Add encryption for content on cache file

[argaasasta]

For fix this issue
#164

[Bohdan-Kim]

Seems like it will work for one specific instance of CachingAndroid while if encrypted content is stored yesterday, restored today it won't decrypt because no guarantee it's the same object and the same secret key

[Bohdan-Kim]

Seems like it was tried in Plain text; GrowthBook provides encryption in PRO:

[argaasasta]

@Bohdan-Kim is the PRO will encrypt this cache, so it not visible to pentester? so all i need is just use the PRO?

[Bohdan-Kim]

yes encryption in PRO

[argaasasta]

@Bohdan-Kim after i see the implementation, only android that have this FeatureCache.txt, can we add encrypt just for the local cache on android?

[Bohdan-Kim]

@argaasasta we can but it's overhead for this case. can we just add ability for you to disable the local cache on android?
cachingEnabled: Boolean = false

[Bohdan-Kim]

If user of the SDK provides localEncryptionKey it seems allow to achieve encryption of FeatureCache.txt in not PRO, but it would complicate caching layer

[Bohdan-Kim]

This is publicly exposed API change. It should be discussed with maintainers @Auz @jdorn

[argaasasta]

@argaasasta we can but it's overhead for this case. can we just add ability for you to disable the local cache on android?
cachingEnabled: Boolean = false

@Bohdan-Kim yes please, can you add this? so the FeatureCache.txt will not be there
thank you

[argaasasta]

internal fun gbSerialize(): JsonElement = when(this) {
is GBBoolean -> JsonPrimitive(this.value)
is GBString -> JsonPrimitive(this.value)
is GBNumber -> JsonPrimitive(this.value)
is GBJson -> JsonObject(
this.mapValues { it.value.gbSerialize() }
)
is Unknown -> JsonNull
}

@Bohdan-Kim could you make this function is not internal, so we can still use on the outside?

[Bohdan-Kim]

@argaasasta I think yes

[argaasasta]

i still want to use the GBFeatureResult for return, and i cant change the GBValue to json that i want

I have copy this
return when(val gbResultValue = gbFeatureResult.gbValue) {
is GBBoolean -> gbResultValue.value as? V
is GBString -> gbResultValue.value as? V
is GBNumber -> gbResultValue.value as? V
is GBJson -> gbResultValue as? V
is GBValue.Unknown -> null
null -> null
}

    but the JSon cannot be transform, and i change to this
    
  val jsonObject: JsonObject = (feature.gbValue as GBJson).gbSerialize() as JsonObject
  Gson().fromJson(jsonObject.toString(), T::class.java)
  
  and it success, so i need the gbSerialize

@Bohdan-Kim

[Bohdan-Kim]

@argaasasta Are you sure that you feature type is JSON? Maybe safe cast.
Seems like we should to move GBValue.gbSerialize() to growthbook-kotlinx-serialization module as Gson using possible instead of kotlinx-serialization

[argaasasta]

@Bohdan-Kim yes, it works previously with this code
val feature = getInstance().feature(featureId)
generateTracker(feature)
val jsonObject: JsonObject = feature.value as JsonObject
Gson().fromJson(jsonObject.toString(), T::class.java)

since value is change to gbValue on new version, we need to make some refactor too

[Bohdan-Kim]

About the next steps with this pull request.
I'm concerned that this would quite sophisticate caching layer.
Seems like was agreed for simpler way to achieve absence of cache file.

[argaasasta]

Sure, i will close this PR