Rewriting Legacy Code - Speaker Deck

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Rewriting Legacy Code THE LEGACY OF SOCRATES | MAY 13, 2020 @afilina

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Anna Filina ‣ Coding since 1997. ‣ Legacy archaeology. ‣ Test automation. ‣ Talks and workshops. ‣ YouTube videos.

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You Inherited a  10-Year-Old Codebase

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You Inherited a  15-Year-Old Codebase

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You Inherited a  20-Year-Old Codebase

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Web in 2000 ‣ Y2K bug. ‣ Internet Explorer 5. ‣ ICQ was starting to be cool. ‣ Background music. ‣ Rounded corners = status symbol.

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Legacy Sadness

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The Methods ‣ Can easily exceed a thousand lines. ‣ Mixing SQL, PHP and HTML. ‣ Receiving dozens of arguments of arbitrary type. ‣ Accessing hundreds of potentially undefined properties. ‣ Expect properties to have been set by a child 10 method calls ago. ‣ methodName_new, methodName_new2

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The Dynamic Types ‣ Null pointer exceptions of every flavor. ‣ Attempting to split an array. ‣ Attempting to divide by a null. ‣ Attempting to count the number of elements in a float. ‣ Attempting to max($array1, $array2),  where array items are of mixed types.

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How to Fail a Rewrite

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Microservices AWS GitHub React CircleCI ElasticSearch Ansible Docker Symfony Ambitious new tech stack

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Other Ambitions ‣ SOLID. ‣ Test-driven development. ‣ Strong typing. Too many new things at once

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Expanding Scope ‣ Rethinking existing features. ‣ New features. ‣ New work methodology.

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Start With the Strategy

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Strategy ‣ Version upgrade. ‣ New framework. ‣ Progressive rewrite. ‣ Refactoring only. ‣ Full rewrite.

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Version Upgrade ‣ PHPCodeSniffer can detect incompatibilities. ‣ Some libs might be easier to swap than to fix (PHPExcel). ‣ Regexes are your friends. ‣ Rector can automatically refactor. ‣ Need to freeze development.

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New Framework ‣ Use dependency injection. ‣ Automate large chunks with Rector. ‣ Use adapters. ‣ Need to freeze development.

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Product/IndexHandler ProductController indexAction viewAction Product/ViewHandler Routes Routes Product/BaseHandler Example: Zend Framework 1 to Zend Expressive

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class IndexHandler extends BaseHandler implements RequestHandlerInterface { public function __construct( TemplateRendererInterface $template, ProductModel $productModel ) { //... } public function handle(ServerRequestInterface $request): ResponseInterface { return new HtmlResponse(  $this->template->render('admin::product/index', $view)  ); } }

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Progressive Rewrite ‣ By class. ‣ By module • Can switch language. • Use design extraction.

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Old Code New Design Old Design New Code

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‣ Some criteria for refactoring: • Need to change. • Hard to understand, but need to work with it. Refactoring Only

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Full Rewrite ‣ Discouraged. ‣ My criteria: • Can disregard existing features. • Few or no integrations. • Can trash old database. • If not, need a team experienced in full rewrites.

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Spot Problems Early ‣ PHPStorm inspections. ‣ Pslam: start with auto-detected level.

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Unknown Unknowns

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Docs ‣ No docs. ‣ Too many, little relevance. ‣ Outdated or misleading.

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Tests ‣ No tests. ‣ Not runnable. ‣ Failing. ‣ Brittle: specific environment or inter-dependencies. ‣ Unreliable.

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Dead Code ‣ Unused endpoints. ‣ Commented-out code. ‣ Unused classes or methods: exercise extreme caution. ‣ Merge duplicated code (bug repeated 80 times).

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Testing Approaches

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Version Upgrade Smoke tests Fix code Should work  for old and new versions. Unit tests

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New Framework Smoke tests Migrate Should work  for old and new versions. Unit tests

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Progressive Rewrite For new code only. Acceptance tests Unit tests Should work  for old and new versions. New code

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Refactoring Only For the code that you want to write. Acceptance tests Unit tests Should work  for old and new versions. Refactor

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Preparing the Environments

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Local Environment ‣ Docker. ‣ Baseline image. ‣ Migration image. ‣ Match server / vagrant.

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services: php: //... mysql: //... acceptance: //... mysql_test: //...

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Gotchas ‣ Pay attention to MySQL mode. ‣ Run composer inside Docker, commit composer.lock ‣ Anonymized production database. ‣ Send e-mails to relay: DebugMail, MailTrap, etc.

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Staging Environment ‣ Baseline server. ‣ Migration server. ‣ Staging config: point to sandboxes.