<?php

# kses 0.2.2 - HTML/XHTML filter that only allows some elements and attributes
# Copyright (C) 2002, 2003, 2005  Ulf Harnhammar
#
# This program is free software and open source software; you can redistribute
# it and/or modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of the License,
# or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA  or visit
# http://www.gnu.org/licenses/gpl.html
#
# *** CONTACT INFORMATION ***
#
# E-mail:      metaur at users dot sourceforge dot net
# Web page:    http://sourceforge.net/projects/kses
# Paper mail:  Ulf Harnhammar
#              Ymergatan 17 C
#              753 25  Uppsala
#              SWEDEN
#
# [kses strips evil scripts!]


function kses($string, $allowed_html, $allowed_protocols =
 							array('http', 'https', 'ftp', 'news', 'nntp', 'telnet',
 										'gopher', 'mailto'))
###############################################################################
# This function makes sure that only the allowed HTML element names, attribute
# names and attribute values plus only sane HTML entities will occur in
# $string. You have to remove any slashes from PHP's magic quotes before you
# call this function.
###############################################################################
{
	$string = kses_no_null($string);
	$string = kses_js_entities($string);
	$string = kses_normalize_entities($string);
	$string = kses_hook($string);
	$allowed_html_fixed = kses_array_lc($allowed_html);
	return kses_split($string, $allowed_html_fixed, $allowed_protocols);
} # function kses


function kses_hook($string)
###############################################################################
# You add any kses hooks here.
###############################################################################
{
	return $string;
} # function kses_hook


function kses_version()
###############################################################################
# This function returns kses' version number.
###############################################################################
{
	return '0.2.2';
} # function kses_version


function kses_split($string, $allowed_html, $allowed_protocols)
###############################################################################
# This function searches for HTML tags, no matter how malformed. It also
# matches stray ">" characters.
###############################################################################
{
	return preg_replace('%(<'.   # EITHER: <
											'[^>]*'. # things that aren't >
											'(>|$)'. # > or end of string
											'|>)%e', # OR: just a >
											"kses_split2('\\1', \$allowed_html, ".
											'$allowed_protocols)',
											$string);
} # function kses_split


function kses_split2($string, $allowed_html, $allowed_protocols)
###############################################################################
# This function does a lot of work. It rejects some very malformed things
# like <:::>. It returns an empty string, if the element isn't allowed (look
# ma, no strip_tags()!). Otherwise it splits the tag into an element and an
# attribute list.
###############################################################################
{
	$string = kses_stripslashes($string);

	if (substr($string, 0, 1) != '<')
		return '&gt;';
		# It matched a ">" character

	if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $string, $matches))
		return '';
		# It's seriously malformed

	$slash = trim($matches[1]);
	$elem = $matches[2];
	$attrlist = $matches[3];

	if (!@isset($allowed_html[strtolower($elem)]))
		return '';
		# They are using a not allowed HTML element

	if ($slash != '')
		return "<$slash$elem>";
	# No attributes are allowed for closing elements

	return kses_attr("$slash$elem", $attrlist, $allowed_html,
 									$allowed_protocols);
} # function kses_split2


function kses_attr($element, $attr, $allowed_html, $allowed_protocols)
###############################################################################
# This function removes all attributes, if none are allowed for this element.
# If some are allowed it calls kses_hair() to split them further, and then it
# builds up new HTML code from the data that kses_hair() returns. It also
# removes "<" and ">" characters, if there are any left. One more thing it
# does is to check if the tag has a closing XHTML slash, and if it does,
# it puts one in the returned code as well.
###############################################################################
{
# Is there a closing XHTML slash at the end of the attributes?

