Re: [nmap-svn] r33632 - in nmap: nselib scripts

[Patrick Donnelly <batrick () batbytes com>]

On Wed, Sep 3, 2014 at 12:49 AM,  <commit-mailer () nmap org> wrote:
> Author: dmiller
> Date: Wed Sep  3 04:49:54 2014
> New Revision: 33632
>
> Log:
> Some string optimizations in NSE
>
> Changes fall into these categories:
>
> 1. Avoid pathological string building. Loops over x = x .. "foo" can
> become very slow. Instead, use strbuf.lua, table.concat, or just one
> continuous concatenation; a = x .. y .. z is one operation, better than
> a = x .. y; a = a .. z

For future reference, Lua 5.2 offers the \z escape sequence which
skips all whitespace characters following it in a literal string:

http://www.lua.org/manual/5.2/manual.html#3.1

The escape sequence '\z' skips the following span of white-space
characters, including line breaks; it is particularly useful to break
and indent a long literal string into multiple lines without adding
the newlines and spaces into the string contents.

So for example:

> [...]
> Modified: nmap/scripts/db2-das-info.nse
> ==============================================================================
> --- nmap/scripts/db2-das-info.nse       (original)
> +++ nmap/scripts/db2-das-info.nse       Wed Sep  3 04:49:54 2014
> @@ -266,12 +266,12 @@
>
>    packet.header = {}
>
> -  packet.header.raw = string.char(0x00, 0x00, 0x00, 0x00, 0x44, 0x42, 0x32, 0x44, 0x41, 0x53, 0x20, 0x20, 0x20, 
> 0x20, 0x20, 0x20)
> -  packet.header.raw = packet.header.raw .. string.char(0x01, 0x04, 0x00, 0x00, 0x00, 0x10, 0x39, 0x7a, 0x00, 0x05, 
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00)
> -  packet.header.raw = packet.header.raw .. string.char(0x00, 0x00, 0x00, 0x00 )
> -  packet.header.raw = packet.header.raw .. bin.pack("C", magic)
> -  packet.header.raw = packet.header.raw .. bin.pack("S", data_len)
> -  packet.header.raw = packet.header.raw .. string.char(0x00, 0x00)
> +  packet.header.raw = "\x00\x00\x00\x00\x44\x42\x32\x44\x41\x53\x20\x20\x20\x20\x20\x20"
> +  .. "\x01\x04\x00\x00\x00\x10\x39\x7a\x00\x05\x00\x00\x00\x00\x00\x00"
> +  .. "\x00\x00\x00\x00"
> +  .. bin.pack("C", magic)
> +  .. bin.pack("S", data_len)
> +  .. "\x00\x00"
>
>    packet.header.data_len = data_len
>    packet.data = data

could be:

packet.header.raw =
"\x00\x00\x00\x00\x44\x42\x32\x44\x41\x53\x20\x20\x20\x20\x20\x20\z
    \x01\x04\x00\x00\x00\x10\x39\x7a\x00\x05\x00\x00\x00\x00\x00\x00\z
    \x00\x00\x00\x00"
    ..bin.pack("C", magic)
    ..bin.pack("S", data_len)
    .."\x00\x00"

[Unfortunately those bin.packs add some concatenations anyway but you
get the idea.]

-- 
Patrick Donnelly
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