From: Scott Thompson <easco@...>
Date: 2003-08-14T07:08:42+09:00
Subject: Ruby listens IPv6

Please forgive me if this sounds a bit juvenile.  I'm not as well 
versed in network programming as I might like to be.  Nevertheless, 
here goes.

I'm looking at the book "Teach Yourself Ruby in 21 days" from Sams 
publishing.  I was reading "day 19" in which the Mr. Slagell presents a 
page of code that implements a very simplistic web server.  Since I've 
done a little socket programming, I was curious to see what would 
happen if I played with the code.  I entered the following program :

#----------
require 'socket'

def main
         listener = TCPServer.new("localhost", (ARGV[0] || 80).to_i)
         loop do
                 puts "listening"
                 session = listener.accept
                         session.each do | line |
                                 puts line
                         end
                 session.close
         end
end

main
#----------

I ran this code on my machine (as a privileged user so I could listen 
to port 80) and happily tried to point my web browser at it to see what 
kind of stuff the browser would send to the script.

Unfortunately, my web browser gave me a "could not connect" error.  
Hrmmmm...

After trying the "server" on several ports with no success, checking my 
firewall settings etc... and generally poking around I finally had the 
wherewithall to run the program and use the "netstat" command to see if 
the port was actually being listened to.

I found the line... it looks like this:

tcp6       0      0  localhost.http         *.*                    
LISTEN

The interesting part is that this is the ONLY port on my whole system 
that is marked as using IPv6.  Hmmm...

What I know about IPv6 could probably fill a couple of sentences.  They 
go something like this, "IPv6 is the proposed standard for future 
Internet communications.  Among a host of features interesting to 
networking type, one of the things it does is expands the pool of 
available addresses that are available to computers in the world".

My question is, can someone tell me why my Ruby script is listening on 
IPv6? Is it because of the way that Ruby was compiled (I built 1.8 from 
sources and am using that)?  Or, do I have to do something in 
particular to tell the Ruby socket that I want it to use IPv4?

I would also welcome pointers to documentation for neophytes about Ruby 
sockets... though you may want to send them to me off-line so the other 
folks on the list don't have to endure them again. :-)

Scott