Merge pull request #341 from loki-project/backup-file-storage

Use Storage Access Framework for Backups

res/values/strings.xml

@@ -1866,4 +1866,6 @@
     <string name="attachment_type_voice_message">Voice Message</string>
     <string name="details">Details</string>
 
+    <string name="dialog_backup_activation_failed">Failed to activate backups. Please try again or contact support.</string>
+
 </resources>

res/xml/preferences_chats.xml

@@ -94,7 +94,7 @@
 
         <org.thoughtcrime.securesms.components.SwitchPreferenceCompat
             android:defaultValue="false"
-            android:key="pref_backup_enabled"
+            android:key="pref_backup_enabled_v2"
             android:title="@string/preferences_chats__chat_backups"
             android:summary="@string/preferences_chats__backup_chats_to_external_storage" />
 
@@ -102,7 +102,7 @@
             android:key="pref_backup_create"
             android:title="@string/preferences_chats__create_backup"
             android:persistent="false"
-            android:dependency="pref_backup_enabled"
+            android:dependency="pref_backup_enabled_v2"
             tools:summary="Last backup: 3 days ago" />
 
     </PreferenceCategory>

src/org/thoughtcrime/securesms/RegistrationActivity.java

@@ -57,7 +57,7 @@ import org.thoughtcrime.securesms.permissions.Permissions;
 import org.thoughtcrime.securesms.push.AccountManagerFactory;
 import org.thoughtcrime.securesms.registration.CaptchaActivity;
 import org.thoughtcrime.securesms.service.RotateSignedPreKeyListener;
-import org.thoughtcrime.securesms.util.BackupUtil;
+import org.thoughtcrime.securesms.util.BackupUtilOld;
 import org.thoughtcrime.securesms.util.DateUtils;
 import org.thoughtcrime.securesms.util.Dialogs;
 import org.thoughtcrime.securesms.util.ServiceUtil;
@@ -76,7 +76,6 @@ import org.whispersystems.signalservice.api.util.PhoneNumberFormatter;
 import org.whispersystems.signalservice.internal.push.LockedException;
 
 import java.io.IOException;
-import java.lang.ref.WeakReference;
 import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
@@ -275,11 +274,11 @@ public class RegistrationActivity extends BaseActionBarActivity implements Verif
 
     if (getIntent().getBooleanExtra(RE_REGISTRATION_EXTRA, false)) return;
 
-    new AsyncTask<Void, Void, BackupUtil.BackupInfo>() {
+    new AsyncTask<Void, Void, BackupUtilOld.BackupInfo>() {
       @Override
-      protected @Nullable BackupUtil.BackupInfo doInBackground(Void... voids) {
+      protected @Nullable BackupUtilOld.BackupInfo doInBackground(Void... voids) {
         try {
-          return BackupUtil.getLatestBackup(RegistrationActivity.this);
+          return BackupUtilOld.getLatestBackup(RegistrationActivity.this);
         } catch (NoExternalStorageException e) {
           Log.w(TAG, e);
           return null;
@@ -287,7 +286,7 @@ public class RegistrationActivity extends BaseActionBarActivity implements Verif
       }
 
       @Override
-      protected void onPostExecute(@Nullable BackupUtil.BackupInfo backup) {
+      protected void onPostExecute(@Nullable BackupUtilOld.BackupInfo backup) {
         if (backup != null) displayRestoreView(backup);
       }
     }.execute();
@@ -304,7 +303,7 @@ public class RegistrationActivity extends BaseActionBarActivity implements Verif
   }
 
   @SuppressLint("StaticFieldLeak")
-  private void handleRestore(BackupUtil.BackupInfo backup) {
+  private void handleRestore(BackupUtilOld.BackupInfo backup) {
     View     view   = LayoutInflater.from(this).inflate(R.layout.enter_backup_passphrase_dialog, null);
     EditText prompt = view.findViewById(R.id.restore_passphrase_input);
 
@@ -661,7 +660,7 @@ public class RegistrationActivity extends BaseActionBarActivity implements Verif
     finish();
   }
 
-  private void displayRestoreView(@NonNull BackupUtil.BackupInfo backup) {
+  private void displayRestoreView(@NonNull BackupUtilOld.BackupInfo backup) {
     title.animate().translationX(title.getWidth()).setDuration(SCENE_TRANSITION_DURATION).setListener(new AnimationCompleteListener() {
       @Override
       public void onAnimationEnd(Animator animation) {

src/org/thoughtcrime/securesms/backup/BackupDialog.java

@@ -1,28 +1,38 @@
 package org.thoughtcrime.securesms.backup;
 
-
 import android.content.ClipData;
 import android.content.ClipboardManager;
 import android.content.Context;
-import androidx.annotation.NonNull;
-import androidx.appcompat.app.AlertDialog;
 import android.widget.Button;
 import android.widget.CheckBox;
 import android.widget.TextView;
 import android.widget.Toast;
 
-import network.loki.messenger.R;
+import androidx.annotation.NonNull;
+import androidx.appcompat.app.AlertDialog;
+
 import org.thoughtcrime.securesms.components.SwitchPreferenceCompat;
-import org.thoughtcrime.securesms.service.LocalBackupListener;
+import org.thoughtcrime.securesms.logging.Log;
+import org.thoughtcrime.securesms.util.BackupDirSelector;
 import org.thoughtcrime.securesms.util.BackupUtil;
-import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.Util;
 
-public class BackupDialog {
+import java.io.IOException;
 
-  public static void showEnableBackupDialog(@NonNull Context context, @NonNull SwitchPreferenceCompat preference) {
+import network.loki.messenger.R;
-    String[]    password = BackupUtil.generateBackupPassphrase();
+
-    AlertDialog dialog   = new AlertDialog.Builder(context)
+public class BackupDialog {
+  private static final String TAG = "BackupDialog";
+
+  public static void showEnableBackupDialog(
+          @NonNull Context context,
+          @NonNull SwitchPreferenceCompat preference,
+          @NonNull BackupDirSelector backupDirSelector) {
+
+    String[] password   = BackupUtil.generateBackupPassphrase();
+    String   passwordSt = Util.join(password, " ");
+
+    AlertDialog dialog = new AlertDialog.Builder(context)
                                           .setTitle(R.string.BackupDialog_enable_local_backups)
                                           .setView(R.layout.backup_enable_dialog)
                                           .setPositiveButton(R.string.BackupDialog_enable_backups, null)
@@ -34,12 +44,21 @@ public class BackupDialog {
       button.setOnClickListener(v -> {
         CheckBox confirmationCheckBox = dialog.findViewById(R.id.confirmation_check);
         if (confirmationCheckBox.isChecked()) {
-          BackupPassphrase.set(context, Util.join(password, " "));
+          backupDirSelector.selectBackupDir(true, uri -> {
-          TextSecurePreferences.setBackupEnabled(context, true);
+            try {
-          LocalBackupListener.schedule(context);
+              BackupUtil.enableBackups(context, passwordSt);
+            } catch (IOException e) {
+              Log.e(TAG, "Failed to activate backups.", e);
+              Toast.makeText(context,
+                      context.getString(R.string.dialog_backup_activation_failed),
+                      Toast.LENGTH_LONG)
+                      .show();
+              return;
+            }
 
