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✏️ Editing: ExtractStyleBlocks.php

<?php

// why is this a top level function? Because PHP 5.2.0 doesn't seem to
// understand how to interpret this filter if it's a static method.
// It's all really silly, but if we go this route it might be reasonable
// to coalesce all of these methods into one.
function htmlpurifier_filter_extractstyleblocks_muteerrorhandler()
{
}

/**
 * This filter extracts <style> blocks from input HTML, cleans them up
 * using CSSTidy, and then places them in $purifier->context->get('StyleBlocks')
 * so they can be used elsewhere in the document.
 *
 * @note
 *      See tests/HTMLPurifier/Filter/ExtractStyleBlocksTest.php for
 *      sample usage.
 *
 * @note
 *      This filter can also be used on stylesheets not included in the
 *      document--something purists would probably prefer. Just directly
 *      call HTMLPurifier_Filter_ExtractStyleBlocks->cleanCSS()
 */
class HTMLPurifier_Filter_ExtractStyleBlocks extends HTMLPurifier_Filter
{
    /**
     * @type string
     */
    public $name = 'ExtractStyleBlocks';

/**
     * @type array
     */
    private $_styleMatches = array();

/**
     * @type csstidy
     */
    private $_tidy;

/**
     * @type HTMLPurifier_AttrDef_HTML_ID
     */
    private $_id_attrdef;

/**
     * @type HTMLPurifier_AttrDef_CSS_Ident
     */
    private $_class_attrdef;

/**
     * @type HTMLPurifier_AttrDef_Enum
     */
    private $_enum_attrdef;

public function __construct()
    {
        $this->_tidy = new csstidy();
        $this->_tidy->set_cfg('lowercase_s', false);
        $this->_id_attrdef = new HTMLPurifier_AttrDef_HTML_ID(true);
        $this->_class_attrdef = new HTMLPurifier_AttrDef_CSS_Ident();
        $this->_enum_attrdef = new HTMLPurifier_AttrDef_Enum(
            array(
                'first-child',
                'link',
                'visited',
                'active',
                'hover',
                'focus'
            )
        );
    }

/**
     * Save the contents of CSS blocks to style matches
     * @param array $matches preg_replace style $matches array
     */
    protected function styleCallback($matches)
    {
        $this->_styleMatches[] = $matches[1];
    }

/**
     * Removes inline <style> tags from HTML, saves them for later use
     * @param string $html
     * @param HTMLPurifier_Config $config
     * @param HTMLPurifier_Context $context
     * @return string
     * @todo Extend to indicate non-text/css style blocks
     */
    public function preFilter($html, $config, $context)
    {
        $tidy = $config->get('Filter.ExtractStyleBlocks.TidyImpl');
        if ($tidy !== null) {
            $this->_tidy = $tidy;
        }
        // NB: this must be NON-greedy because if we have
        // <style>foo</style>  <style>bar</style>
        // we must not grab foo</style>  <style>bar
        $html = preg_replace_callback('#<style(?:\s.*)?>(.*)<\/style>#isU', array($this, 'styleCallback'), $html);
        $style_blocks = $this->_styleMatches;
        $this->_styleMatches = array(); // reset
        $context->register('StyleBlocks', $style_blocks); // $context must not be reused
        if ($this->_tidy) {
            foreach ($style_blocks as &$style) {
                $style = $this->cleanCSS($style, $config, $context);
            }
        }
        return $html;
    }

/**
     * Takes CSS (the stuff found in <style>) and cleans it.
     * @warning Requires CSSTidy <http://csstidy.sourceforge.net/>
     * @param string $css CSS styling to clean
     * @param HTMLPurifier_Config $config
     * @param HTMLPurifier_Context $context
     * @throws HTMLPurifier_Exception
     * @return string Cleaned CSS
     */
    public function cleanCSS($css, $config, $context)
    {
        // prepare scope
        $scope = $config->get('Filter.ExtractStyleBlocks.Scope');
        if ($scope !== null) {
            $scopes = array_map('trim', explode(',', $scope));
        } else {
            $scopes = array();
        }
        // remove comments from CSS
        $css = trim($css);
        if (strncmp('') {
            $css = substr($css, 0, -3);
        }
        $css = trim($css);
        set_error_handler('htmlpurifier_filter_extractstyleblocks_muteerrorhandler');
        $this->_tidy->parse($css);
        restore_error_handler();
        $css_definition = $config->getDefinition('CSS');
        $html_definition = $config->getDefinition('HTML');
        $new_css = array();
        foreach ($this->_tidy->css as $k => $decls) {
            // $decls are all CSS declarations inside an @ selector
            $new_decls = array();
            if (is_array($decls)) {
                foreach ($decls as $selector => $style) {
                    $selector = trim($selector);
                    if ($selector === '') {
                        continue;
                    } // should not happen
                    // Parse the selector
                    // Here is the relevant part of the CSS grammar:
                    //
                    // ruleset
                    //   : selector [ ',' S* selector ]* '{' ...
                    // selector
                    //   : simple_selector [ combinator selector | S+ [ combinator? selector ]? ]?
                    // combinator
                    //   : '+' S*
                    //   : '>' S*
                    // simple_selector
                    //   : element_name [ HASH | class | attrib | pseudo ]*
                    //   | [ HASH | class | attrib | pseudo ]+
                    // element_name
                    //   : IDENT | '*'
                    //   ;
                    // class
                    //   : '.' IDENT
                    //   ;
                    // attrib
                    //   : '[' S* IDENT S* [ [ '=' | INCLUDES | DASHMATCH ] S*
                    //     [ IDENT | STRING ] S* ]? ']'
                    //   ;
                    // pseudo
                    //   : ':' [ IDENT | FUNCTION S* [IDENT S*]? ')' ]
                    //   ;
                    //
                    // For reference, here are the relevant tokens:
                    //
                    // HASH         #{name}
                    // IDENT        {ident}
                    // INCLUDES     ==
                    // DASHMATCH    |=
                    // STRING       {string}
                    // FUNCTION     {ident}\(
                    //
                    // And the lexical scanner tokens
                    //
                    // name         {nmchar}+
                    // nmchar       [_a-z0-9-]|{nonascii}|{escape}
                    // nonascii     [\240-\377]
                    // escape       {unicode}|\\[^\r\n\f0-9a-f]
                    // unicode      \\{h}}{1,6}(\r\n|[ \t\r\n\f])?
                    // ident        -?{nmstart}{nmchar*}
                    // nmstart      [_a-z]|{nonascii}|{escape}
                    // string       {string1}|{string2}
                    // string1      \"([^\n\r\f\\"]|\\{nl}|{escape})*\"
                    // string2      \'([^\n\r\f\\"]|\\{nl}|{escape})*\'
                    //
                    // We'll implement a subset (in order to reduce attack
                    // surface); in particular:
                    //
                    //      - No Unicode support
                    //      - No escapes support
                    //      - No string support (by proxy no attrib support)
                    //      - element_name is matched against allowed
                    //        elements (some people might find this
                    //        annoying...)
                    //      - Pseudo-elements one of :first-child, :link,
                    //        :visited, :active, :hover, :focus

