Wireshark C dissector error when filling subtree - c

Question

I have a simple Wireshark dissector which throws the following bug warning when it is run against a capture:
13:04:12 Warn Dissector bug, protocol usbserial, in packet 353: /wireshark/epan/proto.c:5504:
failed assertion "idx >= 0 && idx < num_tree_types"
The protocol registration function looks like this:
static gint ett_myproto = -1;
void
proto_register_myproto(void)
{
/* Set up field array */
static hf_register_info hf[] = {
{ &hf_myproto_payload,
{"Payload", "myproto.payload", FT_BYTES, BASE_NONE, NULL,
0x0, NULL, HFILL }},
};
/* Register protocol */
proto_myproto = proto_register_protocol("My Protocol", "myproto", "myproto");
/* Register protocol fields */
proto_register_field_array(proto_myproto, hf, array_length(hf));
/* Register the dissector */
register_dissector("myproto", dissect_myproto, proto_myproto);
}
The dissector does some general munging of data, but the core of the problem area seems to be:
static int
dissect_myproto(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
void *data _U_)
{
proto_item *ti;
proto_tree *myproto_tree;
/* Create top tree and add to the item */
ti = proto_tree_add_protocol_format(tree, proto_myproto, tvb, 0, -1,
"My Protocol");
myproto_tree = proto_item_add_subtree(ti, ett_myproto);
proto_tree_add_bytes_format(myproto_tree, hf_myproto_payload,
tvb, 0, payload_len,
NULL, "Payload");
}
What do I need to do to get the protocol to fill the subtree correctly?

Answer 1

The problem here is a failure to register the subtree as part of a subtree array (hint from here).
This is done in the protocol registration function, and requires "packaging" the subtree variables (of which there is only one here: ett_myproto) into an array, and then registering that array using proto_register_subtree_array:
static gint ett_myproto = -1;
void
proto_register_myproto(void)
{
/* Set up field array */
static hf_register_info hf[] = {
....
};
/* Register protocol */
proto_myproto = proto_register_protocol("My Protocol", "myproto", "myproto");
/* Register protocol fields */
proto_register_field_array(proto_myproto, hf, array_length(hf));
/* Setup and register all protocol subtrees */
static gint *ett[] = {
&ett_myproto,
};
proto_register_subtree_array(ett, array_length(ett));
/* Register the dissector */
register_dissector("myproto", dissect_myproto, proto_myproto);
}
The ett variables are indices used to refer to GUI information about the state of the subtree (e.g. expanded or not).