-          preference.setChecked(true);
+            preference.setChecked(true);
-          created.dismiss();
+            created.dismiss();
+          });
         } else {
           Toast.makeText(context, R.string.BackupDialog_please_acknowledge_your_understanding_by_marking_the_confirmation_check_box, Toast.LENGTH_LONG).show();
         }
@@ -62,7 +81,7 @@ public class BackupDialog {
     textView.setOnClickListener(v -> checkBox.toggle());
 
     dialog.findViewById(R.id.number_table).setOnClickListener(v -> {
-      ((ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE)).setPrimaryClip(ClipData.newPlainText("text", Util.join(password, " ")));
+      ((ClipboardManager)context.getSystemService(Context.CLIPBOARD_SERVICE)).setPrimaryClip(ClipData.newPlainText("text", passwordSt));
       Toast.makeText(context, R.string.BackupDialog_copied_to_clipboard, Toast.LENGTH_LONG).show();
     });
 
@@ -75,9 +94,7 @@ public class BackupDialog {
                    .setMessage(R.string.BackupDialog_disable_and_delete_all_local_backups)
                    .setNegativeButton(android.R.string.cancel, null)
                    .setPositiveButton(R.string.BackupDialog_delete_backups_statement, (dialog, which) -> {
-                     BackupPassphrase.set(context, null);
+                     BackupUtil.disableBackups(context, true);
-                     TextSecurePreferences.setBackupEnabled(context, false);
-                     BackupUtil.deleteAllBackups(context);
                      preference.setChecked(false);
                    })
                    .create()

src/org/thoughtcrime/securesms/backup/BackupPassphrase.java

@@ -16,7 +16,7 @@ public class BackupPassphrase {
 
   private static final String TAG = BackupPassphrase.class.getSimpleName();
 
-  public static String get(@NonNull Context context) {
+  public static @Nullable String get(@NonNull Context context) {
     String passphrase          = TextSecurePreferences.getBackupPassphrase(context);
     String encryptedPassphrase = TextSecurePreferences.getEncryptedBackupPassphrase(context);
 

src/org/thoughtcrime/securesms/backup/FullBackupExporter.java

@@ -1,11 +1,12 @@
 package org.thoughtcrime.securesms.backup;
 
-
 import android.content.Context;
 import android.database.Cursor;
+import android.net.Uri;
+import android.text.TextUtils;
+
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import android.text.TextUtils;
 
 import com.annimon.stream.function.Consumer;
 import com.annimon.stream.function.Predicate;
@@ -36,9 +37,10 @@ import org.thoughtcrime.securesms.util.Util;
 import org.whispersystems.libsignal.kdf.HKDFv3;
 import org.whispersystems.libsignal.util.ByteUtil;
 
+import java.io.Closeable;
 import java.io.File;
 import java.io.FileInputStream;
-import java.io.FileOutputStream;
+import java.io.Flushable;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -64,49 +66,54 @@ public class FullBackupExporter extends FullBackupBase {
   public static void export(@NonNull Context context,
                             @NonNull AttachmentSecret attachmentSecret,
                             @NonNull SQLiteDatabase input,
-                            @NonNull File output,
+                            @NonNull Uri fileUri,
                             @NonNull String passphrase)
       throws IOException
   {
-    BackupFrameOutputStream outputStream = new BackupFrameOutputStream(output, passphrase);
+    OutputStream baseOutputStream = context.getContentResolver().openOutputStream(fileUri);
-    outputStream.writeDatabaseVersion(input.getVersion());
+    if (baseOutputStream == null) {
+      throw new IOException("Cannot open an output stream for the file URI: " + fileUri.toString());
+    }
 
-    List<String> tables = exportSchema(input, outputStream);
+    try (BackupFrameOutputStream outputStream = new BackupFrameOutputStream(baseOutputStream, passphrase)) {
-    int          count  = 0;
+      outputStream.writeDatabaseVersion(input.getVersion());
 
-    for (String table : tables) {
+      List<String> tables = exportSchema(input, outputStream);
-      if (table.equals(SmsDatabase.TABLE_NAME) || table.equals(MmsDatabase.TABLE_NAME)) {
+      int          count  = 0;
-        count = exportTable(table, input, outputStream, cursor -> cursor.getInt(cursor.getColumnIndexOrThrow(MmsSmsColumns.EXPIRES_IN)) <= 0, null, count);
+
-      } else if (table.equals(GroupReceiptDatabase.TABLE_NAME)) {
+      for (String table : tables) {
-        count = exportTable(table, input, outputStream, cursor -> isForNonExpiringMessage(input, cursor.getLong(cursor.getColumnIndexOrThrow(GroupReceiptDatabase.MMS_ID))), null, count);
+        if (table.equals(SmsDatabase.TABLE_NAME) || table.equals(MmsDatabase.TABLE_NAME)) {
-      } else if (table.equals(AttachmentDatabase.TABLE_NAME)) {
+          count = exportTable(table, input, outputStream, cursor -> cursor.getInt(cursor.getColumnIndexOrThrow(MmsSmsColumns.EXPIRES_IN)) <= 0, null, count);
-        count = exportTable(table, input, outputStream, cursor -> isForNonExpiringMessage(input, cursor.getLong(cursor.getColumnIndexOrThrow(AttachmentDatabase.MMS_ID))), cursor -> exportAttachment(attachmentSecret, cursor, outputStream), count);
+        } else if (table.equals(GroupReceiptDatabase.TABLE_NAME)) {
-      } else if (table.equals(StickerDatabase.TABLE_NAME)) {
+          count = exportTable(table, input, outputStream, cursor -> isForNonExpiringMessage(input, cursor.getLong(cursor.getColumnIndexOrThrow(GroupReceiptDatabase.MMS_ID))), null, count);
-        count = exportTable(table, input, outputStream, cursor -> true, cursor -> exportSticker(attachmentSecret, cursor, outputStream), count);
+        } else if (table.equals(AttachmentDatabase.TABLE_NAME)) {
-      } else if (!table.equals(SignedPreKeyDatabase.TABLE_NAME)       &&
+          count = exportTable(table, input, outputStream, cursor -> isForNonExpiringMessage(input, cursor.getLong(cursor.getColumnIndexOrThrow(AttachmentDatabase.MMS_ID))), cursor -> exportAttachment(attachmentSecret, cursor, outputStream), count);
-                 !table.equals(OneTimePreKeyDatabase.TABLE_NAME)      &&
+        } else if (table.equals(StickerDatabase.TABLE_NAME)) {
-                 !table.equals(SessionDatabase.TABLE_NAME)            &&
+          count = exportTable(table, input, outputStream, cursor -> true, cursor -> exportSticker(attachmentSecret, cursor, outputStream), count);
-                 !table.startsWith(SearchDatabase.SMS_FTS_TABLE_NAME) &&
+        } else if (!table.equals(SignedPreKeyDatabase.TABLE_NAME)       &&
-                 !table.startsWith(SearchDatabase.MMS_FTS_TABLE_NAME) &&
+                   !table.equals(OneTimePreKeyDatabase.TABLE_NAME)      &&
-                 !table.startsWith("sqlite_"))
+                   !table.equals(SessionDatabase.TABLE_NAME)            &&
-      {
+                   !table.startsWith(SearchDatabase.SMS_FTS_TABLE_NAME) &&
-        count = exportTable(table, input, outputStream, null, null, count);
+                   !table.startsWith(SearchDatabase.MMS_FTS_TABLE_NAME) &&
+                   !table.startsWith("sqlite_"))
+        {
+          count = exportTable(table, input, outputStream, null, null, count);
+        }
       }
-    }
 
