1<?php
2
3// why is this a top level function? Because PHP 5.2.0 doesn't seem to
4// understand how to interpret this filter if it's a static method.
5// It's all really silly, but if we go this route it might be reasonable
6// to coalesce all of these methods into one.
7function htmlpurifier_filter_extractstyleblocks_muteerrorhandler()
8{
9}
10
11/**
12 * This filter extracts <style> blocks from input HTML, cleans them up
13 * using CSSTidy, and then places them in $purifier->context->get('StyleBlocks')
14 * so they can be used elsewhere in the document.
15 *
16 * @note
17 *      See tests/HTMLPurifier/Filter/ExtractStyleBlocksTest.php for
18 *      sample usage.
19 *
20 * @note
21 *      This filter can also be used on stylesheets not included in the
22 *      document--something purists would probably prefer. Just directly
23 *      call HTMLPurifier_Filter_ExtractStyleBlocks->cleanCSS()
24 */
25class HTMLPurifier_Filter_ExtractStyleBlocks extends HTMLPurifier_Filter
26{
27    /**
28     * @type string
29     */
30    public $name = 'ExtractStyleBlocks';
31
32    /**
33     * @type array
34     */
35    private $_styleMatches = array();
36
37    /**
38     * @type csstidy
39     */
40    private $_tidy;
41
42    /**
43     * @type HTMLPurifier_AttrDef_HTML_ID
44     */
45    private $_id_attrdef;
46
47    /**
48     * @type HTMLPurifier_AttrDef_CSS_Ident
49     */
50    private $_class_attrdef;
51
52    /**
53     * @type HTMLPurifier_AttrDef_Enum
54     */
55    private $_enum_attrdef;
56
57    public function __construct()
58    {
59        $this->_tidy = new csstidy();
60        $this->_tidy->set_cfg('lowercase_s', false);
61        $this->_id_attrdef = new HTMLPurifier_AttrDef_HTML_ID(true);
62        $this->_class_attrdef = new HTMLPurifier_AttrDef_CSS_Ident();
63        $this->_enum_attrdef = new HTMLPurifier_AttrDef_Enum(
64            array(
65                'first-child',
66                'link',
67                'visited',
68                'active',
69                'hover',
70                'focus'
71            )
72        );
73    }
74
75    /**
76     * Save the contents of CSS blocks to style matches
77     * @param array $matches preg_replace style $matches array
78     */
79    protected function styleCallback($matches)
80    {
81        $this->_styleMatches[] = $matches[1];
82    }
83
84    /**
85     * Removes inline <style> tags from HTML, saves them for later use
86     * @param string $html
87     * @param HTMLPurifier_Config $config
88     * @param HTMLPurifier_Context $context
89     * @return string
90     * @todo Extend to indicate non-text/css style blocks
91     */
92    public function preFilter($html, $config, $context)
93    {
94        $tidy = $config->get('Filter.ExtractStyleBlocks.TidyImpl');
95        if ($tidy !== null) {
96            $this->_tidy = $tidy;
97        }
98        // NB: this must be NON-greedy because if we have
99        // <style>foo</style>  <style>bar</style>
100        // we must not grab foo</style>  <style>bar
101        $html = preg_replace_callback('#<style(?:\s.*)?>(.*)<\/style>#isU', array($this, 'styleCallback'), $html);
102        $style_blocks = $this->_styleMatches;
103        $this->_styleMatches = array(); // reset
104        $context->register('StyleBlocks', $style_blocks); // $context must not be reused
105        if ($this->_tidy) {
106            foreach ($style_blocks as &$style) {
107                $style = $this->cleanCSS($style, $config, $context);
108            }
109        }
110        return $html;
111    }
112
113    /**
114     * Takes CSS (the stuff found in <style>) and cleans it.
