[samples/ffi] Update sqlite sample

The sample wasn't working for the longest time.

Fixes:

- Null safety, and late fields.
- `dart pub` instead of `pub`.
- Use the new `NativeFinalizer` and `Finalizable` features.

Change-Id: I0a397abae511ab3f6762d1b2c4047226d15e36d6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143804
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Michael Thomsen <mit@google.com>

samples/ffi/sqlite/README.md

@@ -20,25 +20,10 @@ Invalid argument(s): Failed to load dynamic library (126)
 ## Building and Running this Sample
 
 Building and running this sample is done through pub.
-Running `pub get` and `pub run example/main` should produce the following output.
+Running `dart run example/main` should produce the following output.
 
 ```sh
-$ pub get
-Resolving dependencies... (6.8s)
-+ analyzer 0.35.4
-...
-+ yaml 2.1.15
-Downloading analyzer 0.35.4...
-Downloading kernel 0.3.14...
-Downloading front_end 0.1.14...
-Changed 47 dependencies!
-Precompiling executables... (18.0s)
-Precompiled test:test.
-
-```
-
-```
-$ pub run example/main
+$ dart run example/main
 1 Chocolade chip cookie Chocolade cookie foo
 2 Ginger cookie null 42
 3 Cinnamon roll null null

samples/ffi/sqlite/lib/src/bindings/bindings.dart

@@ -34,6 +34,10 @@ class _SQLiteBindings {
       Pointer<Utf8> vfs) sqlite3_open_v2;
 
   late int Function(Pointer<Database> database) sqlite3_close_v2;
+  late Pointer<NativeFunction<sqlite3_close_v2_native_t>>
+      sqlite3_close_v2_native;
+  late Pointer<NativeFunction<Void Function(Pointer<Database> database)>>
+      sqlite3_close_v2_native_return_void;
 
   /// Compiling An SQL Statement
   ///
@@ -214,6 +218,10 @@ class _SQLiteBindings {
   /// statement after it has been finalized can result in undefined and
   /// undesirable behavior such as segfaults and heap corruption.
   late int Function(Pointer<Statement> statement) sqlite3_finalize;
+  late Pointer<NativeFunction<sqlite3_finalize_native_t>>
+      sqlite3_finalize_native;
+  late Pointer<NativeFunction<Void Function(Pointer<Statement> statement)>>
+      sqlite3_finalize_native_return_void;
 
   /// Number Of Columns In A Result Set
   ///
@@ -336,9 +344,10 @@ class _SQLiteBindings {
     sqlite3_open_v2 = sqlite
         .lookup<NativeFunction<sqlite3_open_v2_native_t>>("sqlite3_open_v2")
         .asFunction();
-    sqlite3_close_v2 = sqlite
-        .lookup<NativeFunction<sqlite3_close_v2_native_t>>("sqlite3_close_v2")
-        .asFunction();
+    sqlite3_close_v2_native = sqlite
+        .lookup<NativeFunction<sqlite3_close_v2_native_t>>("sqlite3_close_v2");
+    sqlite3_close_v2_native_return_void = sqlite3_close_v2_native.cast();
+    sqlite3_close_v2 = sqlite3_close_v2_native.asFunction();
     sqlite3_prepare_v2 = sqlite
         .lookup<NativeFunction<sqlite3_prepare_v2_native_t>>(
             "sqlite3_prepare_v2")
@@ -349,9 +358,10 @@ class _SQLiteBindings {
     sqlite3_reset = sqlite
         .lookup<NativeFunction<sqlite3_reset_native_t>>("sqlite3_reset")
         .asFunction();
-    sqlite3_finalize = sqlite
-        .lookup<NativeFunction<sqlite3_finalize_native_t>>("sqlite3_finalize")
-        .asFunction();
+    sqlite3_finalize_native = sqlite
+        .lookup<NativeFunction<sqlite3_finalize_native_t>>("sqlite3_finalize");
+    sqlite3_finalize_native_return_void = sqlite3_finalize_native.cast();
+    sqlite3_finalize = sqlite3_finalize_native.asFunction();
     sqlite3_errstr = sqlite
