Building Quality Code That Lasts: A Dropbox Story. Ashley Nelson-Hornstein

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Building Quality Code That Lasts: A Dropbox StoryAshley Nelson-Hornstein · 10 - 30 - 14

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Product

Testing

Background

Case Studies

Future of iOS at Dropbox

TODAY’S TALK

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Dropbox for iOSDeveloped natively

Team of one engineer

First consumer of Dropbox public APIs

Released for iPhone in 2009

iPad support in 2010

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Sync SDK

UI Code

Core SDK

Data Layer

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TODAY’S TALK

Product

Testing

Background

Case Studies

Future of iOS at Dropbox

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Product RoadmapCollaborative process

Mix of

Infrastructure

User facing features

Code modernization

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Release ManagerRotating role

Feature gatekeeper

Project manager

Task prioritization

Scheduling

Build stabilization

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Development

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BranchingDefault branch

All changes are checked in here first

Release branch

hg graft —log from default branch

Verified by release manager

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Style Guide

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Coding ConventionsPrefix internal methods with db_

Prefer class methods

Hide implementation detail

Class extensions

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// 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

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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Builds

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Continuous IntegrationPool of build machines

Executes functional tests

Builds are available to office

State changes are emailed to team

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Crash ReporterDeveloped in-house

Predates other crash report services

Uploads crash logs from device

Groups crashes by stack trace

Provides symbolication

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TODAY’S TALK

Testing

Case Studies

Future of iOS at Dropbox

Background

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Product

Developer SettingsToggle features on/off

View

Run log

Network and device stats

File cache inspection

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Shake to ReportInternal bug reporting

Captures

Screenshot

Crash log (if applicable)

Run log

Issues reported directly to bug tracking tool

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Helper Apps

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DropolineDeveloped in-house

Tests inter-app workflows

File import/export

Photo backup

Storage provider extension

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Car KeysDeveloped in-house

Keychain

Inspection

Deletion

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Automata

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Automata BackgroundFunctional 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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Automata BenefitsSeparate 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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Automata

Dropbox Dropoline

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Automata

Dropbox Dropoline

Automata FutureSupport for iOS 8 extensions

GUI that records test scripts

Open source

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TODAY’S TALK

Testing

Case Studies

Future of iOS at Dropbox

Background

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Product

File Cache

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BackgroundProvides access to user’s Dropbox files

Coordinates with REST API and disk

Critical component

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IssuesFile 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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/* * 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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/* * 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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GoalsEnsure file name integrity

Operations on separate queue

Smarter file loading system

Defensive return values

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ApproachUnit Tests

Uncovered existing bugs

Set a baseline for expected behavior

Maintained API for consumers

Limited project scope

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ImplementationStore files by UUID instead of Dropbox path

File Cache on background serial queue

Return immutable stubs of file refs

LoadingFileManager

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Consumer FileCache

RO Cached File

Core Data

Disk

Loading File Manager

Single Background Queue

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BenefitsEasier to understand

Performant

Stable

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App Delegate

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[[UIApplication sharedApplication] delegate]

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Issues

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IssuesApp could be entered in a number of ways

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IssuesApp could be entered in a number of ways

User initiated

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IssuesApp could be entered in a number of ways

User initiated

File import

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IssuesApp could be entered in a number of ways

User initiated

File import

API connection

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IssuesApp could be entered in a number of ways

User initiated

File import

API connection

Notification

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IssuesApp could be entered in a number of ways

User initiated

File import

API connection

Notification

Etc.

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IssuesApp entry state could be

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IssuesApp entry state could be

Passcode on

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IssuesApp entry state could be

Passcode on

Passcode off

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IssuesApp entry state could be

Passcode on

Passcode off

Locked out

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IssuesApp entry state could be

Passcode on

Passcode off

Locked out

Already displaying a modal

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Overly complex logic

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GoalsProperly define app states

Encapsulate state logic

Transition easily between states

Speed launches

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ImplementationState Pattern

DBState

Initial

NotLoggedIn

ContinueAs

LoggedInNoPasscode

LoggedInPasscode

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BenefitsReduced 2600 lines to 500 lines

Easier to understand

Encapsulated logic in clear boundaries

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TODAY’S TALK

Testing

Case Studies

Future of iOS at Dropbox

Background

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Product

SwiftExcited by the promise

Practical approach

Tooling

Encapsulated features

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