Replace string uses with code units in Json parser.

samples/buildbot/json.dart

Index: samples/buildbot/json.dart
diff --git a/samples/buildbot/json.dart b/samples/buildbot/json.dart
index 68b4ee4f0290f1e7158e902d1e0b8fe62a3154ec..b02a008b5b0bc48c661578086003243f45a08aa0 100644
--- a/samples/buildbot/json.dart
+++ b/samples/buildbot/json.dart
@@ -19,10 +19,8 @@ dynamic getJson(String host, String resource) {
 }
 
 class JsonParser {
-  int _index = 0;
+  int _offset = 0;
   String _json;
-  String _whitespaceUnits = ' \t\n';
-  String _delimiterUnits = ' \t\n,[]{}';
 
   JsonParser(this._json);
 
@@ -31,37 +29,38 @@ class JsonParser {
     var result = _parseValue();
     _whitespace();
     if (_hasCurrent) {
-      throw "Parse failed to consume: ${_json.substring(_index)}";
+      throw "Parse failed to consume: ${_json.substring(_offset)}";
     }
     return result;
   }
 
-  int get _currentUnit => _json.codeUnitAt(_index);
-  String get _current => _json[_index];
-  bool get _hasCurrent => _index < _json.length;
+  bool get _hasCurrent => _offset < _json.length;
+  int get _current => _json.codeUnitAt(_offset);
+  String get _currentChar => _json[_offset];
+  void _consume() { ++_offset; }
 
-  bool _containsCurrent(String units) {
-    int length = units.length;
-    int unit = _currentUnit;
-    for (int i = 0; i < length; ++i) {
-      if (unit == units.codeUnitAt(i)) return true;
-    }
-    return false;
+  void _whitespace() {
+    while (_hasCurrent && _isWhitespace(_current)) _consume();
   }
 
-  void _whitespace() {
-    while (_hasCurrent && _containsCurrent(_whitespaceUnits)) ++_index;
+  bool _optional(int char) {
+    if (_current == char) {
+      _consume();
+      return true;
+    }
+    return false;
   }
 
-  void _parseToken(String token) {
-    if (!_tryParseToken(token)) {
-      throw "Expected $token at index $_index, found $_current";
+  void _expect(int char) {
+    if (!_optional(char)) {
+      String string = new String.fromCharCodes([char]);
+      throw "Expected $string at index $_offset, found $_currentChar";
     }
   }
 
   bool _tryParseToken(String token) {
     int length = token.length;
-    int start = _index;
+    int start = _offset;
     int end = start + length;
     if (end > _json.length) return false;
     for (int i = 0; i < length; ++i) {
@@ -69,69 +68,107 @@ class JsonParser {
         return false;
       }
     }
-    _index += length;
+    _offset += length;
     return true;
   }
 
-  bool get _isDelimiter => _containsCurrent(_delimiterUnits);
-
   String _readToken() {
-    int start = _index;
-    while (_hasCurrent && !_isDelimiter) ++_index;
-    return _json.substring(start, _index);
+    int start = _offset;
+    while (_hasCurrent && !_isSeparator(_current)) _consume();
+    return _json.substring(start, _offset);
   }
 
   dynamic _parseValue() {
     _whitespace();
-    if (_tryParseToken('{')) return _parseMap();
-    if (_tryParseToken('[')) return _parseList();
-    if (_tryParseToken('"')) return _parseString();
-    if (_tryParseToken('true')) return true;
-    if (_tryParseToken('false')) return false;
-    if (_tryParseToken('null')) return null;
-
-    int tryIndex = _index;
+    if (_optional(_CHAR_BRACE_OPEN)) return _parseMap();
+    if (_optional(_CHAR_SQUARE_OPEN)) return _parseList();
+    if (_optional(_CHAR_DOUBLE_QUOTE)) return _parseString();
+    if (_tryParseToken(_TOKEN_TRUE)) return true;
+    if (_tryParseToken(_TOKEN_FALSE)) return false;
+    if (_tryParseToken(_TOKEN_NULL)) return null;
+
+    int start = _offset;
     String token = _readToken();
     bool error = false;
     // TODO(zerny) floating point numbers.
     int tryInt = int.parse(token, onError: (_) { error = true; return 0; });
     if (!error) return tryInt;
 