         .lookup<NativeFunction<sqlite3_errstr_native_t>>("sqlite3_errstr")
         .asFunction();

samples/ffi/sqlite/lib/src/database.dart

@@ -21,19 +21,19 @@ import "collections/closable_iterator.dart";
 ///
 /// This database interacts with SQLite synchonously.
 class Database {
-  late Pointer<types.Database> _database;
+  late DatabaseResource _database;
   bool _open = false;
 
   /// Open a database located at the file [path].
   Database(String path,
       [int flags = Flags.SQLITE_OPEN_READWRITE | Flags.SQLITE_OPEN_CREATE]) {
     Pointer<Pointer<types.Database>> dbOut = calloc();
-    final pathC = path.toNativeUtf8();
+    final pathC = Utf8Resource(path.toNativeUtf8());
     final int resultCode =
-        bindings.sqlite3_open_v2(pathC, dbOut, flags, nullptr);
-    _database = dbOut.value;
+        bindings.sqlite3_open_v2(pathC.unsafe(), dbOut, flags, nullptr);
+    _database = DatabaseResource(dbOut.value);
     calloc.free(dbOut);
-    calloc.free(pathC);
+    pathC.free();
 
     if (resultCode == Errors.SQLITE_OK) {
       _open = true;
@@ -53,7 +53,7 @@ class Database {
   /// avoid resource leaks.
   void close() {
     assert(_open);
-    final int resultCode = bindings.sqlite3_close_v2(_database);
+    final int resultCode = _database.close();
     if (resultCode == Errors.SQLITE_OK) {
       _open = false;
     } else {
@@ -63,18 +63,17 @@ class Database {
 
   /// Execute a query, discarding any returned rows.
   void execute(String query) {
-    Pointer<Pointer<Statement>> statementOut = calloc();
-    Pointer<Utf8> queryC = query.toNativeUtf8();
-    int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, nullptr);
-    Pointer<Statement> statement = statementOut.value;
+    Pointer<Pointer<Statement>> statementOut = malloc();
+    final queryC = Utf8Resource(query.toNativeUtf8());
+    int resultCode = _database.prepare(queryC, -1, statementOut, nullptr);
+    final statement = StatementResource(statementOut.value);
     calloc.free(statementOut);
-    calloc.free(queryC);
+    queryC.free();
 
     while (resultCode == Errors.SQLITE_ROW || resultCode == Errors.SQLITE_OK) {
-      resultCode = bindings.sqlite3_step(statement);
+      resultCode = statement.step();
     }
-    bindings.sqlite3_finalize(statement);
+    statement.finalize();
     if (resultCode != Errors.SQLITE_DONE) {
       throw _loadError(resultCode);
     }
@@ -82,32 +81,33 @@ class Database {
 
   /// Evaluate a query and return the resulting rows as an iterable.
   Result query(String query) {
-    Pointer<Pointer<Statement>> statementOut = calloc();
-    Pointer<Utf8> queryC = query.toNativeUtf8();
-    int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, nullptr);
-    Pointer<Statement> statement = statementOut.value;
+    Pointer<Pointer<Statement>> statementOut = malloc();
+    final queryC = Utf8Resource(query.toNativeUtf8());
+    int resultCode = _database.prepare(queryC, -1, statementOut, nullptr);
+    final statement = StatementResource(statementOut.value);
     calloc.free(statementOut);
-    calloc.free(queryC);
+    queryC.free();
 
     if (resultCode != Errors.SQLITE_OK) {
-      bindings.sqlite3_finalize(statement);
+      statement.finalize();
       throw _loadError(resultCode);
     }
 
     Map<String, int> columnIndices = {};
-    int columnCount = bindings.sqlite3_column_count(statement);
+    int columnCount = statement.columnCount;
     for (int i = 0; i < columnCount; i++) {
-      String columnName =
