<?php
/* vim: set expandtab tabstop=4 shiftwidth=4 softtabstop=4: */

/**
 * HTML_Safe Parser
 *
 * PHP version 5
 *
 * @category  HTML
 * @package   HTML_Safe
 * @author    Roman Ivanov <thingol@mail.ru>
 * @author    Miguel Vazquez Gocobachi <demrit@mx.gnu.org>
 * @copyright 2004-2009 Roman Ivanov, Miguel Vazquez Gocobachi
 * @license   http://www.debian.org/misc/bsd.license  BSD License (3 Clause)
 * @version   SVN: $Id$
 * @link      http://pear.php.net/package/HTML_Safe
 */

/**
 * This package requires HTMLSax3 package
 */
require_once 'XML/HTMLSax3.php';

/**
 * HTML_Safe Parser
 *
 * This parser strips down all potentially dangerous content within HTML:
 * <ul>
 * <li>opening tag without its closing tag</li>
 * <li>closing tag without its opening tag</li>
 * <li>any of these tags: "base", "basefont", "head", "html", "body", "applet",
 * "object", "iframe", "frame", "frameset", "script", "layer", "ilayer", "embed",
 * "bgsound", "link", "meta", "style", "title", "blink", "xml" etc.</li>
 * <li>any of these attributes: on*, data*, dynsrc</li>
 * <li>javascript:/vbscript:/about: etc. protocols</li>
 * <li>expression/behavior etc. in styles</li>
 * <li>any other active content</li>
 * </ul>
 * It also tries to convert code to XHTML valid, but htmltidy is far better
 * solution for this task.
 *
 * <b>Example:</b>
 * <pre>
 * $parser = new HTML_Safe;
 * $result = $parser->parse($doc);
 * </pre>
 *
 * @category  HTML
 * @package   HTML_Safe
 * @author    Roman Ivanov <thingol@mail.ru>
 * @author    Miguel Vazquez Gocobachi <demrit@mx.gnu.org>
 * @copyright 2004-2009 Roman Ivanov, Miguel Vazquez Gocobachi
 * @license   http://www.debian.org/misc/bsd.license  BSD License (3 Clause)
 * @version   Release: @package_version@
 * @link      http://pear.php.net/package/HTML_Safe
 */
class HTML_Safe
{
    /**
     * Storage for resulting HTML output
     *
     * @var string
     */
    protected $xhtml = '';

    /**
     * Array of counters for each tag
     *
     * @var array
     */
    protected $counter = array();

    /**
     * Stack of unclosed tags
     *
     * @var array
     */
    protected $stack = array();

    /**
     * Array of counters for tags that must be deleted with all content
     *
     * @var array
     */
    protected $dcCounter = array();

    /**
     * Stack of unclosed tags that must be deleted with all content
     *
     * @var array
     */
    protected $dcStack = array();

    /**
     * Stores level of list (ol/ul) nesting
     *
     * @var int
     */
    protected $listScope = 0;

    /**
     * Stack of unclosed list tags
     *
     * @var array
     */
    protected $liStack = array();

    /**
     * Array of prepared regular expressions for protocols (schemas) matching
     *
     * @var array
     */
    protected $protoRegexps = array();

    /**
     * Array of prepared regular expressions for CSS matching
     *
     * @var array
     */
    protected $cssRegexps = array();

    /**
     * Allowed tags
     *
     * @var array
     */
    protected $allowTags = array();


    /**
     * List of single tags ("<tag />")
     *
     * @var array
     */
    public $singleTags = array('area', 'br', 'img', 'input', 'hr', 'wbr', );

    /**
     * List of dangerous tags (such tags will be deleted)
     *
     * @var array
     */
    public $deleteTags = array(
        'applet', 'base',   'basefont', 'bgsound', 'blink',  'body',
        'embed',  'frame',  'frameset', 'head',    'html',   'ilayer',
        'iframe', 'layer',  'link',     'meta',    'object', 'style',
        'title',  'script',
    );

    /**
     * List of dangerous tags (such tags will be deleted, and all content
     * inside this tags will be also removed)
     *
     * @var array
     */
    public $deleteTagsContent = array('script', 'style', 'title', 'xml', );

    /**
     * Type of protocols filtering ('white' or 'black')
     *
     * @var string
     */
    public $protocolFiltering = 'white';