-    for (BackupProtos.SharedPreference preference : IdentityKeyUtil.getBackupRecord(context)) {
+      for (BackupProtos.SharedPreference preference : IdentityKeyUtil.getBackupRecord(context)) {
-      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count));
+        EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count));
-      outputStream.write(preference);
+        outputStream.write(preference);
-    }
+      }
 
-    for (File avatar : AvatarHelper.getAvatarFiles(context)) {
+      for (File avatar : AvatarHelper.getAvatarFiles(context)) {
-      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count));
+        EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, ++count));
-      outputStream.write(avatar.getName(), new FileInputStream(avatar), avatar.length());
+        outputStream.write(avatar.getName(), new FileInputStream(avatar), avatar.length());
-    }
+      }
 
-    outputStream.writeEnd();
+      outputStream.writeEnd();
-    outputStream.close();
+      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.FINISHED, ++count));
-    EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.FINISHED, ++count));
+    }
   }
 
   private static List<String> exportSchema(@NonNull SQLiteDatabase input, @NonNull BackupFrameOutputStream outputStream)
@@ -228,8 +235,9 @@ public class FullBackupExporter extends FullBackupBase {
       byte[] random = cursor.getBlob(cursor.getColumnIndexOrThrow(StickerDatabase.FILE_RANDOM));
 
       if (!TextUtils.isEmpty(data) && size > 0) {
-        InputStream inputStream = ModernDecryptingPartInputStream.createFor(attachmentSecret, random, new File(data), 0);
+        try (InputStream inputStream = ModernDecryptingPartInputStream.createFor(attachmentSecret, random, new File(data), 0)) {
-        outputStream.writeSticker(rowId, inputStream, size);
+          outputStream.writeSticker(rowId, inputStream, size);
+        }
       }
     } catch (IOException e) {
       Log.w(TAG, e);
@@ -268,7 +276,7 @@ public class FullBackupExporter extends FullBackupBase {
   }
 
 
-  private static class BackupFrameOutputStream extends BackupStream {
+  private static class BackupFrameOutputStream extends BackupStream implements Closeable, Flushable {
 
     private final OutputStream outputStream;
     private final Cipher       cipher;
@@ -280,7 +288,7 @@ public class FullBackupExporter extends FullBackupBase {
     private byte[] iv;
     private int    counter;
 
-    private BackupFrameOutputStream(@NonNull File output, @NonNull String passphrase) throws IOException {
+    private BackupFrameOutputStream(@NonNull OutputStream outputStream, @NonNull String passphrase) throws IOException {
       try {
         byte[]   salt    = Util.getSecretBytes(32);
         byte[]   key     = getBackupKey(passphrase, salt);
@@ -292,7 +300,7 @@ public class FullBackupExporter extends FullBackupBase {
 
         this.cipher       = Cipher.getInstance("AES/CTR/NoPadding");
         this.mac          = Mac.getInstance("HmacSHA256");
-        this.outputStream = new FileOutputStream(output);
+        this.outputStream = outputStream;
         this.iv           = Util.getSecretBytes(16);
         this.counter      = Conversions.byteArrayToInt(iv);
 
@@ -408,7 +416,12 @@ public class FullBackupExporter extends FullBackupBase {
       }
     }
 
+    @Override
+    public void flush() throws IOException {
+      outputStream.flush();
+    }
 
+    @Override
     public void close() throws IOException {
       outputStream.close();
     }

src/org/thoughtcrime/securesms/database/DatabaseFactory.java

@@ -32,6 +32,7 @@ import org.thoughtcrime.securesms.database.helpers.ClassicOpenHelper;
 import org.thoughtcrime.securesms.database.helpers.SQLCipherMigrationHelper;
 import org.thoughtcrime.securesms.database.helpers.SQLCipherOpenHelper;
 import org.thoughtcrime.securesms.loki.database.LokiAPIDatabase;
+import org.thoughtcrime.securesms.loki.database.LokiBackupFilesDatabase;
 import org.thoughtcrime.securesms.loki.database.LokiMessageDatabase;
 import org.thoughtcrime.securesms.loki.database.LokiPreKeyBundleDatabase;
 import org.thoughtcrime.securesms.loki.database.LokiPreKeyRecordDatabase;
@@ -74,6 +75,7 @@ public class DatabaseFactory {
   private final LokiMessageDatabase lokiMessageDatabase;
   private final LokiThreadDatabase lokiThreadDatabase;
   private final LokiUserDatabase lokiUserDatabase;
+  private final LokiBackupFilesDatabase lokiBackupFilesDatabase;
   private final SharedSenderKeysDatabase sskDatabase;
 
   public static DatabaseFactory getInstance(Context context) {
@@ -190,6 +192,10 @@ public class DatabaseFactory {
     return getInstance(context).lokiUserDatabase;
   }
 
+  public static LokiBackupFilesDatabase getLokiBackupFilesDatabase(Context context) {
+    return getInstance(context).lokiBackupFilesDatabase;
+  }
+
   public static SharedSenderKeysDatabase getSSKDatabase(Context context) {
     return getInstance(context).sskDatabase;
   }
@@ -232,6 +238,7 @@ public class DatabaseFactory {
     this.lokiMessageDatabase       = new LokiMessageDatabase(context, databaseHelper);
     this.lokiThreadDatabase        = new LokiThreadDatabase(context, databaseHelper);
     this.lokiUserDatabase          = new LokiUserDatabase(context, databaseHelper);
+    this.lokiBackupFilesDatabase   = new LokiBackupFilesDatabase(context, databaseHelper);
     this.sskDatabase               = new SharedSenderKeysDatabase(context, databaseHelper);
   }
 

src/org/thoughtcrime/securesms/database/helpers/SQLCipherOpenHelper.java

@@ -24,6 +24,7 @@ import org.thoughtcrime.securesms.database.GroupDatabase;
 import org.thoughtcrime.securesms.database.GroupReceiptDatabase;
 import org.thoughtcrime.securesms.database.IdentityDatabase;
 import org.thoughtcrime.securesms.database.JobDatabase;
+import org.thoughtcrime.securesms.loki.database.LokiBackupFilesDatabase;
 import org.thoughtcrime.securesms.database.MmsDatabase;
 import org.thoughtcrime.securesms.database.OneTimePreKeyDatabase;
 import org.thoughtcrime.securesms.database.PushDatabase;
@@ -89,8 +90,9 @@ public class SQLCipherOpenHelper extends SQLiteOpenHelper {
   private static final int lokiV11                          = 32;
   private static final int lokiV12                          = 33;
   private static final int lokiV13                          = 34;
+  private static final int lokiV14_BACKUP_FILES             = 35;
 
-  private static final int    DATABASE_VERSION = lokiV13; // Loki - onUpgrade(...) must be updated to use Loki version numbers if Signal makes any database changes
+  private static final int    DATABASE_VERSION = lokiV14_BACKUP_FILES; // Loki - onUpgrade(...) must be updated to use Loki version numbers if Signal makes any database changes
   private static final String DATABASE_NAME    = "signal.db";
 
   private final Context        context;
@@ -161,6 +163,7 @@ public class SQLCipherOpenHelper extends SQLiteOpenHelper {
     db.execSQL(LokiThreadDatabase.getCreatePublicChatTableCommand());
     db.execSQL(LokiUserDatabase.getCreateDisplayNameTableCommand());
     db.execSQL(LokiUserDatabase.getCreateServerDisplayNameTableCommand());
+    db.execSQL(LokiBackupFilesDatabase.getCreateTableCommand());
     db.execSQL(SharedSenderKeysDatabase.getCreateClosedGroupRatchetTableCommand());
     db.execSQL(SharedSenderKeysDatabase.getCreateClosedGroupPrivateKeyTableCommand());
 
