Wireshark-dev: Re: [Wireshark-dev] Another one with dissector questions
From: "Jaap Keuter" <[email protected]>
Date: Tue, 22 Apr 2008 15:58:55 +0200 (CEST)
Hi,

1) You better use a conversation. Read README.developer on what
conversations are and how they are designed for specifically this purpose.
Using globals is never a good way to do this, especially when we intend to
multithread/work with multiple files.

2) ett's are datastructures for subtrees. They hold the expanded/collapsed
state for instance. You can reuse them, but then all these subtrees will
have the same expanded/collapsed state.

3) Remove all display filters and *disable packet coloring* (which is also
display filter based) to get tree==NULL.

Thanx,
Jaap

> Hi,
>
> I'm working on a dissector for about a month and some questions came up
> when doing more than just basic dissection of the packets:
>
> 1) The protocol consists mainly of two different types of packets:
> configuration frames and data frames. Configuration frames are send at
> the beginning of a transmission or when the configuration of the sending
> device changes and describe the content and format of data frames.
> Without the knowledge out of the configuration frames, the data frames
> can't be dissected.
>   So I created a struct, called config_frame to save the information of
> the configuration frames and put these config_frames into a global
> GArray. This global array is (re)initialized in my dissectors init
> function and pinfo->fd->num (also saved in config_frame) is used to
> ensure that every configuration frame just adds one config_frame struct
> to the array. When the dissector comes to a data frame, he searches
> through that global array for a matching config_frame and uses it to
> dissect the data frame. Is that the right way to do that?
>
> 2) What are the ett_... values for? Section 1.6.2 of README.developer
> explains how to initialize and use them, but I didn't get what they are
> good for. Is it save to pass the same ett_ variable multiple times? (The
> data in the data frames is nested and I do that, didn't have a problem
> so far)
>
> 3) To understand the sequence in that the "proto_register_...", the
> "proto_reg_handoff_...", the init and the dissect functions are called,
> I put the following at the beginning of the dissect function:
>
>    printf("dissect(): %s\n", (!tree ? "*tree null" : "*tree valid"));
>
>    and always get "*tree valid". Do i need a special configure switch to
> enable the "Operational dissection" (enable something like a release
> build)?
>
> Thanks,
> Jens
>
>
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> Tel.: +43 5523 507 422, Fax.: +43 5523 507 999
> http://www.omicron.at/  jens.steinhauser AT omicron.at
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