Class: Net::DNS::Header

Inherits:
Object
  • Object
show all
Defined in:
lib/Net/DNS/Header.rb

Overview

NAME

Net::DNS::Header - DNS packet header class

DESCRIPTION

A Net::DNS::Header object represents the header portion of a DNS packet.

COPYRIGHT

Copyright © 1997-2002 Michael Fuhr.

Portions Copyright © 2002-2004 Chris Reinhardt.

Portions Copyright © 2006 AlexD (Nominet UK)

All rights reserved. This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

Net::DNS, Net::DNS::Resolver, Net::DNS::Packet, Net::DNS::Update, Net::DNS::Question, Net::DNS::RR, RFC 1035 Section 4.1.1

Constant Summary collapse

MAX_ID = 
65535
@@next_id = 
rand(MAX_ID)

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ Header

header = Net::DNS::Header.new

header = Net::DNS::Header.new(data)

Without an argument, new creates a header object appropriate for making a DNS query.

If new is passed a reference to a scalar containing DNS packet data, it creates a header object from that data.

Returns nil if unable to create a header object (e.g., if the data is incomplete).



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# File 'lib/Net/DNS/Header.rb', line 168

def initialize(*args)
  
  @qr		= 0
  @opcode	= 0
  @aa		= 0
  @tc		= 0
  @rd		= 1
  @ra		= 0
  @ad		= 0
  @cd		= 0  
  @rcode		= 0
  @qdcount	= 0
  @ancount	= 0
  @nscount	= 0
  @arcount	= 0
  
  if (args != nil && args.length > 0)
    data = args[0];
    
    if (data) 
      
      if (data.length < Net::DNS::HFIXEDSZ )
        return nil;
      end
      
      a = data.unpack("n C2 n4");
      @id		= a[0]
      @qr		= (a[1] >> 7) & 0x1
      @opcode	= (a[1] >> 3) & 0xf
      @aa		= (a[1] >> 2) & 0x1
      @tc		= (a[1] >> 1) & 0x1
      @rd		= a[1] & 0x1
      @ra		= (a[2] >> 7) & 0x1
      @ad		= (a[2] >> 5) & 0x1
      @cd		= (a[2] >> 4) & 0x1
      @rcode		= a[2] & 0xf
      @qdcount	= a[3]
      @ancount	= a[4]
      @nscount	= a[5]
      @arcount	= a[6]
    else
      @id		= nextid()            
    end
  else
    @id		= nextid()
  end
  
  hasKey = Net::DNS::Opcodesbyval.has_key?@opcode
  temp = Net::DNS::Opcodesbyval[@opcode]
  temp2 = Net::DNS::Opcodesbyval
  if (Net::DNS::Opcodesbyval[@opcode] != nil)
    @opcode = Net::DNS::Opcodesbyval[@opcode]
  end
  if (Net::DNS::Rcodesbyval[@rcode]!=nil)
    @rcode = Net::DNS::Rcodesbyval[@rcode]
  end
end

Instance Attribute Details

#aa ⇒ Object

print “answer is ”, (header.aa!=0) ? “” : “non-”, “authoritativen”

header.aa=(0)

Gets or sets the authoritative answer flag.



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# File 'lib/Net/DNS/Header.rb', line 61

def aa
  @aa
end

#ad ⇒ Object

print “The result has ”, header.ad!=0 ? “” : “not”, “been verifiedn”

Relevant in DNSSEC context.

(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 94

def ad
  @ad
end

#ancount ⇒ Object Also known as: prcount

print “# of answer records: ”, header.ancount, “n”

header.ancount=(5)

Gets or sets the number of records in the answer section of the packet. In dynamic update packets, this field is known as prcount and refers to the number of RRs in the prerequisite section.



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# File 'lib/Net/DNS/Header.rb', line 116

def ancount
  @ancount
end

#arcount ⇒ Object Also known as: adcount

print “# of additional records: ”, header.arcount, “n”

header.arcount=(3)

Gets or sets the number of records in the additional section of the packet. In dynamic update packets, this field is known as adcount.



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# File 'lib/Net/DNS/Header.rb', line 131

def arcount
  @arcount
end

#cd ⇒ Object

print “checking was ”, header.cd!=0 ? “not” : “”, “desiredn”

header.cd=(0)

Gets or sets the checking disabled flag.



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# File 'lib/Net/DNS/Header.rb', line 79

def cd
  @cd
end

#id ⇒ Object

The query identification number.



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# File 'lib/Net/DNS/Header.rb', line 46

def id
  @id
end

#nscount ⇒ Object Also known as: upcount

print “# of authority records: ”, header.nscount, “n”

header.nscount=(2)

Gets or sets the number of records in the authority section of the packet. In dynamic update packets, this field is known as upcount and refers to the number of RRs in the update section.



