Class | Net::DNS::Packet |
In: |
lib/net/dns/packet.rb
|
Parent: | Object |
Net::DNS::Packet - DNS packet object class
require 'net/dns/packet'
The Net::DNS::Packet class represents an entire DNS packet, divided in his main section:
You can use this class whenever you need to create a DNS packet, whether in an user application, in a resolver instance (have a look, for instance, at the Net::DNS::Resolver#send method) or for a nameserver.
Some example:
# Create a packet packet = Net::DNS::Packet.new("www.example.com") mx = Net::DNS::Packet.new("example.com", Net::DNS::MX) # Getting packet binary data, suitable for network transmission data = packet.data
A packet object can be created from binary data too, like an answer packet just received from a network stream:
packet = Net::DNS::Packet::parse(data)
Each part of a packet can be gotten by the right accessors:
header = packet.header # Instance of Net::DNS::Header class question = packet.question # Instance of Net::DNS::Question class # Iterate over additional RRs packet.additional.each do |rr| puts "Got an #{rr.type} record" end
Some iterators have been written to easy the access of those RRs, which are often the most important. So instead of doing:
packet.answer.each do |rr| if rr.type == Net::DNS::RR::Types::A # do something with +rr.address+ end end
we can do:
packet.each_address do |ip| # do something with +ip+ end
Be sure you don‘t miss all the iterators in the class documentation.
As Net::DNS::Resolver class, Net::DNS::Packet class has its own logging facility too. It work in the same way the other one do, so you can maybe want to override it or change the file descriptor.
packet = Net::DNS::Packet.new("www.example.com") packet.logger = $stderr # or even packet.logger = Logger.new("/tmp/packet.log")
If the Net::DNS::Packet class is directly instantiated by the Net::DNS::Resolver class, like the great majority of the time, it will use the same logger facility.
Logger level will be set to Logger::Debug if $DEBUG variable is set.
Some error classes has been defined for the Net::DNS::Packet class, which are listed here to keep a light and browsable main documentation. We have:
ArgumentError: | Argument Error for class Net::DNS::Packet |
PacketError: | Generic Packet Error |
Copyright (c) 2006 Marco Ceresa
All rights reserved. This program is free software; you may redistribute it and/or modify it under the same terms as Ruby itself.
additional | [R] | |
answer | [R] | |
answerfrom | [R] | |
answersize | [R] | |
authority | [R] | |
header | [R] | |
question | [R] |
Create a new instance of Net::DNS::Packet class. Arguments are the canonical name of the resourse, an optional type field and an optional class field. The record type and class can be omitted; they default to A and IN.
packet = Net::DNS::Packet.new("www.example.com") packet = Net::DNS::Packet.new("example.com", Net::DNS::MX) packet = Net::DNS::Packet.new("example.com",Net::DNS::TXT,Net::DNS::CH)
This class no longer instantiate object from binary data coming from network streams. Please use Net::DNS::Packet.new_from_data instead.
Create a new instance of Net::DNS::Packet class from binary data, taken out by a network stream. For example:
# udp_socket is an UDPSocket waiting for a response ans = udp_socket.recvfrom(1500) packet = Net::DNS::Packet::parse(ans)
An optional from argument can be used to specify the information of the sender. If data is passed as is from a Socket#recvfrom call, the method will accept it.
Be sure that your network data is clean from any UDP/TCP header, expecially when using RAW sockets.
Assign a Net::DNS::RR object, or an array of RR objects, to a Net::DNS::Packet instance additional section.
Assign a Net::DNS::RR object, or an array of RR objects, to a Net::DNS::Packet instance answer section.
Assign a Net::DNS::RR object, or an array of RR objects, to a Net::DNS::Packet instance authority section.
Return the packet object in binary data, suitable for sending across a network stream.
packet_data = packet.data puts "Packet is #{packet_data.size} bytes long"
Same as Net::DNS::Packet#data, but implements name compression (see RFC1025) for a considerable save of bytes.
packet = Net::DNS::Packet.new("www.example.com") puts "Size normal is #{packet.data.size} bytes" puts "Size compressed is #{packet.data_comp.size} bytes"
Iterate for every address in the answer section of a Net::DNS::Packet object.
packet.each_address do |ip| ping ip.to_s end
As you can see in the documentation for Net::DNS::RR::A class, the address returned is an instance of IPAddr class.
Iterate for every canonical name in the answer section of a Net::DNS::Packet object.
packet.each_cname do |cname| puts "Canonical name: #{cname}" end
Iterate for every exchange record in the answer section of a Net::DNS::Packet object.
packet.each_mx do |pref,name| puts "Mail exchange #{name} has preference #{pref}" end
Iterate for every nameserver in the answer section of a Net::DNS::Packet object.
packet.each_nameserver do |ns| puts "Nameserver found: #{ns}" end
Iterate for every pointer in the answer section of a Net::DNS::Packet object.
packet.each_ptr do |ptr| puts "Pointer for resource: #{ptr}" end
Checks whether a query has returned a NXDOMAIN error, meaning the domain name queried doesn‘t exists.
%w[a.com google.com ibm.com d.com].each do |domain| response = Net::DNS::Resolver.new.send(domain) puts "#{domain} doesn't exist" if response.nxdomain? end #=> a.com doesn't exist #=> d.com doesn't exist
Assign a Net::DNS::Question object, or an array of Questions objects, to a Net::DNS::Packet instance.
Returns the packet size in bytes
Resolver("www.google.com") do |packet| puts packet.size + " bytes"} end #=> 484 bytes