Remove orphaned attachments when creating a new backup.

app/src/main/java/org/thoughtcrime/securesms/database/AttachmentTable.kt

@@ -407,6 +407,14 @@ class AttachmentTable(
     }
   }
 
+  fun getMediaIdCursor(): Cursor {
+    return readableDatabase
+      .select(ARCHIVE_MEDIA_ID, ARCHIVE_CDN)
+      .from(TABLE_NAME)
+      .where("$ARCHIVE_MEDIA_ID IS NOT NULL")
+      .run()
+  }
+
   fun getAttachment(attachmentId: AttachmentId): DatabaseAttachment? {
     return readableDatabase
       .select(*PROJECTION)

app/src/main/java/org/thoughtcrime/securesms/database/BackupMediaSnapshotTable.kt

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.database
+
+import android.content.Context
+import androidx.annotation.VisibleForTesting
+import androidx.core.content.contentValuesOf
+import org.signal.core.util.SqlUtil
+import org.signal.core.util.delete
+import org.signal.core.util.exists
+import org.signal.core.util.readToList
+import org.signal.core.util.requireInt
+import org.signal.core.util.requireNonNullString
+import org.signal.core.util.select
+import org.thoughtcrime.securesms.backup.v2.ArchivedMediaObject
+
+/**
+ * Helper table for attachment deletion sync
+ */
+class BackupMediaSnapshotTable(context: Context, database: SignalDatabase) : DatabaseTable(context, database) {
+  companion object {
+
+    const val TABLE_NAME = "backup_media_snapshot"
+
+    private const val ID = "_id"
+
+    /**
+     * Generated media id matching that of the attachments table.
+     */
+    private const val MEDIA_ID = "media_id"
+
+    /**
+     * CDN where the data is stored
+     */
+    private const val CDN = "cdn"
+
+    /**
+     * Unique backup snapshot sync time. These are expected to increment in value
+     * where newer backups have a greater backup id value.
+     */
+    @VisibleForTesting
+    const val LAST_SYNC_TIME = "last_sync_time"
+
+    /**
+     * Pending sync time, set while a backup is in the process of being exported.
+     */
+    @VisibleForTesting
+    const val PENDING_SYNC_TIME = "pending_sync_time"
+
+    val CREATE_TABLE = """
+      CREATE TABLE $TABLE_NAME (
+        $ID INTEGER PRIMARY KEY,
+        $MEDIA_ID TEXT UNIQUE,
+        $CDN INTEGER,
+        $LAST_SYNC_TIME INTEGER DEFAULT 0,
+        $PENDING_SYNC_TIME INTEGER
+      )
+    """.trimIndent()
+
+    private const val ON_MEDIA_ID_CONFLICT = """
+      ON CONFLICT($MEDIA_ID) DO UPDATE SET
+        $PENDING_SYNC_TIME = EXCLUDED.$PENDING_SYNC_TIME,
+        $CDN = EXCLUDED.$CDN
+    """
+  }
+
+  /**
+   * Creates the temporary table if it doesn't exist, clears it, then inserts the media objects into it.
+   */
+  fun writePendingMediaObjects(mediaObjects: Sequence<ArchivedMediaObject>, pendingSyncTime: Long) {
+    mediaObjects.chunked(999)
+      .forEach { chunk ->
+        writePendingMediaObjectsChunk(chunk, pendingSyncTime)
+      }
+  }
+
+  private fun writePendingMediaObjectsChunk(chunk: List<ArchivedMediaObject>, pendingSyncTime: Long) {
+    SqlUtil.buildBulkInsert(
+      TABLE_NAME,
+      arrayOf(MEDIA_ID, CDN, PENDING_SYNC_TIME),
+      chunk.map {
+        contentValuesOf(MEDIA_ID to it.mediaId, CDN to it.cdn, PENDING_SYNC_TIME to pendingSyncTime)
+      }
+    ).forEach {
+      writableDatabase.execSQL("${it.where} $ON_MEDIA_ID_CONFLICT", it.whereArgs)
+    }
+  }
+
+  /**
+   * Copies all entries from the temporary table to the persistent table, then deletes the temporary table.
+   */
+  fun commitPendingRows() {
+    writableDatabase.execSQL("UPDATE $TABLE_NAME SET $LAST_SYNC_TIME = $PENDING_SYNC_TIME")
+  }
+
+  fun getPageOfOldMediaObjects(currentSyncTime: Long, pageSize: Int): List<ArchivedMediaObject> {
+    return readableDatabase.select(MEDIA_ID, CDN)
+      .from(TABLE_NAME)
+      .where("$LAST_SYNC_TIME < ? AND $LAST_SYNC_TIME = $PENDING_SYNC_TIME", currentSyncTime)
+      .limit(pageSize)
+      .run()
+      .readToList {
+        ArchivedMediaObject(mediaId = it.requireNonNullString(MEDIA_ID), cdn = it.requireInt(CDN))
+      }
+  }
+
+  fun deleteMediaObjects(mediaObjects: List<ArchivedMediaObject>) {
+    SqlUtil.buildCollectionQuery(MEDIA_ID, mediaObjects.map { it.mediaId }).forEach {
+      writableDatabase.delete(TABLE_NAME)
+        .where(it.where, it.whereArgs)
+        .run()
+    }
+  }
+
+  fun hasOldMediaObjects(currentSyncTime: Long): Boolean {
+    return readableDatabase.exists(TABLE_NAME).where("$LAST_SYNC_TIME > ? AND $LAST_SYNC_TIME = $PENDING_SYNC_TIME", currentSyncTime).run()
+  }
+}

