Dealing With Legacy PHP Applications

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Clinton Nixon describes some common problems found when inheriting legacy PHP applications and how to deal with them. He presents a solution that will encapsulate business logic and clean up the view layer without requiring a full-fledged MVC framework.

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Dealing With Legacy PHP Applications

  1. 1. Dealing with Legacy PHP Applications Prepared by Clinton R. Nixon, Viget Labs 2007 July
  2. 2. What is a legacy application? Code you didn't write Code you wouldn't write Untested code Code with competing visions Dealing with Legacy PHP Applications 2007 Jul
  3. 3. What do we do with legacy code? We refactor! Refactoring is safely changing the implementation of code without changing the behavior of code. Dealing with Legacy PHP Applications 2007 Jul
  4. 4. Bad code smells What are some specific problems in legacy PHP code? ‣ No separation between PHP and HTML ‣ Lots of requires, few method calls ‣ Global variables Dealing with Legacy PHP Applications 2007 Jul
  5. 5. 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>'; } ?> Dealing with Legacy PHP Applications 2007 Jul
  6. 6. 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 Dealing with Legacy PHP Applications 2007 Jul
  7. 7. Why do I need to do this? Your code complexity will decrease. echo isn't as fun as it looks. You will find hidden bugs and mistakes. Dealing with Legacy PHP Applications 2007 Jul
  8. 8. The simplest view class class 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(); } } } Dealing with Legacy PHP Applications 2007 Jul
  9. 9. Obvious improvements to make Error handling Assignment by reference Changing view path Display convenience method Use-specific subclasses with helper methods Dealing with Legacy PHP Applications 2007 Jul
  10. 10. 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 Dealing with Legacy PHP Applications 2007 Jul
  11. 11. The rules of view code Allowed: ‣ Control structures ‣ echo, or <?= $var ?> ‣ Display-specific functions, never nested Not allowed: ‣ Assignment ‣ Other function calls Dealing with Legacy PHP Applications 2007 Jul
  12. 12. 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 Dealing with Legacy PHP Applications 2007 Jul
  13. 13. 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>'; } Dealing with Legacy PHP Applications 2007 Jul
  14. 14. 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 $a')) ?> </p> <?php } ?> Dealing with Legacy PHP Applications 2007 Jul
  15. 15. Alternative control structures <?php if ($foo): ?> ... <?php endif; ?> <?php foreach ($this as $that): ?> ... <?php endforeach; ?> Dealing with Legacy PHP Applications 2007 Jul
  16. 16. 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 $a')) ?> </p> <?php endforeach; ?> Dealing with Legacy PHP Applications 2007 Jul
  17. 17. A frustrating problem <?php foreach ($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 $a')) ?> </p> <?php endforeach; ?> Dealing with Legacy PHP Applications 2007 Jul
  18. 18. Dealing with this problem There are two approaches. ‣ You can create a new array of variables for your view. ‣ Or, you can encapsulate this logic in an object. Dealing with Legacy PHP Applications 2007 Jul
  19. 19. Our new order object <?php class Order { ... public function getStatus() { return lookup_status($this->getStatusId()); } public function getTotal() { return array_reduce($this->getPurchases(), create_function('$a, $b', '$a += $b; return $a')); } } ?> Dealing with Legacy PHP Applications 2007 Jul
  20. 20. 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; ?> Dealing with Legacy PHP Applications 2007 Jul
  21. 21. Change all variables to view object variables Assign variables to the view object: $view->assign('foo', $foo); One-by-one, change variables in view code. Test to convince yourself. You will probably iterate back to the previous step. Document inputs to the view. Dealing with Legacy PHP Applications 2007 Jul
  22. 22. 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; ?> Dealing with Legacy PHP Applications 2007 Jul
  23. 23. Separate the files Create a new file for the view code. Important! Search and replace $view with $this. Test one more time. Dealing with Legacy PHP Applications 2007 Jul
  24. 24. Our two files <?php $account = new Account($account_id); $account->loadOrders(); $orders = $account->getOrders(); $view = new View(); $view->assign('orders', $orders); $view->display('orders.tpl'); ?> <h1>Orders</h1> <?php foreach ($view->orders as $order): ?> <h2><?= $order->getId() ?></h2> <p>Status: <?= $order->getStatus() ?> <br /> Total: <?= $order->getTotal() ?> </p> <?php endforeach; ?> Dealing with Legacy PHP Applications 2007 Jul
