Class: Net::DNS::Packet

Inherits:
Object
  • Object
show all
Includes:
Names
Defined in:
lib/net/dns/packet.rb

Overview

Net::DNS::Packet

The Net::DNS::Packet class represents an entire DNS packet, divided in his main section:

  • Header (instance of Net::DNS::Header)

  • Question (array of Net::DNS::Question objects)

  • Answer, Authority, Additional (each formed by an array of Net::DNS::RR objects)

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.

For 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.

Logging facility

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.

Defined Under Namespace

Classes: Error, PacketError

Constant Summary

Constants included from Names

Names::INT16SZ

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Names

#dn_comp, #dn_expand, #names_array, #pack_name, #valid?

Constructor Details

#initialize(name, type = Net::DNS::A, cls = Net::DNS::IN) ⇒ Packet

Creates a new instance of Net::DNS::Packet class. Arguments are the canonical name of the resource, 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.parse instead.



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# File 'lib/net/dns/packet.rb', line 112

def initialize(name, type = Net::DNS::A, cls = Net::DNS::IN)
  @header = Net::DNS::Header.new(qdCount: 1)
  @question = [Net::DNS::Question.new(name, type, cls)]
  @answer = []
  @authority = []
  @additional = []
  @logger = Logger.new $stdout
  @logger.level = $DEBUG ? Logger::DEBUG : Logger::WARN
end

Instance Attribute Details

#additional ⇒ Object

Returns the value of attribute additional.



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# File 'lib/net/dns/packet.rb', line 97

def additional
  @additional
end

#answer ⇒ Object

Returns the value of attribute answer.



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# File 'lib/net/dns/packet.rb', line 95

def answer
  @answer
end

#answerfrom ⇒ Object (readonly)

Returns the value of attribute answerfrom.



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# File 'lib/net/dns/packet.rb', line 98

def answerfrom
  @answerfrom
end

#answersize ⇒ Object (readonly)

Returns the value of attribute answersize.



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# File 'lib/net/dns/packet.rb', line 99

def answersize
  @answersize
end

#authority ⇒ Object

Returns the value of attribute authority.



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# File 'lib/net/dns/packet.rb', line 96

def authority
  @authority
end

#header ⇒ Object

Returns the value of attribute header.



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# File 'lib/net/dns/packet.rb', line 93

def header
  @header
end

#question ⇒ Object

Returns the value of attribute question.



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# File 'lib/net/dns/packet.rb', line 94

def question
  @question
end

Class Method Details

.parse(*args) ⇒ Object

Creates a new instance of Net::DNS::Packet class from binary data, taken out from 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, especially when using RAW sockets.



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# File 'lib/net/dns/packet.rb', line 454

def self.parse(*args)
  o = allocate
  o.send(:new_from_data, *args)
  o
end

Instance Method Details

#data ⇒ Object

Returns 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"



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# File 'lib/net/dns/packet.rb', line 133

def data
  qdcount = ancount = nscount = arcount = 0
  data = @header.data
  headerlength = data.length

  @question.each do |question|
    data += question.data
    qdcount += 1
  end
  @answer.each do |rr|
    data += rr.data # (data.length)
    ancount += 1
  end
  @authority.each do |rr|
    data += rr.data # (data.length)
    nscount += 1
  end
  @additional.each do |rr|
    data += rr.data # (data.length)
    arcount += 1
  end

  @header.qdCount = qdcount
  @header.anCount = ancount
  @header.nsCount = nscount
  @header.arCount = arcount

  @header.data + data[Net::DNS::HFIXEDSZ..data.size]
end

#data_comp ⇒ Object

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"



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# File 'lib/net/dns/packet.rb', line 170

def data_comp
  offset = 0
  compnames = {}
  qdcount = ancount = nscount = arcount = 0
  data = @header.data
  headerlength = data.length

  @question.each do |question|
    str, offset, names = question.data
    data += str
    compnames.update(names)
    qdcount += 1
  end

  @answer.each do |rr|
    str, offset, names = rr.data(offset, compnames)
    data += str
    compnames.update(names)
    ancount += 1
  end

  @authority.each do |rr|
    str, offset, names = rr.data(offset, compnames)
    data += str
    compnames.update(names)
    nscount += 1
  end

  @additional.each do |rr|
    str, offset, names = rr.data(offset, compnames)
    data += str
    compnames.update(names)
    arcount += 1
  end

  @header.qdCount = qdcount
  @header.anCount = ancount
  @header.nsCount = nscount
  @header.arCount = arcount

  @header.data + data[Net::DNS::HFIXEDSZ..data.size]
end

#each_address ⇒ Object

Iterates every address in the answer section of this Net::DNS::Packet instance.

packet.each_address do |ip|
  ping ip.to_s
end

As you can see in the documentation for the Net::DNS::RR::A class, the address returned is an instance of IPAddr class.