    /**
     * List of "dangerous" protocols (used for blacklist-filtering)
     *
     * @var array
     */
    public $blackProtocols = array(
        'about',   'chrome',     'data',       'disk',     'hcp',
        'help',    'javascript', 'livescript', 'lynxcgi',  'lynxexec',
        'ms-help', 'ms-its',     'mhtml',      'mocha',    'opera',
        'res',     'resource',   'shell',      'vbscript', 'view-source',
        'vnd.ms.radio',          'wysiwyg',
    );

    /**
     * List of "safe" protocols (used for whitelist-filtering)
     *
     * @var array
     */
    public $whiteProtocols = array(
        'ed2k',   'file', 'ftp',  'gopher', 'http',  'https',
        'irc',    'mailto', 'news', 'nntp', 'telnet', 'webcal',
        'xmpp',   'callto',
    );

    /**
     * List of attributes that can contain protocols
     *
     * @var array
     */
    public $protocolAttributes = array(
        'action', 'background', 'codebase', 'dynsrc', 'href', 'lowsrc', 'src',
    );

    /**
     * List of dangerous CSS keywords
     *
     * Whole style="" attribute will be removed, if parser will find one of
     * these keywords
     *
     * @var array
     */
    public $cssKeywords = array(
        'absolute', 'behavior',       'behaviour',   'content', 'expression',
        'fixed',    'include-source', 'moz-binding',
    );

    /**
     * List of tags that can have no "closing tag"
     *
     * @var array
     * @deprecated XHTML does not allow such tags
     */
    public $noClose = array();

    /**
     * List of block-level tags that terminates paragraph
     *
     * Paragraph will be closed when this tags opened
     *
     * @var array
     */
    public $closeParagraph = array(
        'address', 'blockquote', 'center', 'dd',      'dir',       'div',
        'dl',      'dt',         'h1',     'h2',      'h3',        'h4',
        'h5',      'h6',         'hr',     'isindex', 'listing',   'marquee',
        'menu',    'multicol',   'ol',     'p',       'plaintext', 'pre',
        'table',   'ul',         'xmp',
    );

    /**
     * List of table tags, all table tags outside a table will be removed
     *
     * @var array
     */
    public $tableTags = array(
        'caption', 'col', 'colgroup', 'tbody', 'td', 'tfoot', 'th',
        'thead',   'tr',
    );

    /**
     * List of list tags
     *
     * @var array
     */
    public $listTags = array('dir', 'menu', 'ol', 'ul', 'dl', );

    /**
     * List of dangerous attributes
     *
     * @var array
     */
    public $attributes = array('dynsrc', 'id', 'name', );

    /**
     * List of allowed "namespaced" attributes
     *
     * @var array
     */
    public $attributesNS = array('xml:lang', );

    /**
     * Constructs class
     *
     * @access public
     */
    public function __construct()
    {
        //making regular expressions based on Proto & CSS arrays
        foreach ($this->blackProtocols as $proto) {
            $preg = "/[\s\x01-\x1F]*";
            for ($i=0; $i<strlen($proto); $i++) {
                $preg .= $proto{$i} . "[\s\x01-\x1F]*";
            }
            $preg .= ":/i";
            $this->protoRegexps[] = $preg;
        }

        foreach ($this->cssKeywords as $css) {
            $this->cssRegexps[] = '/' . $css . '/i';
        }
        return true;
    }

    /**
     * Handles the writing of attributes - called from $this->openHandler()
     *
     * @param array $attrs array of attributes $name => $value
     *
     * @return boolean
     */
    protected function writeAttrs($attrs)
    {
        if (is_array($attrs)) {
            foreach ($attrs as $name => $value) {
                $name = strtolower($name);

                if (strpos($name, 'on') === 0) {
                    continue;
                }

                if (strpos($name, 'data') === 0) {
                    continue;
                }

                if (in_array($name, $this->attributes)) {
                    continue;
                }

                if (!preg_match('/^[a-z0-9]+$/i', $name)) {
                    if (!in_array($name, $this->attributesNS)) {
                        continue;
                    }
                }

                if (($value === true) || (is_null($value))) {
                    $value = $name;
                }

                if ($name == 'style') {
                    // removes insignificant backslahes
                    $value = str_replace("\\", '', $value);

                    // removes CSS comments
                    while (1) {
                        $_value = preg_replace('!/\*.*?\*/!s', '', $value);

                        if ($_value == $value) {
                            break;
                        }

                        $value = $_value;
                    }

                    // replace all & to &amp;
                    $value = str_replace('&amp;', '&', $value);
                    $value = str_replace('&', '&amp;', $value);

                    foreach ($this->cssRegexps as $css) {
                        if (preg_match($css, $value)) {
                            continue 2;
                        }
                    }

                    foreach ($this->protoRegexps as $proto) {
                        if (preg_match($proto, $value)) {
                            continue 2;
                        }
                    }
                }

