def get_missing_links(header, df):
    """ Find missing links in a dataframe
    :param dict header:
    :param pd.Dataframe df:
    :return: a list of dict
    :rtype: list
    """
    links = []
    for transaction_id, transaction_df in df.groupby(['transaction_id']):
        for src in range(header['node_count']):
            for dst in range(header['node_count']):
                if src == dst:
                    continue
                if not ((transaction_df['src'] == src) & (transaction_df[
                    'dst'] == dst)).any():
                    links.append({'transaction_fist_date': transaction_df.
                        index[0], 'transaction_id': transaction_id, 'src':
                        src, 'dst': dst})
    return links
