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<?php
/**
 * Class to validate and to work with IPv6 addresses
 *
 * @package Requests
 * @subpackage Utilities
 */

/**
 * Class to validate and to work with IPv6 addresses
 *
 * This was originally based on the PEAR class of the same name, but has been
 * entirely rewritten.
 *
 * @package Requests
 * @subpackage Utilities
 */
class Requests_IPv6
{
    /**
     * Uncompresses an IPv6 address
     *
     * RFC 4291 allows you to compress consecutive zero pieces in an address to
     * '::'. This method expects a valid IPv6 address and expands the '::' to
     * the required number of zero pieces.
     *
     * Example:  FF01::101   ->  FF01:0:0:0:0:0:0:101
     *           ::1         ->  0:0:0:0:0:0:0:1
     *
     * @author Alexander Merz <alexander.merz@web.de>
     * @author elfrink at introweb dot nl
     * @author Josh Peck <jmp at joshpeck dot org>
     * @copyright 2003-2005 The PHP Group
     * @license http://www.opensource.org/licenses/bsd-license.php
     * @param string $ip An IPv6 address
     * @return string The uncompressed IPv6 address
     */
    public static function uncompress($ip)
    {
        $c1 = -1;
        $c2 = -1;
        if (substr_count($ip, '::') === 1)
        {
            list($ip1, $ip2) = explode('::', $ip);
            if ($ip1 === '')
            {
                $c1 = -1;
            }
            else
            {
                $c1 = substr_count($ip1, ':');
            }
            if ($ip2 === '')
            {
                $c2 = -1;
            }
            else
            {
                $c2 = substr_count($ip2, ':');
            }
            if (strpos($ip2, '.') !== false)
            {
                $c2++;
            }
            // ::
            if ($c1 === -1 && $c2 === -1)
            {
                $ip = '0:0:0:0:0:0:0:0';
            }
            // ::xxx
            else if ($c1 === -1)
            {
                $fill = str_repeat('0:', 7 - $c2);
                $ip = str_replace('::', $fill, $ip);
            }
            // xxx::
            else if ($c2 === -1)
            {
                $fill = str_repeat(':0', 7 - $c1);
                $ip = str_replace('::', $fill, $ip);
            }
            // xxx::xxx
            else
            {
                $fill = ':' . str_repeat('0:', 6 - $c2 - $c1);
                $ip = str_replace('::', $fill, $ip);
            }
        }
        return $ip;
    }

/**
     * Compresses an IPv6 address
     *
     * RFC 4291 allows you to compress consecutive zero pieces in an address to
     * '::'. This method expects a valid IPv6 address and compresses consecutive
     * zero pieces to '::'.
     *
     * Example:  FF01:0:0:0:0:0:0:101   ->  FF01::101
     *           0:0:0:0:0:0:0:1        ->  ::1
     *
     * @see uncompress()
     * @param string $ip An IPv6 address
     * @return string The compressed IPv6 address
     */
    public static function compress($ip)
    {
        // Prepare the IP to be compressed
        $ip = self::uncompress($ip);
        $ip_parts = self::split_v6_v4($ip);

// Replace all leading zeros
        $ip_parts[0] = preg_replace('/(^|:)0+([0-9])/', '\1\2', $ip_parts[0]);

// Find bunches of zeros
        if (preg_match_all('/(?:^|:)(?:0(?::|$))+/', $ip_parts[0], $matches, PREG_OFFSET_CAPTURE))
        {
            $max = 0;
            $pos = null;
            foreach ($matches[0] as $match)
            {
                if (strlen($match[0]) > $max)
                {
                    $max = strlen($match[0]);
                    $pos = $match[1];
                }
            }

$ip_parts[0] = substr_replace($ip_parts[0], '::', $pos, $max);
        }

if ($ip_parts[1] !== '')
        {
            return implode(':', $ip_parts);
        }
        else
        {
            return $ip_parts[0];
        }
    }

/**
     * Splits an IPv6 address into the IPv6 and IPv4 representation parts
     *
     * RFC 4291 allows you to represent the last two parts of an IPv6 address
     * using the standard IPv4 representation
     *
     * Example:  0:0:0:0:0:0:13.1.68.3
     *           0:0:0:0:0:FFFF:129.144.52.38
     *
     * @param string $ip An IPv6 address
     * @return array [0] contains the IPv6 represented part, and [1] the IPv4 represented part
     */
    private static function split_v6_v4($ip)
    {
        if (strpos($ip, '.') !== false)
        {
            $pos = strrpos($ip, ':');
            $ipv6_part = substr($ip, 0, $pos);
            $ipv4_part = substr($ip, $pos + 1);
            return array($ipv6_part, $ipv4_part);
        }
        else
        {
            return array($ip, '');
        }
    }

/**
     * Checks an IPv6 address
     *
     * Checks if the given IP is a valid IPv6 address
     *
     * @param string $ip An IPv6 address
     * @return bool true if $ip is a valid IPv6 address
     */
    public static function check_ipv6($ip)
    {
        $ip = self::uncompress($ip);
        list($ipv6, $ipv4) = self::split_v6_v4($ip);
        $ipv6 = explode(':', $ipv6);
        $ipv4 = explode('.', $ipv4);
        if (count($ipv6) === 8 && count($ipv4) === 1 || count($ipv6) === 6 && count($ipv4) === 4)
        {
            foreach ($ipv6 as $ipv6_part)
            {
                // The section can't be empty
                if ($ipv6_part === '')
                    return false;

// Nor can it be over four characters
                if (strlen($ipv6_part) > 4)
                    return false;

// Remove leading zeros (this is safe because of the above)
                $ipv6_part = ltrim($ipv6_part, '0');
                if ($ipv6_part === '')
                    $ipv6_part = '0';

// Check the value is valid
                $value = hexdec($ipv6_part);
                if (dechex($value) !== strtolower($ipv6_part) || $value < 0 || $value > 0xFFFF)
                    return false;
            }
            if (count($ipv4) === 4)
            {
                foreach ($ipv4 as $ipv4_part)
                {
                    $value = (int) $ipv4_part;
                    if ((string) $value !== $ipv4_part || $value < 0 || $value > 0xFF)
                        return false;
                }
            }
            return true;
        }
        else
        {
            return false;
        }
    }
}

Editing File: IPv6.php