Add helper methods for NSData (#1104)

Author: brianquinlan

pkgs/objective_c/lib/objective_c.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export 'src/core.dart';
+export 'src/ns_data.dart';
 export 'src/ns_string.dart';
 export 'src/c_bindings_generated.dart'
     show

pkgs/objective_c/lib/src/ns_data.dart

@@ -0,0 +1,47 @@
+// Copyright (c) 2024, 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:ffi/ffi.dart';
+
+import 'objective_c_bindings_generated.dart';
+
+extension NSDataExtensions on NSData {
+  /// Return the value of [bytes] at the given index.
+  ///
+  /// The returned value will be in the range 0 to 255.
+  int operator [](int index) {
+    IndexError.check(index, length, indexable: this);
+    return bytes.cast<Uint8>()[index];
+  }
+
+  /// Return a list containing the contents of the [NSData].
+  Uint8List toList() {
+    if (bytes.address == 0 || length == 0) {
+      return Uint8List(0);
+    } else {
+      return Uint8List.fromList(bytes.cast<Uint8>().asTypedList(length));
+    }
+  }
+}
+
+extension NSDataListExtension on List<int> {
+  /// Return a [NSData] containing the contents of the [List] interpreted as
+  /// bytes.
+  ///
+  /// The elements of the [List] should be integers in the range 0 to 255. Any
+  /// integer, which is not in that range, is converted to a byte as if by
+  /// `value.toUnsigned(8)`.
+  NSData toNSData() {
+    if (length == 0) {
+      return NSData.new1();
+    }
+    final buffer = malloc<Uint8>(length);
+    buffer.asTypedList(length).setAll(0, this);
+
+    return NSData.dataWithBytesNoCopy_length_(buffer.cast(), length);
+  }
+}

pkgs/objective_c/test/nsdata_test.dart

@@ -0,0 +1,88 @@
+// Copyright (c) 2024, 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.
+
+// Objective C support is only available on mac.
+@TestOn('mac-os')
+
+import 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+import 'package:objective_c/objective_c.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('NSData', () {
+    group('toNSData', () {
+      test('empty', () {
+        final data = <int>[].toNSData();
+        expect(data.length, 0);
+        data.release(); // Make sure that dealloc succeeds.
+      });
+
+      test('non empty', () {
+        final data = [1, 2, 3].toNSData();
+        expect(data.length, 3);
+        expect(data.bytes.cast<Uint8>()[0], 1);
+        expect(data.bytes.cast<Uint8>()[1], 2);
+        expect(data.bytes.cast<Uint8>()[2], 3);
+        data.release(); // Make sure that dealloc succeeds.
+      });
+
+      test('non-byte', () {
+        final data = [257].toNSData();
+        expect(data.length, 1);
+        expect(data.bytes.cast<Uint8>().value, 1);
+        data.release(); // Make sure that dealloc succeeds.
+      });
+    });
+
+    group('toList', () {
+      test('empty', () {
+        final data = NSData.data();
+        expect(data.toList(), isEmpty);
+      });
+
+      test('non empty', () {
+        using((arena) {
+          final bytes = arena<Uint8>(3);
+          bytes[0] = 1;
+          bytes[1] = 2;
+          bytes[2] = 3;
+
+          final data = NSData.dataWithBytes_length_(bytes.cast(), 3);
+          expect(data.toList(), [1, 2, 3]);
+        });
+      });
+    });
+
+    group('operator[]', () {
+      test('in bounds', () {
+        using((arena) {
+          final bytes = arena<Uint8>(3);
+          bytes[0] = 1;
+          bytes[1] = 2;
+          bytes[2] = 3;
+
+          final data = NSData.dataWithBytes_length_(bytes.cast(), 3);
+          expect(data[0], 1);
+          expect(data[1], 2);
+          expect(data[2], 3);
+        });
+      });
+
+      test('out of bounds', () {
+        using((arena) {
+          final bytes = arena<Uint8>(3);
+          bytes[0] = 1;
+          bytes[1] = 2;
+          bytes[2] = 3;
+
+          final data = NSData.dataWithBytes_length_(bytes.cast(), 3);
+          expect(() => data[3], throwsRangeError);
+          expect(() => data[-1], throwsRangeError);
+        });
+      });
+    });
+  });
+}