decode_utf_slice.dart

import 'dart:convert';
import 'dart:collection';
import 'dart:typed_data';

main() {
  var str = '12345☺';
  var bytes = UTF8.encode(str);
  print(decodeUtf8Slice(bytes, 5, 3));
  print(decodeUtf8Slice(bytes, 5));
  
  var bytes2 = new Uint8List.fromList(bytes);
  print(decodeUtf8Slice(bytes2, 5, 3));
  print(decodeUtf8Slice(bytes2, 5));
  
  var bytes3 = new Uint8ClampedList.fromList(bytes);
  print(decodeUtf8Slice(bytes3, 5, 3));
  print(decodeUtf8Slice(bytes3, 5));
}

String decodeUtf8Slice(List<int> bytes, int offset, [int length]) {
  
  if (length == null) length = bytes.length - offset;
  
  if (offset < 0 || offset > bytes.length) throw new RangeError(offset);
  
  if (bytes is Uint8List || bytes is Uint8ClampedList) {
    bytes = new Uint8ClampedList.view(bytes.buffer, offset, length);
  } else {
    bytes = new UnmodifiableListView(bytes.skip(offset).take(length));
  }
  
  return UTF8.decode(bytes);
}