Interception - Droidcon NYC 2023

Embrace the Interceptor pattern of software design to create cleaner abstractions, enable flexibility, and set yourself up for writing high quality tests. This versatile approach empowers engineers with unmatched control, adaptability, and seamless integration with dependency injection. Join me to explore how interfaces and protocols serve as the foundation for making code flexible, adaptable and composable. We’ll talk about high level design playbooks as well as real-world examples you can start using today to leverage this software design pattern. Examples such as utilizing reflection-based Proxy Objects, employing "Fakes" in unit tests, wrapping 3rd party libraries and modifying network traffic.

Example Code on Github: https://github.com/handstandsam/interception-examples

Transcript

1. Sam Edwards - @HandstandSam - Square Interception Droidcon NYC September 14, 2023 #DCNYC23
2. A Call B Completion Invocation
3. A Call Chain B
4. A Call Chain B
5. Call Chain A B
6. Call Chain with Interceptors A B
7. Telephone Game ☎ A B
8. Interceptor Pattern 💻
9. https://en.wikipedia.org/wiki/Interceptor_pattern Offer a way to change, or augment the usual processing cycle. Interceptor Pattern
10. https://en.wikipedia.org/wiki/Interceptor_pattern The rest of the system does not have to know something has been added or changed and can keep working as before. Interceptor Pattern
11. Call Chain with Interceptors A B
12. Categories of Interception • Passthrough (NoOp) • Logging (Inspect) • Modifying/Transform (Change) • Circuit Breaker (Stop)
13. OkHttp Interceptors
14. OkHttp Interceptor Examples
15. Adding Interceptors for OkHttp val okHttpClient = OkHttpClient.Builder() .build()
16. Adding Interceptors for OkHttp val okHttpClient = OkHttpClient.Builder() .addInterceptor(MyInterceptor) .build()
17. Adding Interceptors for OkHttp val okHttpClient = OkHttpClient.Builder() .addInterceptor(MyInterceptor) .addInterceptor(MyInterceptor2 ) .build()
18. Adding Interceptors for OkHttp val okHttpClient = OkHttpClient.Builder() .addInterceptor(MyInterceptor) .addInterceptor(MyInterceptor2 ) .addInterceptor(MyInterceptor3 ) .build()
19. Passthrough Interceptor 🤷
20. Passthrough Interceptor Interceptor { chain -> val request = chain.request() val response = chain.proceed(request) response }
21. Logging Interceptor 📝
22. Logging Interceptor Interceptor { chain -> val request = chain.request() val response = chain.proceed(request) println(" - - - Request Headers ---") println(request.headers) println(" - - - Response Headers ---") println(response.headers) response }
23. Modifying Interceptor 🥷
24. Modifying Interceptor Interceptor { chain -> val newRequest = chain.request() .newBuilder() .addHeader("Droidcon", "NYC") .build() chain.proceed(newRequest) }
25. Short Circuit Interceptor ⚡
26. Short Circuit Interceptor val ShortCircuitInterceptor = Interceptor { chain -> val request = chain.request() Response.Builder() .code(200) .protocol(Protocol.HTTP_2 ) .request(request) .message("") .body("Short Circuited".toResponseBody()) .build() }
27. Caching Interceptor 🧠
28. Caching Interceptor private val cache = mutableMapOf<HttpUrl, String? > ( ) Interceptor { chain -> val request = chain.request() val bodyStr = cache[request.url] ? : run { val response = chain.proceed(request) response.body?.string().also { cache[request.url] = it } } buildResponseWithBodyStr(request, bodyStr) }
29. OkHttp Interceptors are Beautiful 🌈 • Composable • Flexible • Powerful
30. Pop Quiz! 🏈
31. American Football Interception 🏈
32. When the ball is caught by the defense, instead of the offense. 🏈
33. A Interception American Football B