@@ -619,6 +622,10 @@ public class SQLCipherOpenHelper extends SQLiteOpenHelper {
         db.execSQL(LokiAPIDatabase.getCreateReceivedMessageHashValuesTable3Command());
       }
 
+      if (oldVersion < lokiV14_BACKUP_FILES) {
+        db.execSQL(LokiBackupFilesDatabase.getCreateTableCommand());
+      }
+
       db.setTransactionSuccessful();
     } finally {
       db.endTransaction();

src/org/thoughtcrime/securesms/jobs/LocalBackupJob.java

@@ -1,32 +1,22 @@
 package org.thoughtcrime.securesms.jobs;
 
 
-import android.Manifest;
 import androidx.annotation.NonNull;
 
-import org.thoughtcrime.securesms.backup.BackupPassphrase;
-import org.thoughtcrime.securesms.backup.FullBackupExporter;
-import org.thoughtcrime.securesms.crypto.AttachmentSecretProvider;
-import org.thoughtcrime.securesms.database.DatabaseFactory;
 import org.thoughtcrime.securesms.database.NoExternalStorageException;
+import org.thoughtcrime.securesms.loki.database.BackupFileRecord;
 import org.thoughtcrime.securesms.jobmanager.Data;
 import org.thoughtcrime.securesms.jobmanager.Job;
 import org.thoughtcrime.securesms.logging.Log;
 import org.thoughtcrime.securesms.notifications.NotificationChannels;
-import org.thoughtcrime.securesms.permissions.Permissions;
 import org.thoughtcrime.securesms.service.GenericForegroundService;
 import org.thoughtcrime.securesms.util.BackupUtil;
-import org.thoughtcrime.securesms.util.ExternalStorageUtil;
 
-import java.io.File;
 import java.io.IOException;
-import java.text.SimpleDateFormat;
+import java.util.Collections;
-import java.util.Date;
-import java.util.Locale;
 
 import network.loki.messenger.R;
 
-//TODO AC: Needs to be refactored to use Storage Access Framework or Media Store API.
 public class LocalBackupJob extends BaseJob {
 
   public static final String KEY = "LocalBackupJob";
@@ -59,10 +49,6 @@ public class LocalBackupJob extends BaseJob {
   public void onRun() throws NoExternalStorageException, IOException {
     Log.i(TAG, "Executing backup job...");
 
-    if (!Permissions.hasAll(context, Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
-      throw new IOException("No external storage permission!");
-    }
-
     GenericForegroundService.startForegroundTask(context,
                                                  context.getString(R.string.LocalBackupJob_creating_backup),
                                                  NotificationChannels.BACKUPS,
@@ -71,34 +57,9 @@ public class LocalBackupJob extends BaseJob {
     // TODO: Maybe create a new backup icon like ic_signal_backup?
 
     try {
-      String backupPassword  = BackupPassphrase.get(context);
+      BackupFileRecord record = BackupUtil.createBackupFile(context);
-      File   backupDirectory = ExternalStorageUtil.getBackupDir(context);
+      BackupUtil.deleteAllBackupFiles(context, Collections.singletonList(record));
-      String timestamp       = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss", Locale.US).format(new Date());
-      String fileName        = String.format("session-%s.backup", timestamp);
-      File   backupFile      = new File(backupDirectory, fileName);
 
-      if (backupFile.exists()) {
-        throw new IOException("Backup file already exists?");
-      }
-
-      if (backupPassword == null) {
-        throw new IOException("Backup password is null");
-      }
-
-      File tempFile = File.createTempFile("backup", "tmp", ExternalStorageUtil.getCacheDir(context));
-
-      FullBackupExporter.export(context,
-                                AttachmentSecretProvider.getInstance(context).getOrCreateAttachmentSecret(),
-                                DatabaseFactory.getBackupDatabase(context),
-                                tempFile,
-                                backupPassword);
-
-      if (!tempFile.renameTo(backupFile)) {
-        tempFile.delete();
-        throw new IOException("Renaming temporary backup file failed!");
-      }
-
-      BackupUtil.deleteOldBackups(context);
     } finally {
       GenericForegroundService.stopForegroundTask(context);
     }

src/org/thoughtcrime/securesms/loki/database/BackupFileRecord.kt

@@ -0,0 +1,12 @@
+package org.thoughtcrime.securesms.loki.database
+
+import android.net.Uri
+import java.util.*
+
+/**
+ * Represents a record for a backup file in the [org.thoughtcrime.securesms.database.LokiBackupFilesDatabase].
+ */
+data class BackupFileRecord(val id: Long, val uri: Uri, val fileSize: Long, val timestamp: Date) {
+
+    constructor(uri: Uri, fileSize: Long, timestamp: Date) : this(-1, uri, fileSize, timestamp)
+}

