Initial commit. Could be improved by parsing the backend server request and...

Initial commit. Could be improved by parsing the backend server request and splicing in the original port numbers.

identproxy.rb

+#!/usr/local/bin/ruby19
+require 'socket'
+
+# Address and port to listen on.
+# Normally this is your WAN address.
+addr = '80.112.131.85'
+port = 113
+
+# Create listen server
+server = TCPServer.new( addr, port )
+
+# Forward request to NAT'ed server
+def forwardrequest( host, p1, p2 )
+	begin
+		# Create new socket to NAT'ed server
+		s = TCPSocket.new( host, 113 )
+
+		# Send request to NAT'ed server
+		s.puts "#{p1}, #{p2}"
+
+		return s.gets
+	rescue Exception => e
+		return nil
+	end
+end
+
+# Look up function for NAT table
+def natlookup( p1, p2 )
+	# Execute shell command to get NAT table
+	nattable = %x(pfctl -ss | egrep '(>.*>|<.*<)')
+
+	# Search NAT table for matching enties
+	if( nattable =~ /tcp (.+):(.+) -> (.+):#{p1} -> (.+):#{p2} / )
+		server = $1
+		p1 = $2.to_i
+		return [server, p1, p2]
+	else
+		return nil
+	end
+end
+
+# Main server loop
+loop do
+	# New client connected
+	client = server.accept
+
+	# Read request from socket
+	input = client.gets
+	input.strip!
+
+	sane = true
+	p1 = 0
+	p2 = 0
+
+	# Check if it's something that looks like an ident response
+	if( input =~ /^(\d+)(|\s),(|\s)(\d+)$/ )
+		p1 = $1.to_i
+		p2 = $3.to_i
+	else
+		sane = false
+	end
+
+	# Sanity check on port number
+	if( p1 < 1 || p1 > 65535 || p2 < 1 || p2 > 65535 )
+		sane = false
+	end
+
+	# Send generic error for stuff that does not look like ident requests
+	if(!sane)
+		client.puts "#{input}:ERROR:NO-USER"
+		client.close
+		next
+	end
+
+	# Do NAT table lookup
+	n = natlookup( p1, p2 )
+	
+	# Check if there was a NAT table entry
+	if( n.nil? )
+		client.puts "#{input}:ERROR:NO-USER"
+		client.close
+		next
+	end
+
+	# Forward request to NAT'ed server
+	result = forwardrequest( n[0], n[1], n[2] )
+
+	# Show result to client
+	if( result.nil? )
+                client.puts "#{input}:ERROR:NO-USER"
+                client.close
+                next
+	end
+
+	client.puts result
+
+	# Close connection and wait for the next request
+	client.close
+end