Helpers for null-terminated Utf8

.gitignore

@@ -0,0 +1,3 @@
+.packages
+pubspec.lock
+.dart_tool

lib/ffi.dart

@@ -0,0 +1,7 @@
+// 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.
+
+library ffi;
+
+export 'src/utf8.dart';

lib/src/utf8.dart

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+// 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.
+
+library utf8;
+
+import 'dart:convert';
+import 'dart:ffi';
+import 'dart:typed_data';
+
+/// [Utf8] implements conversion between Dart strings and null-termianted
+/// Utf8-encoded "char*" strings in C.
+class Utf8 extends Struct<Utf8> {
+  static String fromUtf8(Pointer<Utf8> str) {
+    final Pointer<Uint8> array = str.cast();
+    int count = 0x1000;
+    Uint8List string = array.asExternalTypedData(count: count);
+    int i = 0;
+    for (; string[i] != 0; ++i) {
+      if (i == count) {
+        count *= 2;
+        string = array.asExternalTypedData(count: count);
+      }
+    }
+    return Utf8Decoder().convert(Uint8List.view(string.buffer, 0, i));
+  }
+
+  static Pointer<Utf8> toUtf8(String s) {
+    final List<int> units = Utf8Encoder().convert(s);
+    final Pointer<Uint8> result =
+        Pointer<Uint8>.allocate(count: units.length + 1);
+    final Uint8List string =
+        result.asExternalTypedData(count: units.length + 1);
+    string.setAll(0, units);
+    string[units.length] = 0;
+    return result.cast();
+  }
+
+  String toString() => fromUtf8(addressOf);
+}

pubspec.yaml

@@ -12,3 +12,4 @@ dependencies:
 
 dev_dependencies:
   pedantic: ^1.0.0
+  test: ^1.6.8

test/utf8_test.dart

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+// 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 'package:test/test.dart';
+import 'package:ffi/ffi.dart';
+
+main() {
+  test("fromUtf8 . toUtf8 is identity", () {
+    final String start = "Hello World!\n";
+    final String end = Utf8.fromUtf8(Utf8.toUtf8(start));
+    expect(end, equals(start));
+  });
+}