How Can I Enable Resumable Downloads with a PHP Script?

Supporting Resumable Downloads with PHP Scripting

Question:
When using a PHP script to send downloadable files, downloads cannot be resumed by end users. How can resumable downloads be supported with such a solution?

Answer:

To enable resumable downloads, follow these steps:

1. Send the Accept-Ranges: bytes header:

   • This header informs the client that you support partial content.

2. Handle range headers:

   • If a request contains a Range: bytes=x-y header, parse it to determine the requested range.
   • Open the file, seek to the requested offset, and read the requested length of data.

3. Set partial content headers:

   • If the request is for a partial content (Range header is present), set the following headers:

     • HTTP/1.1 206 Partial Content
     • Content-Range: bytes x-y/filesize

4. Send the file data:

   • Output the requested data using print() or similar.

Here's a sample PHP code that demonstrates how to implement partial content downloads:

$filesize = filesize($file);

$offset = 0;
$length = $filesize;

if (isset($_SERVER['HTTP_RANGE'])) {
    preg_match('/bytes=(\d+)-(\d+)?/', $_SERVER['HTTP_RANGE'], $matches);

    $offset = intval($matches[1]);
    $length = intval($matches[2]) - $offset;
}

$file = fopen($file, 'r');

fseek($file, $offset);

$data = fread($file, $length);

fclose($file);

if ($offset > 0) {
    header('HTTP/1.1 206 Partial Content');
    header('Content-Range: bytes ' . $offset . '-' . ($offset + $length) . '/' . $filesize);
}

header('Content-Type: ' . $ctype);
header('Content-Length: ' . $length);
header('Content-Disposition: attachment; filename="' . $fileName . '"');
header('Accept-Ranges: bytes');

print($data);

This code sets the appropriate headers and responds with the requested file data, supporting resumable downloads.

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