src/org/thoughtcrime/securesms/loki/database/LokiBackupFilesDatabase.kt

@@ -0,0 +1,118 @@
+package org.thoughtcrime.securesms.loki.database
+
+import android.content.ContentValues
+import android.content.Context
+import android.database.Cursor
+import android.net.Uri
+import org.thoughtcrime.securesms.database.Database
+import org.thoughtcrime.securesms.database.helpers.SQLCipherOpenHelper
+import java.lang.IllegalArgumentException
+import java.util.*
+import kotlin.collections.ArrayList
+
+/**
+ * Keeps track of the backup files saved by the app.
+ * Uses [BackupFileRecord] as an entry data projection.
+ */
+class LokiBackupFilesDatabase(context: Context, databaseHelper: SQLCipherOpenHelper)
+    : Database(context, databaseHelper) {
+
+    companion object {
+        private const val TABLE_NAME = "backup_files"
+        private const val COLUMN_ID = "_id"
+        private const val COLUMN_URI = "uri"
+        private const val COLUMN_FILE_SIZE = "file_size"
+        private const val COLUMN_TIMESTAMP = "timestamp"
+
+        private val allColumns = arrayOf(COLUMN_ID, COLUMN_URI, COLUMN_FILE_SIZE, COLUMN_TIMESTAMP)
+
+        @JvmStatic
+        val createTableCommand = """
+                    CREATE TABLE $TABLE_NAME (
+                    $COLUMN_ID INTEGER PRIMARY KEY, 
+                    $COLUMN_URI TEXT NOT NULL, 
+                    $COLUMN_FILE_SIZE INTEGER NOT NULL, 
+                    $COLUMN_TIMESTAMP INTEGER NOT NULL
+                    );
+                """.trimIndent()
+
+        private fun mapCursorToRecord(cursor: Cursor): BackupFileRecord {
+            val id = cursor.getLong(cursor.getColumnIndexOrThrow(COLUMN_ID))
+            val uriRaw = cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_URI))
+            val fileSize = cursor.getLong(cursor.getColumnIndexOrThrow(COLUMN_FILE_SIZE))
+            val timestampRaw = cursor.getLong(cursor.getColumnIndexOrThrow(COLUMN_TIMESTAMP))
+            return BackupFileRecord(id, Uri.parse(uriRaw), fileSize, Date(timestampRaw))
+        }
+
+        private fun mapRecordToValues(record: BackupFileRecord): ContentValues {
+            val contentValues = ContentValues()
+            if (record.id >= 0) { contentValues.put(COLUMN_ID, record.id) }
+            contentValues.put(COLUMN_URI, record.uri.toString())
+            contentValues.put(COLUMN_FILE_SIZE, record.fileSize)
+            contentValues.put(COLUMN_TIMESTAMP, record.timestamp.time)
+            return contentValues
+        }
+    }
+
+    fun getBackupFiles(): List<BackupFileRecord> {
+        databaseHelper.readableDatabase.query(TABLE_NAME, allColumns, null, null, null, null, null).use {
+            val records = ArrayList<BackupFileRecord>()
+            while (it != null && it.moveToNext()) {
+                val record = mapCursorToRecord(it)
+                records.add(record)
+            }
+            return records
+        }
+    }
+
+    fun insertBackupFile(record: BackupFileRecord): BackupFileRecord {
+        val contentValues = mapRecordToValues(record)
+        val id = databaseHelper.writableDatabase.insertOrThrow(TABLE_NAME, null, contentValues)
+        return BackupFileRecord(id, record.uri, record.fileSize, record.timestamp)
+    }
+
+    fun getLastBackupFileTime(): Date? {
+        // SELECT $COLUMN_TIMESTAMP FROM $TABLE_NAME ORDER BY $COLUMN_TIMESTAMP DESC LIMIT 1
+        databaseHelper.readableDatabase.query(
+                TABLE_NAME,
+                arrayOf(COLUMN_TIMESTAMP),
+                null, null, null, null,
+                "$COLUMN_TIMESTAMP DESC",
+                "1"
+        ).use {
+            if (it !== null && it.moveToFirst()) {
+                return Date(it.getLong(0))
+            } else {
+                return null
+            }
+        }
+    }
+
+    fun getLastBackupFile(): BackupFileRecord? {
+        // SELECT * FROM $TABLE_NAME ORDER BY $COLUMN_TIMESTAMP DESC LIMIT 1
+        databaseHelper.readableDatabase.query(
+                TABLE_NAME,
+                allColumns,
+                null, null, null, null,
+                "$COLUMN_TIMESTAMP DESC",
+                "1"
+        ).use {
+            if (it != null && it.moveToFirst()) {
+                return mapCursorToRecord(it)
+            } else {
+                return null
+            }
+        }
+    }
+
+    fun deleteBackupFile(record: BackupFileRecord): Boolean {
+        return deleteBackupFile(record.id)
+    }
+
+    fun deleteBackupFile(id: Long): Boolean {
+        if (id < 0) {
+            throw IllegalArgumentException("ID must be zero or a positive number.")
+        }
+        return databaseHelper.writableDatabase.delete(TABLE_NAME, "$COLUMN_ID = $id", null) > 0
+    }
+}

src/org/thoughtcrime/securesms/preferences/ChatsPreferenceFragment.java

@@ -1,16 +1,17 @@
 package org.thoughtcrime.securesms.preferences;
 
-import android.Manifest;
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.content.DialogInterface;
+import android.content.Intent;
 import android.os.Bundle;
+import android.text.TextUtils;
+
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AlertDialog;
 import androidx.preference.EditTextPreference;
 import androidx.preference.Preference;
-import android.text.TextUtils;
 
 import org.greenrobot.eventbus.EventBus;
 import org.greenrobot.eventbus.Subscribe;
@@ -23,6 +24,7 @@ import org.thoughtcrime.securesms.jobs.LocalBackupJob;
 import org.thoughtcrime.securesms.logging.Log;
 import org.thoughtcrime.securesms.permissions.Permissions;
 import org.thoughtcrime.securesms.preferences.widgets.ProgressPreference;
+import org.thoughtcrime.securesms.util.BackupDirSelector;
 import org.thoughtcrime.securesms.util.BackupUtil;
 import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.Trimmer;
@@ -37,6 +39,8 @@ import network.loki.messenger.R;
 public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
   private static final String TAG = ChatsPreferenceFragment.class.getSimpleName();
 
+  private BackupDirSelector backupDirSelector;
+
   @Override
   public void onCreate(Bundle paramBundle) {
     super.onCreate(paramBundle);
@@ -64,6 +68,8 @@ public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
 
 //    initializeListSummary((ListPreference) findPreference(TextSecurePreferences.MESSAGE_BODY_TEXT_SIZE_PREF));
 
+    backupDirSelector = new BackupDirSelector(this);
+
     EventBus.getDefault().register(this);
   }
 
@@ -90,6 +96,12 @@ public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
     Permissions.onRequestPermissionsResult(this, requestCode, permissions, grantResults);
   }
 
+  @Override
+  public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
+    super.onActivityResult(requestCode, resultCode, data);
+    backupDirSelector.onActivityResult(requestCode, resultCode, data);
+  }
+
   @Subscribe(threadMode = ThreadMode.MAIN)
   public void onEvent(BackupEvent event) {
     ProgressPreference preference = (ProgressPreference)findPreference(TextSecurePreferences.BACKUP_NOW);
@@ -107,7 +119,7 @@ public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
 
   private void setBackupSummary() {
     findPreference(TextSecurePreferences.BACKUP_NOW)
-        .setSummary(String.format(getString(R.string.ChatsPreferenceFragment_last_backup_s), BackupUtil.getLastBackupTime(getContext(), Locale.US)));
+            .setSummary(String.format(getString(R.string.ChatsPreferenceFragment_last_backup_s), BackupUtil.getLastBackupTimeString(getContext(), Locale.getDefault())));
   }
 
   private void setMediaDownloadSummaries() {
@@ -137,17 +149,11 @@ public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
   private class BackupClickListener implements Preference.OnPreferenceClickListener {
     @Override
     public boolean onPreferenceClick(Preference preference) {
-      Permissions.with(ChatsPreferenceFragment.this)
+      if (!((SwitchPreferenceCompat) preference).isChecked()) {
-                 .request(Manifest.permission.WRITE_EXTERNAL_STORAGE)
+        BackupDialog.showEnableBackupDialog(getActivity(), (SwitchPreferenceCompat)preference, backupDirSelector);
-                 .onAllGranted(() -> {
+      } else {
-                   if (!((SwitchPreferenceCompat)preference).isChecked()) {
+        BackupDialog.showDisableBackupDialog(getActivity(), (SwitchPreferenceCompat)preference);
-                     BackupDialog.showEnableBackupDialog(getActivity(), (SwitchPreferenceCompat)preference);
+      }
-                   } else {
-                     BackupDialog.showDisableBackupDialog(getActivity(), (SwitchPreferenceCompat)preference);
-                   }
-                 })
-                 .withPermanentDenialDialog(getString(R.string.ChatsPreferenceFragment_signal_requires_external_storage_permission_in_order_to_create_backups))
-                 .execute();
 
