Make HtmlEscape escape '/' again in UNKNOWN mode.

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;
 
-// TODO(floitsch) - Document - Issue 13097
+/**
+ * A `String` converter that converts characters to HTML entities.
+ *
+ * This is intended to sanitice text before inserting the text into an HTML
+ * document. Characters that are meaningful in HTML are converted to
+ * HTML entities (like `&` for `&`).
+ *
+ * The general converter escapes all characters that are meaningful in HTML
+ * attributes or normal element context. Elements with special content types
+ * (like CSS or JavaScript) may need a more specialized escaping that
+ * understands that content type.
+ *
+ * If the context where the text will be inserted is known in more detail,
+ * it's possible to omit escaping some characters (like quotes when not
+ * inside an attribute value).
+ *
+ * The escaped text should only be used inside quoted HTML attributes values
+ * or as text content of a normal element. Using the escaped text inside a
+ * tag, but not inside a quoted attribute value, is still dangerous.
+ */
 const HtmlEscape HTML_ESCAPE = const HtmlEscape();
 
 /**
  * HTML escape modes.
  *
  * Allows specifying a mode for HTML escaping that depend on the context
  * where the escaped result is going to be used.
  * The relevant contexts are:
  *
  * * as text content of an HTML element.
  * * as value of a (single- or double-) quoted attribute value.
  *
  * All modes require escaping of `&` (ampersand) characters, and may
  * enable escaping of more characters.
  */
 class HtmlEscapeMode {
   final String _name;
   /** Whether to escape '<' and '>'. */
   final bool escapeLtGt;
   /** Whether to escape '"' (quote). */
   final bool escapeQuot;
   /** Whether to escape "'" (apostrophe). */
   final bool escapeApos;
+  /**
+   * Whether to escape "/" (forward slash, solidus).
+   *
+   * Escaping a slash is recommended to avoid cross-site scripting attacks by
+   * [the Open Web Application Security Project](https://www.owasp.org/index.php/XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet#RULE_.231_-_HTML_Escape_Before_Inserting_Untrusted_Data_into_HTML_Element_Content)
+   */
+  final bool escapeSlash;
 
   /**
    * Default escaping mode which escape all characters.
    *
    * The result of such an escaping is usable both in element content and
    * in any attribute value.
    *
    * The escaping only works for elements with normal HTML content,
    * and not for, for example, script or style element content,
    * which require escapes matching their particular content syntax.
    */
   static const HtmlEscapeMode UNKNOWN =
-      const HtmlEscapeMode._('unknown', true, true, true);
+      const HtmlEscapeMode._('unknown', true, true, true, true);
 
   /**
    * Escaping mode for text going into double-quoted HTML attribute values.
    *
    * The result should not be used as the content of an unquoted
    * or single-quoted attribute value.
    *
    * Escapes only double quotes (`"`) but not single quotes (`'`).
    */
   static const HtmlEscapeMode ATTRIBUTE =
-      const HtmlEscapeMode._('attribute', false, true, false);
+      const HtmlEscapeMode._('attribute', false, true, false, false);
 
   /**
    * Escaping mode for text going into single-quoted HTML attribute values.
    *
    * The result should not be used as the content of an unquoted
    * or double-quoted attribute value.
    *
    * Escapes only single quotes (`'`) but not double quotes (`"`).
    */
   static const HtmlEscapeMode SQ_ATTRIBUTE =
-      const HtmlEscapeMode._('attribute', false, false, true);
+      const HtmlEscapeMode._('attribute', false, false, true, false);
 
   /**
    * Escaping mode for text going into HTML element content.
    *
    * The escaping only works for elements with normal HTML content,
    * and not for, for example, script or style element content,
    * which require escapes matching their particular content syntax.
    *
    * Escapes `<` and `>` characters.
    */
   static const HtmlEscapeMode ELEMENT =
-      const HtmlEscapeMode._('element', true, false, false);
+      const HtmlEscapeMode._('element', true, false, false, false);
 
-  const HtmlEscapeMode._(
-      this._name, this.escapeLtGt, this.escapeQuot, this.escapeApos);
+  const HtmlEscapeMode._(this._name,
+                         this.escapeLtGt,
+                         this.escapeQuot,
+                         this.escapeApos,
+                         this.escapeSlash);
 
   /**
    * Create a custom escaping mode.
    *
    * All modes escape `&`.
    * The mode can further be set to escape `<` and `>` ([escapeLtGt]),
-   * `"` ([escapeQuot]) and/or `'` ([escapeApos]).
+   * `"` ([escapeQuot]), `'` ([escapeApos]), and/or `/` ([escapeSlash]).
    */
   const HtmlEscapeMode({String name: "custom",
                         this.escapeLtGt: false,
                         this.escapeQuot: false,
-                        this.escapeApos: false}) : _name = name;
+                        this.escapeApos: false,
+                        this.escapeSlash: false}) : _name = name;
 
   String toString() => _name;
 }
 
 /**
  * Converter which escapes characters with special meaning in HTML.
  *
  * The converter finds characters that are siginificant in HTML source and
  * replaces them with corresponding HTML entities.
  *
  * The characters that need escaping in HTML are:
  *
  * * `&` (ampersand) always need to be escaped.
  * * `<` (less than) and '>' (greater than) when inside an element.
  * * `"` (quote) when inside a double-quoted attribute value.
  * * `'` (apostrophe) when inside a single-quoted attribute value.
  *       Apostrophe is escaped as `&#39;` instead of `&apos;` since
  *       not all browsers understand `&apos;`.
+ * * `/` (slash) is recommended to be escaped because it may be used
+ *       to terminate an element in some HTML dialects.
  *
  * Escaping `>` (greater than) isn't necessary, but the result is often
  * found to be easier to read if greater-than is also escaped whenever
  * less-than is.
  */
 class HtmlEscape extends Converter<String, String> {
 
   /** The [HtmlEscapeMode] used by the converter. */
   final HtmlEscapeMode mode;
 
@@ skipping 22 matching lines @@
     StringBuffer result = null;
     for (int i = start; i < end; i++) {
       var ch = text[i];
       String replacement = null;
       switch (ch) {
         case '&': replacement = '&amp;'; break;
         case '"': if (mode.escapeQuot) replacement = '&quot;'; break;
         case "'": if (mode.escapeApos) replacement = '&#39;'; break;
         case '<': if (mode.escapeLtGt) replacement = '&lt;'; break;
         case '>': if (mode.escapeLtGt) replacement = '&gt;'; break;
+        case '/': if (mode.escapeSlash) replacement = '&#46;'; break;

[Siggi Cherem (dart-lang), 2015/04/15 22:09:52]

should this be / (or like it was before /)?

[Lasse Reichstein Nielsen, 2015/04/16 06:42:21]

Argh. Yes, ofcourse.

       }
       if (replacement != null) {
         if (result == null) result = new StringBuffer();
         if (i > start) result.write(text.substring(start, i));
         result.write(replacement);
         start = i + 1;
       }
     }
     if (result == null) return null;
     if (end > start) result.write(text.substring(start, end));
@@ skipping 19 matching lines @@
     if(val == null) {
       _sink.addSlice(chunk, start, end, isLast);
     } else {
       _sink.add(val);
       if (isLast) _sink.close();
     }
   }
 
   void close() => _sink.close();
 }