Wireshark · Wireshark-dev: Re: [Wireshark-dev] Creating a TVB

[Roland Knall <rknall@xxxxxxxxx>]

Hi Paul

Seems you have to create your own tvb chain here, as the data most likely is not presented yet in the packet_info structure, am I correct?

In this case, the corresponding methods would be in epan/tvbuff-int.h, but those are not supposed to be used "by the public", as they are subject to change.

I would go a different route though (admittedly a little bit of a hack). I would create a new tvb with tvb_memdup on the first byte of your protocol tvb, and then add the block data via tvb_new_real_data. In that case you have the luxury of the wmem system, as well as a good cleanup of the tvb.

cheers

Roland

On Wed, Feb 28, 2018 at 10:49 AM, Paul Offord <Paul.Offord@xxxxxxxxxxxx> wrote:

Hi,

 

I’m writing a dissector for a new block type.  I register a block read function for my new block type, and when Wireshark detects one of these blocks, my block read function is called with the following parameters:

 

gboolean tdb_read_block(FILE_T fh, guint32 block_data_len, gboolean c, wtapng_block_t *wtapng_block,   int *err, gchar **err_info)

 

This function then reads the block content like this:

 

    /* read block content */

    if (!wtap_read_bytes(fh, wtapng_block->frame_buffer->data, block_data_len, err, err_info)) {

        wmem_strdup_printf(wmem_file_scope(), "tdb_read_block: failed to read TDB");

        return FALSE;

    }

 

Later I need to parse the serialised data in wtapng_block->frame_buffer->data.  I have been writing my own accessors but I realised I am just duplicating existing TVB accessors.  I’ve looked through README.dissector which describes in detail how to use the TVB accessors, but not about creating a TVB.  There is a section on TVBUFF_SUBSET but that doesn’t seem relevant.

 

How do I get the block data into a TVB, preferably without having to copy it?

 

Thanks and regards…Paul

 

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