create a zip file and send to browser

creat_zip_download.php

<?php
// this file is supposed to be in UTF-8 without BOM
function isRunningOnWindows() {
	$os = php_uname('s'); //PHP_OS see https://stackoverflow.com/q/1482260/3995261
	return preg_match('#win#i',$os) ? true : false;
}
function fixFilenameEncoding($name) {
	// seemingly is needed on Windows only because filename encoding is not utf-8
	return isRunningOnWindows() ? mb_convert_encoding($name, "windows-1251", "utf-8") : $name;
}
function fixInZipFilenameEncoding($name) {
	
	return isRunningOnWindows() ? iconv("cp1251", "cp866", $name) : $name;
}
//# test: presumably these fixes should be removed for PHP 7.1

$files_to_zip = fixFilenameEncoding(...); //# set or calc to your liking
$zip_name = fixFilenameEncoding(...); //# set or calc to your liking

/* creates a compressed zip file */
function create_zip($files = array(), $destination = '', $overwrite = false) {
	if(file_exists($destination) && !$overwrite)
		return false;

	if(is_array($files)) // skip unexisting files
		foreach($files as $name => $file)
			if(!file_exists($file))
				unset($files[$name]);

	if(!count($files)) // no files actually
		return false;
  
	$zip = new ZipArchive();
	if(!$zip->open($destination, $overwrite ? ZIPARCHIVE::OVERWRITE : ZIPARCHIVE::CREATE))
		return false;

	foreach($files as $name => $file) {
		$encoded_file_name = fixInZipFilenameEncoding($file); // prevent zip from corrupting cyrillics
		$zip->addFile($file,$encoded_file_name);
	}
	$zip->close();
	return $destination;  
}

function send_zip($name) { //# cache-preventing headers to be reviewed
	
	header("Pragma: public");
	header("Expires: 0");
	header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
	header("Cache-Control: private",false);
	
	header("Content-Type: application/zip");
	header("Content-Disposition: attachment; filename*=UTF-8''".rawurlencode(basename($name)).";"); // see https://stackoverflow.com/q/93551/3995261
	header("Content-Length: ".filesize($name));
	readfile($name);
}

$zip = create_zip($files_to_zip,$zip_name,false);
if(file_exists($zip_name))
	send_zip($zip_name);
?>