How to write a safe and reliable Open Source Library

You’ve written some code, and you’d like to release it as Open Source. Congratulations!

Publishing an Open Source library goes beyond just releasing your code on Github. New users with different use cases means preparing for the unpredictable. How do you ensure your code is safe and efficient? Is your code easy to read? Do you have a plan for upgrades in the future?

This talk will look at best practices and showcase a checklist to follow when writing and publishing an Open Source Library, from the documentation to ensuring your library works as intended and doesn’t break applications using it.

Transcript

1. How to write
   a safe and reliable
   Open Source Library
   

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2. Xavier F. Gouchet
   Senior Software Engineer
   at Datadog
   @xgouchet / @datadoghq
   2
   

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4. 0
   Introduction
   4
   

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5. github.com/DataDog/dd-sdk-android
   5
   commit 0db48d14dea27ac02e8ddeb9ccf7413feaacc20e
   Author: Xavier F. Gouchet
   Date: Mon Nov 4 13:38:30 2019 +0100
   Initial drop with base gradle config
   

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6. Repository statistics
   - 2400+ commits
   - 3 developers
   - 20+ contributors
   - (internal and community)
   - 30 published versions
   - 10 libraries
   6
   

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7. 1
   MAKING IT SAFE
   7
   

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8. Reliability is key
   8
   ▪ Library lives in hundreds apps…
   ▪ … deployed on thousands devices
   

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9. Ensure the code is safe
   9
   ▪ objective zero crash
   ▫ Static Analysis
   ▫ Code review
   ▫ *-tests
   ▪ Real life use cases
   

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10. Static analysis (Detekt)
    ▪ Forbid throwing exceptions
    ▪ Forbid specific Kotlin syntax
    ▫ check
    ▫ require
    ▫ !!
    ▪ List all third party methods throwing
    exceptions
    10
    

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11. Mandatory Code Review
    ▪ Notice potential issues early
    ▪ Increase readability
    ▪ Generate discussion
    ▫ Data structure
    ▫ Design Patterns
    ▫ Third party libraries
    11
    

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12. “Testing is doubting!”
    12
    

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13. Unit/Integration/End-to-end Testing
    ▪ Strict policy on the coverage
    ▪ Deal with flaky test ASAP
    ▪ Stay confident in our tests
    13
    

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14. Real life use cases
    ▪ Dogfooding in our own apps
    ▪ Regular tests using OSS apps
    ▫ Wikipedia
    ▫ Reddit client
    ▫ HackerNews client
    14
    

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15. Respect privacy
    15
    ▪ Leverage Sandbox storage / Cache
    ▪ Add GDPR option
    ▪ Write doc about Data Collection
    

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16. 2
    MAKING IT EFFICIENT
    16
    

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17. Limit library performance impact
    17
    ▪ Offload heavy computation to background
    threads/workers
    ▪ Track Memory Leaks
    

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18. Monitor library overhead
    18
    ▪ Compute the impact of the library on
    ▫ CPU
    ▫ Memory
    ▫ Network
    ▫ …
    

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19. Keep a focus on performance
    19
    ▪ Track the performance impact for each
    update
    

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20. 3
    MAKING IT USABLE
    20
    

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21. Opt-in or opt-out by default
    21
    ▪ Balance between “it works out of the box”
    and “it doesn’t do anything that I don’t
    know of”
    ▪ Onboarding should work in 15 minutes
    

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22. Every thing can be configured
    ▪ Allow enabling/disabling individual
    features
    ▪ Allow tweaking sampling rates,
    thresholds, …
    22
    

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23. Use sensible defaults
    23
    ▪ New customers don’t need to configure
    everything right now…
    ▪ … or ever
    

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24. Communicate
    ▪ Log any actionable “issue”
    ▫ configuration error
    ▫ feature misuse
    ▫ key internal events
    ▪ Add actions or documentation links in the
    message
    ▪ Provide information about what the
    library is doing
    24
    

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25. 4
    MAKING IT FUTURE PROOF
    25
    

