Template to use moor_ffi with SQLCipher

cipher_db.dart

import 'dart:async';
import 'dart:ffi';
import 'dart:io';
import 'dart:math';

import 'package:moor/backends.dart';
import 'package:moor/moor.dart';
import 'package:moor_ffi/moor_ffi.dart';
import 'package:moor_ffi/open_helper.dart';

/// Tells `moor_ffi` to use `sqlcipher` instead of the regular `sqlite3`.
///
/// This needs to be called before using `moor`, for instance in the `main`
/// method.
void init() {
  const sharedLibraryName = 'libsqlcipher.so';

  open.overrideFor(OperatingSystem.android, () {
    try {
      return DynamicLibrary.open(sharedLibraryName);
    } catch (_) {
      // On some (especially old) Android devices, we somehow can't dlopen
      // libraries shipped with the apk. We need to find the full path of the
      // library (/data/data/<id>/lib/libsqlite3.so) and open that one.
      // For details, see https://github.com/simolus3/moor/issues/420
      final appIdAsBytes = File('/proc/self/cmdline').readAsBytesSync();

      // app id ends with the first \0 character in here.
      final endOfAppId = max(appIdAsBytes.indexOf(0), 0);
      final appId = String.fromCharCodes(appIdAsBytes.sublist(0, endOfAppId));

      return DynamicLibrary.open('/data/data/$appId/lib/$sharedLibraryName');
    }
  });

  open.overrideFor(OperatingSystem.iOS, () => DynamicLibrary.executable());
}

class VmDatabaseEncrypted extends DelegatedDatabase {
  /// Creates a database that will store its result in the [file], creating it
  /// if it doesn't exist.
  factory VmDatabaseEncrypted(
    File file, {
    String password = '',
    bool logStatements = false,
  }) {
    final vmDatabase = VmDatabase(file, logStatements: logStatements);
    return VmDatabaseEncrypted._(vmDatabase, password);
  }

  factory VmDatabaseEncrypted.memory({
    String password = '',
    bool logStatements = false,
  }) {
    final vmDatabase = VmDatabase.memory(logStatements: logStatements);
    return VmDatabaseEncrypted._(vmDatabase, password);
  }

  VmDatabaseEncrypted._(
    VmDatabase vmDatabase,
    String password,
  ) : super(
          _VmEncryptedDelegate(vmDatabase.delegate, password),
          logStatements: vmDatabase.logStatements,
          isSequential: vmDatabase.isSequential,
        );
}

class _VmEncryptedDelegate extends DatabaseDelegate {
  final String password;
  final DatabaseDelegate delegate;

  _VmEncryptedDelegate(
    this.delegate,
    this.password,
  );

  @override
  Future<void> open(QueryExecutorUser db) async {
    await delegate.open(db);
    final keyLiteral = const StringType().mapToSqlConstant(password);
    await delegate.runCustom('PRAGMA KEY = $keyLiteral', const []);
    return Future.value();
  }

  @override
  FutureOr<bool> get isOpen => delegate.isOpen;

  @override
  Future<void> runBatched(BatchedStatements statements) {
    return delegate.runBatched(statements);
  }

  @override
  Future<void> runCustom(String statement, List args) {
    return delegate.runCustom(statement, args);
  }

  @override
  Future<int> runInsert(String statement, List args) {
    return delegate.runInsert(statement, args);
  }

  @override
  Future<QueryResult> runSelect(String statement, List args) {
    return delegate.runSelect(statement, args);
  }

  @override
  Future<int> runUpdate(String statement, List args) {
    return delegate.runUpdate(statement, args);
  }

  @override
  TransactionDelegate get transactionDelegate => delegate.transactionDelegate;

  @override
  DbVersionDelegate get versionDelegate => delegate.versionDelegate;
}

setup.md

Call init before using moor, for instance in your main method.

You can now use an encrypted database by replacing VmDatabase(file) with EncryptedVmDatabase(key, file)

Good point, thank you David! I've changed the class.

Oops, I have just spotted a small bug. The runUpdate method does not call the delegate... 😓