117 lines
4.3 KiB
Kotlin
117 lines
4.3 KiB
Kotlin
package co.electriccoin.zcash.preference
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import android.annotation.SuppressLint
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import android.content.Context
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import android.content.SharedPreferences
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import androidx.security.crypto.EncryptedSharedPreferences
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import androidx.security.crypto.MasterKey
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import co.electriccoin.zcash.preference.api.PreferenceProvider
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import co.electriccoin.zcash.preference.model.entry.PreferenceKey
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import kotlinx.coroutines.CoroutineDispatcher
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import kotlinx.coroutines.asCoroutineDispatcher
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import kotlinx.coroutines.channels.awaitClose
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import kotlinx.coroutines.flow.Flow
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import kotlinx.coroutines.flow.callbackFlow
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import kotlinx.coroutines.flow.flowOn
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import kotlinx.coroutines.flow.map
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import kotlinx.coroutines.withContext
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import java.util.concurrent.Executors
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/**
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* Provides an Android implementation of shared preferences.
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*
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* This class is thread-safe.
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*
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* For a given preference file, it is expected that only a single instance is constructed and that
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* this instance lives for the lifetime of the application. Constructing multiple instances will
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* potentially corrupt preference data and will leak resources.
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*/
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/*
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* Implementation note: EncryptedSharedPreferences are not thread-safe, so this implementation
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* confines them to a single background thread.
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*/
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class AndroidPreferenceProvider(
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private val sharedPreferences: SharedPreferences,
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private val dispatcher: CoroutineDispatcher
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) : PreferenceProvider {
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override suspend fun hasKey(key: PreferenceKey) = withContext(dispatcher) {
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sharedPreferences.contains(key.key)
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}
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@SuppressLint("ApplySharedPref")
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override suspend fun putString(key: PreferenceKey, value: String?) = withContext(dispatcher) {
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val editor = sharedPreferences.edit()
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editor.putString(key.key, value)
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editor.commit()
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Unit
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}
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override suspend fun getString(key: PreferenceKey) = withContext(dispatcher) {
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sharedPreferences.getString(key.key, null)
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}
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override fun observe(key: PreferenceKey): Flow<String?> = callbackFlow<Unit> {
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val listener = SharedPreferences.OnSharedPreferenceChangeListener { _, _ ->
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// Callback on main thread
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trySend(Unit)
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}
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sharedPreferences.registerOnSharedPreferenceChangeListener(listener)
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// Kickstart the emissions
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trySend(Unit)
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awaitClose {
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sharedPreferences.unregisterOnSharedPreferenceChangeListener(listener)
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}
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}.flowOn(dispatcher)
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.map { getString(key) }
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companion object {
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suspend fun newStandard(context: Context, filename: String): PreferenceProvider {
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/*
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* Because of this line, we don't want multiple instances of this object created
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* because we don't clean up the thread afterwards.
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*/
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val singleThreadedDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
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val sharedPreferences = withContext(singleThreadedDispatcher) {
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context.getSharedPreferences(filename, Context.MODE_PRIVATE)
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}
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return AndroidPreferenceProvider(sharedPreferences, singleThreadedDispatcher)
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}
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suspend fun newEncrypted(context: Context, filename: String): PreferenceProvider {
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/*
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* Because of this line, we don't want multiple instances of this object created
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* because we don't clean up the thread afterwards.
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*/
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val singleThreadedDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
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val mainKey = withContext(singleThreadedDispatcher) {
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@Suppress("BlockingMethodInNonBlockingContext")
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MasterKey.Builder(context).apply {
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setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
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}.build()
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}
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val sharedPreferences = withContext(singleThreadedDispatcher) {
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@Suppress("BlockingMethodInNonBlockingContext")
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EncryptedSharedPreferences.create(
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context,
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filename,
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mainKey,
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EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
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EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
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)
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}
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return AndroidPreferenceProvider(sharedPreferences, singleThreadedDispatcher)
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}
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}
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}
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