php

<?

$data = $_POST;

$response = array("status" => "ok");

$error = array();

foreach ($data as $key=>$value){
  $value = trim($value);
  if(empty($value)){
      $response['status'] = "error";
      $error[$key] = "Заполните поле";
  }
}

$response['error'] = $error;

print json_encode($response);