115     * @warning Requires CSSTidy <http://csstidy.sourceforge.net/>
116     * @param string $css CSS styling to clean
117     * @param HTMLPurifier_Config $config
118     * @param HTMLPurifier_Context $context
119     * @throws HTMLPurifier_Exception
120     * @return string Cleaned CSS
121     */
122    public function cleanCSS($css, $config, $context)
123    {
124        // prepare scope
125        $scope = $config->get('Filter.ExtractStyleBlocks.Scope');
126        if ($scope !== null) {
127            $scopes = array_map('trim', explode(',', $scope));
128        } else {
129            $scopes = array();
130        }
131        // remove comments from CSS
132        $css = trim($css);
133        if (strncmp('<!--', $css, 4) === 0) {
134            $css = substr($css, 4);
135        }
136        if (strlen($css) > 3 && substr($css, -3) == '-->') {
137            $css = substr($css, 0, -3);
138        }
139        $css = trim($css);
140        set_error_handler('htmlpurifier_filter_extractstyleblocks_muteerrorhandler');
141        $this->_tidy->parse($css);
142        restore_error_handler();
143        $css_definition = $config->getDefinition('CSS');
144        $html_definition = $config->getDefinition('HTML');
145        $new_css = array();
146        foreach ($this->_tidy->css as $k => $decls) {
147            // $decls are all CSS declarations inside an @ selector
148            $new_decls = array();
149            foreach ($decls as $selector => $style) {
150                $selector = trim($selector);
151                if ($selector === '') {
152                    continue;
153                } // should not happen
154                // Parse the selector
155                // Here is the relevant part of the CSS grammar:
156                //
157                // ruleset
158                //   : selector [ ',' S* selector ]* '{' ...
159                // selector
160                //   : simple_selector [ combinator selector | S+ [ combinator? selector ]? ]?
161                // combinator
162                //   : '+' S*
163                //   : '>' S*
164                // simple_selector
165                //   : element_name [ HASH | class | attrib | pseudo ]*
166                //   | [ HASH | class | attrib | pseudo ]+
167                // element_name
168                //   : IDENT | '*'
169                //   ;
170                // class
171                //   : '.' IDENT
172                //   ;
173                // attrib
174                //   : '[' S* IDENT S* [ [ '=' | INCLUDES | DASHMATCH ] S*
175                //     [ IDENT | STRING ] S* ]? ']'
176                //   ;
177                // pseudo
178                //   : ':' [ IDENT | FUNCTION S* [IDENT S*]? ')' ]
179                //   ;
180                //
181                // For reference, here are the relevant tokens:
182                //
183                // HASH         #{name}
184                // IDENT        {ident}
185                // INCLUDES     ==
186                // DASHMATCH    |=
187                // STRING       {string}
188                // FUNCTION     {ident}\(
189                //
190                // And the lexical scanner tokens
191                //
192                // name         {nmchar}+
193                // nmchar       [_a-z0-9-]|{nonascii}|{escape}
194                // nonascii     [\240-\377]
195                // escape       {unicode}|\\[^\r\n\f0-9a-f]
196                // unicode      \\{h}}{1,6}(\r\n|[ \t\r\n\f])?
197                // ident        -?{nmstart}{nmchar*}
198                // nmstart      [_a-z]|{nonascii}|{escape}
199                // string       {string1}|{string2}
200                // string1      \"([^\n\r\f\\"]|\\{nl}|{escape})*\"
201                // string2      \'([^\n\r\f\\"]|\\{nl}|{escape})*\'
202                //
203                // We'll implement a subset (in order to reduce attack
204                // surface); in particular:
205                //
206                //      - No Unicode support
207                //      - No escapes support
208                //      - No string support (by proxy no attrib support)
209                //      - element_name is matched against allowed
210                //        elements (some people might find this
211                //        annoying...)