                $tempval = preg_replace('/&#(\d+);?/me', "chr('\\1')", $value); //"'
                $tempval = preg_replace(
                    '/&#x([0-9a-f]+);?/mei',
                    "chr(hexdec('\\1'))",
                    $tempval
                );

                if ((in_array($name, $this->protocolAttributes))
                    && (strpos($tempval, ':') !== false)
                ) {
                    if ($this->protocolFiltering == 'black') {
                        foreach ($this->protoRegexps as $proto) {
                            if (preg_match($proto, $tempval)) {
                                continue 2;
                            }
                        }
                    } else {
                        $_tempval = explode(':', $tempval);
                        $proto    = $_tempval[0];

                        if (!in_array($proto, $this->whiteProtocols)) {
                            continue;
                        }
                    }
                }

                $value        = str_replace("\"", '&quot;', $value);
                $this->xhtml .= ' ' . $name . '="' . $value . '"';
            }
        }

        return true;
    }

    /**
     * Opening tag handler - called from HTMLSax
     *
     * @param object &$parser HTML Parser
     * @param string $name    tag name
     * @param array  $attrs   tag attributes
     *
     * @return boolean
     */
    public function openHandler(&$parser, $name, $attrs)
    {
        $name = strtolower($name);

        if (in_array($name, $this->deleteTagsContent)) {
            array_push($this->dcStack, $name);
            $this->dcCounter[$name] = isset($this->dcCounter[$name])
                ? $this->dcCounter[$name]+1 : 1;
        }
        if (count($this->dcStack) != 0) {
            return true;
        }

        if (in_array($name, $this->deleteTags)
            && !in_array($name, $this->allowTags)
        ) {
            return true;
        }

        if (!preg_match("/^[a-z0-9]+$/i", $name)) {
            if (preg_match("!(?:\@|://)!i", $name)) {
                $this->xhtml .= '&lt;' . $name . '&gt;';
            }
            return true;
        }

        if (in_array($name, $this->singleTags)) {
            $this->xhtml .= '<' . $name;
            $this->writeAttrs($attrs);
            $this->xhtml .= ' />';
            return true;
        }

        // TABLES: cannot open table elements when we are not inside table
        if ((isset($this->counter['table']))
            && ($this->counter['table'] <= 0)
            && (in_array($name, $this->tableTags))
        ) {
            return true;
        }

        // PARAGRAPHS: close paragraph when closeParagraph tags opening
        if ((in_array($name, $this->closeParagraph))
            && (in_array('p', $this->stack))
        ) {
            $this->closeHandler($parser, 'p');
        }

        // LISTS: we should close <li> if <li> of the same level opening
        if (($name == 'li') && count($this->liStack)
            && ($this->listScope == $this->liStack[count($this->liStack) - 1])
        ) {
            $this->closeHandler($parser, 'li');
        }

        // LISTS: we want to know on what nesting level of lists we are
        if (in_array($name, $this->listTags)) {
            ++$this->listScope;
        }

        if ($name == 'li') {
            array_push($this->liStack, $this->listScope);
        }

        $this->xhtml .= '<' . $name;
        $this->writeAttrs($attrs);
        $this->xhtml .= '>';
        array_push($this->stack, $name);
        $this->counter[$name] = isset($this->counter[$name])
            ? ($this->counter[$name] + 1) : 1;

        return true;
    }

    /**
     * Closing tag handler - called from HTMLSax
     *
     * @param object &$parser HTML parser
     * @param string $name    tag name
     *
     * @return boolean
     */
    public function closeHandler(&$parser, $name)
    {
        $name = strtolower($name);

        if (isset($this->dcCounter[$name])
            && ($this->dcCounter[$name] > 0)
            && (in_array($name, $this->deleteTagsContent))
        ) {
            while ($name != ($tag = array_pop($this->dcStack))) {
                --$this->dcCounter[$tag];
            }

            --$this->dcCounter[$name];
        }

        if (count($this->dcStack) != 0) {
            return true;
        }

        if ((isset($this->counter[$name])) && ($this->counter[$name] > 0)) {
            while ($name != ($tag = array_pop($this->stack))) {
                $this->closeTag($tag);
            }

