PHP使用get_headers函数判断远程文件是否存在的方法

<?php
$url = 'https://www.jb51.net';
print_r(get_headers($url));
print_r(get_headers($url, 1));
?>

Array
(
    [0] => HTTP/1.1 200 OK
    [1] => Cache-Control: max-age=1800
    [2] => Content-Length: 54874
    [3] => Content-Type: text/html
    [4] => Content-Location: https://www.jb51.net/index.htm
    [5] => Last-Modified: Fri, 28 Nov 2014 03:34:56 GMT
    [6] => Accept-Ranges: bytes
    [7] => ETag: "b66ba847bcad01:bc5"
    [8] => Server: Microsoft-IIS/6.0
    [9] => Date: Fri, 28 Nov 2014 03:37:34 GMT
    [10] => Connection: close
)
Array
(
    [0] => HTTP/1.1 200 OK
    [Cache-Control] => max-age=1800
    [Content-Length] => 54874
    [Content-Type] => text/html
    [Content-Location] => https://www.jb51.net/index.htm
    [Last-Modified] => Fri, 28 Nov 2014 03:34:56 GMT
    [Accept-Ranges] => bytes
    [ETag] => "b66ba847bcad01:bc5"
    [Server] => Microsoft-IIS/6.0
    [Date] => Fri, 28 Nov 2014 03:37:35 GMT
    [Connection] => close
)

//判断远程文件是否存在  
function remote_file_exists($url) {  
        $executeTime = ini_get('max_execution_time');  
        ini_set('max_execution_time', 0);  
        $headers = @get_headers($url);  
        ini_set('max_execution_time', $executeTime);  
        if ($headers) {  
            $head = explode(' ', $headers[0]);  
            if ( !emptyempty($head[1]) && intval($head[1]) < 400) return true;  
        }  
        return false;  
}

<?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; 
} 
?>