212                //      - Pseudo-elements one of :first-child, :link,
213                //        :visited, :active, :hover, :focus
214
215                // handle ruleset
216                $selectors = array_map('trim', explode(',', $selector));
217                $new_selectors = array();
218                foreach ($selectors as $sel) {
219                    // split on +, > and spaces
220                    $basic_selectors = preg_split('/\s*([+> ])\s*/', $sel, -1, PREG_SPLIT_DELIM_CAPTURE);
221                    // even indices are chunks, odd indices are
222                    // delimiters
223                    $nsel = null;
224                    $delim = null; // guaranteed to be non-null after
225                    // two loop iterations
226                    for ($i = 0, $c = count($basic_selectors); $i < $c; $i++) {
227                        $x = $basic_selectors[$i];
228                        if ($i % 2) {
229                            // delimiter
230                            if ($x === ' ') {
231                                $delim = ' ';
232                            } else {
233                                $delim = ' ' . $x . ' ';
234                            }
235                        } else {
236                            // simple selector
237                            $components = preg_split('/([#.:])/', $x, -1, PREG_SPLIT_DELIM_CAPTURE);
238                            $sdelim = null;
239                            $nx = null;
240                            for ($j = 0, $cc = count($components); $j < $cc; $j++) {
241                                $y = $components[$j];
242                                if ($j === 0) {
243                                    if ($y === '*' || isset($html_definition->info[$y = strtolower($y)])) {
244                                        $nx = $y;
245                                    } else {
246                                        // $nx stays null; this matters
247                                        // if we don't manage to find
248                                        // any valid selector content,
249                                        // in which case we ignore the
250                                        // outer $delim
251                                    }
252                                } elseif ($j % 2) {
253                                    // set delimiter
254                                    $sdelim = $y;
255                                } else {
256                                    $attrdef = null;
257                                    if ($sdelim === '#') {
258                                        $attrdef = $this->_id_attrdef;
259                                    } elseif ($sdelim === '.') {
260                                        $attrdef = $this->_class_attrdef;
261                                    } elseif ($sdelim === ':') {
262                                        $attrdef = $this->_enum_attrdef;
263                                    } else {
264                                        throw new HTMLPurifier_Exception('broken invariant sdelim and preg_split');
265                                    }
266                                    $r = $attrdef->validate($y, $config, $context);
267                                    if ($r !== false) {
268                                        if ($r !== true) {
269                                            $y = $r;
270                                        }
271                                        if ($nx === null) {
272                                            $nx = '';
273                                        }
274                                        $nx .= $sdelim . $y;
275                                    }
276                                }
277                            }
278                            if ($nx !== null) {
279                                if ($nsel === null) {
280                                    $nsel = $nx;
281                                } else {
282                                    $nsel .= $delim . $nx;
283                                }
284                            } else {
285                                // delimiters to the left of invalid
286                                // basic selector ignored
287                            }
288                        }
289                    }
290                    if ($nsel !== null) {
291                        if (!empty($scopes)) {
292                            foreach ($scopes as $s) {
293                                $new_selectors[] = "$s $nsel";
294                            }
295                        } else {
296                            $new_selectors[] = $nsel;
297                        }
298                    }
299                }
300                if (empty($new_selectors)) {
301                    continue;
302                }
303                $selector = implode(', ', $new_selectors);
304                foreach ($style as $name => $value) {
305                    if (!isset($css_definition->info[$name])) {
306                        unset($style[$name]);
307                        continue;
308                    }
309                    $def = $css_definition->info[$name];
310                    $ret = $def->validate($value, $config, $context);
311                    if ($ret === false) {
312                        unset($style[$name]);
313                    } else {
314                        $style[$name] = $ret;
315                    }
316                }
317                $new_decls[$selector] = $style;
318            }
319            $new_css[$k] = $new_decls;
320        }
321        // remove stuff that shouldn't be used, could be reenabled
322        // after security risks are analyzed
323        $this->_tidy->css = $new_css;
324        $this->_tidy->import = array();
325        $this->_tidy->charset = null;
326        $this->_tidy->namespace = null;
327        $css = $this->_tidy->print->plain();
328        // we are going to escape any special characters <>& to ensure
329        // that no funny business occurs (i.e. </style> in a font-family prop).
330        if ($config->get('Filter.ExtractStyleBlocks.Escaping')) {
331            $css = str_replace(
332                array('<', '>', '&'),
333                array('\3C ', '\3E ', '\26 '),
334                $css
335            );
336        }
337        return $css;
338    }
339}
340
341// vim: et sw=4 sts=4
342