From: "Jørgen P. Tjernø" <jorgen@...>
Date: 2006-10-05T08:41:33+09:00
Subject: Small SOCKSv4-implementation - comments / feedback appreciated

After having struggeled with libsock/ruby-sockets+socks, etc, and not 
getting any way, I decided to try another approach. The whole 
ruby-builting-socks / libsock idea is to make it as transparent / global 
as possible, seemingly never meant to be controlled directly by the 
application.

So, I implemented my own little TCPSocket-"wrapper"-class, which just 
speaks the one command from SOCKSv4 and which only understands the one 
reply. After that, it lets go of the socket. (SOCKS protocol information 
found on http://en.wikipedia.org/wiki/SOCKS)

Then I just overrode Net::FTP#open_socket, so if ENV['SOCKS_SERVER'] is 
set, it uses this my little class to set up a socks-connection. This can 
of course be used for anything, not just Net::FTP - any other 
Net::-module, or a custom creation of yours. Net::FTP just happens to be 
what I wanted it for. ;-)

Now, I'm curious what you think of the code as a whole (coding style, 
language use, approach, how to "hook into" Net::FTP, etc), and if you 
have any suggestions. I'm thinking I should release this as public 
domain, so anyone else in my situation won't have to bark up all the 
wrong trees for as long as I did. ;-)

Thanks in advance!

Kindest regards, J�rgen P. Tjern�.

  * code follows:

require 'socket'
require 'resolv'

require 'net/ftp'

class SocksProxying
     REQUEST_GRANTED = 0x5A
     REQUEST_FAILED = 0x5B
     REQUEST_FAILED_NOIDENT = 0x5C
     REQUEST_FAILED_IDENTINVALID = 0x5D

     SOCKS_VERSION_4 = 0x04
     SOCKS_CMD_CONNECTION = 0x01
     SOCKS_CMD_BINDING = 0x02

     SOCKS_REPLY_LENGTH = 8

     def initialize
         @socket = nil
     end

     def connect_via(proxy, proxy_port = 1080)
         @socket = TCPSocket.open(proxy, proxy_port)
     end

     def connect(host, port, user = ENV['USER'])
         if @socket.nil?
             raise "Error: Must connect_via first, then connect."
         end

         ip = Resolv.getaddress(host).split(/\./).collect {|part| part.to_i}
         port = port.to_i

         data = [SOCKS_VERSION_4, SOCKS_CMD_CONNECTION, port, ip, 
user].flatten.pack('CCnC4a' + (user.length + 1).to_s)
         @socket.write data
         dud, statuscode, port, ip = 
@socket.recv(SOCKS_REPLY_LENGTH).unpack('CCnC4')
         if statuscode != REQUEST_GRANTED
             if statuscode == REQUEST_FAILED
                 raise "Error: SOCKS-access not granted by SOCKS-server."
             elsif statuscode == REQUEST_FAILED_NOIDENT
                 raise "Error: SOCKS-connection failed; server could not 
reach our ident server."
             elsif statuscode == REQUEST_FAILED_IDENTINVALID
                 raise "Error: SOCKS-connection failed; server could not 
match our ident reply to the one sent."
             else
                 raise "Error: SOCKS-connection failed; unknown error-code."
             end
         end

         @socket
     end
end

# Here is where we override Net::FTP's internal socket creation.
class Net::FTP
     def open_socket(host, port)
       if ENV["SOCKS_SERVER"]
           @passive = true
           proxy_host, proxy_port = ENV["SOCKS_SERVER"].split /:/
           sp = SocksProxying.new
           sp.connect_via(proxy_host, proxy_port)
           return sp.connect(host, port)
       else
           return TCPSocket.open(host, port)
       end
   end
end