Host.php

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<?php

class HTMLPurifier_AttrDef_URI_Host extends HTMLPurifier_AttrDef
{

    protected $ipv4;

    protected $ipv6;

    public function __construct()
    {
        $this->ipv4 = new HTMLPurifier_AttrDef_URI_IPv4();
        $this->ipv6 = new HTMLPurifier_AttrDef_URI_IPv6();
    }

    public function validate($string, $config, $context)
    {
        $length = strlen($string);
        // empty hostname is OK; it's usually semantically equivalent:
        // the default host as defined by a URI scheme is used:
        //
        //      If the URI scheme defines a default for host, then that
        //      default applies when the host subcomponent is undefined
        //      or when the registered name is empty (zero length).
        if ($string === '') {
            return '';
        }
        if ($length > 1 && $string[0] === '[' && $string[$length - 1] === ']') {
            //IPv6
            $ip = substr($string, 1, $length - 2);
            $valid = $this->ipv6->validate($ip, $config, $context);
            if ($valid === false) {
                return false;
            }
            return '[' . $valid . ']';
        }

        // need to do checks on unusual encodings too
        $ipv4 = $this->ipv4->validate($string, $config, $context);
        if ($ipv4 !== false) {
            return $ipv4;
        }

        // A regular domain name.

        // This doesn't match I18N domain names, but we don't have proper IRI support,
        // so force users to insert Punycode.

        // There is not a good sense in which underscores should be
        // allowed, since it's technically not! (And if you go as
        // far to allow everything as specified by the DNS spec...
        // well, that's literally everything, modulo some space limits
        // for the components and the overall name (which, by the way,
        // we are NOT checking!).  So we (arbitrarily) decide this:
        // let's allow underscores wherever we would have allowed
        // hyphens, if they are enabled.  This is a pretty good match
        // for browser behavior, for example, a large number of browsers
        // cannot handle foo_.example.com, but foo_bar.example.com is
        // fairly well supported.
        $underscore = $config->get('Core.AllowHostnameUnderscore') ? '_' : '';

        // Based off of RFC 1738, but amended so that
        // as per RFC 3696, the top label need only not be all numeric.
        // The productions describing this are:
        $a   = '[a-z]';     // alpha
        $an  = '[a-z0-9]';  // alphanum
        $and = "[a-z0-9-$underscore]"; // alphanum | "-"
        // domainlabel = alphanum | alphanum *( alphanum | "-" ) alphanum
        $domainlabel = "$an(?:$and*$an)?";
        // AMENDED as per RFC 3696
        // toplabel    = alphanum | alphanum *( alphanum | "-" ) alphanum
        //      side condition: not all numeric
        $toplabel = "$an(?:$and*$an)?";
        // hostname    = *( domainlabel "." ) toplabel [ "." ]
        if (preg_match("/^(?:$domainlabel\.)*($toplabel)\.?$/i", $string, $matches)) {
            if (!ctype_digit($matches[1])) {
                return $string;
            }
        }

        // PHP 5.3 and later support this functionality natively
        if (function_exists('idn_to_ascii')) {
            return idn_to_ascii($string);

        // If we have Net_IDNA2 support, we can support IRIs by
        // punycoding them. (This is the most portable thing to do,
        // since otherwise we have to assume browsers support
        } elseif ($config->get('Core.EnableIDNA')) {
            $idna = new Net_IDNA2(array('encoding' => 'utf8', 'overlong' => false, 'strict' => true));
            // we need to encode each period separately
            $parts = explode('.', $string);
            try {
                $new_parts = array();
                foreach ($parts as $part) {
                    $encodable = false;
                    for ($i = 0, $c = strlen($part); $i < $c; $i++) {
                        if (ord($part[$i]) > 0x7a) {
                            $encodable = true;
                            break;
                        }
                    }
                    if (!$encodable) {
                        $new_parts[] = $part;
                    } else {
                        $new_parts[] = $idna->encode($part);
                    }
                }
                $string = implode('.', $new_parts);
                if (preg_match("/^($domainlabel\.)*$toplabel\.?$/i", $string)) {
                    return $string;
                }
            } catch (Exception $e) {
                // XXX error reporting
            }
        }
        return false;
    }
}

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