-          bindings.sqlite3_column_name(statement, i).toDartString();
+      String columnName = statement.columnName(i);
       columnIndices[columnName] = i;
     }
 
     return Result._(this, statement, columnIndices);
   }
 
-  SQLiteException _loadError(int errorCode) {
-    String errorMessage = bindings.sqlite3_errmsg(_database).toDartString();
+  SQLiteException _loadError([int? errorCode]) {
+    String errorMessage = _database.errmsg().toDartString();
+    if (errorCode == null) {
+      return SQLiteException(errorMessage);
+    }
     String errorCodeExplanation =
         bindings.sqlite3_errstr(errorCode).toDartString();
     return SQLiteException(
@@ -125,7 +125,7 @@ class Result extends IterableBase<Row> implements ClosableIterable<Row> {
 
   Result._(
     Database database,
-    Pointer<Statement> statement,
+    StatementResource statement,
     Map<String, int> columnIndices,
   ) : _iterator = _ResultIterator(statement, columnIndices) {}
 
@@ -135,7 +135,7 @@ class Result extends IterableBase<Row> implements ClosableIterable<Row> {
 }
 
 class _ResultIterator implements ClosableIterator<Row> {
-  final Pointer<Statement> _statement;
+  final StatementResource _statement;
   final Map<String, int> _columnIndices;
 
   Row? _currentRow;
@@ -148,7 +148,7 @@ class _ResultIterator implements ClosableIterator<Row> {
       throw SQLiteException("The result has already been closed.");
     }
     _currentRow?._setNotCurrent();
-    int stepResult = bindings.sqlite3_step(_statement);
+    int stepResult = _statement.step();
     if (stepResult == Errors.SQLITE_ROW) {
       _currentRow = Row._(_statement, _columnIndices);
       return true;
@@ -168,12 +168,12 @@ class _ResultIterator implements ClosableIterator<Row> {
   void close() {
     _currentRow?._setNotCurrent();
     _closed = true;
-    bindings.sqlite3_finalize(_statement);
+    _statement.finalize();
   }
 }
 
 class Row {
-  final Pointer<Statement> _statement;
+  final StatementResource _statement;
   final Map<String, int> _columnIndices;
 
   bool _isCurrentRow = true;
@@ -201,12 +201,10 @@ class Row {
 
     Type dynamicType;
     if (convert == Convert.DynamicType) {
-      dynamicType =
-          _typeFromCode(bindings.sqlite3_column_type(_statement, columnIndex));
+      dynamicType = _typeFromCode(_statement.columnType(columnIndex));
     } else {
-      dynamicType = _typeFromText(bindings
-          .sqlite3_column_decltype(_statement, columnIndex)
-          .toDartString());
+      dynamicType =
+          _typeFromText(_statement.columnDecltype(columnIndex).toDartString());
     }
 
     switch (dynamicType) {
@@ -230,7 +228,7 @@ class Row {
   /// integer.
   int readColumnByIndexAsInt(int columnIndex) {
     _checkIsCurrentRow();
-    return bindings.sqlite3_column_int(_statement, columnIndex);
+    return _statement.columnInt(columnIndex);
   }
 
   /// Reads column [columnName] and converts to [Type.Text] if not text.
@@ -241,7 +239,7 @@ class Row {
   /// Reads column [columnIndex] and converts to [Type.Text] if not text.
   String readColumnByIndexAsText(int columnIndex) {
     _checkIsCurrentRow();
-    return bindings.sqlite3_column_text(_statement, columnIndex).toDartString();
+    return _statement.columnText(columnIndex).toDartString();
   }
 
   void _checkIsCurrentRow() {
@@ -257,6 +255,93 @@ class Row {
   }
 }
 
+class DatabaseResource implements Finalizable {
+  static final NativeFinalizer _finalizer =
+      NativeFinalizer(bindings.sqlite3_close_v2_native_return_void.cast());
