How Can I Ensure Reliable Large File Downloads in PHP?

Reliable Large File Downloads in PHP

To address the issue of corrupted or incomplete file transfers while sending large files in PHP, it is crucial to implement a reliable download method.

The provided code uses a simple loop to read and output the file in chunks. However, this method can face issues with large files, especially if there are any interruptions during the transfer.

To enhance reliability, consider using PHP's http_send_file or http_send_data functions. These functions streamline the file transfer process and handle resource management more efficiently.

For optimal performance and greater reliability, you can implement file chunking. This involves breaking the file into smaller chunks and sending them sequentially. Below is an example code snippet that demonstrates this approach:

// Determine the file path and filename
$filename = $filePath . $filename;

// Set chunk size (adjust based on server and file size requirements)
$chunkSize = 5 * (1024 * 1024); // 5 MB

// Check if file exists
if (file_exists($filename)) {
    // Set download headers and prepare for transfer
    set_time_limit(300);
    $size = intval(sprintf("%u", filesize($filename)));
    header('Content-Type: application/octet-stream');
    header('Content-Transfer-Encoding: binary');
    header('Content-Length: ' . $size);
    header('Content-Disposition: attachment;filename="' . basename($filename) . '"');

    // If file is larger than chunk size, use loop to send chunks
    if ($size > $chunkSize) {
        $handle = fopen($filename, 'rb');
        while (!feof($handle)) {
            print(@fread($handle, $chunkSize));
            ob_flush();
            flush();
        }
        fclose($handle);
    } else {
        // Read and output the entire file in one go
        readfile($path);
    }

    exit;
} else {
    echo 'File "' . $filename . '" does not exist!';
}

Remember to encode your file in UTF-8 before sending it to prevent potential corruption. Additionally, consider implementing error handling mechanisms to manage any potential interruptions or issues during the transfer process.

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