// handle ruleset
                    $selectors = array_map('trim', explode(',', $selector));
                    $new_selectors = array();
                    foreach ($selectors as $sel) {
                        // split on +, > and spaces
                        $basic_selectors = preg_split('/\s*([+> ])\s*/', $sel, -1, PREG_SPLIT_DELIM_CAPTURE);
                        // even indices are chunks, odd indices are
                        // delimiters
                        $nsel = null;
                        $delim = null; // guaranteed to be non-null after
                        // two loop iterations
                        for ($i = 0, $c = count($basic_selectors); $i < $c; $i++) {
                            $x = $basic_selectors[$i];
                            if ($i % 2) {
                                // delimiter
                                if ($x === ' ') {
                                    $delim = ' ';
                                } else {
                                    $delim = ' ' . $x . ' ';
                                }
                            } else {
                                // simple selector
                                $components = preg_split('/([#.:])/', $x, -1, PREG_SPLIT_DELIM_CAPTURE);
                                $sdelim = null;
                                $nx = null;
                                for ($j = 0, $cc = count($components); $j < $cc; $j++) {
                                    $y = $components[$j];
                                    if ($j === 0) {
                                        if ($y === '*' || isset($html_definition->info[$y = strtolower($y)])) {
                                            $nx = $y;
                                        } else {
                                            // $nx stays null; this matters
                                            // if we don't manage to find
                                            // any valid selector content,
                                            // in which case we ignore the
                                            // outer $delim
                                        }
                                    } elseif ($j % 2) {
                                        // set delimiter
                                        $sdelim = $y;
                                    } else {
                                        $attrdef = null;
                                        if ($sdelim === '#') {
                                            $attrdef = $this->_id_attrdef;
                                        } elseif ($sdelim === '.') {
                                            $attrdef = $this->_class_attrdef;
                                        } elseif ($sdelim === ':') {
                                            $attrdef = $this->_enum_attrdef;
                                        } else {
                                            throw new HTMLPurifier_Exception('broken invariant sdelim and preg_split');
                                        }
                                        $r = $attrdef->validate($y, $config, $context);
                                        if ($r !== false) {
                                            if ($r !== true) {
                                                $y = $r;
                                            }
                                            if ($nx === null) {
                                                $nx = '';
                                            }
                                            $nx .= $sdelim . $y;
                                        }
                                    }
                                }
                                if ($nx !== null) {
                                    if ($nsel === null) {
                                        $nsel = $nx;
                                    } else {
                                        $nsel .= $delim . $nx;
                                    }
                                } else {
                                    // delimiters to the left of invalid
                                    // basic selector ignored
                                }
                            }
                        }
                        if ($nsel !== null) {
                            if (!empty($scopes)) {
                                foreach ($scopes as $s) {
                                    $new_selectors[] = "$s $nsel";
                                }
                            } else {
                                $new_selectors[] = $nsel;
                            }
                        }
                    }
                    if (empty($new_selectors)) {
                        continue;
                    }
                    $selector = implode(', ', $new_selectors);
                    foreach ($style as $name => $value) {
                        if (!isset($css_definition->info[$name])) {
                            unset($style[$name]);
                            continue;
                        }
                        $def = $css_definition->info[$name];
                        $ret = $def->validate($value, $config, $context);
                        if ($ret === false) {
                            unset($style[$name]);
                        } else {
                            $style[$name] = $ret;
                        }
                    }
                    $new_decls[$selector] = $style;
                }
            } else {
                continue;
            }
            $new_css[$k] = $new_decls;
        }
        // remove stuff that shouldn't be used, could be reenabled
        // after security risks are analyzed
        $this->_tidy->css = $new_css;
        $this->_tidy->import = array();
        $this->_tidy->charset = null;
        $this->_tidy->namespace = null;
        $css = $this->_tidy->print->plain();
        // we are going to escape any special characters <>& to ensure
        // that no funny business occurs (i.e. </style> in a font-family prop).
        if ($config->get('Filter.ExtractStyleBlocks.Escaping')) {
            $css = str_replace(
                array('<', '>', '&'),
                array('\3C ', '\3E ', '\26 '),
                $css
            );
        }
        return $css;
    }
}

// vim: et sw=4 sts=4

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