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26. Keep track of API surface
    26
    ▪ Prevent any API breaking change
    ▪ Provide new option but keep the old ones
    working
    ▫ with @Deprecated
    ▫ with a LogCat log
    ▪ Provide migration guide
    

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27. Monitor dependencies
    27
    ▪ Review changelogs
    ▪ Be mindful of transitive dependencies
    

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28. Monitor dependencies
    $ ./gradlew :my-lib:dependencies
    releaseRuntimeClasspath
    +- project :my-lib
    | +- org.jetbrains.kotlin:kotlin-stdlib:1.3.61
    | +- com.example.something:core-lib:1.2.0
    | | \- org.jetbrains.kotlin:kotlin-stdlib:1.3.61 → 1.5.31 (*)
    28
    

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29. Monitor dependencies
    $ ./gradlew :my-lib:dependencies
    releaseRuntimeClasspath
    +- project :my-lib
    | +- org.jetbrains.kotlin:kotlin-stdlib:1.5.31
    | +- com.example.something:core-lib:1.2.0
    | | \- org.jetbrains.kotlin:kotlin-stdlib:1.3.61 → 1.5.31 (*)
    29
    

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30. Protect experimental features
    ▪ Use -alpha and -beta releases
    ▪ Use Kotlin’s opt-in annotations
    30
    

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31. Kotlin Opt-in annotations
    31
    @RequiresOptIn(message = "This API is experimental.")
    @Retention(AnnotationRetention.BINARY)
    @Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION)
    annotation class MyCustomOptIn
    

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32. Kotlin Opt-in annotations
    32
    @MyCustomOptIn
    class MyExperimentalClass {
    // …
    }
    

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33. Kotlin Opt-in annotations
    33
    @OptIn(MyCustomOptIn::class)
    fun doSomething {
    val x = MyExperimentalClass()
    // …
    }
    

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34. 5
    MAKING IT OPEN SOURCE
    34
    

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35. Why an Open Source Library
    35
    ▪ It lives within our customer’s code
    ▫ Readable
    ▫ Editable
    ▪ Allows direct contribution
    ▪ Keeps the engineering team closer to our
    users
    ▪ We also use Open Source every day
    

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36. Contributing.md
    36
    ▪ Developer environment (IDE, tools, …)
    ▪ How to build and run the code
    ▪ How to run the tests / static analysis
    ▪ How to contribute
    ▫ Issues
    ▫ PRs
    ▪ Coding conventions
    

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37. PR & Issue templates
    37
    ▪ Dedicated files
    ▫ .github/ISSUE_TEMPLATE/bug.md
    ▫ .github/PULL_REQUEST_TEMPLATE.md
    ▪ Custom checklist for everyone
    

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38. LICENSE
    38
    ▪ Use an existing license
    ▫ https://choosealicense.com/
    ▪ Apache / MIT
    ▫ Compatible with your dependencies
    

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39. 6
    ANDROID GUIDELINES
    39
    

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40. AndroidManifest.xml
    40
    
    android:name="android.permission.INTERNET" />
    android:name="android.permission.ACCESS_NETWORK_STATE" />
    
    
    

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41. build.gradle[.kts]
    41
    android {
    minSDK = 19
    targetSdk = 31
    defaultConfig {
    aarMetadata {
    minCompileSdk = 29
    }
    }
    }
    

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42. build.gradle[.kts]
    42
    android {
    // …
    testFixtures {
    // uses src/testFixtures
    enable = true
    }
    }
    

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43. Publish to Maven
    ▪ Maven Central
    ▪ Custom Maven Server
    43
    

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44. CONCLUSION
    44
    

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45. Keep an Open Mindset
    45
    ▪ Every mistake is a lesson
    ▪ Look at other Open Source Libraries
    

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46. Thank you!
    ANY QUESTIONS?
    @xgouchet
    @datadoghq
    46
    

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47. CREDITS
    Special thanks to all the people who made and released
    these awesome resources for free:
    ▪ Presentation template by SlidesCarnival
    ▪ Photographs by Unsplash
    47
    

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