如何使用cURL部分下载远程文件？ [英] How to partially download a remote file with cURL?

问题描述

是否可以使用cURL部分下载远程文件？
假设远程文件的实际文件大小为1000 KB。
如何只下载最初的500 KB？

Is it possible to partially download a remote file with cURL? Let's say, the actual filesize of the remote file is 1000 KB. How can I download only first 500 KB of it?

推荐答案

php-curl扩展。

You can also set the range header parameter with the php-curl extension.

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://www.spiegel.de/');
curl_setopt($ch, CURLOPT_RANGE, '0-500');
curl_setopt($ch, CURLOPT_BINARYTRANSFER, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
curl_close($ch);
echo $result;

但是如前所述，如果服务器不承认这个头，但发送整个文件curl会下载所有的。例如。 http://www.php.net 忽略标题。但是，您可以（另外）设置一个写入函数回调，并在收到更多数据时中止请求，例如

But as noted before if the server doesn't honor this header but sends the whole file curl will download all of it. E.g. http://www.php.net ignores the header. But you can (in addition) set a write function callback and abort the request when more data is received, e.g.

// php 5.3+ only
// use function writefn($ch, $chunk) { ... } for earlier versions
$writefn = function($ch, $chunk) { 
  static $data='';
  static $limit = 500; // 500 bytes, it's only a test

  $len = strlen($data) + strlen($chunk);
  if ($len >= $limit ) {
    $data .= substr($chunk, 0, $limit-strlen($data));
    echo strlen($data) , ' ', $data;
    return -1;
  }

  $data .= $chunk;
  return strlen($chunk);
};

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://www.php.net/');
curl_setopt($ch, CURLOPT_RANGE, '0-500');
curl_setopt($ch, CURLOPT_BINARYTRANSFER, 1);
curl_setopt($ch, CURLOPT_WRITEFUNCTION, $writefn);
$result = curl_exec($ch);
curl_close($ch);

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