Zerigo dynamic dns updater

dyndns_update.rb

#!/usr/bin/env ruby
# Dynamic DNS updater by Andruby for Zerigo
# www.andrewsblog.org

ApiKey = 'myzerigoapikey'          # your Zerigo API key
Host = 'test.example.com'          # the host you want to dynamically update
User = 'user@domain.com'           # your Zerigo username
NameServer = 'a.ns.zerigo.net'     # Zerigo nameserver to query
LastIpTmpFile = '/tmp/dyn_update_last_ip'  # a temporary file where we store the last ip adress

# Load libraries
require 'open-uri'
require 'ipaddr'

def with_rescue(msg, &block)
  yield
rescue Exception => e
  puts "Error while #{msg}"
  p e
end

def ip_changed?(current_ip)
  previous_ip = (IPAddr.new(File.read(LastIpTmpFile)) rescue nil)
  File.open(LastIpTmpFile,'w') { |f| f.print current_ip.to_s }
  previous_ip != current_ip
end

real_ip = with_rescue("getting current ip") do
  body = open('http://checkip.dyndns.org').read
  IPAddr.new(body.match(/\d+\.\d+\.\d+\.\d+/).to_s)
end

puts "Real ip: #{real_ip}"

# Check if our ip changed since last time. 
# This saves us from querying the Zerigo DNS server.
unless ip_changed?(real_ip)
  puts "IP Adress is still the same, not updating"
  exit
end

# Load more libraries
require 'resolv'
require 'rubygems'
require 'net/dns/resolver'

# Resolving the IP address stored in the DNS server
# This could be refactored to be cleaner
dns_ip = with_rescue("resolving DNS ip") do
  ns_ip = Resolv.getaddress(NameServer).to_s
  # make sure you query the right Nameserver
  res = Net::DNS::Resolver.new(:nameservers => ns_ip)
  last_ip = nil
  res.search(Host).each_address { |ip| last_ip = ip }
  last_ip
end

puts "DNS ip: #{dns_ip}"

if real_ip == dns_ip
  puts "Real IP matches DNS IP (#{real_ip}), doing nothing"
else
  url = "http://update.zerigo.com/dynamic?host=#{Host}&user=#{User}&password=#{ApiKey}"
  print "Setting new IP address: "
  puts open(url).read
end