	$xhtml_slash = '';
	if (preg_match('%\s/\s*$%', $attr))
		$xhtml_slash = ' /';

# Are any attributes allowed at all for this element?

	if (@count($allowed_html[strtolower($element)]) == 0)
		return "<$element$xhtml_slash>";

# Split it

	$attrarr = kses_hair($attr, $allowed_protocols);

# Go through $attrarr, and save the allowed attributes for this element
# in $attr2

	$attr2 = '';

	foreach ($attrarr as $arreach)
	{
		if (!@isset($allowed_html[strtolower($element)]
														[strtolower($arreach['name'])]))
			continue; # the attribute is not allowed

		$current = $allowed_html[strtolower($element)]
														[strtolower($arreach['name'])];

		if (!is_array($current))
			$attr2 .= ' '.$arreach['whole'];
		# there are no checks

		else
		{
		# there are some checks
			$ok = true;
			foreach ($current as $currkey => $currval)
				if (!kses_check_attr_val($arreach['value'], $arreach['vless'],
 																$currkey, $currval))
				{ $ok = false; break; }

			if ($ok)
				$attr2 .= ' '.$arreach['whole']; # it passed them
		} # if !is_array($current)
	} # foreach

# Remove any "<" or ">" characters

	$attr2 = preg_replace('/[<>]/', '', $attr2);

	return "<$element$attr2$xhtml_slash>";
} # function kses_attr


function kses_hair($attr, $allowed_protocols)
###############################################################################
# This function does a lot of work. It parses an attribute list into an array
# with attribute data, and tries to do the right thing even if it gets weird
# input. It will add quotes around attribute values that don't have any quotes
# or apostrophes around them, to make it easier to produce HTML code that will
# conform to W3C's HTML specification. It will also remove bad URL protocols
# from attribute values.
###############################################################################
{
	$attrarr = array();
	$mode = 0;
	$attrname = '';

# Loop through the whole attribute list

	while (strlen($attr) != 0)
	{
		$working = 0; # Was the last operation successful?

		switch ($mode)
		{
			case 0: # attribute name, href for instance

				if (preg_match('/^([-a-zA-Z]+)/', $attr, $match))
				{
					$attrname = $match[1];
					$working = $mode = 1;
					$attr = preg_replace('/^[-a-zA-Z]+/', '', $attr);
				}

				break;

			case 1: # equals sign or valueless ("selected")

				if (preg_match('/^\s*=\s*/', $attr)) # equals sign
				{
					$working = 1; $mode = 2;
					$attr = preg_replace('/^\s*=\s*/', '', $attr);
					break;
				}

				if (preg_match('/^\s+/', $attr)) # valueless
				{
					$working = 1; $mode = 0;
					$attrarr[] = array
												('name'  => $attrname,
 												'value' => '',
 												'whole' => $attrname,
 												'vless' => 'y');
					$attr = preg_replace('/^\s+/', '', $attr);
				}

				break;

			case 2: # attribute value, a URL after href= for instance

				if (preg_match('/^"([^"]*)"(\s+|$)/', $attr, $match))
 				# "value"
				{
					$thisval = kses_bad_protocol($match[1], $allowed_protocols);

					$attrarr[] = array
												('name'  => $attrname,
 												'value' => $thisval,
 												'whole' => "$attrname=\"$thisval\"",
 												'vless' => 'n');
					$working = 1; $mode = 0;
					$attr = preg_replace('/^"[^"]*"(\s+|$)/', '', $attr);
					break;
				}

				if (preg_match("/^'([^']*)'(\s+|$)/", $attr, $match))
 				# 'value'
				{
					$thisval = kses_bad_protocol($match[1], $allowed_protocols);

					$attrarr[] = array
												('name'  => $attrname,
 												'value' => $thisval,
 												'whole' => "$attrname='$thisval'",
 												'vless' => 'n');
					$working = 1; $mode = 0;
					$attr = preg_replace("/^'[^']*'(\s+|$)/", '', $attr);
					break;
				}

				if (preg_match("%^([^\s\"']+)(\s+|$)%", $attr, $match))
 				# value
				{
					$thisval = kses_bad_protocol($match[1], $allowed_protocols);