       return true;
     }
@@ -157,17 +163,10 @@ public class ChatsPreferenceFragment extends ListSummaryPreferenceFragment {
     @SuppressLint("StaticFieldLeak")
     @Override
     public boolean onPreferenceClick(Preference preference) {
-      Permissions.with(ChatsPreferenceFragment.this)
+      Log.i(TAG, "Queuing backup...");
-                 .request(Manifest.permission.WRITE_EXTERNAL_STORAGE)
+      ApplicationContext.getInstance(getContext())
-                 .onAllGranted(() -> {
+              .getJobManager()
-                   Log.i(TAG, "Queing backup...");
+              .add(new LocalBackupJob());
-                   ApplicationContext.getInstance(getContext())
-                                     .getJobManager()
-                                     .add(new LocalBackupJob());
-                 })
-                 .withPermanentDenialDialog(getString(R.string.ChatsPreferenceFragment_signal_requires_external_storage_permission_in_order_to_create_backups))
-                 .execute();
-
       return true;
     }
   }

src/org/thoughtcrime/securesms/profiles/AvatarHelper.java

@@ -52,9 +52,9 @@ public class AvatarHelper {
     if (data == null)  {
       delete(context, address);
     } else {
-      FileOutputStream out = new FileOutputStream(getAvatarFile(context, address));
+      try (FileOutputStream out = new FileOutputStream(getAvatarFile(context, address))) {
-      out.write(data);
+        out.write(data);
-      out.close();
+      }
     }
   }
 

src/org/thoughtcrime/securesms/util/BackupUtil.java

@@ -1,161 +0,0 @@
-package org.thoughtcrime.securesms.util;
-
-
-import android.content.Context;
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-import org.thoughtcrime.securesms.logging.Log;
-
-import network.loki.messenger.R;
-import org.thoughtcrime.securesms.database.NoExternalStorageException;
-import org.whispersystems.libsignal.util.ByteUtil;
-
-import java.io.File;
-import java.security.SecureRandom;
-import java.util.Arrays;
-import java.util.Calendar;
-import java.util.Locale;
-
-//TODO AC: Needs to be refactored to use Storage Access Framework or Media Store API.
-public class BackupUtil {
-
-  private static final String TAG = BackupUtil.class.getSimpleName();
-
-  public static @NonNull String getLastBackupTime(@NonNull Context context, @NonNull Locale locale) {
-    try {
-      BackupInfo backup = getLatestBackup(context);
-
-      if (backup == null) return context.getString(R.string.BackupUtil_never);
-      else                return DateUtils.getExtendedRelativeTimeSpanString(context, locale, backup.getTimestamp());
-    } catch (NoExternalStorageException e) {
-      Log.w(TAG, e);
-      return context.getString(R.string.BackupUtil_unknown);
-    }
-  }
-
-  public static @Nullable BackupInfo getLatestBackup(Context context) throws NoExternalStorageException {
-    File       backupDirectory = ExternalStorageUtil.getBackupDir(context);
-    File[]     backups         = backupDirectory.listFiles();
-    BackupInfo latestBackup    = null;
-
-    for (File backup : backups) {
-      long backupTimestamp = getBackupTimestamp(backup);
-
-      if (latestBackup == null || (backupTimestamp != -1 && backupTimestamp > latestBackup.getTimestamp())) {
-        latestBackup = new BackupInfo(backupTimestamp, backup.length(), backup);
-      }
-    }
-
-    return latestBackup;
-  }
-
-  @SuppressWarnings("ResultOfMethodCallIgnored")
-  public static void deleteAllBackups(Context context) {
-    try {
-      File   backupDirectory = ExternalStorageUtil.getBackupDir(context);
-      File[] backups         = backupDirectory.listFiles();
-
-      for (File backup : backups) {
-        if (backup.isFile()) backup.delete();
-      }
-    } catch (NoExternalStorageException e) {
-      Log.w(TAG, e);
-    }
-  }
-
-  public static void deleteOldBackups(Context context) {
-    try {
-      File   backupDirectory = ExternalStorageUtil.getBackupDir(context);
-      File[] backups         = backupDirectory.listFiles();
-
-      if (backups != null && backups.length > 2) {
-        Arrays.sort(backups, (left, right) -> {
-          long leftTimestamp  = getBackupTimestamp(left);
-          long rightTimestamp = getBackupTimestamp(right);
-
-          if      (leftTimestamp == -1 && rightTimestamp == -1) return 0;
-          else if (leftTimestamp == -1)                         return 1;
-          else if (rightTimestamp == -1)                        return -1;
-
-          return (int)(rightTimestamp - leftTimestamp);
-        });
-
-        for (int i=2;i<backups.length;i++) {
-          Log.i(TAG, "Deleting: " + backups[i].getAbsolutePath());
-
-          if (!backups[i].delete()) {
-            Log.w(TAG, "Delete failed: " + backups[i].getAbsolutePath());
-          }
-        }
-      }
-    } catch (NoExternalStorageException e) {
-      Log.w(TAG, e);
-    }
-  }
-
-  public static @NonNull String[] generateBackupPassphrase() {
-    String[] result = new String[6];
-    byte[]   random = new byte[30];
-
-    new SecureRandom().nextBytes(random);
-
-    for (int i=0;i<30;i+=5) {
-      result[i/5] = String.format("%05d", ByteUtil.byteArray5ToLong(random, i) % 100000);
-    }
-
-    return result;
-  }
-
-  private static long getBackupTimestamp(File backup) {
-    String   name  = backup.getName();
-    String[] prefixSuffix = name.split("[.]");
-
-    if (prefixSuffix.length == 2) {
-      String[] parts = prefixSuffix[0].split("\\-");
-
-      if (parts.length == 7) {
-        try {
-          Calendar calendar = Calendar.getInstance();
-          calendar.set(Calendar.YEAR, Integer.parseInt(parts[1]));
-          calendar.set(Calendar.MONTH, Integer.parseInt(parts[2]) - 1);
-          calendar.set(Calendar.DAY_OF_MONTH, Integer.parseInt(parts[3]));
-          calendar.set(Calendar.HOUR_OF_DAY, Integer.parseInt(parts[4]));
-          calendar.set(Calendar.MINUTE, Integer.parseInt(parts[5]));
-          calendar.set(Calendar.SECOND, Integer.parseInt(parts[6]));
-          calendar.set(Calendar.MILLISECOND, 0);
-
-          return calendar.getTimeInMillis();
-        } catch (NumberFormatException e) {
-          Log.w(TAG, e);
-        }
-      }
-    }
-
-    return -1;
-  }
-
-  public static class BackupInfo {
-
-    private final long timestamp;
-    private final long size;
-    private final File file;
-
-    BackupInfo(long timestamp, long size, File file) {
-      this.timestamp = timestamp;
-      this.size      = size;
-      this.file      = file;
-    }
-
-    public long getTimestamp() {
-      return timestamp;
-    }
-
-    public long getSize() {
-      return size;
-    }
-
-    public File getFile() {
-      return file;
-    }
-  }
-}

