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tidy08jul00 dumps core with <elt att"val" ...>

From: Richard A. O'Keefe <ok@atlas.otago.ac.nz>
Date: Wed, 12 Jul 2000 15:32:06 +1200 (NZST)
Message-Id: <200007120332.PAA22151@atlas.otago.ac.nz>
To: html-tidy@w3.org
Someone sent me a web page about the team that programs the space shuttle.
Given that the topic is a group working hard to produce *perfect* code, it
is ironic that this page (NOT produced by that group, needless to say) is
riddled with HTML problems.  I decided to try
	tidy -e writestuff.html
HTML Tidy surprised me by dumping code.  Basically, it's due to the fact
that when Tidy meets <element attribute"value" ... (note the missing = sign)
the attribute value that's returned is not the right value nor yet an empty
string, it is a NULL pointer.  With the libraries I'm using,
vfprintf(fp, "....%s....", (args containing NULL)) dumps core.

Here's a stripped down version of the file that gets Tidy into trouble.

<html>
<head>
<title>They Write the Right Stuff</title>
 <META NAME = "generator" CONTENT = "REFLEX v3.0 Online Publishing System">
</head>
<BODY>
<table>
<tr>
<td width="135" height="74" colspan="2" valign="top">
<P ALIGN="right"><A
href="/cgi-bin/autorespond/recommend.cgi?/online/06/writestuff.html">
Send This Page</A>
<A href="/cgi-bin/autorespond/recommend.cgi?/online/06/writestuff.html">
Adsmart Network ad</A>
</td> 
</tr>
<tr>
<td width="135" height="15" colspan="2" valign="top">&nbsp;</td>
</tr> 
<tr>
<td width"37" height="74" valign="top">transparent gif</td>
<td width"98" height="74" valign="top">javascript muck</td>
</tr> 
</table>
</BODY>
</HTML>    
<P>

No, I'm not kidding about the <P> at the end after the </HTML>.
Note the last two <td> elements.

Here's what Tidy says about this.

f% tidy -e dummy.html

Tidy (vers 8th July 2000) Parsing "dummy.html"
line 8 column 1 - Warning: <table> lacks "summary" attribute
line 22 column 1 - Warning: <td> unknown attribute value "Segmentation Fault
 (core dumped)

This is such really c****y HTML that it's not surprising HTML Tidy hasn't
run into this problem before, but I give you my word it's real HTML, and
it's precisely _because_ it's c****y that I'd like to clean it before
passing it on to someone else (the content is interesting, after all).

While trying to figure out a patch, I noticed that when ParseAttribute()
finds a <, it first checks for <% (asp) or <? (php), and if it found
neither, it reports UNEXPECTED_GT.  Surely it should be LT, not GT?
The message talks about a *missing* GT.

More seriously, since <TAG<TAG> is technically legal SGML if your SGML
declaration allows it, HTML Tidy goes on to complain that the following
element name is an unknown attribute.  Here's an example.

f% cat >dimmy.html
<HTML<HEAD<TITLE>FOO</TITLE>
<BODY<P>BAR</BODY</HTML>
% tidy dimmy.html

Tidy (vers 8th July 2000) Parsing "dimmy.html"
line 1 column 1 - Error: <html> missing '>' for end of tag
line 1 column 1 - Warning: unknown attribute "head"
line 1 column 12 - Warning: inserting missing 'title' element
line 1 column 21 - Warning: discarding unexpected </title>
line 2 column 2 - Warning: unknown attribute "p"
line 2 column 2 - Warning: <body> isn't allowed in <body> elements
...

The bug here is that having read the character (H) after the <,
Tidy needs to push back *two* characters (<H), but only pushes ONE.

While trying to fix this, I discovered that
EndOfInput(lxr) returns feof(lxr->in->file)
which doesn't check for pushed-back characters (it'd be nice if this
called a function inside the tidy.c file where StreamIn is mostly managed).

My patched version of Tidy now reports
Tidy (vers 8th July 2000) Parsing "dimmy.html"
line 1 column 1 - Error: <html> missing '>' for end of tag
line 1 column 7 - Error: <head> missing '>' for end of tag
line 2 column 1 - Error: <body> missing '>' for end of tag







The first part of the problem is that HTML Tidy apparently thinks the
attribute name is width"37", and is flummoxed by seeing "height" when
it expects

Returning to <td width"37", it appears that HTML Tidy is perfectly happy
to include quotation marks as part of attribute names.  Since that's
_never_ legal in SGML or XML, something ought to be done when a quotation
mark turns up in a name.  There's a comment about this in lexer.c:
     /* what should be done about non-namechar characters? */
     /* currently these are incorporated into the attr name */
At least for quotation marks, I suggest that the answer is STOP!