					$attrarr[] = array
												('name'  => $attrname,
 												'value' => $thisval,
 												'whole' => "$attrname=\"$thisval\"",
 												'vless' => 'n');
 												# We add quotes to conform to W3C's HTML spec.
					$working = 1; $mode = 0;
					$attr = preg_replace("%^[^\s\"']+(\s+|$)%", '', $attr);
				}

				break;
		} # switch

		if ($working == 0) # not well formed, remove and try again
		{
			$attr = kses_html_error($attr);
			$mode = 0;
		}
	} # while

	if ($mode == 1)
	# special case, for when the attribute list ends with a valueless
	# attribute like "selected"
		$attrarr[] = array
									('name'  => $attrname,
 									'value' => '',
 									'whole' => $attrname,
 									'vless' => 'y');

	return $attrarr;
} # function kses_hair


function kses_check_attr_val($value, $vless, $checkname, $checkvalue)
###############################################################################
# This function performs different checks for attribute values. The currently
# implemented checks are "maxlen", "minlen", "maxval", "minval" and "valueless"
# with even more checks to come soon.
###############################################################################
{
	$ok = true;

	switch (strtolower($checkname))
	{
		case 'maxlen':
		# The maxlen check makes sure that the attribute value has a length not
		# greater than the given value. This can be used to avoid Buffer Overflows
		# in WWW clients and various Internet servers.

			if (strlen($value) > $checkvalue)
				$ok = false;
			break;

		case 'minlen':
		# The minlen check makes sure that the attribute value has a length not
		# smaller than the given value.

			if (strlen($value) < $checkvalue)
				$ok = false;
			break;

		case 'maxval':
		# The maxval check does two things: it checks that the attribute value is
		# an integer from 0 and up, without an excessive amount of zeroes or
		# whitespace (to avoid Buffer Overflows). It also checks that the attribute
		# value is not greater than the given value.
		# This check can be used to avoid Denial of Service attacks.

			if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
				$ok = false;
			if ($value > $checkvalue)
				$ok = false;
			break;

		case 'minval':
		# The minval check checks that the attribute value is a positive integer,
		# and that it is not smaller than the given value.

			if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
				$ok = false;
			if ($value < $checkvalue)
				$ok = false;
			break;

		case 'valueless':
		# The valueless check checks if the attribute has a value
		# (like <a href="blah">) or not (<option selected>). If the given value
		# is a "y" or a "Y", the attribute must not have a value.
		# If the given value is an "n" or an "N", the attribute must have one.

			if (strtolower($checkvalue) != $vless)
				$ok = false;
			break;
	} # switch

	return $ok;
} # function kses_check_attr_val


function kses_bad_protocol($string, $allowed_protocols)
###############################################################################
# This function removes all non-allowed protocols from the beginning of
# $string. It ignores whitespace and the case of the letters, and it does
# understand HTML entities. It does its work in a while loop, so it won't be
# fooled by a string like "javascript:javascript:alert(57)".
###############################################################################
{
	$string = kses_no_null($string);
	$string = preg_replace('/\xad+/', '', $string); # deals with Opera "feature"
	$string2 = $string.'a';

	while ($string != $string2)
	{
		$string2 = $string;
		$string = kses_bad_protocol_once($string, $allowed_protocols);
	} # while

	return $string;
} # function kses_bad_protocol


function kses_no_null($string)
###############################################################################
# This function removes any NULL characters in $string.
###############################################################################
{
	$string = preg_replace('/\0+/', '', $string);
	$string = preg_replace('/(\\\\0)+/', '', $string);

	return $string;
} # function kses_no_null


function kses_stripslashes($string)
###############################################################################
# This function changes the character sequence  \"  to just  "
# It leaves all other slashes alone. It's really weird, but the quoting from
# preg_replace(//e) seems to require this.
###############################################################################
{
	return preg_replace('%\\\\"%', '"', $string);
} # function kses_stripslashes


function kses_array_lc($inarray)
###############################################################################
# This function goes through an array, and changes the keys to all lower case.
###############################################################################
{
	$outarray = array();

	foreach ($inarray as $inkey => $inval)
	{
		$outkey = strtolower($inkey);
		$outarray[$outkey] = array();

