Class: Net::DNS::Header

Inherits:
Object
  • Object
show all
Defined in:
lib/net/dns/header.rb

Overview

DNS packet header class

The Net::DNS::Header class represents the header portion of a DNS packet. An Header object is created whenever a new packet is parsed or as user request.

header = Net::DNS::Header.new
# ;; id = 18123
# ;; qr = 0       opCode: 0       aa = 0  tc = 0  rd = 1
# ;; ra = 0       ad = 0  cd = 0  rcode = 0
# ;; qdCount = 1  anCount = 0     nsCount = 0     arCount = 0

header.format
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |             18123             |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |0|   0   |0|0|1|0|0| 0 |   0   |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               1               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

# packet is an instance of Net::DNS::Packet
header = packet.header
puts "Answer is #{header.auth? ? '' : 'non'} authoritative"

A lot of methods were written to keep a compatibility layer with the Perl version of the library, as long as methods name which are more or less the same.

Defined Under Namespace

Classes: Error, RCode, WrongCountError, WrongOpcodeError, WrongRecursiveError

Constant Summary collapse

QUERY =

Constant for opCode query

0
IQUERY =

Constant for opCode iquery

1
STATUS =

Constant for opCode status

2
OPARR =

Array with given strings

%w[QUERY IQUERY STATUS].freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(arg = {}) ⇒ Header

Creates a new Net::DNS::Header object with the desired values, which can be specified as an Hash argument. When called without arguments, defaults are used. If a data string is passed, values are taken from parsing the string.

Examples:

# Create a new Net::DNS::Header object
header = Net::DNS::Header.new

# Create a new Net::DNS::Header object passing values
header = Net::DNS::Header.new(:opCode => 1, :rd => 0)

# Create a new Net::DNS::Header object with binary data
header = Net::DNS::Header.new(data)

Default values are:

:id => auto generated
:qr      => 0 # Query response flag
:aa      => 0 # Authoritative answer flag
:tc      => 0 # Truncated packet flag
:ra      => 0 # Recursiond available flag
:rCode   => 0 # Response code (status of the query)
:opCode  => 0 # Operational code (purpose of the query)
:cd      => 0 # Checking disable flag
:ad      => 0 # Only relevant in DNSSEC context
:rd      => 1 # Recursion desired flag
:qdCount => 1 # Number of questions in the dns packet
:anCount => 0 # Number of answer RRs in the dns packet
:nsCount => 0 # Number of authoritative RRs in the dns packet
:arCount => 0 # Number of additional RRs in the dns packet

See also each option for a detailed explanation of usage.

Raises:

  • (ArgumentError) 


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# File 'lib/net/dns/header.rb', line 207

def initialize(arg = {})
  raise ArgumentError, "Wrong argument class `#{arg.class}'" unless arg.is_a? Hash

  new_from_hash(arg)
end

Instance Attribute Details

#anCount ⇒ Object

Reader for answer section entries number



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# File 'lib/net/dns/header.rb', line 166

def anCount
  @anCount
end

#arCount ⇒ Object

Reader for addictional section entries number



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

def arCount
  @arCount
end

#id ⇒ Object

Reader for id attribute



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# File 'lib/net/dns/header.rb', line 158

def id
  @id
end

#nsCount ⇒ Object

Reader for authority section entries number



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# File 'lib/net/dns/header.rb', line 168

def nsCount
  @nsCount
end

#opCode ⇒ Object

Reader for the operational code



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# File 'lib/net/dns/header.rb', line 160

def opCode
  @opCode
end

#qdCount ⇒ Object

Reader for question section entries number



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# File 'lib/net/dns/header.rb', line 164

def qdCount
  @qdCount
end

#rCode ⇒ Object

Reader for the rCode instance



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# File 'lib/net/dns/header.rb', line 162

def rCode
  @rCode
end

Class Method Details

.parse(arg) ⇒ Object

Creates a new Net::DNS::Header object from binary data, which is passed as a string object as argument. The configurations parameters are taken from parsing the string.

Example:

# Create a new Net::DNS::Header object with binary data
header = Net::DNS::Header.new(data)

header.auth?
  #=> "true" if it comes from authoritative name server

Raises:

  • (ArgumentError) 


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# File 'lib/net/dns/header.rb', line 225

def self.parse(arg)
  raise ArgumentError, "Wrong argument class `#{arg.class}'" unless arg.is_a? String

  o = allocate
  o.send(:new_from_binary, arg)
  o
end

Instance Method Details

#aa=(val) ⇒ Object

Set the aa flag (authoritative answer) to either true or false. You can also use 0 or 1.