src/org/thoughtcrime/securesms/util/BackupUtil.kt

@@ -0,0 +1,282 @@
+package org.thoughtcrime.securesms.util
+
+import android.app.Activity
+import android.content.Context
+import android.content.Intent
+import android.net.Uri
+import android.os.Build
+import android.os.Environment
+import android.provider.DocumentsContract
+import android.util.Log
+import android.widget.Toast
+import androidx.annotation.WorkerThread
+import androidx.documentfile.provider.DocumentFile
+import androidx.fragment.app.Fragment
+import network.loki.messenger.R
+import org.thoughtcrime.securesms.backup.BackupPassphrase
+import org.thoughtcrime.securesms.backup.FullBackupExporter
+import org.thoughtcrime.securesms.crypto.AttachmentSecretProvider
+import org.thoughtcrime.securesms.database.DatabaseFactory
+import org.thoughtcrime.securesms.loki.database.BackupFileRecord
+import org.thoughtcrime.securesms.service.LocalBackupListener
+import org.whispersystems.libsignal.util.ByteUtil
+import java.io.IOException
+import java.security.SecureRandom
+import java.text.SimpleDateFormat
+import java.util.*
+import kotlin.jvm.Throws
+
+object BackupUtil {
+    private const val TAG = "BackupUtil"
+
+    /**
+     * Set app-wide configuration to enable the backups and schedule them.
+     *
+     * Make sure that the backup dir is selected prior activating the backup.
+     * Use [BackupDirSelector] or [setBackupDirUri] manually.
+     */
+    @JvmStatic
+    @Throws(IOException::class)
+    fun enableBackups(context: Context, password: String) {
+        val backupDir = getBackupDirUri(context)
+        if (backupDir == null || !validateDirAccess(context, backupDir)) {
+            throw IOException("Backup dir is not set or invalid.")
+        }
+
+        BackupPassphrase.set(context, password)
+        TextSecurePreferences.setBackupEnabled(context, true)
+        LocalBackupListener.schedule(context)
+    }
+
+    /**
+     * Set app-wide configuration to disable the backups.
+     *
+     * This call resets the backup dir value.
+     * Make sure to call [setBackupDirUri] prior next call to [enableBackups].
+     *
+     * @param deleteBackupFiles if true, deletes all the previously created backup files
+     * (if the app has access to them)
+     */
+    @JvmStatic
+    fun disableBackups(context: Context, deleteBackupFiles: Boolean) {
+        BackupPassphrase.set(context, null)
+        TextSecurePreferences.setBackupEnabled(context, false)
+        if (deleteBackupFiles) {
+            deleteAllBackupFiles(context)
+        }
+        setBackupDirUri(context, null)
+    }
+
+    @JvmStatic
+    fun getLastBackupTimeString(context: Context, locale: Locale): String {
+        val timestamp = DatabaseFactory.getLokiBackupFilesDatabase(context).getLastBackupFileTime()
+        if (timestamp == null) {
+            return context.getString(R.string.BackupUtil_never)
+        }
+        return DateUtils.getExtendedRelativeTimeSpanString(context, locale, timestamp.time)
+    }
+
+    @JvmStatic
+    fun getLastBackup(context: Context): BackupFileRecord? {
+        return DatabaseFactory.getLokiBackupFilesDatabase(context).getLastBackupFile()
+    }
+
+    @JvmStatic
+    fun generateBackupPassphrase(): Array<String> {
+        val random = ByteArray(30).also { SecureRandom().nextBytes(it) }
+        return Array(6) {i ->
+            String.format("%05d", ByteUtil.byteArray5ToLong(random, i * 5) % 100000)
+        }
+    }
+
+    @JvmStatic
+    fun validateDirAccess(context: Context, dirUri: Uri): Boolean {
+        val hasWritePermission = context.contentResolver.persistedUriPermissions.any {
+            it.isWritePermission && it.uri == dirUri
+        }
+        if (!hasWritePermission) return false
+
+        val document = DocumentFile.fromTreeUri(context, dirUri)
+        if (document == null || !document.exists()) {
+            return false
+        }
+
+        return true
+    }
+
+    @JvmStatic
+    fun getBackupDirUri(context: Context): Uri? {
+        val dirUriString = TextSecurePreferences.getBackupSaveDir(context) ?: return null
+        return Uri.parse(dirUriString)
+    }
+
+    @JvmStatic
+    fun setBackupDirUri(context: Context, uriString: String?) {
+        TextSecurePreferences.setBackupSaveDir(context, uriString)
+    }
+
+    /**
+     * @return The selected backup directory if it's valid (exists, is writable).
+     */
+    @JvmStatic
+    fun getSelectedBackupDirIfValid(context: Context): Uri? {
+        val dirUri = getBackupDirUri(context)
+
+        if (dirUri == null) {
+            Log.v(TAG, "The backup dir wasn't selected yet.")
+            return null
+        }
+        if (!validateDirAccess(context, dirUri)) {
+            Log.v(TAG, "Cannot validate the access to the dir $dirUri.")
+            return null
+        }
+
+        return dirUri;
+    }
+
+    @JvmStatic
+    @WorkerThread
+    @Throws(IOException::class)
+    fun createBackupFile(context: Context): BackupFileRecord {
+        val backupPassword = BackupPassphrase.get(context)
+                ?: throw IOException("Backup password is null")
+
+        val dirUri = getSelectedBackupDirIfValid(context)
+                ?: throw IOException("Backup save directory is not selected or invalid")
+
+        val date = Date()
+        val timestamp = SimpleDateFormat("yyyy-MM-dd-HH-mm-ss", Locale.US).format(date)
+        val fileName = String.format("session-%s.backup", timestamp)
+
+        val fileUri = DocumentsContract.createDocument(
+                context.contentResolver,
+                DocumentFile.fromTreeUri(context, dirUri)!!.uri,
+                "application/x-binary",
+                fileName)
+
+        if (fileUri == null) {
+            Toast.makeText(context, "Cannot create writable file in the dir $dirUri", Toast.LENGTH_LONG).show()
+            throw IOException("Cannot create writable file in the dir $dirUri")
+        }
+
+        FullBackupExporter.export(context,
+                AttachmentSecretProvider.getInstance(context).orCreateAttachmentSecret,
+                DatabaseFactory.getBackupDatabase(context),
+                fileUri,
+                backupPassword)
+
+        //TODO Use real file size.
+        val record = DatabaseFactory.getLokiBackupFilesDatabase(context)
+                .insertBackupFile(BackupFileRecord(fileUri, -1, date))
+
+        Log.v(TAG, "Backup file was created: $fileUri")
+
+        return record
+    }
+
+    @JvmStatic
+    @JvmOverloads
+    fun deleteAllBackupFiles(context: Context, except: Collection<BackupFileRecord>? = null) {
+        val db = DatabaseFactory.getLokiBackupFilesDatabase(context)
+        db.getBackupFiles().forEach { record ->
+            if (except != null && except.contains(record)) return@forEach
+
+            // Try to delete the related file. The operation may fail in many cases
+            // (the user moved/deleted the file, revoked the write permission, etc), so that's OK.
+            try {
+                val result = DocumentsContract.deleteDocument(context.contentResolver, record.uri)
+                if (!result) {
+                    Log.w(TAG, "Failed to delete backup file: ${record.uri}")
+                }
+            } catch (e: Exception) {
+                Log.w(TAG, "Failed to delete backup file: ${record.uri}", e)
+            }
+
+            db.deleteBackupFile(record)
+
+            Log.v(TAG, "Backup file was deleted: ${record.uri}")
+        }
+    }
+}
+
+/**
+ * An utility class to help perform backup directory selection requests.
+ *
+ * An instance of this class should be created per an [Activity] or [Fragment]
+ * and [onActivityResult] should be called appropriately.
+ */
+class BackupDirSelector(private val contextProvider: ContextProvider) {
+
+    companion object {
+        private const val REQUEST_CODE_SAVE_DIR = 7844
+    }
+
+    private val context: Context get() = contextProvider.getContext()
+
+    private var listener: Listener? = null
+
+    constructor(activity: Activity) :
+            this(ActivityContextProvider(activity))
+
+    constructor(fragment: Fragment) :
+            this(FragmentContextProvider(fragment))
+
+    /**
+     * Performs ACTION_OPEN_DOCUMENT_TREE intent to select backup directory URI.
+     * If the directory is already selected and valid, the request will be skipped.
+     * @param force if true, the previous selection is ignored and the user is requested to select another directory.
+     * @param onSelectedListener an optional action to perform once the directory is selected.
+     */
+    fun selectBackupDir(force: Boolean, onSelectedListener: Listener? = null) {
+        if (!force) {
+            val dirUri = BackupUtil.getSelectedBackupDirIfValid(context)
+            if (dirUri != null && onSelectedListener != null) {
+                onSelectedListener.onBackupDirSelected(dirUri)
+            }
+            return
+        }
+
+        // Let user pick the dir.
+        val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)
+
+        // Request read/write permission grant for the dir.
+        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION or
+                Intent.FLAG_GRANT_WRITE_URI_PERMISSION or
+                Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION)
+
+        // Set the default dir.
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val dirUri = BackupUtil.getBackupDirUri(context)
+            intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, dirUri
+                    ?: Uri.fromFile(context.getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS)))
+        }
+
+        if (onSelectedListener != null) {
+            this.listener = onSelectedListener
+        }
+
+        contextProvider.startActivityForResult(intent, REQUEST_CODE_SAVE_DIR)
+    }
+
+    fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
+        if (requestCode != REQUEST_CODE_SAVE_DIR) return
+
+        if (resultCode == Activity.RESULT_OK && data != null && data.data != null) {
+            // Acquire persistent access permissions for the file selected.
+            val persistentFlags: Int = data.flags and
+                    (Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+            context.contentResolver.takePersistableUriPermission(data.data!!, persistentFlags)
+
+            BackupUtil.setBackupDirUri(context, data.dataString)
+
+            listener?.onBackupDirSelected(data.data!!)
+        }
+
+        listener = null
+    }
+
+    @FunctionalInterface
+    interface Listener {
+        fun onBackupDirSelected(uri: Uri)
+    }
+}

