Wireshark-dev: Re: [Wireshark-dev] what parameters for dissector_add() for a non-nested protoco
A follow-up answer to my original post (for posterity sake)...
fulko hew wrote on 07/16/2007 10:02:37 AM:
> I've scoured the READMEs and dissectors for details on the parameters
> for disector_add(). It seems as though all the cases are different
> than my (simple) case, so I'm at a loss as to how to register my
> sub-protocol, so it gets called properly.
>
> I have a private WTAP type for which I have written a simple dissector.
> (so far so good) In that dissector it looks at some data in
> 'pinfo->psuedo_header->acn.proto' that I use to figure out what
> dissector to call next... Ie. call_dissector(ipars_handle, tvb, pinfo,
> tree);
> For example:
>
> if (pinfo->psuedo_header->acn.proto == 0x5) {
> call_dissector(ipars_handle, tvb, pinfo, tree);
> }
>
> But when wireshark tries to call my (sub)dissector I get the error:
>
> Err file packet.c: line 1710 (call_dissector): assertion failed:
(handle
> != NULL)
>
> Thats because right now I'm missing the dissector_add() in my
> (sub)dissector
> ... because I don't know what to code in my case.
>
>
>
> 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);
>
>
> 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). Yes, it can also be found in all sorts of
> other encapsulations (that I'm not going to disect right now)
> but this is the primary case.
>
> What I think I want to is something like:
>
> dissector_add("", NULL, mytype_handle);
>
> just to make it aribitrarily available for that explicit call.
>
> When I code later dissector, I'll probably have more dissector_add()
> entries that _are_ based on super-frame data, but not right now.
>
> Either my approach is wrong, or I'm just missing something...
> Any ideas ?
a) It seems as though register_disector() _is_ the correct routine
to call in this case rather than some version of dissector_add().
I don't know what I was doing wrong (when I started from the
dissector template from README.developer), but I've now started
over by using packet-data.c as my template instead.
b) Whatever I did wrong was causing call_dissector() to call
assert on the 2nd pass through (with a null pointer).
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