def _get_string(data, position, obj_end, dummy):
    """Decode a BSON string to python unicode string."""
    length = _UNPACK_INT(data[position:position + 4])[0]
    position += 4
    if length < 1 or obj_end - position < length:
        raise InvalidBSON("invalid string length")
    end = position + length - 1
    if data[end:end + 1] != b"\x00":
        raise InvalidBSON("invalid end of string")
    return _utf_8_decode(data[position:end], None, True)[0], end + 1
Decode a BSON string to python unicode string.