How can a Packet/Field in a PacketListField/FieldListField find its index or access the preceding Packet/Field neighbor?

[douniwan5788]

In some protocols, a common pattern is followed:	Fields
Payloads Count
Payload 1 Offset
Payload 1 Size
Payload 2 Offset
Payload 2 Size
Payload N Offset
Payload N Size
...
Payload 1
Payload 2
...
Payload N

I have two PacketListFields, one for offsets and sizes and the other for payloads. However, the payload Packet cannot determine its size if it is unable to locate its index within the PacketListFields.

If adding an index attribute similar to parent to Field/Packet is necessary, I can make a PR

[gpotter2]

For very complex cases such as this one, you'll likely have to do a custom field.

[douniwan5788]

That's not a complex scenario. I believe it's a very common variant of the TLV format pattern for protocols with optional fields. Rewriting custom fields similar to PacketListField/FieldListField requires considerable effort and becomes hard to maintain. Would it be considered if I were to submit a PR for this change?

[gpotter2]

Sorry I read that too quickly. In your case the payload PacketListField can use the pkt.parent attribute to go back one layer and get the size.

[douniwan5788]

Yes, the payloadPacket can retrieve PacketListFields through the parent, but cannot determine its size if it is unable to locate its index within the PacketListFields.

[gpotter2]

You can use next_cb_cls which contains the current "list", therefore the index.

[gpotter2]

Please note that this is not a forum but a bugtracker. Please ask your question on stack overflow or on the gitter. Thanks for your understanding