+
+  /// [_statement] must never escape [StatementResource], otherwise the
+  /// [_finalizer] will run prematurely.
+  Pointer<types.Database> _database;
+
+  DatabaseResource(this._database) {
+    _finalizer.attach(this, _database.cast(), detach: this);
+  }
+
+  int close() {
+    _finalizer.detach(this);
+    return bindings.sqlite3_close_v2(_database);
+  }
+
+  int prepare(Utf8Resource query, int nbytes,
+      Pointer<Pointer<Statement>> statementOut, Pointer<Pointer<Utf8>> tail) {
+    int result = bindings.sqlite3_prepare_v2(
+        _database, query.unsafe(), nbytes, statementOut, tail);
+    return result;
+  }
+
+  Pointer<Utf8> errmsg() => bindings.sqlite3_errmsg(_database);
+}
+
+class StatementResource implements Finalizable {
+  static final NativeFinalizer _finalizer =
+      NativeFinalizer(bindings.sqlite3_finalize_native_return_void.cast());
+
+  /// [_statement] must never escape [StatementResource], otherwise the
+  /// [_finalizer] will run prematurely.
+  final Pointer<Statement> _statement;
+
+  StatementResource(this._statement) {
+    _finalizer.attach(this, _statement.cast(), detach: this);
+  }
+
+  int finalize() {
+    _finalizer.detach(this);
+    return bindings.sqlite3_finalize(_statement);
+  }
+
+  int get columnCount => bindings.sqlite3_column_count(_statement);
+
+  String columnName(int index) =>
+      bindings.sqlite3_column_name(_statement, index).toDartString();
+
+  int step() => bindings.sqlite3_step(_statement);
+
+  int columnType(int columnIndex) =>
+      bindings.sqlite3_column_type(_statement, columnIndex);
+
+  Pointer<Utf8> columnDecltype(int columnIndex) =>
+      bindings.sqlite3_column_decltype(_statement, columnIndex);
+
+  int columnInt(int columnIndex) =>
+      bindings.sqlite3_column_int(_statement, columnIndex);
+
+  Pointer<Utf8> columnText(int columnIndex) =>
+      bindings.sqlite3_column_text(_statement, columnIndex);
+}
+
+class Utf8Resource implements Finalizable {
+  static final NativeFinalizer _finalizer = NativeFinalizer(posixFree);
+
+  /// [_cString] must never escape [Utf8Resource], otherwise the
+  /// [_finalizer] will run prematurely.
+  final Pointer<Utf8> _cString;
+
+  Utf8Resource(this._cString) {
+    _finalizer.attach(this, _cString.cast(), detach: this);
+  }
+
+  void free() {
+    _finalizer.detach(this);
+    calloc.free(_cString);
+  }
+
+  /// Ensure this [Utf8Resource] stays in scope longer than the inner resource.
+  Pointer<Utf8> unsafe() => _cString;
+}
+
+final DynamicLibrary stdlib = DynamicLibrary.process();
+final posixFree = stdlib.lookup<NativeFunction<Void Function(Pointer)>>("free");
+
 Type _typeFromCode(int code) {
   switch (code) {
     case Types.SQLITE_INTEGER:

samples/ffi/sqlite/pubspec.yaml

@@ -2,10 +2,9 @@ name: sqlite3
 version: 0.0.1
 description: >-
   Sqlite3 wrapper. Demo for dart:ffi.
-author: Daco Harkes <dacoharkes@google.com>, Samir Jindel <sjindel@google.com>
 environment:
-  sdk: '>=2.12.0-0 <3.0.0'
+  sdk: '>=2.17.0 <3.0.0'
 dependencies:
-  ffi: ^1.1.2
+  ffi: ^2.0.0
 dev_dependencies:
-  test: ^1.16.0-nullsafety.12
+  test: ^1.21.1

samples_2/ffi/sqlite/README.md

@@ -20,25 +20,10 @@ Invalid argument(s): Failed to load dynamic library (126)
 ## Building and Running this Sample
 
 Building and running this sample is done through pub.
-Running `pub get` and `pub run example/main` should produce the following output.
+Running `dart run example/main` should produce the following output.
 
