On Jan 28, 2010, at 11:12 AM, Brian Oleksa wrote:
> Basically... I am having a hard time converting my code below to use the
> built in calls to make sure there is no buffer overrun
The builtin calls *themselves* do the buffer checks - if you pass an
out-of-range offset to, for example, a tvb_get_ call, it will throw an
exception, and dissection of the packet will stop. proto_tree_add_item() uses
tvb_get_ calls to fetch data, so they will also cause an exception to be thrown
if the offset is out of range.
> and to make sure
> that I am on the correct packet I am trying to dissect.
>
> I have a header of size 18 that I want to skip..
No, you have a header of size 18 that you want to *dissect*, with a 2-byte
magic field, an 8-byte checksum field (which, as per "CRC Questions", is
probably 4 bytes of 0 and 4 bytes of CRC32, thanks to Java's lack of unsigned
data types), and an 8-byte transmission time. Don't just skip it, put the
header fields into the dissection along with the rest of the packet.
> then the next packet I am dissecting.
What you're presumably dissecting are part of the *same* packet. The Helen
packet format:
https://www.darkcornersoftware.com/confluence/display/open/Packet+Structure
indicates that a packet has the 18-byte header followed by a series of
extensions; those are all part of the same packet.
The page at
https://www.darkcornersoftware.com/confluence/display/open/Helen+Manual
says this runs over UDP, so there's one Helen packet for each UDP packet. Your
dissector will be called by the UDP dissector for each UDP packet, so it is
handed a tvbuff containing one and only one Helen packet, so you don't have to
worry about whether you're on the correct packet - you will, by definition, be
on the *only* packet within a given UDP packet.
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