Ethereal-dev: Re: [Ethereal-dev] New dissector: IAX2 (Inter-Asterisk eXchange 2) VoIP protocol
On Jan 26, 2004, at 4:06 PM, Alastair Maw wrote:
I've therefore modified things so that the dissector assumes two bytes
for the address header, two for the port and four for the IPv4
address. Unfortunately, there isn't an IAX RFC/spec to make it clear
that this is definitely the right thing to do. One is apparently in
the works. If Asterisk is ported to architectures other than Linux and
FreeBSD this might need some further attention,
Note that {Free,Net,Open}BSD, BSD/OS, and Darwin/Mac OS X have similar
socket address structures that aren't exactly the same as the Linux
ones - instead of a 2-byte address family type, they have a 1-byte
length and 1-byte address family type.
static const value_string iax_ies_type[] = {
That's not used, because the IE type and length aren't put into the
protocol tree. They probably should be put into the protocol tree.
static void
dissect_iax2 (tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
{
char buffer[150];
proto_tree *iax2_tree = NULL, *ies_tree = NULL, *codec_tree = NULL;
proto_item *ti = 0, *ies_base = 0, *codec_base = 0;
guint32 offset = 0, codecs = 0, i = 0, mask = 0, retransmission = 0;
long addr;
const char *data = tvb_get_ptr (tvb, offset, -1);
Dissectors shouldn't just grab a pointer to the entire packet data and
directly reference it. For one thing, if any field in the packet is
not aligned on the natural boundary, that'll crash on some machines
(e.g., SPARC). For another, it means no bounds checking is done.
Instead, fields should be fetched one at a time with the appropriate
"tvb_get" routines.
I've changed the dissector to do that.
struct ast_iax2_full_hdr *h;
That structure uses some GCC-specific features, such as
__attribute((packed)), and some features not in C89, such as
zero-length arrays.
I've replaced references to structure members with references to values
fetched with the appropriate "tvb_get" routines, and removed the
structure definitions from "packet-iax2.h".
if (check_col (pinfo->cinfo, COL_PROTOCOL))
{
col_set_str (pinfo->cinfo, COL_PROTOCOL, PROTO_TAG_IAX2);
}
The Info column should be cleared at that point, so that if the
dissector throws an exception, due to the packet data being cut short,
before setting the Info column, the column doesn't show whatever stuff
the previous dissector put there.
I've checked in the dissector, with the changes in question (except for
putting the IE type and length into the protocol tree).
