. What is
“Legacy Code”?

5. What is
“Legacy Code”?
Code without
tests
Code you've
“inherited”
Code no-one
understands
Technical debt

6. Who has
never
created
Legacy Code?

7. My own
little
story

8. Pragmatic, not ideal
istic
My own
little
story

9. Starting a project

10. Aim to understand
the concepts
and motivations

11. Try using
the application

12. Find and then read
any / all
documentation

13. Official: Che
Project brief ( ) c kli
Requirements ( ) st
Tech. Spec. ( )
Actual:
Emails ( )
Meeting notes ( )
Progress:
Gant charts ( )
Burndowns ( )
Overtime logs ( )
Quality:
Bug tracker ( )
Complaints ( )
User Forums ( )

14. Talk to the
original developers

15. Talk to the users
… especially the
“different” ones

16. Approaching
the code

17. Catalogue the
live platform
& environment

18. Recreate it!

19. Deploy the code

20. PHP: Che
php.ini ( ) c kli
PEAR / PECL modules ( ) st
Compile options ( )
Patches ( )
The Rest:
OS ( )
Package manager ( )
Web server ( )
Web server modules ( )
Site config. ( )
Database ( )
Cache ( )
JS libraries ( )
Firewall rules ( )
Proxies ( )
Services running ( )

21. Time to enter
The Code

22. Time to enter
The Code
Reading
Static analysis
Dynamic analysis

23. http://www.phpdoc.org/
doc
php
Title
phpdoc -ti 'Sweet Application'
-pp -o HTML:Smarty:PHP
-d Libraries Style
-t Docs
Code in here
Docs out here!

24. Beware of type-hiding!
Type-hinting
/**
* @param array $opts Current options
* @return array Options with flag set
*/
function setFlag(array $opts) {
$opts['flag'] = true;
return $opts;
}
Type-hiding
/**
* @param int $fullPence Full price in pence
* @return float Discounted price in pence
*/
function applyDiscount($fullPence) {
return ($fullPence * 0.8);
}

25. ygen
dox
doxygen -s -g ~/doxy.conf
vim ~/doxy.conf
# edit at least this
Code in here OUPUT_DIRECTORY
# play with the rest
cd ~/dev/project
Docs out here
doxygen ~/doxy.conf
http://www.stack.nl/~dimitri/doxygen/

26. http://ctags.sourceforge.net/
ta gs
c
Code in here
#!/bin/bash Tags out here
cd ~/Dev/ &&
ctags-exuberant -f ~/.vimtags
-h ".php" -R
--exclude=".git"
--links=no
--totals=yes
--tag-relative=yes
--PHP-kinds=+cf
--regex-PHP='/abstracts+classs+([^ ]+)/1/c/'
--regex-PHP='/interfaces+([^ ]+)/1/c/'
--regex-PHP='/(publics+|statics+|abstracts+|protecteds+|privates+) ↵
functions+&?s*([^ (]+)/2/f/'
Voodoo

27. ml http://www.bouml.fr/
bou

28. ml http://bouml.free.fr/
bou

29. ml http://bouml.free.fr/
bou

30. ml http://bouml.free.fr/
bou

31. ml http://bouml.free.fr/
bou

32. ml http://bouml.free.fr/
bou

33. ou ml
b

34. ffer
esni
co d
rowan@swordbean:~/Dev/ZendFramework-1.9.4/library/Zend/Service$ phpcs
--standard=Zend Exception.php
FILE: /home/rowan/Dev/ZendFramework-1.9.4/library/Zend/Service/Exception.php
--------------------------------------------------------------------------------
FOUND 1 ERROR(S) AND 2 WARNING(S) AFFECTING 3 LINE(S)
--------------------------------------------------------------------------------
17 | WARNING | Line exceeds 80 characters; contains 87 characters
32 | WARNING | Line exceeds 80 characters; contains 87 characters
36 | ERROR | Opening class brace must be on a line by itself
36 | ERROR | Closing brace must be on a line by itself
--------------------------------------------------------------------------------
http://pear.php.net/package/PHP_CodeSniffer/

35. t in uous
Con io n
Inte grat
http://jenkins-ci.org/
http://phpundercontrol.org/
http://sismo.sensiolabs.org/

36. Decisi
on tim
e!

37. Decisi
on tim
e!
Ign
cod ore
e a it ,
nyw
ay
a cto r,
ref est
ite, st, t
Rewr , te
test

38. Ignore it,
code anyway

39. Ignore it,
code anyway
Please don't.

40. Ignore it,
code anyway
Please don't.
however...

41. Deadlines, clients,
money, etc.

42. Deadlines, clients,
money, etc.
Make everyone
aware of the risks
Secure a
follow-up project

43. Why do you need the code?

44. Why do you need the code?
simple
Library dependency
Adding new behaviour
Changing behaviour
complex

45. Isolate
legacy dependencies

46. Isolate
legacy dependencies
Create an
anti-corruption layer

47. Complete isolation
Create a
legacy service

48. Partial isolation
Wrapper classes
or methods

49. Wrapper class
<?php
include('/home/victorvon/secrets.inc');
/**
* @param array $person willing volunteer
*/
function extract_brain(&$person) {
$brain = $person['brain'];
unset($person['brain']);
}
return $brain; Some code
/**
you need
* @param array $person
* @return bool living or not
:(
*/
function create_life($person) {
require_once(LIB_DIR.'../nuts_n_bolts.inc');
kerzap();
$person['living'] = true;
return $person;
}
?>