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# File 'lib/net/dns/packet.rb', line 347

def each_address
  @answer.each do |elem|
    next unless elem.class == Net::DNS::RR::A

    yield elem.address
  end
end

#each_cname ⇒ Object

Iterates every canonical name in the answer section of this Net::DNS::Packet instance.

packet.each_cname do |cname|
  puts "Canonical name: #{cname}"
end



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# File 'lib/net/dns/packet.rb', line 392

def each_cname
  @answer.each do |elem|
    next unless elem.class == Net::DNS::RR::CNAME

    yield elem.cname
  end
end

#each_mx ⇒ Object

Iterates every exchange record in the answer section of this Net::DNS::Packet instance.

packet.each_mx do |pref,name|
  puts "Mail exchange #{name} has preference #{pref}"
end



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# File 'lib/net/dns/packet.rb', line 377

def each_mx
  @answer.each do |elem|
    next unless elem.class == Net::DNS::RR::MX

    yield elem.preference, elem.exchange
  end
end

#each_nameserver ⇒ Object

Iterates every nameserver in the answer section of this Net::DNS::Packet instance.

packet.each_nameserver do |ns|
  puts "Nameserver found: #{ns}"
end



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# File 'lib/net/dns/packet.rb', line 362

def each_nameserver
  @answer.each do |elem|
    next unless elem.class == Net::DNS::RR::NS

    yield elem.nsdname
  end
end

#each_ptr ⇒ Object

Iterates every pointer in the answer section of this Net::DNS::Packet instance.

packet.each_ptr do |ptr|
  puts "Pointer for resource: #{ptr}"
end



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# File 'lib/net/dns/packet.rb', line 407

def each_ptr
  @answer.each do |elem|
    next unless elem.class == Net::DNS::RR::PTR

    yield elem.ptrdname
  end
end

#inspect ⇒ Object Also known as: to_s

Returns a string containing a human-readable representation of this Net::DNS::Packet instance.



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# File 'lib/net/dns/packet.rb', line 215

def inspect
  retval = ""
  if (@answerfrom != "0.0.0.0:0") && @answerfrom
    retval += ";; Answer received from #{@answerfrom} (#{@answersize} bytes)\n;;\n"
  end

  retval += ";; HEADER SECTION\n"
  retval += @header.inspect

  retval += "\n"
  section = @header.opCode == "UPDATE" ? "ZONE" : "QUESTION"
  retval += ";; #{section} SECTION (#{@header.qdCount} record#{@header.qdCount == 1 ? '' : 's'}):\n"
  @question.each do |qr|
    retval += ";; " + qr.inspect + "\n"
  end

  unless @answer.empty?
    retval += "\n"
    section = @header.opCode == "UPDATE" ? "PREREQUISITE" : "ANSWER"
    retval += ";; #{section} SECTION (#{@header.anCount} record#{@header.anCount == 1 ? '' : 's'}):\n"
    @answer.each do |rr|
      retval += rr.inspect + "\n"
    end
  end

  unless @authority.empty?
    retval += "\n"
    section = @header.opCode == "UPDATE" ? "UPDATE" : "AUTHORITY"
    retval += ";; #{section} SECTION (#{@header.nsCount} record#{@header.nsCount == 1 ? '' : 's'}):\n"
    @authority.each do |rr|
      retval += rr.inspect + "\n"
    end
  end

  unless @additional.empty?
    retval += "\n"
    retval += ";; ADDITIONAL SECTION (#{@header.arCount} record#{@header.arCount == 1 ? '' : 's'}):\n"
    @additional.each do |rr|
      retval += rr.inspect + "\n"
    end
  end

  retval
end

#nxdomain? ⇒ Boolean

Checks whether the query returned a NXDOMAIN error, meaning the queried domain name doesn’t exist.

%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

Returns:

  • (Boolean) 


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# File 'lib/net/dns/packet.rb', line 436

def nxdomain?
  header.rCode.code == Net::DNS::Header::RCode::NAME
end

#query? ⇒ Boolean

Checks if the packet is a QUERY packet

Returns:

  • (Boolean) 


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# File 'lib/net/dns/packet.rb', line 123

def query?
  @header.opCode == Net::DNS::Header::QUERY
end

#size ⇒ Object

Returns the packet size in bytes.

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



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# File 'lib/net/dns/packet.rb', line 422

def size
  data.size
end

#truncated? ⇒ Boolean

Delegates to Net::DNS::Header#truncated?.

Returns:

  • (Boolean) 


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# File 'lib/net/dns/packet.rb', line 262

def truncated?
  @header.truncated?
end