 ```sh
-$ pub get
-Resolving dependencies... (6.8s)
-+ analyzer 0.35.4
-...
-+ yaml 2.1.15
-Downloading analyzer 0.35.4...
-Downloading kernel 0.3.14...
-Downloading front_end 0.1.14...
-Changed 47 dependencies!
-Precompiling executables... (18.0s)
-Precompiled test:test.
-
-```
-
-```
-$ pub run example/main
+$ dart run example/main
 1 Chocolade chip cookie Chocolade cookie foo
 2 Ginger cookie null 42
 3 Cinnamon roll null null

samples_2/ffi/sqlite/lib/src/bindings/bindings.dart

@@ -33,6 +33,9 @@ class _SQLiteBindings {
       int flags, Pointer<Utf8> vfs) sqlite3_open_v2;
 
   int Function(Pointer<Database> database) sqlite3_close_v2;
+  Pointer<NativeFunction<sqlite3_close_v2_native_t>> sqlite3_close_v2_native;
+  Pointer<NativeFunction<Void Function(Pointer<Database> database)>>
+      sqlite3_close_v2_native_return_void;
 
   /// Compiling An SQL Statement
   ///
@@ -213,6 +216,9 @@ class _SQLiteBindings {
   /// statement after it has been finalized can result in undefined and
   /// undesirable behavior such as segfaults and heap corruption.
   int Function(Pointer<Statement> statement) sqlite3_finalize;
+  Pointer<NativeFunction<sqlite3_finalize_native_t>> sqlite3_finalize_native;
+  Pointer<NativeFunction<Void Function(Pointer<Statement> statement)>>
+      sqlite3_finalize_native_return_void;
 
   /// Number Of Columns In A Result Set
   ///
@@ -335,9 +341,10 @@ class _SQLiteBindings {
     sqlite3_open_v2 = sqlite
         .lookup<NativeFunction<sqlite3_open_v2_native_t>>("sqlite3_open_v2")
         .asFunction();
-    sqlite3_close_v2 = sqlite
-        .lookup<NativeFunction<sqlite3_close_v2_native_t>>("sqlite3_close_v2")
-        .asFunction();
+    sqlite3_close_v2_native = sqlite
+        .lookup<NativeFunction<sqlite3_close_v2_native_t>>("sqlite3_close_v2");
+    sqlite3_close_v2_native_return_void = sqlite3_close_v2_native.cast();
+    sqlite3_close_v2 = sqlite3_close_v2_native.asFunction();
     sqlite3_prepare_v2 = sqlite
         .lookup<NativeFunction<sqlite3_prepare_v2_native_t>>(
             "sqlite3_prepare_v2")
@@ -348,9 +355,10 @@ class _SQLiteBindings {
     sqlite3_reset = sqlite
         .lookup<NativeFunction<sqlite3_reset_native_t>>("sqlite3_reset")
         .asFunction();
-    sqlite3_finalize = sqlite
-        .lookup<NativeFunction<sqlite3_finalize_native_t>>("sqlite3_finalize")
-        .asFunction();
+    sqlite3_finalize_native = sqlite
+        .lookup<NativeFunction<sqlite3_finalize_native_t>>("sqlite3_finalize");
+    sqlite3_finalize_native_return_void = sqlite3_finalize_native.cast();
+    sqlite3_finalize = sqlite3_finalize_native.asFunction();
     sqlite3_errstr = sqlite
         .lookup<NativeFunction<sqlite3_errstr_native_t>>("sqlite3_errstr")
         .asFunction();

samples_2/ffi/sqlite/lib/src/database.dart

@@ -23,19 +23,19 @@ import "collections/closable_iterator.dart";
 ///
 /// This database interacts with SQLite synchonously.
 class Database {
-  Pointer<types.Database> _database;
+  DatabaseResource _database;
   bool _open = false;
 
   /// Open a database located at the file [path].
   Database(String path,
       [int flags = Flags.SQLITE_OPEN_READWRITE | Flags.SQLITE_OPEN_CREATE]) {
     Pointer<Pointer<types.Database>> dbOut = calloc();
-    final pathC = path.toNativeUtf8();
+    final pathC = Utf8Resource(path.toNativeUtf8());
     final int resultCode =
-        bindings.sqlite3_open_v2(pathC, dbOut, flags, nullptr);
-    _database = dbOut.value;
+        bindings.sqlite3_open_v2(pathC.unsafe(), dbOut, flags, nullptr);
+    _database = DatabaseResource(dbOut.value);
     calloc.free(dbOut);
-    calloc.free(pathC);
+    pathC.free();
 
     if (resultCode == Errors.SQLITE_OK) {
       _open = true;
@@ -55,7 +55,7 @@ class Database {
   /// avoid resource leaks.
   void close() {
     assert(_open);
-    final int resultCode = bindings.sqlite3_close_v2(_database);
+    final int resultCode = _database.close();
     if (resultCode == Errors.SQLITE_OK) {
       _open = false;
     } else {
@@ -65,18 +65,17 @@ class Database {
 