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# File 'lib/Net/DNS/Header.rb', line 124

def nscount
  @nscount
end

#opcode ⇒ Object

print “query opcode = ”, header.opcode, “n”

header.opcode("UPDATE")

Gets or sets the query opcode (the purpose of the query).



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# File 'lib/Net/DNS/Header.rb', line 55

def opcode
  @opcode
end

#qdcount ⇒ Object Also known as: zocount

print “# of question records: ”, header.qdcount, “n”

header.qdcount=(2)

Gets or sets the number of records in the question section of the packet. In dynamic update packets, this field is known as zocount and refers to the number of RRs in the zone section.



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# File 'lib/Net/DNS/Header.rb', line 108

def qdcount
  @qdcount
end

#qr ⇒ Object

Gets or sets the query response flag.



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# File 'lib/Net/DNS/Header.rb', line 49

def qr
  @qr
end

#ra ⇒ Object

print “recursion is ”, header.ra!=0 ? “” : “not ”, “availablen”

header.ra=(0)

Gets or sets the recursion available flag.



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# File 'lib/Net/DNS/Header.rb', line 85

def ra
  @ra
end

#rcode ⇒ Object

print “query response code = ”, header.rcode, “n”

header.rcode=("SERVFAIL")

Gets or sets the query response code (the status of the query).



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# File 'lib/Net/DNS/Header.rb', line 100

def rcode
  @rcode
end

#rd ⇒ Object

print “recursion was ”, header.rd!=0 ? “” : “not ”, “desiredn”

header.rd=(0)

Gets or sets the recursion desired flag.



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# File 'lib/Net/DNS/Header.rb', line 73

def rd
  @rd
end

#tc ⇒ Object

print “packet is ”, header.tc!=0 ? “” : “not ”, “truncatedn”

header.tc=(0)

Gets or sets the truncated packet flag.



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# File 'lib/Net/DNS/Header.rb', line 67

def tc
  @tc
end

Instance Method Details

#==(other) ⇒ Object 



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# File 'lib/Net/DNS/Header.rb', line 278

def ==(other)
  if (other != nil) && (other.is_a?(Header))
    return false if @qr!=other.qr;
    return false if @opcode!=other.opcode;
    return false if @aa!=other.aa;
    return false if @tc!=other.tc;
    return false if @rd!=other.rd;
    return false if @ra!=other.ra;
    return false if @ad!=other.ad;
    return false if @cd!=other.cd;
    return false if @rcode!=other.rcode;
    return false if @ancount!=other.ancount;
    return false if @nscount!=other.nscount;
    return false if @qdcount!=other.qdcount;
    return false if @id!=other.id;
    return false if @arcount!=other.arcount;
    
    return true;
  else
    return false
  end
end

#data ⇒ Object

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

hdata = header.data



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# File 'lib/Net/DNS/Header.rb', line 267

def data
  opcode = Net::DNS::Opcodesbyname[@opcode];
  rcode  = Net::DNS::Rcodesbyname[@rcode];
  
  byte2 = (@qr << 7) | (opcode << 3) | (@aa << 2) | (@tc << 1) | @rd;
  
  byte3 = (@ra << 7) | (@ad << 5) | (@cd << 4) | rcode;
  
  return [@id, byte2, byte3, @qdcount, @ancount, @nscount, @arcount].pack("n C2 n4");
end

#inspect ⇒ Object

Returns a string representation of the header object.

print header.inspect



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# File 'lib/Net/DNS/Header.rb', line 229

def inspect
  retval = ";; id = #{@id}\n";
  
  if (@opcode == "UPDATE")
    retval += ";; qr = #{@qr}    " +\
       "opcode = #{@opcode}    "+\
       "rcode = #{@rcode}\n";
    
    retval += ";; zocount = #{@qdcount}  "+\
       "prcount = #{@ancount}  " +\
       "upcount = #{@nscount}  "  +\
       "adcount = #{@arcount}\n";
  else
    retval += ";; qr = #{@qr}    "  +\
       "opcode = #{@opcode}    " +\
       "aa = #{@aa}    "  +\
       "tc = #{@tc}    " +\
       "rd = #{@rd}\n";
    
    retval += ";; ra = #{@ra}    " +\
       "ad = #{@ad}    "  +\
       "cd = #{@cd}    "  +\
       "rcode  = #{@rcode}\n";
    
    retval += ";; qdcount = #{@qdcount}  " +\
       "ancount = #{@ancount}  " +\
       "nscount = #{@nscount}  " +\
       "arcount = #{@arcount}\n";
  end
  
  return retval;
end

#nextid ⇒ Object

Get the next Header ID



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# File 'lib/Net/DNS/Header.rb', line 149

def nextid()
  @@next_id += 1
  if (@@next_id > MAX_ID)
    @@next_id = 0
  end
  return @@next_id
end