More on Suricata lua flowints

This morning I added flowint lua functions for incrementing and decrementing flowints. From the commit:

Add flowint lua functions for incrementing and decrementing flowints.

First use creates the var and inits to 0. So a call:

    a = ScFlowintIncr(0)

Results in a == 1.

If the var reached UINT_MAX (2^32), it’s not further incremented. If the
var reaches 0 it’s not decremented further.

Calling ScFlowintDecr on a uninitialized var will init it to 0.

Example script:

    function init (args)
        local needs = {}
        needs["http.request_headers"] = tostring(true)
        needs["flowint"] = {"cnt_incr"}
        return needs
    end

    function match(args)
        a = ScFlowintIncr(0);
        if a == 23 then
            return 1
        end

        return 0
    end
    return 0

This script matches the 23rd time it’s invoked on a flow.

Compared to yesterday’s flowint script and the earlier flowvar based counting script, this performs better:

   Num      Rule         Gid      Rev      Ticks        %      Checks   Matches  Max Ticks   Avg Ticks   Avg Match   Avg No Match
  -------- ------------ -------- -------- ------------ ------ -------- -------- ----------- ----------- ----------- -------------- 
  1        1            1        0        2434188332   59.71  82249    795      711777      29595.35    7683.20     29809.22   
  2        2            1        0        1015328580   24.91  82249    795      154398      12344.57    3768.66     12428.27   
  3        3            1        0        626858067    15.38  82249    795      160731      7621.47     3439.91     7662.28    

The rules:

alert http any any -> any any (msg:"LUAJIT HTTP flowvar match"; luajit:lua_flowvar_cnt.lua; flow:to_server; sid:1;)
alert http any any -> any any (msg:"LUAJIT HTTP flowint match"; luajit:lua_flowint_cnt.lua; flow:to_server; sid:2;)
alert http any any -> any any (msg:"LUAJIT HTTP flowint incr match"; luajit:lua_flowint_incr_cnt.lua; flow:to_server; sid:3;)

Please comment, discuss, review etc on the oisf-devel list.

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