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<?php

/**

 * Forgivingly lexes HTML (SGML-style) markup into tokens.

 *

 * A lexer parses a string of SGML-style markup and converts them into

 * corresponding tokens.  It doesn't check for well-formedness, although its

 * internal mechanism may make this automatic (such as the case of

 * HTMLPurifier_Lexer_DOMLex).  There are several implementations to choose

 * from.

 *

 * A lexer is HTML-oriented: it might work with XML, but it's not

 * recommended, as we adhere to a subset of the specification for optimization

 * reasons. This might change in the future. Also, most tokenizers are not

 * expected to handle DTDs or PIs.

 *

 * This class should not be directly instantiated, but you may use create() to

 * retrieve a default copy of the lexer.  Being a supertype, this class

 * does not actually define any implementation, but offers commonly used

 * convenience functions for subclasses.

 *

 * @note The unit tests will instantiate this class for testing purposes, as

 *       many of the utility functions require a class to be instantiated.

 *       This means that, even though this class is not runnable, it will

 *       not be declared abstract.

 *

 * @par

 *

 * @note

 * We use tokens rather than create a DOM representation because DOM would:

 *

 * @par

 *  -# Require more processing and memory to create,

 *  -# Is not streamable, and

 *  -# Has the entire document structure (html and body not needed).

 *

 * @par

 * However, DOM is helpful in that it makes it easy to move around nodes

 * without a lot of lookaheads to see when a tag is closed. This is a

 * limitation of the token system and some workarounds would be nice.

 */

class HTMLPurifier_Lexer

{

    /**

     * Whether or not this lexer implements line-number/column-number tracking.

     * If it does, set to true.

     */

    public $tracksLineNumbers = false;

    /**

     * @type HTMLPurifier_EntityParser

     */

    private $_entity_parser;

    // -- STATIC ----------------------------------------------------------

    /**

     * Retrieves or sets the default Lexer as a Prototype Factory.

     *

     * By default HTMLPurifier_Lexer_DOMLex will be returned. There are

     * a few exceptions involving special features that only DirectLex

     * implements.

     *

     * @note The behavior of this class has changed, rather than accepting

     *       a prototype object, it now accepts a configuration object.

     *       To specify your own prototype, set %Core.LexerImpl to it.

     *       This change in behavior de-singletonizes the lexer object.

     *

     * @param HTMLPurifier_Config $config

     * @return HTMLPurifier_Lexer

     * @throws HTMLPurifier_Exception

     */

    public static function create($config)

    {

        if (!($config instanceof HTMLPurifier_Config)) {

            $lexer = $config;

            trigger_error(

                "Passing a prototype to

                HTMLPurifier_Lexer::create() is deprecated, please instead

                use %Core.LexerImpl",

                E_USER_WARNING

            );

        } else {

            $lexer = $config->get('Core.LexerImpl');

        }

        $needs_tracking =

            $config->get('Core.MaintainLineNumbers') ||

            $config->get('Core.CollectErrors');

        $inst = null;

        if (is_object($lexer)) {

            $inst = $lexer;

        } else {

            if (is_null($lexer)) {

                do {

                    // auto-detection algorithm

                    if ($needs_tracking) {

                        $lexer = 'DirectLex';

                        break;

                    }

                    if (class_exists('DOMDocument') &&

                        method_exists('DOMDocument', 'loadHTML') &&

                        !extension_loaded('domxml')

                    ) {

                        // check for DOM support, because while it's part of the

                        // core, it can be disabled compile time. Also, the PECL

                        // domxml extension overrides the default DOM, and is evil

                        // and nasty and we shan't bother to support it

                        $lexer = 'DOMLex';

                    } else {

                        $lexer = 'DirectLex';

                    }

                } while (0);

            } // do..while so we can break

            // instantiate recognized string names

            switch ($lexer) {

                case 'DOMLex':

                    $inst = new HTMLPurifier_Lexer_DOMLex();

                    break;

                case 'DirectLex':

                    $inst = new HTMLPurifier_Lexer_DirectLex();

                    break;

                case 'PH5P':

                    $inst = new HTMLPurifier_Lexer_PH5P();

                    break;

                default:

                    throw new HTMLPurifier_Exception(

                        "Cannot instantiate unrecognized Lexer type " .

