Don't seem to be able to skip subnet/lease selection in a hook

What's the proper way to skip lease/subnet selection and delegate everything to a hook library? I'm trying to hook kea up to a custom IPAM system.

The best I can tell is that you implement pkt4_receive/pkt4_send and tell lease4_select and subnet4_select as setStatus(CalloutHandle::NEXT_STEP_SKIP).

The hook documentation for lease4_select says:

Next step status: If any callout installed on the "lease4_select" hook sets the next step action to SKIP, the server will not assign any lease and the callouts become responsible for the lease assignment. If the callouts fail to provide a lease, the packet processing will continue, but client will not get an address.

I'm confused as to which (other) callouts should "provide a lease" if I'm skipping lease4_select? Should I be overwriting the lease4 argument in lease4_select instead, and setting NEXT_STATUS_CONTINUE? If I do this, how do I prevent Kea from recording the lease? Do I need to SKIP lease4_* callouts too?

The only subnet is one from 0.0.0.0 - 255.255.255.255

 int pkt4_receive(CalloutHandle &handle) {
   ... business logic here ...
 }

 int pkt4_send(CalloutHandle &handle) {
   ... business logic here ...
 }

 int lease4_select(CalloutHandle &handle) {
   handle.setStatus(CalloutHandle::NEXT_STEP_SKIP);
   return 0;
 }

 int subnet4_select(CalloutHandle &handle) {
   handle.setStatus(CalloutHandle::NEXT_STEP_SKIP);
   return 0;
 }

Kea 2.4 seems to drop the packet after DHCP4_PACKET_NAK_0003 (even though pkt4_send will eventually fill in everything), the client never receives anything:

2023-10-17 06:44:16.759 DEBUG [kea-dhcp4.packets/657887.140610219676288] DHCP4_BUFFER_RECEIVED received buffer from 127.1.2.3:6671 to 127.0.0.1:6672 over interface lo
2023-10-17 06:44:16.759 DEBUG [kea-dhcp4.options/657887.140610166056640] DHCP4_BUFFER_UNPACK parsing buffer received from 127.1.2.3 to 127.0.0.1 over interface lo
2023-10-17 06:44:16.759 DEBUG [kea-dhcp4.packets/657887.140610166056640] DHCP4_PACKET_RECEIVED [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: DHCPDISCOVER (type 1) received from 127.1.2.3 to 127.0.0.1 on interface lo
2023-10-17 06:44:16.759 DEBUG [kea-dhcp4.packets/657887.140610166056640] DHCP4_QUERY_DATA [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1, packet details: local_address=127.0.0.1:6672, remote_address=127.1.2.3:6671, msg_type=DHCPDISCOVER (1), transid=0x
1,
options:
  type=053, len=001: 1 (uint8)
  type=060, len=015: "HTTPClient::7::" (string)
  type=082, len=012:,
options:
    type=001, len=004: 65:74:68:30
    type=005, len=004: 172.16.42.1 (ipv4-address)
  type=093, len=002: 0(uint16)
2023-10-17 06:44:16.759 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUTS_BEGIN begin all callouts for hook pkt4_receive
2023-10-17 06:44:16.759 INFO  [kea-dhcp4.myhooklib-callouts/657887.140610166056640] LOG_MYHOOKLIB_GENERIC Carbide: type=082, len=012:,
options:
  type=001, len=004: 65:74:68:30
  type=005, len=004: 172.16.42.1 (ipv4-address)
2023-10-17 06:44:16.759 INFO  [kea-dhcp4.myhooklib-callouts/657887.140610166056640] LOG_MYHOOKLIB_PKT4_RECEIVE: CIRCUIT ID [eth0] in packet
2023-10-17 06:44:16.759 INFO  [kea-dhcp4.myhooklib-callouts/657887.140610166056640] LOG_MYHOOKLIB_GENERIC Carbide: type=060, len=015: "HTTPClient::7::" (string)
2023-10-17 06:44:16.759 ERROR [kea-dhcp4.myhooklib-callouts/657887.140610166056640] LOG_MYHOOKLIB_PKT4_RECEIVE: Missing option [93] in packet
2023-10-17 06:44:16.846 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUT_CALLED hooks library with index 1 has called a callout on hook pkt4_receive that has address 0x7fe25b9f3ae3 (callout duration: 87.199 ms)
2023-10-17 06:44:16.846 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUTS_COMPLETE completed callouts for hook pkt4_receive (total callouts duration: 87.199 ms)
2023-10-17 06:44:16.846 DEBUG [kea-dhcp4.dhcpsrv/657887.140610166056640] DHCPSRV_CFGMGR_SUBNET4_ADDR selected subnet 0.0.0.0/0 for packet received by matching address 172.16.42.1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.packets/657887.140610166056640] DHCP4_SUBNET_SELECTED [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: the subnet with ID 1 was selected for client assignments
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.packets/657887.140610166056640] DHCP4_SUBNET_DATA [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: the selected subnet details: 0.0.0.0/0
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_IDENTIFIER get one host with IPv4 reservation for subnet id 1, identified by hwaddr=020000000001
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_IDENTIFIER get all hosts with reservations using identifier: hwaddr=020000000001
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_IDENTIFIER_COUNT using identifier hwaddr=020000000001, found 0 host(s)
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_IDENTIFIER_NULL host not found using subnet id 1 and identifier hwaddr=020000000001
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_IDENTIFIER get one host with IPv4 reservation for subnet id 1, identified by circuit-id=65746830
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_IDENTIFIER get all hosts with reservations using identifier: circuit-id=65746830
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_IDENTIFIER_COUNT using identifier circuit-id=65746830, found 0 host(s)
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_IDENTIFIER_NULL host not found using subnet id 1 and identifier circuit-id=65746830
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.dhcp4/657887.140610166056640] DHCP4_CLASS_ASSIGNED [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: client packet has been assigned to the following class(es): UNKNOWN
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.dhcp4/657887.140610166056640] DHCP4_CLASS_ASSIGNED [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: client packet has been assigned to the following class(es): ALL, VENDOR_CLASS_HTTPClient::7::, UNKNOWN
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.ddns/657887.140610166056640] DHCP4_CLIENT_HOSTNAME_PROCESS [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: processing client's Hostname option
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.dhcpsrv/657887.140610166056640] DHCPSRV_MEMFILE_GET_HWADDR obtaining IPv4 leases for hardware address hwtype=1 02:00:00:00:00:01
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.alloc-engine/657887.140610166056640] ALLOC_ENGINE_V4_OFFER_NEW_LEASE allocation engine will try to offer new lease to the client [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_ADDRESS4 get one host with reservation for subnet id 1 and IPv4 address 0.0.0.1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_ADDRESS4 get all hosts with reservations for IPv4 address 0.0.0.1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ALL_ADDRESS4_COUNT using address 0.0.0.1, found 0 host(s)
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.hosts/657887.140610166056640] HOSTS_CFG_GET_ONE_SUBNET_ID_ADDRESS4_NULL host not found using subnet id 1 and address 0.0.0.1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.dhcpsrv/657887.140610166056640] DHCPSRV_MEMFILE_GET_ADDR4 obtaining IPv4 lease for address 0.0.0.1
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUTS_BEGIN begin all callouts for hook lease4_select
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUT_CALLED hooks library with index 1 has called a callout on hook lease4_select that has address 0x7fe25b9f4647 (callout duration: 0.007 ms)
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.callouts/657887.140610166056640] HOOKS_CALLOUTS_COMPLETE completed callouts for hook lease4_select (total callouts duration: 0.007 ms)
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.dhcpsrv/657887.140610166056640] DHCPSRV_HOOK_LEASE4_SELECT_SKIP Lease4 creation was skipped, because of callout skip flag.

... not sure what's supposed to happen at this point to prevent the WARN/ERROR of not having a lease ...

Then:

2023-10-17 06:44:16.847 WARN  [kea-dhcp4.alloc-engine/657887.140610166056640] ALLOC_ENGINE_V4_ALLOC_FAIL_SUBNET [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: failed to allocate an IPv4 lease in the subnet 0.0.0.0/0, subnet-id 1, shared network (none)
2023-10-17 06:44:16.847 WARN  [kea-dhcp4.alloc-engine/657887.140610166056640] ALLOC_ENGINE_V4_ALLOC_FAIL [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: failed to allocate an IPv4 address after 1 attempt(s)
2023-10-17 06:44:16.847 WARN  [kea-dhcp4.alloc-engine/657887.140610166056640] ALLOC_ENGINE_V4_ALLOC_FAIL_CLASSES [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: Failed to allocate an IPv4 address for client with classes: ALL, VENDOR_CLASS_HTTPClient::7
::, UNKNOWN
2023-10-17 06:44:16.847 DEBUG [kea-dhcp4.bad-packets/657887.140610166056640] DHCP4_PACKET_NAK_0003 [hwtype=1 02:00:00:00:00:01], cid=[no info], tid=0x1: failed to advertise a lease, client sent ciaddr 0.0.0.0, requested-ip-address (no address)

... no further output here ...

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