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BUG: Multiple unterminated <meta> tags in <head> block confuse parser.

From: Lee Passey <lee@novonyx.com>
Date: Fri, 12 Oct 2001 12:56:03 -0600
Message-ID: <3BC73CC3.A2D5397B@novonyx.com>
To: "html-tidy@w3.org" <html-tidy@w3.org>
I am trying to tidy one of those bloated MS-Word .htm files.  In the
<head> block there are multiple untermintated <meta> tags, as follows:

<meta http-equiv=Content-Type content="text/html; charset=windows-1252">
<meta name=ProgId content=Word.Document>
<meta name=Generator content="Microsoft Word 9">
<meta name=Originator content="Microsoft Word 9">
<link rel=File-List href="./filelist.xml">
<title>MS Word document</title>
<!--[if gte mso 9]><xml>
... etc.

The August 2000 version of tidy seems to deal with this fine, but my
build based on CVS of about September 25, 2001 prints the error:

line 7 column 73 - Warning: <meta> element not empty or not closed
line 7 column 73 - Warning: inserting missing 'title' element

Walking through the code shows that parsing the meta element (which has
no content) pushes an empty node onto the token stack which then causes
the ParseHead routine to terminate prematurely.

A diff of the two code bases shows that the following line was inserted
into ParseTag() at line 516 of the new parser.c:

        if (node->tag->parser == null)

with the comment:

       Fix by GLP 2000-12-21.  Need to reset insertspace if this 
       is both a non-inline and empty tag (base, link, meta, isindex,
hr, area).

The effect of this "fix" is to cause the routine to call the ParseEmpty
routine to be called for <meta> elements, which prints the "element not
empty or not closed" message (a good thing), and then calls UngetToken()
for the empty text node (a bad thing).  The pushed token then gets
returned on the next call to GetToken(), which causes the ParseHead()
routine to terminate prematurely.

I don't understand (yet) the theory of operation of the parser well
enough to figure out the best solution to this problem.  Commenting out
the UngetToken() call in ParseEmpty() solves the problem, but may have
unforseen effects in other places where it is called.  Commenting out
the "if (node..." statement added in December also solves the problem,
but then we loose the warning message, and reintroduce whatever problem
it was trying to solve.  We could add a ParseMeta() routine which does
not push the empty node and attach it to tag_meta.  Another solution is
to alter ParseHead() so that it does not abort when it encounters a
TextNode (which are not allowed in <head> blocks), but instead ignores
them, perhaps with a warning.

I noticed that the empty text element is a result of parsing the newline
at the end of the <meta> tag, which gets converted to a space.  It gets
converted rather than just ignored because ParseEmpty calls GetToken
with a "MixedContent" mode rather than passing on the mode that was
passed to it, which in this case was "IgnoreWhitespace".  This simple
change may solve the problems (preliminary testing indicates it will)
but again, there may be consequences that I don't foresee.

In a related observation, I note that in the new version many tests that
were "if (mode != IgnoreWhiteSpace)" are now "if (!(mode &
IgnoreWhiteSpace)".  "IgnoreWhiteSpace" is a #define'ed value, not a
variable or enumeration, and is not a bit value; rather it is defined as
0.  Anything AND 0 will be 0, thus the test will always succeed, which I
don't believe is intended.  Apparently, this has had little impact, or
it would have manifested itself in other bugs already, but it ought to
be looked at and fixed, or the test simply removed.

I have entered this into the bug tracker at SourceForge.
Received on Friday, 12 October 2001 14:52:55 UTC

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