            $this->closeTag($name);
        }
        return true;
    }

    /**
     * Closes tag
     *
     * @param string $tag tag name
     *
     * @return boolean
     */
    protected function closeTag($tag)
    {
        if (!in_array($tag, $this->noClose)) {
            $this->xhtml .= '</' . $tag . '>';
        }

        --$this->counter[$tag];

        if (in_array($tag, $this->listTags)) {
            --$this->listScope;
        }

        if ($tag == 'li') {
            array_pop($this->liStack);
        }

        return true;
    }

    /**
     * Character data handler - called from HTMLSax
     *
     * @param object &$parser HTML parser
     * @param string $data    textual data
     *
     * @return boolean
     */
    public function dataHandler(&$parser, $data)
    {
        if (count($this->dcStack) == 0) {
            $this->xhtml .= $data;
        }

        return true;
    }

    /**
     * Escape handler - called from HTMLSax
     *
     * @param object &$parser HTML parser
     * @param string $data    comments or other type of data
     *
     * @return boolean
     */
    public function escapeHandler(&$parser, $data)
    {
        return true;
    }

    /**
     * Allow tags
     *
     * Example:
     * <pre>
     * $safe = new HTML_Safe;
     * $safe->setAllowTags(array('body'));
     * </pre>
     *
     * @param array $tags Tags to allow
     *
     * @return void
     */
    public function setAllowTags($tags = array())
    {
        if (is_array($tags)) {
            $this->allowTags = $tags;
        }
    }

    /**
     * Returns the allowed tags
     *
     * @return array
     */
    public function getAllowTags()
    {
        return $this->allowTags;
    }

    /**
     * Reset the allowed tags
     *
     * @return void
     */
    public function resetAllowTags()
    {
        $this->allowTags = array();
    }

    /**
     * Returns the XHTML document
     *
     * @return string Processed (X)HTML document
     */
    public function getXHTML()
    {
        while ($tag = array_pop($this->stack)) {
            $this->closeTag($tag);
        }

        return $this->xhtml;
    }

    /**
     * Clears current document data
     *
     * @return boolean
     */
    public function clear()
    {
        $this->xhtml = '';
        return true;
    }

    /**
     * Main parsing fuction
     *
     * @param string $doc HTML document for processing
     *
     * @return string Processed (X)HTML document
     */
    public function parse($doc)
    {
        $result = '';

        // Save all '<' symbols
        $doc = preg_replace("/<(?=[^a-zA-Z\/\!\?\%])/", '&lt;', $doc);

        // UTF7 pack
        $doc = $this->repackUTF7($doc);

        // Instantiate the parser
        $parser = new XML_HTMLSax3;

        // Set up the parser
        $parser->set_object($this);

        $parser->set_element_handler('openHandler', 'closeHandler');
        $parser->set_data_handler('dataHandler');
        $parser->set_escape_handler('escapeHandler');

        $parser->parse($doc);

        $result = $this->getXHTML();

        $this->clear();

        return $result;
    }

    /**
     * UTF-7 decoding fuction
     *
     * @param string $str HTML document for recode ASCII part of UTF-7 back to ASCII
     * @return string Decoded document
     * @access private
     */
    function repackUTF7($str)
    {
       return preg_replace_callback('!\+([0-9a-zA-Z/]+)\-!', array($this, 'repackUTF7Callback'), $str);
    }

    /**
     * Additional UTF-7 decoding fuction
     *
     * @param string $str String for recode ASCII part of UTF-7 back to ASCII
     * @return string Recoded string
     * @access private
     */
    function repackUTF7Callback($str)
    {
       /* If $str[1] is not a valid string for base64_decode than it return false or binary which json_encode cannot identify.
        * So we need to check if the string is valid for base64_decode and then only decode it, otherwise return original string.
        * Source : http://stackoverflow.com/questions/4278106/how-to-check-if-a-string-is-base64-valid-in-php
        */
       if(base64_encode(base64_decode($str[1])) === $str[1]) {
            $str = base64_decode($str[1]);
       }
       else {
           return $str[0];
       }
       $str = preg_replace_callback('/^((?:\x00.)*)((?:[^\x00].)+)/', array($this, 'repackUTF7Back'), $str);
       return preg_replace('/\x00(.)/', '$1', $str);
    }

    /**
     * Additional UTF-7 encoding fuction
     *
     * @param string $str String for recode ASCII part of UTF-7 back to ASCII
     * @return string Recoded string
     * @access private
     */
    function repackUTF7Back($str)
    {
       return $str[1].'+'.rtrim(base64_encode($str[2]), '=').'-';
    }
}
