Wireshark-dev: Re: [Wireshark-dev] smb.time || smb2.time is valid in a filter string but not in
From: Guy Harris <[email protected]>
Date: Thu, 13 Jun 2013 17:46:24 -0700
On Jun 13, 2013, at 5:16 PM, Richard Sharpe <[email protected]> wrote:

> I thought I would try to work around my issue with smb.time vs
> smb2.time by using a custom column field and putting in an expression,
> but it seems not to work. An expression that is acceptable in the
> Filter field is not acceptable in a custom column.
> 
> Why is this?

Because "||" is a Boolean "or", not a human-language "or". :-)

I.e., "a || b" is a packet-matching expression that matches if the expression "a" matches or the expression "b" matches, not a field expression that evaluates to whichever of the fields "a" or "b" is present (with "a" chosen if both are present, presumably).

The Filter field takes packet-matching expressions; the custom column field takes field names.  Field names are valid packet-matching expressions, which match if the field is present in the packet and don't match if it's not, but arbitrary packet-matching expressions aren't valid as custom columns.

Having a separate feature allowing a set of field names for a custom column could be useful.  I'm not sure an "||" operator, given its existing meaning in C (and in packet-matching expressions), would be the right syntax for that.

(Other expressions for custom columns might be useful, e.g. (ip.ttl % 17) + (1/137.035999074)*ip.proto - OK, well, *that* expression might not be useful, but....)