CacheControl for OkHttpClient (to support offline mode without persistence data library)

NetworkModule.kt

// assuming provider is inside Hilt-Android Module
@InstallIn(SingletonComponent::class)
@Module
class NetworkModule {
  ...
  
  @Provides
  @Singleton
  fun providesOkHttpClient(
      @ApplicationContext context: Context
  ): OkHttpClient {
    // setup cache size
    val cacheSize = (5 * 1024 * 1024).toLong()
    val cache = Cache(context.cacheDir, cacheSize)
    
    // setup logging (optional)
    val loggingInterceptor = HttpLoggingInterceptor()
    loggingInterceptor.level = HttpLoggingInterceptor.Level.BODY
    
    val client = OkHttpClient.Builder()
      .cache(cache)
      .connectTimeout(60, TimeUnit.SECONDS)
      .writeTimeout(60, TimeUnit.SECONDS)
      .readTimeout(60, TimeUnit.SECONDS)
      .addNetworkInterceptor(loggingInterceptor)
      .addInterceptor { chain ->
        var request = chain.request()
        try {
          // force fetch from network when online
          request = request.newBuilder().cacheControl(CacheControl.FORCE_NETWORK).build()
          chain.proceed(request)
        } catch (e: UnknownHostException) {
          // retrieve from cache when network is offline
          val cacheControl = CacheControl.Builder()
            .onlyIfCached()
            .maxStale(2, TimeUnit.HOURS)
            .build()
            
          request = request.newBuilder().cacheControl(cacheControl).build()
          chain.proceed(request)
        }
      }
      
    return client.build()
  }
  
  ...
}