Improve the style of code in lib/.

lib/src/base64/decoder_sink.dart

+// Copyright (c) 2015, 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 crypto.base64.decoder_sink;
+
+import 'dart:convert';
+
+import 'decoder.dart';
+
+/// A [ChunkedConversionSink] for decoding chunks of Base64 strings to data.
+class Base64DecoderSink extends ChunkedConversionSink<String> {
+  /// The encoder used to decode each chunk.
+  final Base64Decoder _decoder = new Base64Decoder();
+
+  /// The underlying sink to which to emit the decoded strings.
+  final ChunkedConversionSink<List<int>> _outSink;
+
+  /// The as-yet-unconverted text.
+  ///
+  /// This is used to handle text stopping partway through a four-character
+  /// 32-bit chunk.
+  String _unconverted = "";
+
+  Base64DecoderSink(this._outSink);
+
+  void add(String chunk) {
+    if (chunk.isEmpty) return;
+    if (_unconverted.isNotEmpty) chunk = _unconverted + chunk;
+    chunk = chunk.replaceAll("%3D", "=");
+
+    // The decodable length is the length of the initial substring comprising
+    // full four-character 32-bit chunks. Any leftovers are handled when [add]
+    // or [close] are next called.
+    var decodableLength = chunk.length;
+    if (chunk.length > 3 && chunk.contains("%", chunk.length - 2)) {
+      decodableLength = chunk.lastIndexOf("%");
+    }
+    decodableLength -= decodableLength % 4;
+
+    _unconverted = chunk.substring(decodableLength);
+    if (decodableLength > 0) {
+      _outSink.add(_decoder.convert(chunk.substring(0, decodableLength)));
+    }
+  }
+
+  void close() {
+    if (_unconverted.isNotEmpty) _outSink.add(_decoder.convert(_unconverted));
+    _outSink.close();
+  }
+}