php download all files in directory

Thanks to the help from @maxhud I was able to come up with the complete solution. Here is the final code snippet used to achieve my desired results:

<?php
/* creates a compressed zip file */
function create_zip($files = array(),$destination = '',$overwrite = true) {
  //if the zip file already exists and overwrite is false, return false
  if(file_exists($destination) && !$overwrite) { return false; }
  //vars
  $valid_files = array();
  //if files were passed in...
  if(is_array($files)) {
    //cycle through each file
    foreach($files as $file) {
      //make sure the file exists
      if(file_exists($file)) {
        $valid_files[] = $file;
      }
    }
  }
  //if we have good files...
  if(count($valid_files)) {
    //create the archive
    $zip = new ZipArchive();
    if($zip->open($destination,$overwrite ? ZIPARCHIVE::OVERWRITE : ZIPARCHIVE::CREATE) !== true) {
      return false;
    }
    //add the files
    foreach($valid_files as $file) {
      $zip->addFile($file,$file);
    }
    //debug
    //echo 'The zip archive contains ',$zip->numFiles,' files with a status of ',$zip->status;

    //close the zip -- done!
    $zip->close();

    //check to make sure the file exists
    return file_exists($destination);
  }
  else
  {
    return false;
  }
}



$files_to_zip = array(
  'upload/1_3266_671641323389_14800358_42187034_1524052_n.jpg', 'upload/1_3266_671641328379_14800358_42187035_3071342_n.jpg'
);
//if true, good; if false, zip creation failed
$zip_name = 'my-archive.zip';
$result = create_zip($files_to_zip,$zip_name);

if($result){
header('Content-Type: application/zip');
header('Content-disposition: attachment; filename=filename.zip');
header('Content-Length: ' . filesize($zip_name));
readfile($zip_name);
}
?>