[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

Hi Richard,

When tdb_read_block(...) is called I don't have a TVB to subset.

Best regards...Paul

-----Original Message-----
From: Wireshark-dev [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Richard Sharpe
Sent: 28 February 2018 13:12
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] Creating a TVB

On Wed, Feb 28, 2018 at 1:49 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?

Do functions like tvb_new_subset* not work for you? Check existing dissectors.

--
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)
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