How to Stream Large Zip Files in PHP Without Resource Overwhelm?

Creating .Zip of Large Files on the Fly without Resource Overwhelm

In web services, creating a zip of extensive files for download can be resource-intensive. The conventional approach involves creating a temporary zip file and echoing it to the user or saving it to disk. However, this method leads to issues such as:

• Initial Resource Spikes: A surge in CPU and disk usage during the file creation phase.
• Download Delay: A noticeable delay for users awaiting the archive completion.
• Excessive Memory Footprint: Significant memory consumption during file handling.
• Disk Space Utilization: Creation of temporary disk space for file storage.
• Resource Waste on Cancellation: If a user cancels mid-download, all resources consumed in the initial phase are wasted.

Overcoming Resource Consumption

An alternative approach is to leverage the streaming capabilities of the Linux command-line tool, zip. By employing a pipeline command like ls -1 | zip -@ - | cat > file.zip, zip can operate in streaming mode, resulting in a minimal memory footprint. A pipe in this context functions as a buffer; when the buffer is filled, the operating system temporarily halts the writing program. This ensures that zip operates at a pace that aligns with the writing speed of the accompanying program.

Streaming Zip Files with PHP

To achieve the same streaming mechanism on a LAMP stack using PHP, you can utilize the popen() or proc_open() functions to execute the zip command. The stdout from the command can then be retrieved as a PHP stream. By combining these techniques, the following code snippet demonstrates how to stream a zip file to the user as it's being created:

header('Content-Type: application/octet-stream');
header('Content-disposition: attachment; filename="file.zip"');

$fp = popen('zip -r - file1 file2 file3', 'r');
$bufsize = 8192;
$buff = '';

while(!feof($fp)) {
   $buff = fread($fp, $bufsize);
   echo $buff;
}
pclose($fp);

This code streams the zip file directly to the client without the need for temporary storage or excessive memory consumption. It effectively emulates the functionality of the cat command in the bash snippet.

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