[Hartmut Mueller <hartmut@xxxxxxxxxxxxxxxxx>]

Hi folks,

During the implementation of BACnet (Building Automatition and Control 
Network) I ran across this problem by invoking ethereal (while make'ing):
** ERROR **: file packet.c: line 1216 (dissector_add): assertion failed: 
(sub_dissectors)

It is my first contact with the ethereal sourcecode and I was a little bit 
confused by old/new dissectors. Looking at sources packet-*.c, I recognised 
several different "flavours" of calling the next dissector. Calling the 
BLVC-dissector was easy (udp.port == 47808), but the BACnet-dissector isn't 
(bvlc.function == 0x0b).

A good pointer to documentation addressing this problem would be fine (I've 
read README.developer and README.tvbuff).


In packet-bvlc.c:

next_tvb = tvb_new_subset(tvb,offset+4,-1,npdu_length);
dissect_bacnet(next_tvb, pinfo, tree);

void
proto_register_bvlc(void)
{
        static hf_register_info hf[] = {
                { ... },
                { &hf_bvlc_function,
                        { "Function",           "bvlc.function",
                        FT_UINT8, BASE_HEX, NULL, 0xff,
                        "BLVC Function" }
                },
                { ... },
        };
        static gint *ett[] = {
                &ett_bvlc,
        };
        proto_bvlc = proto_register_protocol("BACnet Virtual Link Control",
            "BVLC", "bvlc");
        proto_register_field_array(proto_bvlc, hf, array_length(hf));
        proto_register_subtree_array(ett, array_length(ett));
        register_dissector("bvlc", dissect_bvlc, proto_bvlc);
}


... and in packet-bacnet.c:

void
proto_reg_handoff_bacnet(void)
{
        dissector_add("bvlc.function", 0x0b, dissect_bacnet, proto_bacnet);
}


It would be better to include the source in the CVS-tree to have everything 
handy for you. Who is in charge of that? I will supply a patch if BACnet is 
wanted in Ethereal and
mail ethereal-dev < "Generate a patch file using "cvs diff [file] > 
my.patch"" upon request.

Details: ethereal-0.8.15 (NOT from CVS), Linux Debian Woody, 
gcc version 2.95.3 20010125 (prerelease), libpcap.0.6.1, libglib-1.2.0.0.8



Cheers, Hartmut