From 6dbab363d01e9c0c2e2cddc62db73957ff17a503 Mon Sep 17 00:00:00 2001
From: Milan <milan@z.cash>
Date: Mon, 19 May 2025 10:42:00 +0200
Subject: [PATCH] Shared preferences object cached in-memory and locked with
 semaphore (#1874)

* Shared preferences object cached in-memory and locked with semaphore

* Documentation update
---
 CHANGELOG.md                                  |  3 ++
 .../preference/AndroidPreferenceProvider.kt   | 52 ++++++++++++-------
 2 files changed, 36 insertions(+), 19 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2d131cbd9..8fe7bc562 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ and this application adheres to [Semantic Versioning](https://semver.org/spec/v2
 
 ## [Unreleased]
 
+### Fixed 
+- Shared preferences object cached in-memory and locked with semaphore in order to improve stability of security-crypto library
+
 ## [2.0.2 (962)] - 2025-05-14
 
 ### Fixed
diff --git a/preference-impl-android-lib/src/main/java/co/electriccoin/zcash/preference/AndroidPreferenceProvider.kt b/preference-impl-android-lib/src/main/java/co/electriccoin/zcash/preference/AndroidPreferenceProvider.kt
index b4ed07698..e25748471 100644
--- a/preference-impl-android-lib/src/main/java/co/electriccoin/zcash/preference/AndroidPreferenceProvider.kt
+++ b/preference-impl-android-lib/src/main/java/co/electriccoin/zcash/preference/AndroidPreferenceProvider.kt
@@ -30,7 +30,7 @@ import java.util.concurrent.Executors
  * this instance lives for the lifetime of the application. Constructing multiple instances will
  * potentially corrupt preference data and will leak resources.
  */
-class AndroidPreferenceProvider private constructor(
+class AndroidPreferenceProvider(
     private val sharedPreferences: SharedPreferences,
     private val dispatcher: CoroutineDispatcher
 ) : PreferenceProvider {
@@ -163,15 +163,26 @@ class AndroidPreferenceProvider private constructor(
         }
     }
 
-    companion object {
-        suspend fun newStandard(
-            context: Context,
-            filename: String
-        ): PreferenceProvider {
-            /*
-             * Because of this line, we don't want multiple instances of this object created
-             * because we don't clean up the thread afterwards.
-             */
+    companion object Factory : AndroidPreferenceFactory by AndroidPreferenceFactoryImpl()
+}
+
+interface AndroidPreferenceFactory {
+    suspend fun newStandard(context: Context, filename: String): PreferenceProvider
+
+    suspend fun newEncrypted(context: Context, filename: String): PreferenceProvider
+}
+
+private class AndroidPreferenceFactoryImpl : AndroidPreferenceFactory {
+    private val semaphore = Mutex()
+    private val standardCache = mutableMapOf<String, PreferenceProvider>()
+    private val encryptedCache = mutableMapOf<String, PreferenceProvider>()
+
+    override suspend fun newStandard(context: Context, filename: String) =
+        getOrCreate(standardCache, filename) {
+        /*
+         * Because of this line, we don't want multiple instances of this object created
+         * because we don't clean up the thread afterwards.
+         */
             val singleThreadedDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
 
             val sharedPreferences =
@@ -182,14 +193,12 @@ class AndroidPreferenceProvider private constructor(
             return AndroidPreferenceProvider(sharedPreferences, singleThreadedDispatcher)
         }
 
-        suspend fun newEncrypted(
-            context: Context,
-            filename: String
-        ): PreferenceProvider {
-            /*
-             * Because of this line, we don't want multiple instances of this object created
-             * because we don't clean up the thread afterwards.
-             */
+    override suspend fun newEncrypted(context: Context, filename: String) =
+        getOrCreate(encryptedCache, filename) {
+        /*
+         * Because of this line, we don't want multiple instances of this object created
+         * because we don't clean up the thread afterwards.
+         */
             val singleThreadedDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
 
             val sharedPreferences =
@@ -212,5 +221,10 @@ class AndroidPreferenceProvider private constructor(
 
             return AndroidPreferenceProvider(sharedPreferences, singleThreadedDispatcher)
         }
-    }
+
+    private suspend inline fun getOrCreate(
+        map: MutableMap<String, PreferenceProvider>,
+        filename: String,
+        block: () -> PreferenceProvider
+    ): PreferenceProvider = semaphore.withLock { map.getOrPut(filename, block) }
 }