Preparing for Network Failures this Holiday Season

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Suppose I’m connecting my home Christmas lights to the Internet. Perhaps I’ll make a mobile app that calls my home control server via an HTTP API: POST /lights/toggle HTTP/1.1 { "subjects": ["maple_tree", "roof"] }HTTP/1.1 200 OK { "toggled": true }It works. I can finally…

Your Company’s DanceService probably doesn’t Dance

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I work on a big product at a big company and we have lots of backend services that have big responsibilities: The messaging service sends customers their emails, SMS messages, and push notifications.The banking service manages the customers’ bank accounts.The identity verification service verifies customers’ identities.Except that…

Farm or Grind

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Suppose your organization has a widely-used internal library for validating customer usernames: private val usernameRegex = Regex("[a-z]{2,40}") fun isValidUsername(username: String): Boolean { return usernameRegex.matches(username) }The function becomes widely adopted: Some callers use it during customer sign-up. We don’t want customers putting slashes in their usernames!…

Read a File in a Kotlin/Multiplatform Test

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I like writing unit tests that read test cases from a data file: Zipline does ECDSA and EdDSA signing. It gets test data from Project Wycheproof.OkHttp does URL parsing. It gets test data from The web-platform-tests Project.OkHttp-ICU does Unicode Normalization. It gets its test data from Unicode’s…

Bob Bent the Universe

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Bob Lee was murdered on April 4 in San Francisco. I met Bob in 2006 when I joined him on the AdWords front end (AWFE) team at Google. He was charismatic, inventive, and kind. With Kevin B. he created Guice, a dependency injector that we could use to make AWFE…

Surprised by Re-entrant Code

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Some of the trickiest bugs I’ve seen happened because a function unexpectedly occurred multiple times on the call stack. Re-entrant ListenersTo illustrate, consider a TextField widget that implements the listener pattern: class TextField { var listeners = mutableListOf<Listener>() var value: String = "" set(value) { val previous = field if (value…

Factory Factory

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I use lots of factory classes in my code. But not everywhere. I don’t like the ceremony they require to create and use: why not a constructor? Factories don’t solve a business problem directly; they solve an architecture problem. They feel enterprisey and architecture astronauty. /** * For example, a…

Code Changes Should Be Small or Mechanical

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Easy code changes are additive: introduce a new database table, network call, or screen. Difficult changes are transformative: split a database table, combine a few network calls, or change a component that’s used on many screens. These changes tend to motivate refactoring: Introduce feature flagsExtract interfacesMove code between modulesAdd…