From: Brian Candler <b.candler@...>
Date: 2009-11-20T18:29:50+09:00
Subject: Re: UDP Proxy

Randy General wrote:
> I attempted to play a game through the proxy, and it
> was exceptionally slow.

Can you measure what you mean by 'slow', in terms of the elapsed time 
between a packet coming in and a packet going out? You can do this 
externally using tcpdump -ttt, or you can add some timing into the code 
itself.

It's possible that Ruby is doing reverse DNS lookups for every incoming 
packet when your C code isn't. tcpdump will show that. You can disable 
it using:

  Socket.do_not_reverse_lookup = true

at the top of your code.

> Here's my code so far:
> 
> http://pastie.org/707258.txt

Why are you using a raw socket? You could just forward using a UDP 
socket. Then you wouldn't need to build an IP header, nor a UDP header, 
nor calculate the UDP checksum, since this is all taken care of for you 
by the kernel. Are you trying to send out a packet with a source address 
which doesn't belong to the sending machine? (which isn't proxying)

> Is the poor performance of the script a result of poor coding on my
> part? Or is an interpreted language like Ruby incapable of efficiently
> doing this sort of task?

Stuff like the checksum calculation is going to be a lot slower in Ruby 
than in C. But you should use the profiler to find out exactly where the 
majority of time is being spent.
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