34. A Interception American Football B 🏈
35. Interception American Football 🏈 B A
36. Recap
37. Interceptor Pattern Benefits • Clean Abstraction • Flexible • Testable • Adaptable • Composable • Injectable
38. Kotlin Flows
39. Chaining Flows and Intercepting flowOf(1, 2, 3 ) .collect()
40. Chaining Flows and Intercepting flowOf(1, 2, 3 ) .onEach { println("Logged $it") } .collect() Logged 1 Logged 2 Logged 3
41. Chaining Flows and Intercepting flowOf(1, 2, 3 ) .onEach { println("Logged $it") } .map { it + 100 } .collect() Logged 1 Logged 2 Logged 3
42. Chaining Flows and Intercepting flowOf(1, 2, 3 ) .onEach { println("Logged $it") } .map { it + 100 } .onEach { println("Collected $it") } .collect() Logged 1 Collected 101 Logged 2 Collected 102 Logged 3 Collected 103
43. Kotlin Flows are Beautiful 🌈 • Composable • Flexible • Powerful
44. Iterating Kotlin Collections
45. Chaining Actions and Intercepting listOf(1, 2, 3 ) .onEach { println("Logged $it") } Logged 1 Logged 2 Logged 3
46. Chaining Actions and Intercepting listOf(1, 2, 3 ) .onEach { println("Logged $it") } .map { it + 100 } Logged 1 Logged 2 Logged 3
47. Chaining Actions and Intercepting listOf(1, 2, 3 ) .onEach { println("Logged $it") } .map { it + 100 } .onEach { println("Collected $it") } Logged 1 Logged 2 Logged 3 Collected 101 Collected 102 Collected 103
48. Interfaces Enable Injection
49. Interfaces Enable Injection interface Logger { fun log(message: String) }
50. Interfaces Enable Injection interface Logger { fun log(message: String) } class SystemOutLogger : Logger { override fun log(message: String) { println(message) } }
51. Interfaces Enable Injection interface Logger { fun log(message: String) } class SystemOutLogger : Logger { override fun log(message: String) { println(message) } } class AndroidLogger : Logger { override fun log(message: String) { Log.d("Logger", message) } }
52. Interfaces Enable Interception
53. A Interfaces Enable Interception B SystemOutLogger Logger
54. A Interfaces Enable Interception B Logger SystemOutLogger Logger
55. A Interfaces Enable Interception B Logger SystemOutLogger Logger Logger
56. Interfaces Enable Interception A B Logger SystemOutLogger Logger Logger Logger
57. Interfaces Enable Fakes
58. A Interfaces Enable Fakes B Interface 3rd Party Lib Fake
59. Kotlin Delegates
60. Kotlin Delegates Passthrough class PassthroughDelegateLogger( private val delegate: Logger ) : Logger { override fun log(message: String) { delegate.log(message) } override fun error(message: String) { delegate.error(message) } }
61. Kotlin Delegates Logging class LoggingDelegateLogger( private val delegate: Logger ) : Logger by delegate { override fun log(message: String) { println("Logged $message") delegate.log(message) } }
62. Kotlin Delegates Modifying class AddTimestampLogger( private val delegate: Logger ) : Logger by delegate { override fun log(message: String) { delegate.log("${Date()} $message") } }
63. Kotlin Delegates Short Circuit class ShortCircuitNoErrorsDelegateLogger( private val delegate: Logger ) : Logger by delegate { override fun log(message: String) { delegate.log("${Date()} $message") } override fun error(message: String) { // Do Not Delegate } }
64. Interception Recap
65. Categories of Interception • Passthrough (NoOp) • Logging (Inspect) • Modifying/Transform (Change) • Circuit Breaker (Stop)
66. Why? • Clean Abstraction • Flexible • Testable • Adaptable • Composable • Injectable
67. Takeaways • Use Interfaces • OkHttp “Interception” • Kotlin Flow “Interception” • Kotlin Delegate “Interception” • Design for “Interception”
68. BONUS LIVE DEMO Java Reflection Dynamic Proxies
69. Sam Edwards - @HandstandSam - Square #DCNYC23 conferenceChain.proceed(talk)