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find broken HTML tags in string

Posted on 2007-03-22
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Last Modified: 2012-06-27
Is it possible to detect if a  string has broken HTML tags in it?

For example: <p>this is my string with <b>broken</b> HTML tags.  Can</b> i find them?</p>

As you can probably tell, im trying to find and remove broken tags from a string.  I am only concerned about <b></b> tags for now...

please advise?
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Question by:ellandrd
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13 Comments
 
LVL 49

Expert Comment

by:Roonaan
ID: 18770229
Hi Ellandrd,

You might look into the htmltidy library if installed on your server.(http://devzone.zend.com/node/view/id/761)

With some work we should also able to use preg_* functionalities of course.

-r-
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LVL 16

Author Comment

by:ellandrd
ID: 18770258
Ive just found this JavaScript code:

http://www.experts-exchange.com/Web_Development/Web_Languages-Standards/CSS/Q_21038792.html

But im not sure if this will work... as i need something in PHP if possible.
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LVL 16

Author Comment

by:ellandrd
ID: 18770286
after looking into this htmltidy stuff - it looks but i dont have control over the server configuration for this project. - the site is hosted on a paid/shared hosting provider.

however i will install on my own server at home for my own use...

what do you think of that JavaScript code?
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LVL 49

Expert Comment

by:Roonaan
ID: 18770347
Javascript isn't the solution.

In php you could use something like this. (Typed from heart, don't have a php server available at this time)

<?php

// create stack
$stack = array();
// Match an html element
$preg = '/(<[^>]+>)/';
// Break $html on each and every tag
$parts = preg_split($preg, $html, PREG_SPLIT_DELIM_CAPTURE);
$newhtml = '';
// Walk through $parts and maintain the $stack:
foreach($parts as $part) {
   if(substr($part, 0, 2) == '</') {
      // check stack, and remove element from stack if ok
      $partname = getElementName(substr($part, 2));
      $stacksize = count($stack);
      // close all tags that are unclosed
      while($stacksize > 0 && $stack[$stacksize-1] != $partname) {
           $newhtml .= '</'.array_pop($stack).'>';
           $stacksize = count($stack);
      }
      // close the current tag
      if($stacksize > 0 && $stack[$stacksize-1] == $partname) {
           $newhtml .= $part;
           array_pop($stack);
      }
   } elseif(substr($part, 0, 1) == '<') {
      $newhtml .= $part;
      // strip attributes from part, and add element to stack
      $partname = getElementName(substr($part,1));
      array_push($stack, $partname);
    } else {
       $newhtml .= $part;
    }
}

function getElementName($tag) {
  return strtolower(preg_replace('/^(\S+)(.*)$/', '\1', $tag));
}

?>

-r-
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Author Comment

by:ellandrd
ID: 18770589
is $html your string or HTML code?
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LVL 16

Author Comment

by:ellandrd
ID: 18770808
my string that i tested:

<p>this is my <b>bold</b> tag and this is a <b>broken tag</p>

with directly copying and pasting your code and running it, the output i get is this:

<p>this is my bold</b> tag and this is a <b>broken tag</p>
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LVL 16

Author Comment

by:ellandrd
ID: 18770823
when i print the contents of the stack, its empty.  when i print the contents of $parts, i get this:

Array
(
    [0] => this is my
    [1] => bold tag and this is a broken tag
)

Array
(
)

Array
(
)
0
 
LVL 49

Accepted Solution

by:
Roonaan earned 500 total points
ID: 18770976
My preg_split statement was wrong, and the getElementName could use a minor adjustment. Please try going with:

<?php

$html = '<p>this is my <b>bold</b> tag and this is a <b>broken tag</p>';

// create stack
$stack = array();
// Match an html element
$preg = '/(<[^>]+>)/';
// Break $html on each and every tag
$parts = preg_split($preg, $html, 0, PREG_SPLIT_DELIM_CAPTURE);

var_export($parts);

$newhtml = '';
// Walk through $parts and maintain the $stack:
foreach($parts as $part) {
   if(substr($part, 0, 2) == '</') {
      // check stack, and remove element from stack if ok
      $partname = getElementName(substr($part, 2));
      $stacksize = count($stack);
      // close all tags that are unclosed
      while($stacksize > 0 && $stack[$stacksize-1] != $partname) {
           $newhtml .= '</'.array_pop($stack).'>';
           $stacksize = count($stack);
      }
      // close the current tag
      if($stacksize > 0 && $stack[$stacksize-1] == $partname) {
           $newhtml .= $part;
           array_pop($stack);
      }
   } elseif(substr($part, 0, 1) == '<') {
      $newhtml .= $part;
      // strip attributes from part, and add element to stack
      $partname = getElementName(substr($part,1));
      array_push($stack, $partname);
    } else {
       $newhtml .= $part;
    }
}

while(count($stack) > 0) {
  echo '</'.array_pop($stack).'>';
}

echo "\n".$html;
echo "\n".$newhtml;

function getElementName($tag) {
  return strtolower(preg_replace('/^([^\s>]+)(.*)$/', '\1', $tag));
}

?>
0
 
LVL 16

Author Comment

by:ellandrd
ID: 18771194
it works brilliant - thank you so much!!
0
 
LVL 16

Author Comment

by:ellandrd
ID: 18772781
ok ive just noticed a bug.  when testing this earlier all i was using was simple strings like this:

<p>this is my <b>bold</b> tag and this is a <b>broken</p> which came out like:

<p>this is my <b>bold</b> tag and this is a <b>broken</b></p>

but when you test some thing like this:

<p>this is my <b>bold</b> tag and this is a <b>broken tag and not too good at all</p> it comes out like this:

<p>this is my <b>bold</b> tag and this is a <b>broken tag and not too good at all</b></p>
0
 
LVL 16

Author Comment

by:ellandrd
ID: 18772790
when actaully it should look like this:

<p>this is my <b>bold</b> tag and this is a <b>broken</b> tag and not too good at all</p>
0
 
LVL 49

Expert Comment

by:Roonaan
ID: 18777955
How can you be sure that <b> only just span one word always?

-r-
0
 
LVL 16

Author Comment

by:ellandrd
ID: 18778199
good question....

i need to have a rethink about how im going to overcome this...
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