   /// Execute a query, discarding any returned rows.
   void execute(String query) {
-    Pointer<Pointer<Statement>> statementOut = calloc();
-    Pointer<Utf8> queryC = query.toNativeUtf8();
-    int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, nullptr);
-    Pointer<Statement> statement = statementOut.value;
+    Pointer<Pointer<Statement>> statementOut = malloc();
+    final queryC = Utf8Resource(query.toNativeUtf8());
+    int resultCode = _database.prepare(queryC, -1, statementOut, nullptr);
+    final statement = StatementResource(statementOut.value);
     calloc.free(statementOut);
-    calloc.free(queryC);
+    queryC.free();
 
     while (resultCode == Errors.SQLITE_ROW || resultCode == Errors.SQLITE_OK) {
-      resultCode = bindings.sqlite3_step(statement);
+      resultCode = statement.step();
     }
-    bindings.sqlite3_finalize(statement);
+    statement.finalize();
     if (resultCode != Errors.SQLITE_DONE) {
       throw _loadError(resultCode);
     }
@@ -84,24 +83,22 @@ class Database {
 
   /// Evaluate a query and return the resulting rows as an iterable.
   Result query(String query) {
-    Pointer<Pointer<Statement>> statementOut = calloc();
-    Pointer<Utf8> queryC = query.toNativeUtf8();
-    int resultCode = bindings.sqlite3_prepare_v2(
-        _database, queryC, -1, statementOut, nullptr);
-    Pointer<Statement> statement = statementOut.value;
+    Pointer<Pointer<Statement>> statementOut = malloc();
+    final queryC = Utf8Resource(query.toNativeUtf8());
+    int resultCode = _database.prepare(queryC, -1, statementOut, nullptr);
+    final statement = StatementResource(statementOut.value);
     calloc.free(statementOut);
-    calloc.free(queryC);
+    queryC.free();
 
     if (resultCode != Errors.SQLITE_OK) {
-      bindings.sqlite3_finalize(statement);
+      statement.finalize();
       throw _loadError(resultCode);
     }
 
     Map<String, int> columnIndices = {};
-    int columnCount = bindings.sqlite3_column_count(statement);
+    int columnCount = statement.columnCount;
     for (int i = 0; i < columnCount; i++) {
-      String columnName =
-          bindings.sqlite3_column_name(statement, i).toDartString();
+      String columnName = statement.columnName(i);
       columnIndices[columnName] = i;
     }
 
@@ -109,7 +106,7 @@ class Database {
   }
 
   SQLiteException _loadError([int errorCode]) {
-    String errorMessage = bindings.sqlite3_errmsg(_database).toDartString();
+    String errorMessage = _database.errmsg().toDartString();
     if (errorCode == null) {
       return SQLiteException(errorMessage);
     }
@@ -126,18 +123,13 @@ class Database {
 /// Please note that this iterator should be [close]d manually if not all [Row]s
 /// are consumed.
 class Result extends IterableBase<Row> implements ClosableIterable<Row> {
-  final Database _database;
   final ClosableIterator<Row> _iterator;
-  final Pointer<Statement> _statement;
-  final Map<String, int> _columnIndices;
-
-  Row _currentRow = null;
 
   Result._(
-    this._database,
-    this._statement,
-    this._columnIndices,
-  ) : _iterator = _ResultIterator(_statement, _columnIndices) {}
+    Database database,
+    StatementResource statement,
+    Map<String, int> columnIndices,
+  ) : _iterator = _ResultIterator(statement, columnIndices) {}
 
   void close() => _iterator.close();
 
@@ -145,10 +137,10 @@ class Result extends IterableBase<Row> implements ClosableIterable<Row> {
 }
 
 class _ResultIterator implements ClosableIterator<Row> {
-  final Pointer<Statement> _statement;
+  final StatementResource _statement;
   final Map<String, int> _columnIndices;
 
-  Row _currentRow = null;
+  Row _currentRow;
   bool _closed = false;
 
