Enabling Resumable Downloads with a PHP File Transfer Script

Introduction

When transferring files using PHP scripts for security purposes, the absolute path of downloadable files often needs to be concealed. However, traditional PHP file transfer scripts may not support resumable downloads, causing inconvenience for end users who experience connection interruptions.

Solution: Supporting Resumable Downloads

To enable resumable downloads, the following steps can be taken:

1. Send the Accept-Ranges: bytes header: This header informs the client that partial content is supported.
2. Handle partial content requests: When receiving a request with the Range: bytes=x-y header, parse the range, seek to the desired offset in the file, and send the requested byte range.
3. Set the partial content HTTP status code: Respond with HTTP/1.0 206 Partial Content to indicate a successful partial transfer.

PHP Implementation

Below is a sample implementation of these principles in PHP:

$filesize = filesize($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: ' . $filesize);
header('Content-Disposition: attachment; filename="' . $fileName . '"');
header('Accept-Ranges: bytes');

print($data);

This script first checks if a partial content request was made. If so, it parses the range from the Range header, seeks to the appropriate offset in the file, and sends the requested byte range. The script also sets the Accept-Ranges header to bytes and sends the appropriate HTTP status code for partial content if necessary.

By implementing these measures, resumable downloads can be supported using PHP file transfer scripts, providing a robust solution for file transfers that can resume after interruptions.