  25. 25. Find duplicated views As you do this to multiple controllers, you will see repetition. There will probably be subtle differences. Take the time to re-work these so you can re-use view files. Note! You can include views in other views with: $this->render('included_file.tpl'); Dealing with Legacy PHP Applications 2007 Jul
  26. 26. Using nested requires instead of function calls <?php require_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'); ... Dealing with Legacy PHP Applications 2007 Jul
  27. 27. Untangling a require web Require statements which call other require statements. Can be very complex. Dependent on application structure. Dealing with Legacy PHP Applications 2007 Jul
  28. 28. Reasons to untangle this web Remove unneeded complexity. Create less procedural code. Prior to PHP 5.2, require_once and include_once are more expensive than you would think. If you are requiring class definitions, and you have a standard file naming method, use __autoload(). Dealing with Legacy PHP Applications 2007 Jul
  29. 29. The untangling process Identify inputs Identify outputs Wrap the file in a method Refactor method Move method to correct location Dealing with Legacy PHP Applications 2007 Jul
  30. 30. Identify inputs and outputs Find all variables expected to be set before this file is included. One possible way: execute this file by itself. Find all variables expected to be set or mutated by this file. Set variables are easy: comment out the require and watch the errors. Mutated is the set of inputs changed. Learn to search for these! Dealing with Legacy PHP Applications 2007 Jul
  31. 31. account_auth_inc.php <?php $auth_token = $_COOKIE['token']; if ($auth_token) { $acct_id = $db->GetOne('SELECT acct_id FROM logins WHERE auth_token = ?', array($auth_token)); } if ($acct_id) { $acct = new Account($acct_id); } else { $acct = null; } $_COOKIE['token'] = gen_new_token($auth_token); Dealing with Legacy PHP Applications 2007 Jul
  32. 32. 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 required file! This is a mess! Dealing with Legacy PHP Applications 2007 Jul
  33. 33. Function-wrapped <?php function account_auth($db, $auth_token) { if ($auth_token) { $acct_id = $db->GetOne('SELECT acct_id FROM logins WHERE auth_token = ?', array($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, $_COOKIE['token']); Dealing with Legacy PHP Applications 2007 Jul
  34. 34. Refactor until complete Tease out the functions, or objects, inside this function. If you are returning a lot of data, see if it can be an object. Leave your temporary big function in place, so that your outside code doesn't break. Keep updating it to deal with your refactoring. Dealing with Legacy PHP Applications 2007 Jul
  35. 35. Moved token handling to Account <?php function account_auth($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']); Dealing with Legacy PHP Applications 2007 Jul
  36. 36. Move to correct location Finally! Figure out where these functions or objects should live in your application. Move them there. Find where the require is called throughout your application, and replace that with your new function call or object method. Dealing with Legacy PHP Applications 2007 Jul
  37. 37. 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; ... } Dealing with Legacy PHP Applications 2007 Jul
  38. 38. Removing globals one by one Common globals: ‣ $_POST and $_GET ‣ Session or cookie data ‣ Database handles ‣ User account ‣ Language Dealing with Legacy PHP Applications 2007 Jul
  39. 39. Do you still have register_globals on? You may have heard: this is a bad idea. You may 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. Dealing with Legacy PHP Applications 2007 Jul
  40. 40. $_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() {...} ... } Dealing with Legacy PHP Applications 2007 Jul
  41. 41. The database global object Very common in PHP code Again, not horrible Prevents testing Prevents multiple databases Dealing with Legacy PHP Applications 2007 Jul
  42. 42. 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 in that variable to the current scope. ‣ Repeat. Dealing with Legacy PHP Applications 2007 Jul
  43. 43. 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; ... } Dealing with Legacy PHP Applications 2007 Jul
  44. 44. 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. Dealing with Legacy PHP Applications 2007 Jul
  45. 45. A quick recap What are some specific problems in legacy PHP code? ‣ Mixed PHP and HTML – confusion between controller and view ‣ Use of require statements instead of function calls ‣ Unnecessary global variables causing dependencies Dealing with Legacy PHP Applications 2007 Jul
  46. 46. Further reading Working Effectively With Legacy Code, Michael Feathers Refactoring, Martin Fowler Dealing with Legacy PHP Applications 2007 Jul
  47. 47. Questions? clinton@viget.com Slides available at http://www.slideshare.net/viget and http://clintonrnixon.net. Dealing with Legacy PHP Applications 2007 Jul

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