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Re: smb.time || smb2.time is valid in a filter string but not in a custom column field?
From: Richard Sharpe <realrichardsharpe () gmail com>
Date: Fri, 14 Jun 2013 06:35:04 -0700

On Fri, Jun 14, 2013 at 6:27 AM, Jeff Morriss <jeff.morriss.ws () gmail com> wrote:
On 06/13/13 20:46, Guy Harris wrote:


On Jun 13, 2013, at 5:16 PM, Richard Sharpe <realrichardsharpe () gmail com>
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.


What would an "or" in the context of columns mean?  In particular in the
case where both fields have a value.

Ahhh, the value of discussion.

Since each is prefaced by a protocol name, in this case it would never
happen. Perhaps it should use short circuit evaluation. The first that
exists is the value that is used.

-- 
Regards,
Richard Sharpe
(何以解憂?唯有杜康。--曹操)
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