Dealing with Legacy PHP Applications

Dealing withLegacy PHPApplications

Clinton R. [email protected]

What is a legacyapplication?

Code you didn't write

Code you wouldn't write

Untested code

Code with competing visions

What do we do withlegacy code?

We refactor!

Refactoring is safely changing theimplementation of code withoutchanging the behavior of code.

Bad code smellsWhat are some specific problems in legacy PHP code?

No separation between PHP and HTML

Lots of requires, few method calls

Global variables

No separation between PHP and HTML

<h1>Orders</h1><?php$account = new Account($account_id);$account->loadOrders();foreach ($account->getOrders() as $order) {echo '<h2>' . $order['id'] . '</h2>';echo '<p>Status: ' .lookup_status($order['status_id']) . '<br />;

echo 'Total: ';$total = array_reduce($order['purchases'],create_function('$a, $b', '$a += $b; return $a'));

echo $total . '</p>';}?>

Separating controllers and views Even without a solid MVC architecture, this helps

You can do this in several safe and easy steps

You absolutely will find pain points

Why do I need to do this? Your code complexity will increase

echo isn't as fun as it looks

Youwill find hidden bugs and mistakes

The simplest view classclass View {

protected static $VIEW_PATH = '/wherever/views/';

public function assign($name, $value) {return $this->$name = $value;

}

public function render($filename) {$filename = self::$VIEW_PATH . $filename;if (is_file($filename)) {

ob_start();include($filename);return ob_get_clean();

}}

}

Obvious improvements to make Error handling

Assignment by reference

Changing view path

Display convenience method

Use-specific subclasses with helper methods

The separation process Gather all your code

Sift and separate controller from view code

Assign variables to the view object

Change all variable references in the view code

Split the files

Find duplicated views

The rules of view codeAllowed:

Control structures

echo, or <?= $var ?>

Display-specific functions, never nested

Not allowed:

Assignment

Other function calls

Gather and sift code The step you won't like: gather all code for this controller

Wipe brow

Draw a line at the top of the code

Move controller code above this line, fixing as necessary

At this point, everything is view code

Code gathered<?php // View code goes below here ?><h1>Orders</h1><?php$account = new Account($account_id);$account->loadOrders();foreach ($account->getOrders() as $order) {echo '<h2>' . $order['id'] . '</h2>';echo '<p>Status: ' .lookup_status($order['status_id']) . '<br />;

echo 'Total: ';$total = array_reduce($order['purchases'],create_function('$a, $b', '$a += $b; return $a'));

echo $total . '</p>';}?>

Some controller code moved<?php$account = new Account($account_id);$account->loadOrders();?><?php // View code goes below here ?><h1>Orders</h1><?php foreach ($account->getOrders() as $order) { ?><h2><?= $order['id'] ?></h2><p>Status: <?= lookup_status($order['status_id'])<br />Total:<?= array_reduce($order['purchases'],create_function('$a, $b', '$a += $b; return $a'))

?></p>

<?php } ?>

Alternative control structures

<?php if ($foo): ?>...<?php endif; ?>

<?php foreach ($this as $that): ?>...<?php endforeach; ?>

Using alternative control structures<?php$account = new Account($account_id);$account->loadOrders();?><?php // View code goes below here ?><h1>Orders</h1><?php foreach ($account->getOrders() as $order): ?><h2><?= $order['id'] ?></h2><p>Status: <?= lookup_status($order['status_id']) ?><br />Total:<?= array_reduce($order['purchases'],create_function('$a, $b', '$a += $b; return $a')) ?>

</p><?php endforeach; ?>

A frustrating problem<?php foreach ($account->getOrders() as $order): ?><h2><?= $order['id'] ?></h2><p>Status: <?= lookup_status($order['status_id'])?><br />Total:<?= array_reduce($order['purchases'],create_function('$a, $b', '$a += $b; return $a'))?></p>

<?php endforeach; ?>

Dealing with this problemThere are two approaches.

You can create a new array of variables for your view.

Or, you can encapsulate this logic in an object.

Our new order object<?phpclass Order {...public function getStatus() {return lookup_status($this->getStatusId());

}

public function getTotal() {return array_reduce($this->getPurchases(),create_function('$a, $b', '$a += $b; return $a'));

}}?>

Logic removed from view code<?php$account = new Account($account_id);$account->loadOrders();$orders = $account->getOrders();?><?php // View code goes below here ?><h1>Orders</h1><?php foreach ($orders as $order): ?><h2><?= $order->getId() ?></h2><p>Status: <?= $order->getStatus() ?><br />Total: <?= $order->getTotal() ?></p>

<?php endforeach; ?>

Change all variables toview object variables Assign variables to the view object.

$view->assign('foo', $foo);

One-by-one, change variables in view code.

Test to convince yourself.

Youwill probably iterate back to the previous step.

Document inputs to the view.

View object created<?php$account = new Account($account_id);$account->loadOrders();$orders = $account->getOrders();$view = new View();$view->assign('orders', $orders);?><?php // View code goes below here ?><h1>Orders</h1><?php foreach ($view->orders as $order): ?><h2><?= $order->getId() ?></h2><p>Status: <?= $order->getStatus() ?><br />Total: <?= $order->getTotal() ?></p>

<?php endforeach; ?>

Separate the files Create a new file for the view code.

Important! Search and replace $view with $this.

