php获取301跳转URL简单实例

/**
 * get_redirect_url()
 * Gets the address that the provided URL redirects to,
 * or FALSE if there's no redirect.
 *
 * @param string $url
 * @return string
 */
function get_redirect_url($url){
    $redirect_url = null;

    $url_parts = @parse_url($url);
    if (!$url_parts) return false;
    if (!isset($url_parts['host'])) return false; //can't process relative URLs
    if (!isset($url_parts['path'])) $url_parts['path'] = 'https://www.jb51.net/';

    $sock = fsockopen($url_parts['host'], (isset($url_parts['port']) ? (int)$url_parts['port'] : 80), $errno, $errstr, 30);
    if (!$sock) return false;

$request = "HEAD " . $url_parts['path'] . (isset($url_parts['query']) ? '?'.$url_parts['query'] : '') . " HTTP/1.1\r\n";
    $request .= 'Host: ' . $url_parts['host'] . "\r\n";
    $request .= "Connection: Close\r\n\r\n";
    fwrite($sock, $request);
    $response = '';
    while(!feof($sock)) $response .= fread($sock, 8192);
    fclose($sock);
    if (preg_match('/^Location: (.+?)$/m', $response, $matches)){
        if ( substr($matches[1], 0, 1) == "https://www.jb51.net/" )
            return $url_parts['scheme'] . "://" . $url_parts['host'] . trim($matches[1]);
        else
            return trim($matches[1]);

    } else {
        return false;
    }

}
/**
 * get_all_redirects()
 * Follows and collects all redirects, in order, for the given URL.
 *
 * @param string $url
 * @return array
 */
function get_all_redirects($url){
    $redirects = array();
    while ($newurl = get_redirect_url($url)){
        if (in_array($newurl, $redirects)){
            break;
        }
        $redirects[] = $newurl;
        $url = $newurl;
    }
    return $redirects;
}