Validate XML with Zend_Form

09 Oct 2012

I needed a simple way to validate user-inputted XML with Zend_Form, so decided to write a simple validator:

class App_Validate_Xml extends Zend_Validate_Abstract
{
    const ERROR_MESSAGE = 'error';
    
    public $xmlError;
    
    protected $_messageVariables = array(
        'xmlError' => 'xmlError'
    );
    
    protected $_messageTemplates = array(
        self::ERROR_MESSAGE => '%xmlError%'
    );
    
    public function isValid($value)
    {
        libxml_use_internal_errors(true);
        
        $dom = new DOMDocument('1.0', 'utf-8');
        $dom->loadXML($value);
        
        $errors = libxml_get_errors();
        
        if(count($errors) > 0) {
            foreach($errors as $error) {
                $this->xmlError = $error->message;
                $this->_error(self::ERROR_MESSAGE);
            }
            return false;
        }
        return true;
    }
}

The validator simply loads the XML from the form element value with DomDocument.

By forcing libxml to allow us to retrieve error information internally, we can check for any errors ourself. It’s then just a case of mapping any error messages to our message template ready for Zend_Validate_Abstract to parse them.