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1<?php
2
3/**
4 * Forgivingly lexes HTML (SGML-style) markup into tokens.
5 *
6 * A lexer parses a string of SGML-style markup and converts them into
7 * corresponding tokens. It doesn't check for well-formedness, although its
8 * internal mechanism may make this automatic (such as the case of
9 * HTMLPurifier_Lexer_DOMLex). There are several implementations to choose
10 * from.
11 *
12 * A lexer is HTML-oriented: it might work with XML, but it's not
13 * recommended, as we adhere to a subset of the specification for optimization
14 * reasons. This might change in the future. Also, most tokenizers are not
15 * expected to handle DTDs or PIs.
16 *
17 * This class should not be directly instantiated, but you may use create() to
18 * retrieve a default copy of the lexer. Being a supertype, this class
19 * does not actually define any implementation, but offers commonly used
20 * convenience functions for subclasses.
21 *
22 * @note The unit tests will instantiate this class for testing purposes, as
23 * many of the utility functions require a class to be instantiated.
24 * This means that, even though this class is not runnable, it will
25 * not be declared abstract.
26 *
27 * @par
28 *
29 * @note
30 * We use tokens rather than create a DOM representation because DOM would:
31 *
32 * @par
33 * -# Require more processing and memory to create,
34 * -# Is not streamable, and
35 * -# Has the entire document structure (html and body not needed).
36 *
37 * @par
38 * However, DOM is helpful in that it makes it easy to move around nodes
39 * without a lot of lookaheads to see when a tag is closed. This is a
40 * limitation of the token system and some workarounds would be nice.
41 */
42class HTMLPurifier_Lexer
43{
44
45 /**
46 * Whether or not this lexer implements line-number/column-number tracking.
47 * If it does, set to true.
48 */
49 public $tracksLineNumbers = false;
50
51 // -- STATIC ----------------------------------------------------------
52
53 /**
54 * Retrieves or sets the default Lexer as a Prototype Factory.
55 *
56 * By default HTMLPurifier_Lexer_DOMLex will be returned. There are
57 * a few exceptions involving special features that only DirectLex
58 * implements.
59 *
60 * @note The behavior of this class has changed, rather than accepting
61 * a prototype object, it now accepts a configuration object.
62 * To specify your own prototype, set %Core.LexerImpl to it.
63 * This change in behavior de-singletonizes the lexer object.
64 *
65 * @param HTMLPurifier_Config $config
66 * @return HTMLPurifier_Lexer
67 * @throws HTMLPurifier_Exception
68 */
69 public static function create($config)
70 {
71 if (!($config instanceof HTMLPurifier_Config)) {
72 $lexer = $config;
73 trigger_error(
74 "Passing a prototype to
75 HTMLPurifier_Lexer::create() is deprecated, please instead
76 use %Core.LexerImpl",
77 E_USER_WARNING
78 );
79 } else {
80 $lexer = $config->get('Core.LexerImpl');
81 }
82
83 $needs_tracking =
84 $config->get('Core.MaintainLineNumbers') ||
85 $config->get('Core.CollectErrors');
86
87 $inst = null;
88 if (is_object($lexer)) {
89 $inst = $lexer;
90 } else {
91 if (is_null($lexer)) {
92 do {
93 // auto-detection algorithm
94 if ($needs_tracking) {
95 $lexer = 'DirectLex';
96 break;
97 }
98
99 if (class_exists('DOMDocument') &&
100 method_exists('DOMDocument', 'loadHTML') &&
101 !extension_loaded('domxml')
102 ) {
103 // check for DOM support, because while it's part of the
104 // core, it can be disabled compile time. Also, the PECL
105 // domxml extension overrides the default DOM, and is evil
106 // and nasty and we shan't bother to support it
107 $lexer = 'DOMLex';
108 } else {
109 $lexer = 'DirectLex';
110 }
111 } while (0);
112 } // do..while so we can break
113
114 // instantiate recognized string names
115 switch ($lexer) {
116 case 'DOMLex':
117 $inst = new HTMLPurifier_Lexer_DOMLex();
118 break;
119 case 'DirectLex':
120 $inst = new HTMLPurifier_Lexer_DirectLex();
121 break;
122 case 'PH5P':
123 $inst = new HTMLPurifier_Lexer_PH5P();
124 break;
125 default:
126 throw new HTMLPurifier_Exception(
127 "Cannot instantiate unrecognized Lexer type " .
