[ffi] Add initial utf16 support (dart-archive/ffi#5)

Author: mit-mit

pkgs/ffi/CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 0.1.1
+
+* Add basic Utf16 support
+
 ## 0.1.0
 
-* Initial release
+* Initial release supporting Utf8

pkgs/ffi/lib/ffi.dart

@@ -3,3 +3,4 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export 'src/utf8.dart';
+export 'src/utf16.dart';

pkgs/ffi/lib/src/utf16.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:ffi';
+import 'dart:typed_data';
+
+/// [Utf16] implements conversion between Dart strings and null-terminated
+/// Utf6-encoded "char*" strings in C.
+///
+/// [Utf16] is respresented as a struct so that `Pointer<Utf16>` can be used in
+/// native function signatures.
+class Utf16 extends Struct<Utf16> {
+  /// Convert a [String] to a Utf16-encoded null-terminated C string.
+  ///
+  /// If 'string' contains NULL bytes, the converted string will be truncated
+  /// prematurely. Unpaired surrogate code points in [string] will be preserved
+  /// in the UTF-8 encoded result. See [Utf8Encoder] for details on encoding.
+  ///
+  /// Returns a malloc-allocated pointer to the result.
+  static Pointer<Utf16> toUtf16(String s) {
+    final units = s.codeUnits;
+    final Pointer<Uint16> result =
+        Pointer<Uint16>.allocate(count: units.length + 1);
+    final Uint16List nativeString =
+        result.asExternalTypedData(count: units.length + 1);
+    nativeString.setAll(0, units);
+    nativeString[units.length] = 0;
+    return result.cast();
+  }
+}

pkgs/ffi/pubspec.yaml

@@ -1,5 +1,5 @@
 name: ffi
-version: 0.1.0
+version: 0.1.1
 author: Dart Team <[email protected]>
 homepage: https://github.com/dart-lang/ffi
 description: Utilities for working with Foreign Function Interface (FFI) code.

pkgs/ffi/test/utf16_test.dart

@@ -0,0 +1,32 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:ffi';
+import 'dart:typed_data';
+
+import 'package:test/test.dart';
+import 'package:ffi/ffi.dart';
+
+main() {
+  test("toUtf16 ASCII", () {
+    final String start = "Hello World!\n";
+    final Pointer<Uint16> converted = Utf16.toUtf16(start).cast();
+    final Uint16List end =
+        converted.asExternalTypedData(count: start.codeUnits.length + 1);
+    final matcher = equals(start.codeUnits.toList()..add(0));
+    expect(end, matcher);
+    converted.free();
+  });
+
+  test("toUtf16 emoji", () {
+    final String start = "😎";
+    final Pointer<Utf16> converted = Utf16.toUtf16(start).cast();
+    final int length = start.codeUnits.length;
+    final Uint16List end =
+        converted.cast<Uint16>().asExternalTypedData(count: length + 1);
+    final matcher = equals(start.codeUnits.toList()..add(0));
+    expect(end, matcher);
+    converted.free();
+  });
+}