Rewriting 15-Year-Old Code

Transcript

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   @afilina Rewriting 15-Year-Old Code Mtl.rb - October 17, 2017

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   Anna Filina • Project rescue expert • Legacy fixer •

   Developer • Conference speaker • Trainer
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   You inherited a
 17-year-old codebase Code doesn't age like wine.

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   The Web Was 600px Wide

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   Feeling Old Yet? • Y2K bug. • Internet Explorer 5.

   • ICQ was starting to be cool. • Rounded corners = status symbol.
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   Code smells

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   Mixed Concerns <% products = Product.all total = 0 products.each

   do |product| total += product.qty * product.price end %> <p>Total: <%= total %></p>
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   Poorly Named Variables a = #... array = #... item3

   = #...
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   Global Functions & Constants require_relative '../../functions.rb' MyClass::my_method(param) # namespaced function?

   my_method(DEV_MODE)
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    Inexplicable Conditions if order_id > 20117 # use this sql

    else # use that sql end # weakness = time to refactor
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    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, ]);
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    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.
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    Codebase • 5,000 classes. • 20,000 methods. • 1,500,000 lines

    of code.
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    Before you code

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    Strategy • Make a strategy based on constraints. • Full

    rewrite vs progressive: ◦By class. ◦By feature. ◦By HTTP call. • How to run code side-by-side: ◦DB/Session sharing. ◦mod_rewrite.
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    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.
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    Build With Real Legacy Data

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    (Failed) rewrite example

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    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).
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    Solution • Rewrite complex forms using a framework: ◦ mod_rewrite

    for concerned pages. • Rewrite biggest feature as OOP: ◦ Design extraction. ◦ Flexible architecture. ◦ Automated tests.
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    New feature should not take longer than a sprint.

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    Design extraction

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    Avoid Code Bias • Old code → design docs. •

    Validate design docs: ◦Clarify business rules. • Improve design: ◦Reduce technical debt. ◦More flexible. • Design docs → new code.
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    Fixing bugs

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    Code Duplication • Sometimes, the bug is repeated 80+ times.

    • Remove duplications ASAP.
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    Fix Long Methods • Extract broken part into its own

    method. • Write unit tests for it. • Fix it. • Call it from the mega-method.
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    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
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    Extract & Test Code block Comment Code block Method Code

    block Comment Call method
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    Name Code block Method Code block Method Call method Call

    method Code block Method Call method conferences_from_csv location_coordinates save_conference
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    Rewrite example #2

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    ASP Classic to PHP 5.6 • 15+ spaghetti and hacks.

    • Language no longer supported. • Huge ERP with lots of code.
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    Solution • Rewrite page by page to a framework. •

    mod_rewrite for concerned pages. • DB session adapter in both apps. • Page in any language = HTTP request. ◦ Automated testing possible!
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    HTTP Tests

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    On Testing Before you code You better test So that

    on weekends You may rest. -- Me
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    Stuck?

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    None
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    Try Something New • Bounce ideas. ◦ New people to

    avoid tunnel vision. • Has this been done before? • Can I try another approach?
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    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.
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    Refactoring: Improving the Design of Existing Code Martin Fowler

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    @afilina afilina.com joind.in