PHP检测远端文件是否存在

<?php/** * Fetches all the real headers sent by the server in response to a HTTP request without redirects * 获取不包含重定向的报头 */ function get_real_headers($url,$format=0,$follow_redirect=0) {  if (!$follow_redirect) {    //set new default options    $opts = array('http' =>        array('max_redirects'=>1,'ignore_errors'=>1)    );    stream_context_get_default($opts);  }  //get headers    $headers=get_headers($url,$format);    //restore default options  if (isset($opts)) {    $opts = array('http' =>        array('max_redirects'=>20,'ignore_errors'=>0)    );    stream_context_get_default($opts);  }  //return    return $headers;}?>