128 htmlspecialchars($lexer)
129 );
130 }
131 }
132
133 if (!$inst) {
134 throw new HTMLPurifier_Exception('No lexer was instantiated');
135 }
136
137 // once PHP DOM implements native line numbers, or we
138 // hack out something using XSLT, remove this stipulation
139 if ($needs_tracking && !$inst->tracksLineNumbers) {
140 throw new HTMLPurifier_Exception(
141 'Cannot use lexer that does not support line numbers with ' .
142 'Core.MaintainLineNumbers or Core.CollectErrors (use DirectLex instead)'
143 );
144 }
145
146 return $inst;
147
148 }
149
150 // -- CONVENIENCE MEMBERS ---------------------------------------------
151
152 public function __construct()
153 {
154 $this->_entity_parser = new HTMLPurifier_EntityParser();
155 }
156
157 /**
158 * Most common entity to raw value conversion table for special entities.
159 * @type array
160 */
161 protected $_special_entity2str =
162 array(
163 '&quot;' => '"',
164 '&amp;' => '&',
165 '&lt;' => '<',
166 '&gt;' => '>',
167 '&#39;' => "'",
168 '&#039;' => "'",
169 '&#x27;' => "'"
170 );
171
172 /**
173 * Parses special entities into the proper characters.
174 *
175 * This string will translate escaped versions of the special characters
176 * into the correct ones.
177 *
178 * @warning
179 * You should be able to treat the output of this function as
180 * completely parsed, but that's only because all other entities should
181 * have been handled previously in substituteNonSpecialEntities()
182 *
183 * @param string $string String character data to be parsed.
184 * @return string Parsed character data.
185 */
186 public function parseData($string)
187 {
188 // following functions require at least one character
189 if ($string === '') {
190 return '';
191 }
192
193 // subtracts amps that cannot possibly be escaped
194 $num_amp = substr_count($string, '&') - substr_count($string, '& ') -
195 ($string[strlen($string) - 1] === '&' ? 1 : 0);
196
197 if (!$num_amp) {
198 return $string;
199 } // abort if no entities
200 $num_esc_amp = substr_count($string, '&amp;');
201 $string = strtr($string, $this->_special_entity2str);
202
203 // code duplication for sake of optimization, see above
204 $num_amp_2 = substr_count($string, '&') - substr_count($string, '& ') -
205 ($string[strlen($string) - 1] === '&' ? 1 : 0);
206
207 if ($num_amp_2 <= $num_esc_amp) {
208 return $string;
209 }
210
211 // hmm... now we have some uncommon entities. Use the callback.
212 $string = $this->_entity_parser->substituteSpecialEntities($string);
213 return $string;
214 }
215
216 /**
217 * Lexes an HTML string into tokens.
218 * @param $string String HTML.
219 * @param HTMLPurifier_Config $config
220 * @param HTMLPurifier_Context $context
221 * @return HTMLPurifier_Token[] array representation of HTML.
222 */
223 public function tokenizeHTML($string, $config, $context)
224 {
225 trigger_error('Call to abstract class', E_USER_ERROR);
226 }
227
228 /**
229 * Translates CDATA sections into regular sections (through escaping).
230 * @param string $string HTML string to process.
231 * @return string HTML with CDATA sections escaped.
