Rewriting 15-Year-Old Code

Did you ever have to maintain a fifteen year old application? Dead code everywhere, database queries in between HTML tags and some pages still in PHP 3. This strategy-level presentation will lead you through a progressive rewrite from very old legacy to the latest shiny version of PHP. Learn how to automate legacy testing, how to seamlessly jump between the old and new parts, and how to overcome other challenges that arise from dealing with legacy.

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1. @afilina Rewriting 15-Year-Old Code IPC, Berlin - May 30, 2017
2. Anna Filina • whoami():\LegacyFixer • Project rescue expert • Dev, trainer, speaker
3. You inherited a
 10-year-old codebase
4. You inherited a
 15-year-old codebase
5. You inherited a
 17-year-old codebase
6. You inherited a
 17-year-old codebase Code doesn't age like wine.
7. The Web Was 600px Wide
8. Feeling Old Yet? • Y2K bug. • Internet Explorer 5. • ICQ was starting to be cool. • Rounded corners = status symbol.
9. Code smells
10. Mixed Concerns <?php mysql_query('...'); $total = 0; foreach ($products as $p) { $total += $p['qty'] * $p['price']; } ?> <p>Total: <?= $total ?></p>
11. Poorly Named Variables $a = //... $array = //... $item3 = //...
12. Global Functions & Constants include("functions.php"); MyClass::myMethod(); // namespaced function? myMethod(DEV_MODE);
13. Inexplicable Conditions if ($order_id > 20117) { // use this sql } else { // use that sql } // weakness = time to refactor
14. Long Methods public function importCsv($path, $googleApiKey, $databaseDsn, $databaseUser, $databasePassword) { // Convert CSV to array of conferences $lines = file($path); $csv = array_map('str_getcsv', $lines); $conferences = []; foreach ($csv as $line) { $conference = new Conference(); $conference->name = $line[0]; $conference->location = $line[1]; $conferences[] = $conference; // Get coordinates for location $location = urlencode($conference->location); $url = 'https://maps.googleapis.com/maps/api/geocode/json?address='.$location.'&key='.$googleApiKey; $curl = curl_init(); curl_setopt($curl, CURLOPT_URL, $url); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); $response = curl_exec($curl); curl_close($curl); $json = json_decode($response); if (count($json->results) == 0) { continue; } $latitude = $json->results[0]->geometry->location->lat; $longitude = $json->results[0]->geometry->location->lng; $coordinates = $latitude.','.$longitude; $conference->coordinates = $coordinates; // Save conference to database $pdo = new PDO($databaseDsn, $databaseUser, $databasePassword); $statement = $pdo->prepare('REPLACE INTO conference (name, location, coordinates) VALUES (?, ?, ?)'); $statement->execute([ $conference->name, $conference->location, $conference->coordinates, ]);
15. Average Legacy Code File • 3000-6000 lines of code. • Half of it is commented "in case we need it later". • Method length of 800 lines. • Abuse of helper classes. • Sometimes no classes at all.
16. Codebase • 5,000 classes. • 20,000 methods. • 1,500,000 lines of code.
17. Before you code
18. Strategy • Make a strategy based on constraints. • Full rewrite vs progressive: ◦By class. ◦By feature/module. ◦By HTTP call. • How to run code side-by-side: ◦Session sharing. ◦mod_rewrite.
19. Data Can Be Lost, Stuff Can Break • Backup: test restore. • Nullify sensitive data. • Staging: simulate deployments/ upgrades/batch processes. • Automate tests before code changes. • Make a risk assessment: ◦ Don't be too optimistic. ◦ Account for side-effects.
20. Rewrite example When it goes wrong.
21. PHP 3 to PHP 5.6 • HTML + PHP + SQL in same file. • Includes all over the place. • IFs that concatenate SQL. • Previous rewrite attempt: ◦ Failed, made things worse. ◦ Folders of dead code. ◦ Classes with static functions (no instances).
22. Solution • Rewrite complex forms in Symfony: ◦ mod_rewrite for concerned pages. • Rewrite biggest module as OOP: ◦ Design extraction. ◦ Flexible architecture. ◦ Automated tests.
23. Design extraction
24. Avoid Code Bias • Old code → design docs. • Validate design docs: ◦Clarify business rules. • Improve design: ◦Reduce technical debt. ◦More flexible. • Design docs → new code.
25. Fixing bugs
26. Code Duplication • Sometimes, the bug is repeated 80+ times. • Remove duplications ASAP.
27. Fix Long Methods • Extract broken part into its own method. • Write unit tests for it. • Fix it. • Call it from the mega-method.
28. Spot Logical Groups Code block Comment Code block Comment Convert CSV to array of conferences. Get coordinates for conference location. Save conference to database. Code block Comment
29. Extract & Test Code block Comment Code block Method Code block Comment Call method
30. Name Code block Method Code block Method Call method Call method Code block Method Call method getConferencesFromCsv getLocationCoordinates saveConference
31. Rewrite example #2
32. ASP Classic to PHP 5.6 • 15+ spaghetti and hacks. • Language no longer supported. • Huge ERP with lots of code.
33. Solution • Rewrite page by page to framework. • mod_rewrite for concerned pages. • DB session adapter in both apps. • Page in any language = HTTP request. ◦ Guzzle tests FTW!
34. Guzzle Tests
35. On Testing Before you code You better test So that on weekends You may rest. -- Anna Filina
36. Testing Static Methods $mock = Mockery::mock('alias:SomeClass'); $mock->shouldReceive('staticMethod')->andReturn(42);
37. Stuck?
38. Try Something New • Bounce ideas. ◦ New people to avoid tunnel vision. • Has this been done before? • Can I try another approach?
39. Takeaways • Make a strategy. • You touch it, you refactor it. • Use known tools & methodologies. • Get inspiration from others. • Refactoring gets easier. • Every problem has a solution.
40. @afilina afilina.com joind.in