adding HtmlEscape to dart:convert

sdk/lib/convert/html_escape.dart

+// Copyright (c) 2013, 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.
+
+part of dart.convert;
+
+const HTML_ESCAPE = const HtmlEscape();
+
+class HtmlEscapeMode {
+  final String _name;
+  final bool escapeLtGt;
+  final bool escapeQuot;
+  final bool escapeApos;
+
+  static const HtmlEscapeMode UNKNOWN =
+    const HtmlEscapeMode._('unknown', true, true, true);
+
+  static const HtmlEscapeMode ATTRIBUTE =
+    const HtmlEscapeMode._('attribute', false, true, false);
+
+  static const HtmlEscapeMode ELEMENT =
+    const HtmlEscapeMode._('element', true, false, false);
+
+  const HtmlEscapeMode._(this._name, this.escapeLtGt, this.escapeQuot,
+    this.escapeApos);
+
+  String toString() => _name;
+}
+
+class HtmlEscape extends Converter<String, String> {
+  final HtmlEscapeMode mode;
+
+  const HtmlEscape([this.mode = HtmlEscapeMode.UNKNOWN]);
+
+  String convert(String text) {
+    StringBuffer result = null;
+    for (int i = 0; i < text.length; i++) {
+      var ch = text[i];

[floitsch, 2013/08/30 15:52:00]

Nit: we usually type everything in the dart: libraries.

Use codeUnitAt instead of operator[]. It avoids allocating a new string. (You
will have to introduce a few constants for the characters that need to be
escaped below. Ex:
const _AMPERSAND = 0x26;

[Jennifer Messerly, 2013/08/30 18:13:59]

it is a shame styles in different parts of the code have diverged.
should we update:
https://www.dartlang.org/articles/style-guide/#prefer-using-var-without-a-typ...
?

+      String replace = null;
+      switch (ch) {
+        case '&': replace = '&'; break;
+        case '\u00A0'/*NO-BREAK SPACE*/: replace = ' '; break;
+        case '"': if (mode.escapeQuot) replace = '"'; break;
+        case "'": if (mode.escapeApos) replace = '''; break;
+        case '<': if (mode.escapeLtGt) replace = '&lt;'; break;
+        case '>': if (mode.escapeLtGt) replace = '&gt;'; break;
+      }
+      if (replace != null) {
+        if (result == null) result = new StringBuffer(text.substring(0, i));
+        result.write(replace);
+      } else if (result != null) {
+        result.write(ch);
+      }
+    }
+
+    return result != null ? result.toString() : text;
+  }
+
+  StringConversionSink startChunkedConversion(
+    ChunkedConversionSink<String> sink) {
+
+    if (sink is! StringConversionSink) {
+      sink = new StringConversionSink.from(sink);
+    }
+    return new _HtmlEscapeSink(this, sink);
+  }
+}
+
+class _HtmlEscapeSink extends StringConversionSinkBase {
+  final HtmlEscape _escape;
+  final StringConversionSink _sink;
+
+  _HtmlEscapeSink(this._escape, this._sink);
+
+  void addSlice(String chunk, int start, int end, bool isLast) {
+    _sink.add(_escape.convert(chunk.substring(start, end)));

[floitsch, 2013/08/30 15:52:00]

Add:
 TODO(floitsch): Optimize.

[kevmoo-old, 2013/09/05 20:30:06]

Does the last change handle your request to optimize?
https://codereview.chromium.org/23492002/diff2/39001:42001/sdk/lib/convert/ht...

+    if (isLast) _sink.close();
+  }
+
+  void close() => _sink.close();
+}