#!/usr/bin/ruby

require 'digest/md5'
require 'socket'

# BEGIN ===== User setup section =====

# Account information
ID = 'your_id'
PASSWD = 'your_password'
HOST = 'example.com'

# How to get my current global IP ?
# If you can't understand what you should do,
# please comment out following paragraph,
# and simply write down, IP_CURRENT = nil.
IP_CURRENT = Proc.new{
	/(?:\d{1,3}\.){3}\d{1,3}/ =~ `ifconfig ppp0`
	$&
}

# Program type setting
# auto background update(IS_DAEMON = true) / user manual update(IS_DAEMON = false) ?
IS_DAEMON = true
UPDATE_PEROID = 60 * 60 #[sec]
LOG_FILE = 'ip-updater.log'

# END   ===== User setup section =====

# Target Servers, SRV_UPDATE means the update server, and SRV_CHECK means the ip check server.
SRV_UPDATE_HOST = 'update.3domain.hk'
SRV_UPDATE_PORT = 9120
SRV_CHECK_HOST = 'myip.3domain.hk'
SRV_CHECK_PORT = 9121

# About this program
AGENT_NAME = 'Ruby-Updater'
AGENT_VERSION = '0.2'
AGENT_MODE = 'MD5'

# main program begins from the next line.

def err? res
	return !(res and !(res =~ /ERR/))
end

def update(ip_previous = nil)

	print("#{Time.now.to_s}, Trying...\n")

	ip_current = nil
	if IP_CURRENT
		ip_current = IP_CURRENT.call
	else
		soc = UDPSocket.open
		soc.send("\n", 0, SRV_CHECK_HOST, SRV_CHECK_PORT)
		begin
			if /(?:\d{1,3}\.){3}\d{1,3}/ =~ soc.recv(32) then
				ip_current = $&
			end
		rescue
			print "WARNING: the IP reporting server is now out of service.\n"
		end
	end
	
	# check IP whether the DDNS registered IP equals my current global IP.
	if ip_previous and ip_previous == ip_current then
		print "MESSAGE: No need to update, now DDNS.IP == IP_CURRENT\n"
		return ip_current
	end

	soc = TCPSocket.open(SRV_UPDATE_HOST, SRV_UPDATE_PORT)
	begin
		if err?(soc.gets) then raise Exception.new("ERROR: Fail to open socket!!") end
	
		soc.write("AGENT #{AGENT_NAME}/#{AGENT_VERSION}\n")		# send about this program
		if err?(soc.gets) then raise Exception.new("ERROR: From the update server; #{$_}") end

		case AGENT_MODE
		when 'MD5'
			soc.write("LOGIN #{ID} digest-md5\n")				# send login cmd
			if !(soc.gets =~ /CHALLENGE\s([0-9a-fA-F]*)/) then raise Exception.new("ERROR: From the update server; #{$_}") end

			md5_passwd = Digest::MD5.digest(PASSWD)
			response = Digest::MD5.hexdigest(md5_passwd + [$1].pack('H*'))
			soc.write("RESPONSE #{response}\n")
			if err?(soc.gets) then raise Exception.new("ERROR: From the update server; #{$_}") end
		else
			soc.write("LOGIN #{ID} plain\n")					# send login cmd
			soc.write("#{PASSWD}")								# send passwd
			if err?(soc.gets) then raise Exception.new("ERROR: From the update server; #{$_}") end
		end

		soc.write("A_UPDATE online #{HOST}#{ip_current ? (' ' + ip_current) : ''}\n")
		if err?(soc.gets) then raise Exception.new("ERROR: From the update server; #{$_}") end
		print "MESSAGE: IP updated successfully; #{$_}"
		/(?:\d{1,3}\.){3}\d{1,3}/ =~ $_
		ip_current = $&
	rescue
		print ($!)
	ensure
		soc.write("EXIT\n")
		soc.close
	end
	return ip_current
end

if IS_DAEMON then

	exit! if fork	# fork
	
	# log file setting
	log_file = nil
	if LOG_FILE then
		log_file = File.open(LOG_FILE, 'w+')
		STDOUT.reopen(log_file)
		STDOUT.sync = true
		STDERR.reopen(log_file)
		STDERR.sync = true
	else
		print("WARNING: No logging, pid is #{Process.pid}\n")
		def print(s) end
	end
	
	Signal.trap('HUP'){exit}
	Signal.trap('TERM'){exit}
	
	END{if log_file then log_file.close end}
	
	ObjectSpace.each_object(IO){|io|
		io.close unless io.closed? || io == log_file || io == STDOUT || io == STDERR
	}
	
	Process.setsid
	
	print("PID: #{Process.pid}\n")
	print("Start #{AGENT_NAME} at #{Time.now.to_s}\n")
	
	ip = nil
	loop{
		ip = update(ip)
		sleep(UPDATE_PEROID)
	}
else
	update
end