Merge pull request #297 from akirk/fix/corrupted-assignments-cache

Fix crash loop caused by corrupted A/B testing cache file

Author: ParaskP7

experimentation/src/main/java/com/automattic/android/experimentation/local/FileBasedCache.kt

@@ -31,20 +31,33 @@ internal class FileBasedCache(
     init {
         scope.launch {
             withContext(context = dispatcher) {
-                latestMutable = getAssignments()
+                runCatching { latestMutable = getAssignments() }
+                    .onFailure { throwable -> logger.e("Failed to load cached assignments", throwable) }
             }
         }
     }
 
     suspend fun getAssignments(): Assignments? {
         return withContext(dispatcher) {
-            assignmentsFile.takeIf { it.exists() }?.readText()?.let { json: String ->
-                val fromJson = cacheDtoJsonAdapter.fromJson(json) ?: return@let null
-
-                fromJson.assignmentsDto.toAssignments(
-                    fetchedAt = fromJson.fetchedAt,
-                    anonymousId = fromJson.anonymousId,
-                )
+            assignmentsFile.takeIf { it.exists() }?.let { file ->
+                val json = file.readText()
+                if (json.isBlank()) {
+                    logger.e("Cached assignments file is empty, deleting: ${file.path}")
+                    file.delete()
+                    return@withContext null
+                }
+                runCatching { cacheDtoJsonAdapter.fromJson(json) }
+                    .onFailure { throwable ->
+                        logger.e("Cached assignments file is corrupted, deleting: ${file.path}", throwable)
+                        file.delete()
+                    }
+                    .getOrNull()
+                    ?.let { fromJson ->
+                        fromJson.assignmentsDto.toAssignments(
+                            fetchedAt = fromJson.fetchedAt,
+                            anonymousId = fromJson.anonymousId,
+                        )
+                    }
             }
         }
     }

experimentation/src/test/java/com/automattic/android/experimentation/local/FileBasedCacheTest.kt

@@ -9,6 +9,7 @@ import kotlinx.coroutines.test.StandardTestDispatcher
 import kotlinx.coroutines.test.TestScope
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
 import org.junit.Assert.assertNull
 import org.junit.Rule
 import org.junit.Test
@@ -66,6 +67,30 @@ internal class FileBasedCacheTest {
         sut.clear()
     }
 
+    @Test
+    fun `getting assignments from empty file returns null and deletes the file`() = runTest {
+        val cacheDir = tempDir.newFolder()
+        val assignmentsFile = File(cacheDir, "assignments.json").apply { createNewFile() }
+        val sut = fileBasedCache(this, cacheDir = cacheDir)
+
+        val result = sut.getAssignments()
+
+        assertNull(result)
+        assertFalse(assignmentsFile.exists())
+    }
+
+    @Test
+    fun `getting assignments from corrupted file returns null and deletes the file`() = runTest {
+        val cacheDir = tempDir.newFolder()
+        val assignmentsFile = File(cacheDir, "assignments.json").apply { writeText("{corrupted") }
+        val sut = fileBasedCache(this, cacheDir = cacheDir)
+
+        val result = sut.getAssignments()
+
+        assertNull(result)
+        assertFalse(assignmentsFile.exists())
+    }
+
     @Test
     fun `saving cache when cache dir doesnt exist is successful`() = runTest {
         val cacheDir = File(tempDir.newFolder(), "cache").apply { assert(!this.exists()) }