50. class VictorWrapper
{ Wrapper class
public function __construct()
{
require_once '/home/victorvon/tragedy.php';
}
public function extractBrain(Person $p) {
// format to legacy style
$pLgcy = $this->toArray($p);
// run legacy code
$bLgy = extract_brain($pLgcy);
// format to new style
$p = $this->toPerson($pLgcy); Some code
$b = $this->toBrain($bLgcy);
return array($p, $b); you can use
}
:)
public function createLife(Person $p)
{
// validate
if ($person->isAlive()) throw new LivingException();
// format to legacy style
$pLgcy = $this->toArray($p);
// run legacy code
$pLgy = create_life($pLgcy);
// format to new style
return $this->toPerson($pLgcy);
}
}

51. Changing the code

52. Changing the code
Take an
incremental
approach
Commit to 1 day
at a time

53. Why?
Difficult to estimate
Hidden dependencies
Unknown behaviour

54. 1. Get it into
version control

55. 2. Identify the
inflection point

56. 3. Create integration
& acceptance tests

57. 4. Set up your
continuous integration
environment

58. 5. Rewrite and refactor!

59. Types
of
changes

60. Mixed → Procedural

61. includes
HTML PHP HTML
HTML PHP HTML
PHP HTML PHP
PHP
HTML PHP HTML
HTML PHP HTML
PHP

62. includes
function
function
function
includes
HTML PHP HTML HTML echo HTML
HTML PHP HTML HTML echo HTML
PHP HTML PHP if HTML if
PHP foreach
HTML PHP HTML HTML echo HTML
HTML PHP HTML HTML echo HTML
PHP foreach

63. Procedural → OO

64. includes
function
function
function
function
free code

65. includes includes
function static method
function static method
function static method
function static method
free code static method

66. includes includes includes
function static method constructor
function static method method
function static method method
function static method method
free code static method method

67. Sprout method / class

68. public function createInvoice(Account $acc, array $charges)
{
$invoice = new Invoice();
foreach ($charges as $chg) {
$invoice->addLine($chg->getDesc(), $chg->getAmount());
}
return $invoice;
}
The existing code
“We just need to be able to give
each client their own personal
discount on certain charges.”

69. public function createInvoice(Account $acc, array $charges)
{
$invoice = new Invoice();
foreach ($charges as $chg) {
$invoice->addLine($chg->getDesc(), $chg->getAmount());
}
return $invoice;
}
The new code
private function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = new AccountDiscounter($acc);
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
}

70. public function createInvoice(Account $acc, array $charges)
{
$invoice = new Invoice();
Call it
foreach ($charges as $chg) {
// Sprout new behaviour!
$chg = $this->calcDiscount($acc, $chg);
$invoice->addLine($chg->getDesc(), $chg->getAmount());
}
return $invoice;
}
private function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = new AccountDiscounter($acc);
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
}

71. Untestable OO → testable OO

72. Dependency Inversion / Extraction

73. The Problem
public function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = new AccountDiscounter($acc);
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
} Untestable!

74. The Problem
public function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = new AccountDiscounter($acc);
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
} Untestable!
class AccountDiscounter
{
public function __construct(Account $acc)
{
// check cache
// contact the database
// call a web service
}
}

75. Quick Solution
public function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = $this->getAccountDiscounter($acc);
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
}
Mock object in your test
Override method
protected function getAccountDiscounter(Account $acc)
{
return new AccountDiscounter($acc);
}

76. Dependency Injection Solution
public function __construct(AccountDiscounter $ad)
{
$this->discounter = $ad;
}
Pass it into the class
public function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = $this->discounter;
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
}

77. (v2) → Dependency Injection Solution
public function __construct(IAccountDiscounter $ad)
{
$this->discounter = $ad;
}
Make an interface
public function calcDiscount(Account $acc, Charge $chg)
{
$accDisc = $this->discounter;
$discountedCharge = $accDisc->calculate($chg);
return $discountedCharge;
}

78. Summary
Analyse
Plan
Test
IsolatE
Change
Test MORE

79. Any questions?
Feedback to:
https://joind.in/6020
@rowan_m

80. Further reading:
Michael Feathers
Martin Fowler
http://www.flickr.com/photos/flatlinevision/1514971535/
http://commons.wikimedia.org/wiki/File:Weird_Tales_November_1950.jpg
http://commons.wikimedia.org/wiki/File:AdventuresIntoDarkness1401.jpg
http://www.flickr.com/photos/locationscout/3594432797/
http://www.flickr.com/photos/rawhead/3466304669/
http://commons.wikimedia.org/wiki/File:Rocket_to_the_Moon_54893.jpg
http://commons.wikimedia.org/wiki/File:Weird_Chills_July.jpg
http://commons.wikimedia.org/wiki/File:Terrific_01.jpg
http://commons.wikimedia.org/wiki/File:Strange_Fantasy_01.jpg
http://commons.wikimedia.org/wiki/File:Beware_01.JPG
http://www.flickr.com/photos/erokcom/2873449983/
http://www.flickr.com/photos/locationscout/3594433235/
http://commons.wikimedia.org/wiki/File:Weird_Chills_Sept.JPG
http://commons.wikimedia.org/wiki/File:Weird_Comics_01.JPG
http://www.flickr.com/photos/x-ray_delta_one/3972988193/
http://commons.wikimedia.org/wiki/File:Weird_Tales_January_1950.jpg
ts
di
http://commons.wikimedia.org/wiki/File:Plan_nine_from_outer_space.jpg
http://www.flickr.com/photos/javyer/3545217741/
http://www.flickr.com/photos/76074333@N00/318034222/
http://commons.wikimedia.org/wiki/File:Dime_Mystery_Magazine_July_1934.jpg
http://www.flickr.com/photos/quinnanya/3802177022/ C re