Re: Index of multiple protocol frames in one packet?

[Anders Broman <anders.broman () ericsson com>]

From: wireshark-dev-bounces () wireshark org [mailto:wireshark-dev-bounces () wireshark org] On Behalf Of Pascal Quantin
Sent: den 12 oktober 2015 17:43
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] Index of multiple protocol frames in one packet?



2015-10-12 17:35 GMT+02:00 Jeff Morriss <jeff.morriss.ws () gmail com<mailto:jeff.morriss.ws () gmail com>>:
On 10/06/15 02:17, Pascal Quantin wrote:


2015-10-06 8:07 GMT+02:00 Petr Gotthard <petr.gotthard () centrum cz<mailto:petr.gotthard () centrum cz>
<mailto:petr.gotthard () centrum cz<mailto:petr.gotthard () centrum cz>>>:

    Hello,

    Is there a way to distinguish multiple frames of the same protocol
    in one TCP/IP packet? I have several small AMQP frames which all fit
    into a single IP frame, so they share a single packet_info
    structure.When I call p_add_proto_data() for the second AMQP frame,
    it (obviously) overwrites data stored for the first frame, so I need
    to distibguish between them somehow.

    Is there a counter that would tell me "this is a third AMQP frame in
    this pinfo"? I found packet_info->curr_layer_num, but this is useful
    for nested frames (like IP in IP). Is there something similar for
    groupped frames, please?


Hi Peter,

I'm not sure we have such counter, but
https://code.wireshark.org/review/#/c/10579/ suggested the use of
tvb_raw_offset as key for p_(add|get)_proto_data() functions which seems
a good tradeoff.

Actually there is such a counter in frame_data: subnum.  But it's not widely used: for now it's only used in EPL, RRC, 
and UMTS_FP.

Thanks for the hint Jeff (I did not know this one).
It appears that frame_data.c is only setting it to 0, and that increment need to be handled directly by dissectors. So 
it means that for a wider usage, (tcp|udp)_dissect_pdus() function (among others) should be modified so as to increment 
it when calling a new subdissector.
Cheers,
Pascal.

Pinfo-> curr_layer_num is supposed to handle it I think but the problem may be to have the TCP/UDP/?/ Dissector call 
the same dissector again if the complete tvb wasn’t used. If the dissector itself is looping over the data it should 
probably use call_disector() or something rather than do an internal loop.
Regards
Anders

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