'mask or unmask data. Just do xor for each byte
mask_key: 4 byte string(byte).
data: data to mask/unmask.'

@staticmethod
def mask(mask_key, data):

    if (data == None):
        data = ''
    if isinstance(mask_key, six.text_type):
        mask_key = six.b(mask_key)
    if isinstance(data, six.text_type):
        data = six.b(data)
    _m = array.array('B', mask_key)
    _d = array.array('B', data)
    return _mask(_m, _d)
