由于Drupal7本身的api不完善，不能使用Drupal API提供的函数来创建zip包，只能使用php的方法来创建。

$zip = new ZipArchive;
// Store current directory.
$site_path = getcwd();

if ($zip->open($zip_path, ZipArchive::CREATE) === TRUE) {
// Change directory to "tagert" directory.
chdir($file_path);

foreach (glob('*') as $file) {
$zip->addFile($file);
}
$zip->close();
}

// Restore directory to site root directory.
chdir($site_path);

$header = array(
'Content-Type' => 'application/zip',
'Content-Length' => filesize($zip_path),
);

file_transfer($zip_uri, $header);