How to use the pybatfish.datamodel.flow.HeaderConstraints function in pybatfish

localIP = loopbacks[loopbacks['Node'] == fromNode]['IP'][0]
    leaves = set(loopbacks[loopbacks['Node'].str.contains('leaf')]['IP'])
    leaves.remove(localIP)
    spines = set(loopbacks[loopbacks['Node'].str.contains('spine')]['IP'])
    mpath = len(spines)

    logging.info("Progress: Analyzing traceroute from Leaf-3 to Leaf-1 and Leaf-2")
    # Set up the resulting data structure
    troute = dict()
    for leaf in leaves:
        troute[leaf] = dict()

    # Build headers for traceroute flows
    for leaf in leaves:
        troute[leaf]['header'] = header(srcIps=localIP,dstIps=leaf)

    # Ask questions about traceroute
    for leaf,data in troute.items():
        troute[leaf]['trace'] = bfq.traceroute(startLocation=fromNode, headers=data['header']).answer()
    
    # Get first flow disposition for traces
    for leaf,data in troute.items():
        troute[leaf]['result'] = data['trace'].get('answerElements')[0]['rows'][0]['Traces'][0]['disposition']

    # Get traceroute paths to reach Leaf-1 and  Leaf-2
    for leaf,data in troute.items():
        troute[leaf]['paths'] = data['trace'].get('answerElements')[0]['rows'][0]['Traces']

    # Get traceroute hops to reach Leaf-1 and Leaf-2
    for leaf,data in troute.items():
        troute[leaf]['hops'] = data['trace'].get('answerElements')[0]['rows'][0]['Traces'][0].get('hops',[])

failed_link1_index = random.randint(0, len(links) - 1)
    failed_link2_index = random.randint(0, len(links) - 1)
    print(" - Deactivating Links:{} + {}".format(links.loc[failed_link1_index].Interface,
                                                  links.loc[failed_link2_index].Interface))

    FAIL_SNAPSHOT_NAME = "fail_snapshot"
    bf_fork_snapshot(
        BASE_SNAPSHOT_NAME,
        FAIL_SNAPSHOT_NAME,
        deactivate_interfaces=[links.loc[failed_link1_index].Interface,
                               links.loc[failed_link2_index].Interface],
        overwrite=True
    )

    answer = bfq.differentialReachability(
        headers=HeaderConstraints(dstIps='server2')
    ).answer(
        snapshot=FAIL_SNAPSHOT_NAME,
        reference_snapshot=BASE_SNAPSHOT_NAME
    ).frame()

    if len(answer) > 0:
        print("[FAIL] No reachability discovered for the following flow(s)...")
        print_diff_reachability(answer)
        sys.exit(1)

print("[SUCCESS] No reachability issues found after {} rounds of chaos!".format(MAX_CHAOS))