Transfrom relative path into absolute URL using PHP

function rel2abs($rel, $base)
{
    /* return if already absolute URL */
    if (parse_url($rel, PHP_URL_SCHEME) != '')
        return ($rel);

    /* queries and anchors */
    if ($rel[0] == '#' || $rel[0] == '?')
        return ($base . $rel);

    /* parse base URL and convert to local variables: $scheme, $host, $path, $query, $port, $user, $pass */
    extract(parse_url($base));

    /* remove non-directory element from path */
    $path = preg_replace('#/[^/]*$#', '', $path);

    /* destroy path if relative url points to root */
    if ($rel[0] == '/')
        $path = '';

    /* dirty absolute URL */
    $abs = '';

    /* do we have a user in our URL? */
    if (isset($user)) {
        $abs .= $user;

        /* password too? */
        if (isset($pass))
            $abs .= ':' . $pass;

        $abs .= '@';
    }

    $abs .= $host;

    /* did somebody sneak in a port? */
    if (isset($port))
        $abs .= ':' . $port;

    $abs .= $path . '/' . $rel . (isset($query) ? '?' . $query : '');

    /* replace '//' or '/./' or '/foo/../' with '/' */
    $re = ['#(/\.?/)#', '#/(?!\.\.)[^/]+/\.\./#'];
    for ($n = 1; $n > 0; $abs = preg_replace($re, '/', $abs, -1, $n)) {
    }

    /* absolute URL is ready! */

    return ($scheme . '://' . $abs);
}