This flag indicates whether a DNS answer packet contains authoritative data, meaning that is was generated by a nameserver authoritative for the domain of the question.

Must only be set to true in DNS answer packets.



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# File 'lib/net/dns/header.rb', line 415

def aa=(val)
  case val
  when true
    @aa = 1
  when false
    @aa = 0
  when 0, 1
    @aa = val
  else
    raise ArgumentError, ":aa must be true(or 1) or false(or 0)"
  end
end

#ad=(val) ⇒ Object

Set the ad flag to either true ot false. You can also use 0 or 1.

The AD bit is only set on answers where signatures have been cryptographically verified or the server is authoritative for the data and is allowed to set the bit by policy.



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# File 'lib/net/dns/header.rb', line 570

def ad=(val)
  case val
  when true
    @ad = 1
  when false
    @ad = 0
  when 0, 1
    @ad = val
  else
    raise ArgumentError, ":ad must be true(or 1) or false(or 0)"
  end
end

#auth? ⇒ Boolean

Checks whether the response is authoritative

if header.auth?
  puts "Response is authoritative"
else
  puts "Answer is NOT authoritative"
end

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 402

def auth?
  @aa == 1
end

#cd=(val) ⇒ Object

Set the cd flag (checking disabled) to either true ot false. You can also use 0 or 1.



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# File 'lib/net/dns/header.rb', line 542

def cd=(val)
  case val
  when true
    @cd = 1
  when false
    @cd = 0
  when 0, 1
    @cd = val
  else
    raise ArgumentError, ":cd must be true(or 1) or false(or 0)"
  end
end

#checking? ⇒ Boolean

Checks whether checking is enabled or disabled.

Checking is enabled by default.

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 535

def checking?
  @cd == 0
end

#data ⇒ Object

Returns the header data in binary format, appropriate for use in a DNS query packet.

hdata = header.data
puts "Header is #{hdata.size} bytes"



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# File 'lib/net/dns/header.rb', line 312

def data
  arr = []
  arr.push(@id)
  arr.push((@qr << 7) | (@opCode << 3) | (@aa << 2) | (@tc << 1) | @rd)
  arr.push((@ra << 7) | (@ad << 5) | (@cd << 4) | @rCode.code)
  arr.push(@qdCount)
  arr.push(@anCount)
  arr.push(@nsCount)
  arr.push(@arCount)
  arr.pack("n C2 n4")
end

#error? ⇒ Boolean

Checks for errors in the DNS packet

unless header.error?
  puts "No errors in DNS answer packet"
end

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 601

def error?
  @rCode.code > 0
end

#format ⇒ Object

The Net::DNS::Header#format method prints out the header in a special ascii representation of data, in a way similar to those often found on RFCs.

p Net::DNS::Header.new.format
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |             18123             |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |0|   0   |0|0|1|0|0| 0 |   0   |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               1               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
#  |               0               |
#  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This can be very usefull for didactical purpouses :)



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# File 'lib/net/dns/header.rb', line 286

def format
  del = ("+-" * 16) + "+\n"
  len = del.length
  str = del + "|" + @id.to_s.center(len - 3) + "|\n"
  str += del + "|" + @qr.to_s
  str += "|" + @opCode.to_s.center(7)
  str += "|" + @aa.to_s
  str += "|" + @tc.to_s
  str += "|" + @rd.to_s
  str += "|" + @ra.to_s
  str += "|" + @ad.to_s
  str += "|" + @cd.to_s.center(3)
  str += "|" + @rCode.to_s.center(7) + "|\n"
  str += del + "|" + @qdCount.to_s.center(len - 3) + "|\n"
  str += del + "|" + @anCount.to_s.center(len - 3) + "|\n"
  str += del + "|" + @nsCount.to_s.center(len - 3) + "|\n"
  str += del + "|" + @arCount.to_s.center(len - 3) + "|\n" + del
  str
end

#inspect ⇒ Object

Inspect method, prints out all the options and relative values.

p Net::DNS::Header.new
# ;; id = 18123
# ;; qr = 0       opCode: 0       aa = 0  tc = 0  rd = 1
# ;; ra = 0       ad = 0  cd = 0  rcode = 0
# ;; qdCount = 1  anCount = 0     nsCount = 0     arCount = 0

This method will maybe be changed in the future to a more pretty way of display output.



