mirror of
https://github.com/ezyang/htmlpurifier.git
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363 lines
12 KiB
PHP
363 lines
12 KiB
PHP
<?php
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/**
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* Forgivingly lexes HTML (SGML-style) markup into tokens.
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*
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* A lexer parses a string of SGML-style markup and converts them into
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* corresponding tokens. It doesn't check for well-formedness, although its
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* internal mechanism may make this automatic (such as the case of
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* HTMLPurifier_Lexer_DOMLex). There are several implementations to choose
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* from.
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*
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* A lexer is HTML-oriented: it might work with XML, but it's not
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* recommended, as we adhere to a subset of the specification for optimization
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* reasons. This might change in the future. Also, most tokenizers are not
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* expected to handle DTDs or PIs.
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*
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* This class should not be directly instantiated, but you may use create() to
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* retrieve a default copy of the lexer. Being a supertype, this class
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* does not actually define any implementation, but offers commonly used
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* convenience functions for subclasses.
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*
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* @note The unit tests will instantiate this class for testing purposes, as
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* many of the utility functions require a class to be instantiated.
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* This means that, even though this class is not runnable, it will
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* not be declared abstract.
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*
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* @par
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*
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* @note
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* We use tokens rather than create a DOM representation because DOM would:
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*
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* @par
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* -# Require more processing and memory to create,
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* -# Is not streamable, and
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* -# Has the entire document structure (html and body not needed).
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*
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* @par
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* However, DOM is helpful in that it makes it easy to move around nodes
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* without a lot of lookaheads to see when a tag is closed. This is a
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* limitation of the token system and some workarounds would be nice.
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*/
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class HTMLPurifier_Lexer
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{
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/**
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* Whether or not this lexer implements line-number/column-number tracking.
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* If it does, set to true.
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*/
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public $tracksLineNumbers = false;
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// -- STATIC ----------------------------------------------------------
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/**
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* Retrieves or sets the default Lexer as a Prototype Factory.
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*
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* By default HTMLPurifier_Lexer_DOMLex will be returned. There are
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* a few exceptions involving special features that only DirectLex
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* implements.
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*
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* @note The behavior of this class has changed, rather than accepting
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* a prototype object, it now accepts a configuration object.
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* To specify your own prototype, set %Core.LexerImpl to it.
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* This change in behavior de-singletonizes the lexer object.
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*
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* @param HTMLPurifier_Config $config
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* @return HTMLPurifier_Lexer
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* @throws HTMLPurifier_Exception
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*/
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public static function create($config)
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{
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if (!($config instanceof HTMLPurifier_Config)) {
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$lexer = $config;
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trigger_error(
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"Passing a prototype to
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HTMLPurifier_Lexer::create() is deprecated, please instead
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use %Core.LexerImpl",
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E_USER_WARNING
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);
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} else {
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$lexer = $config->get('Core.LexerImpl');
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}
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$needs_tracking =
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$config->get('Core.MaintainLineNumbers') ||
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$config->get('Core.CollectErrors');
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$inst = null;
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if (is_object($lexer)) {
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$inst = $lexer;
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} else {
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if (is_null($lexer)) {
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do {
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// auto-detection algorithm
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if ($needs_tracking) {
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$lexer = 'DirectLex';
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break;
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}
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if (class_exists('DOMDocument') &&
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method_exists('DOMDocument', 'loadHTML') &&
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!extension_loaded('domxml')
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) {
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// check for DOM support, because while it's part of the
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// core, it can be disabled compile time. Also, the PECL
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// domxml extension overrides the default DOM, and is evil
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// and nasty and we shan't bother to support it
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$lexer = 'DOMLex';
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} else {
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$lexer = 'DirectLex';
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}
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} while (0);
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} // do..while so we can break
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// instantiate recognized string names
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switch ($lexer) {
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case 'DOMLex':
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$inst = new HTMLPurifier_Lexer_DOMLex();
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break;
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case 'DirectLex':
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$inst = new HTMLPurifier_Lexer_DirectLex();
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break;
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case 'PH5P':
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$inst = new HTMLPurifier_Lexer_PH5P();
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break;
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default:
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throw new HTMLPurifier_Exception(
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"Cannot instantiate unrecognized Lexer type " .
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htmlspecialchars($lexer)
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);
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}
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}
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if (!$inst) {
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throw new HTMLPurifier_Exception('No lexer was instantiated');
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}
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// once PHP DOM implements native line numbers, or we
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// hack out something using XSLT, remove this stipulation
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if ($needs_tracking && !$inst->tracksLineNumbers) {
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throw new HTMLPurifier_Exception(
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'Cannot use lexer that does not support line numbers with ' .
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'Core.MaintainLineNumbers or Core.CollectErrors (use DirectLex instead)'
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);
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}
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return $inst;
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}
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// -- CONVENIENCE MEMBERS ---------------------------------------------
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public function __construct()
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{
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$this->_entity_parser = new HTMLPurifier_EntityParser();
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}
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/**
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* Most common entity to raw value conversion table for special entities.
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* @type array
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*/
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protected $_special_entity2str =
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array(
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'"' => '"',
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'&' => '&',
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'<' => '<',
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'>' => '>',
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''' => "'",
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''' => "'",
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''' => "'"
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);
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/**
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* Parses special entities into the proper characters.
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*
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* This string will translate escaped versions of the special characters
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* into the correct ones.
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*
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* @warning
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* You should be able to treat the output of this function as
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* completely parsed, but that's only because all other entities should
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* have been handled previously in substituteNonSpecialEntities()
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*
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* @param string $string String character data to be parsed.
