Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] master 04c39bb: Add Lua heuristic dissec
From: Bill Meier <[email protected]>
Date: Fri, 14 Mar 2014 17:06:39 -0400

  doc/README.heuristic          |   10 +--

+     * but ONLY do this if your heuristic sits directly on top of UDP
        or TCP (ie, you did heur_dissector
+     * otherwise you'll be overriding the dissector that called your
        heuristic dissector.

I think this is not correct. There is at least one "transport" protocol other than TCP & UDP (i.e., DCCP) which currently has a heuristic table and calls 'try_conversation()' and thus heuristic sub-dissectors can use conversation_set_dissector().
I think, in theory, any protocol associated with the known
'port_type's [1] can establish a conversation for that port_type and then have heuristic sub-dissectors which can call conversation_set_dissector().
In actuality, only a few dissectors currently do so.

How about the something like following wording:

... but only do this if your heuristic sits directly on top of
    (was called by) a dissector which established a conversation
    for the protocol "port type". IOW: directly over TCP, UDP, ...

Looking at the Wireshark dissectors: I see at least one
possibly problematical case:

packet-soupbintcp has heuristic sub-dissectors and uses try_conversation() even though it actually uses (I think) the conversation established bu packet-tcp.
I thinks this means that if packet-tcp has "try heuristic first" that 
things won't work right.
I'll have to research this further.


/* Types of port numbers Wireshark knows about. */
typedef enum {
    PT_NONE,		/* no port number */
    PT_SCTP,		/* SCTP */
    PT_TCP,		/* TCP */
    PT_UDP,		/* UDP */
    PT_DCCP,		/* DCCP */
    PT_IPX,		/* IPX sockets */
    PT_NCP,		/* NCP connection */
    PT_EXCHG,		/* Fibre Channel exchange */
    PT_DDP,		/* DDP AppleTalk connection */
    PT_SBCCS,		/* FICON */
    PT_IDP,		/* XNS IDP sockets */
    PT_TIPC,		/* TIPC PORT */
    PT_USB,		/* USB endpoint 0xffff means the host */
    PT_IBQP,		/* Infiniband QP number */
} port_type;