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Bug: LI containing FRAME, FRAMESET, OPTGROUP, or OPTION causes infinite loop in parser.c

From: Randy Waki <rwaki@flipdog.com>
Date: Thu, 10 Aug 2000 21:36:07 -0600
To: <html-tidy@w3.org>, <dsr@w3.org>
Message-ID: <000001c00345$48c4d5e0$51eee13f@rwaki>
The following HTML document causes an infinite loop in both Tidy and
JTidy, 8-Jul-2000 and 4-Aug-2000.  View the document in IE or Netscape
to see how they interpret it.

The middle four li's contain an illegal element, each of which triggers
an infinite loop.  Of course, only the first infinite loop is actually
executed.  To verify that each one causes an infinite loop, delete three
of the four illegal elements; all four variations should loop.

This appears to encompass the problem reported last June by Franco
Crivellari and partially diagnosed by Terry Teague:

   http://lists.w3.org/Archives/Public/html-tidy/2000AprJun/0180.html
   http://lists.w3.org/Archives/Public/html-tidy/2000AprJun/0185.html

I think the following patch to ParseBlock() in parser.c fixes the
problem.  I'm actually working with JTidy so please forgive any
translation errors.  The comments explain what I think is happening.

@@ -713,28 +713,55 @@
         /*
           Allow CM_INLINE elements here.

           Allow CM_BLOCK elements here unless
           lexer->excludeBlocks is yes.

           LI and DD are special cased.

           Otherwise infer end tag for this element.
         */

         if (!(node->tag->model & CM_INLINE))
         {
             if (node->type != StartTag && node->type != StartEndTag)
             {
                 ReportWarning(lexer, element, node, DISCARDING_UNEXPECTED);
                 continue;
             }

+            /*
+             If an LI contains an illegal FRAME, FRAMESET, OPTGROUP, or OPTION
+             start tag, discard the start tag and let the subsequent content get
+             parsed as content of the enclosing LI.  This seems to mimic IE and
+             Netscape, and avoids an infinite loop: without this check,
+             ParseBlock (which is parsing the LI's content) and ParseList (which
+             is parsing the LI's parent's content) repeatedly defer to each
+             other to parse the illegal start tag, each time inferring a missing
+             </li> or <li> respectively.
+
+             NOTE: This check is a bit fragile.  It specifically checks for the
+             four tags that happen to weave their way through the current series
+             of tests performed by ParseBlock and ParseList to trigger the
+             infinite loop.
+            */
+            if (element->tag == tag_li)
+            {
+                if (node->tag == tag_frame ||
+                    node->tag == tag_frameset ||
+                    node->tag == tag_optgroup ||
+                    node->tag == tag_option)
+                {
+                    ReportWarning(lexer, element, node, DISCARDING_UNEXPECTED);
+                    continue;
+                }
+            }
+
             if (element->tag == tag_td || element->tag == tag_th)
             {
                 /* if parent is a table cell, avoid inferring the end of the cell */

                 if (node->tag->model & CM_HEAD)
                 {
                     MoveToHead(lexer, element, node);
                     continue;
                 }

------------------------ Example HTML document -------------------------
<html>
  <head><title>x</title></head>
  <body>
    <ul>
      <li>first item</li>
      <li><frame>frame item</frame></li>
      <li><frameset>frameset item</frameset></li>
      <li><optgroup>optgroup item</optgroup></li>
      <li><option>option item</option></li>
      <li>last item</li>
    </ul>
  </body>
</html>
------------------------------------------------------------------------

Randy
Received on Thursday, 10 August 2000 23:37:42 GMT

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