Wireshark-dev: Re: [Wireshark-dev] what parameters for dissector_add() for a non-nested protoco
On Jul 16, 2007, at 7:02 AM, Fulko.Hew@xxxxxxxxx wrote:
The normal approach is to have (for a frame level dissector):
dissector_add("wtap_encap", WTAP_ENCAP_MYTYPE, mytype_handle);
OR something like this for a nested dissector (where its based
on data in the super-frame (I think)):
dissector_add("ip.proto", SOME_INDICATOR, mytype_handle);
The normal approach, if you have a value of *any* sort (whether it's
the link-layer encapsulation type, a field in a protocol, a field in a
pseudo-header, a user preference, the current phase of the moon, ...)
is to have
dissector_add(dissector table name, value in that table,
mytype_handle);
The distinction between the two cases you give is not a distinction
that the Wiretap code makes, nor is it a distinction that we want to
make in the documentation.
But I in my case, my (sub)dissector protocol isn't a WTAP type,
nor is it (really) sub-protocol of a super-frame type (in my
first scenario).
As indicated, that doesn't mean you shouldn't have a dissector table
and have sub-dissectors register in it. You could, for example,
create a dissector table named "acn.proto" (or "acn_proto", or
"roland.the.headless.thomson.gunner" - the name is not tied to
anything else in Wireshark other than the calls that add to it) by
calling "register_dissector_table()":
acn_dissector_table = register_dissector_table("acn.proto", "ACN
protocol number", FT_UINT32, BASE_HEX);
have the dissector for your private WTAP type do
if (!dissector_try_port(acn_dissector_table, pinfo->pseudo_header-
>acn.proto, tvb, pinfo, tree))
call dissect_data to dissect the data, or something such as that
rather than checking for different values of pinfo->pseudo_header-
>acn.proto, and, for example, have the "ipars" dissector do
dissector_add("acn.proto", 0x5, ipars_handle);
What I think I want to is something like:
dissector_add("", NULL, mytype_handle);
just to make it aribitrarily available for that explicit call.
As you've discovered, if you want to have a dissector callable via
call_dissector(), you have to register that dissector by name with
register_dissector() - and you find the handle for the dissector by
calling find_dissector() with that name.
However, that's not necessarily what you want to do.
