Tracking a conversation across a source port change

I have a protocol in which the client changes source ports regularly (the server has a single well known port). I'm trying to maintain a single conversation through this (each host can only have a single instance of the client). For example, I would expect this kind of traffic (52230 is the well known port):

client:12345 -> server:52230
server:52230 -> client:12345
client:23456 -> server:52230
server:55230 -> client:23456

This is one conversation. I've been trying to build a dissector that will handle this, and expected NO_PORT_B to be exactly what I needed, but I haven't been able to get it to work. In its most basic form, I try finding the conversation this way:

conversation_t *conversation = find_conversation(pinfo->fd->num,
                &pinfo->src, &pinfo->dst,
                pinfo->ptype, 
                pinfo->srcport, pinfo->destport, 
                NO_PORT_B);

If it doesn't exist, I try creating it this way:

    conversation = conversation_new(pinfo->fd->num,
                &pinfo->src, &pinfo->dst,
                pinfo->ptype, 
                pinfo->srcport, pinfo->destport,
                NO_PORT2);

That leads to:

first column: CONV + "!" if a conversation was not found and was created
second column: source
third column: destination
forth column: found conversation (possibly created)
fifth column: counter number attached to conversation conversation_add_proto_data
CONV!:  172.16.244.1:61661  ->  172.16.244.160:52230    =>  0x10cd02d68 1
CONV!:  172.16.244.160:52230    ->  172.16.244.1:61661  =>  0x10cd02fe8 2
CONV!:  172.16.244.1:61669  ->  172.16.244.160:52230    =>  0x10cd033c8 3
CONV!:  172.16.244.160:52230    ->  172.16.244.1:61669  =>  0x10cd03578 4
CONV:   172.16.244.1:61669  ->  172.16.244.160:52230    =>  0x10cd033c8 3
CONV:   172.16.244.160:52230    ->  172.16.244.1:61669  =>  0x10cd03578 4
CONV:   172.16.244.1:61669  ->  172.16.244.160:52230    =>  0x10cd033c8 3

No wildcarding appears to be happening. It isn’t even joining symmetric communications like the first two packets.

I’ve tried many other combinations, including passing 0 instead of the port, or passing 52230 as the srcport rather than pinfo->srcport. I’ve even played with CONVERSATION_TEMPLATE, but I’m not quite certain what it’s doing. Every combination has created multiple conversations.

Below is my full test code. I can post a small pcap if that’s helpful.

#include <stdio.h> 

#include <config.h>
#include <epan/packet.h>
#include <epan/conversation.h>

#define AMP_PORT 52230
static dissector_handle_t amp_handle;
static int proto_amp = -1;
static gint ett_amp = -1;
static int counter = 1;
static int
dissect_amp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {
col_set_str(pinfo-> cinfo, COL_PROTOCOL, "AMP");
col_clear(pinfo->cinfo, COL_INFO);
int newConv = 0;
conversation_t *conversation = find_conversation(pinfo-&gt;fd-&gt;num,
                &amp;pinfo-&gt;src, &amp;pinfo-&gt;dst,
                pinfo-&gt;ptype, 
                pinfo-&gt;srcport, pinfo-&gt;destport, 
                NO_PORT_B);
if (! conversation) {
    /* If we make a conversation, stick some unique data on it */
    newConv = 1;
    conversation = conversation_new(pinfo-&gt;fd-&gt;num,
                &amp;pinfo-&gt;src, &amp;pinfo-&gt;dst,
                pinfo-&gt;ptype, 
                pinfo-&gt;srcport, pinfo-&gt;destport,
                NO_PORT2);

    int *writeValue = malloc(sizeof(int));
    *writeValue = counter++;
    conversation_add_proto_data(conversation, proto_amp, writeValue);
    // conversation_set_dissector(conversation, amp_handle);
}

int *readValue = conversation_get_proto_data(conversation, proto_amp);

printf(&quot;CONV%s:\t%s:%u\t-&gt;\t%s:%u\t=&gt;\t%p\t%d\n&quot;,
    newConv ? &quot;!&quot; : &quot;&quot;,
    ep_address_to_str(&amp;pinfo-&gt;src), 
    pinfo-&gt;srcport,
    ep_address_to_str(&amp;pinfo-&gt;dst),
    pinfo-&gt;destport,
    conversation,
    readValue ? *readValue : 0);

return tvb_length(tvb);

}
void
proto_register_amp(void) {
static hf_register_info hf_amp[] = {};
static gint *ett_amp_arr[] = { &ett_amp };
proto_amp = proto_register_protocol(&quot;KACE Agent Messaging Protocol&quot;, &quot;AMP&quot;, &quot;amp&quot;);
proto_register_field_array(proto_amp, hf_amp, array_length(hf_amp));
proto_register_subtree_array(ett_amp_arr, array_length(ett_amp_arr));

}
void
proto_reg_handoff_amp(void)
{
amp_handle = new_create_dissector_handle((new_dissector_t)dissect_amp, proto_amp);
dissector_add_uint("tcp.port", AMP_PORT, amp_handle);
}