[ok_http] Proguard/R8 is removing OkHttp in Android release mode #1950

Proguard/R8 is removing OkHttp classes when running the Android app in release mode:

java.lang.ClassNotFoundException: Didn't find class "okhttp3/OkHttpClient$Builder" on path: DexPathList[[zip file

Causing the app to crash.

Steps to reproduce:

1. Create a new Flutter app
2. Add ok_http depednency, create OkHttpClient and consume it

• see also: chore(ok_http): migrate to jni 1.0.0 #1943

3. Run the app using flutter run --release -d <ANDROID_DEVICE_ID_HERE>

Workarounds

Disabling R8 / minification fully

// android/app/build.gradle.kts

    buildTypes {
        release {
+            isMinifyEnabled = false
+            isShrinkResources = false
        }
    }
}

Test the app again: flutter run --release -d <ANDROID_DEVICE_ID_HERE>
and it works as intended.

Keep all OkHttp classes

+ -keep class okhttp3.** { *; }
+ -dontwarn okhttp3.**

Propused fix

Add android/proguard.txt file keep the Okhttp classes that are declared in jnigen.yaml.
flutter_plugin_android_lifecycle plugin (from flutter/packages) follows a similar pattern.

This way the consumers of ok_http will not need to modify their Android platform runner files, and only the necessary classes were kept without disabling minification or including all OkHttp classes.