   _ResultIterator(this._statement, this._columnIndices) {}
@@ -157,8 +149,10 @@ class _ResultIterator implements ClosableIterator<Row> {
     if (_closed) {
       throw SQLiteException("The result has already been closed.");
     }
-    _currentRow?._setNotCurrent();
-    int stepResult = bindings.sqlite3_step(_statement);
+    if (_currentRow != null) {
+      _currentRow._setNotCurrent();
+    }
+    int stepResult = _statement.step();
     if (stepResult == Errors.SQLITE_ROW) {
       _currentRow = Row._(_statement, _columnIndices);
       return true;
@@ -176,14 +170,14 @@ class _ResultIterator implements ClosableIterator<Row> {
   }
 
   void close() {
-    _currentRow?._setNotCurrent();
+    _currentRow._setNotCurrent();
     _closed = true;
-    bindings.sqlite3_finalize(_statement);
+    _statement.finalize();
   }
 }
 
 class Row {
-  final Pointer<Statement> _statement;
+  final StatementResource _statement;
   final Map<String, int> _columnIndices;
 
   bool _isCurrentRow = true;
@@ -211,12 +205,10 @@ class Row {
 
     Type dynamicType;
     if (convert == Convert.DynamicType) {
-      dynamicType =
-          _typeFromCode(bindings.sqlite3_column_type(_statement, columnIndex));
+      dynamicType = _typeFromCode(_statement.columnType(columnIndex));
     } else {
-      dynamicType = _typeFromText(bindings
-          .sqlite3_column_decltype(_statement, columnIndex)
-          .toDartString());
+      dynamicType =
+          _typeFromText(_statement.columnDecltype(columnIndex).toDartString());
     }
 
     switch (dynamicType) {
@@ -226,7 +218,6 @@ class Row {
         return readColumnByIndexAsText(columnIndex);
       case Type.Null:
         return null;
-        break;
       default:
     }
   }
@@ -241,7 +232,7 @@ class Row {
   /// integer.
   int readColumnByIndexAsInt(int columnIndex) {
     _checkIsCurrentRow();
-    return bindings.sqlite3_column_int(_statement, columnIndex);
+    return _statement.columnInt(columnIndex);
   }
 
   /// Reads column [columnName] and converts to [Type.Text] if not text.
@@ -252,7 +243,7 @@ class Row {
   /// Reads column [columnIndex] and converts to [Type.Text] if not text.
   String readColumnByIndexAsText(int columnIndex) {
     _checkIsCurrentRow();
-    return bindings.sqlite3_column_text(_statement, columnIndex).toDartString();
+    return _statement.columnText(columnIndex).toDartString();
   }
 
   void _checkIsCurrentRow() {
@@ -268,6 +259,93 @@ class Row {
   }
 }
 
+class DatabaseResource implements Finalizable {
+  static final NativeFinalizer _finalizer =
+      NativeFinalizer(bindings.sqlite3_close_v2_native_return_void.cast());
+
+  /// [_statement] must never escape [StatementResource], otherwise the
+  /// [_finalizer] will run prematurely.
+  Pointer<types.Database> _database;
+
+  DatabaseResource(this._database) {
+    _finalizer.attach(this, _database.cast(), detach: this);
+  }
+
+  int close() {
+    _finalizer.detach(this);
+    return bindings.sqlite3_close_v2(_database);
+  }
+
+  int prepare(Utf8Resource query, int nbytes,
+      Pointer<Pointer<Statement>> statementOut, Pointer<Pointer<Utf8>> tail) {
+    int result = bindings.sqlite3_prepare_v2(
+        _database, query.unsafe(), nbytes, statementOut, tail);
+    return result;
+  }
+
+  Pointer<Utf8> errmsg() => bindings.sqlite3_errmsg(_database);
+}
+
+class StatementResource implements Finalizable {
+  static final NativeFinalizer _finalizer =
+      NativeFinalizer(bindings.sqlite3_finalize_native_return_void.cast());
+
+  /// [_statement] must never escape [StatementResource], otherwise the
+  /// [_finalizer] will run prematurely.
+  final Pointer<Statement> _statement;
+
+  StatementResource(this._statement) {
+    _finalizer.attach(this, _statement.cast(), detach: this);
+  }
+
+  int finalize() {
+    _finalizer.detach(this);
+    return bindings.sqlite3_finalize(_statement);
+  }
+
+  int get columnCount => bindings.sqlite3_column_count(_statement);
+
+  String columnName(int index) =>
+      bindings.sqlite3_column_name(_statement, index).toDartString();
+
+  int step() => bindings.sqlite3_step(_statement);
+
+  int columnType(int columnIndex) =>
+      bindings.sqlite3_column_type(_statement, columnIndex);
+
+  Pointer<Utf8> columnDecltype(int columnIndex) =>
+      bindings.sqlite3_column_decltype(_statement, columnIndex);
+
+  int columnInt(int columnIndex) =>
+      bindings.sqlite3_column_int(_statement, columnIndex);
+
+  Pointer<Utf8> columnText(int columnIndex) =>
+      bindings.sqlite3_column_text(_statement, columnIndex);
+}
+
+class Utf8Resource implements Finalizable {
+  static final NativeFinalizer _finalizer = NativeFinalizer(posixFree);
+
+  /// [_cString] must never escape [Utf8Resource], otherwise the
+  /// [_finalizer] will run prematurely.
+  final Pointer<Utf8> _cString;
+
+  Utf8Resource(this._cString) {
+    _finalizer.attach(this, _cString.cast(), detach: this);
+  }
+
+  void free() {
+    _finalizer.detach(this);
+    calloc.free(_cString);
+  }
+
+  /// Ensure this [Utf8Resource] stays in scope longer than the inner resource.
+  Pointer<Utf8> unsafe() => _cString;
+}
+
+final DynamicLibrary stdlib = DynamicLibrary.process();
+final posixFree = stdlib.lookup<NativeFunction<Void Function(Pointer)>>("free");
+
 Type _typeFromCode(int code) {
   switch (code) {
     case Types.SQLITE_INTEGER:
@@ -297,7 +375,6 @@ Type _typeFromText(String textRepresentation) {
     case "null":
       return Type.Null;
   }
-  if (textRepresentation == null) return Type.Null;
   throw Exception("Unknown type [$textRepresentation]");
 }
 

