def METHOD_NAME(self, direction):
    """
    Get a list of message io signatures for this flow graph.
    Args:
        direction: a string of 'in' or 'out'
    Returns:
        a list of dicts with: type, label, vlen, size, optional
    """
    return [p for p in self.get_hier_block_io(direction) if p['type'] == "message"]