-    String context = _json.substring(tryIndex, _min(tryIndex + 10, _json.length));
-    throw "Parse failed at index: $_index (context: '$context...')";
+    String context = _json.substring(start, _min(start + 10, _json.length));
+    throw "Parse failed at index: $_offset (context: '$context...')";
   }
 
   Map _parseMap() {
     Map map = new Map();
     _whitespace();
-    while (!_tryParseToken('}')) {
-      var key = _parseValue();
-      _whitespace();
-      _parseToken(':');
-      var value = _parseValue();
-      map[key] = value;
-      _whitespace();
-      _tryParseToken(',');
-      _whitespace();
+    if (_current != _CHAR_BRACE_CLOSE) {
+      do {
+        var key = _parseValue();
+        _whitespace();
+        _expect(_CHAR_COLON);
+        var value = _parseValue();
+        map[key] = value;
+        _whitespace();
+      } while (_optional(_CHAR_COMMA));
     }
+    _expect(_CHAR_BRACE_CLOSE);
     return map;
   }
 
   List _parseList() {
     List list = new List();
     _whitespace();
-    while (!_tryParseToken(']')) {
-      list.add(_parseValue());
-      _whitespace();
-      _tryParseToken(',');
-      _whitespace();
+    if (_current != _CHAR_SQUARE_CLOSE) {
+      do {
+        list.add(_parseValue());
+        _whitespace();
+      } while (_optional(_CHAR_COMMA));
     }
+    _expect(_CHAR_SQUARE_CLOSE);
     return list;
   }
 
   String _parseString() {
-    int start = _index;
-    while (_hasCurrent && _current != '"') ++_index;
-    return _json.substring(start, _index++);
+    int start = _offset;
+    while (_hasCurrent && _current != _CHAR_DOUBLE_QUOTE) {
+      if (_current == _CHAR_BACKSLASH) _consume();
+      _consume();
+    }
+    _expect(_CHAR_DOUBLE_QUOTE);
+    return _json.substring(start, _offset - 1);
   }
+
+  static bool _isWhitespace(int char) =>
+    char == _CHAR_TAB ||
+    char == _CHAR_LINE_FEED ||
+    char == _CHAR_SPACE;
+
+  static bool _isSeparator(int char) =>
+    _isWhitespace(char) ||
+    char == _CHAR_PAREN_OPEN ||
+    char == _CHAR_PAREN_CLOSE ||
+    char == _CHAR_COMMA ||
+    char == _CHAR_COLON ||
+    char == _CHAR_SQUARE_OPEN ||
+    char == _CHAR_SQUARE_CLOSE ||
+    char == _CHAR_BRACE_OPEN ||
+    char == _CHAR_BRACE_CLOSE;
+
+  static const String _TOKEN_TRUE = 'true';
+  static const String _TOKEN_FALSE = 'false';
+  static const String _TOKEN_NULL = 'null';
+
+  static const int _CHAR_TAB = 9;
+  static const int _CHAR_LINE_FEED = 10;
+  static const int _CHAR_SPACE = 32;
+  static const int _CHAR_DOUBLE_QUOTE = 34;
+  static const int _CHAR_PAREN_OPEN = 40;
+  static const int _CHAR_PAREN_CLOSE = 41;
+  static const int _CHAR_COMMA = 44;
+  static const int _CHAR_COLON = 58;
+  static const int _CHAR_SQUARE_OPEN = 91;
+  static const int _CHAR_BACKSLASH = 92;
+  static const int _CHAR_SQUARE_CLOSE = 93;
+  static const int _CHAR_BRACE_OPEN = 123;
+  static const int _CHAR_BRACE_CLOSE = 125;
 }