Guy Harris <guy@...> writes:
> On Nov 26, 2013, at 7:58 AM, Christopher Maynard <Christopher.Maynard <at>
gtech.com> wrote:
>
> > Maybe the snaplen column should display the actual snaplen value instead of
> > “default”? The GTK version does this too, which I’m also not a fan of, as
> > “default” doesn’t actually tell you anything.
>
> In the best of all possible worlds, libpcap - and the pcap file format -
would have allowed a value of 0 to mean
> "unlimited", and we wouldn't have to worry about code reading pcap files
allocating buffers based on the
> snaplen and never changing the buffer size.
>
> Unfortunately, "allocating buffers based on the snaplen and never changing
the buffer size" is exactly
> what most versions of libpcap do, and have done going back at least to
libpcap 0.7 and probably all the way
> back to 0.4, at least.
>
> This means that a value of 0 in the capture file for "unlimited" would
produce files that can't be read by many
> versions of libpcap, and thus by programs linked with those versions, and
a value of 2^32-1 or 2^31-1 would
> cause libpcap to try to allocate a *huge* chunk of memory, almost
certainly failing in 32-bit code.
>
> In addition, libpcap has traditionally treated a captured length > 65535
as an indication that the record
> for the packet was corrupt.
>
> So this means we can't *truly* have an "unlimited" snapshot length.
>
> Nevertheless, I definitely think the UI should provide a way to easily
tell Wireshark "I don't want packets
> cut short", so they shouldn't have to explicitly type "6" "5" "5" "3" "5"
to get that; there should be a check
> box to request "largest possible snaplen".
>
> I might also be tempted to display that as "none" - or as the "has
snaplen" checkbox not being checked and the
> large value used for that purpose displayed but grayed out.
There seems to be some confusion, although maybe it's just my own. I can't
quite tell if the patch is being rejected or not.
The patch I provided doesn't force the user to explicitly type "6" "5" "5"
"3" "5". Rather, it merely displays the default value (currently 65535) in
the Capture Options dialog rather than the text, "default", so that the user
is made aware of the actual default snaplength value; otherwise the user is
not explicitly shown what that default value is. I simply think it's better
to show the actual value. The "Limit each packet to" is still insensitive
until the user manually checks it and is then allowed to change the
snaplength (or leave it at the default value).
Anyway, the intent of the patch was simply to display the default value,
rather than "default", to make the user explicitly aware of it. If the
patch somehow introduces some other side-affects, then that was not my intent.
- Chris
