[Bro] Bro Types Not Following Bro Types Documention

Johanna Amann johanna at icir.org
Mon May 18 07:43:59 PDT 2015

On Mon, May 18, 2015 at 08:37:04AM -0500, John Omernik wrote:
> That all said... why put anything in a field (as a default) to represent
> unset or empty? Are we at risk of evasion?

I am not sure what you would should do instead. From a protocol point of
view, there is often a huge difference between "an empty string was
transferred" and "this was not seen at all". For example, in HTTP a
Referrer of "-" means that no referrer header was set at all. "" (the
empty string) instead means that it was seen, but empty. Same for sets,
there is a difference between the set was not seen at all ("-"), the set
was seen but empt ("(empty)") and the set was seen and contains one
element with an empty string ("").

> Besides obviously breaking typing, what about when the type actually
> accepts the unset character...  what if the user-agent is - or (empty)
> couldn't that cause downstream errors?

In that case, the character should be replaced by the escaped version of
it (i.e. you should find \x[ascii-code] or similar) in the log-file
instead of the -. Hence, it should still be decideable which of the two
cases happened.

> "You can change the logs to log however you want" is likely the
> answer, and correct I can, but shouldn't we try be logical in our approach
> so assumptions aren't made on the default material?

I hope this helps,

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