ving
Li
with
Legacy
Code

@rowan_m

@rowan_m
Plusnet
Ibuildings

What is
“Legacy Code”?

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

Who has
never
created
Legacy Code?

My own
little
story

Pragmatic, not ideal
istic
My own
little
story

Starting a project

Aim to understand
the concepts
and motivations

Try using
the application

Find and then read
any / all
documentation

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 ( )

Talk to the
original developers

Talk to the users
… especially the
“different” ones

Approaching
the code

Catalogue the
live platform
& environment

Recreate it!

Deploy the code

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 ( )

Time to enter
The Code

Time to enter
The Code
Reading
Static analysis
Dynamic analysis

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!

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);
}

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/

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

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

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

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

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

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

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

ou ml
b

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/

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

Decisi
on tim
e!

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

Ignore it,
code anyway

Ignore it,
code anyway
Please don't.

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

Deadlines, clients,
money, etc.

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

Why do you need the code?

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

Isolate
legacy dependencies

Isolate
legacy dependencies
Create an
anti-corruption layer

Complete isolation
Create a
legacy service

Partial isolation
Wrapper classes
or methods

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;
}
?>

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);
}
}

Changing the code

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

Why?
Difficult to estimate
Hidden dependencies
Unknown behaviour

1. Get it into
version control

2. Identify the
inflection point

3. Create integration
& acceptance tests

4. Set up your
continuous integration
environment

5. Rewrite and refactor!

Types
of
changes

Mixed → Procedural

includes
HTML PHP HTML
HTML PHP HTML
PHP HTML PHP
PHP
HTML PHP HTML
HTML PHP HTML
PHP

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

Procedural → OO

includes
function
function
function
function
free code

includes includes
function static method
function static method
function static method
function static method
free code static method

includes includes includes
function static method constructor
function static method method
function static method method
function static method method
free code static method method

Sprout method / class

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.”

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;
}

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;
}

Untestable OO → testable OO

Dependency Inversion / Extraction

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

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
}
}

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);
}

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;
}

(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;
}

Summary
Analyse
Plan
Test
IsolatE
Change
Test MORE

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

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