		foreach ($inval as $inkey2 => $inval2)
		{
			$outkey2 = strtolower($inkey2);
			$outarray[$outkey][$outkey2] = $inval2;
		} # foreach $inval
	} # foreach $inarray

	return $outarray;
} # function kses_array_lc


function kses_js_entities($string)
###############################################################################
# This function removes the HTML JavaScript entities found in early versions of
# Netscape 4.
###############################################################################
{
	return preg_replace('%&\s*\{[^}]*(\}\s*;?|$)%', '', $string);
} # function kses_js_entities


function kses_html_error($string)
###############################################################################
# This function deals with parsing errors in kses_hair(). The general plan is
# to remove everything to and including some whitespace, but it deals with
# quotes and apostrophes as well.
###############################################################################
{
	return preg_replace('/^("[^"]*("|$)|\'[^\']*(\'|$)|\S)*\s*/', '', $string);
} # function kses_html_error


function kses_bad_protocol_once($string, $allowed_protocols)
###############################################################################
# This function searches for URL protocols at the beginning of $string, while
# handling whitespace and HTML entities.
###############################################################################
{
	return preg_replace('/^((&[^;]*;|[\sA-Za-z0-9])*)'.
											'(:|&#58;|&#[Xx]3[Aa];)\s*/e',
											'kses_bad_protocol_once2("\\1", $allowed_protocols)',
											$string);
} # function kses_bad_protocol_once


function kses_bad_protocol_once2($string, $allowed_protocols)
###############################################################################
# This function processes URL protocols, checks to see if they're in the white-
# list or not, and returns different data depending on the answer.
###############################################################################
{
	$string2 = kses_decode_entities($string);
	$string2 = preg_replace('/\s/', '', $string2);
	$string2 = kses_no_null($string2);
	$string2 = preg_replace('/\xad+/', '', $string2);
 	# deals with Opera "feature"
	$string2 = strtolower($string2);

	$allowed = false;
	foreach ($allowed_protocols as $one_protocol)
		if (strtolower($one_protocol) == $string2)
		{
			$allowed = true;
			break;
		}

	if ($allowed)
		return "$string2:";
	else
		return '';
} # function kses_bad_protocol_once2


function kses_normalize_entities($string)
###############################################################################
# This function normalizes HTML entities. It will convert "AT&T" to the correct
# "AT&amp;T", "&#00058;" to "&#58;", "&#XYZZY;" to "&amp;#XYZZY;" and so on.
###############################################################################
{
# Disarm all entities by converting & to &amp;

	$string = str_replace('&', '&amp;', $string);

# Change back the allowed entities in our entity whitelist

	$string = preg_replace('/&amp;([A-Za-z][A-Za-z0-9]{0,19});/',
 												'&\\1;', $string);
	$string = preg_replace('/&amp;#0*([0-9]{1,5});/e',
 												'kses_normalize_entities2("\\1")', $string);
	$string = preg_replace('/&amp;#([Xx])0*(([0-9A-Fa-f]{2}){1,2});/',
 												'&#\\1\\2;', $string);

	return $string;
} # function kses_normalize_entities


function kses_normalize_entities2($i)
###############################################################################
# This function helps kses_normalize_entities() to only accept 16 bit values
# and nothing more for &#number; entities.
###############################################################################
{
	return (($i > 65535) ? "&amp;#$i;" : "&#$i;");
} # function kses_normalize_entities2


function kses_decode_entities($string)
###############################################################################
# This function decodes numeric HTML entities (&#65; and &#x41;). It doesn't
# do anything with other entities like &auml;, but we don't need them in the
# URL protocol whitelisting system anyway.
###############################################################################
{
	$string = preg_replace('/&#([0-9]+);/e', 'chr("\\1")', $string);
	$string = preg_replace('/&#[Xx]([0-9A-Fa-f]+);/e', 'chr(hexdec("\\1"))',
 												$string);

	return $string;
} # function kses_decode_entities

?>
