Add encoding functionality for int list to string

Author: szakarias

pkg/_pub_shared/lib/format/encoding.dart

@@ -0,0 +1,28 @@
+// 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:convert';
+import 'dart:typed_data';
+
+/// Base64 encodes [dataPoints] as 32-bit unsigned integers serialized with
+/// big endian byte order.
+String encodeIntsAsBigEndianBase64String(List<int> dataPoints) {
+  final byteData = ByteData(4 * dataPoints.length);
+  for (int i = 0; i < dataPoints.length; i++) {
+    byteData.setUint32(4 * i, dataPoints[i]);
+  }
+  return base64Encode(byteData.buffer.asUint8List());
+}
+
+/// Counter part to [encodeIntsAsBigEndianBase64String].
+List<int> decodeIntsFromBigEndianBase64String(String encoded) {
+  final bytes = base64Decode(encoded);
+  final resLength = bytes.length ~/ 4;
+  final dataPoints = List.filled(resLength, -1);
+  final sublist = ByteData.sublistView(bytes);
+  for (int i = 0; i < resLength; i++) {
+    dataPoints[i] = sublist.getUint32(4 * i);
+  }
+  return dataPoints;
+}

pkg/_pub_shared/test/format/encoding_test.dart

@@ -0,0 +1,29 @@
+// 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 'package:_pub_shared/format/encoding.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('encode/decode success', () {
+    final data = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    final encoded = encodeIntsAsBigEndianBase64String(data);
+    expect(encoded, 'AAAAAQAAAAIAAAADAAAABAAAAAUAAAAGAAAABwAAAAgAAAAJ');
+    expect(decodeIntsFromBigEndianBase64String(encoded), data);
+  });
+
+  test('encode/decode empty', () {
+    final data = <int>[];
+    final encoded = encodeIntsAsBigEndianBase64String(data);
+    expect(encoded, '');
+    expect(decodeIntsFromBigEndianBase64String(encoded), data);
+  });
+
+  test('encode/decode failure with negative integers', () {
+    final data = <int>[-1, -2];
+    final encoded = encodeIntsAsBigEndianBase64String(data);
+    expect(encoded, '//////////4=');
+    expect(decodeIntsFromBigEndianBase64String(encoded), isNot(data));
+  });
+}