                        htmlspecialchars($lexer)

                    );

            }

        }

        if (!$inst) {

            throw new HTMLPurifier_Exception('No lexer was instantiated');

        }

        // once PHP DOM implements native line numbers, or we

        // hack out something using XSLT, remove this stipulation

        if ($needs_tracking && !$inst->tracksLineNumbers) {

            throw new HTMLPurifier_Exception(

                'Cannot use lexer that does not support line numbers with ' .

                'Core.MaintainLineNumbers or Core.CollectErrors (use DirectLex instead)'

            );

        }

        return $inst;

    }

    // -- CONVENIENCE MEMBERS ---------------------------------------------

    public function __construct()

    {

        $this->_entity_parser = new HTMLPurifier_EntityParser();

    }

    /**

     * Most common entity to raw value conversion table for special entities.

     * @type array

     */

    protected $_special_entity2str =

        array(

            '"' => '"',

            '&' => '&',

            '&lt;' => '<',

            '>' => '>',

            ''' => "'",

            ''' => "'",

            ''' => "'"

        );

    public function parseText($string, $config) {

        return $this->parseData($string, false, $config);

    }

    public function parseAttr($string, $config) {

        return $this->parseData($string, true, $config);

    }

    /**

     * Parses special entities into the proper characters.

     *

     * This string will translate escaped versions of the special characters

     * into the correct ones.

     *

     * @param string $string String character data to be parsed.

     * @return string Parsed character data.

     */

    public function parseData($string, $is_attr, $config)

    {

        // following functions require at least one character

        if ($string === '') {

            return '';

        }

        // subtracts amps that cannot possibly be escaped

        $num_amp = substr_count($string, '&') - substr_count($string, '& ') -

            ($string[strlen($string) - 1] === '&' ? 1 : 0);

        if (!$num_amp) {

            return $string;

        } // abort if no entities

        $num_esc_amp = substr_count($string, '&');

        $string = strtr($string, $this->_special_entity2str);

        // code duplication for sake of optimization, see above

        $num_amp_2 = substr_count($string, '&') - substr_count($string, '& ') -

            ($string[strlen($string) - 1] === '&' ? 1 : 0);

        if ($num_amp_2 <= $num_esc_amp) {

            return $string;

        }

        // hmm... now we have some uncommon entities. Use the callback.

        if ($config->get('Core.LegacyEntityDecoder')) {

            $string = $this->_entity_parser->substituteSpecialEntities($string);

        } else {

            if ($is_attr) {

                $string = $this->_entity_parser->substituteAttrEntities($string);

            } else {

                $string = $this->_entity_parser->substituteTextEntities($string);

            }

        }

        return $string;

    }

    /**

     * Lexes an HTML string into tokens.

     * @param $string String HTML.

     * @param HTMLPurifier_Config $config

     * @param HTMLPurifier_Context $context

     * @return HTMLPurifier_Token[] array representation of HTML.

     */

    public function tokenizeHTML($string, $config, $context)

    {

        trigger_error('Call to abstract class', E_USER_ERROR);

    }

    /**

     * Translates CDATA sections into regular sections (through escaping).

     * @param string $string HTML string to process.

     * @return string HTML with CDATA sections escaped.

     */

    protected static function escapeCDATA($string)

    {

        return preg_replace_callback(

            '/<!\[CDATA\[(.+?)\]\]>/s',

            array('HTMLPurifier_Lexer', 'CDATACallback'),

            $string

        );

    }

    /**

     * Special CDATA case that is especially convoluted for <script>

     * @param string $string HTML string to process.

     * @return string HTML with CDATA sections escaped.