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* @return string Parsed character data.
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*/
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public function parseData($string)
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{
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// following functions require at least one character
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if ($string === '') {
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return '';
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}
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// subtracts amps that cannot possibly be escaped
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$num_amp = substr_count($string, '&') - substr_count($string, '& ') -
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($string[strlen($string) - 1] === '&' ? 1 : 0);
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if (!$num_amp) {
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return $string;
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} // abort if no entities
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$num_esc_amp = substr_count($string, '&');
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$string = strtr($string, $this->_special_entity2str);
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// code duplication for sake of optimization, see above
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$num_amp_2 = substr_count($string, '&') - substr_count($string, '& ') -
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($string[strlen($string) - 1] === '&' ? 1 : 0);
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if ($num_amp_2 <= $num_esc_amp) {
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return $string;
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}
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// hmm... now we have some uncommon entities. Use the callback.
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$string = $this->_entity_parser->substituteSpecialEntities($string);
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return $string;
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}
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/**
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* Lexes an HTML string into tokens.
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* @param $string String HTML.
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* @param HTMLPurifier_Config $config
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* @param HTMLPurifier_Context $context
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* @return HTMLPurifier_Token[] array representation of HTML.
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*/
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public function tokenizeHTML($string, $config, $context)
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{
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trigger_error('Call to abstract class', E_USER_ERROR);
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}
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/**
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* Translates CDATA sections into regular sections (through escaping).
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* @param string $string HTML string to process.
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* @return string HTML with CDATA sections escaped.
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*/
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protected static function escapeCDATA($string)
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{
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return preg_replace_callback(
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'/<!\[CDATA\[(.+?)\]\]>/s',
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array('HTMLPurifier_Lexer', 'CDATACallback'),
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$string
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);
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}
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/**
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* Special CDATA case that is especially convoluted for <script>
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* @param string $string HTML string to process.
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* @return string HTML with CDATA sections escaped.
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*/
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protected static function escapeCommentedCDATA($string)
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{
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return preg_replace_callback(
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'#<!--//--><!\[CDATA\[//><!--(.+?)//--><!\]\]>#s',
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array('HTMLPurifier_Lexer', 'CDATACallback'),
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$string
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);
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}
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/**
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* Special Internet Explorer conditional comments should be removed.
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* @param string $string HTML string to process.
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* @return string HTML with conditional comments removed.
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*/
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protected static function removeIEConditional($string)
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{
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return preg_replace(
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'#<!--\[if [^>]+\]>.*?<!\[endif\]-->#si', // probably should generalize for all strings
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'',
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$string
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);
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}
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/**
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* Callback function for escapeCDATA() that does the work.
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*
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* @warning Though this is public in order to let the callback happen,
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* calling it directly is not recommended.
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* @param array $matches PCRE matches array, with index 0 the entire match
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* and 1 the inside of the CDATA section.
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* @return string Escaped internals of the CDATA section.
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*/
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protected static function CDATACallback($matches)
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{
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// not exactly sure why the character set is needed, but whatever
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return htmlspecialchars($matches[1], ENT_COMPAT, 'UTF-8');
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}
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/**
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* Takes a piece of HTML and normalizes it by converting entities, fixing
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* encoding, extracting bits, and other good stuff.
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* @param string $html HTML.
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* @param HTMLPurifier_Config $config
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* @param HTMLPurifier_Context $context
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* @return string
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* @todo Consider making protected
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*/
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public function normalize($html, $config, $context)
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{
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// normalize newlines to \n
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if ($config->get('Core.NormalizeNewlines')) {
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$html = str_replace("\r\n", "\n", $html);
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$html = str_replace("\r", "\n", $html);
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}
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if ($config->get('HTML.Trusted')) {
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// escape convoluted CDATA
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$html = $this->escapeCommentedCDATA($html);
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}
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// escape CDATA
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$html = $this->escapeCDATA($html);
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$html = $this->removeIEConditional($html);
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// extract body from document if applicable
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if ($config->get('Core.ConvertDocumentToFragment')) {
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$e = false;
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if ($config->get('Core.CollectErrors')) {
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$e =& $context->get('ErrorCollector');
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}
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$new_html = $this->extractBody($html);
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if ($e && $new_html != $html) {
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$e->send(E_WARNING, 'Lexer: Extracted body');
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}
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$html = $new_html;
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}
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// expand entities that aren't the big five
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$html = $this->_entity_parser->substituteNonSpecialEntities($html);
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// clean into wellformed UTF-8 string for an SGML context: this has
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// to be done after entity expansion because the entities sometimes
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// represent non-SGML characters (horror, horror!)
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$html = HTMLPurifier_Encoder::cleanUTF8($html);
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// if processing instructions are to removed, remove them now
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if ($config->get('Core.RemoveProcessingInstructions')) {
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$html = preg_replace('#<\?.+?\?>#s', '', $html);
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}
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return $html;
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}
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/**
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* Takes a string of HTML (fragment or document) and returns the content
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* @todo Consider making protected
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*/
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public function extractBody($html)
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{
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$matches = array();
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$result = preg_match('|(.*?)<body[^>]*>(.*)</body>|is', $html, $matches);
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if ($result) {
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// Make sure it's not in a comment
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$comment_start = strrpos($matches[1], '<!--');
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$comment_end = strrpos($matches[1], '-->');
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if ($comment_start === false ||
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($comment_end !== false && $comment_end > $comment_start)) {
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return $matches[2];
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}
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}
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return $html;
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}
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}
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// vim: et sw=4 sts=4
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