Rewriting 15-Year-Old Code

Transcript

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

   View Slide

2. Anna Filina
   • Project rescue expert
   • Legacy fixer
   • Developer
   • Conference speaker
   • Trainer
   

   View Slide

3. You inherited a

   17-year-old codebase
   Code doesn't age like wine.
   

   View Slide

4. The Web Was 600px Wide
   

   View Slide

5. Feeling Old Yet?
   • Y2K bug.
   • Internet Explorer 5.
   • ICQ was starting to be cool.
   • Rounded corners = status symbol.
   

   View Slide

6. Code smells
   

   View Slide

7. Mixed Concerns
   <%
   products = Product.all
   total = 0
   products.each do |product|
   total += product.qty * product.price
   end
   %>
   Total: <%= total %>
   

   View Slide

8. Poorly Named Variables
   a = #...
   array = #...
   item3 = #...
   

   View Slide

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

   View Slide

10. Inexplicable Conditions
    if order_id > 20117
    # use this sql
    else
    # use that sql
    end
    # weakness = time to refactor
    

    View Slide

11. 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,
    ]);
    

    View Slide

12. 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.
    

    View Slide

13. Codebase
    • 5,000 classes.
    • 20,000 methods.
    • 1,500,000 lines of code.
    

    View Slide

14. Before you code
    

    View Slide

15. 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.
    

    View Slide

16. 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.
    

    View Slide

17. Build With Real Legacy Data
    

    View Slide

18. (Failed) rewrite example
    

    View Slide

19. 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).
    

    View Slide

20. Solution
    • Rewrite complex forms using a
    framework:
    ◦ mod_rewrite for concerned pages.
    • Rewrite biggest feature as OOP:
    ◦ Design extraction.
    ◦ Flexible architecture.
    ◦ Automated tests.
    

    View Slide

21. New feature should not
    take longer than a sprint.
    

    View Slide

22. Design extraction
    

    View Slide

23. Avoid Code Bias
    • Old code → design docs.
    • Validate design docs:
    ◦Clarify business rules.
    • Improve design:
    ◦Reduce technical debt.
    ◦More flexible.
    • Design docs → new code.
    

    View Slide

24. Fixing bugs
    

    View Slide

25. Code Duplication
    • Sometimes, the bug is
    repeated 80+ times.
    • Remove duplications
    ASAP.
    

    View Slide

26. Fix Long Methods
    • Extract broken part into its own method.
    • Write unit tests for it.
    • Fix it.
    • Call it from the mega-method.
    

    View Slide

27. 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
    

    View Slide

28. Extract & Test
    Code block
    Comment
    Code block
    Method
    Code block
    Comment
    Call method
    

    View Slide

29. Name
    Code block
    Method
    Code block
    Method
    Call method
    Call method
    Code block
    Method
    Call method
    conferences_from_csv
    location_coordinates
    save_conference
    

    View Slide

30. Rewrite example #2
    

    View Slide

31. ASP Classic to PHP 5.6
    • 15+ spaghetti and hacks.
    • Language no longer supported.
    • Huge ERP with lots of code.
    

    View Slide

32. 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!
    

    View Slide

33. HTTP Tests
    

    View Slide

34. On Testing
    Before you code
    You better test
    So that on weekends
    You may rest.
    -- Me
    

    View Slide

35. Stuck?
    

    View Slide

36. View Slide

37. Try Something New
    • Bounce ideas.
    ◦ New people to avoid tunnel vision.
    • Has this been done before?
    • Can I try another approach?
    

    View Slide

38. 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.
    

    View Slide

39. Refactoring: Improving the
    Design of Existing Code
    Martin Fowler
    

    View Slide

40. @afilina afilina.com
    joind.in
    

    View Slide