     */

    protected static function escapeCommentedCDATA($string)

    {

        return preg_replace_callback(

            '#<!--//--><!\[CDATA\[//><!--(.+?)//--><!\]\]>#s',

            array('HTMLPurifier_Lexer', 'CDATACallback'),

            $string

        );

    }

    /**

     * Special Internet Explorer conditional comments should be removed.

     * @param string $string HTML string to process.

     * @return string HTML with conditional comments removed.

     */

    protected static function removeIEConditional($string)

    {

        return preg_replace(

            '#<!--\[if [^>]+\]>.*?<!\[endif\]-->#si', // probably should generalize for all strings

            '',

            $string

        );

    }

    /**

     * Callback function for escapeCDATA() that does the work.

     *

     * @warning Though this is public in order to let the callback happen,

     *          calling it directly is not recommended.

     * @param array $matches PCRE matches array, with index 0 the entire match

     *                  and 1 the inside of the CDATA section.

     * @return string Escaped internals of the CDATA section.

     */

    protected static function CDATACallback($matches)

    {

        // not exactly sure why the character set is needed, but whatever

        return htmlspecialchars($matches[1], ENT_COMPAT, 'UTF-8');

    }

    /**

     * Takes a piece of HTML and normalizes it by converting entities, fixing

     * encoding, extracting bits, and other good stuff.

     * @param string $html HTML.

     * @param HTMLPurifier_Config $config

     * @param HTMLPurifier_Context $context

     * @return string

     * @todo Consider making protected

     */

    public function normalize($html, $config, $context)

    {

        // normalize newlines to \n

        if ($config->get('Core.NormalizeNewlines')) {

            $html = str_replace("\r\n", "\n", (string)$html);

            $html = str_replace("\r", "\n", (string)$html);

        }

        if ($config->get('HTML.Trusted')) {

            // escape convoluted CDATA

            $html = $this->escapeCommentedCDATA($html);

        }

        // escape CDATA

        $html = $this->escapeCDATA($html);

        $html = $this->removeIEConditional($html);

        // extract body from document if applicable

        if ($config->get('Core.ConvertDocumentToFragment')) {

            $e = false;

            if ($config->get('Core.CollectErrors')) {

                $e =& $context->get('ErrorCollector');

            }

            $new_html = $this->extractBody($html);

            if ($e && $new_html != $html) {

                $e->send(E_WARNING, 'Lexer: Extracted body');

            }

            $html = $new_html;

        }

        // expand entities that aren't the big five

        if ($config->get('Core.LegacyEntityDecoder')) {

            $html = $this->_entity_parser->substituteNonSpecialEntities($html);

        }

        // clean into wellformed UTF-8 string for an SGML context: this has

        // to be done after entity expansion because the entities sometimes

        // represent non-SGML characters (horror, horror!)

        $html = HTMLPurifier_Encoder::cleanUTF8($html);

        // if processing instructions are to removed, remove them now

        if ($config->get('Core.RemoveProcessingInstructions')) {

            $html = preg_replace('#<\?.+?\?>#s', '', $html);

        }

        $hidden_elements = $config->get('Core.HiddenElements');

        if ($config->get('Core.AggressivelyRemoveScript') &&

            !($config->get('HTML.Trusted') || !$config->get('Core.RemoveScriptContents')

            || empty($hidden_elements["script"]))) {

            $html = preg_replace('#<script[^>]*>.*?</script>#i', '', $html);

        }

        return $html;

    }

    /**

     * Takes a string of HTML (fragment or document) and returns the content

     * @todo Consider making protected

     */

    public function extractBody($html)

    {

        $matches = array();

        $result = preg_match('|(.*?)<body[^>]*>(.*)</body>|is', $html, $matches);

        if ($result) {

            // Make sure it's not in a comment

            $comment_start = strrpos($matches[1], '<!--');

            $comment_end   = strrpos($matches[1], '-->');

            if ($comment_start === false ||

                ($comment_end !== false && $comment_end > $comment_start)) {

                return $matches[2];

            }

        }

        return $html;

    }

}

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