Index based on multiple fields, was Re: Adding comparision function

[Jim Mellander <jmellander@...>]

I think I'm over the optional comparison function hurdle, I'm trying 
something like:

function abc(x,f)
	...
	f = f or function(a,b) return ( a > b ) end

	....

and use f to compare...


I have another question which may be of more interest to the group (I 
got the feeling my previous question was responded to with a silent RTFM 
- if so, I apologize to the group):

I'm indexing a table on the following parameters:

1. Proto (i.e. tcp, udp, etc.)
2. Source IP
3. Source port
4. Destination IP
5. Destination port

I originally tried indexing with an anonymous table as the key, ie

connection_record[ {proto="tcp", source_ip="1.2.3.4", source_port="123", 
dest_ip="3.4.5.6", dest_port="567"} ] = whatever

When I want to update the table I tried constructing another anonymous 
table with the exact same keys & values.  This didn't work, I presume 
due to the fact that they pointed to different tables, albeit with the 
same values.

So what I did was borrow from awk, and create a string key, i.e.:

connection_record[ 
"tcp"..SUBSEP.."1.2.3.4"..SUBSEP.."123"..SUBSEP.."3.4.5.6"..SUBSEP..567" 
] = whatever


where SUBSEP is a character guaranteed to not be in the fields making up 
the key.

This, however, seems kludgy.  Is there a "lua" way to accomplish this 
task more elegantly?




Jim Mellander wrote:
> Hi everyone:
>
> For a custom application (parsing netflow data into input records for a 
> custom IDS called Bro), I embarked on a search for the proverbial 
> "language that didn't suck", which would combine performance with simple 
> syntax and ease of use and understanding....
>
> So I found lua....  In a week and a half, from a standing start, I've 
> written a prototype application that uses the socket library, parses 
> input records, pastes the (possible) two sides of netflow data into a 
> connection record with a timeout, along with heuristics for determining 
> source/destination of the traffic.  The only real stumbling block has 
> been (aside from learning lua - not a steep learning curve at all!) the 
> lack of built-in libraries for common tasks - although I soon found the 
> libraries I needed, and added them in.
>
> I've attached a simple binary-heap priority queue implementation I wrote 
> for the timeouts, but would like to generalize it, ala lua sort, by 
> allowing an optional comparison function -- Can anyone help??
>
> BTW - I spent a fair amount of time optimizing the code, and I eschewed 
> the use of table.getn after looking at the C code for the lua 
> interpreter, since table.getn appears to be using a binary search 
> function to find the size of the table - so, I just store the size as a 
> specific key whic is incremented/decremented as needed - any comments on 
> that?


--
Jim Mellander
Incident Response Manager
Computer Protection Program
Lawrence Berkeley National Laboratory
(510) 486-7204

Your fortune for today is:

life, n.:
	A whim of several billion cells to be you for a while.