On Tue, 22 May 2007 13:37:41 -0700
Stephen Fisher <stephentfisher@xxxxxxxxx> wrote:
> On Thu, May 17, 2007 at 11:08:57AM +0200, Tomasz Noi?ski wrote:
> > On Wed, 16 May 2007 15:48:36 -0700
> > Guy Harris <guy@xxxxxxxxxxxx> wrote:
> >
> > > Perhaps we need to have the key for the protocol data routines be a
> > > frame number and an offset within the frame, so that there can be
> > > multiple protocol data items within a link-layer frame.
> >
> > I think "offset within a frame" might be not enough: For example, in
> > my case, I decode the packets first, creating a nev tvb with
> > tvb_new_real_data(). So, unless there's some tvb-magic I don't know
> > about, simple offset just isn't enough.
> >
> > Numbering packets manually inside a frame (for example, as an
> > alternative to providing an offset, as Steve suggested) might be the
> > best solution...
>
> Would you mind sharing the code you have so far so we can study it and
> see if the offset would work or not?
I solved this particular problem, but it's not an elegant solution:
- my own id for pdus inside one frame (with help of a global variable -
yuck!),
- my own GHashTable in proto_data with those ids as a key.
However, if it might help develop a better solution, I'll be happy to
provide my example!
It's a lot of code and it doesn't work together yet, so I'll just post
simplified fragments/pseudocode that I think are most relevant.
/* The dissector routine passed to wireshark.
"P5 Datagrams" are COBS-encoded, so every datagram is
between two '\0' (\0-s are escaped).
Each such COBS-encoded datagram (without \0-s) is passed
to dissect_p5_cobsed_datagram.
BTW did I get the TCP-desegmentation thing?
I had some issues with the TCP dissector :(
*/
int dissect_p5(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {
// (...)
while (1) {
separator_offset = tvb_find_guint8(tvb, offset, -1, '\0');
if (separator_offset == -1) {
if (offset==available) {
return offset;
} else {
pinfo->desegment_offset = 0;
pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT;
return -1;
}
}
pdu_len = separator_offset - offset;
if (pdu_len > 0) {
pdu_tvb = tvb_new_subset(tvb, offset, pdu_len, pdu_len);
dissect_p5_cobsed_datagram(pdu_tvb, pinfo, tree);
}
offset += pdu_len + 1;
}
}
/* this one dissects one COBS-encoded "P5 datagram" */
static int dissect_p5_cobsed_datagram(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {
guint8 *uncobs = NULL;
tvbuff_t *uncobs_tvb = NULL;
// ...
uncobs = (guint8*) ep_alloc(bufsiz + 1);
// fill "uncobs" with unCOBSed tvb
uncobs_tvb = tvb_new_real_data(uncobs, bufsiz, bufsiz);
dissect_p5_datagram(uncobs_tvb, pinfo, new_tree);
}
/* single "P5 datagram" dissector */
static int dissect_p5_datagram(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree) {
// ...
// and here is where I want to use "proto data"!
}
Noix