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# File 'lib/net/dns/header.rb', line 244

def inspect
  ";; id = #{@id}\n" +
      if false # @opCode == "UPDATE"
        # do stuff
      else
        ";; qr = #{@qr}\t" \
          "opCode: #{opCode_str}\t" \
          "aa = #{@aa}\t" \
          "tc = #{@tc}\t" \
          "rd = #{@rd}\n" \
          ";; ra = #{@ra}\t" \
          "ad = #{@ad}\t" \
          "cd = #{@cd}\t" \
          "rcode = #{@rCode.type}\n" \
          ";; qdCount = #{@qdCount}\t" \
          "anCount = #{@anCount}\t" \
          "nsCount = #{@nsCount}\t" \
          "arCount = #{@arCount}\n"
      end
end

#opCode_str ⇒ Object

Returns a string representation of the opCode

puts "Packet is a #{header.opCode_str}"
#=> Packet is a QUERY



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# File 'lib/net/dns/header.rb', line 370

def opCode_str
  OPARR[@opCode]
end

#qr=(val) ⇒ Object

Set the qr query response flag to be either true or false. You can also use the values 0 and 1. This flag indicates if the DNS packet contains a query or an answer, so it should be set to true in DNS answer packets. If qr is true, the packet is a response.



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# File 'lib/net/dns/header.rb', line 345

def qr=(val)
  case val
  when true
    @qr = 1
  when false
    @qr = 0
  when 0, 1
    @qr = val
  else
    raise ArgumentError, ":qr must be true(or 1) or false(or 0)"
  end
end

#query? ⇒ Boolean

Checks whether the header is a query (qr bit set to 0)

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 335

def query?
  @qr == 0
end

#r_available? ⇒ Boolean

Checks whether recursion is available. This flag is usually set by nameservers to indicate that they support recursive-type queries.

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 509

def r_available?
  @ra == 1
end

#ra=(val) ⇒ Object

Set the ra flag (recursion available) to either true or false. You can also use 0 and 1.

This flag must only be set in DNS answer packets.



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# File 'lib/net/dns/header.rb', line 518

def ra=(val)
  case val
  when true
    @ra = 1
  when false
    @ra = 0
  when 0, 1
    @ra = val
  else
    raise ArgumentError, ":ra must be true(or 1) or false(or 0)"
  end
end

#rCode_str ⇒ Object

Returns an error array for the header response code, or nil if no error is generated.

error, cause = header.rCode_str
puts "Error #{error} cause by: #{cause}" if error
  #=> Error ForErr caused by: The name server
  #=> was unable to interpret the query



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# File 'lib/net/dns/header.rb', line 591

def rCode_str
  [rCode.type, rCode.explanation]
end

#rd=(val) ⇒ Object

Alias for Header#recursive= to keep compatibility with the Perl version.



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# File 'lib/net/dns/header.rb', line 501

def rd=(val)
  self.recursive = val
end

#recursive=(val) ⇒ Object

Sets the recursion desidered bit. Remember that recursion query support is optional.

header.recursive = true
hdata = header.data # suitable for sending

Consult RFC1034 and RFC1035 for a detailed explanation of how recursion works.



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# File 'lib/net/dns/header.rb', line 483

def recursive=(val)
  case val
  when true
    @rd = 1
  when false
    @rd = 0
  when 1
    @rd = 1
  when 0
    @rd = 0
  else
    raise WrongRecursiveError, "Wrong value (#{val}), please specify true (1) or false (0)"
  end
end

#recursive? ⇒ Boolean

Checks whether the packet has a recursion bit set, meaning that recursion is desired

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 469

def recursive?
  @rd == 1
end

#response? ⇒ Boolean

Checks whether the header is a response (qr bit set to 1)

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 361

def response?
  @qr == 1
end

#tc=(val) ⇒ Object

Set the tc flag (truncated packet) to either true ot false. You can also use 0 or 1.

The truncated flag is used in response packets to indicate that the amount of data to be trasmitted exceedes the maximum allowed by the protocol in use, tipically UDP, and that the data present in the packet has been truncated. A different protocol (such has TCP) need to be used to retrieve full data.

Must only be set in DNS answer packets.



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# File 'lib/net/dns/header.rb', line 453

def tc=(val)
  case val
  when true
    @tc = 1
  when false
    @tc = 0
  when 0, 1
    @tc = val
  else
    raise ArgumentError, ":tc must be true(or 1) or false(or 0)"
  end
end

#truncated? ⇒ Boolean

Checks whether the packet was truncated

# Sending packet using UDP
if header.truncated?
  puts "Warning, packet has been truncated!"
  # Sending packet using TCP
end
# Do something with the answer

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 437

def truncated?
  @tc == 1
end

#verified? ⇒ Boolean

Checks whether ad flag has been set.

This flag is only relevant in DNSSEC context.

Returns:

  • (Boolean) 


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# File 'lib/net/dns/header.rb', line 559

def verified?
  @ad == 1
end