232 */
233 protected static function escapeCDATA($string)
234 {
235 return preg_replace_callback(
236 '/<!\[CDATA\[(.+?)\]\]>/s',
237 array('HTMLPurifier_Lexer', 'CDATACallback'),
238 $string
239 );
240 }
241
242 /**
243 * Special CDATA case that is especially convoluted for <script>
244 * @param string $string HTML string to process.
245 * @return string HTML with CDATA sections escaped.
246 */
247 protected static function escapeCommentedCDATA($string)
248 {
249 return preg_replace_callback(
250 '#<!--//--><!\[CDATA\[//><!--(.+?)//--><!\]\]>#s',
251 array('HTMLPurifier_Lexer', 'CDATACallback'),
252 $string
253 );
254 }
255
256 /**
257 * Special Internet Explorer conditional comments should be removed.
258 * @param string $string HTML string to process.
259 * @return string HTML with conditional comments removed.
260 */
261 protected static function removeIEConditional($string)
262 {
263 return preg_replace(
264 '#<!--\[if [^>]+\]>.*?<!\[endif\]-->#si', // probably should generalize for all strings
265 '',
266 $string
267 );
268 }
269
270 /**
271 * Callback function for escapeCDATA() that does the work.
272 *
273 * @warning Though this is public in order to let the callback happen,
274 * calling it directly is not recommended.
275 * @param array $matches PCRE matches array, with index 0 the entire match
276 * and 1 the inside of the CDATA section.
277 * @return string Escaped internals of the CDATA section.
278 */
279 protected static function CDATACallback($matches)
280 {
281 // not exactly sure why the character set is needed, but whatever
282 return htmlspecialchars($matches[1], ENT_COMPAT, 'UTF-8');
283 }
284
285 /**
286 * Takes a piece of HTML and normalizes it by converting entities, fixing
287 * encoding, extracting bits, and other good stuff.
288 * @param string $html HTML.
289 * @param HTMLPurifier_Config $config
290 * @param HTMLPurifier_Context $context
291 * @return string
292 * @todo Consider making protected
293 */
294 public function normalize($html, $config, $context)
295 {
296 // normalize newlines to \n
297 if ($config->get('Core.NormalizeNewlines')) {
298 $html = str_replace("\r\n", "\n", $html);
299 $html = str_replace("\r", "\n", $html);
300 }
301
302 if ($config->get('HTML.Trusted')) {
303 // escape convoluted CDATA
304 $html = $this->escapeCommentedCDATA($html);
305 }
306
307 // escape CDATA
308 $html = $this->escapeCDATA($html);
309
310 $html = $this->removeIEConditional($html);
311
312 // extract body from document if applicable
313 if ($config->get('Core.ConvertDocumentToFragment')) {
314 $e = false;
315 if ($config->get('Core.CollectErrors')) {
316 $e =& $context->get('ErrorCollector');
317 }
318 $new_html = $this->extractBody($html);
319 if ($e && $new_html != $html) {
320 $e->send(E_WARNING, 'Lexer: Extracted body');
321 }
322 $html = $new_html;
323 }
324
325 // expand entities that aren't the big five
326 $html = $this->_entity_parser->substituteNonSpecialEntities($html);
327
328 // clean into wellformed UTF-8 string for an SGML context: this has
329 // to be done after entity expansion because the entities sometimes
330 // represent non-SGML characters (horror, horror!)
331 $html = HTMLPurifier_Encoder::cleanUTF8($html);
332
333 // if processing instructions are to removed, remove them now
334 if ($config->get('Core.RemoveProcessingInstructions')) {
335 $html = preg_replace('#<\?.+?\?>#s', '', $html);
336 }
337
338 return $html;
339 }
340
341 /**
342 * Takes a string of HTML (fragment or document) and returns the content
343 * @todo Consider making protected
344 */
345 public function extractBody($html)
346 {
347 $matches = array();
348 $result = preg_match('!<body[^>]*>(.*)</body>!is', $html, $matches);
349 if ($result) {
350 return $matches[1];
351 } else {
352 return $html;
353 }
354 }
355}
356
357// vim: et sw=4 sts=4