Wireshark · Wireshark-dev: [Wireshark-dev] How to parse a protocol with two different PDU types in a single connection?

[Kaul <mykaul@xxxxxxxxx>]

Hello,

I have a protocol that begins with a PDU of type A ('link' state), then switches after it performed some negotiation to a PDU type B ('data' state).
I've tried something similar to:
conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
    if (!conversation) {
        conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
    }
   
    myproto_info = (myproto_conversation_t*)conversation_get_proto_data(conversation, proto_myproto);
    if(!myproto_info) {
        /* We don't yet have a conversation, so create one. */
        myproto_info = se_alloc0(sizeof(myproto_conversation_t));
        myproto_info->destport = pinfo->destport; /* Useful to differ between c2s and s2c packets */
        myproto_info->pdu_type_A = TRUE;
        conversation_add_proto_data(conversation, proto_myproto, myproto_info);
    }

    if (myproto_info->pdu_type_A == TRUE) {
        /* If we are still in the link state part of the protocol */
        tcp_dissect_pdus(tvb, pinfo, tree, myproto_desegment, 16, get_myproto_link_pdu_len, dissect_myproto_link_pdu);
    } else {
        tcp_dissect_pdus(tvb, pinfo, tree, myproto_desegment, 16, get_myproto_data_pdu_len, dissect_myproto_data_pdu);
    }

And in dissect_myproto_link_pdu():
if (myproto_info->destport == pinfo->destport) {
    /* dissectC2S messages */
} else {
  /* S2C messages - and turn off pdu_type_A ! */
 myproto_info->pdu_type_A = FALSE;
}

This doesn't work well. Once I turn it off, nothing is dissected any more - as if it won't reach the first tcp_dissect_pdus() line anymore - even for other conversations.

1. Is my approach correct?
2. Any hint as to what I'm doing wrong here?

TIA,
Yaniv.