src/org/thoughtcrime/securesms/util/BackupUtilOld.java

@@ -0,0 +1,61 @@
+package org.thoughtcrime.securesms.util;
+
+
+import android.content.Context;
+
+import androidx.annotation.Nullable;
+
+import org.thoughtcrime.securesms.loki.database.BackupFileRecord;
+
+import org.thoughtcrime.securesms.database.NoExternalStorageException;
+
+import java.io.File;
+
+//TODO AC: Delete this class when its functionality is
+// fully replaced by the BackupUtil.kt and related classes.
+/** @deprecated in favor of {@link BackupUtil} */
+public class BackupUtilOld {
+
+  private static final String TAG = BackupUtilOld.class.getSimpleName();
+
+  /**
+   * @deprecated this method exists only for the backward compatibility with the legacy Signal backup code.
+   * Use {@link BackupUtil} if possible.
+   */
+  public static @Nullable BackupInfo getLatestBackup(Context context) throws NoExternalStorageException {
+    BackupFileRecord backup = BackupUtil.getLastBackup(context);
+    if (backup == null) return null;
+
+
+    return new BackupInfo(
+            backup.getTimestamp().getTime(),
+            backup.getFileSize(),
+            new File(backup.getUri().getPath()));
+  }
+
+  @Deprecated
+  public static class BackupInfo {
+
+    private final long timestamp;
+    private final long size;
+    private final File file;
+
+    BackupInfo(long timestamp, long size, File file) {
+      this.timestamp = timestamp;
+      this.size      = size;
+      this.file      = file;
+    }
+
+    public long getTimestamp() {
+      return timestamp;
+    }
+
+    public long getSize() {
+      return size;
+    }
+
+    public File getFile() {
+      return file;
+    }
+  }
+}

src/org/thoughtcrime/securesms/util/ContextProvider.kt

@@ -0,0 +1,37 @@
+package org.thoughtcrime.securesms.util
+
+import android.app.Activity
+import android.content.Context
+import android.content.Intent
+import androidx.fragment.app.Fragment
+
+/**
+ * A simplified version of [android.content.ContextWrapper],
+ * but properly supports [startActivityForResult] for the implementations.
+ */
+interface ContextProvider {
+    fun getContext(): Context
+    fun startActivityForResult(intent: Intent, requestCode: Int)
+}
+
+class ActivityContextProvider(private val activity: Activity): ContextProvider {
+    
+    override fun getContext(): Context {
+        return activity
+    }
+
+    override fun startActivityForResult(intent: Intent, requestCode: Int) {
+        activity.startActivityForResult(intent, requestCode)
+    }
+}
+
+class FragmentContextProvider(private val fragment: Fragment): ContextProvider {
+
+    override fun getContext(): Context {
+        return fragment.requireContext()
+    }
+
+    override fun startActivityForResult(intent: Intent, requestCode: Int) {
+        fragment.startActivityForResult(intent, requestCode)
+    }
+}

src/org/thoughtcrime/securesms/util/SaveAttachmentTask.kt

@@ -18,9 +18,11 @@ import java.io.File
 import java.io.IOException
 import java.lang.ref.WeakReference
 import java.text.SimpleDateFormat
+import kotlin.jvm.Throws
 
 /**
  * Saves attachment files to an external storage using [MediaStore] API.
+ * Requires [android.Manifest.permission.WRITE_EXTERNAL_STORAGE] on API 28 and below.
  */
 class SaveAttachmentTask : ProgressDialogAsyncTask<SaveAttachmentTask.Attachment, Void, Pair<Int, String?>> {
 

src/org/thoughtcrime/securesms/util/TextSecurePreferences.java

@@ -141,11 +141,12 @@ public class TextSecurePreferences {
   private static final String ACTIVE_SIGNED_PRE_KEY_ID = "pref_active_signed_pre_key_id";
   private static final String NEXT_SIGNED_PRE_KEY_ID   = "pref_next_signed_pre_key_id";
 
-  public  static final String BACKUP_ENABLED              = "pref_backup_enabled";
+  public  static final String BACKUP_ENABLED              = "pref_backup_enabled_v2";
   private static final String BACKUP_PASSPHRASE           = "pref_backup_passphrase";
   private static final String ENCRYPTED_BACKUP_PASSPHRASE = "pref_encrypted_backup_passphrase";
   private static final String BACKUP_TIME                 = "pref_backup_next_time";
   public  static final String BACKUP_NOW                  = "pref_backup_create";
+  private static final String BACKUP_SAVE_DIR             = "pref_save_dir";
 
   public static final String SCREEN_LOCK         = "pref_android_screen_lock";
   public static final String SCREEN_LOCK_TIMEOUT = "pref_android_screen_lock_timeout";
@@ -296,6 +297,14 @@ public class TextSecurePreferences {
     return getLongPreference(context, BACKUP_TIME, -1);
   }
 
+  public static void setBackupSaveDir(@NonNull Context context, String dirUri) {
+    setStringPreference(context, BACKUP_SAVE_DIR, dirUri);
+  }
+
+  public static String getBackupSaveDir(@NonNull Context context) {
+    return getStringPreference(context, BACKUP_SAVE_DIR, null);
+  }
+
   public static int getNextPreKeyId(@NonNull Context context) {
     return getIntegerPreference(context, NEXT_PRE_KEY_ID, new SecureRandom().nextInt(Medium.MAX_VALUE));
   }