app/src/main/java/org/thoughtcrime/securesms/database/SignalDatabase.kt

@@ -77,6 +77,7 @@ open class SignalDatabase(private val context: Application, databaseSecret: Data
   val inAppPaymentTable: InAppPaymentTable = InAppPaymentTable(context, this)
   val inAppPaymentSubscriberTable: InAppPaymentSubscriberTable = InAppPaymentSubscriberTable(context, this)
   val chatFoldersTable: ChatFolderTables = ChatFolderTables(context, this)
+  val backupMediaSnapshotTable: BackupMediaSnapshotTable = BackupMediaSnapshotTable(context, this)
 
   override fun onOpen(db: net.zetetic.database.sqlcipher.SQLiteDatabase) {
     db.setForeignKeyConstraintsEnabled(true)
@@ -122,6 +123,7 @@ open class SignalDatabase(private val context: Application, databaseSecret: Data
     executeStatements(db, NotificationProfileDatabase.CREATE_TABLE)
     executeStatements(db, DistributionListTables.CREATE_TABLE)
     executeStatements(db, ChatFolderTables.CREATE_TABLE)
+    db.execSQL(BackupMediaSnapshotTable.CREATE_TABLE)
 
     executeStatements(db, RecipientTable.CREATE_INDEXS)
     executeStatements(db, MessageTable.CREATE_INDEXS)
@@ -566,5 +568,10 @@ open class SignalDatabase(private val context: Application, databaseSecret: Data
     @get:JvmName("chatFolders")
     val chatFolders: ChatFolderTables
       get() = instance!!.chatFoldersTable
+
+    @get:JvmStatic
+    @get:JvmName("backupMediaSnapshots")
+    val backupMediaSnapshots: BackupMediaSnapshotTable
+      get() = instance!!.backupMediaSnapshotTable
   }
 }

app/src/main/java/org/thoughtcrime/securesms/database/helpers/SignalDatabaseMigrations.kt

@@ -113,6 +113,7 @@ import org.thoughtcrime.securesms.database.helpers.migration.V253_CreateChatFold
 import org.thoughtcrime.securesms.database.helpers.migration.V254_AddChatFolderConstraint
 import org.thoughtcrime.securesms.database.helpers.migration.V255_AddCallTableLogIndex
 import org.thoughtcrime.securesms.database.helpers.migration.V256_FixIncrementalDigestColumns
+import org.thoughtcrime.securesms.database.helpers.migration.V257_CreateBackupMediaSyncTable
 
 /**
  * Contains all of the database migrations for [SignalDatabase]. Broken into a separate file for cleanliness.
@@ -228,10 +229,11 @@ object SignalDatabaseMigrations {
     253 to V253_CreateChatFolderTables,
     254 to V254_AddChatFolderConstraint,
     255 to V255_AddCallTableLogIndex,
-    256 to V256_FixIncrementalDigestColumns
+    256 to V256_FixIncrementalDigestColumns,
+    257 to V257_CreateBackupMediaSyncTable
   )
 
-  const val DATABASE_VERSION = 256
+  const val DATABASE_VERSION = 257
 
   @JvmStatic
   fun migrate(context: Application, db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {

app/src/main/java/org/thoughtcrime/securesms/database/helpers/migration/V257_CreateBackupMediaSyncTable.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.database.helpers.migration
+
+import android.app.Application
+import net.zetetic.database.sqlcipher.SQLiteDatabase
+
+@Suppress("ClassName")
+object V257_CreateBackupMediaSyncTable : SignalDatabaseMigration {
+  override fun migrate(context: Application, db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
+    db.execSQL(
+      """
+      CREATE TABLE backup_media_snapshot (
+          _id INTEGER PRIMARY KEY,
+          media_id TEXT UNIQUE,
+          cdn INTEGER,
+          last_sync_time INTEGER DEFAULT 0,
+          pending_sync_time INTEGER
+      )
+      """.trimIndent()
+    )
+  }
+}