Net::DNS

Net::DNS is a DNS library written in pure Ruby. It started as a port of Perl Net::DNS module, but it evolved in time into a full Ruby library.

Features:

• Complete OO interface
• Clean and intuitive API
• Modular and flexible

Install

Just use Rubygems:

     $ sudo gem install net-dns

If you want to install from source, you can use Rake:

   $ rake install

Or directly from install.rb

   $ sudo ruby install.rb

API Documentation

Visit the page marcoceresa.com/net-dns

Trivial resolver

The simplest way to use the library is to invoke the Resolver() method:

    require 'net/dns/resolver'
    p Resolver("www.google.com")

The output is compatible with BIND zone files and it’s the same you would get with the dig utility.

    ;; Answer received from localhost:53 (212 bytes)
    ;;
    ;; HEADER SECTION
    ;; id = 64075
    ;; qr = 1       opCode: QUERY   aa = 0  tc = 0  rd = 1
    ;; ra = 1       ad = 0  cd = 0  rcode = NoError
    ;; qdCount = 1  anCount = 3     nsCount = 4     arCount = 4

    ;; QUESTION SECTION (1 record):
    ;; google.com.                  IN      A

    ;; ANSWER SECTION (3 records):
    google.com.             212     IN      A       74.125.45.100
    google.com.             212     IN      A       74.125.67.100
    google.com.             212     IN      A       209.85.171.100

    ;; AUTHORITY SECTION (4 records):
    google.com.             345512  IN      NS      ns1.google.com.
    google.com.             345512  IN      NS      ns4.google.com.
    google.com.             345512  IN      NS      ns2.google.com.
    google.com.             345512  IN      NS      ns3.google.com.

    ;; ADDITIONAL SECTION (4 records):
    ns1.google.com.         170275  IN      A       216.239.32.10
    ns2.google.com.         170275  IN      A       216.239.34.10
    ns3.google.com.         170275  IN      A       216.239.36.10
    ns4.google.com.         170275  IN      A       216.239.38.10

An optional block can be passed yielding the Net::DNS::Packet object

   Resolver("www.google.com") {|packet| puts packet.size + " bytes"}
     #=> 484 bytes

Same for Net::DNS::Resolver.start():

    Net::DNS::Resolver.start("google.com").answer.size
      #=> 5

As optionals parameters, TYPE and CLASS can be specified.

   p Net::DNS::Resolver.start("google.com", Net::DNS::MX)

   ;; Answer received from localhost:53 (316 bytes)
   ;;
   ;; HEADER SECTION
   ;; id = 59980
   ;; qr = 1       opCode: QUERY   aa = 0  tc = 0  rd = 1
   ;; ra = 1       ad = 0  cd = 0  rcode = NoError
   ;; qdCount = 1  anCount = 4     nsCount = 4     arCount = 8

   ;; QUESTION SECTION (1 record):
   ;; google.com.                  IN      MX

   ;; ANSWER SECTION (4 records):
   google.com.             10800   IN      MX      10 smtp2.google.com.
   google.com.             10800   IN      MX      10 smtp3.google.com.
   google.com.             10800   IN      MX      10 smtp4.google.com.
   google.com.             10800   IN      MX      10 smtp1.google.com.

Handling the response packet

The method Net::DNS::Resolver.start is a wrapper around Resolver.new. It returns a new Net::DNS::Packet object.

A DNS packet is divided into 5 sections:

• header section # => a Net::DNS::Header object
• question section # => a Net::DNS::Question object
• answer section # => an Array of Net::DNS::RR objects
• authority section # => an Array of Net::DNS::RR objects
• additional section # => an Array of Net::DNS::RR objects

You can access each section by calling the attribute with the same name on a Packet object:

    packet = Net::DNS::Resolver.start("google.com")

    header = packet.header
    answer = packet.answer

    puts "The packet is #{packet.data.size} bytes"
    puts "It contains #{header.anCount} answer entries"

    answer.any? {|ans| p ans}

The output is

    The packet is 378 bytes
    It contains 3 answer entries
    google.com.             244     IN      A       74.125.45.100
    google.com.             244     IN      A       74.125.67.100
    google.com.             244     IN      A       209.85.171.100

A better way to handle the answer section is to use the iterators directly on a Packet object:

    packet.each_address do |ip|
      puts "#{ip} is alive" if Ping.pingecho(ip.to_s, 10, 80)
    end

Gives:

    74.125.45.100 is alive
    74.125.67.100 is alive
    209.85.171.100 is alive

Licence

Net::DNS is distributed under the same license Ruby is.

Author

© Marco Ceresa 2006