How to Stream Large Zip Files on LAMP Stack for Faster Downloads?

Creating On-the-Fly Zip Files for Large Files on a LAMP Stack

Problem:

When creating zip files of multiple large files for user download, conventional methods result in significant performance issues during the initial phase due to heavy CPU and disk usage.

Solution Using Streaming:

To address this problem, we can leverage the streaming capabilities of zip by using popen() or proc_open() to execute the zip command pipeline and retrieve the stdout as a PHP stream. By combining this with a web server process, we can stream the zip file to the user as it's being created on the fly.

Implementation Using popen():

<?php
// Set necessary headers
header('Content-Type: application/zip');
header('Content-disposition: attachment; filename="file.zip"');

// Execute zip command and retrieve stdout as a stream
$fp = popen('zip -r - file1 file2 file3', 'r');

// Read and echo data in chunks
$bufsize = 65535;
$buff = '';
while (!feof($fp)) {
    $buff = fread($fp, $bufsize);
    echo $buff;
}
pclose($fp);
?>

Tips for Optimization:

• Use an appropriate buffer size (e.g., 8192 as suggested by Benji in the comments).
• Turn off magic quotes if necessary.
• Set mb_http_output('pass') for optimal performance.

• Use the appropriate content-related headers:

  • Content-Type: application/zip
  • Content-disposition: attachment; filename="file.zip"

Unfortunately, it's not straightforward to set a header to indicate streaming or unknown content length in this context.

Note on flush():

It's important to note that calling flush() within the read/echo loop may cause issues with large files and slow networks due to Apache's internal output buffer getting overrun. Therefore, it's best to omit flush() calls in the code.

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