Class: Nesser::Unpacker

Inherits:
Object
  • Object
show all
Defined in:
lib/nesser/packets/unpacker.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data) ⇒ Unpacker

Returns a new instance of Unpacker.



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# File 'lib/nesser/packets/unpacker.rb', line 31

def initialize(data)
  @data = data
  @offset = 0
end

Instance Attribute Details

#data ⇒ Object

Returns the value of attribute data.



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# File 'lib/nesser/packets/unpacker.rb', line 23

def data
  @data
end

#offset ⇒ Object

Returns the value of attribute offset.



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# File 'lib/nesser/packets/unpacker.rb', line 23

def offset
  @offset
end

Instance Method Details

#to_s ⇒ Object 



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# File 'lib/nesser/packets/unpacker.rb', line 158

def to_s()
  return HexHelper::to_s(@data, offset: @offset)
end

#unpack(format) ⇒ Object 



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# File 'lib/nesser/packets/unpacker.rb', line 54

def unpack(format)
  if @offset >= @data.length
    raise(DnsException, "DNS packet was invalid!")
  end

  results = @data[@offset..-1].unpack(format + "a*")
  remaining = results.pop
  @offset = @data.length - remaining.length

  _verify_results(results)

  return *results
end

#unpack_name(depth: 0) ⇒ Object 



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# File 'lib/nesser/packets/unpacker.rb', line 120

def unpack_name(depth:0)
  segments = []

  if depth > MAX_RECURSION_DEPTH
    raise(DnsException, "It looks like this packet contains recursive pointers!")
  end

  loop do
    # If no offset is given, just eat data from the normal source
    len = unpack_one("C")

    # Stop at the null terminator
    if len == 0
      break
    end

    # Handle "pointer" records by updating the offset
    if (len & 0xc0) == 0xc0
      # If the first two bits are 1 (ie, 0xC0), the next
      # 10 bits are an offset, so we have to mask out the first two bits
      # with 0x3F (00111111)
      offset = ((len << 8) | unpack_one("C")) & 0x3FFF

      _with_offset(offset) do
        segments << unpack_name(depth:depth+1).split(/\./)
      end

      break
    end

    # It's normal, just unpack what we need to!
    segments << unpack("a#{len}")
  end

  return segments.join('.')
end

#unpack_one(format) ⇒ Object 



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# File 'lib/nesser/packets/unpacker.rb', line 76

def unpack_one(format)
  results = unpack(format)

  _verify_results(results)
  if results.length != 1
    raise(DnsException, "unpack_one() was passed a bad format string")
  end

  return results.pop()
end