Memory efficient dynamic ZIP file generation and streaming

<?php

// Input files to be included in the zip. Should perform sanity check on this
$files_to_package = array('catalog.pdf', '3dview.dwg');

bring_files_locally_from_cloud_files_if_we_dont_have_a_local_cache_of_the_file($files_to_package); // nodoc :), @todo implement

// This file will be deleted once the PHP process ends
$zip_path = tmpfile();

// Create zip file with all files on the base of the zip regardless of their path
exec("zip --junk-paths $zip_path ". join(" ", absolute_file_paths($files_to_package))); // @todo implement absolute_file_paths

// Sending headers
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: public"); 
header("Content-Type: application/zip");
header("Content-Disposition: attachment; filename=Archive.zip");
header("Content-Transfer-Encoding: binary");
header('Content-Length: '.filesize($zip_path));

// Send the buffer as soon as it is echoed
ob_implicit_flush();

// Sends the file without taking all the ram
$buffer_size = 4096;
$fp = fopen($zip_path, "rb");
while (!feof($fp)) {
  echo fread($fp, $buffer_size);
}

// In case we don't trust on tmpfile effectiveness
unlink($zip_path);