Complete secure log viewing and retention

app/src/main/java/se/ajpanton/notificationlog/data/EncryptedImageStore.kt

@@ -1,6 +1,7 @@
 package se.ajpanton.notificationlog.data
 
 import android.content.Context
+import android.util.AtomicFile
 import java.io.File
 import java.io.DataInputStream
 import java.io.FileNotFoundException
@@ -12,11 +13,19 @@ class EncryptedImageStore(context: Context) {
 
     fun save(id: String, bytes: ByteArray) {
         require(id.matches(IMAGE_ID_PATTERN)) { "Invalid notification image ID." }
+        require(bytes.size <= MAX_IMAGE_BYTES) { "Notification image exceeds the 5 MiB retention limit." }
         val payload = cipher.encrypt(bytes)
-        File(directory, "$id.bin").outputStream().use { output ->
+        val file = AtomicFile(File(directory, "$id.bin"))
+        val output = file.startWrite()
+        try {
             output.write(payload.initializationVector.size)
             output.write(payload.initializationVector)
             output.write(payload.cipherText)
+            output.flush()
+            file.finishWrite(output)
+        } catch (error: Exception) {
+            file.failWrite(output)
+            throw error
         }
     }
 
@@ -38,7 +47,13 @@ class EncryptedImageStore(context: Context) {
         }
     }
 
+    fun delete(id: String) {
+        require(id.matches(IMAGE_ID_PATTERN)) { "Invalid notification image ID." }
+        File(directory, "$id.bin").delete()
+    }
+
     private companion object {
         val IMAGE_ID_PATTERN = Regex("[0-9a-f-]{36}")
+        const val MAX_IMAGE_BYTES = 5 * 1024 * 1024
     }
 }

app/src/main/java/se/ajpanton/notificationlog/data/EncryptedNotificationLogStore.kt

@@ -27,7 +27,9 @@ class EncryptedNotificationLogStore(context: Context) {
 
     fun append(entry: NotificationLogEntry) = synchronized(lock) {
         val entries = (readPayloadOrNull()?.let { NotificationLogEntryJson.decode(cipher.decrypt(it)) } ?: emptyList())
-        write(entries + entry)
+        val retained = retain(entries + entry)
+        write(retained)
+        (entries.mapNotNull { it.imageId } - retained.mapNotNull { it.imageId }.toSet()).forEach(::deleteImage)
     }
 
     fun replaceAll(entries: List<NotificationLogEntry>) = synchronized(lock) {
@@ -39,6 +41,14 @@ class EncryptedNotificationLogStore(context: Context) {
         imageDirectory.listFiles()?.forEach(File::delete)
     }
 
+    fun delete(id: String): Boolean = synchronized(lock) {
+        val entries = readPayloadOrNull()?.let { NotificationLogEntryJson.decode(cipher.decrypt(it)) } ?: return false
+        val entry = entries.firstOrNull { it.id == id } ?: return false
+        write(entries.filterNot { it.id == id })
+        entry.imageId?.let(::deleteImage)
+        true
+    }
+
     private fun write(entries: List<NotificationLogEntry>) {
         val payload = cipher.encrypt(NotificationLogEntryJson.encode(entries))
         val output = file.startWrite()
@@ -57,6 +67,21 @@ class EncryptedNotificationLogStore(context: Context) {
         }
     }
 
+    private fun retain(entries: List<NotificationLogEntry>): List<NotificationLogEntry> {
+        var retained = entries.takeLast(MAX_ENTRIES)
+        while (retained.size > 1 && NotificationLogEntryJson.encode(retained).size > MAX_PLAINTEXT_BYTES) {
+            retained = retained.drop(1)
+        }
+        require(NotificationLogEntryJson.encode(retained).size <= MAX_PLAINTEXT_BYTES) {
+            "A notification event exceeds the encrypted log retention limit."
+        }
+        return retained
+    }
+
+    private fun deleteImage(id: String) {
+        if (id.matches(IMAGE_ID_PATTERN)) File(imageDirectory, "$id.bin").delete()
+    }
+
     private fun readPayloadOrNull(): EncryptedPayload? {
         val input = try {
             file.openRead()
@@ -82,6 +107,9 @@ class EncryptedNotificationLogStore(context: Context) {
         const val FILE_VERSION = 1
         const val MAX_IV_BYTES = 32
         const val MAX_CIPHER_TEXT_BYTES = 50 * 1024 * 1024
+        const val MAX_PLAINTEXT_BYTES = 20 * 1024 * 1024
+        const val MAX_ENTRIES = 10_000
         const val IMAGE_DIRECTORY_NAME = "notification-images"
+        val IMAGE_ID_PATTERN = Regex("[0-9a-f-]{36}")
     }
 }