Building Quality Code That Lasts: A Dropbox Story

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2. Building Quality Code That Lasts: A Dropbox Story
Ashley Nelson-Hornstein · 10 - 30 - 14
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3. Product
Testing
Background
Case Studies
Future of iOS at Dropbox
TODAY’S TALK
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4. Dropbox for iOS
Developed natively
Team of one engineer
First consumer of Dropbox public APIs
Released for iPhone in 2009
iPad support in 2010
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5. Sync SDK
UI Code
Core SDK
Data Layer
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9. 6

10. TODAY’S TALK
Product
Testing
Background
Case Studies
Future of iOS at Dropbox
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11. Product Roadmap
Collaborative process
Mix of
Infrastructure
User facing features
Code modernization
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12. Release Manager
Rotating role
Feature gatekeeper
Project manager
Task prioritization
Scheduling
Build stabilization
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13. Development
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14. Branching
Default branch
All changes are checked in here first
Release branch
hg graft —log from default branch
Verified by release manager
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18. Style Guide
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19. Coding Conventions
Prefix internal methods with db_
Prefer class methods
Hide implementation detail
Class extensions
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20. 16
// DBFile.h
!
@interface DBFile : NSObject
!
@property (readonly, strong) NSData
*contents;
!
@property (readonly, strong) NSURL
*publicShareLink;
!
@property (strong) NSDictionary
*permissions;
!
- (void)copyToNewPath:(NSString
*)newPath;
!
@end
// DBFile.m
!
@interface DBFile ()
!
@property (readwrite, strong) NSData
*contents;
!
@property (strong)
NSString *localFilePath;
@end
!
@implementation DBFile
!
- (void)copyToNewPath:(NSString
*)newPath
{
...
}
@end

21. Comments
// TODO: (ashleynh) 2014-10-30
Reminder for future improvement
// FIXME: (ashleynh) 2014-10-30
Generates compiler warning, not for release
// HAX: (ashleynh) 2014-10-30
Non-obvious API workaround
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22. Builds
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23. Continuous Integration
Pool of build machines
Executes functional tests
Builds are available to office
State changes are emailed to team
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25. Crash Reporter
Developed in-house
Predates other crash report services
Uploads crash logs from device
Groups crashes by stack trace
Provides symbolication
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27. TODAY’S TALK
Testing
Case Studies
Future of iOS at Dropbox
Background
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Product

28. Developer Settings
Toggle features on/off
View
Run log
Network and device stats
File cache inspection
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29. Shake to Report
Internal bug reporting
Captures
Screenshot
Crash log (if applicable)
Run log
Issues reported directly to bug tracking tool
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30. Helper Apps
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31. Dropoline
Developed in-house
Tests inter-app workflows
File import/export
Photo backup
Storage provider extension
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32. Car Keys
Developed in-house
Keychain
Inspection
Deletion
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33. Automata
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34. Automata Background
Functional testing framework
Developed in-house
Run tests locally or using Jenkins
Python API
Rich set of libraries to simplify automation
High productivity
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35. Automata Benefits
Separate process enables inter-app testing
Single test can manipulate two apps
Automating screenshots and screenshot diffs
Objective-C experience not required
Hooks into Objective-C runtime
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36. 32
Automata
Dropbox Dropoline

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Automata
Dropbox Dropoline

38. Automata Future
Support for iOS 8 extensions
GUI that records test scripts
Open source
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39. TODAY’S TALK
Testing
Case Studies
Future of iOS at Dropbox
Background
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Product

40. File Cache
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41. Background
Provides access to user’s Dropbox files
Coordinates with REST API and disk
Critical component
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42. Issues
File names of stored files are Dropbox paths
Unusually long file paths
Unsupported unicode characters
File loading race conditions
Providing readwrite access to file refs
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43. /*
* Hello there, friend. I wish you luck in your voyage through the following code.
*
* We need to avoid doing disk I/O in this callback, because it will be called in quick succession
* repeatedly on photos tab as we load lots of thumbs. Since we're on the main thread right now,
* we can't afford to do costly disk I/O. It will seriously impact scroll performance on photos tab
* if we do.
*
* The following code checks to see if what we just loaded has only a thumbnail repr. If it does,
* it updates the cacheSize property of the file to -1. -1 is a special flag, indicating to the LRU cleanup
* mechanism that this file doesn't need to be purged from the disk during LRU cleanup.
*
* Why not cleanup these files during LRU cleanup? Because with the release of photos tab, we may
* have thousand of files on disk. And starting them all during LRU cleanup is much too slow. So,
* we've opted to just not clean up files that only have thumbnail reprs.
*
* This code is not "correct". For example, if you load a thumbnail *AND* the BestFit repr, the thumbnail
* could now be cleaned up during LRU cleanup.
*
* This is basically a huge hack to make scrolling performance not stutter in photos tab.
*
*/
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44. /*
* Hello there, friend. I wish you luck in your voyage through the following code.
!
* This is basically a huge hack to make scrolling performance not stutter in photos tab.
*/
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45. Goals
Ensure file name integrity
Operations on separate queue
Smarter file loading system
Defensive return values
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46. Approach
Unit Tests
Uncovered existing bugs
Set a baseline for expected behavior
Maintained API for consumers
Limited project scope
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47. Implementation
Store files by UUID instead of Dropbox path
File Cache on background serial queue
Return immutable stubs of file refs
LoadingFileManager
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48. Consumer FileCache
RO Cached File
Core Data
Disk
Loading File
Manager
Single Background Queue
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49. Benefits
Easier to understand
Performant
Stable
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50. App Delegate
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51. [[UIApplication
sharedApplication] delegate]
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53. Issues
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54. Issues
App could be entered in a number of ways
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55. Issues
App could be entered in a number of ways
User initiated
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56. Issues
App could be entered in a number of ways
User initiated
File import
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57. Issues
App could be entered in a number of ways
User initiated
File import
API connection
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58. Issues
App could be entered in a number of ways
User initiated
File import
API connection
Notification
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59. Issues
App could be entered in a number of ways
User initiated
File import
API connection
Notification
Etc.
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60. Issues
App entry state could be
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61. Issues
App entry state could be
Passcode on
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62. Issues
App entry state could be
Passcode on
Passcode off
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63. Issues
App entry state could be
Passcode on
Passcode off
Locked out
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64. Issues
App entry state could be
Passcode on
Passcode off
Locked out
Already displaying a modal
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65. Overly complex logic
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66. Goals
Properly define app states
Encapsulate state logic
Transition easily between states
Speed launches
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67. Implementation
State Pattern
DBState
Initial
NotLoggedIn
ContinueAs
LoggedInNoPasscode
LoggedInPasscode
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68. Benefits
Reduced 2600 lines to 500 lines
Easier to understand
Encapsulated logic in clear boundaries
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69. TODAY’S TALK
Testing
Case Studies
Future of iOS at Dropbox
Background
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Product

70. Swift
Excited by the promise
Practical approach
Tooling
Encapsulated features
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