Test one more time.

Our two files<?php$account = new Account($account_id);$account->loadOrders();$orders = $account->getOrders();$view = new View();$view->assign('orders', $orders);$view->display('orders.tpl');?>

<h1>Orders</h1><?php foreach ($this->orders as $order): ?><h2><?= $order->getId() ?></h2><p>Status: <?= $order->getStatus() ?><br />Total: <?= $order->getTotal() ?></p>

<?php endforeach; ?>

Find duplicated views As you do this to multiple controllers, you will seerepetition.

There will probably be subtle differences.

Take the time to re-work these so you can re-use viewfiles.

Note! You can include views in other views with

$this->render('included_file.tpl');

Using nested requiresinstead of function calls

<?phprequire_once('db_setup_inc.php');require_once('account_auth_inc.php');require_once('i18n_inc.php');

echo '<h1>Orders for account #' . $account_id .'</h1>';

require('get_all_orders_inc.php');

...

Untangling a require web Require statements which call other require statements.

Can be very complex.

Dependent on application structure.

Important reasons tountangle this web Remove unneeded complexity.

Create less procedural code.

Prior to PHP 5.2, require_once and include_onceare more expensive than you would think.

If you are requiring class definitions, and you have astandard file naming method, use __autoload().

The untangling process Identify inputs

Identify outputs

Wrap the file in a method

Refactor method

Move method to correct location

Identify inputs and outputs Find all variables expected to be set before this file isincluded.

One possible way: execute this file by itself.

Find all variables expected to be set or mutated by thisfile.

Set variables are easy: comment out the require andwatch the errors.

Mutated is the set of inputs changed. Learn to search forthese!

account_auth_inc.php<?php$auth_token = $_COOKIE['token'];

if ($auth_token) {$acct_id = $db->GetOne('SELECT acct_id FROMlogins WHERE auth_token = ?', array($auth_token));

}if ($acct_id) {$acct = new Account($acct_id);

} else {$acct = null;

}$_COOKIE['token'] = gen_new_token($auth_token);

Wrap the file in a function Wrap the entire include in a function.

Pass all input variables.

Return all output variables as an array.

And then, call that function at the bottom of the requiredfile!

This is a mess!

Function-wrapped<?phpfunction account_auth($db, $auth_token) {if ($auth_token) {$acct_id = $db->GetOne('SELECT acct_id FROMlogins WHERE auth_token = ?',array($auth_token));

}if ($acct_id) {$acct = new Account($acct_id);

} else {$acct = null;

}return array($acct, gen_new_token($auth_token));

}list($acct, $_COOKIE['token']) = account_auth($db,

$_COOKIE['token']);

Refactor until complete Tease out the functions, or objects, inside this function.

If you are returning a lot of data, see if it can be anobject.

Leave your temporary big function in place, so that youroutside code doesn't break. Keep updating it to deal withyour refactoring.

Moved token handling to Account<?phpfunction account_auth($db, $auth_token) {// Instead of null, we now return an unloaded Account.$acct = new Account();if ($auth_token) {// SQL code from before$acct->loadFromToken($auth_token);// Token generation and cookie setting$acct->genNewToken($auth_token);

}return $acct;

}$acct = account_auth($db, $_COOKIE['token']);

Move to correct location Finally!

Figure out where these functions or objects should live inyour application.

Move them there.

Find where the require is called throughout yourapplication, and replace that with your new function callor object method.

Global variables everywhere<?php

$account_id = $_POST['acct_id'];$account = new Account($account_id);

function getPurchases() {global $account;global $database;...

}

function getLanguage() {global $account;global $database;global $i18n;...

}

Removing globals one by oneCommon globals:

$_POST and $_GET

Session or cookie data

Database handles

User account

Language

Do you still haveregister_globals on? Youmay have heard: this is a bad idea.

Youmay think that it will be impossible to fix.

It's not. Turn on E_ALL.

Spider your site and grep for uninitialized variables.

It's some work, but not as hard as you think. It's worth it.

$_POST and $_GET These aren't horrible.

But not horrible isn't a very high standard.

class InputVariable {public function __construct($name) {...}public function isSet() {...}public function isGet() {...}public function isPost() {...}public function getAsString() {...}public function getAsInt() {...}...

}

The database global object Very common in PHP code

Again, not horrible

Prevents testing

Prevents multiple databases

Parameterizing the DB handle Does it need to be everywhere?

Can you pass it in to a function or to a constructor?

The process is simple.

Add database parameter.

Pass in that global variable.

If the call is not in global scope, find out how to pass inthat variable to the current scope.

Repeat.

Parameterizing globals<?php

$account_id = $_POST['acct_id'];$account = new Account($database, $account_id);

function getPurchases($account) {global $account;global $database;...

}

function getLanguage($account, $i18n) {global $account;global $database;global $i18n;...

}

Maybe it does have to be everywhere. Use a singleton.

But not really.

Make a way to change the singleton instance.

Global define or environment variable.

Static mutator.

A quick recapWhat are some specific problems in legacy PHP code?

Mixed PHP and HTML – confusion between controllerand view

Use of require statements instead of function calls

Unnecessary global variables causing dependencies

Further reading Working Effectively With Legacy Code, Michael Feathers

Refactoring, Martin Fowler

Questions?

[email protected]

Slides available at:http://clintonrnixon.net