def set_chunk_size(data_type, stream_id, new_size):
    """
    Construct a 'SET_CHUNK_SIZE' message to adjust the chunk size at which the RTMP library works with.
    :param data_type: int the RTMP datatype.
    :param stream_id: int the stream which the message will be sent on.
    :param new_size: int the new size of future message chunks from the client (1<=size<=2147483647).
                         NOTE: All sizes set after 16777215 are equivalent.
    """
    msg = {'msg': data_type,
           'stream_id': stream_id,
           'chunk_size': new_size}
    return msg