With that and a couple of other patches, my patched copy of Tidy now
reports

Tidy (vers 8th July 2000) Parsing "dummy.html"
line 7 column 1 - Warning: <table> lacks "summary" attribute
line 21 column 1 - Warning: <td> missing '=' before value
line 22 column 1 - Warning: <td> missing '=' before value
line 27 column 1 - Warning: content occurs after end of body
line 28 column 1 - Warning: trimming empty <p>

I needed to touch four files.
Here's the result of sccs diffs html.h localize.c tidy.c lexer.c
------------------------------cut here------------------------------
------- html.h -------
259,260c259,260
<     Bool pushed;
<     int c;
---
>     int pushed;	   /* 0 .. 2 characters may be pushed back */
>     int c[2];	   /* the pushed-back characters */
625a626
> #define MISSING_EQUAL_SIGN      12

------- localize.c -------
229c229
<             lexer->errors++;;
---
>             lexer->errors++;
258a259,264
>         else if (code == MISSING_EQUAL_SIGN)
> 	{
>             tidy_out(lexer->errout, "Warning: ");
>             ReportTag(lexer, node);
>             tidy_out(lexer->errout, " missing '=' before value");
>         }
268c274
<         lexer->errors++;;
---
>         lexer->errors++;

------- tidy.c -------
188,189c188,190
<     in->pushed = no;
<     in->c = '\0';
---
>     in->pushed = 0;
>     in->c[0] = '\0';
>     in->c[1] = '\0';
321,324c322,325
<     if (in->pushed)
<     {
<         in->pushed = no;
<         c =  in->c;
---
>     if (in->pushed != 0) {
>         c = in->c[0];
> 	in->c[0] = in->c[1];
> 	in->pushed--;
405a407,422
> void UngetTwo(int c0, int c1, StreamIn *in)
> {
>     /* This should only be used when two characters have been read */
>     /* so in->pushed should be 0 */
>     assert(in->pushed == 0);
>     in->c[0] = c0;
>     in->c[1] = c1;
>     in->pushed = 2;
> 
>     if (c1 == '\n') --in->curline;
>     if (c0 == '\n') --in->curline;
> 
>     /* Is this right? */
>     in->curcol = in->lastcol;
> }
> 
408,409c425,428
<     in->pushed = yes;
<     in->c = c;
---
>     assert(in->pushed <= 1);
>     in->c[1] = in->c[0];
>     in->c[0] = c;
>     in->pushed++;
411,412c430
<     if (c == '\n')
<         --(in->curline);
---
>     if (c == '\n') --in->curline;

------- lexer.c -------
193c193
<     return  (feof(lexer->in->file));
---
>     return  lexer->in->pushed == 0 && feof(lexer->in->file);
1762c1762
<                 while (c != '>')
---
>                 while (c != '>' && c != '<')
1775c1775,1779
< 
---
>                 if (c == '<')
>                 {
> 		    /* should issue a warning here */
> 		    UngetChar(c, lexer->in);
> 		}
1790c1794
<                     if (c == '/')
---
>                     if (c == '/' || c == '<')
2295c2299
<             UngetChar(c, lexer->in);
---
>             UngetTwo('<', c, lexer->in);
2324c2328,2330
<         if (c == '=' || c == '>')
---
>         if (c == '=' || c == '>'
>          || c == '"' || c == '\''
>          || c == '<' || c == EndOfStream)
2330,2335d2335
<         if (c == '<' || c == EndOfStream)
<         {
<             UngetChar(c, lexer->in);
<             break;
<         }
< 
2463,2468c2463,2474
< /*
<   c should be '=' if there is a value
<   other legal possibilities are white
<   space, '/' and '>'
< */
< 
---
>  /*
>    The only legal possibilities for c are = (when there is a value)
>    or / or > (when there is not).  However, some HTML file omit the
>    = sign, and browsers can appearently cope with that, so when c
>    is a quotation mark, we put it back, complain bitterly, and then
>    pretend we saw an equal sign.
>  */
>     if (c == '"' || c == '\'')
>     {
>         UngetChar(c, lexer->in);
>         ReportAttrError(lexer, lexer->token, null, MISSING_EQUAL_SIGN);
>     } else
2545a2552
> fprintf(stderr, "At < inside ParseValue\n");

------------------------------cut here------------------------------

With those changes, HTML Tidy now gets to the end of writestuff.html
without crashing.  And oh, the c*** it finds along the way!  There's
one problem left:  the output doesn't look anywhere near as good in
a browser as the input.  Oh well...
Received on Tuesday, 11 July 2000 23:32:14 GMT

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