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.我怎样才能只下载它的前 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

您还可以使用 php-curl 扩展名设置范围标头参数.

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;

但如前所述，如果服务器不接受此标头但发送整个文件 curl 将下载所有文件.例如.http://www.php.net 忽略标题.但是您可以(另外)设置一个写函数回调并在接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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