如何从外部服务器上的文件推送标题进行下载？

Question

以下脚本是我通常用来将标头推送到浏览器的脚本，以便出现对话框供用户下载文件。

但是，在这种情况下，文件位于不同的服务器上。我虽然这应该没有什么区别，但是当我使用 externam MP3 文件的 URL 执行此脚本时，它会给我一个“错误：找不到文件”。但是，此文件存在，我可以使用传递给此脚本的相同 URL 来访问它。

任何想法为什么？我将不胜感激。

<?php session_start();

//below variable contains full path to external site where file resides
$filename = $_SESSION['$serverURL'].'audio/'.$_SESSION['fileName'].'.mp3';
//below variable contains a chosen filename of the file to be downloaded
$properFilename = $_GET['properFilename'].'.mp3';

// required for IE, otherwise Content-disposition is ignored
if(ini_get('zlib.output_compression'))
  ini_set('zlib.output_compression', 'Off');

// addition by Jorg Weske
$file_extension = strtolower(substr(strrchr($filename,"."),1));

if( $filename == "" ) 
{
  //echo "download file NOT SPECIFIED";
  exit;
} elseif ( ! file_exists( $filename ) ) 
{
  //echo "ERROR: File not found";
  exit;
};
switch( $file_extension )
{
  case "pdf": $ctype="application/pdf"; break;
  case "exe": $ctype="application/octet-stream"; break;
  case "zip": $ctype="application/zip"; break;
  case "doc": $ctype="application/msword"; break;
  case "xls": $ctype="application/vnd.ms-excel"; break;
  case "ppt": $ctype="application/vnd.ms-powerpoint"; break;
  case "gif": $ctype="image/gif"; break;
  case "png": $ctype="image/png"; break;
  case "jpeg":
  case "jpg": $ctype="image/jpg"; break;
  default: $ctype="application/force-download";
}
header("Pragma: public"); // required
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false); // required for certain browsers 
header("Content-Type: $ctype");
// change, added quotes to allow spaces in filenames, by Rajkumar Singh
header("Content-Disposition: attachment; filename=\"".basename($properFilename)."\";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($filename));
readfile("$filename");
exit();   

?>

Answer 1

单引号字符串不会被解析为变量，所以$_SESSION['$serverURL'] 可能不会像你期望的那样工作。我怀疑你的意思是$_SESSION[$serverURL] 或$_SESSION['serverURL']。

同时调用filesize() 和readfile() 可能会导致您的脚本发出两个HTTP 请求以从另一台服务器获取文件（除非它以某种方式被缓存）。您可以使用 cURL 在一个 HTTP 请求中执行此操作，这可能是一个更好的选择。这是一个简短的示例，您应该能够对其进行调整以做您想做的事情。您可能还需要考虑从其他服务器（如果可靠）转发其他标头，例如 Content-Type 标头，而不是自己重新生成它们。

<?php

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, 'http://example.com');

//set callbacks to receive headers and content
curl_setopt($ch, CURLOPT_HEADERFUNCTION, 'on_receive_header');
curl_setopt($ch, CURLOPT_WRITEFUNCTION, 'on_receive_content');

//send your other custom headers somewhere like here

if (false === curl_exec($ch)) {
    //handle error better than this.
    die(curl_error($ch));   
}

function on_receive_header($ch, $string) {
    //You could here forward the other headers received from your other server if you wanted

    //for now we only want Content-Length
    if (stripos($string, 'Content-Length') !== false) {
        header($string);   
    }

    //curl requires you to return the amount of data received
    $length = strlen($string);
    return $length;
}

function on_receive_content($ch, $string) {
    echo $string;

    //again return amount written
    $length = strlen($string);
    return $length;
}