samples_2/ffi/sqlite/lib/src/ffi/dylib_utils.dart

@@ -7,8 +7,7 @@
 import 'dart:ffi';
 import 'dart:io' show Platform;
 
-String _platformPath(String name, {String path}) {
-  if (path == null) path = "";
+String _platformPath(String name, String path) {
   if (Platform.isLinux || Platform.isAndroid || Platform.isFuchsia)
     return path + "lib" + name + ".so";
   if (Platform.isMacOS) return path + "lib" + name + ".dylib";
@@ -16,7 +15,7 @@ String _platformPath(String name, {String path}) {
   throw Exception("Platform not implemented");
 }
 
-DynamicLibrary dlopenPlatformSpecific(String name, {String path}) {
-  String fullPath = _platformPath(name, path: path);
+DynamicLibrary dlopenPlatformSpecific(String name, {String path = ""}) {
+  String fullPath = _platformPath(name, path);
   return DynamicLibrary.open(fullPath);
 }

samples_2/ffi/sqlite/pubspec.yaml

@@ -2,10 +2,9 @@ name: sqlite3
 version: 0.0.1
 description: >-
   Sqlite3 wrapper. Demo for dart:ffi.
-author: Daco Harkes <dacoharkes@google.com>, Samir Jindel <sjindel@google.com>
 environment:
-  sdk: '>=2.1.0 <3.0.0'
+  sdk: '>=2.17.0 <3.0.0'
 dependencies:
-  ffi: ^1.1.2
+  ffi: ^2.0.0
 dev_dependencies:
-  test: ^1.5.3
+  test: ^1.21.1

samples_2/ffi/sqlite/test/sqlite_test.dart

@@ -49,8 +49,7 @@ void main() {
       expect(true, 1 <= id && id <= 3);
       String name = r.readColumnByIndex(1);
       expect(true, name is String);
-      String alternativeName = r.readColumn("alternative_name");
-      expect(true, alternativeName is String || alternativeName == null);
+      final alternativeName = r.readColumn("alternative_name") as String;
       dynamic multiTypedValue = r.readColumn("multi_typed_column");
       expect(
           true,
@@ -76,8 +75,7 @@ void main() {
       expect(true, 1 <= id && id <= 3);
       String name = r.readColumnByIndex(1);
       expect(true, name is String);
-      String alternativeName = r.readColumn("alternative_name");
-      expect(true, alternativeName is String || alternativeName == null);
+      final alternativeName = r.readColumn("alternative_name") as String;
       dynamic multiTypedValue = r.readColumn("multi_typed_column");
       expect(
           true,